Effect of different dentin moisture on the push-out strength of bioceramic root canal sealer

Abstract

Background/purpose: Different moisture condition may affect the adhesion between obturation materials and root canal walls, thus further affect the quality of root canal obturation. The aim of this study was to evaluate the influence of dentin moisture conditions after different root canal drying protocols on the push-out strength of bioceramic root canal sealer.

Materials and methods: Twenty root canals from extracted human decoronated premolars were prepared in vitro to #30/0.09 taper and assigned to 4 moisture condition groups after using different root canal drying protocols: normal moisture (paper point) group: the canals were blot dried with paper points until the last one appeared dry. Ethanol dry group: the canals were dried with paper points followed by dehydration with 95% ethanol. Isopropanol dry group: the canals were dried with paper points followed by dehydration with 70% isopropanol. Complete dry group: the canals were dried in an air-blowing thermostatic oven for at least 6 h until there was no change in weight at an interval of 1 h. After drying, the canals were obturated with bioceramic sealer iRoot SP. Then, each root was sectioned into eight slices with 1-mm-thick using a diamond saw (40 slices each group). The push-out strength was tested for each slice between the sealer and dentin wall using a universal testing machine at a crosshead speed of 0.5 mm/min, and failure modes were recorded. Two-way analysis of variance and Tukey test were used to analyze the push-out strength. Logarithmic linear regression analysis was used to compare the failure modes.

Results: Push-out strength was statistically different in different moisture groups (P < 0.05). After drying using paper point, iRoot SP specimens showed the highest push-out strength (2.04 ± 0.03 MPa), followed by 95% ethanol, 70% isopropanol. The lowest push-out strength (0.68 ± 0.04 MPa) was observed under complete dry. For the failure modes, the majority were cohesive failures in the coronal and middle thirds of the root; while in the apical third, mixed failure was common.

Conclusion: Different drying protocols influenced the push-out strength between bioceramic sealer and canal wall.

Keywords: Dentin moisture; Push-out strength; Root canal sealer.

Figure 1

Universal testing machine for the push-out test (left) and representative failure mode images under a stereoscopic microscope (right). The shaft (yellow arrow) was placed over the tooth slice (blue arrow). (a) adhesive failure: failure occurred between the sealer and the inner wall of the root canal. (b) cohesive failure: failure occurred inside the sealer. (c) mixed failure: the above failure modes both occurred. Arrows indicate the interface after bond failure. D, dentin; S, Sealer.

Figure 2

Push-out strength (MPa) of iRoot SP with respect to the experimental dentin moisture conditions. Different letters represent statistically significant differences between groups (P < 0.05).

Figure 3

Failure mode percentage distribution (%) in different root regions. There was a significant difference between the different root regions (P < 0.05).