INTRODUCTION Restorative dentistry plays an important role in the field of dentistry in restoring the tooth tissue to its form, function esthetics and in maintaining the physiologic integrity in harmony with the surrounding hard and soft tissues. Many of the restorative material used did not adhere to enamel to dentin by physical and / or clinical interactions thus increasing the chances of microleakage at restoration tooth interface. The production of a stable long term bond to the tooth substance is an ideal requirement for the success of all restorations. An adhesion permits the placement of a more conservative restoration, reduces microleakage and dentin sensitivity. A solid understanding of biological, chemical and physical aspects of these adhesives is very essential for their proper use in field of dentistry. HISTORY ďƒ˜ After the success of adhesion to enamel through acid etching by Buonocore in 1952, adhesion to dentin was the main concern as
1
most of the materials used than such as silicate cements, unfilled resins lacked this property. First reports of in vitro studies were those by Kramer and Mclean in 1952 and Buonocore in 1955. Kramer and Mclean speculated that the material used might contain a methacrylic acid. The adhesive described by Buonocore was essentially a dimethacrylate with appended phosphate groups. The groups bonded to calcium of tooth via ionic bonding (chemical bond). Bond strength reported was 5.7Mpa. Bonds were hydrolytically unstable. In 1965 Bowen described a system containing surface active Nphenyl glycine glycidyl methacrylate (NPG-GMA) to enhance wetting of the dentin surface and thereby improve adhesion – This was the first generation system. Later second generation system changed the calcium phosphate – resin concept by modifying the resin such as BIS-GMA. These were also not reliable clinically.
2
ďƒ˜ Later in 1980’s a series of solutions were used to increase the wettability of the dentin surface before application of the resin. These systems used more hydrophilic resins. Another systems GLUMA contained HEMA and glutaraldehyde. Glutaraldehyde reacted with amino acids of collagen to form charged compounds which than reacted with hydroxyl (OH -) ion of HEMA by mechanical interlocking. This was the third generation of dentin bonding agents. Disadvantages: -
Time consuming.
-
Technique sensitive.
Advantages: -
Increased bond strength but were still less to withstand stresses generated by polymerization shrinkage of resins (17Mpa).
Definition of Dentin Bonding Agents The dentine bonding agents are di or multi functional organic molecules that contain reactive groups which interact with dentin and the monomer of the restorative resin.
REQUIREMENTS OF DENTIN BONDING AGENTS 3
(Dental Update 2000, 27: 85-93) When developing a clinically acceptable dentin bonding agent following goals must be met. 1) Bond strength – The adhesive should be capable of achieving an acceptable bond strength to withstand the stresses caused by polymerization contraction of composites. Optimum bond strength ďƒ 17Mpa – 20Mpa. 2) Biocompatibility of the material. The adhesion used should be biocompatible with structures in contact with it. 3) Long-term durability of the bond it is a highly desired factor. 4) Prevents microleakage by reduced gap formation between tooth structure and restorative material. 5) Prevents recurrent caries and marginal staining. 6) Be easy to use and minimally technique sensitive. 7) Have a reasonable shelf-life. 8) Have no potential for sensitization of patients or operators. 9) Be compatible with a wide range of resins.
4
10) Show no reduction in bond strength when applied to moist surface. ADHESION Definition: is a process of solid and / or liquid interaction of one material (adhesive/adherent) with another (adhered) at a single interface. Most instances of dental adhesion are also called “Dental Bonding”. Adhesive is defined by the “American society for testing and materials” as a substance capable of holding materials together by surface attachment. Adhesion is a fundamental objective universal to most restorative procedures. Adhesion (according to DCNA 1993) can be classified as: a) Chemical. b) Mechanical. c) Physical. Physical adhesion is by Vander Waals or other electrostatic interactions is relatively weak. Chemical adhesion involves bonding at the atomic or molecular level.
5
Mechanical adhesion is based on retention by the interlocking of one phase into the surface of the other. Mechanical is can be due to: a) Geomechanical effects – These are caused by microscopic porosity or roughness of the surface i.e. mechanical locking provided due to undercuts, grooves. b) Rheological effects – This is caused by the flow of the materials in both liquid or semi solid phase e.g. use of adhesives or cements to hold two substances together. Requirements for adhesion: i)
These must be good wetting in order to produce good bonding.
ii)
Surfaces to be joined must be cleaned.
CHEMISTRY OF ADHESIVE AGENTS (OP Dent Supp / 1992; 5) The dentin adhesives are characterized by containing monomers that have hydrophilic or hydrophobic groups. The polymerized adhesive system should provide a stable link with structure and bulk of the restoration.
6
The chemistry of adhesive agents can be explained as follows: 1) Chemical adhesion. 2) Adhesion by coupling agent. 3) Adhesion by Grafting reaction. a) Chemical adhesion These are of two types: i)
ii)
By primary valence forces which can be by: -
Covalent bonds – strongest
-
Co-ordinative bonds
-
Ionic bonds
are electron pair bonds
By secondary valence forces which can be: -
Intermolecular attraction (Vander Waals forces).
