Effect of Intermediate Irrigation on Temperature Rise during Broken NiTi File Removal Using Ultrasonic Device

Endodontic preparation with ultrasonic instruments can lead to temperature rise (TR) on the external root surface (ERF), which may damage the periodontium. The aim was to measure the TR due to the ultrasonic preparation applied at different energy levels and durations during the removal of broken endodontic instrument from the root canal. Thirty-five maxillary central incisors were decoronated and 4 mm of NiTi instruments were fractured 5 mm from the most coronal part of the root. The roots were divided into seven groups according to the preparation mode (endodontic-E5, periodontal-P3) and preparation duration (30 s, 45 s, 60 s). Ultrasonic preparation was performed in periods consisting of four preparation phases with intermediate irrigations and drying. During all preparations, the TR was recorded on ERF using a K-type thermocouple. The results demonstrated that the TR measured at the end of the preparation period was higher than at baseline in all groups (p < 0.001). The largest TR (8.0 ± 0.5 °C) occurred at high energy level (P3) with 60 s preparation duration (p < 0.001). The TR measured after rinsing was significantly lower than before rinsing (p < 0.001). In conclusion, rinsing between ultrasonic preparation phases can reduce the TR, which might be potentially harmful using high-energy exceeding 60 s.