Research on multi-class orthodontic image recognition system based on deep learning network model / 中华口腔医学杂志

Objective: To develop a multi-classification orthodontic image recognition system using the SqueezeNet deep learning model for automatic classification of orthodontic image data. Methods: A total of 35 000 clinical orthodontic images were collected in the Department of Orthodontics, Capital Medical University School of Stomatology, from October to November 2020 and June to July 2021. The images were from 490 orthodontic patients with a male-to-female ratio of 49∶51 and the age range of 4 to 45 years. After data cleaning based on inclusion and exclusion criteria, the final image dataset included 17 453 face images (frontal, smiling, 90° right, 90° left, 45° right, and 45° left), 8 026 intraoral images [frontal occlusion, right occlusion, left occlusion, upper occlusal view (original and flipped), lower occlusal view (original and flipped) and coverage of occlusal relationship], 4 115 X-ray images [lateral skull X-ray from the left side, lateral skull X-ray from the right side, frontal skull X-ray, cone-beam CT (CBCT), and wrist bone X-ray] and 684 other non-orthodontic images. A labeling team composed of orthodontic doctoral students, associate professors, and professors used image labeling tools to classify the orthodontic images into 20 categories, including 6 face image categories, 8 intraoral image categories, 5 X-ray image categories, and other images. The data for each label were randomly divided into training, validation, and testing sets in an 8∶1∶1 ratio using the random function in the Python programming language. The improved SqueezeNet deep learning model was used for training, and 13 000 natural images from the ImageNet open-source dataset were used as additional non-orthodontic images for algorithm optimization of anomaly data processing. A multi-classification orthodontic image recognition system based on deep learning models was constructed. The accuracy of the orthodontic image classification was evaluated using precision, recall, F1 score, and confusion matrix based on the prediction results of the test set. The reliability of the model's image classification judgment logic was verified using the gradient-weighted class activation mapping (Grad-CAM) method to generate heat maps. Results: After data cleaning and labeling, a total of 30 278 orthodontic images were included in the dataset. The test set classification results showed that the precision, recall, and F1 scores of most classification labels were 100%, with only 5 misclassified images out of 3 047, resulting in a system accuracy of 99.84%(3 042/3 047). The precision of anomaly data processing was 100% (10 500/10 500). The heat map showed that the judgment basis of the SqueezeNet deep learning model in the image classification process was basically consistent with that of humans. Conclusions: This study developed a multi-classification orthodontic image recognition system for automatic classification of 20 types of orthodontic images based on the improved SqueezeNet deep learning model. The system exhibitted good accuracy in orthodontic image classification.

Ability and inability of artificial intelligence in orthodontics / 中华口腔医学杂志

With the development of artificial intelligence (AI) technology, it has a wide range of explorations in orthodontics. AI has greater application prospects in precise measurement, multidimensional diagnosis, treatment planning and efficacy prediction. At the same time, there are certain limitations in the application of AI, such as risks caused by individual variability, black box properties and unclear delineation of medical responsibilities. This paper summarized the history and current status of AI applications in orthodontics and discussed future development trends, to provide reference for clinical orthodontics.

Minimally invasive treatment of hallux valgus with bandage for external fixation: Finite element analysis of stability of the osteotomy end / 中国组织工程研究

