THE JOURNAL OF HOKKAIDO ORTHODONTIC SOCIETY

The purpose of this investigation was to evaluate the correlation between the existence of third molar germs and sagittal maxillo-mandibular jaw relationships and dimensions. The selected subjects were 365 patients of the Orthodontic Clinic of Hokkaido University Dental Hospital who were less than 15 years old at the first examination. Panoramic radiographs and lateral cephalograms were used as materials. The subjects were divided into skeletal Class (sk Cl) I, II, III groups and also divided into the ANS-PNS(+) and (-)groups or into the GP/SN(+) and (-)groups according to the dimensions of each jaw. The following results were obtained : 1. The prevalences of maxillary third molars in the sk Cl I and n groups were higher than that in the sk Cl III group. There were no significant difference between the prevalences of mandibular third molars in the sk Cl I, II and III groups. 2. The prevalence of maxillary third molars in the ANS-PNS(+) group was higher than that in the ANS-PNS(-) group. There was no significant difference between the prevalences of mandibular third molars in the GP/SN(+) and GP/SN(-)groups. 3. There were significantly larger numbers of sk Cl n patients in the ANS-PNSC+) and GP/SN(-) groups than in other groups. These results suggest that the prevalence of third molars is not related to antero-posterior dimensions of the mandible but to those of the maxilla.

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The purpose of this study was to investigate the relationship between sound in the temporomandibular joint (TMJ) and morphological aspects in adolescent orthodontic patients with anterior open bite. The selected subjects were 40 patients of the Orthodontic Clinic of Hokkaido University Dental Hospital who had anterior open bite and were less than 15 years old at the first examination. ClassIII patients were excluded from the study. The subjects were divided into two groups : one group of 17 patients who exhibited sound in TMJ before and/or during orthodontic treatment (symptomatic group) and one group of 23 patients who did not exhibit temporomandibular disorders (asymptomatic group) . Lateral cephalograms were used as materials. The following results were obtained : 1. The symptomatic group included 42.5% of the subjects. 2. In skeletal pattern, patients in the symptomatic group had a significantly more-posteriorly inclined ramus and narrower gonial angle than did patients in the asymptomatic group. Patients in the symptomatic group tended to exhibit more skeletal Class n jaw relationships and a shorter ramus than did patients in the asymptomatic group. 3. In denture pattern, there were no differences between anterior tooth inclinations in the two groups. These results suggested that many adolescent orthodontic patients with anterior open bite have sound in the TMJ as well as a posteriorly inclined and short ramus.

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It seems that a person recognizes the face of another person by subconsciously determining a subjective facial midline unconsciously. We have defined such a subjectively defermined facial midline as an imaginary facial midline. It appears to be important to understand the ability of human visuognosis of space in order to elucidate the setting mechanism of an imaginary facial midline. In this study, we tried to clarify the ability of visuognosis that is thought to be the setting of an imaginary facial midline, by investigating 34 orthodontists with 3 years or more experience. The results were as follows. 1. The abillities of visuognosis of the orthodontists with the experience over 3 years were eguivalent. 2. Only in the case of ΔX, both the displacement and the variance changed in proportion to the distance between 2 points. 3. The recognition of middle points was significantly accurate if the distance between the 2 points was less than 60 mm. The results of this study are thought to be applicable to human faces.

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Coincidence in dental and facial midlines is one of the goals of orthodontic treatment. The setting of a facial midline is important to achieve this treatment goal. However, there is no objective method for obtaining a facial midline, and the difference between the cognizance of orthodontists and laypersons is also uncertain. It is therefore important to specify a comparatively accurate facial midline. We defined a subjectively defermined facial midline as an imaginary facial midline, and we tried to elucidate the mechanism of the setting. We tried to limit the areas or structures of a face that we thought to be involved in the setting of an imaginary facial midline. The subjects of this study, 34 orthodontists with 3 years or more experience, were instracted to draw their own imaginary facial midlines in facial photostats of two adult Japanese with facial symmetry. As a result, we found the standard way by which orthodontists set an imaginary facial midline. The standard method is to set the imaginary facial midline so that it is as perpendicular as possible to a relatively horizontal line with attention given to both or either the middle point of the alares and/or the bottom point of the cupid bow as signposts.

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