-
Hydrogen bonds.
b) Adhesion by coupling agents -
Coupling agents utilizing the concept of hydrophobic and hydrophilic groups are the monomers based on phosphate or phosphonates.
-
Phosphate group (hydrophilic) reacts with calcium ions of dentin.
7
c) Grafting reaction adhesion: -
Here the specially selected initiators such as rare earth ion Corium IV or butylborones are used.
Adhesion of Restorative Resin to Dentin -
To obtain bonds of desired strength specially formulated dentin bonding agents must be applied to the conditioned dentin before resin placement.
DENTIN BONDING AGENTS MAY ACT a) By way of chemical reaction. b) By their ability to penetrate not only the dentinal tubules but also the intertubular substance of the surface layer of dentin known as “intertubular bonding�.
8
CHEMICAL ASPECTS The dentin bonding agents with chemical activity have the formula: CH3 | CH2 =C | CO – O – R – X
M–R–X
Where M – Methacrylate group R – A spacer X – A group reactive capable of bonding to dentin surface
When applied to dentinal surface dentin is covered wit a layer of double bonds. Application of resin opens up the double bonds resulting in a copolymerization with restorative resin. Thus the methacrylate group of M – R – X molecule reacts with composite resin. The x group may react either with: -
Inorganic component via Ca++ ion bonding or with
-
Organic component via collagen bonding. Ca++
M–R–X
H2 N
Dentin
HO
9
Ca++ bonding adhesives:
1)
The bond between X group and Ca++ is an ionic bond. These include three main groups: i)
Phosphate – based adhesives.
ii)
Adhesives based on amino acids or amino alcohols.
iii)
Adhesives based on dicarboxylates. Examples – Scotchbond and Bondlite.
When adhesives of this type are used alone – strength attained is 6 Mpa. But, when used in combination / conjunction with special conditioning treatments of dentin strength achieved increases upto 1015Mpa. 2)
Collagen bonding adhesives: The bonding sites of the collagen molecule include-
Hydroxyl.
-
Carboxyl.
-
Amino.
-
Amido groups.
10
The four groups of adhesives under this category are: -
Isocyanate (M-R1-NCO)
-
Carboxyl acid chloride (M-R2-COSL) d
-
Aldehyde (M-R3-CHO) CO
-
Anhydride (M-R4 –
O CO
-
The reactions form urethano, urea, ester or amido linkages.
-
The bond is of covalent type.
PHYSICOCHEMICAL ASPECTS -
It involves the interfacial attraction between the tooth surface and the adhesive.
-
Each treatment of the dentin leaves it to a specific condition that requires specific polarity and solubility parameters of the ensuing treatment in the bonding procedure.
-
If this requirement is met, the bonding system will possess maximum efficacy (Amussen and Uno, 1992).
Factors affecting adhesion 1)
There must be an intimate contact between tooth structure and restorative materials. 11
2)
Salivary
and
/
or
blood
contamination
from
contamination. 3)
Moisture handpiece or air-water syringes.
4)
Oil contamination of handpieces or air-water syringes.
5)
Surface roughness of tooth surface.
6)
Mechanical
undercuts
in
tooth
preparation. 7)
Fluoride content of teeth.
8)
Use of fluoride after restorations have been placed.
9)
Dentinal canal characteristics.
10)
Presence of plaque, calculus, intrinsic stains or debris.
11)
Presence of bases or liners on prepared teeth.
12)
Tooth dehydration. 12
13)
Constituents of temporary cements. Dentin surface characterization and problems in bonding with
dentin (Dental Update March 2000). A great deal of difficulties in achieving bonding to dentin is as a result of the complex histologic structure and variable composition of dentin itself. 1.
Enamel is 92% inorganic (hydroxyapatite) by volume dentin has about 65% inorganic component and rest being collagen and water.
2.
Dentin is more hetrogenous in nature.
3.
Hydroxyapatite crystals in enamel are regularly arranged, where as in dentin are randomly arranged in an organic matrix.
4.
Within the dentin there are many variations in the substratei)
Change in volume of dentinal tubules (1%) near surface towards the pulp (22%) of surface.
ii)
Sclerosed dentin, if present is difficult to penetrate.
13
iii)
Presence of intertubular, peritubular dentin.
5.
Presence of smear layer reduces the bond strength.
6.
Presence of surface deposits such as plaque, calculus, pellicle etc.
7.
Dentin is a vital tissue.
8.
Dentin is hydrophilic while most adhesives are hydrophobic.
9.
Low surface energy of dentine.
10.
Concerns of pulpal compatibility.
