A cone-beam computed tomographic study evaluating the efficacy of incisor movement with clear aligners: Assessment of incisor pure tipping, controlled tipping, translation, and torque.

INTRODUCTION: This retrospective clinical study aimed to evaluate the efficacy of different types of incisor movements with clear aligners in the sagittal plane. METHODS: Pretreatment and posttreatment cone-beam computed tomography (CBCT) scans were collected from 69 patients who underwent nonextraction treatment with clear aligners (Invisalign; Align Technology, San Jose, Calif). Integrated 3-dimensional models of the virtual incisor position (ClinCheck; Align Technology) and the posttreatment incisor position (from posttreatment CBCT scans) were superimposed over the pretreatment position (from pretreatment CBCT scans) using Mimics software (Materialise, Leuven, Belgium). On the basis of the location of the rotation center, incisors showing pure tipping (>10°), controlled tipping (>10°), translation (>1 mm), or torque (>10°) movements were selected. Efficacy was determined by comparing the predicted and achieved incisor movement, and differences with efficacy were analyzed using Kruskal-Wallis and Shapiro-Wilk tests (α = 0.05). RESULTS: In measurements for 231 incisors, the mean efficacy of incisor movements in the sagittal plane was 55.58%. The most and least predictable movements were pure tipping (72.48%) and torque (35.21%), respectively. Labial root movement was significantly more predictable than lingual root movement, and labial movement of the mandibular incisors was significantly easier than that of the maxillary incisors. The type of tooth movement achieved was different from the type designed. CONCLUSIONS: The efficacy of incisor movement in the sagittal plane using clear aligners varies with designed movement type, and labial root movement appears to be more accurate than the lingual root movement. The biomechanics of clear aligners remains to be further elucidated to achieve more predictable treatment results.

Influence of the three-dimensional printing technique and printing layer thickness on model accuracy.

OBJECTIVE: The accuracies of three-dimensional (3D) printed dental models using various digital light processing (DLP) and stereolithography (SLA) printers at different thicknesses were compared. MATERIALS AND METHODS: Based on digital dental models (originally digitized using R700; 3Shape, Copenhagen, Denmark), physical dental models were printed using three types of DLP printers: (1) EvoDent (UnionTec, Shanghai, China) with layer thicknesses of 50 µm and 100 µm; (2) EncaDent (Encashape, WuXi, China) with layer thicknesses of 20, 30, 50 and 100 µm; (3) Vida HD (Envisioned, Dearborn, MI, USA) with layer thicknesses of 50 and 100 µm. Models with the SLA printer Form 2 (Formlabs, Somerville, MA, USA) were printed with layer thicknesses of 25, 50 and 100 µm. All 22 printed models were converted to digital dental models using a D2000 model scanner (3 Shape, Copenhagen, Denmark) and compared three-dimensionally to the source files using Geomagic Qualify 12.0 (3D Systems, Rock Hill, SC, USA). RESULTS: The printing accuracy of all printers was higher at 50 µm. When the layer thickness was set at 100 µm, the printing speed and printing accuracy of DLP printer were both superior to those of the SLA printer. In all groups, the EvoDent 50 µm group had the highest consistency with the source files (mean absolute deviation of 0.0233 mm in the maxilla and 0.0301 mm in the mandible). While the accuracy of Form 2 100 µm group was the lowest (mean absolute deviation of 0.0511 mm in the maxilla and 0.0570 mm in the mandible). CONCLUSION: For the 3D printers studied, 50 µm was the optimum layer thickness for DLP technology, and the printing accuracy using SLA technology increased with decreasing layer thickness. The DLP technology also had higher printing accuracy at a layer thickness of 100 µm. EvoDent 50 µm had the highest and Form 2 100 µm the lowest printing accuracy.

[Effect of cyclic tensile stress on expression of type â ¡ collagen and Sox9 in rat cranial base synchondrosis].

