A comparative microfluorescent study of the effects of acrylic-reinforced and acrylic-free rapid palatal expansion appliances on the alveolus and palatal shelves

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Seven rhesus monkeys were used, with matched pairs having the same or different appliances. There was one control animal. Previous to and at regular intervals throughout treatment the monkeys were given intravenous injections of oxytetracycline to label new cellular activity in the bone. Sections of the maxillae were taken and analyzed by means of microfluorescence for changes in the bone and soft tissue. Evidence indicates that the two appliances are equally effective in widening the maxillary palates. Differences included both a wider maintained palatal vault with the acrylic-free appliances, and more softand hard-tissue necrosis with the acrylic-reinforced appliances. Both appliances tipped the teeth to the same degree in the early stages of activation, and the teeth became equally uprighted with either appliance. The retention and maintenance of the increased arch width were the same with both appliances, as also were the rate and degree of relapse. Both appliances proved to be very effective in achieving increased arch width, although the acrylic-free (Hyrax) appliance permitted healthier soft tissue and a wider vault maintenance.