Lec
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- Words: 1,564
- Pages: 32
10/14/08
1
Manipulation:
10/14/08
Selection of composite, type and shade Field isolation Pulp protection Matricing and wedging. Pre-treatment of the substrate surface. Packing. Carving. Polymerization. Finishing and polishing. 2
Pre-treatment of enamel and dentin surfaces:
10/14/08
Rationale for pre-treatment : The polymerization shrinkage of composite resin often leads to marginal gap formation, allowing for the passage of bacteria, fluids and ions between the restoration and the cavity wall. This microleakage seems to predispose to secondary caries, marginal discoloration and pulpal damage reducing the longevity of the restoration. 3
Pre-treatment of enamel and dentin surfaces:
10/14/08
Therefore, the capability of establishing a strong and permanent bond to both enamel and dentin is a highly desirable property of a composite resin.
4
Advantages of adhesive techniques:
Bonded restorations have a number of advantages over traditional, non-adhesive methods: Traditionally, retention and stabilization of restorations often required the removal of sound tooth structure. This is not necessary, in many cases, when adhesive techniques are used.
10/14/08
5
Advantages of adhesive techniques:
10/14/08
Adhesion reduces microleakage at the restoration interface. Prevention of microleakage or the ingress of oral fluids and bacteria along the cavity wall, reduces clinical problems such as postoperative sensitivity, marginal staining and recurrent caries.
6
Advantages of adhesive techniques:
10/14/08
Adhesive restorations better transmit and distribute functional stresses across the bonding interface to the tooth and have the potential to reinforce weakened tooth structure. In contrast, a traditional metal intracoronal restoration may act as a wedge between the buccal and lingual cusps and increase the risk of cuspal fracture. 7
Advantages of adhesive techniques:
10/14/08
Adhesive techniques allow deteriorating and debonded restorations to be repaired with minimal or no additional loss of tooth material. Adhesive techniques have expanded the range of possibilities for esthetic restorative dentistry (correction of unesthetic shapes, positions, dimensions, or shades).
8
10/14/08
9
10/14/08
10
Steps in Forming Good Adhesion (1) Clean adherend (2) Good wetting (3) Intimate adaptation (4) Bonding (5) Good curing 10/14/08
– +
chemical physical mechanical bondingbonding bonding
11
(1) Clean Adherend (Substrate): The adherend must not contain any surface debris or adsorbed films of oil or dirt that would prevent an adhesive from coming into good contact with the adherend. Surfaces can be cleaned with water, solvent, or acid.
(2) Good Wetting: The adhesive must spread onto the adherend with a low contact angle so that it wets the surface and develops good intimate contact. Unfortunately some adhesives are not well-matched to the surface energies of certain substrates. Hydrophilic materials do not wet hydrophobic surfaces very well, and vice versa. Enamel and dentin are hydrophilic while most composites are hydrophobic. The challenge for dental adhesives is to provide acceptable wetting for both of these materials.
10/14/08
12
(3) Intimate Adaptation: If good wetting occurs and the material flows adequately, then it can penetrate into all the surface interstices and develop good adaptation. This process should occur without entrapping air or leaving unfilled surface spaces.
(4) Bonding: The adhesive should interact in as many ways as possible with the substrate. It should develop physical bonding, chemical bonding, and micromechanical bonding. The last is the most important and contributes the most (>90%) to the strength of the joint.
(5) Good Curing: The entire process depends on the adhesive (and restorative filling materials) becoming fully cured. Under-curing allows chemical erosion and/or debonding of the adhesive system.
10/14/08
13
Design of Bonding Systems
(3-component, 2-component, 1-component) 1. Conditioning (cleaning) 2. Priming (wetting, adapting) 3. Bonding (mechanical adhesion, curing)
Instrumentation of the tooth substrate during cavity preparation produces a smear layer with a low surface free energy. Therefore, the natural tooth surface should be thoroughly cleaned and pretreated prior to bonding procedures to increase its surface free energy and hence to render it more receptive to bonding.
10/14/08
14
Adhesion to enamel:
Structure of enamel: It consists of 96% by weight inorganic hydroxyapatite and 4% matrix containing proteins and water. Enamel has a crystalline structure, the crystals form socalled enamel rods. A pellicle consisting of a protein-fat-carbohydrate complex (organic material) is found on the enamel surface. When the enamel is cut, the pellicle forms an organic smear layer. Therefore, enamel surface should be conditioned before each adhesion.
10/14/08
15
SEM shows the direction of enamel crystals within a single enamel rod.
10/14/08
On the uncleaned E. surface there is a pellicle consisting of organic material.
The aprismatic E. layer proceeds parallel to the surface of the tooth and perpendicular to the underlying prismatic layer.
