Micro-computed Tomographic (Micro-CT) Analysis of the Effect of Low Intensity Pulsed Ultrasound on Orthodontically Induced Inflammatory Tooth Root Resorption Caused by Torque Type of Orthodontic Movement in Human Patients

Objectives: Previous studies reported that low intensity pulsed ultrasound (LPUS) can minimize orthodontically induced root resorption (OIRR) after simple tipping movement in human and in animals. The aim of this study was to evaluate the effect of LPUS on root resorption after buccal root torque in human premolars.
Methods: Twenty premolars were buccally torqued using 0.019 x 0.025 TMA wire producing a torque at the bracket level of 4.439 N-mm. Torque value was calibrated by torque machine at University of Alberta. LIPUS was applied for twenty minutes per day for four weeks at an intensity of 30mW/cm². After 4 weeks, all premolars were extracted for regular orthodontic treatment and a micro-CT analysis was performed. Following parameters were measured; location and number of resorption lacunae, height of lacunae, depth of the lacunae and part of the root mostly effected by the orthodontic force. Comparison between the two groups was performed using student t-test.
Results: LIPUS treated teeth showed decreased number of resorption lacunae (4.6 +/- 2.9) compared to control non LIPUS treated teeth (7.8+/-4.1) (P<0.05). Maximum number of resorption lacunae where found on the apical third of the root in both the upper and lower premolars (17.2+/-5.04) followed by middle third (7.9+/-5.91) and coronal third (4.66+/-2.41).
Conclusions: Based on the preliminary data analysis, there was only decreased number of root resorption lacunae in the LIPUS treated teeth however there was no significant decrease of resorption depth or height. The apical third of the root was found to be most affected by the orthodontic force. Detailed micro CT analysis on larger sample size is needed to evaluate the effect of LIPUS on root resorption caused by torque.