Evaluation of Effectiveness of Carious Dentin Removal by Combination of Nd:YAG Laser and Prototype of Chemo-mechanical Caries Removal Reagent

Abstract

The chemo-mechanical method of removing caries is safer and less painful than conventional caries treatment with rotary instruments, but takes longer. Therefore, a prototype of a new caries removal reagent was developed to solve this disadvantage. This reagent (BO reagent) consists mainly of bromelain and orange oil, and removes caries approximately 2 minutes faster than Carisolv, but still takes longer to remove caries completely than the conventional method. To reduce the time further, we evaluated the effects of using this BO reagent with an Nd:YAG laser. Forty-five extracted human permanent teeth with caries were used in this study and were divided into nine groups with various laser irradiation conditions (60, 80, 100, and 120 mJ) with air-cooling or without air-cooling, and no laser irradiation. The time required for caries removal was measured for all specimens. To evaluate the temperature rise, thermal changes were also measured by thermometer during laser irradiation. After caries removal, each cavity was filled with composite resin and a micro-leakage test was performed. Then, all samples were transversely bisected with a diamond saw disc, and observed by stereomicroscopy. The mean time for the group with BO reagent without Nd:YAG laser irradiation was 388 seconds. For the groups irradiated by Nd:YAG laser, the times were 132 to 205 seconds on average and were statistically shorter than for the non-irradiated group. However, there was no statistical difference between the groups with and without air-cooling. The measured temperature rise was 2.1°C (80 mJ) to 4.4°C (120 mJ) for the groups without air-cooling, but was less than 2°C for all the groups with air-cooling. The rate of temperature rise and the time required for caries removal were similar for the 100 and 120 mJ-irradiated groups. In the micro-leakage test, there were no statistical differences among all groups. From these results, the BO reagent with Nd:YAG laser and air-cooling is a new candidate method for caries removal instead of conventional caries removal with rotary instruments. Especially, BO reagent with Nd:YAG laser irradiation of 100-120 mJ and air-cooling might be an effective and safe method of removing caries.