Adhesion to Dental Tooth Tissue PDF

Adhesion to dental tooth tissue Dr. Howaida Fakhry B.D.S., M.D.Sc., D.D.S (Conservative Dentistry, Cairo University) Lecturer, Faculty of Oral and Dental Medicine, ACU  Universal adhesives 1) Compatibility with any etching Why called universal...

Adhesion to dental tooth tissue Dr. Howaida Fakhry B.D.S., M.D.Sc., D.D.S (Conservative Dentistry, Cairo University) Lecturer, Faculty of Oral and Dental Medicine, ACU  Universal adhesives 1) Compatibility with any etching Why called universal ? method (total-etch, self-etch, and selective-etch techniques). 2) Compatibility with light-cure, dual- cure, and self-cure materials. 3) Can adhere to all dental substrates for both direct and indirect procedures.  Universal adhesives 1) Incorporates adhesive monomer MDP with two-fold bonding What’s different? mechanisms; micro-mechanical interlocking & chemical bonding. (Advantages) 2) This multi-approach capability enables the clinician to apply the adhesive with selective enamel etching technique that combines the advantages of the etch-and-rinse technique on enamel, with the simplified self-etch approach on dentine with additional chemical bonding on remnant apatite crystallites in those bonding substrates. 3) May contain silane in their formulation, potentially eliminating the silanization step when bonding to glass ceramics or resin composites. 4) May contain nano-fillers which increases the penetration of resin monomers and the hybrid layer thickness, which improves the mechanical properties of the bonding systems.  Universal adhesives The bonding mechanism of universal adhesive systems is two-fold bonding mechanisms: micro-mechanical chemical bonding interlocking provide strength reduces hydrolytic degradation, against mechanical keeping the marginal sealing of stress restorations for a longer period  Universal adhesives How MDP works? (MDP) is a functional adhesive hydrophilic monomer. It has the ability to form chemical bonds with Ca++ ions in the hydroxyapatite in dentin. Therefore, the residual hydroxyapatite that remains around the collagen fibrils after the demineralization serves as a receptor for chemical interaction with MDP and subsequently contributes to adhesive performance. Although the immediate bond strengths of contemporary adhesives have been shown to be quite high, substantial decreases in resin-dentin bond strength occurred after aging, failure and continuous loss of bonded restorations over time for both etch-and-rinse and self-etch adhesive systems Bond durability is critical for the longevity of restoratives, because degradation can weaken adhesion and lead to gaps between teeth and restoratives.  I. Introduction VI. Adhesive strategies II. Indication for 1) Etch & rinse adhesive dentistry 2) Self-etch 3) Universal III. History IV. Fundamental principle of adhesion to tooth structure VII.Mechanism of dentin-adhesive interface degradation V. The challenge in bonding to dental VIII.Factors affecting interface durability substrate IX. Potential prevention solutions for bond degradation Mechanism of dentin-adhesive interface degradation Mechanism of dentin-adhesive interface degradation Degradation of the hybrid layer Degradation of methacrylate adhesive  Mechanism of dentin-adhesive interface degradation 1) Degradation of the hybrid layer: Disruption of the tooth structure by drilling, when the dentin is acid-etched ↓ stimulates proteolytic enzymes such as matrix metalloproteinases (MMPs) ↓ degrade the exposed collagen component of the hybrid layer ↓ hydrolysis and ingress of water into the loosely cross-linked or hydrophilic domains of the adhesive ↓ consequent extraction of the adhesive resins that have infiltrated the demineralized dentin matrix  Mechanism of dentin-adhesive interface degradation 1) Degradation of the hybrid layer: adhesive phase separation and lack of compatibility between the photoinitiator & hydrophilic phase ↓ hydrophilic domain exhibits limited monomer/polymer conversion ↓ poorly polymerized hydrophilic phase degrades rapidly in the aqueous environment ↓ resin elution continues to occur through the nanoleakage channels ↓ water movement along hybrid layer becomes more rapid ↓ previously resin-infiltrated collagen matrix is exposed & vulnerable to attack by MMPs  Mechanism of dentin-adhesive interface degradation 2) Degradation of methacrylate adhesive: at neutral pH- On prolonged exposure of the restoration to oral fluids relatively slow ↓ In low pH– rapid water begins to penetrate the resin ↓ chemical hydrolysis of ester bonds in methacrylate materials ↓ degradation products of ester hydrolysis are more hydrophilic than the parent ester ↓ further enhancing the local ingress of water  I. Introduction VI. Adhesive strategies II. Indication for 1) Etch & rinse adhesive dentistry 2) Self-etch 3) Universal III. History IV. Fundamental principle of adhesion to tooth structure VII.Mechanism of dentin-adhesive interface degradation V. The challenge in bonding to dental VIII.Factors affecting interface durability substrate IX. Potential prevention solutions for bond degradation  Factors affecting the interface durability Micro-mechanics Dentin related Adhesive system of the adhesive factors related factors interface Extrinsic and Role of saliva in Miscellaneous intrinsic water bond degradation factors sorption  Factors affecting the interface durability 1. Dentin related factors: bonding to enamel is regarded as reliable & durable bonding to dentin does not match the durability of its neighboring hard tissue  Factors affecting the interface durability Definition: disturbed film of organic Dentin smear layer and hydroxyl-apatite particles, generally less than 2 μm thick. Bonding to deep versus Can be removed by acid etching superficial Dentin dentin Disadvantages: could inhibit the related formation of an impervious seal at factors Bonding to the adhesive/dentin interface; it could gingival marginal be one factor contributing to the dentin weak link in the coupling of adhesive Bonding to to dentin altered dentin  Factors affecting the interface durability The variation in number & diameter of dentinal tubules Dentin smear layer and amount of solid dentin dictates the mechanism of Bonding to bonding. deep versus Superficial dentin: few tubules are available, superficial the prevailing bonding mechanism is Dentin dentin through hybrid layer formation due to large related amounts of intertubular dentin. factors Bonding to gingival marginal Deep dentin: dentinal tubules are abundant dentin with limited amounts of intertubular dentin, Bonding to the resin tags bonding is achieved. altered dentin  Factors affecting the interface durability Gingival margin in class II composite Dentin smear layer restorations is the most common location of bonding failures. Bonding to deep versus superficial Dentin dentin related factors Bonding to gingival marginal dentin Bonding to altered dentin  Factors affecting the interface durability Dentin at gingival margin Dentin at proximal wall Dentin smear Less mineralized More mineralized layer density and size of tubules density and size of tubules Bonding to are greater are smaller deep versus superficial Higher water content Less water content Dentin dentin related factors Bonding to gingival Acids etch deep dentin faster and deeper marginal The cumulative effect of the increased water led to reduced dentin adhesive infiltration and lower monomer/polymer conversion Bonding to of the adhesive at the gingival margin making it a difficult altered dentin bonding substrate.  Factors affecting the interface durability 30–40% drop in bond strength with caries Dentin smear layer affected dentin substrates. Bonding to Disorganized collagen fibers due to caries deep versus superficial ↓ Dentin dentin acid-etching related factors Bonding to ↓ gingival marginal promote phase transition of this disorganized dentin collagen to a gel Bonding to ↓ altered dentin The gel could inhibit adhesive infiltration  Factors affecting the interface durability 2. Adhesive system related factors Difference between depth of Etch & rinse demineralization and resin Self-etch infiltration leaving exposed All-in-one demineralized dentin zone within the bond structure. The exposed collagen fibrils here may be structurally unstable due to hydrolysis, reducing long-term bond strength.  Factors affecting the interface durability 2. Adhesive system related factors The self-etching ability of one-bottle Etch & rinse adhesives is commonly achieved by Self-etch incorporation of water in resin monomers that enables ionization of All-in-one acidic monomers. In addition to the water in the compounds, the ionizable moieties of acidic monomers are also hydrophilic. The presence of such a more hydrophilic layer may thus induce water sorption and water uptake, in turn, endangering the stability of the polymer network.  