Purpose: The effects of incremental filling technique and flowable liner on the bond strength of resin composite in different sized cavities were investigated in this study. Materials and Methods: Two sizes of cylindrical Class I cavities were prepared in bovine dentin (98.1 mm3 and 21.2 mm3). A light-curing resin composite (Clearfil Photocore) with a self-etching primer adhesive (Clearfil SE Bond) was used to bulk fill the cavities (C-factor 5), with and without flowable liner (Clearfil FLOW-FX) or incremental filling (2 layers, Cfactor 3). As control, a 3-mm or 5-mm buildup was placed on the flat dentin surface (C-factor 0.2). After 24 h storage in 37°C water, the microtensile bond strength was measured at a crosshead speed of 1 mm/min. Mode of failure in the fractured specimens was observed using a scanning electron microscope. The obtained results were statistically analyzed. Results: In large cavities, incrementally filled and lined cavities showed higher bond strength values than the bulk-filled subgroup (p < 0.05). However, in small cavities, neither the incremental technique nor flowable liner improved the bond strength. Conclusion: Not only the filling techniques but also the cavity size affected the bond strength to the cavity floor in cylindrical Class I cavities.

Keywords: cavity size, incremental technique, flowable liner, C-factor, microtensile bond strength