Calcium hydroxide (final)/ dental implant courses by Indian dental academy

“FOR A LONG TIME I FELT THAT THE MUMMIFIED LAYER CREATED A SEAL, LIKE A SCAB, WHICH WAS IMMUNOLOGICALLY SIMILAR TO THE VITAL TISSUE BENEATH AND SOMEHOW INTIATED THE HEALING PROCESS. FOR 200 YEARS NATURE WAITED FOR US TO FIND THE EQUIVALENT OF THE SCAB”

Harold R Stanley

INTRODUCTION During the last 200 years there have been many changes in the rationale governing the treatment of the exposed dental pulp as it was long ago observed that an exposed pulp healed with great difficulty, if at all. The earliest account of pulp therapy was way back in 1756, when Phillip Pfaff packed a piece of gold (leaf?) over an exposed vital pulp to promote healing.

Since then hundreds of investigations, thousands of hours and innumerable words have been directed towards maintaining the vitality of an exposed dental pulp.

In the light of his experiences Rebel summarized his thoughts in the expression “the exposed pulp is a doomed organ” he concluded that the recovery of the pulp once exposed was impossible and that one must consider it a lost organ. The influence of Rebel was so strong that for many years further efforts for direct pulp treatment and pulpotomy techniques in Europe were discouraged.

Until Hermann’s (1920) introduction of a material so eminent, which marked a new era in pulp therapy, when he demonstrated that a Calcium hydroxide formulation called Calzyl induced dentinal bridging of the exposed pulpal surface. Since then the emphasis has shifted from the “doomed organ” concept of an exposed pulp to one of hope and recovery.

These properties of calcium hydroxide is related to the ability of calcium hydroxide to hype the pH to such a position where the bacteria find it almost impossible to survive and the hard tissue formation is also indirectly related to it.

Since its introduction calcium hydroxide has found different arenas to show it’s capability in dentistry. Whether being used as simple as a liner or as in the repair of perforations and fractures calcium hydroxide has been the first choice.

Definition : Calcium hydroxide is a strong alkali, which can be formed by the reaction of calcium oxide. If the oxide is treated with only sufficient water to make it crumble to a fine, white, dry powder slaked lime is produced.

Synonyms : calcium hydrate, caustic lime, hydrated lime, lime, lime hydrate, slaked lime.

Chemical formula : H2CaO2 H

H

O

O Ca

Formula weight : 74.09 Registry number or chemical abstract service number : 1305-62-0 Density: 2.4 Melting point : 580 degree Celsius Calcium hydroxide is a caustic substance and is used extensively in a strong solution of pH in various ways. Other than dentistry calcium hydroxide is used for liming and un-hairing the hides and skins in leather industries, used in decalcification of paper. It is also used in making mortar, cements, calcium salts, paints, hard rubber products and petrochemicals.

THE FLASH BACK Year 1920 Year 1930 Year 1939 Year 1941 Year 1959 Year 1960

Year 1966 Year 1975 Year 1976 Year 1983 Year 1985 Year 1985 Year 2000 Year 2002

Hermann introduced calcium hydroxide for the treatment of infected root canals.

Calcium hydroxide became frequently used in the vital pulp therapies.

Before the second World War an European immigrant Zander introduced dentists in USA to its use.

The first literature regarding the successful healing using calcium hydroxide appeared.

The use of calcium hydroxide for apical closure was first reported by Granath.

Matsumiya and Kitumura clearly demonstrated, in a dog whose infected root canals were packed with calcium hydroxide, showed a drastic reduction in the number of microorganisms.

Frank popularized the use of calcium hydroxide for the apical closure.

Maisto classified the calcium hydroxide paste as an alkaline paste because of its high pH. Cvek successfully used calcium hydroxide for induction of hard tissue in the apical portions of the root canal, especially of immature teeth with infected pulp necrosis.

Garcia considered calcium hydroxide as the best medicament to induce hard tissue deposition and promote healing of vital Pulpal and periapical tissues.

Bystrom and Sundquist promoted calcium hydroxide as an antibacterial agent and showed that 97% of the cases showed great success with calcium hydroxide.

Bystrom showed that some microorganism for example Enterococcus faecalis which are found almost invariabally in the infected root canals tolerated calcium hydroxide.

Haapsalo suggested the probable reasons for the decreased action of calcium hydroxide could dentin debris and tissue remnants.

Peters questioned the effectiveness of calcium hydroxide and suggested that calcium hydroxide may not be as effective as it was once believed.

COMPOSITION OF CALCIUM HYDROXIDE Calcium hydroxide is in the powder form and can be carried to the tooth in a variety of ways depending upon the need and vehicles or may be applied in the pure powder form with any carrier.

The most common way of introducing calcium hydroxide into the cavity preparation is through calcium hydroxide cements. They are supplied in a two paste system.

The acidic paste :  Alkyl salicylates (iso-butyl salicylates or 1-methyl triethylene salicylates)  Inter fillers – titanium oxide 12-14%  Radiopacifier – barium sulphate 32-35%  Calcium tungstate or calcium sulphate 14-15% The basic paste  Calcium hydroxide 50-60%  Plasticizer (sulfonamide or paraffin oil) The single paste or the light cured calcium hydroxide composes of :  Urethane dimethacrylate  Hydroxymethacrylate (HEMA)  Calcium hydroxide  Polymerization activators  Barium sulphate The chemical reaction of calcium hydroxide :

Mixing equal parts of the pastes together will start an acid base reaction resulting in weakly bond (mostly secondary forces) composite structure.

Chelates of calcium alkyl salicylates and water (the reaction byproduct) will form the continuous phase and the unreacted ingredients will form the interrupted phase. The mass is hydrolytically unstable ingredients will form the interrupted phase. The mass is hydrolytically unstable and contains a large percentage of unreacted calcium hydroxide. Calcium ions, hydroxyl ions and salicylates ions are released continuously from the mass. The release is mostly controlled by the percentage of continuous phase and the type of plasticizer (sulfonamide allows more erosion and ion release than paraffin oil).

When calcium hydroxide is carried by methylcellulose or any other biologically compatible and degradable polymeric material calcium hydroxide does not actually take part in the chemical reaction. Here the methylcellulose

monomers

will

polymerize

creating

a

porous

meshwork. There is a chemical coherence of the ingredients creating bonding between the polymer macromolecules. The free calcium hydroxide is carried to the pulp-dentin organ, where it is available to engage in therapeutic action.

PROPERTIES OF CALCIUM HYDROXIDE Setting time and the factors affecting it The setting is approximately 2.5 to 5.5 minutes.

The setting time for polymer carried calcium hydroxide can be increased by increasing the ratio of the catalyst to base paste. The setting time of calcium hydroxide alkyl salicylates cement can be accelerated by moisture and heat. Conversely, the setting time will be retarded by dryness and cold.

Dimensional stability and factors affecting it Setting shrinkage : The maximum setting shrinkage is that of polymer carried calcium hydroxide which is 5% by volume. However, in the dimensions and locations that this material is used, such shrinkage is of no clinical significance.

Fluid and water absorption The more porous the material is the greater will be the chance of absorbing fluids with subsequent dimensional change. This is observed more with the non carried calcium hydroxide.

Solubility and disintegration Clinical tests reveal that calcium hydroxide in any form is the most soluble material. Although it should be emphasized that in most cases it is not the material per se that will be responsible for the degree of solubility rather that the solubility will be the result of the factors:  The greater the percentage of the original (or dispersed) particles bound to the matrix, lesser will be its solubility, that is increasing the powder: liquid ratio to the full bonding capacity of the liquid will definitely decrease the solubility and disintegration.  Solubility is directly proportional to the acidity of the environment.

 The earlier during the setting time that he calcium hydroxide is exposed to moisture, the greater will be the solubility.  For alkyl salicylate cement, paraffin oil plasticizer decreases the solubility as compared to sulfonamide one.  Chelating acids increase the solubility.

Flow (viscosity) : Although high flows are required during the insertion of the material low flows are necessary for the mechanical well being. Polymer carried and cement type calcium hydroxide have the highest flow and its flow is decreased by increasing the degree of polymerization of the carrying polymer or the percentage of calcium alkyl salicylate in the mix. Calcium hydroxide is also thermoplastic in nature and hence the flow increases with an increase in the temperature.

Strength : Carried calcium hydroxide and those with the continuous phase in the form of calcium alkyl salicylate chelate can have compressive strength up to 800 psi, while non carried calcium hydroxide has virtually no strength. The tensile strength is very low of about 1.0 MPa. Calcium hydroxide cements are visco-elastic. That is why they react more favorably in resisting deformation failure with high rates of stressing rather than lower ones.

Adaptability : Film thickness : The lower the film thickness of the material, the better is its wetting ability and better is its adaptability.

Calcium hydroxide has the highest possible film thickness, ranging from 70-90 microns. Calcium hydroxide has none of the adaptability enhancing properties and thus lowest adaptability to the tooth surfaces.

Biological compatibility of calcium hydroxide with the pulp-dentin organ : Calcium hydroxide is an irritant to the pulp-dentin organ, if it comes in direct contact with it. The irritating factors could be the forces with which the material is introduced into the pulp tissues and the high alkalinity of the material.

Provided the pulp and the periapical tissues are healthy and devoid of any degeneration, the following Pulpal reaction to calcium hydroxide can occur:  Whenever there is an effective depth of 100 microns or more, a healthy reparative dentin can form.  With less than 100 microns an unhealthy reparative can be expected.  When calcium hydroxide comes in contact with the pulp or root canals the area of tissues in direct contact would undergo chemical necrosis. Also calcium hydroxide can stimulate the formation barrier when in direct contact thus decreasing the permeability of the dentin. Calcium hydroxide can be friendly with the pulp-dentin organ by acting as a thermal insulator, especially if carried with a methylcellulose or used in alkyl salicylate cement form. The effective thickness for proper insulation is 0.5mm. Calcium hydroxide in any form is not an electrical insulator at any thickness.

Toxicity of calcium hydroxide : Some calcium hydroxide preparations like Dycal, Life and Sealapex have been associated with toxicity in the form of cytotoxicity, genotoxicity, neurotoxicity, phototoxicity, necrotic and inflammatory manifestations compatible with the pathology and symptoms observed in Neuro Cutaneous Syndrome (NCS). Ethyltoulene sulfonamide, common to these three preparations is considered the primary cause of the NCS. The toluene component, a known nerve toxin, is believed to be responsible, at least in

part, for the neurological symptoms. Neurological abnormalities are related to nerve damage associated with vasometric reactions due to the direct influence on the peripheral nerve endings. The sulfonamide component is the cause of the cutaneous symptoms, especially in sulfa-sensitive patients who usually have elevated sulfonamide / sulfa levels in the blood tests and allergy to sulfa in skin sensitive tests. Resolving the symptoms (effect) by removing these sealers (cause) in patients undergoing the treatments, confirms the cause-effect relationship.

Compatibility of calcium hydroxide with restorative materials and techniques : Calcium hydroxide has no effect on the setting reaction or the properties of any permanent restorative material. It does not discolor any permanent restorative material. However, in translucent tooth-colored materials, especially with thin cross-sections, calcium hydroxide will show through as a chalky patch.

Calcium hydroxide base can be used under the amalgam and direct tooth-colored materials but when used under the direct filling gold and cast restorations calcium hydroxide should be covered with zinc phosphate or polycarboxylate cement. Calcium hydroxide in methylcellulose reacts with the zinc oxide eugenol and hence not used together.

