Influência da ciclagem térmica na resistência da união à dentina, nanodureza e módulo de elasticidade da interface de adesivos dentários universais = Influence of the thermal cycling on dentin bond strength, nanohardness and Young's modulus of dental universal adhesives interface

The purpose of this study was to evaluate the nanohardness (H) and Young's modulus (Y) of the adhesive interface and the adhesive bond strength immediately and after submitted to 10,000 thermal cycles. One hundred and sixty non-carious human third molar were randomly divided in eight groups according to the adhesive system and dentin approach (Scotchbond Universal self-etch; Scotchbond Universal etch-andrinse; Prime & Bond Elect self-etch; Prime & Bond Elect etch-and-rinse; Clearfil Universal Bond self-etch; Clearfil Universal Bond etch-and-rinse; All-Bond Universal self-etch and All-Bond Universal etch-and-rinse), and posteriorly subdivided according to the storage period of 24 h or 10,000 thermal cycles (n=10). Three teeth were selected for nanoindentation test and seven for the microtensile test. The teeth were prepared to obtain flat dentin surfaces. The adhesive systems application and photoactivation followed the manufacturer’s instructions. The composite resin restoration was incrementally constructed, and the restored teeth were submitted to the respective aging protocols. For the microtensile bond strength test, the samples were sectioned to obtain dentin-resin sticks with a sectional area of 1 mm. For the nanoindentation test, samples were sectioned to obtain 1.5 mm-thick bonded slices, embedded in epoxy resin and manually polished using wet SiC papers. Five nanoindentations were made in each adhesive layer, hybrid layer and dentin with load of 1000 μN in trapezoidal cycle mode. The bond strength values (μTBS) did not show statistically significant difference among the four adhesive systems tested after 24 h and submitted to 10.000 thermal cycles for any application mode (PBE E&R 33,85 29,62; PBE SE 21,74 22,65; SBU E&R 33,40 31,63; SBU SE 27,82 27,03; ABU E&R 34,09 29,73; ABU SE 23,85 26.88; CUB 34,62 27,59 and CUB 28,64 24,06). Application mode (etch-and-rinse E&R/self-etch SE) has significant influences on μTBS of Prime & Bond Elect and All-Bond Universal adhesives only for no thermocycling condition. The test condition (with/without thermocycling) was statistically significant only for Clearfil Universal Bond with etch-and-rinse technique. Scotchbond Universal applied in the E&R and SE modes showed stable bond strength values after storage for 24 h or after thermal cycling. For nanohardness and Young’s modulus were not found statistically significant difference among the Universal adhesives systems immediately tested. After thermocycling, Prime & Bond Elect applied in E&R mode showed significantly lower values for H and Y than other systems, and All-bond Universal in E&R mode showed the lowest H values in adhesive layer for both aging protocols. Young’s modulus values were significantly different among dentin, hybrid and adhesive layers (dentin>hybrid layer>adhesive layer). The application mode showed significant influence on μTBS values for Prime & Bond Elect and All-Bond Universal adhesives only when no thermocycled. The test condition was statistically significant in the μTBS values for Clearfil Universal Bond in E&R mode, and in the H and Y values for PBE in E&R mode.