Piezocision can set in motion a cascade of physiologic events that lead to accelerated orthodontics, but do all ultrasonic frequencies generate the same effects on bone? Two different Piezotome modulation frequencies (10 and 30 Hz) were tested on the rat maxilla. The animals were sacrificed at days 1, 3, 7, 14, 28, and 70, and MRI, histologic, and biochemical analyses were performed. The results indicated that at 30 Hz, the demineralization process started at day 1 and peaked at day 7, and was initiated by osteocyte apoptosis. The process was different in the two groups, with bone demineralization increasing significantly in the 30-Hz group compared to the 10-Hz group (P .05). These results could indicate that bone biomodification is frequency-dependent.