BACKGROUND: The clinical effect of minimally invasive treatment of hallux valgus is significant. The osteotomy end is stabilized only by external fixation of the bandage. There is currently no research on the stability of the osteotomy end. OBJECTIVE: To study the effect of minimally invasive treatment of the "8" bandage external fixation on the stress and displacement of the osteotomy end in the balanced standing condition after hallux valgus. METHODS: In the minimally invasive treatment of the "8" bandage external fixation finite element model after the hallux valgus operation, three vertical axes (X-axis, Y-axis, Z-axis) were established with the first tibial osteotomy as the center. The X-axis and Y-axis were parallel to the horizontal plane of the foot, pointing to the medial and anterior sides of the foot respectively. The Y axis was perpendicular to the horizontal plane of the foot, pointing upwards. The four nodes defining the distal osteotomy surface were A1 on the upper side, B1 on the outer side, and C1 on the outer side, and D1 on the inner lower side. The proximal end osteotomy surface corresponded to four nodes as A2, B2, C2 and D2. The displacement was positive when it coincided with the direction of the coordinate axis, and negative when it was opposite. Through the finite element analysis, the direction and magnitude of the stress and displacement of the distal and proximal nodes of the osteotomy surface in the balanced standing condition were obtained. RESULTS AND CONCLUSION: (1) The finite element model of the "8" bandage after minimally invasive treatment of hallux valgus was used in a balanced standing condition. The maximum stress at the osteotomy end was at the dorsal side of the osteotomy surface (B2), which was 0.632 MPa. (2) The first principal stress at the osteotomy surface was at Z-axis. The direction was opposite to the Z-axis, and was the same as the total stress, which was a compressive stress. The shear force was the largest on the XY plane, and the maximum stress was at the dorsal inner side (A2) of the proximal osteotomy surface, which was 0.058 MPa. (3) The major displacements of the distal and proximal ends of the first patella osteotomy were on the X-axis, and the displacements were on the medial condyle (D1) of the osteotomy surface, i.e., -1.002 mm and medial condyle (A2), and 0.621 mm, respectively. (4) The results confirm that the external fixation of "8" bandage can maintain the stability of the osteotomy end after minimally invasive treatment of hallux valgus, and is conducive to the healing of the osteotomy end.

North China bariatric & metabolic surgery clinical database registry report(2018) / 中国实用外科杂志

OBJECTIVE: To report an overview of bariatric & metabolic surgery performed in 2018 in North China. METHODS: Based on prospective and observational North China Bariatric & Metabolic Surgery Clinical Database(NC-BMD), the study of evaluating the number and the type of bariatric &metabolic surgery procedures was performed in North China. Demographic characteristic, obesityrelated diseases and operational information were also analyzed. RESULTS: In 2018, 17 centers from 7 regions in North China contributed a total of 728 registration data. Valid data were analyzed from 16 centers. The patients' median (minimum, maximum) BMI pre-surgery was 38.4(24.7,95.2). The overall proportion of female patients was 74.7%, and mean±SD age was(32.5±8.29) years, while male patients was 25.3%, and mean±SD age was (32.7±9.90) years. According the data 93.9% laparoscopic sleeve gastrectomy(LSG), 4.4% laparoscopic Roux-en-Y gastric bypass (LRYGB) and 1.7% other operation types. 29.2% of patients had a history of type 2 diabetes, 69.4% had sleep apnea, and 22.6% had polycystic ovary syndrome before operation. CONCLUSION: The establishment of NC-BMD has laid a solid foundation for data registration in North China. Based on current data, LSG is the mainstream of bariatric and metabolic surgery in North China this year.

Integrated three-dimensional digital assessment of accuracy of anterior tooth movement using clear aligners / 대한치과교정학회지

OBJECTIVE: To assess the accuracy of anterior tooth movement using clear aligners in integrated three-dimensional digital models. METHODS: Cone-beam computed tomography was performed before and after treatment with clear aligners in 32 patients. Plaster casts were laser-scanned for virtual setup and aligner fabrication. Differences in predicted and achieved root and crown positions of anterior teeth were compared on superimposed maxillofacial digital images and virtual models and analyzed by Student's t-test. RESULTS: The mean discrepancies in maxillary and mandibular crown positions were 0.376 +/- 0.041 mm and 0.398 +/- 0.037 mm, respectively. Maxillary and mandibular root positions differed by 2.062 +/- 0.128 mm and 1.941 +/- 0.154 mm, respectively. CONCLUSIONS: Crowns but not roots of anterior teeth can be moved to designated positions using clear aligners, because these appliances cause tooth movement by tilting motion.