Factors affecting the interface durability 3. Micro-mechanics of the adhesive interface: Under clinical function, dentin adhesives are subjected to both chemical and mechanical stresses. The interplay between the two forms of stress is expected to result in an alteration of the properties of the adhesive with time and gradual loss of mechanical integrity.  Factors affecting the interface durability 4. Extrinsic and intrinsic water sorption: Absorption of water leads to plasticization of the adhesive and loss of interfacial a/d bond strength as a result of water attack.  Factors affecting the interface durability 5. Role of saliva in bond degradation: Human saliva contains a variety of enzymes which may participate in the degradation of the adhesive as well as the composite.  Factors affecting the interface durability 6. Miscellaneous factors: Clinical Operator Patient Socioeconomic Materials related related related factors related factors factors factors factors  Factors affecting the interface durability 6. Miscellaneous factors: a) Clinical related factors: Position of the tooth in the mouth or the tooth type, cavity size, cavity type, and the number of restored surfaces are related to the failure risk. Position of the tooth: risk of restoration failure in molars is twice premolars due to restorations placed in molar teeth are subjected to higher masticatory stresses. Number of restored surfaces: multisurface restorations, extensive cavities, and Class II restorations, are more likely to fail than single-surface and Class I restorations with increased risk of failure of 40%.  Factors affecting the interface durability 6. Miscellaneous factors: b) Operator related factors: The operator significantly influences the longevity of a restoration To have knowledge of different bonding techniques. Experience of operator. Availability of recent technology to perform the most conservative cavities. Application of restorative materials and adhesive systems according to manufacturer instruction  Factors affecting the interface durability 6. Miscellaneous factors: c) Patient related factors: The type of patient and the oral environment play an important role in the survival of dental restorations. The caries risk of patients has been shown to significantly influence the durability of restorations. High caries risk patients Low caries risk patients have increased risk of have more durable dentin failure of posterior adhesive interfaces with composite restorations. less rates of leakage.  Factors affecting the interface durability 6. Miscellaneous factors: d) Socioeconomic factors: As dental caries are strongly associated with social determinants experienced during the life course, it is possible that social determinants can also influence the longevity of restorations by the same pathway.  Factors affecting the interface durability 6. Miscellaneous factors: e) Material related factors: There has been considerable differences among commercially available materials in flexural and compressive strength, elastic modulus, fracture strength and toughness, hardness, and wear resistance.  I. Introduction VI. Adhesive strategies II. Indication for 1) Etch & rinse adhesive dentistry 2) Self-etch 3) Universal III. History IV. Fundamental principle of adhesion to tooth structure VII.Mechanism of dentin-adhesive interface degradation V. The challenge in bonding to dental VIII.Factors affecting interface durability substrate IX. Potential prevention solutions for bond degradation  Potential prevention solutions for bond degradation a) Modifying the methacrylate side chains b) Photo-initiator incorporation Material dependent c) Adhesives with antibacterial, remineralization ability d) Addition of protease inhibitors e) Collagen cross-linking agents f) Biomimetic remineralization a) Dentinal occlusion b) Ethanol-wet bonding Technique c) Rubber dam isolation dependent d) Adhesive application e) Warm air dryness Potential prevention solutions for bond degradation a) Modifying the methacrylate side chains: with functional monomers, such as MDP, lead to a chemical bond to calcium ions of the hydroxyapatite crystals. It is believed to minimize nanoleakage, leave a substantial amount of hydroxyapatite around the collagen fibrils to mask the collagen cleavage site and keep the enzymes “fossilized”. Thus, the collagen could not be degraded Potential prevention solutions for bond degradation b) Photo-initiator incorporation: To address the In-adequate monomer/ polymer conversion. but it should be compatible with the hydrophilic components Potential prevention solutions for bond degradation c) Adhesives with antibacterial, remineralization ability: It is necessary