Adhesives

Question 1

Types of bonding

Answer 1

Macromechanical
Visible interlocking btw dissimilar materials
Eg pins, removable dentures, posts for endo

Micromechanical
Microscopic mechanical interlocking btw dissimilar materials
Eg enamel/resin bond, dentine/resin bond, sandblasting (aluminium oxide)

Interfacial (adhesion btw 2 very different materials; usually chemical + mechanical)
Resin to ceramic: etch enamel → adhesive → resin cement → silane (C=C + OH → Si-O- porcelain, C-C-resin) → etched porcelain (hydrofluoric acid)
Resin to metal: adhesive → resin cement → metal primer (C=C + O → oxide bonds) → gold sandblasted metal (improves retention w metal primer)

Question 2

Adhesive vs cohesive failure

Answer 2

Adhesive:
Occurs in adhesive layer eg luting cement
Bond not strong enough
Caused by moisture contamination

Cohesive:
Failure within the material (eg GIC breakdown)
Caused by heavy bite

Question 3

Generations of bonding protocols

Answer 3

4th gen is the gold standard: 3-step etch-and-rinse adhesive
5th to 7th all have issues
5th: 2step etch-and-rinse adhesive - etch & primer-adhesive
Self-etch adhesives
6th: 2step etch-primer and adhesive
7th: 1 step All-in-one Self etch/primer/adhesive. Eg G-bond
8th: Universal adhesive - G-Premio

Problems with etch-and-rinse adhesives
Incomplete infiltration of primer into demineralised collagen
Long-term water sorption into the hybrid layer w HEMA-based adhesives

Problems with self-etch adhesives
Formation of water blisters at the resin/dentine interface
Forms Semi-permeable membranes
Phase separation occurs between hydrophilic and hydrophobic components
Shorter resin tag formation because of weaker acidity
Greater failure rates and poorer bonding strengths c.f. e&r adhesives.

8th gen promising but req more research
Universal adhesive: compatible w both etch-and rinse & self-etch systems (choice of total etch or no etch)
4MET monomer is less moisture-sensitive than HEMA as no swelling and phase separation.
Chemical bonding with Ca of teeth
Utilises nano-sized filler particles: penetrate and create stronger cross-links within the smear layer
Total etch/no etching → apply 8th gen for 10s → dry 5s at MAX pressure → LC 10s → place CR

Question 4

Conditions for optimal adhesion

Answer 4

Clean bonding surfaces
Close contact btw surfaces
Good wetting of adhesive (low viscosity)
Large surface area
Dimensionally-stable adhesive
Correct protocol for bonding