Effects of irradiation time and post diameter on resin photopolymerization

Objectives: The purpose of this study is to clarify the effects of post diameter, and exposure time on resin photopolymerization when using fiber posts (FP, Fiber Post, GC).

Methods: The FP was inserted into the fluid composite resin (BEAUTIFIL Flow A3T, SHOFU) in a 0.5ml microtube. The upper end of the post was irradiated using a light generator (Curenos, SHOFU). Irradiation time was 10 (A) and 20 seconds (B) for the 1.6-mm diameter post, and 20 seconds (C) for the 1.2-mm diameter post. After polymerization, the unpolymerized resin was removed by soaking in acetone. Then, the diameter of hardened resin around the FP was measured at a point 13 mm from the upper end of the post. Each sample was measured 3 times, and the mean value was calculated. Three samples were prepared under each set of conditions (A and B, C). The data were analyzed using Student's t-test.

Results: The mean value for A was 2.935±0.172 (mm; mean±S,D) for B, in which the resin was exposed for a significantly longer time(p<0.0001), the value was 6.116±0.036. The diameter for C (5.928±0.142)was not significantly different from that for B. Macroscopic observation showed that B was covered in polymerized resin up to the post tip, whereas no resin was observed near the tip on A or C.

Conclusions: When using fiber posts, it is important that sufficient light be transmitted through the post to polymerize the surrounding resin. In this study we found that polymerization around the post was imperfect due to insufficient irradiation through the post. Therefore, the use of the photopolymerization-type resin, which has excellent optical transparency, or dual-cure resin is desirable in cases in which exposure time is limited or in which small-diameter fiber posts are used.