The technique of manipulation of calcium hydroxide Two paste Equal parts of base and catalyst paste are squeezed out and incorporated in each other with a stiff spatula on a paper pad until a homogenous mix is obtained.

Calcium hydroxide in powder form Calcium hydroxide powder is carried between the beaks of a tweezers and delivered to the indicated area by releasing the tweezers beaks.

Calcium hydroxide in endodontics There are various ways with which calcium hydroxide can be placed in the root canals. Using a messing gun, vertical compaction, an inejctable formulation of calcium hydroxide, a lentilo spiral, a hand file and paper points. The use of a lentilo spiral was thought to be the most effective form of delivering calcium hydroxide into the root canals.

CLASSIFICATION AND CLINICAL INDICATIONS Since the introduction of calcium hydroxide into dentistry, it has been indicated to promote healing in many situations. Various formations have been suggested by adding various substances to be calcium hydroxide powder to improve properties such as the antibacterial action, radiopacity, flow and consistency. Furthermore pasts may be prepared at the chair side before use and there have been many proprietary brands which have been tested in both animals and humans. However, it seems that no one paste has been proved to be superior to the others, either biologically or clinically.

In spite of the variations, literature lacks a classification of these different paste formulations. Holland [1994] has been the only author to suggest a classification according to the vehicle of the paste.

When calcium hydroxide paste is mixed with a suitable vehicle, a high pH paste is formed and hence these formulations are known as alkaline pastes.

According to Maisto [1975], Goldberg [1982], these pasts should have the following characteristics : 1) It should be composed mainly of calcium hydroxide which be used in association with other substances to improve some of the physicochemical properties such as radiopacity, flow and consistency.

2) Should be non-setting.

3) Should be rendered soluble or resorb with in vital tissues either slowly or rapidly depending on the vehicle and other components.

4) Should be prepared for the use at the chair side or be available as a proprietary paste.

5) Should be used as only temporary dressing material and not as a definitive filling material.

The easiest method to prepare a calcium hydroxide paste is to mix calcium hydroxide powder with water until the desired consistency is

achieved. However such a paste doesn’t have good physicochemical properties because it is not radiopaque, is permeably to tissue fluids and is rendered soluble and resorbed from the periapical area and from within the root canal.

For these reasons and the following below it is recommended to that other substances be added to the paste.

1. To maintain the paste consistency of the material which doesn’t harden or set?

2. To improve the flow.

3. To maintain the high pH of calcium hydroxide; 4. To improve the radiopacity; 5. To make clinical use easier; 6. Not to alter the excellent biological properties of calcium hydroxide itself.

TYPES OF VEHICLES AND THEIR IMPORTANCE It has been asserted that all biologic actions of calcium hydroxide will be progressed by the ionic dissociation of Ca + and OH- ions. The vehicle plays an important role in the overall process therefore it determines the velocity of the ionic dissociation causing the paste to be solubilized and resorbed at various rates any the periapical tissues and from with in the root canal. According to Fava [1991] an ideal vehicle should: 1. Allow gradual and slow release of Ca+ and OH2. Allow slow diffusion in the tissues with low solubility in the tissue fluids.

3. Have no adverse effect on the induction of the hard tissue deposition.

The differences in the velocity of the ionic dissociation are related directly to the vehicle employed to obtain the paste. Furthermore, it is important to consider that viscosity is the measurement of the inner friction

of a fluid. Thus, if a solution flows easily it has a low viscosity and the interactions between the particles are small. As the paste is considered chemically to be a colloid (a solid dispersed into a liquid), this liquid may facilitate or inhibit the ionic dispersion from the paste: the lower the viscosity the higher the ionic dissociation.

VEHICLES USED FOR CALCIUM HYDROXIDE According to Fava [1991] Holland [1994] the vehicles used are divided into  Aqueous  Viscous  Oily AQUEOUS Includes: 1. Water 2. Saline 3. Dental anaesthetics with or without vasoconstrictors.

4. Ringer’s solution.

5. Aqueous suspension of Methylcellulose or Carboxymethyl cellulose.

6. Anionic detergent solution.

CLINICAL IMPORTANCE : When calcium hydroxide is mixed with one of these substances Ca 2+ and OH- are rapidly released. This type of vehicle promotes a high degree of solubility when the paste remains in direct contact with the tissue and the tissue fluids causing it to be rapidly solubilized and resorbed by the macrophages. The root canal must be redressed several times until the desired effect is achieved there by increasing the number of appointments.

VISCOUS : 1. Glycerin 2. Polyethylene glycol

3. Prophylene glycol CLINICAL IMPORTANCE : Some various vehicles are also water soluble substances that release calcium and hydroxyl ions more slowly for extended periods. They promote a lower solubility of the paste when compared with aqueous vehicles probably because of their higher molecular weights.

The high molecular weight of these vehicles minimize the dispersion of the calcium hydroxide into the tissues and maintain the paste in the desired area for longer periods. This factor prolongs the action of the paste and calcium and hydroxyl ions will be given off at lower velocity. It is through this mechanism that these pastes remain in direct contact with the vital tissues for extended time intervals. As a viscous vehicle containing paste may remain in the root canal for a two to four month interval the number of appointments and redressings of the root canal is drastically reduced.

OILY : 1. Olive oil 2. Silicone oil 3. Camphor (the essential oil of camphorated parachlorophenol) 4. Metacresylacetate 5. Some fatty acids such as oleic linoleic isostearic acids Oily vehicles are non water soluble substances that promote the lower solubility and diffusion of the paste with in the tissues. Pastes containing this kind of vehicle may remain with in the root canal for longer periods than pastes containing aqueous and viscous vehicles.

The description of the following clinical example may clarify why the type of vehicle is so important. In cases of dental replantation, as soon a treatment is performed, a paste an aqueous vehicle should is employed because of the need for rapid ionic release and pH turnover to avoid

replacement resorption. Subsequently, a calcium hydroxide paste with a viscous vehicle should be used in the periodical redressings, because the paste may remain in the root canal for longer period.

Summarizing, clinical situations that require a rapid ionic liberation at the beginning of the treatment require an aqueous vehicle containing calcium hydroxide paste whilst in calcium situations that require a gradual and uniform ionic liberation, a viscous vehicle containing paste should be used. Pastes containing oily vehicles have restricted use and are only employed in those that require a very slow ionic dissociation.

AQUEOUS VEHICLES Pastes prepared at the chair side Water : The easiest method to prepare a calcium hydroxide paste is to mix the powder with water. However, the literature describes different types of water with which to prepare the paste, including sterile water, distilled water, sterile distilled water, bidistilled water and sterile bidistilled water.

Usually this paste is prepared on a sterile glass slab with a sterile spatula. The powder is mixed with the liquid until the desired consistency is achieved.

Indications : 1. For capping the vital pulp tissue after pulpotomy.

2. As a long term dressing in cases of non vital teeth with associated large periapical lesions.

3. In apexification procedures.

Sterile water : Indications 1. As a direct pulp capping agent.

2. In pulpotomy and apex genesis.

3. In apexification procedures.

4. As an apical plug before gutta-percha filling in non vital teeth with an open apex.

5. In cases of internal resorption with perforation of the dentinal wall.

Distilled water : Indications 1. For the induction of the hard tissue deposition in apexification procedures.

2. In pulpotomy of deciduous or permanent teeth.

3. As a temporary dressing after vital pulp extirpation.

4. In bon vital teeth associated with chronic periapical disease.

5. In internal resorptions.

6. In perforations.

7. To arrest external cervical resorption after bleaching of pulpless teeth.

Sterile distilled water : Used in 1. Direct pulp capping.

2. In apexifications procedures.

Bidistilled water : Used in 1. Pulp therapy.

2. Cases of infected non vital teeth, some drops of camphorated parachlorophenol were added to the paste.

Sterile bidistilled water : Recommended in 1. Apexogenesis 2. Apexification

Saline or sterile saline : Preparation of saline: according to United States Pharmacopeia [1989] saline in prepared by dissolving 9 grams of sodium chloride in water to make 1000 mL. It was recommended in 1. Non vital immature teeth.

2. Perforations.

3. Internal and external resorptions.

4. Luxated non vital teeth.

5. Antibacterial dressing in infected teeth with or without acute or chronic periodontitis.

6. In cases of sinus tracts.

7. Endodontic retreatment after endodontic and surgical failures.

8. As a dressing after partial pulpectomy.

Anesthetic solution : Anesthetic solutions with or without vasoconstrictors have been used as a vehicle of the paste because these solutions are readily available, sterile and easy to handle.

It is interesting to note that most of these solutions have an acidic pH, but when mixed with a calcium hydroxide powder, the final paste has a high pH which is maintained overtime. They also promote a rapid ionic release.

Indicated in : 1. Apexification 2. Pulp capping material.

Ringer’s solution : According to the United States Pharmocopeia [1989] this solution has sodium chloride (8.6g), potassium chloride (0.3g), calcium chloride (0.33g) and water to 1000mL. Indicated in : 1. Indirect pulp treatment.

2. Apexification procedures.

3. Temporary dressing after pulpectomy.

4. Treatment of post traumatic sequlea such as luxation and replantation.

Methylecllulose and Carboxymethylcellulose : Maisto and Capurro [1964] introduced a paste composed of equal volumes of calcium hydroxide and iodoform mixed with a 5% aqueous solution of methylcellulose.

It was indicated in apexification procedures, indirect pulp treatment.

The above formula was a modified by Laurichesse [1980] as calcium hydroxide. And iodoform in ratio 2/3:1/3, two drops of camphorated parachlorophenol and a 3% aqueous solution of methylcellulose as the vehicle. More recently, the use of carboxymethylether of cellulose, as the vehicle in the following formula: 0.5g of calcium hydroxide to 0.5mL. of a 1.66% solution of carboxymethylcellulose, in another suggested formula, 0.25g of zinc oxide was added for radiopacity was proposed.

Anionic detergent solution : It is known that the detergents decrease the surface tension between two surfaces and facilitate substance penetration. This is why calcium hydroxide powder has been mixed with an aqueous detergent solution to increase the action of calcium hydroxide deeper into the tissues.

VISCOUS VEHICLES Pastes prepared at the time of use : Glycerine : It is a viscous, colorless transparent liquid with a characteristic odor, sweetish in taste and hydroscopic; because of its hygroscopic properties glycerine is very useful as a moistening substance. It is also soluble in water, and easily removed. Furthermore it is non-toxic and is used as an intra canal lubricant.

The paste is obtained by mixing calcium hydroxide with synthetic glycerine.

Indicated in : 1. Cases of chronic abscesses with extra oral fistulae.

2. Acute or chronic periapical lesion.

3. Internal resorption with or without root perforation.

4. Repair of a fractured root even with an associated site of internal resorption.

Polyethylene glycol : It is a viscous, colorless liquid with a characteristic odor and is slightly hydroscopic. According to the United States Pharmacopeia [1989] it is a polymer of ethylene glycol and water. It is represented by a formula H(OCH2 CH2)nOH in which “n” represents the average number of oxyethylene groups. It’s pH ranges between 4.5 and 7.5. Various combinations have been suggested to be used with calcium hydroxide and polyethylene glycol such as iodoform, antibacterial agents like sulfonamide, eugenol camphorated parachlorophenol and radiopacifiers like barium sulphate depending upon the demanding clinical situation.

