Introduction: The original approach for the treatment of caries was purely surgical. It was thought that the only effective method of eliminating the disease was to completely remove all of the demineralised area of the tooth structure. Even the smallest area of demineralization required the removal of standard amount of sound tooth structure to prevent the progression of disease. This technique had been developed by Dr. G.V. Black as “Extension for prevention” which led to specific of sound tooth structure. Over recent years, the dental profession has shifted towards practicing preventive dentistry and adapting more conservative and tooth preserving procedures. In today’s seminar, I would like to discuss about newer invasive techniques for caries excavation. The techniques available to excavate caries clinically can be classified according to B.D.J. 2000 as: Category
Techniques
1. Mechanical, rotary
Hand pieces + burs
2. Mechanical, non-rotary
Hand excavation, air abrasion Ultrasonics, sonoabrasion
3. Chemo-mechanical
Caridex, carisolv and enzymes
4. Photo-ablation
Lasers
Each of the above mentioned techniques have their own claims of removing demineralise dentin selectively Chemomechanical Method: An ideal method should fulfill certain factors to satisfy, both the operator as well as the patient. They are: a. Comfort and ease of use in the clinical environment. b. The ability to disseminate and remove diseased tissue only. c. Being painless, silent, requiring only minimal pressure for optimal use. d. Not generating vibration or heating during periods of operation. e. Being affordable and easy to maintain. The handpieces and burs are in universal use with their obvious disadvantages like: -
Sensitive to vital pulp.
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Pressure/heat on tooth.
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Necessity of L.A.
It was at this point that chemo-mechanical approach came in. It was claimed to be a non-invasive alternative for removal of caries. The technique involved applying a solution onto the decayed dentinal tissue allowing it to soften the tissue and finally scraping it off with blunt hand instrument. Many solutions were introduced and marketed since 1970’s which I would be discussing in detail. Before discussing individual products I would first like to enlighten the layers present in carious dentin, which have importance in our seminar regarding the chemicals. Carious dentin consists of two layers: 1. Outer layer. 2. Inner layer. 1. Outer layer: -
Decalcified – degenerated collagen fibres.
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Infected – non remineralizable.
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Necrotic (This layer should be removed).
2. Inner layer. -
Between outer and normal dentin.
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Less decalcified.
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Bacteria free.
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Remineralized collagen fibres present.
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Vital odontoblastic process present. This layer should be left intact.
Ideally, when preparing the decayed tooth one should remove the outer decayed dentin layer while retaining the inner remineralizable layer intact. The chemomechanical method claims to do so. Let us now see the different products available to us. Chemo-mechanical approach: The chemo-mechanical approach was initially introduced in 1972 in the form of G.K. 101 solution. In 1976, Goldman and Kronman reported on the possibility of removing caries chemically using GK-101 (NMG), which consists of:
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N-monochloroglycine (NMG).
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Sodium hypochlorite.
Glycine was added to counteract the corrosive effect of NaOCl. (Also called as GK-101G.) Its mode of action has been described as chlorination of free amino groups i.e. chlorination of amino groups of peptide bonds of protein forming NMG compounds This NMG has the ability to convert hydroxy proline an important factor to pyrole-2-(its glycine peptide carboxy glycine.) Therefore the partially degraded collagen in carious dentin was chlorinated by NMG solution and this also affected the secondary and quaternary structure of collagen by disrupting hydrogen bond. In this way carious material removal was facilitated. GK-101 (NMG) was tested in bovine Achilles tendon collagen to observe as what actually happens to the collagen fibres. SEM evaluation showed. 1. Fraying fibrils – i.e. essential structure was intact, but there was separation of few peripheral fibres. 2. Spiraling fibrils – i.e. attraction between adjacent fibres was lost and there was shortening of individuals fibres. 3. Dissociating fibrils – i.e. structure was totally separating; fibre orientation was poor and hard to define. 4. Amorphous material – i.e. there was little definitive structure and material which was hard to define as collagen. Advantages: 1. Absence of pain. 2. Absence of any deleterious effects on pulp. 3. Studies done by Kurosaki et al and Brannstorm et al showed that it removed only outer carious diseased layer. They presumed that the softening may be due to a selective attack of the solution specifically on degenerated collagen fibres, without affecting sound fibres of the inner layer and normal dentin underneath. Disadvantages: The process was very slow. Later they found that the system was more effective if glycine was replaced by amino-butyric acid, which evolved in the GK-101E, which was approved by FDA (food and drug administration) in 1984 and was commercialized as “CARIDEX” GK-101E, contained instead of NMG – “N-monochloro-DL-2aminobutyric acid” (NMAB). The system consists of:
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Reservoir.
