Liner type and chewing simulation effect on marginal/internal composite adaptation

Objectives: To evaluate the marginal and internal gap formation by SEM of composite restorations using different resin liners and submitted to thermo-mechanical degradation.

Methods: enamel was ground flat at buccal surface and a conical shape cavity was prepared with #3131 diamond tip. They were distributed into 8 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. Degradation protocol was accomplished in an Erios-thermo-mechanical cycling machine: 500 thermal cycles and 100,000 mechanical cycles, simultaneously made. The restorative procedure was standardized in all groups using Single Bond 2 and composite Filtek P60, according to manufacturer instructions; liner was applied according to the group. Specimens were 24h stored(37^OC/100% relative humidity) and finished and polished using sandpaper(# 600 and 1200). They were subjected to the degradation protocol according to the group. Replicas from surface restoration were obtained. Then, specimens were sectioned on center restoration and replicas from internal interface restoration obtained. Gap percentage was measured along of interfaces (suface/internal) and analyzed in SEM. Data were submitted Kruskal Wallis test(p<0.05).

Results: Marginal adaptation wasn`t influenced by restorative technique and thermo-mechanical cycling. Concerning internal adaptation G3 showed the lowest percentage of gaps; G5 intermadiate results, and G1 and G7 the highest gap percentage. Concerning TMC there was significantly increasing on internal gaps by low elastic modulus liners (G4, G6 and G8). G2 didn`t show significantly increase in the internal gaps when submitted to TCM.

Conclusions: The use of 3 adhesive layers can improve internal immediate adaptation of composite restorations, however, TMC increases the internal gaps when low elastic modulus liners are used.