Adhesion Systems Flashcards
1
Q
Procedure for bonding to enamel?
A
- Acid etch with 37% phosphoric acid for 15s: This step removes ~10um of enamel surface and creates a morphologically porous layer ranging from 5-50um deep that allows for adhesive to penetrate to form tag-like extensions
- Adhesive: Low viscosity resin contacts prepared enamel surface, where it flows and fills the produced irregularities, mechanically bonding to enamel; Attracted to interior of pores on enamel created by capillary attraction
- Composite resin bonds to adhesive via chemical means
2
Q
Procedure for bonding to dentin?
A
- Dentin conditioner: 10% polyacrylic acid for 15s
- Primer: Contains monomers with both hydrophilic and hydrophobic functional groups (ie. HEMA), dissolved in an organic solvent (alcohol/acetone/water) to enhance wettability and promote penetration into hydrophilic dentin; This influences the bond strength between tooth structure and composite resin. The hydrophilic groups bond to dentin while the hydrophobic groups bond to composite resin
- Adhesive: Low viscosity resin that contains hydrophilic molecules that can penetrate into porous dentin and hybrid layer to bond to primer and collagen fibres by means of mechanical interlocking
- Composite resin bonds to adhesive via chemical means
3
Q
What are the problems of bonding in dentin?
A
- Constant outward flow of dentinal fluid from pulp reduces the adhesion of composite resin to dentin
- Dentinal tubules contain odontoblasts and vital processes of the pulp, hence, closer the proximity to the pulp, the greater the chance of pulpal irritation from chemicals used in etching and bonding dentin
- Overdrying dentin leads to collapse of collagen network and demineralisation of dentin. This results in a low bond strength due to inefficient penetration of adhesive into dentin
- If dentin is too wet (not dried sufficiently), water dilutes the resin primer and out-compete it for sites in the collagen network, preventing hybridisation
