下顎第一大臼歯または第二大臼歯抜歯後の下顎第三大臼歯萌出について

[On eruption of mandibular third molar after extraction of mandibular first or second molar].

抄録

矯正歯科診療において、治療計画に基づく必要性から第一大臼歯や第二大臼歯を抜歯することがある。このような場合、第三大臼歯が咀嚼機能に関与していることが望ましい。本研究は、第一大臼歯または第二大臼歯抜歯後の萌出第三大臼歯の自然な動きを、連続側面セファロX線写真およびオルソパントモグラフで検討するために行われた。被験者は3群に分けられた。第1群は下顎第2大臼歯を抜歯した群である。第二は、第一大臼歯を抜歯して第三大臼歯の萌出に成功したグループである。3番目は、第一大臼歯を抜歯した結果、第三大臼歯の萌出に失敗したグループである。すべての症例において、第3大臼歯に矯正力は加えなかった。結果は以下の通りである：1.第1群では、すべての第3大臼歯の萌出に成功し、第2大臼歯抜歯後のスペースの多くが第3大臼歯の萌出に利用された。2.第2群では、すべての第3大臼歯の萌出に成功し、第1大臼歯の抜歯後のスペースの多くが第2大臼歯の近心移動に利用された。3.3.第3群では、第3大臼歯のimpactionのパターンが様々であった。第3大臼歯の萌出には第2大臼歯遠位のスペースが関係しているが、下顎骨体の前後長とはあまり関係がないことが示唆された。

In the orthodontic practice, the first or second molars are extracted by reason of a necessity based on the treatment planning. In these cases, it is desirable that the third molar would be taken part in the masticatory function. This study was made to investigate the natural movement of the erupting third molars after the extraction of the first or second molar on the serial lateral cephalometric radiographs and orthopantomographs. Subjects were divided into three groups. The first is the group which the mandibular second molars were extracted. The second is the group which the first molars were extracted bringing about the successful eruption of the third molars. The third is the group which the first molars were extracted with resultant in the failure of the third molar eruption. In all cases, the orthodontic forces were not applied to the third molars. The results were as follows: 1. In the first group, all third molars were successfully erupted and a lot of the spaces after the extraction of second molars were utilized for the eruption of third molars. 2. In the second group, all third molars were successfully erupted and a lot of the spaces after the extraction of first molars were utilized for the mesial movement of the second molars. 3. In the third group, there were various patterns of the impaction of the third molars. It was suggested that the eruption of the third molar was related to the space distal to the second molar but it was not related to the anterio-posterior length of the mandibular body significantly.