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A heater.
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A pump.
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A handpiece with application tip with various shapes and sizes.
In vitro studies done by – Goldman et al stated that Caridex removed both the layers of caries leaving behind sound dentin. Schertz et al reported that in histological evaluation after using Caridex exhibited 90% of caries with residual decay therefore he concluded that Caridex should be used with a spoon excavator. Clinical studies done by: 1. Zinek et al showed 90-100% removal of decay with Caridex (but it took a very long time.) Rompen and Chorpentier found Caridex not bactericidal in 17 samples cultured from the decay. 2. Yip et al combined NMAB + 2 urea in deciduous teeth and found it to be better. Pioch and Stachle investigated the shear strength at the DEJ after treatment of Caridex for adhesive and bonding systems. Caridex was found to reduce the shear strength at the DEJ in bovine teeth. This was attributed because of the denaturation of the collagen. This disadvantage is to be related to fracture of tooth still needs further clinical studies and investigations. 3. Kurusaki et al, Walkman et al and Wedenberg and Burnstein investigated individually the biocompatibility of Caridex to pulp. They found it to be biocompatible because of the alkalinity of Caridex; it was found to produce a hard tissue matrix formation below the necrotic zone. Zones: 1. Transient. 2. Dark. 3. Body of lesion. 4. Surface. Yip et al investigated the mineralization of dentinal surface remaining after Caridex usage in a small sample. They used “back scattered electron imaging” (BSI) and “electron probe micro-analysis” (EPMA) which measured the surface level of Ca + + and P - . The authors concluded that the amount of Ca and P was 2:1 which matched with the sound dentin because it is better.
5. Other studies have reported that often usage of Caridex, the dentinal surface produced. -
High degree of roughness.
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Undercuts.
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Dentin scales.
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Dentin tubules were partially patent.
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Smear free surface.
They postulated that it was better for adhesive restorative material without the necessity of acid etching. 6. Zinck et al also evaluated patient acceptance and found out 93% acceptance level. Although Caridex had many advantages it was -
Very expensive. -
Time consuming.
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Had bulky delivery system.
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Needed additional mechanical means to remove decay.
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Large volumes of solutions were required from (200-500ml.)
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Following this, a gel based system was introduced in collaboration with medical team (Dental attracting: Gotiberg AB) in 1998 called Carisolv (Dental update 2000).
Carisolv was initially approved for clinical use in dental practice by the Swedish counter part to US FDA. Composition: The formulation is isotonic in nature and consists of 2 syringes. I.
Syringes – 0.5% NaOCl
II.
Syringe 3 amino acids
glutanic Lucine. Lysine.
Gel substance – carboxy methyl cellulose Sodium chloride Sodium hydroxide
Erythrosine – to make the gel visible Saline solution (i.e. colonizing indicator). Mode of action: Carisolv is alkaline in nature with a pH of around 11. Upon mixing, the positively and negatively charged groups of amino acids become chlorinated due to presence of NaOCl and NaOCl constituents. This leads to interaction with dentin which involves proteolytic degradation of collagen rather than demineralization of collagen, this softening and removal of the carious altered dentin and preserving the sound dentin. The gel consistency allows the active molecules access to the dentin for a longer period than the equivalent irrigating solution in Caridex system. This gel also helps by lubricating the hand instrument specifically designed for Carisolv. The instrument consists of 4 different handle with 8 interchangeable tips ranging from 0.3mm-2mm. These instruments resemble excavators, but they are designed to be used in rapid whisking or curetting fashion, thereby limiting only to diseased tissue. The configuration of instrument allows access to all areas of lesion. Helps to give a tactile sensation. Helps in differentiating between carious and non-carious. Helps to apply the gel. Cavity preparation: The two syringes should be mixed just prior to use, as its efficiency decreases after 20-30mts. The two gels are mixed till a uniform colour is obtained in a dapen dish. The mixed gel is then applied to carious lesion and left in place for 30 seconds to allow it to degrade the diseased dentin before instrumentation. Rapid, light pressure is applied with instrument to facilitate caries removal. As the caries removal, the gel becomes cloudy with debris indicating cleaning with water. Gel is applied again for further removal. Assessment (i.e. when to stop): 1.
When the gel no longer becomes cloudy.
2.
Tactile sensation on the carious dentin will present with “a catch” whereas in a sound dentin the instrument will pass easily.
