Failure of composites
- 1. FAILURES IN COMPOSITE RESTORATIONS • Composite restorations are very technique sensitive and therefore utmost care should be taken before, during and after their placement. • Failures include: • Discolouration (esp in the margins) • Recurrent caries • Post-operative sensitivity • Gross fracture of restoration • Lack of maintaining contact • Accumulation of plaque around the restoration
- 2. FEATURES THAT LEADS TO FAILURE • Incomplete excavation of caries • Leftover caries hinder with the bonding mechanism • Incomplete removal of ZnO eugenol from the base of the cavity and the walls
- 3. • Incomplete etching and failure to remove residual acid from the enamel tags • Proper concentration of acid and etching time mandatory to achieve requisite tags • Flourosed enamel – more etching time • Total etching time <60 seconds • Repeated touch after etching, blowing with compressed air under pressure (chip syringe preferred), use of cotton over the etched surface causes fracture of tips of tags • Wash off the acid properly or else lack of residual acids hinder with the bonding • Gel etchant – 20-30 seconds washing and Liquid etchant – 10-15 secs
- 4. • Excess or non-uniform application of bonding agent • Non-Uniform application – Hinders union of material with bonding agent • Excess bonding agent – marginal leakage • Lack of isolation • Rubber dam isolation mandatory • If not cotton rolls is a must • Gingival retraction cords in Class III & V and also in laminates • Uncontrolled salivation in patients – use antisialogouge drugs
- 5. • Touch of composite with finger • Use Teflon coated instruments • Composite contaminated with saliva should not be packed and cured • Avoid bulk placement of composite • Placed in increments • Each increment as small as possible since the contraction after polymerization leads to gaps at tooth restoration interface • This can lead to marginal leakage and secondary caries
- 6. • Improper curing • From all the sides and for stipulated time • The filter and the bulb intensity should be checked in routine • For proximal restoration – fine tips can be used • Improper finishing and polishing • Composites should be finished and polished thoroughly • Occlusion check before final polishing • Antagonist tooth, if impinging can be grinded off
- 7. GUIDELINES TO MINIMIZE CHANCES OF FAILURE • Small cavity preparation (composite in bulk leads to failure) • Avoid sharp internal line angles (increases stress) • Deeper cavities – Ca hydroxide or RMGIC base • Strict isolation • Avoid inadequate curing – leads to breakdown of composites • Use small increments, holding each increment with tefflon coated instruments. • Curing should be done from all sides for adequate time using proper intensity of light.
- 8. STUDIES REGARDING FAILURE • Electric hot air for drying after washing the etchant off increases bond strength by about 29%. Three-way syringe is the least preferred (Henry Wadsworth Longfellow 2002 Albers-Resin polymerization, Harry F 2002 Albers Resin Bonding Marconi BC Deecker Inc Hamilton, London) • For smooth surface etching – liquids and gels gives same result. But for pits and fissures – liquid is recommended (Harry F 2002 Albers Resin Bonding Marconi BC Deecker Inc Hamilton, London)
- 9. • Over-etching can cause an insoluble reaction product mono-calcium phosphate dehydrate which weakens bonding • 45% exit angle most preferred as it results in least microleakage. • A study after 7 days observation showed that 40 sec curing cycle for 1mm thickness of composite restoration gave 68-84% hardness and 3 mm thickness gave only 34% hardness • Darker shades of composites cures slowly and deeply than the lighter shades • Using burs with more number of flutes for polishing causes lesser damage to the composite filling