Propylene glycol : It is a clear, colourless, odourless liquid with a slightly characteristic taste resembling that of glycerine. Chemically it is a dihydric alcohol with a syrupy consistency, hygroscopic nature.

According to the United States Pharmacopeia [1989], it’s formula is CH3CH(OH)CH2OH and it’s molecular weight is 76.09. It demonstrated a strong antibacterial action against common micro-organisms found in the infected root canals and suggested it’s wider applications in endodontics as a gentle vehicle for intracanal medicaments. It’s hygroscopic nature permits the absorption of water which ensures a good sustained release of calcium hydroxide for longer periods. Another advantage of this substance is it’s consistency which improves the handling qualities of the paste. It was

recommended as an intracanal dressing after a vital pulpectomy and for the non-surgical treatment of large periapical lesions.

OILY VEHICLES Pastes prepared at the time of use : Olive oil : Purified olive oil is a primrose or slightly green colored liquid with a characteristic odor which is insoluble in water but fairly soluble in alcohol.

Chemically it is composed of esters of fatty acids such as oleic, linoleic, palmitoleic, esteric and linolenic acids. It must be kept in an amber colored bottle. It promotes low solubility for calcium hydroxide. But improves its physical properties. Because of the low solubility, the paste has allowed diffusion with tissues.

Fatty acids : Two formulations called New B and New B-2 with a powder liquid ratio of 1.2gmL-1. The first formulation was calcium hydroxide powder 100% and olive oil 100% as the vehicle. New B-2 was composed of calcium hydroxide. 65%, bismuth carbonate 15%, resin and zinc 20% whilst the liquid vehicle was composed of fatty acids 85% and glycol 15%.

Camphorated parachlorophenol : It is also known as camphorated paramonochlorophenol (CMCP) was introduced

by

Walkhoff

in

1891. It

comprises

of

33-37%

of

parachlorophenol and 63-67% camphor (United States Pharmacopeia 1989).

Parachlorophenol {(C6H5Ohl)- molecular weight 128.56} It has a characteristic phenolic odor and is presented in crystal form. Camphor {(C10H16O) molecular weight 152.54} is a cetone obtained from cinnamomum camphora or synthetically in the laboratory. It has a characteristic and a penetrating odor, bitter taste and low solubility in water.

The pronounced disinfectant action of parachlorophenol depends on the liberation of the chlorine in the presence of phenol.

When camphorated parachlorophenol is the vehicle of calcium hydroxide it is considered as oily because camphor is thought to be an essential oil with a low solubility in water. The paste containing the above formulation was introduced by Frank [1964] and Kaiser [1964] and became very popular in the United States after the publication of an article by Frank in 1966 describing the guidelines for specifications in non-vital teeth.

Indicated in : 1. Apexification procedures.

2. Reversal or external resorption.

3. Intra canal dressing with large periapical lesions.

Metacresyl acetate : This was introduced to dentistry by Coolidge in 1912 for the treatment of necrotic pulps. Chemically, metacresyl acetate is the acetic ester of metacresol in combination with benzene. It is an oily liquid with antibacterial, analgesic and sedative properties. It showed minimal inflammatory potential and less cytotoxic activity compared with camphorated parachlorophenol. When calcium hydroxide is mixed with metacresyl acetate, a chemical reaction occurs yielding calcium cresilate and acetic acid. The acetic acid suffers an ionic dissociation and gives off H+ ions, an increase in the pH. This paste has been used for pulp treatment, pulpotomy, and root end induction in immature non-vital teeth, retreatment after endodontic and surgical failures.

Eugenol : Eugenol (C10H12O2, molecular weight 164.20) is obtained from oil of cloves (United States Pharmcopeia 1989) it was employed as an intracanal dressing for vital and non-vital deciduous teeth.

OTHER PASTES Apart from those already reviewed, other pastes have been cited in the literature. They are the following : • Calcium

hydroxide,

methylcresilate

and

camphorated

parachlorophenol –Blanc-Benon [1967].

• Calcium hydroxide was mixed with sterilized dentin chips and alkaline blood salts-Flohr [1936].

• Calcium hydroxide in a 1% aqueous solution of parachlorophenol [1979].

• Calcium hydroxide and collagen gel-Pissiotis and Spanberg.

PROPRIETARY BRANDS WITH COMPOSITION AND CLINICAL INDICATIONS AQUEOUS Calxyl : (Otto and Co., Frankfurt, Germany). This paste represents the oldest manufactured calcium hydroxide paste and was introduced by Hermann [1920]. He was the first to suggest this material be employed as a dressing with the purpose of maintaining vital pulp tissue and inducing healing by hard tissue formation at the site of amputation.

This paste is a solution of calcium hydroxide in water with the addition of the following blood salts: sodium carbonate, sodium chloride, calcium chloride, potassium chloride and traces of magnesium. It is manufactured both with (red label) and with out radiopacifier (blue label).

Marmasse [1953] was the first to indicate Calxyl and other resorbable pastes such as Walkhoff’s and Dentinigene (Lab. Pierre Roland, Paris, France) in cases requiring apexifications.

Indicated in : 1. Direct pulp treatment.

2. Pulpotomy.

3. Apexification.

4. Orthograde root canal treatment.

5. Calxyl + corticosteroids substance (2% methyl prednisolone stearate) reduces postoperative pain and inflammation following direct pulp treatment.

Pulpdent and Tempcanal (pulpdent Corp., Brookline M A, USA).

Pulpdent is a commercial paste consisting of calcium hydroxide (52.5%) in an aqueous medium of methylcelulose.

It has been successfully used in 1. Indirect pulp treatment.

2. Direct pulp treatment.

3. Apexification procedures.

4. As an apical plug prior to the obturation of the root canal.

5. Treatment of chronic periapical lesions.

6. In the management of post bleaching cervical resorption.

Tempcanal is a similar calcium hydroxide in aqueous methylcellulose but modified to allow flow through 22, 25 and 27 gauge needles and has barium sulphate as the radiopacifier.

Calvital : (Neo Dental Chemical a Products Co., Tokyo Japan). This paste was originally proposed in 1963 and its composition is as follows : Powder Calcium hydroxide Iodoform Guanaflacin Sulphatiazol

78.5% 20% 0.1% 1.4%

Liquid T- cain Propyleneglycol Distilled water

0.5% 50% 49.5%

Recommend in : 1. Direct pulp treatment.

2. Pulpotomy in deciduous and permanent teeth.

3. Intra canal dressing after vital pulpectomy.

4. As a final filing coupled with gutta-percha points.

Modifications : Various modifications were suggested to the original composition.

Kitagawa 1969 : According to him the powder composition remained the same but the liquid contained the following : T – cain Polysorbate Distilled water As proposed in 1981 Powder contained Calcium hydroxide Iodoform CMC Others Liquid was composed of Tween 20 Propyleneglycol Sterile water

0.5% 20.30% 69.5% 67% 29% 1% 3% 30% 10% 60%

As proposed by Ida in 1989 using the original powder and the liquid composed of the following : Diethyl aminoethyl hydrochloride Guanofuracin Distilled water

0.5% 0.02% 99.48%

Reogan ; (Vivadent, Schaan, Liechtenstein). This paste is composed of : Calcium hydroxide Casein Barium sulphate Magnesium It is indicated in : 1. Apexification.

2. Routine dressing in vital or non-vital with or without periapical lesions.

Calasept : (Scania Dental A B, Knvista, Sweden). This paste was introduced in the 1980s and is composed of : Calcium hydroxide

56%

Calcium chloride

8mg

Sodium chloride

0.35mg

Sodium bicarbonate

4mg

Potassium chloride

8mg

Water sufficient for 100g of the paste.

It was employed in the following cases : 1. Indirect and direct pulp treatment.

2. Retreatment cases.

3. Luxated non-vital teeth.

4. A soluble iodide organic substance may be added for a better radiographic intracanal visualization of the paste.

Hypocal (Ellinam Co., Hewlatt, NY, USA), this paste contained : Calcium hydroxide

45%

Barium sulphate

5%

Hydroxy methylcellulose

2% as according to Goldberg

Or

Glycol cellulose

2% as according to Ida

Water

48%

Indicated in apexification procedures in deciduous and permanent teeth.

Calcicur : (Voco, Auxhaven, Germany) according to the manufacturer this paste composed of radiopaque calcium hydroxide in an aqueous vehicle.

DT Temporary dressing : (Dental Therapeutics AB, Nacka, Sweden).

According to the manufacturer, this paste composed of unoxygenated calcium hydroxide and sterilized distilled water.

Calcipulpe : (Specialitis Septodent, Saint-Maur, France). This paste composed of calcium hydroxide and carboxyl methylcellulose.

Hidropulpe : (Lab, Zizine, France). This paste composed of barium sulphate in a solution of methyl benzoate.

Serocalcium : (Casa Wild, Basel, Switzerland). This paste has a similar composition to Calxyl and has been employed in pulp treatment and pulpotomy.

Calcigel : (Lab, Septodent, France), Endocal: (Lab, Biodica, France), Hydroxine: (Lab, Ato, Zizine, France). These three proprietary brands are basically composed of calcium hydroxide, methylcellulose and water.

Acrical : (Bames-Hind Laboratories, USA). This paste is composed of : 9 amino acridine hydrochloride

0.2%

Benzalkonium chloride

0.1%

Calcium hydroxide

28%

Barium sulphate

5%

Benzalkonium chloride is a cationic detergent and thus a water soluble vehicle.

Calnex : (Associated Dental Products Ltd, London, UK). This paste contains

sterilized

calcium

hydroxide,

methylcellulose. It is used in pulpotomies.

VISCOUS

blood

serum

salts

and

Calen : (SS. White-Artigos Dentarios, Rio de Janeiro, RJ, Brazil). This paste is the proprietary brand for Leonardo and Leal’s paste, the formulation of which is: Calcium hydroxide Zinc oxide Hydrogenised colophony Polyethylene glycol 400

2.5g 0.5g 0.05g 1.75mL

This is the unique proprietary brand of calcium hydroxide containing this viscous vehicle Recommended in 1. Apexification.

2. In the treatment of large periapical lesions originating from infected root canals.

3. Inter appointment dressings in cases of vital pulpectomy.

4. Acute apical periodontitis.

5. In endodontic retreatment after endodontic and surgical failures.

Calen + camphorated parachlorophenol; (SS. White-Artigos Dentarios, Rio de Janeiro, RJ, Brazil). In 1991 CMCP 0.15mL was added to the original Calen formulation.

Chemically, it has been shown that CMCP + calcium hydroxide yield calcium-para-chlorophenolate, a weak salt. In solution with water the salt takes up the H+ ions and goes back into p-chlorophenol which gives an excess of OH- ions from water. Thus maintaining the high pH, prolonging the antibacterial action.

Calen + p-chlorophenol : This is the most recent formulation suggested in which camphor was regarded as unnecessary for the release of Ca 2+ ions, pH and solubility.

OIY

Endoapex : (Lab, Inodon Ltda. Porto Alerge, RS, Brazil). This paste composed of calcium hydroxide, liquid silicone and iodoform.

L and C : (Herpo Products Dent Arios Ltda., Rio de Janeiro RJ, Brazil).

Here the powder consisted of : Calcium hydroxide Bismuth carbonate Hydrogenised colophony

2g 1g 0.05g

Liquid Olive oil

0.16mL

It was indicated in apexification procedures and other clinical situations like resorptions and perforations.

