Heat generation during ultrasonic instrumentation of dentin as affected by different irrigation methods

Heat is produced by magnetostrictive ultrasonic scalers which may cause injury to pulpal and periodontal tissues. Water coolant flows around the instrument stack and is directed at the instrument tip to reduce the generation of heat. Sound surgical practice requires the use of a sterile coolant for ultrasonic scaling during surgery. Intermittent bulb irrigation is one way to deliver sterile coolant when using ultrasonic scalers not equipped with a dedicated sterile water reservoir. The purpose of this study was to compare the temperature rise in dentin during ultrasonic scaling using either ultrasonic handpiece irrigation or intermittent bulb irrigation. Twenty dentin/cementum root slabs were prepared for each thickness of 0.5, 1.5, and 2.5 mm. A 3.0 mm x 1.5 mm field was outlined on each slab to indicate the area of intended instrumentation. Each slab was mounted such that a thermocouple placed in contact with dentin opposite the area of instrumentation was shielded from irrigation. Twenty samples of each thickness were ultrasonically scaled during which dentin temperature was recorded every 5 seconds over a 30-second period. All 60 slabs were first treated with dental unit ultrasonic handpiece water irrigation, followed by no irrigation, and finally by bulb irrigation with sterile saline. Repeated measures analysis of variance indicated that there were differences among the three treatment groups for temperature change over the course of the study (P < 0.001). Dentin temperature increased with both decreasing slab thickness and with increasing duration of instrumentation. However, only scaling without irrigation produced a rise in dentin temperature from baseline to a level reported as deleterious to pulpal and periodontal tissues. Bulb syringe irrigation delivered as a continuous drip and ultrasonic unit water spray minimized heat generation to physiologically tolerable levels. Intermittent bulb irrigation appears to be a satisfactory alternative to use of ultrasonic scaler water spray for cooling during ultrasonic scaling at surgery.