Repair of orthodontically induced root resorption by ultrasound in humans

Root resorption is an adverse outcome of orthodontic tooth movement. In addition to the iatrogenic response and compromising the crown-root ratio, root resorption has led to increased malpractice litigation against orthodontists. A clinically acceptable method of treating root resorption has not been validated in the literature to date. Previous research has shown that low-intensity pulsed ultrasound (LIPUS) can enhance healing of various types of traumatized connective tissues and stimulate dental tissue formation. The purpose of this study was to evaluate the effect of LIPUS on the healing process of orthodontically induced tooth-root resorption in humans. Twelve orthodontic patients who were seeking orthodontic treatment that necessitated extracting the first premolars before mechanotherapy participated in this study. For each patient, buccally activated springs were used to tip the maxillary first premolars buccally, with an initial force level of 50 g; the springs were checked weekly to ensure continuous force levels. A short period of LIPUS was applied to 1 side of each patient's mouth, with the other side used as a control. After 4 weeks, the experimental premolars of all patients were extracted, and the premolars of 6 patients were studied by scanning electron microscopy (SEM); the premolars of the other 6 patients were studied histologically. The number and total area of resorption lacunae as examined by SEM were compared between the LIPUS-treated and the control premolars with a t test. The SEM study showed a statistically significant decrease in the areas of resorption and the number of resorption lacunae in the LIPUS-exposed premolars. Histologic examination showed healing of the resorbed root surface by hypercementosis. The results of this study provide a noninvasive method for reducing root resorption in humans.