3.
After completion, the cavity appears frosted and irregular appearance as compared to smooth preparation of conventional bur and hand piece.
The reason for their visual difference is that in a conventional preparation the presence of smear layer, which is over the underlying dentin, gives a smooth, glossy appearance. In contrast, in chemo-mechanically treated dentin lacks smear layer and also forms irregular dentin layer giving a matt finish. Patient’s acceptance: 1. Shorter time. 2. No pain and discomfort. A number of theories have been postulated as to why there is reduce pain. They are: a.
Lack of cutting into caries-free dentin.
b.
Relatively few dentinal tubes are exposed.
c.
There are no vibrations from drilling.
d.
No temperature variations.
e.
Dentin is always covered with a isotonic gel at body temperature.
f.
Psychologically quiet and less traumatic experience.
Indications: 1.
Where preservation of tooth structure is important.
2.
Removal of root / cervical caries.
3.
Management of coronal caries without cavitation.
4.
Removal of caries at the margins of crown and bridge abutments.
5.
Completion of tunnel preparation.
6.
Where L.A. is contraindicated.
7.
in anxious patients.
8.
in deciduous dentition.
9.
A traumatic restorative technique (ART).
Advantages over Caridex: 1.
Three amino groups are incorporated instead of one because interaction and degradation efficiency is increased.
2.
Carisolv has higher viscosity, which allows for application of higher concentration of amino acids and NaOCl without increasing the total volume or amount (only 0.2-1.0ml Carisolv required as compared to Caridex i.e. 250-500ml).
3.
Increased viscosity also helps in precision placement.
4.
The gel does not need to be heated or supplied through a pump.
5.
Improved shelf life.
In vitro studies: ďƒ˜ Jepsen et al analyzed collagen structure of residual dentin after usage of Carisolv. They found that it differed from sound dentin and had characteristic denatured collagen. In clinical studies: From the abstracts published in Stockholm different authors concluded individually that although Carisolv removed 99% of decay, it was slower as compared to conventional techniques.
Enzymes: Studies have examined that caries could be removed by enzymes: 1989, Goldberg and Keil successfully removed soft carious dentin using bacterial achromobacter collagenase which did not effect sound dentin. Enzyme pronase, a non specific proteolytic enzyme originating from streptomyces griseus also helps in removing caries. Still experiments are going on for the validity of such enzyme. Lasers Laser technology making great inroads into lot of areas of dentistry today.Lasers have been tried out in dentistry for over two decades but have come into the forefront as an everyday not only in the last 3 or 4 years. The laser is an acronym for the Light Amplification by Stimulated Emission of Radiation.
A) 1. 2. 1.
Lasers are classified: Based on wavelength: Soft lasers Hard lasers Soft lasers – are lower power lasers with a wavelength of around 632nm eg. He-Ne, Diode.
2. Hard lasers – are well known laser systems for possible surgical applications and have a higher wavelength. B) Based on the lasing medium: Lasers can be classified according to the state of the active medium i.e. 1. Solid e.g. Nd: YAG, Diode. 2. Liquid e.g. Dye (toludine blue). 3. Gas e.g. CO 2 , Argon, Er: YAG. Nitrogen C) Lasers are classified into four groups according to the international system: The basis of the third classification is the potential danger posed to the exposed skin and to the unaccommodated eye Details about the individual lasers: A) CO 2 Lasers - The CO 2 laser first developed by Patel et al in 1964 is a gas laser, which has a wavelength of 10.6µ or 10,600 nanometers deep in the infrared range of the electromagnetic spectrum - CO 2 lasers have an affinity for wet tissues regardless of tissue color. - The laser energy weakens rapidly in most tissues because it is absorbed by water. Because of the water absorption, the CO 2 laser generates a lot of heat, which readily carbonizes tissues. Since this carbonized or charred layer acts as a biological dressing, it should not be removed. - They are highly absorbed in oral mucosa, which is more than 90% water. High absorption in small volume, results in a penetration depth as shallow as 0.2 to 0.3mm. - There is no scattering, reflection, or transmission in the oral mucosa. Hence, what you see is what you get. - CO 2 lasers reflect off mirrors, allowing access to difficult areas. Unfortunately, they also reflect off dental instruments, making accidental reflection to non-target tissue a concern. - CO 2 lasers cannot be delivered fiber optically. Advances in articulated arms and hollow wave-guide technologies now provide easy access to all areas of the mouth. - Regardless of the delivery method used, all CO 2 lasers work in a non-contact mode. Of all the lasers for oral use, CO 2 is the fastest in removing tissue. As CO 2 lasers are invisible, an aiming helium – neon (He-Ne) beam must be used in conjunction with this laser. B) Nd: YAG Laser -
Developed in 1964 by Gensic et al, it stands for neodymium: yttrium- aluminumgarnet. This solid-state laser consists of crystals of yttrium-aluminum-garnet doped with neodymium (1-3% a rare earth element).
