2. Resin-Dentine bonding + misc

13. Degradation
Resin degradation
1. Absorption of water into resin results in resin degradation by plasticisation
2. Covalent bonds between polymers are disrupted when water is present
3. Results in leaching out of resin material and reduction in long-term bond strength
4. Partially-cured adhesives exhibit increased water absorption, further compromising CR-adhesive bond
5. Resin/collagen hydrolysis may degrade hybrid layer = Loss of resin from inter-fibrillar spaces and disorganisation of collagen fibrils = weaker resin-dentine bond
Degradation of Hybrid Layer
1. Hybrid layer is 70% resin + residual solvent and 30% collagen
2. Approx 70% of collagen in hybrid layer disappeared within 4 years. 35-70% bond strength lost within 12-14 months
3. Hybrid layer degradation due to enzymes in dentine & saliva (Matrix metalloproteinases MMPs + Cysteine cathepsins)
4. MMPs are bound in dentine and are exposed by acid etching
5. Enzymes activate after etching, causing collagen fibril unwinding (degradation)
6. Chlorhexidine most promising way to stabilise collagen (because enzyme inhibitor)
7. But CHX is soluble in water and can leach out of the interface over time

14. Substrate (dentine) variables affecting resin-dentine bond
1. Over-dry dentine surface – Collage fibril collapse & stick together, preventing primer and adhesive infiltration. Poor hybrid layer development
2. Over-wet dentine surface – Prevents complete infiltration of primer & adhesive (high volume suction adequate to remove moisture)
3. Excessively deep etching (>15-20s) – Demineralised intertubular dentine. If demin >2-3um, incomplete infiltration of primer & adhesive, leaving fluid at base of hybrid layer
4. Depth of cavity wall – Bonding more predictable to ‘superficial dentine’ cavity wall because of less proportion of dentine tubules present
5. Carious dentine – Bonding compromised in zones of carious dentine due to unpredictable presence of sclerotic & demin dentine
6. Sclerotic dentine – Common on worn lower anteriors/exposed root surfaces. Research recommends mechanical removal of sclerotic dentine surface OR etch 2x as long

Leave a Reply

Your email address will not be published. Required fields are marked *