16
Adhesion to enamel:
Such conditioning is achieved through acid etching of this highly mineralized substrate which substantially enlarges its surface area for bonding. Enamel etching transforms the smooth enamel surface into an irregular surface with a high surface free-energy. An unfilled liquid acrylic resin with low viscosity (bonding agent) wets the high energy surface and is drawn into the microporosities by capillary attraction.
10/14/08
17
The ends of the enamel prisms form a typical etch pattern.
10/14/08
18
Adhesion to enamel:
The bond between enamel and the restorative material is established by polymerization of monomers inside the microporosities and by copolymerization of bonding agent with the matrix phase of resin composite, producing strong chemical bond. The form of the etchant : gel, semi-gel, or aqueous solution. An acid gel is generally preferred over a liquid because its application is more controllable.
10/14/08
19
Adhesion to enamel
Use of a phosphoric acid concentration between 30-40%, an etching time of not less than 15 seconds, and washing time of 10-20 seconds are recommended. Rinsing times of at least 15 seconds are required to remove dissolved calcium phosphates from the etched surface (which otherwise might impair infiltration of monomer into the etched enamel microporosities).
10/14/08
20
Adhesion to enamel
10/14/08
Etching of enamel dissolves the rods with faster effect on prism cores than on organic rich inter-prismatic substance. Thus it produces: Inter-prismatic. etching Intra-prismatic.
21
Adhesion to dentin
Structure of dentin: Dentin is a mineralized hard tissue, consisting of; peritubular dentin with high mineral content, intertubular dentin (collagen rich), and dentinal tubules containing odontoblastic process and tubular fluid. Thus dentin characterized by an intrinsic wetness. Dentin consists of 50(volume)% inorganic material,30% organic and 20% water. The organic matrix of dentin consists of 91-92% collagen and 8-9% noncollagen ground substance. The inorganic components consist mainly of hydroxyapatite crystals. During cutting, smear layer forms, consisting of burnished components and hydroxyapatite fragments.
10/14/08
22
Smear layer that is pressed approx. 5-10 um into the dentin tubules. 10/14/08
23
Adhesion to dentin
10/14/08
This smear layer closes the dentinal tubules and prevents the seepage of the dentinal fluid, thus providing a drier surface for adhesion, minimizing post operative hypersensitivity and preventing the ingress of irritants from restorative materials to the tubules. However, it keeps any material from direct contact to the dentin.
24
Different approaches to handle the smear layer:
1- It can be used as a substrate: which means that the adhesive makes use of the porosities within the smear layer low bond strength unacceptable. 2- Partly dissolved and incorporated into the adhesive layer. 3- Or it can be totally removed. Both approaches 2&3 can be achieved by etching procedure.
10/14/08
25
10/14/08
26
The etching procedures not only dissolves the smear layer but also demineralizes the dentin surface. After etching the dentin and rinsing the acid from the cavity wall, the demineralizes dentin remains as a collagen network since it lost the support from the hydroxyapatite. This collagen-rich layer has a low free energy level. The space between the fibers previously filled with hydroxyapatite now contains water. This water has to be replaced by the monomer. 10/14/08 27
10/14/08
Collagen network
28
Be aware: Any drying of the dentin would result in a loss of water with a collapse of the collagen fibers, hindering the monomers from penetrating the decalcified dentin. N.B Etching of dentin 1- Elimination of smear layer. 2- Exposure of dentin collagen.
10/14/08
29
Priming:
10/14/08
Primers serves as adhesive–promoting agents. They are composed of bifunctional hydrophilic and hydrophobic groups of monomers, e.g. HEMA ( hydroxyethylmethacrylate ), in ethanol or acetone solvent. They are used to promote the resin-bondability of substrate E. and D. surfaces. The solvent displaces compositional water and trapped air at the depth of pores. ( Acetone is miscible with water and evaporated with it from the substrate surface and moist collagen network during the air drying ). 30
Priming:
The hydrophilic group (e.g. hydroxyl) increase the Wettability of demineralized substrate surface to bonding resins and facilitate their full depth infiltration. The hydrophobic group ( monomer e.g. methacrylate ) interdiffuse to demineralized substrate E. & D. They are subsequently polymerized in situ forming intra & interprismatic resin micro-tags in E. They form resin microtags in inter & peri-tubular demineralized D. and encapsulate the uncollapsed collagen fibers to form resin-collagen hybrid.
10/14/08
31
Priming:
The bonding resin is subsequently copolymerized to the primer resin, to support it and complete the establishment of the intermediary adhesive resin joint. N.B. Primer must be polymerized after been applied and before application of bonding resin, to effect optimum conversion.
