Adhesion To Dental Tooth Tissues PDF

ADHESION TO DENTAL TOOTH TISSUES DR. FATEMA khalil ALDABBAR. MASTER DEGREE OF OPREATIVE DENTISTRY I. INTRODUCTION: Adhesive dentistry evolves rapidly. Two main incentives drive this evolution. Adhesive techniques combined with using tooth-colored restorative materials are freq...

ADHESION TO DENTAL TOOTH TISSUES DR. FATEMA khalil ALDABBAR. MASTER DEGREE OF OPREATIVE DENTISTRY I. INTRODUCTION: Adhesive dentistry evolves rapidly. Two main incentives drive this evolution. Adhesive techniques combined with using tooth-colored restorative materials are frequently requested by patients. They want us to restore their teeth not only anatomically and functionally, but also esthetically and thus, nearly invisibly. From our perspective, today’s conservative dentistry should primarily involve “minimally invasive” or “minimum intervention”. This means that only the lost or diseased tooth tissue is replaced by the restorative material that is directly bonded to the remaining sound tissue. ADVANTAGES AND CLINICAL SIGNIFICANCE OF ADHESION: 1. Allow stabilization and long-term retention of restorations. 2. Provides better resistance against fracture of tooth or restoration by allowing better transmission and distribution of functional stresses across the bonded interface to the tooth. Thus, the tooth and restoration will act as one unit. 3. Maximize tooth conservation, compared to non- bonded restorations which require additional removal of sound tooth structure to provide for the necessary resistance and retention features ADVANTAGES AND CLINICAL SIGNIFICANCE OF ADHESION: 4. Reduce microleakage at the tooth/restoration interface. This would minimize the ingress of oral fluids and bacteria along the cavity wall, thus reducing clinical problems such as postoperative hypersensitivity, marginal staining and recurrent caries. 5. Expand the range of possibilities for esthetic restorative dentistry; as correcting dimensions and color of teeth, bonding indirect resin-based restorations, repairing existing restorations in addition to producing highly esthetic “invisible” direct restorations. REQUIREMENTS FOR ADHESION: To produce good bonding, the adhesive or adherent should be able to flow easily over the adherend to produce good wetting. Wetting is the degree of spreading of one drop of liquid on a solid surface and is measured by the contact angle. Contact angle is the angle formed by the adhesive with the adherend at their interface it : may be 0 or 180 degrees ––––––––––> maximum adhesion Less than 90 degrees –––––––> moderate adhesion More than 90 degrees ––––––> poor adhesion REQUIREMENTS FOR ADHESION: A SUCCESSFUL ADHESIVE JOINT SHOULD BE 1. Gap free. 2. Of sufficient bond strength to resist debonding under polymerization shrinkage stresses of resin composite or under function. The bond strength is the measure of the bond-bearing capability of the adhesive and is evaluated by the force needed to debond the adhesive. 3. Compatible to tooth tissues and restorative material. 4. Dimensionally and hydrolytically stable in the complex oral environment. This would provide bond durability which is the time period during which the bond remains effective. CLASSIFICATION OF DENTAL ADHESIVES: Based on the adhesion strategy, Van Meerbeek in 2001 has classified dental adhesives into three main categories; etch-and-rinse adhesives, selfetch adhesives and glass ionomer adhesives All three categories of adhesives exhibit a common adhesion mechanism of hybridization. This is the process of micro mechanical interlocking which occurs by infiltration of resin into demineralized substrate. The resultant resin-infiltrated hybrid layer to dentin CLASSIFICATION OF DENTAL ADHESIVES: CLASSIFICATION OF DENTAL ADHESIVES: II. INDICATIONS FOR ADHESIVE DENTISTRY: 1. Conservative restorations of class I, II, III, IV, V, VI carious or non carious lesion 2. Change shape and color of anterior teeth 3. Fractured tooth reattachment 4. Bond all indirect restorations 5. Provide foundations for crowns 6. Seal pits and fissures 7. Bond orthodontic brackets 8. Periodontal splints 9. Repair of restorations III. FUNDAMENTAL PRINCIPLE OF ADHESION TO TOOTH SUBSTRATE: is based upon an exchange process as the inorganic tooth material is exchanged for synthetic resin. This process involves two phases: a. Removal of calcium phosphate contents to expose microporosities in both enamel and dentin surfaces. b. The second phase “Hybridization phase” polymerization of resin within the created surface microporosities. This result in micromechanical interlocking that is primarily based upon mechanism of diffusion. IV. THE CHALLENGE IN BONDING TO DENTAL SUBSTRATES: Bonding to dental tissues is a very sensitive challenge facing dentists because of the marked difference between different dental substrates aiming to obtain reliable immediate bond strength between the synthetic resinous materials. Bonding to enamel (nearly homogenous structure) is a relatively simple process; however; bonding to dentin, on the other hand, presents a much greater challenge. V. RESIN / ENAMEL INTERFACE: Adhesive resin absorbed by capillary attraction within the created etched enamel surface enveloping individually exposed hydroxyapatite crystals followed by in situ polymerization of resin to create two types of resin tags: Macrotags fill up the space surrounding the enamel prisms. Microtags result from resin infiltration/polymerization within the tiny etch pits and at the cores of etched enamel prisms. The latter are thought to be the major contributors to retention to enamel. V. RESIN / ENAMEL INTERFACE: Conditioning Enamel : Objectives : 1. Removal of organic pellicle and prismless enamel 2. Removal of the smear layer 3. Creation of enamel microporosities (5-50μm) 4. Increase Enamel surface energy from 32 to 72 dynes/cm2 V. RESIN / ENAMEL INTERFACE: Methods: 1. Chemical conditioners: a. Phosphoric acid 37% for 20 to 30 seconds: the most widely used etchant. b. Nitric acid 2.5% c. Citric acid 10% d. Maleic acid 10% e. Oxalic acid 1.6-3.5% V. RESIN / ENAMEL INTERFACE: f. EDTA: it’s a strong decalcifying agent (Chelator) but prompted low bond strength to enamel as it does not etch preferentially. g. Hcl acid 15% may also be used for deeper enamel etching, followed by resin infiltration (Icon) to modify the refractive spectral of enamel white lesion V. RESIN / ENAMEL INTERFACE: 2. Physical conditioners (LASER): The substrate surface is altered by microscopic explosions caused by thermal transients increasing the bondable fraction of inorganic dentin. This will lead to a decrease in the organic fraction of the substrate. Laser leads also to a desensitized dentin due to occlusion of dentinal tubules. V. RESIN / ENAMEL INTERFACE: 3. Mechanical conditioners (Air Abrasion): It is based on applying aluminum oxide particles of different sizes and velocities to the enamel and dentin surfaces. · It allows removal of demineralized and discolored tooth tissues. · It has been suggested that air abrasion could be useful in self etching adhesive systems. Factors affecting successful acid etching: Type of acid Acid concentration Time of etching Form of etchant Rinsing time Method of activation of etching (rubbing, agitation, and/or repeated application of fresh acid) Factors affecting successful acid etching: · Instrumented or non-instrumented enamel Chemical composition and condition of enamel Primary or permanent teeth Enamel is prism-structured or prismless PATTERNS OF ETCHING: Three enamel-etching patterns have been described :- Type I etching pattern: preferential removal of enamel prism cores Type II etching pattern: preferential removal of prism peripheries Type III etching pattern: not related to prism morphology Or simply enamel etching patterns could be in the form of inter prismatic and intra-prismatic pattern of etching. Clinical features: The etched surface appears white frosted (chalky white)