Effect of Ultrasound on Severe Orthodontically induced Root Resorption

Objectives: To investigate the effect of Low Intensity Pulsed Ultrasound (LIPUS) on the repair of severe root resorption during orthodontic tooth movement.

Methods: Heavy orthodontic force (200gm) been exerted on lower premolars of two adult female beagle dogs by fixed orthodontic appliances, The  appliance consists of cast orthodontic tubes on metal crowns cemented on the 3^rd and 4^th lower premolars to move the 3^rd premolar into the space of extracted 2^nd premolar by push coil spring.

The control side and test side in the split mouth model were randomly selected. The test side received LIPUS daily for 20 minutes for four weeks. Each pulse has a square envelop with duration of 200 microseconds and a carrier frequency of 1.5 MHz. The ultrasound transducer has an area of 1.32 cm2 and it generates an intensity of 30 mW/cm². Movements were measured using a digital caliper that can read up to 0.01mm.

Dissected mandible samples were scanned using high resolution SkyScan 1076 Micro-CT imager with vendor-supplied software (V2.6.0), and raw image data was reconstructed using NRecon software (V1.4.4). Reconstructed images were analyzed using CT Analyzer software (V1.6.1.0), and used to assess resorption lacunae characteristics – quantity, depth, volume, location and corono-apical extension along the root surface.

Results: The Wilcoxon signed rank test shows a statistically significant decrease in the volume of the resorption lacunae in the LIPUS sides in comparison to the control sides (P<0.05 ) and there was no significant difference in the depth of the resorption lacunae between the two groups (P>0.05).

Conclusions: Daily application of LIPUS for 20 minutes to premolars in dogs during orthodontic tooth movement decreases the volume of root resorption.