Impact of Photothermal Disinfection on Root Dentin Temperature

Objectives: Photothermal disinfection procedures are suggested for adjunctive endodontic treatment regimens. Therefore, the aim of the study was to assess the impact of photothermal disinfection on root dentin temperature and to evaluate the effect of a simulated periodontal blood flow on thermal characteristics.
Methods: A total of 30 freshly extracted human single-rooted teeth were endodontically prepared with a master apical file size 45/.02. Root surfaces were coated with thin wax layers and thereafter covered with a thermoforming sheet, leaving a circumferential space of 0.25mm mm after wax removal. The sheet was perforated on opposite sides in the apical third to allow fluid circulation through the simulated periodontal space. Irradiation of the root canals was performed in two groups (n=30 each): (I) 810nm laser (Q-810, A.R.C.) (1.5W, cw) for 4x5s, (II) indocyanine green (EmunDo, A.R.C.) and 810nm laser (A.R.C.) (200mW, cw) for 20s. Temperature measurements were performed with different water flow rates (6ml/min, 2.6ml/min and 0ml/min) at 37°C baseline temperature, using an thermographic infrared camera (VarioCAM HD, InfraTec). The primary outcome measure was the maximum temperature difference (delta t) after laser irradiation. Statistical analysis was performed with a non-parametric test (Wilcoxon).
Results: Highest temperature changes (median:7.52K, max: 18.32, min: 0.82) could be observed for the 810nm laser irradiation in group (I) without any simulated blood flow. Fluid circulation resulted in a statistically significant reduction of temperature changes in this group (median: 2.14K, max: 9.83, min: 0.37) (p<0.05). Lowest temperature changes could be observed for the photothermal group (II) with a water flow rate of 6ml/min (median: 0.79, max: 3.88, min: 0.00) (p<0.05).
Conclusions: Photothermal disinfection of root canals can cause a temperature increase of root canal dentin. However, periodontal fluid circulation has a cooling effect on the outer root surface, reducing the risk of a potential thermal injury of periodontal tissue.