Effect of C-factor on microtensile bond strengths of low-shrinkage composites

This study evaluated the microtensile bond strength (μ-TBS) of low-shrinkage composites with their corresponding adhesive systems, Filtek Silorane/Silorane adhesive (SIL, 3M ESPE AG, Seefeld, Germany) and Aelite LS/One-Step Plus (AL, BISCO Inc, Schaumburg, IL, USA) in cavities with different C-factors. Filtek Z250/Adper Single Bond Plus (Z, 3M ESPE, St Paul, MN, USA) was used as a control.

Standardized Class I cavities were prepared in extracted human molars after removing occlusal enamel. Cavities were assigned into six different C-factors by applying nail polish to four walls, three walls, two walls adjacent to each other, two walls opposite to each other, one wall, or no walls. Resin composites with their corresponding adhesive systems were applied according to manufacturer instructions. Specimens were sectioned to obtain four rectangular beams from the center of the restorations and μ-TBS was measured. Data were analyzed by Weibull survival analysis. Shrinkage stresses of the resin composites were determined after 30 minutes from the start of light-curing using a tensometer testing machine. Flexure elastic modulus was determined using standard procedures, in accordance with ISO 4049. Data for shrinkage stress and elastic modulus were analyzed by one-way analysis of variance followed by a Tukey multiple-comparisons test (p<0.05).

μ-TBS of both SIL and AL were not affected by different C-factors; however, the bond strength of Z decreased significantly when the C-factor increased. Shrinkage stress results were 0.94 ± 0.1, 1.79 ± 0.18, and 2.14 ± 0.23 MPa for SIL, AL, and Z, respectively. The flexural modulus of both the SIL and the AL was significantly lower than that of Z.

Increasing C-factor did not negatively affect the bond strength of low-shrinkage composites.