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Nd:YAG laser, has a wavelength of 1.064 nm (0.106) placing it in the near infrared range of the magnetic spectrum.
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It shows low absorption with water as well as hydroxyapatite. Therefore the laser power diffuses deeply through the enamel and dentin and finally heats the pulp. Thus, they have various degrees of optical scattering and penetration to the tissue, minimal absorption and no reflection.
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Nd:YAG lasers work either by a contact or non-contact mode. When working on tissue, however, the contact mode in highly recommended.
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The Nd:YAG laser is delivered fiber optically and many sizes of contact fibers are available.
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Carbonized tissue remnants often buildup on the tip of the contact fiber, creating a ‘hot tip’. This increased temperature enhances the effect of the Nd:YAG laser, and it is not necessary to rinse the build up away. Special tips like the coated sapphire tip can be used to limit the lateral thermal damage. A black enhancer can be used to speed the action of laser. A helium-neon-aiming beam is generally used with Nd:YAG laser. Penetration depth is 2 to 4mm. Most dental Nd:YAG lasers work in a pulsed mode. At higher powers and pulsing, a superheated gas called plasma can form on the tissue surface. It is this plasma that can be responsible for the effects of Coagulation, vaporization or cutting. If not cooled (eg. by running a water stream down the fiber), the plasma can cause damage to the surrounding tissues. The Nd:YAG beam is readily absorbed by amalgam, titanium and non-precious metals, requiring careful operation in the presence of these dental materials.
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C) Er:YAG laser (Erbium :YAG) The Er:YAG is a very promising laser system because the emission wavelength of 2.94 µm coincides with the main absorption peak of water resulting in good absorption in all biological tissues including enamel and dentin. This is the first laser to be cleared by the FDA on May 7, 1997 for use in preparing human cavities. - A number of researchers have demonstrated the Er:YAG lasers ability to cut, or ablate dental hard tissue effectively and efficiently. - A variety of restorative materials such as zinc phosphate, zinc carboxylate, glass ionomer cements and silver amalgam can be effectively removed by the Er:YAG laser. - Pulpal response to cavity preparation with an Er:YAG laser was minimal, reversible and comparable with the pulpal response created by a high-speed drill. - Er:YAG can also be used for bone ablation and has indications in soft tissue surgeries where no coagulation effect is desired such as removal of hyperplastic gingival tissue, periodontal surgery and ablation of large benign lesions of the oral mucosa and skin.
APPLICATION OF LASERS IN CAVITY PREPARATION The use of lasers for cavity preparation has been under scrutiny for 20 years as many investigators found that pulpal necrosis occur with the use of lasers. The reasons for necrosis are: i. The heat produced. ii. The total power output (J/cm²).
The search for a laser that can be used to cut hard tissues began in 1964 by Dr. Leon Goldman who used laser on his brother Bernard’s teeth. The subsequent search included many laser wavelengths such as CO 2 but its disadvantages include cracking with flaking of the enamel surface. Nd:YAG laser at 10 J/cm² has shown to inhibit incipient carious lesions but at higher densities, it causes irreversible pulpal damage. Other lasers have been investigated. Er: YAG at the wavelength of 2.94 µm has shown most promising results. A number of researchers have demonstrated the Er:YAG laser’s ability to cut or ablate dental hard tissues effectively and efficiently. Animal studies have reported that the pulpal response with Er:YAG laser was minimal, reversible and comparable to a high speed drill. The temperature use with this type of laser was less than 3°C. Moreover, a water coolant can also be used. More recently Er, Cr:YSGG (erbium, chromium: yttrium - scandium-gallium garnet) with a wavelength of 2.97µ has also shown to be effective for cutting enamel, dentin and bone. This device has been shown to create precise hard tissue cuts by virtue of lasers interaction with water at the tissue interface and has therefore been termed, hydrokinetic system or HKS. Animal studies carried out by Eversole et al 1997 has shown that Er, Cr:YSGG HKS is effective for dental hard tissue surgery and fails to exit any adverse pulpal periodontal reactions.