A novel protein-repellent dental composite containing 2-methacryloyloxyethyl phosphorylcholine / 国际口腔科学杂志·英文版

Secondary caries due to biofilm acids is a primary cause of dental composite restoration failure. To date, there have been no reports of dental composites that can repel protein adsorption and inhibit bacteria attachment. The objectives of this study were to develop a protein-repellent dental composite by incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC) and to investigate for the first time the effects of MPC mass fraction on protein adsorption, bacteria attachment, biofilm growth, and mechanical properties. Composites were synthesized with 0 (control), 0.75%, 1.5%, 2.25%, 3%, 4.5% and 6% of MPC by mass. A commercial composite was also tested as a control. Mechanical properties were measured in three-point flexure. Protein adsorption onto the composite was determined by the microbicinchoninic acid method. A human saliva microcosm biofilm model was used. Early attachment at 4 h, biofilm at 2 days, live/dead staining and colony-forming units (CFUs) of biofilms grown on the composites were investigated. Composites with MPC of up to 3% had mechanical properties similar to those without MPC and those of the commercial control, whereas 4.5% and 6% MPC decreased the mechanical properties (P<0.05). Increasing MPC from 0 to 3% reduced the protein adsorption on composites (P<0.05). The composite with 3% MPC had protein adsorption that was 1/12 that of the control (P<0.05). Oral bacteria early attachment and biofilm growth were also greatly reduced on the composite with 3% MPC, compared to the control (P<0.05). In conclusion, incorporation of MPC into composites at 3% greatly reduced protein adsorption, bacteria attachment and biofilm CFUs, without compromising mechanical properties. Protein-repellent composites could help to repel bacteria attachment and plaque build-up to reduce secondary caries. The protein-repellent method might be applicable to other dental materials.

Reliability assessment and correlation analysis of evaluating orthodontic treatment outcome in Chinese patients / 国际口腔科学杂志·英文版

This study aimed to assess the reliability of experienced Chinese orthodontists in evaluating treatment outcome and to determine the correlations between three diagnostic information sources. Sixty-nine experienced Chinese orthodontic specialists each evaluated the outcome of orthodontic treatment of 108 Chinese patients. Three different information sources: study casts (SC), lateral cephalometric X-ray images (LX) and facial photographs (PH) were generated at the end of treatment for 108 patients selected randomly from six orthodontic treatment centers throughout China. Six different assessments of treatment outcome were made by each orthodontist using data from the three information sources separately and in combination. Each assessment included both ranking and grading for each patient. The rankings of each of the 69 judges for the 108 patients were correlated with the rankings of each of the other judges yielding 13 873 Spearman rs values, ranging from -0.08 to +0.85. Of these, 90% were greater than 0.4, showing moderate-to-high consistency among the 69 orthodontists. In the combined evaluations, study casts were the most significant predictive component (R(2)=0.86, P<0.000 1), while the inclusion of lateral cephalometric films and facial photographs also contributed to a more comprehensive assessment (R(2)=0.96, P<0.000 1). Grading scores for SC+LX and SC+PH were highly significantly correlated with those for SC+LX+PH (r(SC+LX)vs.(SC+LX+PH)=0.96, r(SC+PH)vs.(SC+LX+PH)=0.97), showing that either SC+LX or SC+PH is an excellent substitute for all three combined assessment.

Clinical value of three kinds of helicobacter pylori detection methods / 重庆医学

Objective To discuss the clinical value of three kinds of helicobacter pylori (HP) detection methods and find out the appropriate method for clinical application of the HP detection .Methods A total of 109 patients received gastroscopy ,the efficacy of RUT ,13C-urea breath test(13C-UBT) and the immunoCard STAT helicobacter pylori stool antigen (HpSA) for detection of HP were compared .Results RUT positive rate of the two pieces of gastric mucosa (the gastric antrum and the gastric body) was 34 .86% ,higher than that of single piece of gastric mucosa (gastric antrum or stomach body ) and two pieces of gastric mucosa (stomach) ,the difference was statistically significant (P0 .05) .The diagnosis of HP infection was based on 13C-UBT ,the immunoCard STAT HpSA sensi-tivity ,specificity and accuracy were 86 .49% ,95 .83% ,92 .66% ,respectively ,which were higher than RUT .Conclusion Two pieces of gastric mucosa (the gastric antrum and the gastric body) materials is appropriate for clinical promotion RUT based solution . RUT ,13C-UBT and hpsas immune quick check card are all clinical detection of HP and reliable methods ,but hpsas immune quick check card is more suitable for clinical promotion .

