상악 제1소구치 발치공간 폐쇄 시 치아이동 양상과 저작압에 관한 유한 요소 해석

Abstract

The purpose of this study was to investigate the closing patterns of the maxillary first premolar extraction space, the stress distribution of bite force and the displacement of teeth according to bite frequency for the sliding and the loop mechanics using a 3-dimensional finite element analysis model on the cranium, maxillary complex, maxillary teeth and alveolar bone. In this study, the 3-D finite element analysis was used to illustrate the pattern of tooth movement and the stress distribution of bite force and to measure the displacement of teeth according to bite frequency. In order to compare the loop mechanics and the sliding mechanics, 250 g retraction force from canine to the second molar on the 016x022 SS wire was applied in the sliding mechanics and the extraction space was closed through repeated reactivating the loop with each 1 mm activation in the loop mechanics. In the sliding mechanics, a 15° gable bend was given between canine and the second premolar and in the loop mechanics, a 15° gable bend was given behind bull loop. The results of this study were as follows : 1. In the sagittal plane, no differences were found between the sliding mechanics and loop mechanics. 2. In the occlusal plane, the second molar showed mesial-in rotation. In the case of the second molar, there was no difference between the two mechanics. The second premolar and the first molar also were found to show mesial-in rotation in both the mechanics. However, the amounts of the rotation of the posterior teeth were found to be greater in the sliding mechanics than that in the loop mechanics. 3. In buccopalatal movement of the crown, it was found that the second premolar and the first molar moved more toward the palatal side in the sliding mechanics than the loop mechanics, indicating that the intermolar distance is less in the sliding mechanics than the loop mechanics. 4. In both the mechanics, the stress distribution of bite force was found not only in the periodontal ligament and alveolar bone but also in Zygomatic arc and Inferior border of infraorbital fossa and around Masteoid process. 5. The order of the displacement was observed to be the second premolar, the second molar and the first molar steps in both the mechanics by comparing the patterns of tooth movement according to the vibration. The amounts of the displacement of teeth in the loop mechanics were found to be less than sliding mechanics, and also the response of the displacement of teeth in the loop mechanics were found to be less bite frequency than sliding mechanics. 6. The order of the displacement of teeth was found to be the second premolar, the second molar and the first molar steps in 016×022 SS and 017×025 SS. The order of the displacement of teeth according to the bite frequency was not dependent upon the thickness of a wire. The displacement of the teeth in 016×022 SS was found to occur at lower bite frequency than that in 017×025 SS but the amount of the displacement in 016×022 SS was found to be more than 017×025 SS. The percentage of the effect of the bite force on the closing pattern were found to be 0.2 % - 0.3 % of the total amount of tooth movement during orthodontic treatment. Although a little differences between the sliding and loop mechanics were found, those are less important in term of clinics.;본 연구에서는 교정의 목적과 생체의 조건에 보다 근사한 해석을 하고자 치조골을 비선형 소성재(non-linear plasticity)로 가정하여 두개골이 포함된 상악치열궁의 3차원 유한요소 모델을 제작하였다. 상악 제1소구치 발치공간 폐쇄를 위해 활주역학과 루프역학을 설계하여 단계별 치아이동 양상을 3차원적으로 비교, 분석하고 치아이동 시 나타나는 응력분포 양상을 유한요소해석으로 구명하였다. 또한, 저작이 교정에 미치는 영향을 분석하기 위하여 선행 연구에서 보고된 수치를 참고하여 각각의 역학에서 활성화 단계에 저작압을 분당 저작횟수의 형태로 가하여 치아 변위량을 알아보았다. 제1소구치를 발치한 상악 유한요소 모델에서 활주역학은 0.016“x0.022"SS 호선상에서 측절치와 견치 사이에 후크(hook)를 위치시키고 호선상의 견인 후크로 부터 제2대구치 튜브의 후크 방향으로 후방 250g의 견인력을 부과하였고, 루프역학은 0.016“x0.022”SS 호선에 bull 루프를 제작하고 루프 후방에 15°의 gable bend를 부여한 후 한번에 1mm 씩 활성화 시키며 총 300회의 반복해석을 통해 폐쇄 과정의 치아 이동을 관찰하였다. 또한, 치아 주위 구조물에 나타나는 응력분포 양상을 유한요소법으로 해석하였고 두 역학의 활성화 단계에서 최대 평균 저작압 80kg을 제2소구치, 제1대구치, 제2대구치에 3:5:2 의 비율로 가하여 분당 저작회수에 따른 치아 이동량을 관찰하였다. 이상의 연구 결과, 제2소구치와 제1대구치의 근심 회전량과 구치간 폭경의 감소량은 루프역학 보다 활주역학에서 더 크게 나타났다. 치아이동 시 치아 장축을 따라 나타나는 응력분포는 두개골의 안와 하방까지 나타났으며, 두 역학에서 뚜렷한 차이는 보이지 않았다. 분당 저작회수와 치아 변위량은 호선의 길이와 두께에 따른 차이를 보였다. 활주역학 보다 호선의 길이가 더 긴 루프역학과 0.017“x0.025”SS 호선보다 얇은 0.016“x0.022”SS 호선에서 더 적은 저작횟수에 대해 치아 변위에 대한 반응이 먼저 나타났다. 그러나 유한요소해석에서 저작압이 치아 이동양에 미치는 영향은 치아 이동양의 0.2～0.3%제 임상에서는 의미있는 영향을 미치지 않는 것으로 나타났다.