Influence of different liners and degradation on composite restoration performance

Objectives: to evaluate the effect of different liners and thermo-mechanical degradation(TMC) on push-out bond strength and gap formation(Scanning Electron Microscopy-SEM).

Methods: 80 bovine incisors were selected and ground flat at buccal and lingual surfaces in order to obtain a 2 mm thick dentin block. In the central area of the dentin block, a conical cavity was prepared with #3131 diamond tip, in a standard preparation machine. Dentin blocks were distributed into eight groups(n=10), according to restorative technique and degradation protocol: G1:conventional technique:no liner+ no degradation;G2:conventional technique:no liner+degradation;G3: 3 layers of Scotchbond Multi Purpose+no degradation;G4: 3 layers of Scotchbond Multi Purpose+degradation; G5:Lining with Fluoroshield+no degradation; G6:Lining with Fluoroshield+degradation;G7:Lining with Filtek Z350 flow+no degradation; G8:Lining with Filtek Z350 flow+degradation. The degradation protocol was accomplished in an Erios-thermo-mechanical cycling machine with 500 thermal cycles and 100,000 mechanical cycles made simultaneously. The restorative procedure was standardized in all groups: Single Bond 2 was applied according to manufacturer instructions and the composite Filtek P60 was inserted in a single increment; the liner was applied according to the group. Specimens were stored for 24h and then, finished and polished using sandpaper(# 600 and 1200). The specimens were subjected to the degradation protocol according to the group. Next, a replica of each surface restoration was obtained in epoxy resin to marginal evaluation in SEM. Bond strength was determined in a universal testing machine, with compressive load speed of 0.5 mm/min until the restoration dislodgment. Data were submitted to two way-ANOVA and Tukey’s test(p<0.05).

Results: No statistically significant differences were found between groups(p>0.05) regardless restorative technique and TMC degradation, concerning marginal adaptation and push-out bond strength.

Conclusions: resin liners did not improve marginal quality and bond strength of composite restorations and also thermo-mechanical cycling does not jeopardize bonding interface at the conditions tested in this study.