[Experimental study on the effect of tooth movement with thin and thick aligners in rabbits].

PURPOSE: To explore the effect of tooth movement on lower incisors of rabbits with thin and thick aligners. METHODS: A group of 6 male New Zealand rabbits were randomly divided into 2 groups, the experimental group(n=3) was designed to move the lower incisors distally by 3 steps with thin and thick aligners(0.625 and 0.75 mm)，0.33 mm each；the control group (n=3) was designed to move the teeth by 3 steps with aligner of conventional thickness (0.75 mm), 0.20 mm each. Polyvinyl siloxane impressions were taken before and after aligner placement. The data of tooth movement were measured. SPSS 19.0 software package was used for statistical analysis. RESULTS: The accuracy of tooth movement expression in both groups decreased gradually from the incisal part to the gingival part. The rate of tooth movement in the experimental group was significantly higher than that of the control group（P<0.001）. CONCLUSIONS: The tooth movement of rabbit mandibular central incisor was tipping with the clear aligner. The rate of tooth movement was increased by applying thin and thick aligners，but the accuracy of tooth movement was decreased.

[Finite element analysis of clear aligners in extractive cases].

PURPOSE: This study analysed the mechanical features of the extraction space closure in clear aligners through mechanical research. METHODS: A patient with four first premolars extraction was chosen as sample, and four plans with clear aligners for space closure were designed, including anterior retraction entirely, anterior retraction dispersedly, posterior movement mesially and posterior movement dispersedly. Finite element analysis was performed separately. RESULTS: In anterior retraction, when there was no anterior space, the force acted on them more evenly, and the posteriors needed to provide more anchorage; when anterior space existed, the force acted on the central incisors first and largely, and the posteriors needed to provide less anchorage. In posterior anchorage, when the posteriors moved entirely with mesial movement, it might help to protect second premolar's anchorage while molars would receive more mesial force; when the posteriors moved separately without designed movement, the second premolar would undertake more anchorage and more tendency to incline mesially; when the posteriors moved entirely without designed movement, the anchorage would distribute more evenly. CONCLUSIONS: Selection of the way of retracting anteriors should be based on the difference of stress distribution in different ways in addition to individual discrepancy and clinical facts. Selection of the way of moving posteriors should be based on the distribution of anchorage as well as avoiding posterior open bite. Less amount of correction in each step has better axial control.

[Maxillary protraction with and without maxillary expansion on unilateral cleft lip and palate model: a finite element analysis].

PURPOSE: The aim of this finite element study was to investigate biomechanical effects of maxillary protraction with and without maxillary expansion on unilateral cleft lip and palate(UCLP)model before and after alveolar bone graft (ABG). METHODS: Orthopedic force (30° downward and forward to the occlusal plane, 5N/side) with expansion and without expansion were loaded on models before ABG, and after ABG respectively. Initial displacement and sutural stress were analyzed by using ANSYS12.0 software. RESULTS: The amount of displacement at the cleft side was larger than that at the non-cleft side before ABG, a more symmetrical pattern was obtained after ABG. Regardless of ABG, maxillary protraction with maxillary expansion exhibited more evident forward displacement of maxilla. The sutural stress values after maxillary protraction with maxillary expansion were significantly higher than without expansion. CONCLUSIONS: Analysis of these results showed that maxillary protraction with expansion could presumably promote the orthopedic effects of the facemask on UCLP patients, and more uniform force would obtain after ABG.

Impact of rapid maxillary expansion in unilateral cleft lip and palate patients after secondary alveolar bone grafting: review and case report.

The purpose of this article was to analyze the effects and short-term stability of rapid maxillary expansion performed after secondary alveolar bone grafting in unilateral cleft lip and palate (UCLP) patients. Two UCLP patients with severe maxillary constriction who had previous bone grafting were involved in this study. A hyrax rapid expansion appliance was placed on 4 abutment teeth and activated twice daily. An opening of the midpalatal suture was found on the posttreatment occlusal radiographs, which was clinically confirmed by the diastema. Posteroanterior cephalometric tracing analysis demonstrated significant increases in maxillary and dental arch width. No obvious radiographic alteration was observed in the grafted areas.

[The reliability and accuracy of the digital models reconstructed by cone-beam computed tomography].

PURPOSE: To evaluate the reliability of the digital models scanned by cone-beam computed tomography (CBCT). METHODS: Forty plaster models of patients with orthodontic treatment were selected. These plaster models were scanned and measured by 3DX cone beam CT, compared with manual measurement via concordance correlation coefficient (CCC) and mean difference (MD). RESULTS: The CCC of all the measurement was from 0.847 to 0.993. The value of MD of all the measurement was below 0.25mm except CFF6, PWF5 and PWF6, which was 0.34mm, 0.63mm and 1.49mm, respectively. CONCLUSIONS: The reliability and accuracy of the digital models scanned by cone-beam CT is very high. The accuracy of measurement of the dental cusp is the highest, the dental fossa is the second, and the lowest point of palatal gingival is the third.

[The effectiveness of asymmetric extraction in treatment of Class II division 1 malocclusions].

