2021 Volume 64 Issue 1 Pages 57-65
Purpose: The purpose of this study was to evaluate the effect of irradiation of low-power Er: YAG laser and chemical pretreatment after irradiation of high-power Er: YAG laser to promote the tensile bond strength (TBS) of the resin-lased dentin interface.
Methods: Extracted human molars were prepared with flat dentin surfaces, and ground with wet 800-grit silicon carbide paper. The specimens were set on an X-Y-Z moving stage and mechanically irradiated at an energy setting of 150 mJ (C400F)/10 pps and/or 30 mJ (C800F)/10 pps while being sprayed with cooling water. We chose 6% sodium hypochlorite (NaClO), p-toluenesulfinate (Accel) and 10% citric acid/3% ferric chloride (FeCl3/citric acid) as chemical pretreatment agents. Then, the Clearfil Mega Bond System and resin composite (Beautifil Flow F00) were placed. The TBS was measured after storage for 24 hours in an environment with 99% humidity at 37°C. The irradiated specimens were divided into six groups (A1, A2, A3, B1, B2, B3, n=10), and a control group (Cont1, 2, n=10) that did not receive any laser irradiation. Each group was follows: {Cont1: No irradiation, Cont2: No irradiation→Accel→FeCl3/citric acid, A1: Irradiation with C400F, A2: Irradiation with C400F→Accel→FeCl3/citric acid, A3: Irradiation with C400F→NaClO→Accel→FeCl3/citric acid, B1: Irradiation with C400F and C800F, B2: Irradiation with C400F and C800F→Accel→FeCl3/citric acid, B3: Irradiation with C400F and C800F→NaClO→Accel→FeCl3/citric acid}. After the TBS testing, the type of failure was inspected by a stereomicroscope. The pretreatment conditioning patterns of the lased dentin were evaluated under SEM.
Results: The order of the TBS (mean value±SD, MPa) for each group was follows: A1 (10.5±3.5)<B1 (11.2±3.3)<A3 (13.1±2.4)<B3 (15.0±4.6)<A2 (16.7±5.5)<Cont1 (17.6±5.6)<B2 (19.2±5.9)<Cont2 (22.4±6.7). The TBS of groups Cont1, Cont2, A2 and B2 were significantly higher than those of groups A1 and B1. Moreover, there was no significant difference among groups A1, B1, A3 and B3 (Fisher’s PLSD test, p<0.05). The predominant mode of failure of groups B2 and Cont2 exhibited cohesive failure of adhesive or tooth substrate. There was a clear tendency that more cohesive failures occurred in the groups with higher TBS. From SEM observation of the chemical pretreated dentin surface, groups A2 and B2 produced a more homogeneous smooth inter-tubular dentin surface, however, micro-cracks were clearly detectable on the peritubular and inter-tubular dentin surface. Groups A3 and B3 showed roughening of the inter-tubular dentin surface.
Conclusion: Within the limitations of this study, it is concluded that p-toluenesulfinate and FeCl3/citric acid conditioning have the effect of promoting resin bonding to irradiated dentin.
