PURPOSE To determine the performance of a silorane-based resin composite, compared to that of a methacrylate-based resin composite, when used with their corresponding adhesive systems, and to determine the effects of c-factor and water storage time in Class I occlusal preparation, by means of microtensile bond strength (microTBS) test. METHODS Extracted human third molars were ground flat to expose dentin, and randomly divided into eight groups, according to the type of resin composite, c-factor, and water storage time: (1) Filtek P90/ high c-factor/24 hours, (2) Filtek P90/low c-factor/24 hours, (3) Filtek Z250/high c-factor/24 hours, (4) Filtek Z250/low c-factor/24 hours, (5), Filtek P90/ high c-factor/3 months, (6) Filtek P90/low c-factor/3 months, (7) Filtek Z250/high c-factor/3 months, and (8) Filtek Z250/ low c-factor/3 months. After 24 hours or 3 months of water storage, the bonded hourglass specimens were tested for microTBS, and failure types were also noted. Data were analyzed using three-way ANOVA and Tamhane post-hoc test (alpha = 0.05). RESULTS Filtek Z250/low c-factor/24 hours exhibited the highest microTBS (54.19 +/- 9.05 MPa), and Filtek P90/high c-factor/3 months exhibited the lowest (6.94 +/- 2.07 MPa). All groups tested in high c-factor (> 4) preparations and 3-month water storage time showed significant decrease in microTBS, except when comparing between Filtek P90/high c-factor/24 hours and Filtek P90/high c-factor/3 months as there was no statistical difference.