Vitapex : (Neo Dental Chemical Products Co. Ltd, Tokyo, Japan). This paste is very popular in Japan and was introduced in 1979. It is composed of: Calcium hydroxide Iodoform Silicone oil Other substances

30.3% 40.4% 22.4% 6.9%

A lot of experimental research has been carried out to evaluate the biologic behavior of this paste and its components with in the tissues.

OTHER INGREDIENTS Radiographic contrast media : Calcium hydroxide lacks radiopacity, this is the main reason why a radiopaque materials are added to the paste, thereby allowing identification of lateral and accessory canals, resorptive defects, fractures and other structures. A radiopacifier should have an atomic weight higher than calcium for radiopacity purposes. Some examples for such substances are barium sulphate, and bismuth and other substances containing iodine and bromine.

As bismuth salts have some degree of toxicity and soluble barium salts are extremely toxic materials and relatively insoluble, the actual alternative is to use a more soluble radiopaque substance. Hence iodine compounds like soluble iodine organic substances, non soluble iodine oils and slowly absorbable iodine oils were developed.

When mixed with calcium hydroxide these substances will become the vehicle of the paste as well as being the radiopaque agent. Examples of such substances used we are lipidol, sodium ditrizoate and iothalmate.

Corticosteroid – antibiotic solutions : The use of corticosteroids to reduce inflammation and maintain the vitality and integrity of the injured pulp tissue is an established procedure.

As calcium hydroxide has been proved to offer better clinical results, some attempts have been made to mix these two substances and evaluate these formulations for endodontic purposes in vital pulp therapy.

A very popular formulation is paste composed of calcium hydroxide and ledermix. Ladermix is an anti-inflammatory antibiotic compound which has triamcinolone acetonide and demethyl chlortetracycline calcium. Other corticosteroid antibiotic solutions used were prednisolone-sulphacetamide with neomycine, otosporine composed of polymixin B sulphate, neomycin and hydrocortisone. Ciprofloxacin and metronidazole have also been with calcium hydroxide.

DENTAL FORUMULATION OF CALCIUM HYDROXIDE PASTES: Calcium hydroxide pastes can also be classified according to whether they are setting or non-setting materials. Setting materials are generally used for the lining or sub-lining of the cavities, as root canal sealers. Non-setting cements are used for dressing root canals.

Setting materials : The therapeutic properties of calcium hydroxide materials are related to their pH. The latter is dependent on the levels of unbound calcium and

hydroxyl ions that after the material has set. It follows that egress of ions from the set material will lead to the regression of the mass. One factor which increases the availability of the hydroxyl ions is the hydrophobic nature of the material. More the hydrophobicity less likely is the diffusion to occur. A now withdrawn product, hydrex. For example was more hydrophobic than Dycal due to the presence of a paraffin solvent which prevented the diffusion of water into the set material.

An additional factor to be considered is the dissolution of set calcium hydroxide cement which depends on the effect of the microorganisms on the cement. Watts and Paterson (1987) established that bacteria maybe present in contact with calcium hydroxide. This could lower the pH of the material by converting it into calcium carbonate and might explain why early Dycal preparation seemed to disappear from beneath permanent restoration.

It is possible to rank the setting calcium hydroxide pastes according to the availability of the hydroxyl ions. It is evident that if antibacterial activity is required as in direct pulp treatment the paste should be selected from near the top of the list as per the table, where the diffusion of the hydroxyl ions is the greatest. Where as if the antibacterial property is not required as in lining, the calcium hydroxide should be selected from near the bottom of the list because such materials are less likely to leach out from beneath the restoration.

The rationale for inclusion of calcium hydroxide in such nontherapeutic materials, where its antibacterial effect is not required, is said to be its ability to react readily in the setting process.

Non-setting materials : Analar calcium hydroxide may be applied either dry, or using distilled water as the vehicle. Clinically this has a disadvantage that the mixture forms slurry which may separate and can be difficult to manipulate with I the root canal by puddling ; alternatively, it may be mixed into very

thick paste which can be placed into the root canal with an amalgam carrier and condensed with root canal pluggers. The proprietary brands overcome this problem by using methyl cellulose as a vehicle with varying consistency and good handling properties.

CALCIUM HYDROXIDE, HOW DOES IT WORK? Since the introduction of Calxyl by Hermann, it has become the standard clinical agent for promoting the formation of reparative dentin. The precise mechanism by which this occurs is still not clearly understood ; however the antimicrobial activity of calcium hydroxide is believed to enhance this formation. It is proposed that the elimination of the bulk of the bacteria in the dentin, the “balance of power” is shifted from a gradually dying pulp to one with the potential for complete resolution. The antimicrobial activity has been attributed to calcium hydroxide’s high pH. Mechanism of antimicrobial activity : Calcium hydroxide is a strong alkaline substance with a pH of approximately 12.5. Most of the endopathogens are unable to survive in this high alkaline environment. When in direct contact several bacterial species found in infected root canals are eliminated in only a short period of time.

Antimicrobial activity of calcium hydroxide is related to the release of hydroxyl ions in aqueous environment. Hydroxyl ions are highly oxidant, free radicals that show extreme reactivity, with several biomolecules. This reactivity is high and indiscriminate, so this free radical rarely diffuses from the site of generation.

Their lethal effects on the bacterial cells are probably due to the following mechanisms : Damage to the bacterial cytoplasmic membrane : The bacterial cytoplasmic membrane possesses important functions to the survival of the cell, such as : • Selective permeability and transport of solutes • Electron transport and oxidative phosphorylation in aerobic species • Excretion of hydrolytic exoenzymes.

• Bearing enzymes and carrier molecules that function in the biosynthesis of DNA, cell wall polymers and membrane lipids and • Bearing the receptors and proteins of the chemotatic and other sensory transduction systems.

Hydroxyl ions induce lipid per oxidation, resulting in the destruction if phospholipids, structural components of the cellular membrane. Hydroxyl ions remove hydrogen atoms from the unsaturated fatty acids, generating a free lipid radical. This free radical reacts with oxygen, resulting in the formation of a lipidic peroxidase radical, which removes another hydrogen atom from a second fatty acid, generating another lipidic peroxidase. Thus, peroxidases act as free radicals, initiating an autocatalytic chain reaction and resulting in further loss of unsaturated fatty acids and extensive tissue damage.

Protein denaturation : Cellular metabolism is highly dependent on enzymatic activities.

Enzymes have optimum activity and stability in a narrow range of pH, which turns around neutrality. The alkalinization provided by calcium hydroxide induces the breakdown of the ionic bonds that maintain the tertiary structures of proteins. As a consequence the enzyme maintains its covalent structure but the polypeptide chain is randomly unraveled in variable and irregular special conformation. These changes frequently result in the loss of biological activity of the enzyme and disruption of the cellular metabolism. Structural may also be damaged by hydroxyl ions.

Damage to the DNA : Hydroxyl ions react with the bacterial DNA and induce the splitting of the strands. Genes are then lost. Consequently DNA replication is inhibited and the cellular activity is disarranged. Free may also induce the lethal mutations.

It has been suggested that the ability of calcium hydroxide to absorb carbon dioxide may contribute to its antibacterial activity.

However, cementum is permeable to water, ions and small molecules.

Hence carbon dioxide supply to the remaining bacteria in the root canal system is maintained from the outside. In addition, bacteria located in the ramifications have direct access to carbon dioxide from the periradicular tissues. Hence there is little reason to consider that calcium hydroxide impedes the carbon dioxide supply to the bacteria.

Destruction of bacteria when calcium hydroxide is used as pulp dressing : Some of the healing properties of calcium hydroxide may be attributed to its antibacterial effects. Under normal conditions healing is due to the antibacterial activity of calcium hydroxide, rather than any effect it may exert on mineralization. The bacterial properties are thought to be related to pH, and are directly proportional to the ability of calcium hydroxide to diffuse from the set material.

There would appear to be no clinical indications for the use of calcium hydroxide in large old exposures with deep penetration of bacteria and chronic inflammation of the pulp, unless a radical pulpotomy has been performed first. In this situation, calcium hydroxide does not have the same healing potential that it exhibits when used as a root canal dressing to treat a chronically inflamed periapical tissue. This is possibly because of the ready availability of healthy blood vessels in the periapical tissues, compared to the paucity in dying tissues in the enclosed environment of the pulp. It has been found that calcium hydroxide kills only the bacteria on the surface of the pulp and not those that have penetrated the necrotic tissue. Thus the material has no beneficial effect on the healing of the inflamed pulp, and its use would appear to be indicated for healthy or superficially contaminated pulp where bacteria have not penetrated deep.

As a root canal medicament : There is some uncertainty as to the efficacy of calcium hydroxide compared with the other medicaments when used as an intra canal dressing.

When used as a root canal medicament any material must be judged entirely on its antibacterial potential acting with out support from the tissue defense mechanisms. Thus in contrast to its mode of action in mineralization, calcium hydroxide has a non-specific bactericidal action within the confines of the root canal. Alkalis in general have a pronounced destructive effect on cell membranes and protein structures. Although most microorganisms are destroyed at pH 9.5 a few survive at pH 11 or higher. The main issue is not “how bacteria are killed� but how the vital tissues can be protected from the toxicity of calcium hydroxide. This is brought about by the separation of the material from the vital tissues by a zone of necrosis.

For calcium hydroxide to act effectively as an intra canal dressing, the hydroxyl ions must diffuse through dentin and pulpal tissue remnants at sufficient concentrations. It has been reported that dentin has buffering ability because of the presence of proton donors such as H 2PO4,H2CO3 and HCO3, in the hydrated layer of hydroxapatite, which furnish additional protons to keep the pH unchanged. Therefore, in order to have antibacterial effects with in the dentinal tubules, the ionic diffusion of calcium hydroxide should exceed the dentin buffer action, reaching pH levels sufficient to destroy bacteria. After short term use of calcium hydroxide, microorganisms are probably exposed to the lethal levels of hydroxyl ions only at the tubule orifice.

Another factor can also help to explain the inefficacy of calcium hydroxide in disinfecting dentinal tubules is that the arrangement of the bacterial cells colonizing the root canal walls can reduce the antibacterial

effects of calcium hydroxide, since the cells located at the periphery of the colonies can protect those located more inside the tubules.

Bacteria colonizing necrotic tissue in the ramifications, isthmus and the irregularities are also, probably protected from the action of calcium hydroxide due to the neutralization of the pH. Therefore, as a short term dressing which appears to eliminate mainly bacterial cells in direct contact with this substance, such as bacteria located in the main root canal or in the circumpulpal dentin.

The activity of a medicament to dissolve and diffuse in the root canal system would seem essential for its successful action. A saturated aqueous suspension of calcium hydroxide possesses a high pH, which has a great cytotoxic potential. Nevertheless, this substance owes its biocompatibility to its low water solubility and diffusibility. Because of these properties, cytotoxicity is limited to the tissues which are in direct contact with calcium hydroxide. On the other hand the low solubility and diffusibility of calcium hydroxide may make it difficult to reach a rapid and significant increase in the pH to eliminate the bacteria located in the dentinal tubules and enclosed in the anatomic variations. Likewise the tissue buffering ability controls the pH changes. Prolonged exposure may allow for saturation of dentin and tissue remnants. Theoretically, long term use of calcium hydroxide may be necessary to obtain a bacteria free root canal system. However, in most instances, the routine use of an intra canal medicament for a long period does not seem to be an acceptable practice in endodontics.

