4)ADHESION MECHANISM AND PRINCIPLES .pdf

Adhesion Mechanism and Principles Asst. Prof. Dr. Gülşah YENİER Istanbul Okan University Faculty of Dentistry Adhesion Bonding Adhesion is a process of solid or liquid interaction of one material (adhesive or adherent) with another (adherend) at a single interface. Mechanical adhesion Interlocking o...

Adhesion Mechanism and Principles Asst. Prof. Dr. Gülşah YENİER Istanbul Okan University Faculty of Dentistry Adhesion Bonding Adhesion is a process of solid or liquid interaction of one material (adhesive or adherent) with another (adherend) at a single interface. Mechanical adhesion Interlocking of the adhesive with irregularities in the surface of the substrate or adherend Adsorption adhesion Chemical bonding between the adhesive and the adherend; primary (ionic and covalent) or secondary (hydrogen bonds, dipole interaction, or van der Waals) valence forces Diffusion adhesion Interlocking between mobile molecules, such as the adhesion of two polymers through diffusion of polymer chain ends across an interface Electrostatic adhesion An electrical double layer at the interface of a metal with a polymer that is part of the total bonding mechanism adhesive, surface or structure: adherend Adhesion is classified as physical, chemical, or mechanical bonding. Physical bonding Physical bonding involves van der Waals, Hydrogen bonding or other electrostatic interactions that are relatively weak It may be the only type of bonding if surfaces are smooth Chemical bonding Involves bonds between atoms formed across the interface from the adhesive to the adherend. The materials are often dissimilar, bonding possible is limited, Quite low. Mechanical bonding An interface that involves undercuts and other irregularities (etched enamel and dentin) that produce interlocking of the materials (adhesive system). Almost every case of dental adhesion is based primarily on mechanical bonding. Strong bonding Adhesion Surface properties of adherent Physical and chemical properties of the adhesive Wetting properties External factors (humidity, physical stress, temperature changes, pH) Contact angle and wetting Wetting is a qualitative description of the contact angle. The contact angle is the angle, a drop of liquid makes with the surface on 0 ° Good wetting, or spreading, Approaching 90 ° poor wetting Viscosity In order to be effective adhesive, not only to fully contact the substrate but also to spread into the substrate Surface energy and roughness Surface energy wettability Surface energy with micro-irregularities > nonprepared tooth surface The basis of adhesion to the tooth tissues is the replacement of the resin with the inorganic part of the tooth structure. Hybridisation of demineralized tooth tissue and adhesion of restorative material to tooth tissue. Dr. Buonocore 85% phosphoric acid to etch enamel for sealing pits and fissures. Etching enamel Phosphoric acid 30-40% Min. 15 sec. etch Min. 15 sec. rinse Bonding to enamel tissue Removing prismatic and inter prismatic mineral crystallite producing porosity Increases its surface free energy The resin based material penetrates into the surface, aided by capillary action. The penetration of resin monomer into microporosities in enamel tissue formed resin tag to produce micromechanical adhesion Resin tags that form between the enamel rod peripheries are called macrotags smaller tags forms across the end of each rod microtags diameters of resin tags Microtags are probably more important because of their large number and great surface area of contact. 10 μm remove from enamel tissue by etching 5-50 μm porose layer is formed. Chemical composition of enamel Fluor content Primary / permanent tooth Type I etching pattern the dissolution of prism cores without prism peripheries Type II etching pattern the peripheral enamel is dissolved, Type III etching pattern resemble the other patterns Bonding to dentin tissue Bonding to dentin presents a much complex. Composition Heterojen structure Dentinal tubules Odontoblastic process Intertubular dentin, Peritubular dentin Diameter Numbers Dentino-enamel junction 0.5-0.9 µm; Dentino-enamel junction 15.000/ mm² - 20.000/mm² Pulp 2-3 µm Pulp 45.000/ mm² - 60.000/ mm² First, etching enamel tissue At least 15 s. Second, etching dentin tissue At dentin 15 s. Smear layer During normal cutting procedures, a layer of debris, is created that covers the cut surfaces of the enamel and dentin. Hydroxyapatite Denaturated kollagen Smear plug blocking the entrance of a dentinal tubule. Dentin permeability. Dentin etching Smear layer Demineralisation underlying dentin Open dentinal tubules Intertubular and peritubular collagen exposed Acid type Application time 7,5μm demineralization depends on the concentration Air-drying dentin tissue More water contents of dentin Air -drying, Sponge usage, Retweeting after well-drying Bonding to dentin tissue by adhesive systems Remove smear layer Modified smear layer Caries affected dentin When remove caries, the surrounding dentin is partially demineralized. Mineral crystallite in dentin More resistant to etching Decrease permeability of dentin Not to form ideal resin tags Less penetration of adhesive resin Sclerotic dentin Partially or completely blocked dentin canals, hypermineralise dentin tissue The peritubular dentin becomes wider, gradually filling the tubules with calcified material