MECHANISM OF BONDING (latest discoveries) The adhesion agents bonds to dentin via the chemical or micromechanical bond. -
The chemical bond is generated between the intertubular dentin and the primer through the primer’s bifunctional molecules – “intertubular bonding”.
-
The micromechanical bond is obtained through a double mechanism: 14
i)
The bonding agent penetration inside the tubules, where it originates resin tags.
ii)
Creation of resin – dentine into diffusing area. Called hybrid layer- This area is created by the penetration of liquid resin into the etched dentin, and its thickness will be determined by the relation between the depth of action of the etching acid and the penetration capacity of the resin itself. The action of these two mechanisms i.e. the resin tags, which
increases the surface area and hybrid layer, create an excellent tooth restoration junction. The most recent studies carried out by various schools regarding hybrid layers quality drew attention to three points: i)
Need for a wet dentin (wet bonding).
ii)
Importance of exact concentration of acid used and an optimum application time.
iii)
A type of polymerization allowing a good flow of the composite resin on the cavity walls and a perfect saturation of the resin chains.
WET BONDING
15
-
Early bonding systems were highly hydrophobic and the presence of water on dentin surface was inappropriate.
-
Kanca in 1992 demonstrated that bond could be achieved on moist surfaces too.
-
Water may arise from dentinal tubules, fluid atmospheric water, rinsing procedure etc.
-
Currently available systems are likely to contain hydrophilic resins such as HEMA and are much more tolerant of moisture than their predecessors.
-
Dentin surface must be left moist and hot dessicated – which may cause collapse of collagen left intact.
-
Wet bonding has also been shown to improve significantly the marginal seal of restoration in which an acetone based primer is used. However large amount of water on surface may interface with bonding known as “overwet phenomenon�.
-
Acetone containing DBA can tolerate more moist surface without much affect on bond strength.
-
Other systems such as containing ethanol e.g. Scotchbond MP require the dentin surface to be blot dried but not dessicated.
16
-
When acetone containing DBA is applied, acetone primer contacts water, there is increase in its boiling point where as boiling point of water reduces – a process known as “Azeotrophism”.
-
This causes the evaporation of both the acetone and water and the resin is left intact.
-
A wet surface must also be fuel of contaminants from saliva, blood, GCF etc.
Dentin Adhesive System Components of dentin adhesive systems: The three main components are: a) Conditioner. b) Primer. c) Bonding agents / adhesives. A) Conditioners: Definition: Conditioning of dentin is defined as any alteration of the dentin done after the creation of dentin cutting debris usually termed the smear layer. Objective:
17
To create a surface capable of micromechanical and possibly chemical bonding to a dentin bonding agent. Principal effects of conditioner on the dentin are: a. Physical changes. b. Chemical changes.
18
a.
Physical changes: -
Increase or decrease in the thickness and morphology of smear layer.
-
Changes in the shape of dentinal tubules.
b.
Chemical changes: -
Modification of the function of organic matter (usually about 20% by volume).
-
Decalcification of the inorganic portion.
Conditioning of dentin may be done by several means: i)
Chemical modification a. Acidic conditioner. b. Calcium chelators.
ii)
Thermal modifications a. Lasers.
iii)
Mechanical modifications a. Microabrasion.
19
Usually the conditioners employed are: i)
17% EDTA (Gluma).
ii)
1% Nitric acid.
iii)
Tenure (Ferric oxalate).
iv)
Aluminium oxalates.
v)
37% phosphoric acid (All bond-10%).
vi)
2.5% maleic acid.
vii)
10% citric acid.
viii)
Hard tissue lasers viz. pulsed Nd:YAG lasers.
1.
Smear layer removal: -
The initial dentinal surface available for adhesion is covered with a smear layer.
-
This layer is created whenever a dentin is cut or ground and it consists of debris that is smeared across the dentinal surface.
-
It is approximately 1.0mm thick although the thickness may vary depending upon the instrument used in cutting process.
20
-
Along with the smear layers the cutting process results in plug of debris that can extend several micrometers into the tubules.
-
The smear layer and smear plugs thus acts as barrier to the fluid movement to the surface via the tubules and may also limit the access of microorganisms and toxins to the pulp.
-
Removal of the smear plugs increase the permeability of dentin 5-20 times (Pashley 1989) and the following fluid movement would then be detrimental for adhesion.
Dentin permeability changes due to conditioners: -
Conditioner removes the smear layer thus resulting in an increased permeability of dentin.
-
The depth of decalcification and removal of smear layer is affected by various factors including pH concentration, viscosity and application time of etchant.
2. Demineralization effects of conditioners on dentin surface: -
The conditioning agent present in certain dentin bonding agents not only remove the smear layer, but also cause demineralization of underlying dentin.
21
-
Some demineralization may be favourable in order to open up the collagen network and facilitate monomer infiltration but the question then arise as to how much of demineralization is essential for optimum adhesion.
