Evaluation of the bubble mixture rate and the bond strength of post to dentin according to the technique of applying resin cement

Abstract

Purpose: Previous clinical studies have indicated that the loss of retention between post and tooth is a major cause of failure in the restoration of endodontically treated teeth. Since bubble-like defects were found in the cement layer of the debonded post, we hypothesized that this cement defect decreases the adhesive strength. The purpose of this study was to evaluate if the technique used to insert resin cement influences the presence of bubbles and the push-out bond strength.

Methods: The root canal of a transparent resin block and bovine tooth were parallel-wall drilled with a Peeso Reamer to achieve a post length of 10 mm. Prefabricated metal posts were cemented using self-adhesive resin cement, for nine combinations of three tools and three cement application sites. The resin block was scanned with a digital camera, then image analysis software was used to calculate the percentage of bubbles in the cement layer. Bovine teeth were sectioned into five 1-mm thick slices for the push-out bond strength test.

Results: The bubbles were concentrated at the apical side for all methods. When we used the plastic needle to apply cement to the post and root canal, the bubble mixture rate was significantly lower than that of the other methods. Using the brush resulted in a significant decrease in the push-out bond strength at the apical side, whereas there was no significant difference in the push-out bond strength between the sites with other tools.

Conclusions: It is considered that there is less adherence at the site of air bubbles, and therefore a decrease in the adhesive strength. We conclude that it is important to use a tool that reaches the deepest part of the prepared root canal to reduce the air bubble mixture rate and to obtain the highest adhesive strength.