to combine antibacterial and remineralization strategies in adhesives to protect the bonding interface and prevent secondary caries. Antimicrobials such as quaternary ammonium methacrylate monomer as MDPB have been applied in dental materials to inhibit caries. Calcium/phosphate (Ca/P)-containing materials, serve as mineral reservoirs to help prevent demineralization and facilitate remineralization. Adhesives containing nanoparticles of amorphous calcium phosphate (NACP) have been developed. Potential prevention solutions for bond degradation c) Adhesives with antibacterial, remineralization ability: Potential prevention solutions for bond degradation d) Addition of protease inhibitors: Matrix metalloproteinase inhibitors (MMPIs) e.g., Chlorhexidine (CHX). Most are under development and have no proven biocompatibility to be used on human subjects despite being potent MMPIs. CHX has proven biocompatibility and good anti- bacterial action, MMP inhibitor and anti-enzyme properties even at low concentrations. Potential prevention solutions for bond degradation e) Collagen cross-linking agents: Enhance mechanical properties of dentin matrix, reduce biodegradation rates of collagen and extend the life of adhesive restorations. Proanthocyanidins (PA) are natural biocompatible collagen cross-linker broadly distributed in the plant kingdom. They have high affinity to organic matrix of collagen forming effective cross-linking. Potential prevention solutions for bond degradation f) Biomimetic remineralization: In dentin bonding, the mineral phase of dentin is intentionally removed by acids, chelating agents, or acidic resin monomers to expose the collagen for creating micromechanical retention of resins. Unfortunately, it seems that contemporary etch and-rinse and self-etch adhesives are incapable of completely replacing water from the extrafibrillar and intrafibrillar collagen compartments with resin monomers. Biomimetic remineralization utilizes nanotechnology principles to mimic what occurs in biomineralization. It replaces water from resin-sparse regions of the hybrid layer with apatite crystallites that are small enough to occupy the extrafibrillar and intrafibrillar compartments of the collagen matrix, and has been adopted for remineralization of resin dentin bonds.  Potential prevention solutions for bond degradation a) Modifying the methacrylate side chains b) Photo-initiator incorporation Material dependent c) Adhesives with antibacterial, remineralization ability d) Addition of protease inhibitors e) Collagen cross-linking agents f) Biomimetic remineralization a) Dentinal occlusion b) Ethanol-wet bonding Technique c) Rubber dam isolation dependent d) Adhesive application e) Warm air dryness Potential prevention solutions for bond degradation a) Dentinal occlusion (Oxalate occlusion): outward flow of dentinal tubules ↓ interferes with the resin monomer infiltration ↓ negatively affects both total etch and self etch adhesives. The Rationale for using potassium oxalate desensitizers to decrease the outward dentinal flow by formation of calcium oxalate crystals on the surface that occlude the patent tubules. Therefore, extend the bond durability. Potential prevention solutions for bond degradation b) Ethanol-wet bonding: In ethanol wet bonding, ethanol is used to chemically dehydrate acid-etched demineralized dentin matrices to reduce collagen hydrophilicity and facilitate the infiltration of more hydrophobic monomers to dentin. Potential prevention solutions for bond degradation c) Rubber dam isolation to limit the impact of water or saliva contamination, careful attention to handling, management. d) Extended adhesive application time with rubbing action, allowing proper resin penetration and solvent evaporation. e) Warm air dryness to accelerate solvent & water evaporation.  I. Introduction VI. Adhesive strategies II. Indication for 1) Etch & rinse adhesive dentistry 2) Self-etch 3) Universal III. History IV. Fundamental principle of adhesion to tooth structure VII.Mechanism of dentin-adhesive interface degradation V. The challenge in bonding to dental VIII.Factors affecting interface durability substrate IX. Potential prevention solutions for bond degradation Conclusion The a/d bond can be the first defense against substances that may penetrate and ultimately undermine the composite restoration The success of clinical restorations depends on a variety of factors including proper technique, appropriate materials, and proper patient selection. Thank you for listening