Potential hazardous temperature-riser at root-surface during ultrasonic-removal of fractured files

Objective: To investigate the temperature rise on the external root-surface during ultrasonic removal of separated files (SF) without coolant.

Methods: Fifty extracted lower incisors were decoronated leaving 10 mm of root length. 4 mm lengths of F2 ProTaper files were fractured in situ 2.5 mm from the coronal access. CPR ultrasonic tips were used to trephine a gutter of dentine around the SF with 5 groups for tip type and power–setting: CPR2, CPR5 and CPR6 at power–setting 1; CPR5 at power–settings 2.5 and 5. Temperature changes were recorded continuously at 3 different sites but were inspected at 30s intervals up to 120s. The three root-surface sites were as fillows: two at mesio-distal and bucco-lingual surfaces adjust to the most coronal aspect of the SF and the third adjust to the most apical aspect of the SF. Data were analyzed by one-way ANOVA and the Bonferroni post-hoc test at p ≤ 0.05.

Results: Power-setting 5 induced a significantly higher temperature rise (p ≤ 0.05) than power–settings 1 and 2.5. However, averaged over all groups and power-settings, the highest mean temperature rise was recorded at the bucco-lingual surface (11.2 ^°C), followed by that at the mesio-distal and the more apical site surfaces (7.1 and 2.7 ^°C respectively). At the lowest power-setting of 1, CPR6 produced a significantly lower (p ≤ 0.05) temperature rise (4.8 ^°C) compared with CPR5 (11.7 ^°C) at 120s.

Conclusion: When ultrasonic tips are used without coolant for removal of SF, the temperature rise on the external root-surface was found to be a function of time, location, ultrasonic tip type and activation power-setting. While CPR6 tips can be safely used for 120s, CPR5 tips can be used for 60s when activated at power-setting1. Power-setting 5 activation is not recommended for removal of separated files.