Resin-Composite Restorations, Can They Be Repaired Using Any Composite System?

Objectives: Dentists frequently repair composite restorations in clinical practice. The current study compared the microtensile bond strengths (MTBS) of a hybrid methacrylate-based composite [Filtek Z250,3M-ESPE (HMBC)], silorane-based composite [Filtek Silorane, 3M-ESPE (SBC)], and a microfilled methacrylate-based composite [Durafill VS, Heraeus Kulzer, (MMBC)] to aged (A) SBC or HMBC blocks. Methods: Fresh(F) SBC, HMBC or MMBC, using the respective manufacturers' self etch adhesives, were bonded to aged blocks of SBC (n=48) or HMBC (n=48), giving eight groups. Group 1; AHMBC/FHMBC, Group 2; AHMBC/FMMBC, Group3; AHMBC/FSBC, Group4; ASBC/FSBC, Group5; ASBC/FHMBC, Group6; ASBC/FMMBC. Group7; FHMBC/FHMBC, and Group 8; FSBC /FSBC, served as controls. Samples were stored in distilled water for 24h in a dark container and thermo cycled between 5°C and 55°C for 4000 cycles. Tensile bond strengths were measured using a microtensile tester (Bisco, USA). Failure modes were assessed by SEM. Data were analyzed by Kruskal-Wallis non-parametric ANOVA (95% significance). Results: MTBS values in MPa [mean(SD)] were: Group1, 38.30(9.34); Group2, 26.80(7.33); Group3, 27.90(7.34); Group4, 19.80(5.29); Group5, 13.70(6.95); Group6, 7.9 (4.83); Group7, 35.30(11.88); and Group8, 18.70(3.80). Fractures were almost always in the adhesive layer apart from AHMBC to FMMBC which demonstrated high percentage of cohesive fractures in the FMMBC samples (83%). Irrespective of fresh material, bonding to AHMBC gave significantly higher MBTS than bonding to ASBC (p<0.05). With respect to aged materials, bonding of matching fresh material gave higher MTBS than other materials (p<0.05). Conclusions: Highest MTBS were obtained when fresh material was bonded to the corresponding aged material. The clinical significance is that if the material of an existing restoration is known it is best to use the same material and the manufacture's self etch adhesive when repairing. If the substrate material is not known then the best bond strength is achieved using hybrid composite.