PURPOSE: To analyze hard and soft tissue profile changes before and after asymmetric extraction treatment of Angle Class II division 1 malocclusion. METHODS: Thirty patients of Angle Class II division 1 malocclusions (11 males, 19 females, average age 13.6 years) were divided into two groups according to their extraction approach. In asymmetric extraction group, 2 first maxillary premolars and 1 first mandibular premolar were extracted. In the control group, all 4 first premolars were extracted. Lateral cephalometric radiographs were taken before and after treatment to compare hard and soft-tissue changes between the two groups, and the cephalometric measurements were analysed by SAS6.12 software package for independent sample t test. RESULTS: In comparison of the changes between the two groups, significant differences in dentoskeletal measurements were observed with NAPog, SNA, ANB, MP-SN and with the inclinations of the upper and lower incisors (P<0.01). Significant differences in soft-tissue changes were also observed in the thickness of upper lip, the Z angle (P<0.01) and the nasolabial angle (P<0.05). Compared to the profile before treatment,only inclination of lower incisors changed significantly after treatment (P<0.01). CONCLUSIONS: Asymmetric extractions is feasible in treatment of Class II division 1 malocclusions evidenced by retractions of both upper and lower incisors and improves sagittal soft-tissue profile. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality (Grant No.08DZ2271100).

[Sagital position of glenoid fossa in Angle Class II malocclusion with mandibular retrusion].

PURPOSE: To evaluate and compare the morphology and position of the glenoid fossa in patients with Class II malocclusion associated with mandibular retrusion and Class I malocclusion in the permanent dentition. METHODS: A sample of 26 subjects(12 males, 14 females, average age 13.4 years) with skeletal and dental Class II malocclusion associated with mandibular retrusion, was compared with a matched group of 31 subjects(12 males, 19 females, aged 12.9 years) with skeletal and dental Class I relationships. The lateral cephalograms were traced and the cephalometric analysis was taken by Nemotec Dental Studio 2006 software before orthodontic treatment. The comparisons between the two groups on the cephalometric measures for the assessment of glenoid fossa were performed by means of an independent samples t test using SPSS 15.0 software package. The correlation and regression analysis was also performed within the measures in the Class II group. RESULTS: The results showed there was significant difference of Wits, GF/Ptm-FH and GF-FMN between the two groups (P<0.01). There was a significant correlation between the GF-FMN vs. AOBO, GF-FMN vs. GF/S-FH, GF/S-FH vs.GF/Ptm-FH, S/Ptm-FH vs. GF/Ptm-FH in the Class II group. The regression equations of the GF-FMN vs. AOBO and GF-FMN vs. GF/S-FH were also obtained (P<0.05). CONCLUSIONS: The Class II malocclusion associated with mandibular retrusion patients have a posteriorly displaced glenoid fossa compared with Class I patients. Cephalometric measurement is a useful tool to evaluate the glenoid fossa morphology and position.

The association between lower incisal inclination and morphology of the supporting alveolar bone--a cone-beam CT study.

AIM: To investigate the relationship between the positioning of the lower central incisor and physical morphology of the surrounding alveolar bone. METHODOLOGY: Thirty-eight patients (18 males, 20 females), with mean age of 13.4 years, were included in this study. As part of orthodontic treatment planning the patients were required to take dental Cone-beam CT (CBCT) covering the region of lower incisors, the surrounding alveolar bone and the mandibular symphysis. The cephalometric parameters were designed and measured to indicate the inclination of lower central incisor and physical morphology of the adjacent alveolar bone. Computer-aided descriptive statistical analysis was performed using SPSS 15.0 software package for Windows. A correlation analysis and a linear regression analysis between the incisor inclination and the alveolar bone morphology were performed. RESULTS: Significant positive correlations were found between the lower central incisor inclination and the morphological contour of the alveolar bone (P < 0.05). The lower central incisor root apex was closer to the lingual alveolar crest when it was buccally inclined. CONCLUSION: The morphology of the alveolar bone may be affected by incisal inclination.

[Diagnostic value of dental implants in the posterior maxilla using cone beam computed tomography].

PURPOSE: To compare the diagnostic value of cone beam computed tomography (CBCT) with orthpantomography(OPG) for dental implants at the posterior maxilla. METHODS: 75 patients (89 positions) with dental implants in the posterior maxilla were assessed with CBCT and orthopantomography. The horizontal height from the top of the alveolar bone to the floor of sinus was measured through CBCT and OPG. The results were processed statistically with SPSS 11.5 software package for Chi-square test. RESULTS: Bone deficiency was detected in 30.34% and 16.85% cases by CBCT and OPG respectively with significant difference(P=0.034). Bone osteointegration was detected in 4.95% and 11.88% cases with CBCT and OPG respectively without significant difference(P=0.413). CONCLUSIONS: The quantity of bone could be evaluated more precisely by CBCT than OPG. The peri-implant bone could be demonstrated more clearly by CBCT than OPG.

[A preliminary study of combined periodontal-orthodontic approach for treating labial displacement of incisors in patients with periodontal diseases].