-
It has been stated that demineralization depths of 1015mm are first adequate and below this it is doubtful whether the monomer would effectively penetrate.
-
The demineralization of dentin to a depth greater than monomer can infiltrate and reinforce the collagen network, can lead to decreased adhesion, causes collapse of meshwork. The tooth surface is dried (not dessicated).
B) Primer Definition: Primers are defined as chemicals capable of improving the wettability of adherents or capable of being incorporated into the surface of the substrate to form chemical bonds across the interface (Causton, 1982). The distinction between conditioners and primers is often arbitrary. Acids have been considered dental conditioners and HEMA solutions have been called “Primers�.
22
Whenever an acidic agent is applied to the dentin surface, it either removes, dissolves or modifies the smear layer and partially demineralize the dentin surface. This creates the space within the collagen network by dissolving or removing the calcified apatite crystals and is roughly analogue to the microporosity created by etching the enamel. Once the acid is rinsed off after an appropriate treatment time unlike the enamel, this treatment of dentin produces a low surface energy. This in turn makes the dentin surfaces difficult to wet with normal bonding resins. In order to correct this a primer is necessary. Structure: Primer is a bifunctional molecule i.e. it contains a hydrophobic and a hydrophilic group. i)
Hydrophobic – CH3 – C – C – has the affinity for resin.
ii)
Hydrophilic group – OH – has affinity for the dentinal surface.
Available in three forms: a) Primer. b) Primer with acidic conditions i.e. self etching primer – Example, Clearfil liner bond-2
23
c) One
bottle
bonding system
– Primer
and
resin
combinations.
Role of primer: -
Increases the surface wettability and spreadability of the monomer.
-
Stabilize the collagen fibers.
-
Restores the surface energy.
-
Enhances the monomer penetration.
Examples: i)
HEMA – Hydroxy ethyl methacrylate.
ii)
4META – 4 Methacryloxyethyl trimellitic anhydride.
iii)
BPDM – Biphenyl dimethacrylate.
24
C. Bonding Agents The concepts of using bonding agents are: 1)
Bonding via the dentinal tubules to etched dentine.
2)
Formation
of
precipitates
on
pretreated dentinal tubules with the adhesive resin bonding either chemically or mechanically. 3)
Chemical union to the inorganic, organic or both the components.
4)
Diffusion
and
impregnation
of
monomer into the subsurface of pretreated dentin getting polymerized in site. Creating “resin impregnated layer” or “hybrid layer”. Dentin bonding agents can be classified into six groups of compounds: a) Polyurethane. b) Polyacrylic acids. c) Organic phosphates. d) Mellitic anhydride and methyl methacrylate (4-META). 25
e) Hydroxyethyl methacrylate plus glutaraldehyde (HEMA + GA). f) Ferric oxalate and NPG-GMA (N-phenyl glycerine and glycidal
methacrylate)
and
PMDM
(pyromellitic
dianhydride and 2-hydroxyethyl methacrylate).
1)
Polyurethanes The urethane bonding type is formed by the reaction polyol and
diisoeyanate such as:
HOCH2 –
OH | CH2 | C– | CH2 | OH
+
– N = C = O = Polyurethane
CH2OH N=C=O Diisocyanate
The object is for the diisocyanate to react with the polyol and the –OH or –NH2 groups in the dentin mineral or organic components. The composite can then bond to the polyurethane. 2)
Polyacrylic acids These are comparable to the polymers used in Glass ionomer
cements and are copolymers of acrylic and itaconic acids. The claim is that these organic acids attach irreversible to hydroxyapatite in dentin by
26
displacing the phosphate ions. The composite then attaches to the polyacrylic acids. 3)
Organic phosphonates:
The phosphonate bonding type may or may not be halogenated. O || CH2 = C – C – O – CH2 CH2 – O – | CH3
O | P – CL | CL
Or O || CH2 = C – C – O – CH2 CH2 – O – | CH3
O | P – OH | CL
It is claimed that phosphate end reacts with calcium in hydroxyapatite and the C = C double bond at the other end reacts with the composite. 4)
Mellitic anhydride plus methyl methacrylate The mellitic anhydride is dissolved in methyl methacrylate and is
referred to as 4-META.
