Factors related to microimplant-assisted rapid palatal expansion in teenagers and young adults: A cone-beam computed tomography study.

INTRODUCTION: For patients with maxillary transverse deficiency, selecting an appropriate therapeutic method is important for the treatment effect and prognosis. Our study aimed to explore factors related to microimplant-assisted rapid palatal expansion (MARPE) in teenagers and young adults using cone-beam computed tomography. METHODS: Twenty-five patients who underwent MARPE were included in this retrospective study from February 2014 to June 2019. Midpalatal suture density (MPSD) ratio, midpalatal suture maturation (MPSM), bone effect, dentoalveolar effect, and dental effect in maxillary first molar were evaluated using cone-beam computed tomography. Spearman correlation analysis was used to analyze the correlation between the MPSD ratio, MPSM, age, and the expansion amount generated by MARPE. RESULTS: Twenty-five patients (mean age, 19.84 ± 3.96 years; range, 15-29 years) with maxillary transverse deficiency were analyzed. Age was negatively correlated with bone expansion, alveolar expansion, and alveolar change (all P <0.05). There was a negative correlation between MPSM and nasal cavity variation, bone expansion, and alveolar change (all P <0.05). The bone expansion was negatively correlated with MPSD ratio 3 (r = -0.417; P <0.05) and MPSD ratio 4 (all P <0.05). CONCLUSIONS: Age, MPSM, and MPSD ratio were significantly related to the MARPE effect. Age, MPSM, and MPSD ratio should be considered when choosing MARPE.

[Efficiency of clear aligners in extrusion of posterior teeth evaluated by 3-dimensional model superimposition].

PURPOSE: To explore the efficiency of posterior teeth extrusion with clear aligners by 3-dimensional model superimposition, which provides a reference for the design of clinical programs. METHODS: We selected 24 patients with clear aligners whose posterior teeth were designed to extend more than 0.5 mm, and a total of 126 teeth were included. Digital models were obtained before and after treatment by intraoral scanning with iTero, named as "actual initial" and "achieved" digital models. Initial and final models from the ClinCheck, labeled as "virtual initial" and "predicted" models respectively. Initial, predicted, and achieved digital dental models were exported as stereolithography files and subsequently imported into Geomagic Studio. Extrusive measurements were made from the superimposition of the initial and predicted models (predicted movement) and from the superimposed initial and achieved models (achieved movement). Statistical analysis was performed with SPSS 23.0 and GraphPad Prism 5.0 software package. The extrusion efficiency of the posterior teeth was calculated, at the meanwhile the influencing factors were analyzed. RESULTS: The mean extrusion efficiency of posterior teeth during clear aligners treatment was 30.2%. The actual extrusion was linearly related to the expected(P<0.05), and the linear regression equation was y=0.305x-0.010. The difference between the actual and the predicted extrusion was positively correlated with the number of appliances(P<0.05), and also positively correlated with the predicted extrusion value(P<0.001). This difference was larger in low-angle patients than in patients with average angle (P<0.05). CONCLUSIONS: The extrusion rate of posterior teeth is relatively low during clear aligners treatment, and the average efficiency is 30.2%. Vertical growth pattern affects the extrusion efficiency. So more overcorrections can be designed for average angle patients.

[Cone-beam CT study of the characteristics of midpalatal suture at different age groups in a southern China population].

PURPOSE: The purpose of this cone-beam CT (CBCT) based study was to investigate the stages of palatal suture at different age groups as well as the bone density of the palatal suture in a south Chinese population. METHODS: The CBCT data of 113 patients with an age range from 4 to 36 years old were selected. All of them were reported to have normal growth. CBCT image data were selected in accordance with the inclusion criteria. By using Angelieri method, the palate was divided into 5 groups, and Chad Evans Larson bone density ratio was calculated for each patient. One-way ANOVA and LSD analysis were used to evaluate the average bone density ratio of the mid-palatal at each age stage as well as the mean value of palatal suture bone density at different stages with SPSS 22.0 software package. RESULTS: By comparing the density ratio of mid-palatal suture for each age group, no significant difference was noticed for the same stage regardless of the age (stage B, C and D) (P＞0.05), significant difference was noticed between C and D(P＜0.05),no significant difference was noticed for the suture density between group A and B as well as group C and D (P＞0.05), significant difference was found for the suture density between A/C, A/D, A/E, B/C, B/D, B/E, C/D, and C/E groups(P＜0.05). CONCLUSIONS: The mid-palatal suture density in children under 15 years may belong to stage A, B or C , which is significantly lower than group D and E; Patients of a palatal stage C stay within an age range from 11 to 18. No inner group difference is noticed inside group C. The average suture density of group C is significantly larger than group A and B, whereas smaller than group D and E. The results showed that CBCT can be a useful tool to guide rapid mid-palatal expansion in clinical practice. Patients who have a lower density mid-palatal suture can be expanded.

[MBT straight wire for Class II division I malocclusion cases].

OBJECTIVE: To evaluate the therapeutic effects of MBT straight wire on extraction case of Class II division I. METHODS: Thirty-six class II division I malocclusion patients were treated with MBT straight wire by extracting 4 bicuspid premolars or 2 maxillary bicuspid premolars. The X-ray cephalograms were analyzed before and after the treatment of MBT straight wire. RESULTS: After the treatment, the overjet was reduced by 6.04 mm (P < 0.01); U1-NA was reduced by 15.43 degrees (P <0.01); and U1-NA (mm) was reduced by 4.71 mm (P <0.01). ANB was significantly reduced (P < 0.05). CONCLUSION: MBT straight wire not only shortens the operation but also shows superior effect for Class II division I malocclusion cases.

[A preliminary study on the functional occlusion characters of the patients who had essential root resorption in anterior teeth].

PURPOSE: In order to determine the effect of functional occlusion on the essential root resorption, we compared the characters of functional occlusion between the patients who had essential root resorption in anterior teeth and who didn't have. METHODS: Panoramic radiography, periapical films and clinical data were used to diagnose the essential root resorption before the patients received orthodontic treatment. Fifteen patients who had 2-3 degree root resorption were divided into the experimental group, while 15 patients who didn't have were chosen as control group according to their age and sex. The functional occlusion of the cases in the experimental group and control group was checked on Denar Mark II articulator and via clinical examination, and the indexes of functional occlusion during protrusive and lateral movement in two groups were recorded. SPSS 13.0 software package was used for statistical analysis. RESULTS: The results showed that the number of anterior teeth occlusal interferences during lateral movement in the experimental group was more than that in control group by clinical (P<0.05) or articulator examination (P<0.05), but the number of posterior teeth occlusal interferences didn't have significant difference between the two groups. There was no significant difference in the retrusive range (RCP-ICP) in vertical, anterior-posterior and lateral direction respectively. CONCLUSION: It is suggested that as a kind of long-standing and minor trauma, the anterior teeth occlusal interferences during lateral movement might be a cause of essential root resorption in anterior teeth.