Effect of orthodontic force on expression of Asporin after tooth auto-transplantation: an experimental study in Beagle dogs / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effect of orthodontic light force on the expression of Asporin, bone morphogenetic proteins-2 (BMP-2) and alkaline phosphatase (ALP) after auto-transplantation.</p><p><b>METHODS</b>Thirty-two maxillary and mandibular incisors in four 13 month-old male Beagle dogs were auto-transplanted to the other side of the same jaw. The teeth were all endodontically treated and divided into four groups, control (group 1) and three experimental groups (groups 2, 3 and 4).In control group, the teeth were unloaded. In the other three experimental groups, continuous force was applied in the 1st week (group 2), 2nd week (group 3) and 4th week (group 4) after auto-transplantation, respectively. The dogs were sacrificed in the 8th week. The mRNA expressions of Asporin,BMP-2 and ALP were examined by real time PCR. The expression of periodontal ligament associated protein-1 (PLAP-1) was examined by Western blotting. The data were statistically analyzed using SPSS 17.0 and one-way analysis of variance (ANOVA).</p><p><b>RESULTS</b>In group 3, the expression of Asporin mRNA (2.047 ± 0.281) was higher than that in the other three groups, while the expression of BMP-2 (1.358 ± 0.095) was lower than that in group 2 and control group (P < 0.05). The expression of PLAP-1 (1.054 ± 0.113) in group 3 was higher than other groups, while significant difference was found between any two groups.</p><p><b>CONCLUSIONS</b>Orthodontic force could stimulate the expression of Asporin and PLAP-1. The orthodontic force applied in the 2nd week after the tooth auto-transplantation, the expression of Asporin and PLAP-1 reached the highest level.</p>

Repeatability of three-dimensional measurements based on cone-beam CT images / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the repeatability of three-dimensional (3-D) cephalometric measurements for the clinical application of 3-D cephalometry.</p><p><b>METHODS</b>Forty-nine measurements that widely used in traditional cephalometric analyses were defined in 3-D cone-beam CT (CBCT) images. Three examiners identified landmarks on CBCT images of 17 subjects with normal occlusion, respectively, and 3-D measurements were exported automatically by software SimPlant. Inter-examiner reliability correlation coefficients (ICC) were obtained for all measurements.</p><p><b>RESULTS</b>Repeatability of 36 measurements was high (ICC value greater than 0.9), including SNA, SNB. Repeatability of 11 measurements was moderate (ICC value between 0.8 and 0.9), including CoL-GoL, CoL-MSP. Repeatability of 2 measurements was low (ICC value lower than 0.8), including Gn-MSP and MPR-MSP.</p><p><b>CONCLUSIONS</b>Most 3-D cephalometric measurements based on CBCT had high repeatability. However, some 3-D cephalometric measurements had limited repeatability.</p>

Bond strengths of customized titanium brackets manufactured by selective laser melting / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the bond strengths of customized titanium bracket manufactured by selective laser melting.</p><p><b>METHODS</b>Eighty human premolars which had been extracted for orthodontic purpose were collected and divided randomly (by random table) into two groups (customized bracket group and 3M bracket group, 40 molars in each group). The 35% phosphoric acid was used for etching and the brackets were bonded with 3M Unitek bonding adhesive. All bonded specimens were placed in saline for 24 hours at room temperature and were tested on DWD3050 electronic testing machine to determine the shear bond strength and tensile bond strength. After debonding, the adhesive remnant indexes (ARI) were recorded.</p><p><b>RESULTS</b>The shear bond strengths of customized brackets was 6.80 (6.20, 8.32) MPa, which was significantly lower than that of the 3M brackets [10.46 (9.72, 11.48) MPa] (Z = -3.463, P < 0.05). And the tensile bond strengths of customized brackets was (6.93 ± 1.21) MPa, which was significantly higher than that of the 3M brackets [(5.88 ± 1.23) MPa] (t = 2.81, P < 0.05). No significant difference was found in the ARI between two different kinds of the brackets.</p><p><b>CONCLUSIONS</b>The shear bond strength and tensile bond strength of both kinds of brackets were enough for clinic application.</p>

