Protraction of maxilla in rhesus monkeys by controlled extraoral forces

Abstract

0 rthodontic treatment not only involves establishment of physiologically and anatomically functional occlusion but also envisages correction of the relationship of the maxilla and mandible to each other and to the rest of the craniofacial complex. To achieve a harmonious dentofacial relationship as a result of orthodontic treatment, extraoral devices using the neck or cranium as anchorage have been employed since the turn of the century. These extraoral appliances have been used to influence the maxillary and mandibular growth patterns by inhibiting and/or redirecting their normal growth potentials in children before and during maximal pubertal growth. Several clinical studies have shown that posteriorly directed extraoral forces applied to the maxillary first molars can inhibit or redirect the growth of the maxilla.22, 23 In retrospect, the use of extraoral forces in orthodontics was based on the premise that they inhibit the normal growth of the maxilla or mandible. Later it was noted that “heavy” extraoral forces, such as cervical or occipital headgear, will also move molars distally.2 However, as a result of clinical findings that extraoral forces “probably” remodel the midfacial bones and condyle, several animal studies have been performed to study the bony changes at the histologic level. Sproule2’ studied the effects of continuous extraoral cervical traction on the dentofacial complex of Mucaca mulutta monkeys. He reported that in the experimental group the maxilla rotated in a clockwise fashion as a result of its growth in a downward and backward direction as compared to downward and forward growth in control animals. Similar results have been reported by other investigators”, 24, 2g using the same or different species of monkeys. A histologic examination of experimental animals in these investigations revealed that the maxillofacial sutures respond significantly to extraoral forces as seen by resorption and appositional changes at these sites. The changes in the spatial