10/14/08
32
1
Manipulation:
10/14/08
Selection of composite, type and shade Field isolation Pulp protection Matricing and wedging. Pre-treatment of the substrate surface. Packing. Carving. Polymerization. Finishing and polishing. 2
Pre-treatment of enamel and dentin surfaces:
10/14/08
Rationale for pre-treatment : The polymerization shrinkage of composite resin often leads to marginal gap formation, allowing for the passage of bacteria, fluids and ions between the restoration and the cavity wall. This microleakage seems to predispose to secondary caries, marginal discoloration and pulpal damage reducing the longevity of the restoration. 3
Pre-treatment of enamel and dentin surfaces:
10/14/08
Therefore, the capability of establishing a strong and permanent bond to both enamel and dentin is a highly desirable property of a composite resin.
4
Advantages of adhesive techniques:
Bonded restorations have a number of advantages over traditional, non-adhesive methods: Traditionally, retention and stabilization of restorations often required the removal of sound tooth structure. This is not necessary, in many cases, when adhesive techniques are used.
10/14/08
5
Advantages of adhesive techniques:
10/14/08
Adhesion reduces microleakage at the restoration interface. Prevention of microleakage or the ingress of oral fluids and bacteria along the cavity wall, reduces clinical problems such as postoperative sensitivity, marginal staining and recurrent caries.
6
Advantages of adhesive techniques:
10/14/08
Adhesive restorations better transmit and distribute functional stresses across the bonding interface to the tooth and have the potential to reinforce weakened tooth structure. In contrast, a traditional metal intracoronal restoration may act as a wedge between the buccal and lingual cusps and increase the risk of cuspal fracture. 7
Advantages of adhesive techniques:
10/14/08
Adhesive techniques allow deteriorating and debonded restorations to be repaired with minimal or no additional loss of tooth material. Adhesive techniques have expanded the range of possibilities for esthetic restorative dentistry (correction of unesthetic shapes, positions, dimensions, or shades).
8
10/14/08
9
10/14/08
10
Steps in Forming Good Adhesion (1) Clean adherend (2) Good wetting (3) Intimate adaptation (4) Bonding (5) Good curing 10/14/08
– +
chemical physical mechanical bondingbonding bonding
11
(1) Clean Adherend (Substrate): The adherend must not contain any surface debris or adsorbed films of oil or dirt that would prevent an adhesive from coming into good contact with the adherend. Surfaces can be cleaned with water, solvent, or acid.
(2) Good Wetting: The adhesive must spread onto the adherend with a low contact angle so that it wets the surface and develops good intimate contact. Unfortunately some adhesives are not well-matched to the surface energies of certain substrates. Hydrophilic materials do not wet hydrophobic surfaces very well, and vice versa. Enamel and dentin are hydrophilic while most composites are hydrophobic. The challenge for dental adhesives is to provide acceptable wetting for both of these materials.
10/14/08
12
(3) Intimate Adaptation: If good wetting occurs and the material flows adequately, then it can penetrate into all the surface interstices and develop good adaptation. This process should occur without entrapping air or leaving unfilled surface spaces.
(4) Bonding: The adhesive should interact in as many ways as possible with the substrate. It should develop physical bonding, chemical bonding, and micromechanical bonding. The last is the most important and contributes the most (>90%) to the strength of the joint.
(5) Good Curing: The entire process depends on the adhesive (and restorative filling materials) becoming fully cured. Under-curing allows chemical erosion and/or debonding of the adhesive system.
10/14/08
13
Design of Bonding Systems
(3-component, 2-component, 1-component) 1. Conditioning (cleaning) 2. Priming (wetting, adapting) 3. Bonding (mechanical adhesion, curing)
Instrumentation of the tooth substrate during cavity preparation produces a smear layer with a low surface free energy. Therefore, the natural tooth surface should be thoroughly cleaned and pretreated prior to bonding procedures to increase its surface free energy and hence to render it more receptive to bonding.
10/14/08
14
Adhesion to enamel:
Structure of enamel: It consists of 96% by weight inorganic hydroxyapatite and 4% matrix containing proteins and water. Enamel has a crystalline structure, the crystals form socalled enamel rods. A pellicle consisting of a protein-fat-carbohydrate complex (organic material) is found on the enamel surface. When the enamel is cut, the pellicle forms an organic smear layer. Therefore, enamel surface should be conditioned before each adhesion.
10/14/08
15
SEM shows the direction of enamel crystals within a single enamel rod.
10/14/08
On the uncleaned E. surface there is a pellicle consisting of organic material.
The aprismatic E. layer proceeds parallel to the surface of the tooth and perpendicular to the underlying prismatic layer.
