Effect of simulated pulpal fluid circulation on intrapulpal temperature values

Objective: It is suggested that pulpal fluid circulation has an impact on pulp temperature increase during heat generating dental treatment procedures. Thus, the aim of the study was to assess the effect of a simulated pulpal fluid circulation on temperature changes inside the pulp chamber following laser irradiation of the tooth surface.

Method: 20 freshly extracted human multirooted teeth were included and cross-sectioned along the long axis exposing two root canals each. The pulp chamber and root canals were cleaned from remaining soft tissues to achieve access for a temperature sensor and two cannulas to allow fluid circulation. Cross-sections were glued together and the roots encased with silicone impression material to ensure the position of the connected devices. Each tooth was irradiated employing an Nd:YVO₄ laser at 1064 nm with a pulse duration of 9 ps and a repetition rate of 500 kHz. A commercially available scanning system (ScanCube 7, Scanlab) deflected the beam providing rectangular irradiated areas of 0.5 mm edge length. Measurements were performed with 4 different settings for fluid circulation: without any water, water (23°C) with a flow rate of 6 ml/min, 3 ml/min and 0 ml/min. The primary outcome measure was the maximum temperature difference (ΔT) after laser irradiation.

Result: Highest temperature changes (median: 3.6 K, range: 0.5-7.1 K) could be observed without any fluid inside the pulp chamber. Water without circulation decreased ΔT values statistically significantly (median: 1.4 K, range: 0.2-4.9 K) (p<0.05). Lowest temperature changes could be observed with a water flow rate of 6 ml/min (median: 0.8 K, range: 0.2-3.7 K) (p<0.05).

Conclusion: Pulpal fluid circulation has a cooling effect on temperature increase caused by laser irradiation of dental hard tissues. Studies on heat generation during dental treatment procedures should include this aspect to assess a potential thermal injury of pulp tissue.