CH3 |
O ||
27
O || C ||
CH2 = C – C – O – CH2 CH2 – O – C – O – C – O || || O C || O The objective is for the anhydride to hydrolyse to a diacid with – OH groups on the surface of dentin and function like an acrylic acid the carbon- carbon double bond will react with the composite. 5)
Hydroxyethyl
methacrylate
and
glutaraldehyde HEMA 35%
H–
CH3 | C = CH2
+
Glutaraldehyde 5%
O O || || + H – C – C – CH2 CH2 CH2 – C – H
| C=O | OCH2 CH2 OH HEMA
Glutaraldehyde
The glutaraldehyde reacts with an amino group in the organic portion of dentin and also reacts with HEMA, which in turn will react with the composite through carbon double bond. 6)
Ferric oxalate – NPG-GMA / PMDM systems
This consists of three components:
28
i)
Ferric oxalate: Fe2 (C2O4)3, 6H2O
ii)
NPG-GMA – CH3 H O O | || || || CH2 = C – C – O – CH2 – C - CH2 – N – CH2 – C – OH || | O OH
29
iii)
PMDM
CH3 | CH2 = C – C – O – CH2 CH2 – O – C + || || O O O || OH – e – O O CH3 || || – O – C – C – CH2 CH2 - O – C – C = CH2 | C=O | O | H The ferric oxalate removes the smear layer from dentin and serves as a mordent, while the NPG-GMA and PMDM bond to the dentin and contain carbon-carbon double bonds to react with the composite. Classification of Dentin Bonding Agents: I) On the basis of chemistry II) On the basis of smear layer: i)
Removed -
EDTA
-
Mirage bond
-
Clearfil liner bond system.
30
-
Phosphoric acid and oxalates.
-
Removes the smear layer and opens the dentinal tubules to allow penetration of resin tags for first generation DBA.
ii)
Reversed -
Prisma universal
-
Bond lite
The smear layer is partially removed or left intact. Here the phosphate – calcium bond is used but methacrylate is replaced with BIS-GMA, which will bond to both enamel and dentin. Used for second generation bonding agents. iii)
Modified
1.
-
Tenure
-
Gluma
-
Scotch bond-2 Smear
layer
is
either
fixed
with
glutaraldehyde tannic acid or ferric chloride. Or 2.
Smear layer is removed, and replaced with an artificial crystalline precipitate.
31
III) On the basis of chronology, chemistry and shear bond strength: It was stated by Erick et al (Quintessence Int. 1993; 22 : 967977). Category I Include dentinal adhesives which produces shear bond strength values of 5-7Mpa. Examples: -
Scotchbond dual cure.
-
Dentin adhesit.
-
Gluma.
The failures occurred at the interface or in the resin adhesive. Category II Included the experimental and commercial products derived from Bowen’s work with ferric and aluminium oxalates and have produced shear bond strength values between 8-14 Mpa. Examples: -
Tenure.
-
Mirage bond.
32
As the strength increased, wetability also increased. Category III: Included dentinal adhesives which produced shear bond strength values of about 17-20Mpa Examples: -
Superbond
-
Scotchbond-2
-
Scotchbond multipurpose.
-
All bond
-
The failure is mainly cohesive in nature. This result is attributed to a combination of factors that include effective wetting and penetration of dentinal tubules as well as tendency to leave collagen fibres at the adhesive dentin interface in an apparently structurally intact state (Quintessence Int. 1993; 24: 571-582).
IV) On the basis of Generations: There are six generations of dentin bonding agents: 1)
First generation dentin bonding agents. The agents used in this generation are as follows:
i)
Glycophosphoric acid dimethacrylate.
33
ii)
Cyanoacrylates.
iii)
N-phenyl glycine and glycidyl methacrylate (NPG-GMA).
iv)
Polyurethane.
This mainly consisted of a surface active compomer viz. NPGGMA, added to BIS-GMA resin to facilitate adhesion. The NPG-GMA acted as an adhesion promoter between the tooth structure and resin material by chelating with surface calcium. Disadvantages of 1st generation bonding agents: a)
Hydrolysis
of
glyco-phosphoric
acid
dimethacrylate in the oral environment. b)
Difficulty
in
bulk
polymerization
of
the
cyanoacrylates. c)
Instability of NPG-GMA in solution. These factors in combination with very low bond strengths (3
Mpa) prevented the successful clinical use of these bonding agents. The first commercially available agent was (CERVIDENT (Stainless steel white). Others are: Palakav (Kulzer, USA). 34
Cosmic bond (Amalgamated Dental, England) 2)
Second Generation Dentin Bonding System: In general, these were improved compared to the first generation
bonding agents. The agents used were: i)
Halophosphorous esters of Bisphenyl A glycidal methacrylates (BIS-GMA).
ii)
Polyurethanes : It requires the presence of a smear layer.
Some of the commercial products are: 1. Clearfil (Kurrary Co. Japan) : this product utilizes a reaction product of 2-HEMA and a phenyl phosphate ester. 2. Scotchbond
(3M
Dental
Products)
utilizes
the
halophosphorous esters of BIS-GMA. 3. Bondlite (Kurr). 4. Creation bonding agent (Dent. Mat. Corp.). 5. Prisma Universal Bond (Caulk/Dentsply). Bond Strength – Relief and others 1986 reported the low bond strength.
35
As reported by Solomon and Beech – 1-3Mpa II nd generation bonding systems require a smear layer intact. This was to create a calcium rich layer where the organophosphate can combine with calcium. Disadvantage: It was not possible to achieve a long-lasting bond possibly due to: a) Low bond strength. b) Hydrolysis of the phosphate calcium bond. 3)
Third Generation Bonding Systems: -
This is the most successful group of dentin bonding agents introduced so far, with increased bond strength and improved clinical performance.
