ADHESION TO TEETH

  • adhesives can help fill the gap caused by shrinkage

  • conservation of tooth structure because no undercutting like with silver amalgams to give mechanical retention

  • sealing interface can reduce post-op sensitivity which may happen with exposure of dentinal tubules.

  • Pulpal reaction can be caused by change in pressure gradient and movement of fluid.

  • sealing gap will decrease marginal leakage

  • many restorations only possible with adhesion eg ortho bracket, incise tip class 4 restoration, veneers

FACTORS FOR IDEAL BONDING-

  1. clean adherend or else adhesive won’t adapt very well. Etch can be a cleaner too

  2. good wetting- viscosity, has to be able to adapt to all surfaces because of etch

  3. intimate adaptation- consequence of etching by increasing amount of surface.

  4. bonding- resin composites are hydrophobic so have to be adapted by other resins but more hydrophilic, find solvents inside eg ethanol in these adhesives. interlocking in micro structure to Give strength.

    -physical bonds by electrostatic attraction

    -primary mechanical retentive interlocking

    -chemical bonds- chelation to tooth surface

  5. good curing- not as big as a problem than with composites because it is a much thinner layer with less penetration, filler increases making it more viscous so adhesives have no to Low filler EASIER TO CURE.

BONDING RESIN COMPSOITES TO ENAMEL-

  • predictable bonding- because when using etchant it is primarily attacking the inorganic phase (microstructure of enamel is made up of rods and prisms) getting underneath rods making micro undercuts giving this rough surface feature creating a high surface energy. When resin is applied it can readily flow into gaps

  • homogenous structure

  • inorganic content (86%) hydroxyapatite

  • high surface energy

  • 37% phosphoric acid gel (stability and control). Predominantly mechanical bonding. weak physical bonding. macro tags between prisms, micro tags within prisms (most bond strength because highest SA)

  • dryness is essential especially for enamel because water can impact penetration of bond. IMPACT OF MOISTURE

  • tag length doesn’t affect bond strength

  • curing affects tag formation


BONDING RESIN COMPOSITES TO DENTINE-

  • composition changes compared to enamel there is a higher organic/ moisture content

  • less predictable

  • higher variability

  • etching surface of dentine will expose tubules can get resin to penetrate down and into branches to cause a micro-mechanically retentive bond

  • ISSUE- microstructure through dentine changes because of sigmoidal shape of tubules ‘S shaped’ tubules get wider (to pulp) and more dense compared to with enamel. More connection to pulp there is more moisture. THEREFORE, less chance of bonding successfully

  • acid-etching demineralises surface of IT dentine

  • contains very small porosities (containing water)

  • bonding resin needs to penetrate porosities

  • BIG ISSUE IS DRYING- pores are very small and will close up because water will evaporate and nice spongy matrix formed by etching will collapse…. if done successfully can create a hybrid layer of demineralised fibril network and resin. = responsible for most of bond strength and longevity of bond.

  • overwet = resin cannot penetrate porosities in collagen fibrous matrix

  • TECHNIQUE SENSIITVE GET NOT TOO WET NOT TOO DRY.

  • water based primers can rehydrate collagen

ADHESIVE CATEGORIES-

  • Etch and rinse adhesives

    -3 step; etch, prime and bond

    -2 step; etch, (prime+bond)

  • self-etch adhesives

    -2 step; (etch+prime), bond

    -1 step; (etch+prime+bond)

***elimnate dying stage

etch/rinse:

-ADVATAGES:

  • reliable bond strength to enamel

  • good long-term data

-DISADVANTAGES:

  • removal of smear layer may increase post-op sensitivity

  • wet bonding so get formation of hybrid layer in enamel. IMPORTANT FOR DENTINE technique sensitive

  • risk of fibril collapse

self-etch:

-ADVANATGES:

  • smear layer intact. bonding to smear layer but material is acidic enough so can penetrate smear layer and bind to dentine.

  • decrease risk of post op sensitivity. tubules not exposed

  • decrease risk of over drying so get formation of hybrid layer in enamel. IMPORTANT FOR DENTINE

-DISADVANTAGES:

  • long term data????

  • mild/less acidic SE systems have low bond strengths in enamel

  • more hydrophilic/ acid degrade faster

  • lower shelf life

***smear layer = all small particles of tiny inorganic matter but because of heat/friction of drill layer created of tooth particles. REMOVED BY ETCH thereby exposing tubule