The effect on approximal drift of cheek teeth of dividing mandibular molars of adult monkeys (Macaca irus).
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The integration of interspecialty treatment before the restorative and prosthodontic efforts of the dentist can eliminate conditions that have the potential to jeopardize successful completion of the proposed treatment. Adult dentitions that have deteriorated because of neglect, fear, caries, extractions, or trauma can be restored to stability, health, function, and esthetics. In "Part I, The biomechanic aspects," the orthodontic paralleling of proposed abutment teeth displays premolar (buccolingual) and molar (mesiodistal) uprighting procedures that achieve improved force distribution to these teeth. Molar intrusion (occlusoapical) to improve an occlusal plane distribution of adverse forces to the proposed opposing fixed partial denture is discussed. These vexing problems facing successful reintegration of the altered states of occlusal relationships frequently can be answered by the incorporation of preprosthodontic corrections.
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Surgical exposure may be an integral part of orthodontic treatment of impacted teeth. In some cases the surgical procedure alone results in eruption and alignment of such teeth. The nature of the mechanism that starts concomitantly with the removal of covering tissues is not known. The aim of this investigation was to study factors associated with eruption as well as the eruption route of impacted and unerupted teeth following surgical exposure. The material consisted of 542 impacted teeth in 389 patients. The findings given strong support to the hypothesis that forces within surrounding tissues act upon the exposed crown in such a way as to direct it toward the area where the tissues were removed.
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This second article discusses how the inclusion of a vertical component (the infraocclusion of the deciduous molar) into the otherwise horizontal band of transseptal fibers affects the vertical development of the two adjacent teeth. From the hypothesis proposed in the first article of this series, it seemed logical to assume that the occlusal heights of the teeth adjacent to the affected tooth would themselves be lowered, when measured to the inferior border of the mandible and compared with the height of the occlusal table of the control side. Secondly, since the vertical component affects only one side of each adjacent tooth, these teeth would be tilted about a center of rotation which is much higher (coronal) than is seen in a tooth that merely tips forward as the result of available space in the immediate vicinity in the arch. In this study, both these assumptions were confirmed, with a very high degree of statistical significance.
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Transmigration of impacted mandibular cuspid is a rare finding. A cuspid is classified as "transmigrated" when more than half of its length has passed the mid-line. 13 cases of transmigration of impacted mandibular cuspids are presented, 3 of which occurred in pairs, raising the total number of teeth to 16. Radiographs showed positions ranging from a vertical impaction, to a cuspid having crossed the mid-line completely, reaching the first molar area of the opposite side.
Recently, the mechanism of action of prostaglandins in promoting bone resorption has received wide attention. Prostaglandins are used in orthodontics to shorten the period of tooth movement. PGE1 was administered locally (5 micrograms/kg every 12 hours) and systemically (7.5 ng/kg/min) to rats to study the difference in the efficacy of the two methods of administration in accelerating bone resorption. The Waldo method was used on 72 Wistar rats (8 weeks old) for 5 days to induce mesial movement of the first molar. The body weight of the rats was measured every 12 hours from the start of the experiment. Tissues were examined in the mesial surface of the mesial root and in the interradicular septum between the linguomesial root and the linguodistal root of the upper first molar. The pressure side of the mesial surface of the mesial root was studied, as well as the pressure side of the interradicular septum. The results showed that decrease in body weight during the experiment was more prominent in the local administration group than in the systemic administration group. In both the group receiving PGE1 through local administration and the group receiving PGE1 through systemic administration, the numbers of osteoclasts and Howship's lacunae were markedly increased over those in the control groups. Moreover, compared with local administration, systemic administration of PGE1 had a more marked effect on bone resorption.
Mesial drift and change in crowding over a 5-year period were compared in 30 subjects whose lower second molars were extracted between ages 11 and 17 years and 30 subjects whose lower second molars were not extracted. Significant differences were found. The nonextraction subjects showed an average forward movement of first molars and an increase in crowding. The extraction group showed slight distal movement of first molars and a decrease in crowding. It is concluded that lower second molar extraction reduces the tendency to forward movement of buccal segments and increased crowding by relieving eruptive pressure from third molars and that the presence of a developing lower third molar with insufficient space can be one cause of late lower arch crowding.
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