歯の垂直的位置の安定に関与する因子の研究 : 特に上下の歯の接触時間, 接触回数および咬合力について

Abstract

In spite of the fact that man has free-way space and that this state is thought to exist for a considerable time per day, the teeth in eruption will cease erupting at a certain position and be stabilized when they reach the occlusal plane. Upon conducting a preliminary experiment to eliminate the contact relation with the antagonistic teeth, which is seemd to be one of the causes, it was found that the teeth that had been in stability clinically extruded 0.247mm in six months. Judging from these facts, the most important factor that stops extrusion is determined to be the contacts between the upper and lower teeth. The author, therefore, chose as the subjects of the experiment adult males who had metal crowns on the upper and lower first molars and took continuous measurements by telemetering for 24 consecutive hours of the contact time and frequency of the upper and lower teeth contacts, which are considered to be the most important among other factors of the dental contact, and, at the same time, of deglutition which is deemed to be a major cause of the tooth contact. In addition, occlusal force which is also considered to be another important factor and the vertical displacement at the time of occlusion were measured and their correlation was examined comprehensibly. The results obtained were as follows : 1. The average time of the daily tooth contact was 1 hour 7 minutes 17 seconds. The range was from a minimum of 16 minutes 31 seconds to a maximum of 3 hours 13 minutes 18 seconds. 2. The average frequency of the daily tooth contact was 4, 269 times. The range was from a minimum of 2, 309 times to a maximum of 7, 797 times. The incidents of contacts for less than one second accounted for about 84% of the total number of contacts, whereas the incidents of contacts for more than three seconds accounted for only 4.5%. About 28% of the contacts, excluding those at the time of mastication, was related to deglutition. 3. The average number of deglutition was 980. The range was from a minimum of 625 to a maximum of 1, 472. The first molars that came into contact at the centric relation did not necessarily come into contact at the time of deglutition. 4. The occlusal force at the time of deglutition averaged 1, 403 g. The occlusal force at the time of mastication averaged 3 to 8 kg. 5. If a force of about 1 kg, as at the time of deglutition, is applied, it required about 10 seconds for the teeth to restore themselves to the former positions after the removal of the load. On the other hand, when the subjects were left free, the incidents of contacts with intervals of less than 5 seconds, the time of which is considered not sufficient for the teeth to restore themselves completely, averaged 1, 436 times. At the same time, when the contacts were prolonged, the time required for the teeth to restore themselves to the former positions was longer even with an application of the same force of 1 kg. When the subjects were asleep, continuous state of non-contact during which the teeth would restore fully were frequent. Thus, the upper and lower teeth come into contact daily for about one hour in time and about 4, 000 times in frequency, with an appropriate interval between contacts. The foregoings are the most important factors that stops eruption and restrains further eruption and extrusion and also stabilizes occlusion.