PURPOSE: To establish an in vitro mechanical stimulation model of cranial base synchondrosis chondrocytes, and to study the effect of cyclic tensile stress on the main extracellular matrix of rat cranial base synchondrosis. METHODS: Cyclic tensile stress was imposed to the second passage of cranial base synchondrosis chondrocytes for 3, 6, 12 and 24 hours respectively by using a Flexcell Strain Unit-5000T(10% surface elongation, 1 Hz). After mechanical loading, the total RNA of the cells harvested from six-well BioFlex was extracted. Real-time quantitative RT-PCR was performed to quantify the mRNA levels of type Ⅱ collagen and Sox9. The data were analyzed with SPSS 17.0 software package. RESULTS: Compared with the control group(0 h group), the mRNA expression of type Ⅱ collagen was decreased after 3 hours of loading, but not statistically significant; While the expression of Sox9 decreased significantly (P<0.05). In the 6 h group, the expression of Col-Ⅱ and Sox9 decreased significantly (P<0.01 and 0.05, respectively). The expression of Col-Ⅱ and Sox9 increased in the 12 h group. The 24 h group showed significant increase in both type Ⅱ collagen and Sox9 (P<0.05). CONCLUSIONS: The results illustrate that cyclic tensile stress can affect the synthesis of the main extracellular matrix of cranial base synchondrosis in vitro. Expression of type Ⅱ collagen and Sox9 can be inhibited during early stage of mechanical loading. However, when loading time extends, the mechanical stimuli greatly promotes the expression of type Ⅱ collagen and Sox9. The reaction of Sox9 in this in vitro mechanical stimulation model happens earlier than that of type Ⅱ collagen.

Tension-loaded bone marrow stromal cells potentiate the paracrine osteogenic signaling of co-cultured vascular endothelial cells.

Co-culture of bone marrow stromal cells (BMSCs) and vascular endothelial cells (VECs) is a promising strategy for better osteogenesis and pre-vascularization in bone tissue engineering. Recent reports have shown that mechanical stretching further promotes osteogenesis in BMSC/VEC co-culture systems, but the underlying mechanism of this process remains unclear. In this study, noncontact co-cultures of rat primary BMSCs and VECs were employed to interrogate paracrine cell-to-cell communications in response to tension. Exposure of VECs to 6% tension for 48 h elicited neither ALP activity nor mRNA expression of OCN and OPN in BMSCs incubated in a shared culture medium. Instead, BMSCs subjected to tension induced robust VEGF release, and its conditioned medium enhanced the proliferation and tubular formation of VECs with a concurrent increase in BMP-2 and IGF-1 production. Conditioned medium from activated VECs in turn promoted expression of osteogenic genes in BMSCs, followed by an increase in matrix mineralization. The addition of VEGF-R inhibitor Tivozanib to these systems abrogated the tension-induced paracrine effects on VECs and subsequently impaired BMSC osteogenesis. These results clearly demonstrate that the response of BMSCs to tension potentiates paracrine osteogenic signaling from VECs; this positive feedback loop is initiated by VEGF release.

[Morphological and histological adaptation after mandibular functional positioning only in vertical dimension].

PURPOSE: To elucidate the role of mandibular vertical functional positioning in condylar adaptive remodeling. METHODS: Forty female Sprague-Dawley rats at the age of 5 weeks were randomly divided into 4 control and experimental groups. All the animals were sacrificed on day 3, 6, 9 and 12 (n=5). Bite plates on upper posterior teeth were fitted on the experimental animals to induce functional repositioning of the mandible. Morphological and histological analysis was carried out to quantitatively analyze the amount of the adaptive changes of condylar cartilage. Independent-samples t test and One-Way ANOVA using SPSS11.0 software package were performed. RESULTS: Twelve days after mandibular vertical functional positioning the condylar height increased. Nine days after mandibular vertical functional positioning the thickness of prechondroblast layer and chondroblast layer increased significantly compared with control groups. However the thickness of hypertrophic layer decreased significantly after 6 days' mandibular repositioning. No change was found in the thickness of mesenchymal layer during the experimental period. CONCLUSIONS: Mandibular vertical functional positioning could enhance the growth of condyle. The resulted adaptive remodeling in condylar cartilage plays an important role in the treatment mechanism of mandibular deficiency via functional appliances.

[Bolton tooth-size discrepancy among different skeletal malocclusion groups].

