Adhesion and Applied Phenomena (King Salman International University) Fall 2024-2025

Field of Dental medicine Dental biomaterials I (PDD131) Lecture : Adhesion and applied surface phenomena Assoc.Prof.Dr : Enas Mahmoud Elddamony Date : 8 / 12/2024  References Philips science of dental Introduction to dental materials...

Field of Dental medicine Dental biomaterials I (PDD131) Lecture : Adhesion and applied surface phenomena Assoc.Prof.Dr : Enas Mahmoud Elddamony Date : 8 / 12/2024  References Philips science of dental Introduction to dental materials materials (Richard van Noort) 12th edition 4th edition Chapter 2: Structure of matter Chapter 1: 9. Principles of and principles of adhesion adhesion Pp: 24-29 Pp:51-61  Objectives Know the meaning of cohesion and adhesion Be aware with different mechanisms and types of adhesion Enumerate different factors that affect good adhesion Be familiar with the steps and precautions to be followed to obtain good adhesion with tooth structure  Adhesion Bonding between two solids Intimate contact Liquid adhesive to produce thin layer  Cohesion Adhesion Adhesive Adherend  Cohesion Bonding of similar materials resulting from attraction between molecules  Adhesion Attraction between dissimilar molecules Adhesive (adherent, bonding agent): liquid or material used to produce adhesion Adherend (substrate): substrate to which adhesive is applied  Examples of cohesion Bonding between 2 pieces of pure gold under pressure (metallic bond) Pressure welding  Examples of adhesion Retention of complete denture Importance of adhesion in dentistry Pit and fissure Bonding of sealants orthodontic brackets Aesthetic coating for Adhesion of plaque treating enamel and calculus on defects tooth surface Enamel hypoplasia Dental caries and Reduce marginal leakage between restoration and bacteria cavity walls Cosmetic dentistry Bonding agents Ceramo-metallic restoration Attachment or mechanical adhesion  True adhesion Mechanical interlocking Bonding between dissimilar Bonding between dissimilar materials through chemical materials through reaction mechanical interlocking (no actual bond is formed) Glass ionimer and zinc Amalgam , composite, zinc polycarboxylate with tooth phosphate cement Both contains COOH group Liquid flows into solid that reacts with calcium of surface pores and set tooth (harden) forming strong mechanical bond Factors affecting the strength of adhesive junction  Wettability Irregularities Adherend Cleanliness solid Stresses due to setting contraction Adherent adhesive Thermal stresses liquid Thickness Type of bond  Wettability Definition Ability of the liquid to spread over a solid surface Measured by Contact angle  Contact angle Angle between surface of the liquid and surface of the solid Contact angle wettabilit y  Importance of wettability in dentistry Good wetting by saliva is important for denture retention Natural appearance for restorative materials when wetted by thin film of saliva  Wax pattern is coated by surface wetting agent or debubblizer (surfactant) as it has low surface energy before investing. Surface energy and surface tension  Factors affecting wettability 1. Surface energy of the solid (reactivity of solid surface) Atoms at the surface have high energy as they are not equally attracted in all directions Atoms at the centre have low energy as they are equally attracted in all directions  Metals have high surface energy Wax and Teflon ( non sticky pans) have low surface energy 2. Surface tension of the liquid Cohesive force between liquid molecules Atoms at the surface have different reactivity from that of the bulk Surface tension decreases by increasing temperature and impurities 3. Surface irregularities of the adherend (surface roughness) Prevent adhesive from completely wet the surface of adherent Air pockets may be formed Surface irregularities favourable unfavourable Shallow deep Wide Narrow regular irregular 4. Viscosity of liquid adhesive Resistance to flow  Summary For good wetting Surface energy of adherend Surface of the adherend favourable The viscosity of the adhesive Surface tension Factors affecting the strength of adhesive junction 1. Wettability  2. Cleanliness Bonding to clean and dry surface is better than to wet contaminated surface Impurities lower surface energy of solid so decrease wetting by adhesive 3.Thickness of the adhesive the thinner the adhesive film, the stronger the adhesive junction (more intimate contact)  4. Thermal stresses Difference in coef. between adhesive and adherend leads to stress at the interface Close matching is required http://www.dental-picture-show.com/dentists-crowns/gold-crowns/porcelain-metal-crown.gif  5. Stresses due to setting contraction of adhesive Less setting contraction, less stress at interface, stronger junction 6. The type of bond formed Soldered joint (1ry bond) is stronger than glued joint (2ry bond)  Thin adhesive Intimate contact between two adherends Less setting contraction stresses Less thermal stresses  Ideal adhesion requires: Contact angle Wettability Surface energy Surface tension Viscosity  Ideal adhesion requires: Surface roughness Favourable Surface cleanliness Primary Type of bond Setting stresses Thermal stresses  Adhesion or Cohesion Denture base with saliva and soft tissues adhesion Acrylic artificial teeth with acrylic denture base cohesion  Types of adhesion chemically Glass ionimer bonds to tooth…………….. mechanically Amalgam bond to tooth………………………. Failure in adhesive junction  Types of failure Cohesive failure Adhesive failure In the adhesive Between adhesive and In restoration substrate (tooth, restoration) In tooth Difficulties to produce adhesion in the oral cavity 1. Inhomogeneous composition of enamel and dentin 2. Surface irregularities in prepared cavity  3. Debris in the prepared cavity Smear layer: Formed on prepared tooth cavity formed of: 5-10 microns Blood Saliva Collagen Bacteria Cutting tooth structure  4.Prescence of water on prepared cavity Not water from saliva, but water always on tooth surface that prevents adhesive from coming into intimate contact with tooth Bonding to tooth structure  Bonding to enamel 1.Acid etching 2.Bonding agent 3.Application of composite filling  1.Acid etching 30-50% Phosphoric or citric acid For 15-30 sec Removes 5 microns, produce micro-irrigularities  Benefits of acid etching to enamel Removal of surface debris (produce clean surface) Producing pores into which resin penetrates and form tag-like extensions (micromechanical interlocking) Increasing the surface energy of the enamel (increase wettability) Exposure of greater surface area  2. Application of adhesive Rinse ,dry the tooth Apply adhesive Penetrates int pores forming microtages 3. Application of composite filling material  Bonding to dentin 1.Acid etching 2.Primer 3.Bonding agent 4.Application of composite filling  G.R: Bonding to dentin is more difficult than to enamel?? Presence of high amount of water (hydrophilic) Presence of smear layer?  Primer Acid Adhesive Smear layer Dentinal tubule Dentin  1. Acid etching Diluted acid (10% citric acid) 10-15 seconds Etching will lead to: 1. Removal of smear layer 2. Micro-irregularities 3. Reduction of surface energy (exposure of more collagen)  Removal of smear layer over dentin Producing pores to form tag-like extensions Opening dentinal tubules creating micropores into which bonding agent will interlock  2. Priming To increase surface energy of dentin to increase wetting  3. Dentin bonding agent 2 functional groups Hydrophilic to bond with dentin Hydrophobic to bond with composite resin  Adhesive Composite Primer Acid Smear layer Dentinal tubule Dentin Composite resin bonds to tooth structure through micromechanical interlocking