An Invitro Study on The Temperature Changes of Dentin, Irradiated by CO 2 and Er: Cr;YSGG Laser

Abstract

Introuduction: The aim of this in-vitro study was the evaluation of temperature changes due to irradiation of two different lasers used for the reduction of dentinal hypersensitivity and their effect on the pulp damage. The study was done for two dentin thicknesses. Material & Methods: Twenty intact extracted third molars were prepared by longitudinal ground sectioning for 1 and 2 mm dentin thicknesses while a thermocouple was positioned at the inner surface of the dentin disk. Thermal evaluation was assessed by a KJT digital thermometer. During the test, the data produced by the thermometer was transferred and logged into a PC via RS232 serial port. CO 2 laser (Ultra pulse, 50W, 100μsec, Spot size: 0.5 mm) and Er,Cr;YSGG laser (Free-running pulse mode,0. 25W, 140μsec, 12.50 milli-joules) irradiations were randomly performed upon the dentin surfaces. The collected data was analyzed by two-way ANOVA test. Results: The mean temperature rise in 1mm dentinal thickness was 8.57°C which was significantly higher than 3.63°C in 2mm dentin thickness (P<0.001) and higher than the threshold temperature for pulp damage; however, no significant difference was noted between the two lasers (P=0.355). After removing the CO 2 laser, the temperature decreased to the initial level faster than the time needed for Er,Cr;YSGG laser (44.47°C versus 62.82°C)(P<0.001). In other words, in both lasers the temperature decrease in 2mm dentinal disc was faster than 1mm dentinal disc. Conclusion: The temperature rise due to both lasers for 1mm of dentinal thickness was in excess of safe limit for the tissue and it would probably result in pulpal damage. In the case of 2mm dentinal thickness, the temperature rise was not higher than the safe limit and it would not damage the pulp in clinical conditions.