Effect of Increasing Low-Intensity Pulsed Ultrasound and a Functional Appliance on the Mandibular Condyle in Growing Rats.

Objectives: Functional appliances are used for treatment of lower-jaw deficiencies in growing individuals; however, their effectiveness is debatable. Low-intensity pulsed ultrasound (US) is a noninvasive method, which has been shown to stimulate cartilage and bone formation with 20 minutes of application. This study was designed to test the hypothesis that increasing low-intensity pulsed US application from 20 to 40 min/d will enhance mandibular condylar growth in growing rats, especially when combined with a functional appliance.

Methods: Fifty-four Sprague Dawley rats were divided into 6 groups (n = 9): control, low-intensity pulsed US for 20 minutes, low-intensity pulsed US for 40 minutes, the functional appliance, the functional appliance plus low-intensity pulsed US for 20 minutes, and the functional appliance plus low-intensity pulsed US for 40 minutes. Low-intensity pulsed US was applied for 28 days. All rats were then euthanized, and their mandibles were dissected for morphometric, histomorphometric, and micro-computed tomographic analyses.

Results: Among all study groups, the 20-minute US group showed significant increases in most of the measured variables (P < .05) except for condylar process length (P = .18), whereas the functional appliance-plus-40-min US group showed the least favorable results. The 20-minute US group showed increases in proliferative and hypertrophic cell counts and widths and enhanced microarchitecture of trabecular bone compared with the 40-minute US group. The functional appliance-plus-20-minute US group showed better results compared with the functional appliance-alone and functional appliance-plus-40-minute US groups.

Conclusions: A daily application of low-intensity pulsed US for 20 minutes in growing rats affects mandibular growth, either alone or in combination with a functional appliance. Further study with a longer observation period is required to study the long-term effects and stability of newly formed bone.