PURPOSE: The purpose of this study was to evaluate the effect of combined periodontal-orthodontic treatment for patients who had chronic periodontitis with labial displacement of incisors and radiological evidence on migrated incisors. METHODS: Twenty-one adult patients were included in the study. Fifty-two migrated incisors were randomly assigned to treatment with circumferential supracrestal fibrotomy or non-surgery. The mean orthodontic treatment time was 12 months. Before surgery (circumferential supracrestal fibrotomy) and at the end of orthodontic treatment, the following parameters were registered clinically: CAL(clinical attachment loss), TM(tooth mobility), SBI (sulcus bleeding index), PD (probing depth),CEJAC (distance from the CEJ to the alveolar crest) and RL (root length). Standardized intraoral radiographs were taken. SPSS12.0 software package was used for data analysis. Student's t test was performed for coupled data including PD, CAL, CEJAC and RL. Results of SBI and TM were analyzed statistically with Wilcoxon signed rank test. RESULTS: Comparison of pre- and post-treatment values showed a statistically significant improvement for all parameters without remarkable root apex resorption. TM and CAL reduction were greater in the surgical group compared to the non-surgical group (P<0.05). The reduction of CEJAC between the two groups were significantly different (P<0.01). CONCLUSION: The results show the efficacy of combined periodontal-orthodontic approach with circumferential fibrotomy on patients with incisors migration. After proper periodontal surgical therapy, orthodontic movement can positively improve both the alveolar bone and the soft periodontal tissues.

[Dental arch form reverting by four-point method].

PURPOSE: To explore a simple method of reverting individual dental arch form template for wire bending. METHODS: Individual dental arch form was reverted by four-point method. By defining central point of bracket on bilateral lower second premolar and first molar, certain individual dental arch form could be generated. The arch form generating procedure was then be developed to computer software for printing arch form. Four-point method arch form was evaluated by comparing with direct model measurement on linear and angular parameters. The accuracy and reproducibility were assessed by paired t test and concordance correlation coefficient with Medcalc 9.3 software package. RESULTS: The arch form by four-point method was of good accuracy and reproducibility (linear concordance correlation coefficient was 0.9909 and angular concordance correlation coefficient was 0.8419). CONCLUSION: The dental arch form reverted by four-point method could reproduce the individual dental arch form.

[Current clinical studies on slow palatal expansion].

Palatal expansion is frequently applied in correction of maxillary transverse deficiency and upper dental arch constriction. Palatal expansion includes rapid palatal expansion and slow palatal expansion. Slow palatal expansion generated physiological expansion force compared to strong forces by rapid palatal expansion with some side effects. Satisfied clinical results will be achieved in selected cases. This paper reviews the types of appliance, skeletal and dental changes, and comparison with rapid palatal expansion.

[Evaluations of self-perceived orthodontic treatment need using 2 different scales in adolescents].

PURPOSE: To evaluate the self-perceived dental aesthetics through visualized analogue scale (VAS) and aesthetic component (AC) of index of orthodontic treatment (IOTN) among adolescents in Shanghai area. METHODS: The investigation was carried out among 302 students (148 boys and 144 girls) aged 11-13 years. Self-perception of the dental aesthetic appearance was evaluated through VAS and AC. Additionally, the objective dental aesthetics were scored by orthodontists using AC and the actual dental attractiveness satisfaction was determined by a simple question. The data was analyzed using SPSS11.0 software package for Spearman correlation analysis. RESULTS: Generally, no statistically significant sex differences were found in relation to the VAS score and SAC degree (P > 0.05). No correlation was found between actual dental attractiveness satisfaction and self-perceived AC grade (r = 0.04. P = 0.441). However, statistically significant, positive, strong correlations were found between the actual dental attractiveness satisfaction and VAS score (r = 0.80, P = 0.000). And meaningful relation between the AC and VAS score was found. CONCLUSIONS: VAS showed high ability to predict the self-perceived dental aesthetics and act as a simple and useful tool, which can be used in further investigations.

[Analysis of the efficacy of Twin-block appliance on maxillofacial growth of six pairs of monozygotic twins].

PURPOSE: The purpose of this study was to investigate the efficacy of Twin-block appliance on maxillofacial growth by using monozygotic twins. METHODS: 6 pairs of non-high angle monozygotic twins aged 12.2 with class II division 1 malocclusion were selected from 32 pairs of twins. In the first year Twin A of each pair was functionally treated using Twin-block appliance; meanwhile, Twin B underwent non-extracted fixed treatment without any treatment procedure which might cause changes like functional appliances such as Class II elastics. The difference of the cephalometric changes of maxilla and mandible before and after treatment between Twin A and Twin B was compared using paired-t test. RESULTS: Compared with those of Twin A after one year treatment, SNA, Cd-A and Cd-Go of Twin B had little chang (P>0.05), but Cd-S' reduced (P<0.05), Cd-Gn and SNB increased (P=0.01), (Cd-Gn)-(Cd-A) and ANB increased (P<0.05) significantly. CONCLUSION: Twin-block appliance can stimulate forward mandibular growth and cause forward mandibular displacement, but has little effect on ramus height and maxillary growth.