Bacteria may survive after intra canal medication for several reasons.

First, bacterial strains present in the root canal infection may be intrinsically resistant to the medicament. Secondly bacterial cells may be enclosed with an anatomical variation inaccessible to the medicament. Thirdly, the medicament may be neutralized by the tissue components and by the bacterial cells or products, losing its antibacterial effects. Fourthly, the

medicaments may remain in the root canals for insufficient time o reach and kill the bacterial cells. Finally, bacteria may alter their pattern of gene expression after changes in the environmental conditions. Good clinical results have been attributed to the use of calcium hydroxide as an intra canal medicament. Nonetheless, the antibacterial activity of calcium hydroxide is still controversial and it is not clear whether the benefits of this substance are based upon the superior antibacterial activity.

Influence of the vehicle on the antimicrobial activity : A plethora of substances have been used as vehicles for calcium hydroxide. Vehicles have different solubility and ideally they must not change the pH of calcium hydroxide significantly.

Endodontic infections are polymicrobial and no medicament is effective against all the bacteria found in the infected root canals. Most of the substances used as vehicles for calcium hydroxide do not have significant antibacterial activities. Combination of two medicaments was thought to produce additive and synergistic effects. Evidence suggests that the association of calcium hydroxide with CMCP has a broader antibacterial action, and kills bacteria faster than mixtures of calcium hydroxide with inert vehicles.

Phenolic compounds such as CMCP possess strong antibacterial properties and halogenation intensifies its antibacterial properties. Phenol is believed to act by disrupting lipid containing bacterial membranes resulting in leakage of cellular contents. At higher concentrations, these components act by precipitating the cytoplasmic cell proteins. At lower concentrations these inactivate essential enzyme systems and may also cause bacterial cell lysis. Some properties of phenolic compounds, such as low surface tension and lipid solubility confer penetrability and spreading of the material. Thus, the calcium hydroxide and CMCP mixture possesses a high radius of action,

eliminating bacteria located in regions more distant from the vicinity where the paste was applied.

Therefore CMCP cannot be considered as a vehicle for calcium hydroxide but an additional medicament especially against anaerobic bacteria such as a enterococcus faecalis.

Physical barrier : In preparation of the root canal, intra canal medicament have been advocated for other reasons also like, they should act as a physico-chemical barrier, precluding proliferation of residual microorganisms and preventing the reinfection of the root canals by bacteria from the oral cavity.

Intra canal medicaments may prevent the penetration of bacteria from saliva in the root canal basically in two ways. First the medicament possessing antibacterial properties may act as a chemical barrier against leakage by killing bacteria, thereby preventing their ingress into the root canal. Secondly, medicaments that fill the entire length of the canal act as a physical barrier against penetration thereby preventing recontamination.

The filling ability of calcium hydroxide pastes is probably more important in retarding root canal recontamination than the chemical effect because calcium hydroxide has low water solubility, it is slowly dissolved in saliva, remaining in the canal for a long period, delaying the bacterial progression towards the apical foramen.

Despite the vehicle used, calcium hydroxide seems to act as an effective physical barrier. Medicaments that act as a physical barrier can kill remaining microorganisms by withholding substrate for the growth and limiting space for multiplication. It certainly may be one of the growth and limiting space for multiplication. It certainly may be one of the factors possible for the antibacterial actions of calcium hydroxide.

Dissolution of necrotic material :

The ability of calcium hydroxide to dissolve necrotic material is similar to that of sodium hypochlorite but is less effective. However, its prolonged presence in the root canal, where it has a continuous therapeutic effect, may largely compensate for this.

THE GREAT CALCIFIC WALL Calcium hydroxide is a material which has been used for a variety of purposes. The mode of therapeutic activity of calcium hydroxide for calcific bridge formation is not clear despite extensive literature. The pulpal and the periapical connective tissue responses to calcium hydroxide will not be the same since odontoblast precursors are unique to the pulp and inherently different preparations of calcium hydroxide are used in root canals compared to the pulp capping agents.

Calcific bridge formation is the generic term describing repair y osteodentin bridge formation in pulpal exposure and cementun like material or cementoid formation in periapical or periodontal tissues.

Biochemical actions : Before considering the specific effects of calcium hydroxide, it will be helpful to describe the theories of mineralization with in the mesenchymal tissues. Three theories are now widely accepted.

The booster / homogenous mineralization theory The seeding / epitactic / heterogeneous mineralization theory The matrix vesicular theory The booster / homogenous mineralization theory : It is considered that the soft tissue contains inhibitors of mineralization. In order to initiate nucleation these same inhibitors have to be inhibited at the site of hard tissue formation. The energy required for the formation of crystal nuclei is higher than that needed for continued crystal growth. Once the nuclei are established, the level of super saturation of the interstitial fluids is high enough for the growth of hydroxyapatite crystal.

The energy needed for the nucleation is met by elevating the local ionic concentration of calcium ions and phosphate ions. This is brought about by an enzyme known as alkaline phosphatase. Hence this theory is also known as alkaline phosphatase theory. This process brings about homogenous mineralization.

The seeding theory : Another way of overcoming the energy barrier is to provide substrate that can bind calcium ions and or phosphate ions in a sufficient quantity and in a topologic organization that mimics the anatomic lattice distribution of the crystal phase by concentrating the ionic participants in close and stereological correct position, the crystal nuclei are formed in a “seeding mechanism�. Because of the need for substrate and in the absence of locally increased ionic concentration this process is called the heterogeneous nucleation. Heterogeneous nucleation is an effective way to create oriented crystal architecture as in enamel, bone and dentin.

The matrix vesicular theory : In this mechanism the vesicle exists in relation to initial mineralization only. The vesicle is small, membrane – bound structure that buds off from the cell to form an independent unit within the first formed organic matrix of the hard tissue. Within this vesicle the first morphologic evidence of a crystallite is seen. The matrix vehicle provides a microenvironment in which all the proposed mechanisms of initial memeralization

exist.

Thus

it

contains

alkaline

phosphatase,

pyrophosphatase, Ca-ATPase, metalloproteinases, proteoglycans and anionic phospholipids, which are able to bind to calcium and inorganic phosphate and there by calcium inorganic phosphate phospholipid complexes are formed. These complexes are unique to mineralizing situations and when they are selectively removed, the matrix vesicle is no longer able to initiate mineralization. Although it is possible that membrane control might increase the local concentration of ions to permit homogenous nucleation, it is likely that heterogeneous nucleation takes place within the vesicle.

The magic mantra of calcium hydroxide :

It seems that calcium hydroxide has the unique potential to induce mineralization, even in tissues which have not been programmed to mineralize.

Calcium ions and the alkaline pH have been proposed to act separately or synergistically in promoting calcification.

It was once believed that the calcium ions present in the applied calcium hydroxide does not become incorporated in the mineralized repair tissue, which derives its mineral content solely from the dental pulp, presumably via the blood supply. However the present day belief is that the calcium ions from the medicament do enter into the bridge formation.

Calcium hydroxide may act as a local buffer against the acidic reactions produced by the inflammatory process. An alkaline pH also neutralized the lactic acid secreted by the osteoclasts and this may help to prevent the further destruction of mineralized tissue.

It has been speculated that the material exerts a mitogenic and osteogenic effect, the high pH combined with the availability of calcium ions and hydroxyl ions has an effect on the enzymatic pathways and hence mineralization. The high pH may also activate alkaline phosphatase activity which is postulated to play an important role in the hard tissue formation.

The optimum pH for alkaline phosphatase activity is 10.2, a level of alkalinity which is produced by many of the calcium hydroxide preparations.

Calcium ions may reduce the permeability of new capillaries, so that less intracellular serum is produced, thus increasing the concentration of calcium ions at the mineralization site. The presence of a high calcium ions concentration may also increase the activity of calcium dependant pyrophosphatase, which represents an important part of mineralization process.

Once the mineralization process ahs been initiated, it can continue unabated if the normal self limiting enzymes (pyrophosphatases) fail to operate. The reduced capillary permeability following the increase in the calcium ions could reduce the serum flow with in the dental pulp, and consequently the concentration of the inhibitory pyrophosphatase ion would be decreased. This would coincide with an increase in the levels of calcium dependent pyrophosphatase resulting in uncontrolled mineralization of the pulp tissue. Thos could possibly explain the high incidence of mineralized canals observed following pulpotomy and direct pulp treatment.

Uncontrolled mineralization of the pulp would therefore be dependent on reduced blood supply to the remaining vital tissues and not necessarily the amount of reparative dentin formed with time.

The dentin bridge : A mineralized barrier or “dentin bridge� is usually produced following the application of calcium hydroxide to a vital pulp (pulpotomy).

This repair material appears to be the product of odontoblasts and connective tissue cells. There appears to be some variation in the way the dentin bridge is formed, depending on the pH of the material that is used to dress the tooth. In the case of a necrotic zone is formed adjacent to the material and the dentin bridge then forms between this necrotic layer and the underlying vital pulp. The necrotic tissue eventually degenerates and disappears, leaving a void between the capping material and the bridge.

In case of the material of lower pH, such as Dycal, the necrotic zone is similarly formed but is resorbed prior to the formation of the dentin bridge, which then comes to be formed directly against the capping material.

Dentin bridges formed by the high pH materials are histologically similar to those produced by lower pH materials, but are easier to distinguish on a radiograph because of the space between the bridge and calcium hydroxide.

The periapical response to calcium hydroxide may depend on the preexisting periapical inflammation, either as a consequence of apically extending pulpal disease or the resulting from poor endodontic technique.

The latter situation may include pushing infected or necrotic material through the apical foramen or over instrumentation leading to a “zipped� apical constriction. Overfilling into the periapex with calcium hydroxide may promote an acute inflammatory reaction followed by phagocytosis and calcium hydroxide resorption with areas of ankylosis. The possible sequelae to calcium hydroxide filling overfilling include connective tissue in growth and cementogenesis along the root canal walls leading to partial or complete closure, osteiod bridging across the calcium hydroxide / connective tissue interface or persistent mile to moderate chronic inflammation.

APPLICATIONS OF CALCIUM HYDROXIDE Operative dentistry : As a liner : The calcium hydroxide pastes are now in general use as lining materials. Their perceived advantages, in addition to their therapeutic effects are as follows : • They have a rapid initial set in the cavity under the accelerating effect of moisture in the ambient air of the oral cavity and from within the tubules.

• They do not interfere with the setting reaction of the Bis-GMA resins and are therefore the lining material of choice under the composite resins.

• It is generally considered that the initial set of the material in thin sections is sufficiently hard to resist the applied condensation pressures that are required even for the lathe cut amalgam alloys.

Application of the liner : The cavity is dried properly with short blasts of warm air and dry cotton pellets. A small cotton pellet is held with the tweezers and soaked in the liner. Starting from corner of the cavity the liner is squeezed out of ht pellet. This procedure is repeated until a continuous film is achieved. The liner is left to dry for about 2-3 mins following which a permanent restoration is placed.

As a base and a sub base : Calcium hydroxide can be used both as a sub base and base. When as a sub bas it provides therapeutic properties. It should be placed deep in deep portions of the cavity preparation subsequently covered by a definitive supporting base.

• It helps in repair of pulpal tissue

• It provides chemical insulation • It replaces the lost portion of the dentin which could be due to caries or cavity preparation.