Application of side to side anastomosis between the lesser curvature of stomach and jejunum in laparoscopic Roux-en-Y gastric bypass / 中华胃肠外科杂志

<p><b>OBJECTIVE</b>To evaluate the application of side-to-side anastomosis of the lesser curvature of stomach and jejunum in laparoscopic Roux-en-Y gastric bypass (LRYGB).</p><p><b>METHODS</b>Clinical data of 29 patients with type 2 diabetes mellitus (T2DM) undergoing side to side anastomosis of the lesser curvature of stomach and jejunum in LRYGB from May 2012 to November 2012 in Department of General Surgery, Beijing Tiantan Hospital, Capital Medical University were analyzed retrospectively.</p><p><b>RESULTS</b>All the procedures were successfully completed without conversion to laparotomy. The side-to-side anastomosis of the lesser curvature of stomach and jejunum avoided the laparoscopic suture. No gastrojejunostomy anastomotic bleeding, fistula, obstruction and other complications occurred after operation and no complications of gastrojejunostomy anastomosis were found during a follow up of 1 to 7 months.</p><p><b>CONCLUSIONS</b>Side-to-side anastomosis of the lesser curvature of stomach and jejunum in LRYGB can manipulate the size of anastomosis accurately and avoid the laparoscopic suturing. It is simple and easy to learn.</p>

The effects of gastric bypass procedures on blood glucose, gastric inhibitory polypeptide and glucagon-like peptide-1 of normal glucose tolerance dogs / 中华外科杂志

<p><b>OBJECTIVE</b>To observe postoperative glucose tolerance, gastric inhibitory polypeptide (GIP) , and glucogan-like peptide-1 (GLP-1) in normal glucose level dogs after undergoing gastric bypass procedures, and to explore the mechanism of gastric bypass procedures to treat type 2 diabetes.</p><p><b>METHODS</b>The 6 dogs with normal glucose tolerance had undergone gastric bypass procedures, and measure preoperative and postoperative oral and intravenous glucose tolerance (at time points 1, 2, and 4 weeks) through changes in blood glucose, insulin, gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and measure preoperative and postoperative week 4 pancreatic tissue morphology.</p><p><b>RESULTS</b>Second weeks after operation, the fasting blood sugar was (3.58 ± 0.33) mmol/L, and significantly lower than preoperative (t = 3.571, P < 0.05). The GLP-1 level before oral glucose tolerance test (OGTT) and 30 minutes after OGTT were (0.90 ± 0.21) and (0.91 ± 0.19) pmol/L respectively, and significantly higher than preoperative (t value were -3.660 and -2.971, P < 0.05). GLP-1 levels began to decrease in the second week after surgery. After 4 weeks, the index recovered to the preoperative level. Four weeks after surgery when compared with preoperative, islet morphology, islet number (6.8 ± 0.8 and 7.1 ± 0.8 respectively) and islet cells (16.7 ± 2.5 and 16.3 ± 3.1 respectively) did not change significantly (P > 0.05).</p><p><b>CONCLUSION</b>Gastric bypass procedures could be briefly affect normal glucose tolerance in dogs' blood glucose, insulin and diabetes-related gastrointestinal hormones.</p>

