Temperature changes during ultrasonic irrigation with different inserts and modes of activation.

This study evaluated temperature changes during passive ultrasonic irrigation. Root canals of three extracted maxillary canines were enlarged to size #45. Thermocouples were mounted 3, 6, and 9 mm from the apical foramen. Teeth were placed in a water bath at 37 degrees C. Distilled water (20 degrees C) was continuously delivered through an ultrasonic unit (group 1) or deposited into the root canal before ultrasonic activation (group 2); for activation, noncutting nickel-titanium (NiTi) inserts or stainless steel K-files #15, #25, and #35 were used. Before and during ultrasonic activation, temperatures were continuously measured for 210 seconds. Statistical analysis was performed using analysis of variance and Scheffé post hoc tests. Temperatures initially decreased by up to 7.4 degrees C; these drops were significantly smaller in group 1 than in group 2 (p < 0.001) in the middle and apical root canal third. The decreases were followed by temperature rises for all inserts in group 2. However, in group 1, temperatures just reached baseline values in middle and apical thirds; in the coronal root canal third, lower temperatures were measured. In group 2, mean temperature rises were 7.7 degrees , 7.5 degrees , and 4.2 degrees C in coronal, middle, and apical root canal thirds. Here, K-file type inserts size #35 generated highest and inserts size #15 the lowest temperatures rises; NiTi inserts were more effective than size #15 K-files and less effective than #35 K-files. Continuous flow negated the potential of ultrasonic activation to heat irrigation solutions. Noncutting NiTi instruments and large K-files were more effective than small K-files in warming deposited irrigants.