-
This
generation
DBA
requires
either
removal,
modification or dissolution of the smear layer. These agents used a conditioning step on the dentin in conjunction with a bonding agent. -
The chemistry of these agents is more diverse than 2nd generation systems and includes various agents for conditioning the dentin.
36
-
This conditioning either modifies or removes the smear layer and subsequently interacts with superficial dentin.
37
Some of the commercially available agents of this systems are: 1)
GLUMA (Bayer Dental, Germany).
2)
Tenure (Dent. Mat. Corp.).
3)
4-META.
4)
Scotchbond 2 and 3 (3M Dental Products).
5)
Prisma Universal Bond 2 & 3.
6)
XR Bond.
7)
Clearfil liner bond (Kurrary Co.).
Description about these systems: 1)
Tenure:
Oxalate was the first available DB system developed by Bowen. This consisted of: a)
Dentin conditioner – 2.5% citric acid + ferric oxalate (stains the teeth).
b)
Resins – NTG-GMA (adduct of N(p-toly glycine and 2-HEMA). -
RMDM (adduct of pyromellitic diahydride and 2-HEMA).
These two resins were applied in powder mixed with acetone.
38
Dentin Bond Strength – 10.2 – 18.2 Mpa Later ferric oxalate was replaced by aluminium oxalate. The present day tenure comprises of : 1)
Conditoner - Phosphoric acid. - 35% aluminium oxalate - 25% HNO3
2)
Primer - 5% NTG-GMA – Tenure A - 10% PMDM – Tenure B
Primer A and B are mixed and applied to conditioned dentin surface. 3)
Resin – BIS-GMA
2)
Gluma:
1) Conditioner - EDTA 2) Primer :
35% HEMA 5% Glutaraldehyde
3) Resin :
55% BIS-GMA -
Dissolves / removes the smear layer.
39
3) Scotch Bond 2 – Dissolves / removes the smear layer. 1)
Conditioner
–
Solubilizes
and
dissolves the smear layer. 2)
Primer - 55% HEMA - 2.5% maleic acid.
3)
Resin - 62.5% BISGMA - 37.5% HEMA
4)
XR-PRIMER / XR-BOND (KERR) This as a newer generation polysystems prepared as a two
component systems. 1)
Conditioner –
2)
Primer – 3.75% phosphonated dimethacrylate ester.
3)
Resin
- 60% UDMA
- 30% TEG-DMA - 10% Phosp-DMA Preserves or modifies the smear layer. 5)
Prisma Universal Bond 2 & 3 (Caulk, Dentsply). 40
Conditioners – Primers- 30% HEMA - 6% PENTA Resin - 50% UDMA - 25% TEG-DMA - 45% PENTA - 0.5% Glutaraldehyde Preserves / modifies the smear layer. The difference between PUB 2 & 3 is : 4) Glutaraldehyde PUB 3 5) Bond strength
PUB 2 – 16.6 Mpa PUB 3 – 18.6 Mpa
6) Clearfil liner system 1.
Dissolves / removes the smear layer. Conditioners - 10% citric acid - 20% CaCl2
2.
Primer – 3% NMSA (N-methacryloyl Saminosalicylic acid).
3.
Resin – MDP.
41
Disadvantages of 3 generation system: 1)
Increased chairside complexity.
2)
More time consuming.
3)
Technique sensitive.
Fourth Generation Bonding System The fourth generation bonding systems are based on the complete removal of smear layer. -
It allows the use of both conservative and alt etch technique.
-
Also known as universal bonding systems as these bond to dentin, enamel, amalgam, porcelain, composite.
Mechanism of bonding (as proposed by Nakabayashi) -
Diffusion and impregnation of resin into the substrate of partially decalcified dentin followed by polymerization creating a hybrid resin reinforced layer.
-
The hybrid layer formed is an acid resistance mixture of polymerize and tooth structure components creating a resin / dentin composite.
42
The recently developed fourth and fifth generation of DBA rely on this hybridization as the primary mechanisms for bonding and sealing.
43
The examples are: 4) All-bond 2 5) Amalgam bond plus 6) Scotchbond multipurpose. 7) Probond 8) Liner bond 2. 1)
Scotch bond MP-
Conditioner – 10% maleic acid and a non-silver containing thickness. Primer – Aqueous solution of HEMA and a polyalkeonic acid compomer. Adhesion - Hydrophobic BIS-GMA. -
Hydrophilic HEMA
-
Photoinitiator Bond strength 21.0±6.0
2)
Probond -
It is unique in that it does not require dentine conditioning for dentin adhesion to occur. c) Primer
- Acetone / ethanol - PENTA
44
d) Resin
- UDMA - PENTA - Glutaraldehyde
3)
Liner bond 2 (Kurary, Japan) This system introduced the concept of no rinse self-etching
primer. a) Primer
- Pheny P - HEMA - 5-NMSA
b) Bonding resin
- BIS-GMA - Colloidal silica - MDP
4)
Amalgam bond a) Conditioner
- 10% citric acid - 3% ferric chloride
b) Primer – HEMA with water c) Resin – 4 META - MMATBB (Methyl methacrylate tri-N-butylchlorine)
45
5)
All bond -
All bond is a unique development in the field of adhesive dentistry.