Research on Chinese orthodontic specialists' subjective evaluation of orthodontic treatment outcome / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To analyze the results of multiple Chinese orthodontic specialists' subjective evaluation of orthodontic treatment outcome, to investigate the relevance of different experiment items and to explore the weight of each monomial material.</p><p><b>METHODS</b>As a randomized clinical trial, with six orthodontic treatment centers and Angle's classification being regarded as two stratification factors, it contained 108 cases with integrity data, which was random extracted from 2383 cases that received orthodontic treatment in six orthodontic treatment centers during the past five years, gathering post-treatment study casts, cephalometrics and photographs of 48 cases as the research subject. Similarly taking Angle's classification as a stratification factor, 108 cases were randomly divided into 9 groups. The randomization of sampling and grouping were both generated by a pseudo-random number generator. According to the monomial and combined subjects, 69 orthodontic specialists were regarded as the raters to rank the 12 cases in each group, and to judge whether the case was qualified.</p><p><b>RESULTS</b>Correlation analysis: the Spearman r between Post-M + C and Post-M + C + P and the Spearman r between Post-M + P and Post-M + C + P were both greater than 0.950. The Spearman r between Post-M and Post-P and the Spearman r between Post-M and Post-C were about 0.300. The Spearman r between Post-P and Post-C was 0.505. Regression analysis: the linear regression results: M + C = 0.782M + 0.308C - 0.150, M + P = 0.804M + 0.233P - 0.091, M + C + P = 0.764M + 0.243P + 0.131C - 0.291. The r(2) of above three models was greater than 0.9.</p><p><b>CONCLUSIONS</b>It was applicable to use M + C and M + P instead of M + C + P. Study casts could not replace cephalometrics or photographs when doing subjective evaluation. Cephalometrics and photographs could not substitute for each other either. In the combined materials evaluation, model accounted for the largest percentage. Based on the regression model, for the greater part, the integration of several monomial materials could replace the combined material assessment effectively.</p>

Application of integrated digital maxillodental model in computer aided design of individualized lingual brackets / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To create an integrated digital maxillodental model and to apply it in computer aided design (CAD) of individualized lingual brackets in order to align both crowns and roots without fenestration and dehiscence.</p><p><b>METHODS</b>Cone-beam computerized tomography (CBCT)-based maxillodental model and laser-scanned dental model were integrated by auto registration in 10 patients with malocclusions. The registration error was calculated automatically. Three observers tested the method independently. The inter-observer difference was investigated. An integrated model was selected randomly and the setup was created with roots and jaws in good relationship without fenestration and dehiscence. The individualized lingual brackets were designed by CAD on the setup.</p><p><b>RESULTS</b>No significant difference was found in inter observers (P > 0.05). The registration errors of maxilla and mandible were (0.144 ± 0.020) mm and (0.141 ± 0.022) mm, respectively. The digital individualized lingual brackets based on the virtual treatment in integrated digital maxillodental model were produced.</p><p><b>CONCLUSIONS</b>An integrated digital maxillodental model was created in good accuracy. By applying the integrated model, individualized lingual brackets were designed.</p>

Effect of orthodontic force on periodontal healing after autotransplantation: an experimental study / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effect of the continuous light force to the donor teeth on the periodontal healing after transplantation.</p><p><b>METHODS</b>Thirty-two maxillary and mandibular incisors in four 10-month-old male Beagle dogs were autotransplanted. The pulps were removed in all teeth. The teeth were divided into four groups, one control and three experimental groups. In control group (group 1), the teeth were unloaded. In the other three experimental groups, continuous force (0.49 N) was applied in the 1st (group 2), 2nd (group 3) and 4th (group 4) week, respectively. The dogs were sacrificed in the 8th week. The tissue blocks were demineralized and sectioned perpendicular to the long axis of the teeth. The histological analysis was made.</p><p><b>RESULTS</b>Histomophometric analysis revealed a significantly lower occurrence of replacement root resorption in the group 3 (2.1%) than in the control group (12.5%, P < 0.05). The significant lower incidence of replacement root resorption, and a higher surface and inflammatory root resorption were found in group 2 (6.3% and 68.8%) than in the control group (12.5% and 41.7%, P < 0.05). No significant difference was found between group 4 and control group (P > 0.05).</p><p><b>CONCLUSIONS</b>The orthodontic force promoted the regeneration of the periodontal ligament and prevented dentoalveolar ankylosis, whereas excessive initial force might cause root and bone resorption.</p>

