Bond strength and ultimate tensile strength of resin composite filled into dentine cavity; effect of bulk and incremental filling technique

Objectives The aim of this study was to evaluate the relationship between micro-tensile bond strength (μTBS) and ultimate tensile strength (UTS) of resin composite restorations in cavities filled by a bulk or incremental technique using the micro-tensile test. Methods Class I cavities (4 mm long, 3 mm wide, 3 mm deep) were prepared into dentine of sixteen human molars. All cavities were bonded with Clearfil SE Bond and restored with AP-X composite with either a bulk or incremental technique. After storage in water for 24 h, the teeth were vertically sectioned to yield two slabs. Each slab was sectioned into three sticks. Sticks of one slab were trimmed into an hourglass of 0.7 mm2 area at resin–dentine interface for bond strength measurement while the other sticks were trimmed at the centre of the restoration for UTS measurement. Specimens were tested in tension at 1 mm/min until failure. The results obtained were statistically analysed using two-way ANOVA and post hoc test (α = 0.05). Pearsonʹs correlation test was used to identify any correlation between μTBS and UTS for each filling method. Results Both μTBS and UTS of resin composite decreased towards the bottom of the cavity (p < 0.05). The bulk technique group presented lower μTBS than the incremental technique groups at all regions (p < 0.05). In bulk filled restoration, there was a strong positive linear relationship between mean values of μTBS and UTS of resin composite based on the depth (r2 = .99; p < 0.05), while in incremental restoration there was no relationship between the variables. Conclusions There was a relationship between μTBS and UTS of resin composite filled into dentin cavity in bulk technique.