-
It is a universal bonding system that will bond composite to all dental related surface. dentin, enamel, metal alloy, amalgam, porcelain and composite.
-
It is also the only system that allows the use of both the conservative and all etch technique.
Composition: a) Conditioner – A reaction product of SA (Succinic anhydride and HEMA PH 4.4) b) Primer
- 2% NTG-GMA - 16% BPDM
c) Resin
- BIS-GMA - UDMA - HEMA
Bond strength – 15.6 ± 4.9
46
Mechanism of Bonding -
Bonding occur by hybridization.
-
Research by Nakayabashi has shown that strong bond is formed between dentin and resin when a monomer such as 4-META, penetrates the tissue and polymerizes.
-
The resin impregnation creates a transitional “Hybrid layer that is neither resin not tooth, but a hybrid of the two. This direct chemical interaction which the inner tubular dentin is the key to bond strength.
Advantages of All-Bond -
Bond strength –18Mpa.
-
Leaves no residue on dentine surface (because of semi-gel form).
-
Wets better.
-
Rinse easier.
-
Bonds to wet surface.
47
All-bond provides a special resin called “Pre-bond� to be used in place of light curing bonding resin when cementing inlays, onlay or crown in order to avoid filling problems while sealing. Fifth Generation Denting Bonding Systems The distinct characteristic of the so-called fifth generation is the combination of the primer and bonding resin application steps to achieve bonding with a one component resin formula. (One bottle bonding system). These systems rely on the hybridization of dentine for achieving adhesion. Examples are: a) One step (Bisco Inc.). b) Primer and bond 2.0 (Dentsply). c) Perma Quik d) Prime and Bond NT e) Single bond Composition: Conditioner - 36% H3PO4 - Acetone
48
Primer : - Acetone + Bonding agent : Penta / TEGMA / UDMA 1) One step. 2) Single step system. 3) Bond strength – 27-29Mpa. 4) High resistance to microleakage. 5) It has low film thickness 10-20µm and so it is effective for indirect procedures as well. 6) Bonds to moist dentine. 7) Chemistry same as All bond. Perma Quik Features a. Bond strength – 22-35 Mpa. b. It has a syringe delivery system. c. It consist of a microfilled bonding resin and also is fluoride releasing.
-
High bond strength of these systems is due to the availability of single system which reduces the number of intermediary layers.
49
-
As compared to 4th generation where number of steps are more due to mixing of primer A and Primer B there by reducing the strength.
Advantages of Vth generation -
Increased bond strength.
-
Less technique sensitive.
-
Reduce treatment time.
Sixth Generation Dentin Bonding System Example – Clearfil bond 2 system (Kurrary Co.). -
In this etchant and primer are combined. Also known as self etching primer.
-
It contains phosphate derivatives of hydrophilic monomer such as phenyl-P (20-25%).
-
It also contains 50% HEMA or other hydrophilic monomer, so they both etch and primer the dentin.
-
Self etching primer must have sufficient acidity to overcome the buffering potential of the dentine, but they must also, contain sufficient monomer to compete with water when they diffuse through the smear layer.
50
-
As the smear layer might not be totally removed by these systems, the partially demineralized smear layer becomes incorporated into a hybrid layer. Thus, self etching primer produce a thinner hybrid layer than systems using etchants such as phosphoric acid.
-
This does not has any effect on the bond strength.
Prime and Bond NT (Dentsply) Conditioner – Silica thickened 35% H3PO4 Adhesive
- PENTA - UDMA
Primer – T – resin (Cross linking agent). -
D-resin (small hydrophilic molecule)
-
Butylated hydroxyloluene.
-
4 ethyl dimethyl aminobinzole.
-
Citriamine hydrofluoride.
-
Accelose
-
Silica Nanofiller.
51
Single bond (3M) Conditioner – Silica thickened 50% H3PO4 + Adhesive
– BIS-GMA
Primer- HEMA -
Dimethacrylate
-
Polyalkenoic acid copolymer.
-
Initiator.
-
Water.
-
Ethanol.
Filler adhesive liner Adhesive resin systems with fillers are: a) One step with resinomer as a filler (Vth generation DBA). b) All bond 2 with resinomer as a filler (IV th generation DBA) c) Amalgabond plus with HPA powder (IV th generation DBA) d) Prime and Bond NT with silica nanofiller (Vth generation DBA) -
The incorporation of fillers increased the bond strength to dentine (Cobb and Diefendeifer 1997).