Three-dimensional analysis of craniofacial growth in adolescents with normal occlusion in Beijing / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To analyze craniofacial growth three-dimensionally for adolescents with normal occlusion in Beijing.</p><p><b>METHODS</b>One hundred and twenty-six adolescents with normal occlusion were selected according to the criteria. The sample was divided into four age groups (53 within 4 years, 30 within 7 years, 27 within 10 years and 16 within 13 years). Information of growth was collected. Three-dimensional cephalometric system based on cone-bean CT was established.</p><p><b>RESULTS</b>From 4 to 13 years Co-A increased (14.55 ± 1.15) mm on average on the left and (13.66 ± 1.14) mm on the right, and Co-Gn increased (22.89 ± 1.40) mm on the left and (22.82 ± 1.38) mm on the right; and U1-NA increased (2.20 ± 0.44) mm on the left and (1.60 ± 0.46) mm on the right; and CoL-CoR and GoL-GoR increased (13.31 ± 1.21) mm and (18.59 ± 1.40) mm, and N-Me increased (18.03 ± 1.32) mm.SN-PP and SN-MPL basically remained unchanged.</p><p><b>CONCLUSIONS</b>Adolescents with normal occlusion in Beijing grew obviously in three-dimensions and developed harmoniously.</p>

A comparative study of mechanical properties of commercialized dental thermoplastic materials / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the mechanical properties of different dental optimal material selection for orthodontic appliance.</p><p><b>METHODS</b>Four commercialized thermoplastic products under different test conditions, and provide the suggestion of thermoplastic products were tested. The tear strength, elongation at break and stress relaxation of these materials were measured under different test conditions.</p><p><b>RESULTS</b>The tear strength declined after thermoforming, and rose again after 2 weeks of distilled water immersion. The elongation at break rose after thermoforming, and declined after 2 weeks of distilled water immersion. No significant changes were observed for brand A under different test conditions. Brand A showed the slowest stress relaxation of 0.0148 N/s.</p><p><b>CONCLUSIONS</b>The mechanical properties of thermoplastic materials were influenced by environmental factors. Brand A exhibited optimal comprehensive properties.</p>

Establishment of the micro-stress sensor measurement system for invisible aligner technique / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To design and build the micro-stress sensor measurement system for invisible aligner technique.</p><p><b>METHODS</b>A measurement system based on silicon-on-insulator piezoresistive stress sensor was developed. A four-point-bending based experimental apparatus was constructed to calibrate the piezoresistive coefficients of this stress sensor. A chemical-mechanical polishing process was developed for thinning the stress sensor dies. A packaging solution using flexible printed circuit to get signals out was designed.</p><p><b>RESULTS</b>The developed silicon stress sensor chip was 7.0 mm × 6.0 mm × 0.1 mm in size, and 13 sensor rosettes and 4 calibration rosettes were fabricated in one sensor. And a main testing PCB and a Lab View program were designed to carry out the automation measurement of the stress sensor. The stress state during the process was obtained through this test system. And measuered the stress of the 13 sensor unit.</p><p><b>CONCLUSIONS</b>A stress measurement system was established for measuring stress during orthodontic treatment with invisable aligner.</p>

Three-dimensional digital dental model based on micro-CT / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To establish a three-dimensional digital dental model through scanning dental impression directly with micro-CT.</p><p><b>METHODS</b>The polyvinyl siloxane (PVS) impression of the plaster model was taken and scanned with micro-CT. VGStudio MAX and Imageware softwares were used to obtain the digital dental model.</p><p><b>RESULTS</b>The three-dimensional digital model was established successfully. The scanning layer was 90 µm.</p><p><b>CONCLUSIONS</b>A new way of establishing the digital dental models could be achieved with micro-CT.</p>