16
Adhesion to enamel:
Such conditioning is achieved through acid etching of this highly mineralized substrate which substantially enlarges its surface area for bonding. Enamel etching transforms the smooth enamel surface into an irregular surface with a high surface free-energy. An unfilled liquid acrylic resin with low viscosity (bonding agent) wets the high energy surface and is drawn into the microporosities by capillary attraction.
10/14/08
17
The ends of the enamel prisms form a typical etch pattern.
10/14/08
18
Adhesion to enamel:
The bond between enamel and the restorative material is established by polymerization of monomers inside the microporosities and by copolymerization of bonding agent with the matrix phase of resin composite, producing strong chemical bond. The form of the etchant : gel, semi-gel, or aqueous solution. An acid gel is generally preferred over a liquid because its application is more controllable.
10/14/08
19
Adhesion to enamel
Use of a phosphoric acid concentration between 30-40%, an etching time of not less than 15 seconds, and washing time of 10-20 seconds are recommended. Rinsing times of at least 15 seconds are required to remove dissolved calcium phosphates from the etched surface (which otherwise might impair infiltration of monomer into the etched enamel microporosities).
10/14/08
20
Adhesion to enamel
10/14/08
Etching of enamel dissolves the rods with faster effect on prism cores than on organic rich inter-prismatic substance. Thus it produces: Inter-prismatic. etching Intra-prismatic.
21
Adhesion to dentin
Structure of dentin: Dentin is a mineralized hard tissue, consisting of; peritubular dentin with high mineral content, intertubular dentin (collagen rich), and dentinal tubules containing odontoblastic process and tubular fluid. Thus dentin characterized by an intrinsic wetness. Dentin consists of 50(volume)% inorganic material,30% organic and 20% water. The organic matrix of dentin consists of 91-92% collagen and 8-9% noncollagen ground substance. The inorganic components consist mainly of hydroxyapatite crystals. During cutting, smear layer forms, consisting of burnished components and hydroxyapatite fragments.
10/14/08
22
Smear layer that is pressed approx. 5-10 um into the dentin tubules. 10/14/08
23
Adhesion to dentin
10/14/08
This smear layer closes the dentinal tubules and prevents the seepage of the dentinal fluid, thus providing a drier surface for adhesion, minimizing post operative hypersensitivity and preventing the ingress of irritants from restorative materials to the tubules. However, it keeps any material from direct contact to the dentin.
24
Different approaches to handle the smear layer:
1- It can be used as a substrate: which means that the adhesive makes use of the porosities within the smear layer low bond strength unacceptable. 2- Partly dissolved and incorporated into the adhesive layer. 3- Or it can be totally removed. Both approaches 2&3 can be achieved by etching procedure.
10/14/08
25
10/14/08
26
The etching procedures not only dissolves the smear layer but also demineralizes the dentin surface. After etching the dentin and rinsing the acid from the cavity wall, the demineralizes dentin remains as a collagen network since it lost the support from the hydroxyapatite. This collagen-rich layer has a low free energy level. The space between the fibers previously filled with hydroxyapatite now contains water. This water has to be replaced by the monomer. 10/14/08 27
10/14/08
Collagen network
28
Be aware: Any drying of the dentin would result in a loss of water with a collapse of the collagen fibers, hindering the monomers from penetrating the decalcified dentin. N.B Etching of dentin 1- Elimination of smear layer. 2- Exposure of dentin collagen.
10/14/08
29
Priming:
10/14/08
Primers serves as adhesive–promoting agents. They are composed of bifunctional hydrophilic and hydrophobic groups of monomers, e.g. HEMA ( hydroxyethylmethacrylate ), in ethanol or acetone solvent. They are used to promote the resin-bondability of substrate E. and D. surfaces. The solvent displaces compositional water and trapped air at the depth of pores. ( Acetone is miscible with water and evaporated with it from the substrate surface and moist collagen network during the air drying ). 30
Priming:
The hydrophilic group (e.g. hydroxyl) increase the Wettability of demineralized substrate surface to bonding resins and facilitate their full depth infiltration. The hydrophobic group ( monomer e.g. methacrylate ) interdiffuse to demineralized substrate E. & D. They are subsequently polymerized in situ forming intra & interprismatic resin micro-tags in E. They form resin microtags in inter & peri-tubular demineralized D. and encapsulate the uncollapsed collagen fibers to form resin-collagen hybrid.
10/14/08
31
Priming:
The bonding resin is subsequently copolymerized to the primer resin, to support it and complete the establishment of the intermediary adhesive resin joint. N.B. Primer must be polymerized after been applied and before application of bonding resin, to effect optimum conversion.
10/14/08
32