Calcium hydroxide bases are of relatively of low strength when compared to the other bases. These bases are used only for their therapeutic benefits, chemical insulation or for retaining the sub bases.

Calcium hydroxide for pulp protection : Indirect pulp treatment : The demineratlization and staining precedes bacterial invasion of dentin. This presents the basis for the indirect pulp treatment.

Indirect pulp treatment is defined as “the application of a medicament over a thin layer of remaining carious dentin, after deep excavation, with no exposure of the pulp”.

Carious dentin actually consists of two layers having different ultramicroscopic and chemical structures. The outer carious layer is irreversibly denatured, infected and incapable of being remineralized and hence should be removed. The inner carious layer is reversibly denatured but not infected and is capable of being remineralized and hence should be preserved. The two layers can be differentiated clinically by a solution of basic fuschin.

The technique : The indirect pulp treatment can be performed as a two appointment technique or in a single appointment.

In a two appointment procedure the peripheral carious dentin is removed with a sharp spoon excavator and a hard set calcium hydroxide dressing is given to cover the remaining affected dentin. The remainder of the cavity is then filled with a reinforced zinc oxide eugenol cement or GIC. This sealed cavity is not disturbed for a minimum of 6-8 weeks. At the next appointment radiographs of the affected tooth are taken to assess the

presence of reparative dentin. The temporary filling with calcium hydroxide is removed carefully. The reparative dentin layer is not disturbed. Over this another fresh application of calcium hydroxide is given over which a permanent filling is done with a suitable base.

Single appointment technique : The value of the re- entry and re- excavation has been questioned. It has been suggested that re – entry to remove the residual minimal carious dentin after pulp treatment with calcium hydroxide may not be necessary if the final restoration maintains a seal and the tooth is asymptomatic.

Response to the treatment : Three distinct types of new dentin in response to indirect pulp treatment are seen : • Cellular fibrillar dentin at two months post treatment.

• Presence of globular dentin during the first three months • Tubular dentin in amore uniformly mineralized pattern.

New dentin forms fastest in teeth with the thinnest dentin remaining after the cavity preparation the longer the treatment time the more enhanced is the dentin formation.

The histological evaluation : The pulp reactions to the indirect pulp treatment are as follows : Four layers have been demonstrated • Carious decalcified dentin • Rhythmic layers of irregular reparative dentin • Regular tubular dentin • Normal pulp with a slight increase in the fibrous elements.

Direct pulp treatment : Direct pulp treatment involves the placement of a biocompatible agent on the healthy pulp tissue that has been inadvertently exposed by

caries excavation or traumatic injury. The treatment objective is to seal the pulp against bacterial leakage and encourage the pulp to wall off the exposure site by initiating a dentin bridge and maintain the vitality of the underlying pulp tissue organ.

Success with direct pulp treatment is dependant on the coronal and radicular pulp being healthy and free from bacterial invasion.

The clinician must rely on the physical appearance of the exposed pulp tissue, radiographic assessment and the diagnostic tests to determine the pulpal status.

Treatment considerations: Debridement : Necrotic and infected dentin chips are invariably pushed into the exposed pulp during the last stages of caries removal. This debris can impede healing in the area by causing further pulpal inflammation and encapsulation of the dentin chips. Therefore it is prudent to remove peripheral masses of carious dentin before beginning the excavation when an exposure occurs. The areas of exposure should be appropriately irrigated with non-irritating solutions such as saline to keep the pulp tissue moist.

Hemorrhage and clotting : Hemorrhage at the exposure site can be controlled with cotton pellet pressure. A blood clot must not be allowed to form after the cessation of hemorrhage from the exposure site as it will impede pulpal healing. The capping material should directly contact pulp tissue to exert a reparative dentin bridge formation. Hemolysis of erythrocytes results in an excess of hemosiderin and inflammatory cellular infiltrate, which prolongs pulpal healing.

Exposure enlargement :

There have been recommendations that the exposure site be enlarged by a modification of the direct pulp treatment known as pulp curettage or partial pulpotomy prior to the placement of the medicament.

Enlarging this opening into the pulp itself serves three purposes : • It removes the inflamed or the infected pulp in the exposed area • It facilitates removal of carious and non – carious debris, particularly the dentin chips • It ensures intimate contact of the calcium hydroxide with the healthy pulp tissue below the exposure site.

Direct pulp treatment in primary teeth : Calcium hydroxide is frequently utilized a wound dressing in primary and premature permanent teeth. However, the usefulness of calcium hydroxide has been found to be limited the primary teeth as the success rate is not very high and also the fear of causing internal resorption.

The reason for the internal resorption : Pulp healing capability is affected by endogenous factors of coronal cellularity and apical vascularity. Both are increased in primary and young permanent teeth. Pulps become more fibrous, less cellular ad vascular with age. Histologically no differences exist between primary and young permanent pulp tissue with exception of the presence of cap like zone of reticular and collagenous fibers in the primary coronal pulp. However, there exists a difference in the pulp responses between both to trauma, bacterial invasion, irritation and medication. Anatomic differences may contribute to these responses.

Primary roots have an enlarged apical foramen, in contrast to the foramen in contrast to the enlarged foramen of permanent roots, which are constricted. The resultant blood supply in mature permanent tooth favors a calcific response and healing by “calcific scarring”. This hypothesis is

exemplified in the older pulps, in which more calcified nodules and ground substance are found than in the young pulps. Primary teeth have an abundant blood supply and hence demonstrate a more typical inflammatory response than that seen in permanent teeth.

Hence pulpotomy is preferred in primary teeth than direct pulp treatment especially in cariously exposed pulps.

Histology of healing after direct pulp treatment : As adjustments are made in the pH of calcium hydroxide in the recent years there are now two different modes of healing.

Healing with calcium hydroxide products of high pH (11-13) {calcium hydroxide and water, calcium hydroxide and saline, Pulpdent} Zone of obliteration (early changes ; caustic effect ; area of superficial debris) : The pulp tissue immediately in contact with the calcium hydroxide is usually completely deranged and distorted because of the caustic effect of the drug (chemical cautery). This zone consists of debris, dentinal fragments hemorrhage, blood clot, blood pigment and particles of calcium hydroxide.

This zone can be visualized after one hour of contact between the calcium hydroxide and the pulp tissue.

Zone of coagulation necrosis (Schroder’s layer of “firm necrosis”, Stanley’s “mummified zone”).

The tissue together with its plasma proteins within the “zone of obliteration” takes the brunt of the calcium hydroxide chemical thrust, a weaker chemical effect reaches the subjacent, more apical tissue an results in a zone of coagulation necrosis and thrombosis.

The zone of coagulation necrosis (0.3 to 0.7) mm thick) represents devitalized tissue without complete obliteration of its structural architecture.

Although the cellular detail is diminished, outlines of capillaries, nerve bundles, and pyknotic nuclei can still be recognized.

The line of demarcation : Between the deepest level of coagulative necrosis and the subjacent vital tissue, a line of demarcation develops. This line results from the reaction of the calcium hydroxide with the tissue protein to form proteinate globules.

The coagulated necrotic layer causes a slight but sufficient stimulation to the subjacent vital pulp tissue for it to respond with all its healing potential. The sequence of tissue reactions is basically that o the wounded

connective

tissue,

starting

with

vascular

changes

and

inflammatory cell migration to control and eliminate irritating agent. The migration of inflammatory cells in the wound area can begin as early as six hours after the injury. If the treatment has been successful, a very few inflammatory cells will be found in the vital tissue below the line of demarcation after several days.

Intermediate changes of organization : The dense zone (early stages of bridge formation) Within several days, as the repair process progress, immediately subjacent to the line of demarcation, proliferation of mesenchymal cells occurs. As early as two days a dense accumulation of connective tissue fibers, at first the matted and disorganized, consisting of both the fine and coarse fibers lying parallel to the applied medicament can be seen, with a concomitant increase in the argyrophilic fibers. The increase in the collagen formation becomes apparent at three days and more extensive at after seven days. By the time the argyrophilic fibers have organized, collagen is being formed and the number of mesenchymal and fibroblasts subjacent have developed sufficiently to present the modified cell rich layer. The cells within this layer proliferate and gradually differentiate into the

preodontoblasts and the columnar shaped odontoblasts. In a more subjacent position fine argyrophilic fibers predominate and get organized in a pattern perpendicular to the line of demarcation. These fibers, till late were known as Korffs fibers, begin to splay and take on the characteristics of collagen.

Splaying of fibers is accompanied by sporadic tubular formation within the collageneous matrix. By seven days as the matrix thickens and becomes more differentiated excess cellular inclusions and superficial non functional capillaries become engulfed and obliterated. The more basic, alkaline environment favors differentiation and replication of odontoblasts (as with osteoblasts) over fibroblasts.

Calcification of the bridge : Calcification occurs soon after the predentin is formed. In some teeth, where the capacity for forming tubular matrix is delayed, the primitive matrix calcifies as very irregular dentin. But later tubular dentin is formed.

In older teeth the ability of the pulp to differentiate cells capable of producing tubular predentin may seldom occur and the bridge may consist almost entirely of irregular (reparative) dentin. However, in sound teeth especially with open roots, the stage of tubular predentin formation may be reached in two weeks.

After one month the barrier consists of a more coronal layer of irregular osteodentin –like tissue cellular inclusions and the pulpal part consists of predentin lined with odontoblasts.

After three months the barrier becomes definitely two layered, consisting coronally of dentin like tissue with irregular tubules and cellular inclusions ; the tissue nearest to the pulp exhibits predentin, densely packed collagen fibrils and tubules with cellular extensions (Tome’s fibers) indicative of higher level of differentiation.

With Pulpdent or calcium hydroxide preparation healing leading to bridge formation occurs at the junction of the firm necrotic layer and the

remaining subjacent vital pulp tissue (the line of demarcation). Over a period of time the coagulated necrotic tissue above the line of demarcation degenerates completely and collapses. When the tooth is reopened the calcium hydroxide is removed. The clinician’s instrument drops into the chamber or a pit (”the coffin”), the bottom of which is the calcified dentinal bridge.

The bridge is more readily visualized radiographically with the radiolucent Pulpdent paste because the degenerated, necrotic zone separates the calcium hydroxide from the bridge.

Healing with calcium hydroxide products of lower pH (9.0-10.0) {Life, VLC Dycal} : With some of the new hard setting formulations bridging at the calcium hydroxide – pulp interface has been reported without the formation of a visible intermediate coagulated necrotic layer, an indication of less extensive initial chemical injury than that is produced by calcium hydroxide and water. May be one or two cells closest to the calcium hydroxide dressing are affected. There is not enough tissue destruction to require an army of macrophages to carry off the dead and wounded cells, and there is little need for any quantity of granulation to fill in. haling and regeneration occur right up against the calcium hydroxide dressing. These differences in tissue responses are related to such factors as lower pH values and varying rates of calcium and hydroxyl ions dependant on the composition and water solubility of the material.

Although there is much less damage with the newer formulas with a reduced pH as compared to the tissue damage caused by calcium hydroxide and water, there is still a sufficient wound. A sufficient hydroxyl environment capable of stimulating the differentiation and regeneration of odontoblasts still exists to produce a high quality dentinal bridge.

• The success of direct pulp treatment depends on :

• The maintenance of pulp vitality • Absence of sensitivity or pain • Minimal pulp inflammatory responses • Absence of radiographic signs of dystrophic changes.

