Comparison of alveolar bone changes in maxillary anterior area secondary to different kinds of retraction method of anterior teeth: a cone-beam computed tomography study / 上海交通大学学报（医学版）

Objective • Using cone-beam computed tomography (CBCT) to compare alveolar bone changes in maxillary anterior area secondary to maxillary incisor retraction adjunct with tip (R&Tp) and retraction adjunct with torque (R&Tq) movements. Methods • Forty teenagers with Angle's class Ⅱ division 1 malocclusion who had completed orthodontic treatment met the inclusion criteria and were selected, and all of their 160 maxillary incisors were classified into two categories, namely R&Tp group and R&Tq group, according to their actual retraction pattern. Pre- and post-treatment CBCT images and 3D measurement software were used to measure and analyze tooth retraction and alveolar bone height and thickness changes within each group and to compare treatment changes of teeth and alveolar bone between two groups. Results • Anterior teeth in each group were intensively retracted and uprighted, with a longer retraction distance of incisal edge and a greater retraction angle of teeth in R&Tp group than in R&Tq group (both P=0.000). Alveolar bone thickness was significantly decreased at L3 and P1 in R&Tp group (both P<0.05), while it was significantly decreased at P1 and P2 in R&Tq group (both P<0.05). Total alveolar bone thickness decreased at T1 in R&Tp group (P=0.000) and at all levels in R&Tq group (all P=0.000). Finally, alveolar ridge height in two groups dropped both in the buccal (both P=0.000) and palatal (both P=0.000) sides, with a more prominent extent in the palatal side, and ridge height dropped most in palatal side of the teeth in R&Tq group. Conclusion • The buccal root apex area and the palatal alveolar ridge area of alveolar bone in the R&Tp group and the cervical and middle area of incisor root in palatal side of alveolar bone in the R&Tq group are high-risk areas for alveolar bone resorption when anterior teeth in teenagers with Angle's class Ⅱ division 1 malocclusion are intended to have en masse retraction.

The vertical location of the center of resistance for maxillary six anterior teeth during retraction using three dimensional finite element analysis / 대한치과교정학회지

The delivery of optimal orthodontic treatment is greatly influenced by clinician's ability to predict and control tooth movement by applying well-known force system to dentition. It is very important to determine the location of the centers of resistance of a tooth or teeth in order to have better understanding the nature of displacement characteristics under various force levels. In this study, three dimensional finite element analysis was used to measure the initial displacement of the consolidated teeth under loading. The purpose of this study was to define the location of the centers of resistance at the upper six anterior segment. To observe the changes of six anterior segment, 200gm, 250gm, 300gm, and 350gm forces at right and left hand side each were imposed toward lingual direction. For this study, two cases, six anterior teeth and six anterior teeth after corticotomy, were reviewed. In addition, it was reviewed the effects of changes on the location of the center of resistance in both cases based on different degree of forces aforementioned. The results were that : 1. The instantaneous center of resistance for the six anterior teeth was vertically located between level 4 and level 5, which is, at 6.76mm, 44.32 % apical to the cementoenamel junction level. 2. The instantaneous center of resistance for the six anterior teeth after corticotomy was located vertically between level 4 and level 5, that is, at 7.09mm, 46.38 % apical to the cementoenamel junction level. 3. Changes of force showed little effect on the location of the center of resistance in each case. 4. It was observed that the location of the instantaneous center of resistance for the six anterior teeth after corticotomy was changed more than the six anterior teeth without corticotomy to the apical part, and the displacement of the consolidated anterior teeth moved further in case of the consolidated teeth after corticotomy.

Changes in soft tissue chin resulting from premolar extraction and incisor retraction in adult female patients / 대한치과교정학회지

The purpose of this study was to evaluate changes in soft tissue chin thickness and to investigate correlations between hard and soft tissues measurements after orthodontic treatment conducted by premolars extraction and incisor retraction. The sample consisted of 35 female adults with Angle classification class I or class II division 1 malocclusion. Using lateral cephalometric radiographs taken before and after treatment, hard and soft tissue structures were measured and reproducible six landmark on soft chin tissue were used to locate the various points of soft tissue contour of the chin. The results were as follows : 1. There were signigicant correlations between pretreatment B-B', Pm-Pm' and pretreatment vertical skeletal measurements such as angle of MP & HP, angle of MP & PP, ALFH and between a-a', b-b', Me-Me' and measurements of symphyseal morphology such as SL, SW, PL. 2. There were significant decreases at B-B', Pm-Pm' and significant increases at a-a', b-b' between pre-and posttreatment measurements. 3. There were significant correlations among soft tissues changes and hard tissue changes except for changes at B-B' and the range of correlation coefficient was about 0.3-0.4. 4. There were significant differences at deltaUI-VP, angle of LI &