Bonded amalgam restorations: microleakage and tensile bond strength evaluation

The objective of this study was to evaluate the tensile bond strength (BS) and microleakage (MI) of bonded amalgam restorations to dentin when an unfilled and a filled system are used under three application modes.

Seventy-two and 96 human molars, respectively, were employed for BS and MI tests. For BS, the occlusal surface of the molars was ground flat until dentin exposure. A 3-mm area was delimited for bonding. For MI, Class V cavities were prepared in the CEJ (4 mm x 4 mm x 2 mm). For each test, the molars were randomly divided into six treatment groups defined by a combination of the levels: Adhesive system (Scotchbond Multi-Purpose Plus [SBMP], Optibond dual cure [OPTB]) and Application mode (light-LC, chemical-C and combination of light and chemical curing-LCC). After adhesive application, the amalgam was condensed into a Teflon mold (BS) and into the cavities (MI). After storage in saline solution for seven days at 37 degrees C, the specimens were subjected to the BS test at 0.5 mm/minute. For microleakage evaluation, the restorations were sealed with nail varnish, except for an area 1 mm around the restoration, immersed in 5% methylene blue solution for 24 hours and sectioned into two halves. Each half was evaluated by two trained examiners at 25x magnification in a 0-3 score system and the highest score was recorded. The BS data was evaluated by two-way ANOVA and Tukey's test (alpha=0.05). The MI data were analyzed by Kruskal Wallis and Mann-Whitney tests (alpha=0.05).

The main factors were significant for the BS test: the highest BS mean was obtained using the LCC technique and the OPTB system. Regarding the MI test, only the application mode was significant: lower dye infiltration was observed for LC and LCC.