Analysis of Temperature Rise and the Use of Coolants in the Dissipation of Ultrasonic Heat Buildup During Post Removal
Introduction: This study was designed to calculate probabilities for tissue injury and to measure effectiveness of various coolant strategies in countering heat buildup produced by dry ultrasonic vibration during post removal. Methods: A simulated biological model was used to evaluate the cooling efficacy of a common refrigerant spray, water spray, and air spray in the recovery of post temperatures deep within the root canal space. The data set consisted of cervical and apical measures of temperature increase at 1-second intervals from baseline during continuous ultrasonic instrumentation until a 10^oC increase in temperature at the cervical site was registered, wherein instrumentation ceased, and the teeth were allowed to cool under ambient conditions or with the assistance of 4 coolant methods. Results: Data were analyzed with analysis of variance by using the independent variables of time of ultrasonic application (10, 15, 20 seconds) and cooling method. In addition to the customary means, standard deviations, and analysis of variance tests, analyses were conducted to determine probabilities that procedures would reach or exceed the 10^oC threshold. Both instrumentation time and cooling agent effects were significant at P <.0001. Conclusions: Under the conditions of this study, it was shown that injurious heat transfer occurs in less than 1 minute during dry ultrasonic instrumentation of metallic posts. Cycles of short instrumentation times with active coolants were effective in reducing the probability of tissue damage when teeth were instrumented dry. With as little as 20 seconds of continuous dry ultrasonic instrumentation, the consequences of thermal buildup to an individual tooth might contribute to an injurious clinical outcome.
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