-
Nanofillers penetrated the hybrid layer to form triangular tag necks. These were uniformly dispersed over the adhesive layer (Pedigo et al 1999).
52
Biocompatibility of Dentin Bonding Agents (Endo Dent Traumatology 1993) -
Biological testing of DBA is a delicate and complex process.
-
Unlike most dental materials, many dentin bonding systems are made up of more than one material e.g. cleanser, primer, bonding resin etc.
First generation Dentin bonding agent -
A very limited number of reports have been published on the biocompatibility of the first generation DBA (which may be due to their inferior physical properties).
-
Van Leeuwen et al showed no severe reactions even in extremely deep caries in their study carried out on monkey teeth.
Second generation DBA -
The most of the studies are carried out using Scotch bond
53
-
Scotch bond might have an adverse effect on the pulp tissue when placed in contact with vital tooth and proper pulpal protection was recommended.
Third generation: Test carried out with F N-P system showed that the bonding material as well as the individual components were not toxic. Application / Clinical uses of dentin bonding systems: 1) Bonding of directly placed resin based restoration materials. These can be used to: i)
To release the fractured incisal edges.
ii)
Restoration of cervical erosion without the need for drilling and anaesthesia.
iii)
Restoration of carious lesions in enamel or dentine with minimal cavity preparation.
iv)
To close diastema.
2) As pit and fissure sealants. 3) For placement of porcelain veneers, inlays, onlays and crowns.
54
4) Adhesive splinting of teeth. 5) Adhesive can be applied to exposed root surface dentin in order to prevent the hypersensitivity and also protect it from caries attack. 6) For bonding of amalgam restorations. 7) Reattachment of fractured tooth fragments. 8) Pulp capping. 9) For direct bonding to orthodontic brackets. 10)For esthetic restoration of tetracycline stains, fluorosis and hypoplasia of enamel e.g. Amelogenesis imperfecta. 11)For retaining orthodontically straightened or torqued tooth in place. 12)To build up fractured tooth for temporary crowns as chairside without the need for lab work. 13)In root end fillings.
55
Advantages and disadvantages of dentin adhesive system: Advantages: 1)
With the use of dentine adhesive systems marginal contraction gap formation at the tooth, and the restoration interface is significantly reduced resulting in: -
Reduced microleakage of the restoration.
-
Reduced hypersensitivity.
-
Decreased incidence of secondary caries.
-
Decreasing the frequency of restoration thereby enhancing the durability of the restoration.
2)
Until recently macromechanical retention factors were the only means of providing retention for a restoration with the advent of dentin adhesion systems, the micromechanical retentive modes have taken the priority eliminating the need for removal of healthy tooth structure thereby conserving and strengthening the same.
3)
Dentine adhesive systems have a wide range of application in dentistry owing to its versatility.
4)
Better aesthetics. 56
Disadvantages: 1)
It is highly technique sensitive. All the instruments to be used should be free of contamination. Utmost care is taken to keep the operative site free of saliva, blood or plaque from the oral environment and oil and moisture contamination from the operating instruments and equipments.
2)
It
involves
a
time
consuming
procedure. 3)
Long term durability of bonding is yet under speculation.
4)
High cost factor involved limits its use in every patient.
5)
Shelf life is limited and storage conditioners have to be followed critically.
57
Conclusion: The reliability of dentine bonding has improved during 1990s and as a result the number of minimally invasive techniques available to the restorative dentist have increased. It may be anticipated that the effectiveness of adhesive technique to be dentin will improve further and that in due course all restorations including crowns, will be placed using an adhesive procedure and that reattachment technique will become the accepted mode of treatment for fractured cusps and teeth.
58
References: 1) Operative Dentistry Supplement 5, 1992 – International Symposium on adhesive in dentistry. 2) Dental Update 2000; 27 : 85-93 and 1240130 – Dentine bonding systems : 1 Mode of action. Dentine bonding systems : 2 Clinical uses. 3) Latest discoveries in adhesion : Recent studies. 4) Biocompatibility of dentin bonding agents – Endod. Dent. Traumatology 1993. 5) Adhesion and its application with restorative materials. DCNA; vol. 37, No.3, July 1993. 6) Bonding to enamel and dentin : a brief history and state of the art, 1995 – Quintessence Int 1995; 26: 95-110.
59
DENTIN BONDING SYSTEMS CONTENTS
Introduction History Requirements of Denting Bonding Agents Adhesion Chemistry of Adhesion Mechanism of Bonding Components of Dentin Bonding Agents Classification of Dentin Bonding Agents Generation of Dentin Bonding Agents Biocompatibility of Dentin Bonding Agents Clinical application Advantages Disadvantages Conclusion
60