Adhesion in Dentistry Operative 5

Adhesion in Dentistry Operative 5 Definitions Bondodontics: is the science that studies adherence of materials to tooth structure. Adhesion: the force that binds two dissimilar materials together when they are brought into intimate contact. Adherend: Substrate to which the material adhere. Adherent: Adhesive material used to produce adhesion. Adaptation: maximum degree of proximity between two adjacent surfaces. Mechanisms of adhesion involved in dentistry A. Mechanical adhesion. It occurs when the solidified adhesive interlocks micromechanically with the roughness and irregularities of the surface of the adherend (substrate) B. Chemical adhesion It is the bonding of dissimilar materials by the interaction of atoms or molecules at an interface that holds two phases together. C. Electrostatic adhesion Involves electrostaticinteractions that are relatively weak.It may be the only type of adhesion if surfaces are smooth and chemically dissimilar. Requirements for adhesion: To produce good bonding, the adhesive or adherent should be able to flow easily over the adherend to produce good wetting. Wettability is: Spontaneous flow and full spread of a liquid phase (adhesive) over a solid phase (substrate surface),and is measured by the contact angle. 1 The contact angle is: the angle between the liquid and the solid surface. - 0 or 180 degrees ---> maximum adhesion - Less than 90 degrees ---> moderate adhesion - More than 90 degrees ---> poor adhesion In addition, sufficient wetting of the adhesive will only occur if its surface tension is less than the surface energy of the adherend. Surface energy is: The inward attractive forces of the molecule of a solid. The surface energy of a liquid is known as the surface tension. Thus, the requirements for successful wetting of adhesive are: 1. Intimate molecular contact between adhesive and tooth tissues (adherend). 2. Cleanliness, smoothness and dryness of the tooth tissues. 3. High surface energy of the tooth tissues to be able to attract the atoms of the adhesive. 4. Low-surface tension of the adhesive material (adherent) to be able to properly wet the adherend. 5. Low viscosity of the adhesive to penetrate into the micro-porosities 6. To be able to displace air and moisture during the bonding process. Advantages of adhesive techniques: Bonded restorations have a number of advantages over traditional nonadhesive methods: • Ultra conservation of tooth structure: through elimination of macromechanical preparations and excessive removal of tooth structure. • Long term restoration retention: strong bond provides longevity of the restoration and prompted patient acceptance. • Adhesive restorations better transmit and distribute functional stresses across the bonding interface to the tooth thus provide better resistance. • Reinforcement of the remaining tooth structure: (still a controversy) due to the ability of bonding between the restoration and tooth that participate in its load carrying ability. • Decrease microleakage and its sequelae, which are: postoperative hypersensitivity, recurrent caries, cytotoxic pulp reaction, discoloration, fracture or dislodgment. • Expanded the range of esthetic restorative dentistry. Indications for adhesive dentistry: • Conservative restorations of class I, II, III, IV, V, VI carious or traumatic defects • Change shape and color of anterior teeth • Fractured tooth reattachment • Bond all indirect restorations • Provide foundations for crowns • Seal pits and fissures • Bond orthodontic brackets • Periodontal splints • Repair of restorations • Dentin desensitization Fundamental principle of adhesion to tooth substrate: The 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 and phosphate content to expose microporosities in both enamel and dentin surfaces. b. The second phase (hybridization phase) involves infiltration and subsequent in situ polymerization of resin within the created surface microporosities. This results in micromechanical interlocking that is primarily based upon mechanism of diffusion. Challenges in bonding to dental substrates: - Enamel is formed of 96% inorganic materials and only 4% of organic and water while dentin is formed of 75% inorganic and 25% organic substances and water by weight. -Bonding to enamel (nearly homogemous structure) is a relatively simple process; however; bonding to dentin, on the other hand, presents a much greater challenge. • Several factors account for this difference between enamel and dentin bonding: 1. Heterogeneous composition of dentin: The Inorganic and organic constitutes are unevenly distributed in the intertubular dentin and peritubular dentin. 2. Complex histological structure of dentin Peritubular dentin hypermineralized Intertubular dentin high collagen and organic components Intratubular dentin odontoblastic process and fluid. 3. Inherent dentin wetness