Calcium hydroxide in pediatric endodontics : Pulpotomy : Pulpotomy is the most widely used technique in vital pulp therapy for primary and young permanent teeth with carious pulp exposures. A pulpotomy is defined as the surgical removal of the entire coronal pulp presumed to be partially or totally inflamed and quite possibly infected, leaving intact the vital radicular pulp with in the canals. A germicidal medicament is then placed over the remaining vital radicular pulp. Dentin bridging may occur as a treatment outcome of this procedure.

Historically, calcium hydroxide was the first medicament used in the “regenerative” capacity because of its ability to stimulate hard tissue barrier formation. The “regenerative” approach includes pulpotomy agents that have cell- inductive capacity to either replace lost cells or induce existent cells to differentiate into hard tissue – forming elements. The calcium hydroxide pulpotomy is predicted on the healing of pulp tissue beneath the overlying dentin bridge. Recently, its regenerative capacity has been questioned owing to the fact that the calcium hydroxide is more reactive than inductive. The failures were in the form of chronic pulpal inflammation and internal resorption. Internal resorption may result from the over stimulation of the primary pulp by the highly alkaline calcium hydroxide.

This alkaline – induced over stimulation could cause metaplasia within the pulp tissue, leading to the formation of odotnoclasts. In addition, undetected micro leakage could allow large numbers of bacteria to overwhelm the pulp and nullify the beneficial effects of calcium hydroxide. Contradicting to

this, it is seen that some low pH commercial preparations of calcium hydroxide, showed earlier and more consistent bridging. Many extensive studies on calcium hydroxide concluded that the state of the pulp, surgical trauma, or the amputation treatment could be the important than the calcium hydroxide per se in inducing success.

Calcium hydroxide for the pulpotomy of young permanent teeth Pulp therapy : permanent teeth Pain symptoms ?

Hot ? Cold ?

“Sweets” ?

Mobility ?

Swelling ?

Oral health assessment Contraindications – Health history ?

Yes

No

Radiographic assessment Possible carious exposure ?

Consultation Referral

Yes

No

Periapical pathosis Routine operative procedure or small mechanical exposure Ca(OH)2 + restoration

No

Yes

Clinical assessment Carious lesion – possible exposure ? exposure ?

Open apex ?

Yes

Yes

No

No Restorable tooth ?

Apexification

Root canal therapy Yes

Root canal therapy

Indirect pulp therapy : Remove deep caries No pulp exposure !

Ca(OH)2 + interim restorative material + restoration

Periodic reassessment Radiographic and clinical reevaluation

Routine operative procedure Ca(OH)2 + restoration

No Extraction + space maintainer

The improved clinical outcomes with the use of calcium hydroxide in young permanent teeth make it the most recommended pulpotomy agent for carious an traumatically exposed teeth. Its use is of particular importance in incompletely formed apex (Apexogenesis).

Procedure : • Anesthetize the teeth to be treated and isolate under rubber dam.

• Excavate all caries and establish the cavity outline.

• Irrigate the cavity with water and lightly dry with cotton pellets.

• Remove the roof of the pulp chamber with a high speed fissure bur.

• Amputate the coronal pulp with a large low speed round bur or a high speed diamond stone with a light touch.

• Control haemorrhage with a cotton pellet applied with pressure or a damp pellet of hydrogen peroxide.

• Place a calcium hydroxide mixture over the radicular pulp stumps at the canal orifices and dry with a cotton pellet.

• Place a quick setting setting zinc oxide eugenol cement or resin reinforced glass ionomer cement over he calcium hydroxide to seal and fill the chamber.

• If the crown is weak stainless steel crown is given instead of an amalgam filling.

The healing process with calcium hydroxide pulpotomy in young permanent teeth is similar to that which occurs in direct pulp treatment.

Apexification : The upper central incisors are the teeth most commonly traumatized in children. Immature roots with open apices may be managed with calcium

hydroxide in either a pulpotomy procedure with calcium hydroxide placement over the vital radicular pulp (apexogenesis) or as temporarty root canal filling material in cases of nonvital immature teeth (apexification).

Procedure : The following steps are involved in the apexfication techniques : • The affected tooth is isolated with a rubber dam, and an access opening is made into the pulp chamber.

• A file is placed in the root canal and a radiograph is made to establish the root length accurately. It is important to avoid placing the • Instrument through the apex, which might injure the epithelial diaphragm.

• After the remnants of the pulp are removed using the barbed broaches and files, the canal is flooded with hydrogen peroxide to aid in the removal of debris. The canal is then irrigated with sodium chloride and saline.

• The canal is dried with large paper points and loose cotton.

• A thick paste of calcium hydroxide and CMCP or calcium hydroxide in polymethyl cellulose is transferred to the canal with the help of an amalgam carrier. An endodontic plunger may be used to push the material to the apical end, but an excess material should not be forced beyond the apex of the tooth.

• A cotton pled get is placed over the calcium hydroxide, and the seal is completed with a layer of reinforced zinc oxide eugenol cement.

The apexification procedure can be carried out in a single or multiple appointments depending upon the signs and symptoms of the presenting case.

As a general rule the treatment paste is allowed to remain for six months. The root canal is then reopened to determine if the tooth is ready

for conventional gutta-percha filling as determined by the presence of a “positive stop” when the apical area is probed with a file.

The closure of the root end, may occur either by continued root development if the formative elements (Hertwig’s sheath) remain, or by the formation of a calcific barrier of the mineralized scar tissue across the apical foramen.

The histological appearance of the apical hard tissue barrier could comprise of cementum, dentin and pulp or cementum like tissue with loose vital connective tissue inclusions or cementum alone either of cellular or accelular type.

The successful outcomes of apexification can be described as follows: • A continued closure of the canal and the apex to a normal appearance.

• A domed shaped apical closure with the canal retaining a blunderbuss appearance.

• No apparent radiographic change but a positive stop in the apical area.

• A positive stop and a radiographic evidence of a barrier but coronal to the anatomic apex of the teeth.

Calcium hydroxide as a root canal filling material for primary teeth.

The best treatment of a primary pulp is the prevention of pulpal disease through preventive and therapeutic measures. A healthy primary tooth is the ideal space maintainer. Pulpectomy is always just a compromise, but with which is, taking proper indication into account, preferred to an extraction. The therapeutic goals are to eliminate the necrotic pulp and the microorganisms and to ensure the hermetic seal of the root canals, so that the primary tooth can complete its function until the normal exfoliation.

Ideal requirements of the primary root canal filling :

• Should resorb at a similar rate as that of the primary root.

• Should be harmless to the periapical tissues and the succedenous permanent tooth germ.

• Should resorb readily if pressed beyond the apex.

• Should be antiseptic.

• Should be easy to manipulate and fill the root canals.

• Should adhere to the walls of the canals and not shrink.

• Should be easy to remove if necessary.

• Should be radiopaque.

• Should be discolor the tooth filled.

None of the materials currently available meet all the above mentioned criteria.

Presently, the most commonly used materials are the zinc oxide eugenol, iodoform based pastes and calcium hydroxide.

Studies have shown that calcium hydroxide is the material of choice for the in the primary teeth as it shown to have less periapical reaction when the material extrudes the beyond the apex, when compared to the materials.

Though it is thought to resorb faster than the root (not very significant), it is said that it creates a sterile environment in the canal thereby inhibiting the infectious process. Calcium hydroxide is especially indicated in children undergoing irradiation therapy as other materials are considered mutagenic, toxic and allergic.

The common commercial calcium hydroxide preparations used as a filling material are Vitapex and Endoflas.

Vitapex, is a viscous mix of calcium hydroxide and iodoform which used initially in Japan and more recently in the USA and South America with good clinical and radiographic results.

Endoflas (sancor and Cia.S.en C.S., Cali, Columbia), is a resorbable paste produced in South America, it contains similar components as Vitapex, with the addition of zinc oxide eugenol. This paste is obtained by mixing a powder containing tri-iodomethane, zinc oxide, calcium hydroxide, barium sulphate and iodine dibutilorthocresol with a liquid containing eugenol and paramonochlorophenol. The main difference between Endoflas and other pastes is that the latter resorbs when extruded extraradicularly, but does not wash out intra-radicularly. These preparations are available in premixed syringes with disposable tips and hence make the filling of the primary root canal much easier.

Apical plug : In situations where there is an open apex or indeed normal apical anatomy the dentin chip plug in the periapical tissue has been advocated as an artificial but biological apical stop against which gutta-percha can be condensed. The intentional extrusion of calcium hydroxide powder to act as an apical stop enabling condensing of gutta-percha has been advocated with good clinical success rates.

A slightly different technique of packing calcium hydroxide as a mechanical plug into the apical 2 mm of the tooth followed by laterally condensed gutta-percha resulted in less dye penetration than in apices without the plug.

Dressing of the root canal : It is doubtful whether a routine calcium hydroxide dressing is necessary for the root canal therapy in the canals that contain vital pulp tissue as these are not infected prior to the instrumentation, or in contaminated canals which have been cleaned and shaped with modern instrumentation techniques. However, if a root canal is heavily infected prior to instrumentation, it is highly probable that a few bacteria will

remain. In these circumstances, a dressing with calcium hydroxide which can be placed the full length of the canal is the treatment of choice.

Long-term temporary dressing : When a dressing is placed in the root canal it is removed after a few days and the root canal permanently filled with gutta-percha. On occasion it is necessary, for reasons of personal convenience, to leave the dressing in the root canal for a considerable period of time. Under these circumstances calcium hydroxide may be regarded as the dressing material of choice because its antimicrobial effect may last for weeks, whilst that of other materials.

Treatment of infected root canals and periapical lesions : Periapical granulomata may be formed by the immunological responses of the apical tissues to chronic infection within the root canal.

When small they are sterile, but as they increase in size they may contain in increasing variety of bacteria. In such cases it seems reasonable to use a dressing which can be placed as close to the lesion as possible. Calcium hydroxide can be used as a root canal dressing un teeth with large periapical lesions, and in cases where it is necessary to control the passage of periapical exudates into the canal. Calcium hydroxide accelerated the natural healing of periapical lesions, regardless of the bacterial status of the root canal at the time of placement of the material.

Treatment of weeping canals : Calcium hydroxide is now widely used to reduce the seepage of apical fluids into the canal so as to allow the placement of a satisfactory root filling. The mechanism whereby the reduction of the seepage occurs is probably due to : •

The formation of a fibrous barrier when calcium hydroxide is placed in direct contact with the host tissues.

•

The contraction of the capillaries

•

Acts as a mechanical barrier The ability of calcium hydroxide to dissolve necrotic tissue is useful,

as anatomical problems often make it difficult for the irrigating solutions to reach all the areas of the root canal. In this respect, it has been found that when a calcium hydroxide dressing was used in addition to irrigation with solutions sodium hypochlorite, the canal was cleaned as effectively as when ultrasonic instrumentation was used.

Calcium hydroxide in the prevention of root resorption : Idiopathic : Calcium hydroxide is frequently used as a dressing for the treatment of both the internal and external inflammatory resorption, in order to halt the process and encourage remineralization. It is doubtful whether the material has any real beneficial effect on internal resorption, as this is now considered to be sustained by infection within the dentinal tubules coronal to the resorptive process. At one time it was thought that the osteoclasts and osteocytes originated from the same progenitor cells, and that osteoclasts could divide into osteoblasts, presumably under the influence of calcium hydroxide. However, it is now considered that these two cell types have different origins. Whether the resorption is external, or internal with communication to the periodontal membrane, calcium hydroxide is probably the initial treatment of choice, and used in the same manner as described for apexification.

