Despite an abundant published literature on the morphology and function of jaws in the realm of dentistry, their studies from an orthodontic point of view are yet relatively few, detailed research on the movement of jaw being particularly scanty in this field. Of the previous studies by the native investigators, changes in the jaw articulation between the maxillary and mandibular movements were reported by OTA (1936), radiological study on the jaw articulation of mandibular distal occlusal subjects by TSUIKI (1937) and, in their wake, KAMIYAMA (1959) and TOKURA (1961) respectively published their research results on the relationship between mandibular resting position and jaw movement in terms of Thompson's function analytical method. In recent years, ISHIDA et al. (1972) published an oblique cephalography of jaw articulation and FUJII et al. (1972) on its application to orthodontic treatment, thus paving the way for a clinical application on the basis of normal and oblique cephalograms (1973). In 1973, the present author, ANDO et al. studied the backward movement of jaw in quantitative terms and the author reported on analyses of the forward and backward movement of jaw by use of oblique cephalography (1974). In the present study, the author was concerned Mith several orthodontic considerations based on the previous findings with a particular reference to the forward movement of jaw.
For the purpose of determining an influence in the gnathofacial region by a distal movement of the maxillary second molars, the author compared 19 cases of the maxillary protrusion who had worn the Kloehn type cervical pullgear longer than 1 year and 3 months with 19 controls who were diagnosed as the maxillary protursion cases but did not receive an orthodontic treatment. As a result of analyses of the serial cephalograms taken of these two groups, the author arrived at the following conclusions : 1. Movement of the maxillary second molars by use of a maxillary headgear influences the overall maxillary region of human face. 2. With the experimental or treated cases, both the palatal and occlusal planes were observed to perform a clockwise rotation. On the other hand, SNA and point A became deviated downward. 3. In the upper portion of face, the growths of individuals were found to play a stronger part than an orthodontic force and, for this reason, a degree of change owing to an orthodontic force was less than in other facial portions. 4. Changes in the gnathofacial region were diverse in individual cases. However, within the scope of the present study in which the school-age subjects (111A and 111B) were selectively used, it was confirmed that as the general tendency an application of a maxillary headgear tended to inhibit the foreward growth of gnathofacial region with an attendant increased growth in the downward direction. Moreover, its effect extended to the sphenoid bone and its neighborhood. From this fact, its possible influence on the base of skull may be reasonally inferred.
The present study dealt with the curves of Spee, respective incisal cusp ridge distances and degrees of overbite before and after a dynamic treatment as well as after retention of a selected number of orthodontic patients. As a result, the following conclusions were arrived at : 1. On preoperative 1-6 o.p., the largest curves were observed with the maxillary right and left first premolars and with the mandibular right and left second premolars. On 1-7 o.p., the deepest curves were observed with the right and left second premolars, the pattern being similar to the maxilla and mandible. The deepest curve at the second premolars is in agreement with the reports of previous investigators. In some cases in whom the pronounced curves were formed, distal inclination of the maxillary first and second molars was noteworthy, being mesially positioned. Because of a pronounced mesial inclination of the mandibular together with premature loss of deciduous molars at the successional replacement period, enough space had not been provided for the second premolars which are much later in their eruption. For this reason, it is thought, the occlusal position tended to be lower. 2. On postoperative 1-6 o.p., a slight reverse mode resembling almost at raight line was observed with the maxilla, while a shallow curve was observed with the mandible. On 1-7 o.p., on the other hand, a smooth and shallow curve was observed with the maxillary right and left first molars (disto-buccal cusps) and the mandibular right and left first molars (mesio-buccal cusps). Since there was confirmed a tendency that the occlusal plane would become deeper after an orthodontic treatment, the treatment policy was adopted to render it either even or reverse at the finish. 3. On 1-6 o.p. after retention, a slight curve was observed similar to that of posttreatment cases with a somewhat noticeable trend, this fact being in common to the maxilla and mandible. On 1-7 o.p. after retention, the findings were similar to those of postoperative cases but, as compared with the maxilla, the curve became somewhat deeper in the mandible. It was not possible to establish definitely whether this deepening of curve in the mandible was due to relapse, natural result by reason of treatment or occlusal movement on the part of patients. 4. When the curve of Spee in normal occlusal subjects was compared with those of orthodontic patients both after dynamic treatment and retention, the latter were found to be either reverse or straight line. In the former, the curve was smooth and slight. Except for the lateral incisal region, the curve of Spee in the mandible was similar to that of normal occlusal subjects but with a tendency of being somewhat flat or even. Similarly, on 1-7 o.p., the findings of postoperative and after retention curves were nearly the same, and this is particularly true of the mandible. 5. The degrees of overbite were 59.2% preoperatively, 42.6% postoperatively and 41.4% after retention. As shown by these changes, a reducing tendency took place in proportion to an improved occlusion. 6. The following values were measured regarding intervals or distances of the incisal cusp ridges. Preoperative Postoperative After retention Maxilla 131.8 mm 113.2 mm 111.1 mm Mandible 115.4 mm 199.2% 98.8 mm It may be inferred that these changes were brought about by the extraction of first premolars and closure 'adjustment of the band space.