Evaluation of The Maxillary Basal Bone and Molar Change of Skeletal Class II Malocclusion Treated by Saggital-Guidance Twin-Block

Objective: To investigate the effects of Saggital-guidance Twin-block appliance(SGTB) on maxillary basal bone and molar with skeletal class II malocclusion. Methods: The cephalometric datas, including thirty-four skeletal Class II patients with SGTB and non-extraction treatment, was quantitatively analyzed with Pancherz. Results: After orthopedic treatment, the maxillarretruded(0.68mm,P ＜ 0.01), the upper molar teeth were changed posteriorly(1.33mm,P ＜ 0.01).After orthodontic treatment, the maxillary bone still turned out posterior position (0.65mm, P ＜ 0.05),and the molar teeth slightly retruded(0.53,P ＞ 0.05). Conclusions: The correction of skeletal Class II malocclusion would be achieved by semi-fixed Twin-block. Saggital-Guidance Twin-Block. Biomed Sci & Tech

maxillary dental arch stenosis to expand the width of the upper jaw facilitates the advancement of the lower jaw. The lower jaw is a movable occlusal pad that extends forward from the tip of the second premolar (or second milk molar) of the lower jaw to the second premolar (or second milk molar) on the other side.
The cusp of the tooth and the occlusal cushion of the second premolar (or the second milk molar) and the maxillary70°~ 45 ° staggered relation to the inclined surface, while the cutting head is provided between the card and the adjacent hook retention increases.Saggital-guidance Twin-block has obtained the national practical patent certification No: ZL201320028895.0, which is used to correct bony type II malocclusion, and the related effects on the jaw and occlusal plane have been studied [5][6][7], However there is no relevant research data on the effect of maxillary bone and maxillary dentition. The purpose of this study is to collect skeletal class II malocclusion patients treated with SGTB appliance using x-ray cephalometry to evaluate SGTB's osteopathic II The effect of maxillary molar relocation and fixed fixtures on maxillary retreat in this type of patients, and the clinical application and development prospects of SGTB are discussed.

Case Selection
Collecting growth-stage bone type ii non-extraction cases that

Case inclusion Criteria:①The clinical examination was
Antarctic II malocclusion, the bilateral molar relationship was distant, and the anterior teeth covered ≥5mm; ②X-ray skull lateral radiograph shows ANB angle ≥5° [8,9]，The mandibular plane angle is average or low angle (FMA ≤ 32°); ③No tooth extraction during phase ii treatment; ④According to the cervical vertebrae bone maturity index (CVMIs) to judge the bone age, all patients were in the pre-peak and peak stages of growth and development (S1~ S3).

Cephalometry Analysis
The time point T0 is set before the appliance is worn, the time point T1 is after the appliance is deactivated and removed, and   After the test has no significant difference, take the average value as the final measurement result [11]. The measurement error is calculated by randomly selecting 20 pieces from all the lateral films, Import the difference between the two measurement results into the formula: Se = √∑d 2 / 2n.

Statistical Analysis:
The measurement data were analyzed by SPSS 20.0 software package, and the difference before and after treatment was analyzed by paired t test. P <0.05 was statistically significant.

Test Results of Measurement Errors
The paired T test was used for the two measurement results, and the P value was 0.217, which was greater than 0.05. There was no statistical difference between the two measurement results, so the average value was taken. After measurement and analysis, the measurement error was 0.09~0.16mm. It indicates that the data is reliable, that is, the measurement Errors are negligible in this study.

Comparison of Cephalometric Measurements and their Differences
Changes in the maxilla and mandible: After SGTB treatment,

Go-Me increases, S-Go increases, N-Me increases, and APDI
increases, N-ANS increased, Me-ANS increased, ODI decreased, and N-ANS/Me-ANS decreased, and the differences were statistically significant. Changes in upper and lower dentition: After SGTB treatment, U1/PP decreased, U6/PP decreased, L1/MP increase, OB decrease, and OJ decrease were statistically significant, while U1/ L1 and L6/MP increased to some extent, but the differences before and after treatment were not statistically significant.After the end of SGTB treatment, the maxillary first molars moved distantly   Table 2: Differences in maxillary molars and maxillary bones before and after treatment (mm, mean ± SD). , it was found that The incisor's backward movement is mainly inclined. Although it is beneficial to reduce the anterior teeth coverage, it is a burden on the type II deep overbite, which indicates that the SGTB mandibular device must not only guide the mandible, but also To rotate the mandible clockwise while opening the occlusion, the mandibular plane angle increases, so the SGTB appliance is more suitable for all low-angle bone type II cases.