PURPOSE: To evaluate the differences in tooth size ratios and distributions of Bolton anterior and overall ratios among different skeletal malocclusions. METHODS: 180 subjects were involved in this study, each malocclusion group consisted of 60 subjects(30 males and 30 females). The mesio-distal width from left first molar to right first molar was measured, Bolton anterior and overall ratios were calculated. Student's t test, ANOVA, LSD and chi2 test were performed for statistical analysis with SPSS15.0 software package. RESULTS: No statistically significant sex difference was found in anterior or overall ratio in any malocclusion. Significant difference was found for all ratios between skeletal Class III and skeletal Class I, so with skeletal Class II. No significant differences in all ratios between skeletal Class I and Class II were noted. Significant difference was found in the distribution of subjects with anterior and overall ratio discrepancies between skeletal Class III and skeletal Class II. CONCLUSIONS: The mean anterior and overall ratios for skeletal Class III malocclusions are significantly greater than those for skeletal Class I and Class II. The number of subjects with anterior ratio discrepancies for skeletal Class III malocclusions are larger than that for skeletal Class I and Class II malocclusion.

[Indications for non-extraction treatment of dental crowding with Damon appliance].

PURPOSE: To analyze the indications for successful non-extraction correction of dental crowding with Damon appliance. METHODSú 19 patients with non-extraction orthodontic treatment were reviewed. They had Class I skeletal pattern and both arches were treated with Damon 3 or Damon MX appliances. According to the initial diagnosis before treatment (T1), 7 cases needed extraction, but they rejected it. After correction of crowding (T2), they were allotted into either successful group or unsuccessful group. The successful group contained those subjects in whom the Z angle at T2 was no less than 70 degrees or that of T1. Others were allotted into the unsuccessful group. The dental casts and cephalometric radiophotographs were analyzed at T1 and T2. The difference between the two groups was analyzed with SPSS15.0 software package for Student's t test. RESULTS: There were 11 cases in successful group. All the 7 cases rejecting extraction were finally allotted into the unsuccessful group. No significant difference in upper arch perimeter and arch width was detected between the two groups at both T1 and T2. The upper and lower incisors and upper lip showed a more retruded position in successful group at T1, although they showed a similar amount of protrusion from T1 to T2 in both groups. The forward movement of lower lip was 3.4mm in the unsuccessful group, which was significantly larger than that of 1.6mm in successful group(P<0.05). Z angle decreased 10.7 degrees in the unsuccessful group, while no significant change was detected in the successful group. The Holdaway upper lip strain was comparable in two groups, but the successful group showed significantly less soft chin strain than unsuccessful group (P<0.05). CONCLUSIONS: Damon appliance can not rescue extraction cases. Straight soft tissue profile and upright incisor position are prerequisite for non-extraction treatment. And a harmonious chin and lip position is the key leading to the successful non-extraction treatment with Damon appliance.

Mandibular functional positioning only in vertical dimension contributes to condylar adaptation evidenced by concomitant expressions of L-Sox5 and type II collagen.

OBJECTIVE: Concerted expressions of L-Sox5 and type II collagen play an important part in osteogenic transition in epiphyseal cartilage. This study was designed to elucidate the role of mandibular vertical functional positioning in condylar adaptive remodelling by examining L-Sox5 and type II collagen expressions in condylar cartilage. DESIGN: 40 female Sprague-Dawley rats at age of 5 weeks were randomly divided into the experimental (n=20) and control groups (n=20). Bite plates were fitted on the upper posterior teeth of the experimental animals to induce functional repositioning of mandible in vertical dimension. The animals in both experimental and matched control groups were sacrificed on days 3, 6, 9 and 12, respectively. Tissue sections were cut in the sagittal plane through the mandibular condyles and processed with histomorphological examination for cellular response and immunohistochemical test for expressions of L-Sox5 and type II collagen. Quantitative assessment was conducted with computer-assisted imaging system to reveal the correlation between these two factors. RESULTS: (1) Both L-Sox5 and type II collagen were expressed in prechondroblastic cells and chondroblastic cells. (2) When mandible was downward positioned, the amount of L-Sox5 expression was significantly higher by 16.1% (day 9) and 24.2% (day 12) than that of the control (P<0.05); Similarly, type II collagen expression in the experimental group was also significantly stronger by 9.3% (day 9) and 12.3% (day 12) than control group (P<0.05), indicating an enhanced osteogenic transition occurring in condylar cartilage. (3) There was a similarity in temporospatial patterns between the expressions of these two factors, indicating their integral functions in facilitating condylar adaptation. CONCLUSIONS: It is suggested that L-Sox5 plays a key role in adaptive remodelling of condylar cartilage resulting from downward positioning of the mandible. Integration with type II collagen enables L-Sox5 to induce osteogenic transition and consequently to encourage endochondral ossification.

[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.