Recently, further doubt has been expressed about the usefulness of calcium hydroxide in cases of early external cervical inflammatory resorption, where there is no direct communication with the surface of the root, as it has shown that calcium ions and hydroxyl ions could not diffuse through the dentin. Hence the important aspect of treatment seems to be the elimination of the source of infection from the root canal, and its obturation.

Following the replacement of an avulsed tooth, or transplantation of a tooth

Once an avulsed tooth has been splinted in position for about two weeks the root canal should be thoroughly cleaned and dressed with calcium hydroxide for a period of 3-6 months, prior to the placement of a conventional root canal filling. Although it has been shown that calcium ions and hydroxyl ions do not diffuse through the dentin, the calcium hydroxide may still permeate through the lateral canals. One should note that the immediate placement of calcium hydroxide may stimulate early resorption. This is because calcium hydroxide diffuses through the apical foramen, further injuring the cementum and initiating resorption. Calcium hydroxide treatment has not effect on the replacement (ankylosis) once it has been established. The principles of managing the transplanted teeth, once pulpal necrosis has been confirmed, are essentially the same as those that relate to replantation.

Calcium hydroxide in the repair of iatrogenic perforations : It has been reported that perforations of the root canal wall, by the instruments or by posts, may be treated in a similar way to the apical closure, in an attempt to hard tissue formation. The timing of this procedure is similar in both the cases, and is very much related to the size of the perforation and the avoidance of extrusion of excess material through the perforation. The early preliminary dressing of the perforation with calcium hydroxide is very important to prevent the in growth of granulation tissue.

This is attributed to the fact that the fibroblasts from the periodontal membrane lack the capacity of the pulpal fibroblasts to differentiate into odontoblasts. The success rate for non-surgical treatment of perforated root canals, which included calcium hydroxide dressing, was the poorest in the cervical region, and could be attributed to the close proximity of the epithelial attachment leading to a permanent periodontal defect.

Calcium hydroxide in the treatment of horizontal root fractures :

When root canal therapy is required in these teeth it is difficult to retain the root filling, particularly the sealer, within the coronal section of the root, from which it tends to extrude into the fracture site. In these cases it has been suggested that a preliminary dressing of calcium hydroxide left in place for 3-6 months may encourage soft tissue healing and possibly mineralization at the fracture site. This will provide a barrier for the subsequent condensation of the filling material.

Calcium hydroxide as a root canal sealer : Calcium hydroxide has had such a long association with endodontics but it is surprising that the commercially available calcium hydroxide root canal sealers were not developed till recently. Calcium hydroxide – based root canal sealers which have introduced as an alternative to the conventional zinc oxide eugenol – based sealers are Sealapex and Calcioboitic Root Canal Sealer (CRCS). In case of the former the setting mechanism is retarded, by the placement of the hydroxide with calcium oxide, compared with the lining cement.

The rationale for the use of these materials is that if they are used in canals with wide apical foramina, perforations or fractures, mineralized repair may further be induced.

When the pattern of release of calcium ions and hydroxyl ions from different sealers was investigated, it was found that Sealapex released more ions and disintegrated more rapidly than CRCS. It was also found that, the although the release of calcium ions from CRCS was negligible, the material continued to alkalize its environment, possibly due to the free eugenol combining with calcium ions as they were released.

In this context it is important to note that whether these root canal sealers promote a quicker healing or a more predictable tissue response than non-calcium hydroxide sealers has not yet been evaluated.

Miscellaneous applications of calcium hydroxide :

As a dentin desensitizing agent : Calcium hydroxide has been advocated for the relief of hypersensitive root dentin. The proposed mechanisms for reducing dentin permeability include : •

Physical blockage of the tubule orifices.

•

Production of precipitates or mineralization.

•

Stimulation of secondary dentin.

As a micro leakage demonstrator : A relatively novel application of calcium hydroxide is an a micro leakage demonstrator. This based on the solubility and hydroxyl ions release of the cements. The pH paper change of the filling lined with calcium hydroxide can be noted by placing a pH paper over the fillings which are then treated with ice water (pH 7). Subsequent micro leakage can be detected by noting the color change of the pH paper. This method is a simple, biocompatible and a quick way to detect micro leakage.

Calcium hydroxide in the treatment of coronal radiolucency : Coronal radiolucency is a term used to describe an anomaly presenting as an abnormal radiolucency resembling caries within the coronal tissues of un-erupted permanent teeth.

Etiology : •

Periapical infections of the primary teeth

•

Pre-eruptive caries

•

Developmental aberrations

•

Inclusion of uncalcified enamel

•

Idiopathic external resorption After the proper diagnosis if the lesion is progressive then immediate

surgical intervention is carried out. Caries is removed with proper

debridement and subsequent dressing of calcium hydroxide which promotes healing.

Calcium hydroxide in the pin retained restorations : In the event that the pulp chamber is penetrated with the twist drill or the pin, in order to enhance the possibilities of healing, a bead of calcium hydroxide is taken on the tip of the absorbent paper points and applied as deep as possible in the pin channel. The tip of the pin is then soaked in the calcium hydroxide paste and inserted very gradually into the pin channel stopping short of the pulpal penetration. This promotes healing by calcific barrier provided by the pulp-dentin organ is healthy originally.

ADVANTAGES OF CALCIUM HYDROXIDE 1. It is initially bactericidal to bacteriostatic 2. It promotes healing and repair 3. The high pH stimulates fibroblasts 4. It neutralizes the low pH of the acids present at the inflammation site 5. It stops internal resorption 6. It is inexpensive and is very easy to use when compared to most of the materials sharing the same properties 7. The calcium hydroxide particles may be used to obturate open tubules DISADVANTAGES OF CALCIUM HYDROXIDE : 1. Does not exclusively stimulate dentinogensis 2. Does not exclusively stimulate dentin bridge formation 3. Associated with primary tooth root resorption 4. May dissolve after one year with cavo surface dissolution 5. Acids may degrade the interface during the etching process 6. Degrades upon tooth flexure 7. Interfacial failure upon amalgam condensation 8. Associated with recurrent caries upon loss 9. Tunnel defects seen in the bridges after one year

10.It does not adhere to the vital dentin 11.Does not adhere to bonding resin composite systems 12.Toxicity seen in the form of neurocutaneous syndrome 13.Bacteria like enterococcus faeclis, fusobacterium nucleatum etc survive and show a stable growth even at that high pH.

DISCUSSION - CALCIUM HYDROXIDE : A CHIMERA ?

Calcium hydroxide agents have been used since the 1930s as a base, liner, apical closure etc., and perhaps the most widely used dental restorative material around the world. As seen earlier pulp and periapical tissues have an inherent capacity to heal and repair when treated with different calcium hydroxide systems. however, a number of questions plague the clinician when confronted with the choice of using calcium hydroxide.

Does calcium hydroxide provide a true seal ?

Certain two paste calcium hydroxide materials do provide in vivo antisepsis of carious dentin, an important property for indirect pulp treatment. However this antibacterial property is transient, and there is not long term mechanical seal of the restoration interface due to the material’s non-adhesive property. Traditionally calcium hydroxide liners adhere to dentin by weak van der Waals forces, conferring no adhesive capacity.

Moreover, currently available adhesives fail to bond to the interface of most two-paste calcium hydroxide agents. The placement of a two-paste calcium hydroxide liner or base to the cavity wall decreases the hybridization reaction, reducing the formation of a seal against the dentin interface.

Calcium hydroxide and dentin bridge defects : Calcium hydroxide materials have been popular due to their reported ability to stimulate reactionary and reparative dentin bridge formation.

However, the clinical utility of this property is reduced by the demonstration of incomplete dentin bridge formation.

Certainly the dentin bridges are permeable. They are less permeable as they get older and thicker but will always be somewhat permeable, although probably not as permeable as the vital primary and secondary dentin around them. In fact, the mineralization of the first layer of a new dentinal bridge is least permeable and most protective. As the coronal

surface of the bridge has a few dentinal tubules or none at all, the contact between an irritating agent and the odontoblastic processes is more difficult.

One must not compare a thin porous reparative dentin bridge formed in several weeks after calcium hydroxide application with a dense, thick barrier of reparative dentin formed over the years. Several writers have indicated that the hard tissue barriers are not so permeable to compromise the benefit of the treatment.

Certainly if bacteria, toxins, dyes or isotopes reach the bridge, these elements will penetrate it as they would normal primary and secondary dentin. If a completely non-porous bridge is thought to be the desired ideal result, this is more than nature requires of itself. Certainly a permeable bridge is better than no bridge.

Calcium hydroxide : resorption versus stimulation : Pediatric dentists have reported that calcium hydroxide is responsible for causing and early exfoliation of the primary teeth. Certainly there is an increase in the resorption in primary teeth and this could be attributed to the fact that root resorption is already in progress at the time of pulp treatment.

The root resorption may not be apparent radiographically in terms of root blunting, but the vascular changes may be in progress.

When the pulp treatment is performed on the occlusal or incisal portion of the pulp of a primary tooth with physiologic root resorption in progress and the coagulated necrotic tissue has to be replaced by granulation tissue, an exaggerated blood supply on both the ends results with the speed up of the already present resorptive process.

On the other hand endodontists utilize calcium hydroxide agents as a predictable interim procedure for the non-surgical treatment if internal resorption, perforations and canal asepsis before obturation or final repair.

Restorative dentists also use calcium hydroxide materials for pulp

treatments. Hence calcium hydroxide can cause resorption as well as stimulation of hard tissue depending upon the ambience.

CONCLUSION Calcium hydroxide has been around the century and the research surround it’s properties and use, has increased dramatically in the recent years. Many newer materials are now available in the market, which claim to be superior to calcium hydroxide. But how possible is the use of these materials in the Indian scenario?

When compared to the prices of the newer materials calcium hydroxide is more cost effective. Some preparations of calcium hydroxide are still, expensive but a simple calcium hydroxide powder and sterile water can serve many purposes and works out to be reasonable and affordable to many patients who visit the Indian dental clinics. One must also consider the ease in manipulation and the time factor associated with the calcium hydroxide preparations.

Though calcium hydroxide has limited use in the primary teeth, it has innumerable applications in permanent teeth, especially the young.

Although calcium hydroxide has become one of the most widely accepted materials in the dental office and catholicon to most of the problems if not all!!!.

What makes calcium hydroxide so special to dentistry? Probably the answer to this question could be that it is one of those few materials which has both an antibacterial property and an august property of inducing a hard tissue barrier, an elixir of life for the dying teeth!

CALCIUM HYDROXIDE Outline 1.

INTRODUCTION

2.

THE FLASH BACK

3.

COMPOSITION OF CALCIUM HYDROXIDE

4.

PROPERTIES OF CALCIUM HYDROXIDE

5.

CLASSIFICATION AND CLINICAL INDICATIONS

6.

CALCIUM HYDROXIDE, HOW DOES IT WORK ?

7.

APPLICATIONS OF CALCIUM HYDROXIDE

8.

DISCUSSION - CALCIUM HYDROXIDE : A CHIMERA ?

9.

CONCLUSION

CALCIUM HYDROXIDE

PRESENTED BY

DR.R.SUNEETHA DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS