Alveolar bone morphology in patients with palatally-displaced maxillary lateral incisors before and after orthodontic treatment: A cone-beam computed tomography study.

INTRODUCTION: Palatal displacement of maxillary anterior teeth is common in clinical practice. Previous studies have reported that the labial bone around palatally-displaced incisors is thinner than that around normally-placed teeth. Therefore, it is necessary to elucidate alveolar bone changes after alignment to guide orthodontic treatment. In this study, we investigated the alveolar bone changes around palatally-displaced maxillary lateral incisors before and after treatment, and the effects of extraction and age using cone-beam computed tomography. METHODS: In this retrospective study, 55 patients with unilateral palatally-displaced maxillary lateral incisors were included. Three-dimensional alveolar bone changes were measured at three levels (25%, 50% and 75% of the root length) using cone-beam computed tomography. Group comparisons were made between displaced and control teeth, extraction and non-extraction groups, and adult and minor groups. RESULTS: After orthodontic treatment, labiopalatal and palatal alveolar bone widths decreased at all measured levels. Labial alveolar bone width increased significantly at P25, but decreased at P75. Concavity decreased, while tooth-axis angle, tooth length, B-CEJ and P-CEJ increased. Changes in LB and LP at P75, B-CEJ and P-CEJ were statistically significant. After treatment, the tooth-axis angle on the PD side increased by 9.46°. The change in tooth-axis angle on the PD side was significantly smaller, and LB and LP decreased more at P75, in the extraction group. CONCLUSIONS: Compared to the control teeth, alveolar bone thickness and height for the displaced teeth decreased more significantly after treatment. Tooth extraction and age also influenced alveolar bone changes.

Quantification and visualization of the tooth extraction effects on face with spatially dense geometric morphometrics.

PURPOSE: To apply geometric morphometrics and multivariate statistics to evaluate changes of the face for female Chinese patients who underwent orthodontic treatment with different type of anchorage control. METHODS: Forty-six adult female patients were enrolled including 33 four first premolar extraction cases (17 patients with mini-implants for maximum anchorage control and 16 patients without mini-implants) and 13 non-extraction cases with minimum treatment duration of 15 months. Spatially dense correspondence was established among all the images The pre-and post-treatment average faces of the two extraction groups and the non-extraction group were generated. Partial least squares regression was used to test the statistical significance of the effects of treatment for different anchorage choice. RESULTS: The upper and lower lips were retruded significantly after treatment in the extraction groups. In the maximum anchorage control group, the temple and cheek were depressed by approximately 1 mm, and the zygomatic regions were increased in the mid-face. However, these changes were not statistically significant. In comparison, no statistically significant facial changes occurred in the non-extraction group. CONCLUSIONS: The anchorage choice and the removal of four first premolar extraction influence lip shape as well as the perioral regions. However, extraction treatment does not impact the appearance of the cheeks and temples on a statistically level, as compared to orthodontic treatment without premolar extractions. Spatially dense geometric morphometric facilitates comprehensive treatment effect quantification and visualization on the full facial changes for improving orthodontic outcome evaluation.

Subjective and objective analysis of orthodontic expert consensus on the assessment of orthodontic treatment outcomes.

OBJECTIVE: The objective of the study was to explore and validate the consensus of orthodontic experts on the assessment of orthodontic treatment outcomes based on subjective and objective analysis. MATERIALS AND METHODS: The research consisted of two parts: the exploration and verification of expert consensus. First, a sample of 108 cases randomly selected from six dental schools in China were evaluated by 69 orthodontic experts and measured by researchers based on post-treatment study casts and lateral cephalograms, respectively. Then, through statistical analysis, the objective indicators significantly correlated with experts' subjective evaluations were selected, their weights were determined, and the critical values of satisfactory, acceptable and unacceptable grades were screened. Subsequently, another sample of 72 cases were evaluated by another 36 orthodontic experts, and the subjective evaluation results were compared with the objective measurement results. RESULTS: There were six model indicators and seven cephalometric indicators being significantly correlated with the experts' subjective evaluations, including occlusal contact, overjet, midline, interproximal contact, alignment, occlusal relationship, L1/NB, ANB, SN/OP, U1/SN, LL-EP, Cm-Sn-UL and Ns-Prn-Pos, with a cumulative R2 of 0.704. In the verification part, the correlation coefficient between the 36 experts' subjective scores and objective regression scores was 0.716 (P < .001); the correlation coefficient between the 36 experts' subjective grades and objective grades was 0.757 (P < .001). CONCLUSIONS: Orthodontic experts had good consistency in the subjective evaluation of the combined records of post-treatment study casts and lateral cephalograms. The objective indicators selected from subjective and objective analysis had good reliability and validity and could further improve the existing occlusal indices.

Accuracy of integration of dental cast and cephalograms compared with cone-beam computed tomography: a comparative study.

This study proposes a method that integrates maxillary dental cast and cephalograms and evaluates its accuracy compared with cone-beam computed tomography (CBCT) scans. The study sample comprised 20 adult patients with records of dental casts, cephalograms, and craniofacial CBCT scans. The maxillary dental cast was integrated with lateral and frontal cephalograms based on best-fit registration of palatal and dental outline curves from dental cast with cephalogram tracings. Linear measurement was conducted to assess the intra- and inter-examiner reproducibility of the proposed integration method using intraclass correlation coefficients; linear and angular measurements were conducted to assess its accuracy with CBCT scans as a standard reference. Paired t test, one sample t test, and mean ± standard deviation of the absolute value of difference were used to compare the integrated images and CBCT. The integration method showed good intra- and inter-examiner reproducibility (intraclass correlation coefficients > 0.98). The differences in linear and angular measurements between the integrated images and CBCT were not statistically significant but with a large deviation. When absolute value of difference was computed, the linear distance error was 0.51 ± 0.34 mm, the tooth point coordinate errors in X, Y and Z axes were 0.22 ± 0.22, 0.38 ± 0.32 and 0.21 ± 0.21 mm, respectively; the angular error in pitch, roll and yaw of the dental cast was 0.82 ± 0.51, 0.92 ± 0.59 and 0.80 ± 0.41 degree, respectively. The proposed method for integration of dental cast and cephalograms showed good reproducibility and acceptable accuracy compared with CBCT. It could be helpful for researchers to study three-dimensional tooth growth changes using the existing craniofacial growth data especially cephalograms.

Early and 1-year postsurgical stability and its factors in patients with complicated skeletal Class â ¢ malocclusion treated by conventional and surgery-first approach: A prospective cohort study.

INTRODUCTION: This study aimed to compare postsurgical stability between conventional (CSA) and surgery-first (SFA) approaches and investigate its prognostic factors in patients with a skeletal Class Ⅲ extraction. METHODS: Twenty and 19 patients treated with LeFort I osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) with premolar extraction were enrolled in SFA and CSA groups, respectively. Serial cone-beam computed tomography images obtained before surgery, immediately after surgery (T1), 3 months after surgery, and 12 months after surgery were used for 3-dimensional quantitative analysis. The condyle was segmented for analyzing volumetric changes. Repeated measures analysis of variance, independent t test, and chi-square test were used to compare time-course and intergroup differences. Pearson and Kendall correlation and multivariate linear regression analyses were used to explore prognostic factors affecting skeletal stability. RESULTS: In both CSA and SFA, postsurgical relapse mainly occurred in the mandible sagittal and vertical dimensions and during the first 3 months after surgery. Stability in SFA was significantly less than that in CSA. Intraoperatively, inferolateral condylar displacement with proximal segment inwards, clockwise rotation, and return movements after surgery were observed regardless of the treatment approach. The condylar volume remained stable over time. Multivariate regression analysis showed that posterior vertical dimension (VD) at T1 (-1.63 mm), surgical amount of mandibular setback (-10.33 mm), surgical condylar downwards displacement (-1.28 mm), and anterior overjet at T1 (6.43 mm) were the most important predictors of early mandibular relapse (r2 = 0.593). CONCLUSIONS: The risk of early relapse could be reduced by controlling the anterior, middle, and posterior constraints provided by the prediction model.

Natural reference structures for three-dimensional maxillary regional superimposition in growing patients.

BACKGROUND: Assessment of growth-related or treatment-related changes in the maxilla requires a reliable method of superimposition. Such methods are well established for two-dimensional (2D) cephalometric images but not yet for three-dimensions (3D). The aims of this study were to identify natural reference structures (NRS) for the maxilla in growing patients in 3D, opportunistically using orthodontic mini-screws as reference; and to test the applicability of the proposed NRS for maxillary superimposition by assessing the concordance of this approach with Björk's 'stable reference structures' in lateral projection. METHODS: The stability of the mini-screws was tested on longitudinal pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images by measuring the distance changes between screws. After verifying the stability of the mini-screws, rigid registration was performed for aligning the stable mini-screws. Then, non-rigid registration was used to establish the dense voxel-correspondence among CBCT images and calculate the displacement of each voxel belonging to the maxilla relative to the mini-screws. The displacement vectors were transformed to a standardized maxillary template to categorize the stability of the internal structures statistically. Those voxels that displaced less relative to the mini-screws were considered as the natural reference structures (NRS) for the maxilla. Test samples included another dataset of longitudinal CBCT scans. They were used to evaluate the applicability of the proposed NRS for maxillary superimposition. We assessed whether aligning the maxilla with proposed NRS is in concordance with the maxillary internal reference structures superimposition in the traditional 2D lateral view as suggested by Björk. This was quantitively assessed by comparing the mean sagittal and vertical tooth movements for both superimposition methods. RESULTS: The stability of the mini-screws was tested on 10 pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images (T1: 12.9 ± 0.8 yrs, T2: 14.8 ± 0.7 yrs). Both the loaded and the unloaded mini-screws were shown to be stable during orthodontic treatment, which indicates that they can be used as reference points. By analyzing the deformation map of the maxilla, we confirmed that the infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than  1 cm distal to incisor foramen except the palatal suture) were stable during growth. Another dataset of longitudinal CBCT scans (T1: 12.2 ± 0.63 yrs, T2: 15.2 ± 0.96 yrs) was used to assess the concordance of this approach with Björk's 'stable reference structures'. The movement of the maxillary first molar and central incisor showed no statistically significant difference when superimposing the test images with the proposed NRS or with the classic Björk maxillary superimposition in the lateral view. CONCLUSIONS: The infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than 1 cm posterior to incisal foramen except the palatal suture) were identified as stable regions in the maxilla. These stable structures can be used for maxillary superimposition in 3D and generate comparable results to Björk superimposition in the lateral view.

Nasal characteristics in patients with asymmetric mandibular prognathism.

INTRODUCTION: To objectively quantify nasal characteristics of patients with asymmetric mandibular prognathism and to evaluate the association between nasal asymmetry and dentofacial abnormalities. METHODS: Ninety adult patients with asymmetric mandibular prognathism were included. Images were captured during pretreatment using 3-dimensional stereophotogrammetry. A total of 7160 uniformly sampled quasi-landmarks were automatically identified on each facial image to establish correspondence using a template mapping technique. Fifteen commonly used anatomic landmarks were automatically located on each image through barycentric to Cartesian coordinate conversion. Nasal characteristics and asymmetry were quantified by anthropometric linear distances, angular measurements, and surface-based analysis. The degree of the nasal, chin, and periorbital asymmetry in a patient was scored using a root-mean-squared error between the left and right sides. The correlations among these regional asymmetries were evaluated. RESULTS: The nasal tip was significantly shifted to the deviated side of the chin, and the nostrils were asymmetrical. The location and degree of nasal asymmetry varied among patients with asymmetric mandibular prognathism. The level of nasal asymmetry was significantly and positively correlated with chin and periorbital asymmetry. CONCLUSIONS: Nasal asymmetry is present in asymmetric mandibular prognathism patients. Furthermore, it is positively associated with periorbital deviation and chin deviation. Individualized nasal asymmetry evaluation should be performed, and clinicians should inform patients about preexisting nasal asymmetry.

Automated assessment of mandibular shape asymmetry in 3-dimensions.

INTRODUCTION: This study aimed to develop an automatic pipeline for analyzing mandibular shape asymmetry in 3-dimensions. METHODS: Forty patients with skeletal Class I pattern and 80 patients with skeletal Class III pattern were used. The mandible was automatically segmented from the cone-beam computed tomography images using a U-net deep learning network. A total of 17,415 uniformly sampled quasi-landmarks were automatically identified on the mandibular surface via a template mapping technique. After alignment with the robust Procrustes superimposition, the pointwise surface-to-surface distance between original and reflected mandibles was visualized in a color-coded map, indicating the location of asymmetry. The degree of overall mandibular asymmetry and the asymmetry of subskeletal units were scored using the root-mean-squared-error between the left and right sides. These asymmetry parameters were compared between the skeletal Class I and skeletal Class III groups. RESULTS: The mandible shape was significantly more asymmetrical in patients with skeletal Class III pattern with positional asymmetry. The condyles were identified as the most asymmetric region in all groups, followed by the coronoid process and the ramus. CONCLUSIONS: This automated approach to quantify mandibular shape asymmetry will facilitate high-throughput image processing for big data analysis. The spatially-dense landmarks allow for evaluating mandibular asymmetry over the entire surface, which overcomes the information loss inherent in conventional linear distance or angular measurements. Precise quantification of the asymmetry can provide important information for individualized diagnosis and treatment planning in orthodontics and orthognathic surgery.

Facial asymmetry assessment in skeletal Class III patients with spatially-dense geometric morphometrics.

OBJECTIVE: Quantification and visualization of the location and magnitude of facial asymmetry is important for diagnosis and treatment planning. The objective of this study was to analyze the asymmetric features of the face for skeletal Class III patients using spatially-dense geometric morphometrics. METHODS: Three-dimensional facial images were obtained for 86 skeletal Class III patients. About 7160 uniformly sampled quasi-landmarks were automatically identified on each face using template mapping technique. The pointwise surface-to-surface distance between original and mirror face was measured and visualized for the whole face after robust Procrustes superimposition. The degree of overall asymmetry in an individual was scored using a root-mean-squared-error. Automatic partitioning of the face was obtained, and the severity of the asymmetry compared among seven facial regions. RESULTS: Facial asymmetry was mainly located on, but not limited to, the lower two-thirds of the face in skeletal Class III patients. The lower cheek and nose asymmetry were detected to have more extensive and of a greater magnitude of asymmetry than other facial anatomical regions but with various individual variations. The overall facial asymmetry index and the regional facial asymmetry indices were higher in males and patients with chin deviation. CONCLUSIONS: Soft tissue asymmetry is predominately presented in the lower-third of the face in skeletal Class III patients and with various variations on other facial anatomical regions. Morphometric techniques and computer intensive analysis have allowed sophisticated quantification and visualization of the pointwise asymmetry on the full face.

Automated landmarking for palatal shape analysis using geometric deep learning.

OBJECTIVES: To develop and evaluate a geometric deep-learning network to automatically place seven palatal landmarks on digitized maxillary dental casts. SETTINGS AND SAMPLE POPULATION: The sample comprised individuals with permanent dentition of various ethnicities. The network was trained from manual landmark annotations on 732 dental casts and evaluated on 104 dental casts. MATERIALS AND METHODS: A geometric deep-learning network was developed to hierarchically learn features from point-clouds representing the 3D surface of each cast. These features predict the locations of seven palatal landmarks. RESULTS: Repeat-measurement reliability was <0.3 mm for all landmarks on all casts. Accuracy is promising. The proportion of test subjects with errors less than 2 mm was between 0.93 and 0.68, depending on the landmark. Unusually shaped and large palates generate the highest errors. There was no evidence for a difference in mean palatal shape estimated from manual compared to the automatic landmarking. The automatic landmarking reduces sample variation around the mean and reduces measurements of palatal size. CONCLUSIONS: The automatic landmarking method shows excellent repeatability and promising accuracy, which can streamline patient assessment and research studies. However, landmark indications should be subject to visual quality control.

Exploring palatal and dental shape variation with 3D shape analysis and geometric deep learning.

OBJECTIVES: Palatal shape contains a lot of information that is of clinical interest. Moreover, palatal shape analysis can be used to guide or evaluate orthodontic treatments. A statistical shape model (SSM) is a tool that, by means of dimensionality reduction, aims at compactly modeling the variance of complex shapes for efficient analysis. In this report, we evaluate several competing approaches to constructing SSMs for the human palate. SETTING AND SAMPLE POPULATION: This study used a sample comprising digitized 3D maxillary dental casts from 1,324 individuals. MATERIALS AND METHODS: Principal component analysis (PCA) and autoencoders (AE) are popular approaches to construct SSMs. PCA is a dimension reduction technique that provides a compact description of shapes by uncorrelated variables. AEs are situated in the field of deep learning and provide a non-linear framework for dimension reduction. This work introduces the singular autoencoder (SAE), a hybrid approach that combines the most important properties of PCA and AEs. We assess the performance of the SAE using standard evaluation tools for SSMs, including accuracy, generalization, and specificity. RESULTS: We found that the SAE obtains equivalent results to PCA and AEs for all evaluation metrics. SAE scores were found to be uncorrelated and provided an optimally compact representation of the shapes. CONCLUSION: We conclude that the SAE is a promising tool for 3D palatal shape analysis, which effectively combines the power of PCA with the flexibility of deep learning. This opens future AI driven applications of shape analysis in orthodontics and other related clinical disciplines.

Comparison of achieved and predicted crown movement in adults after 4 first premolar extraction treatment with Invisalign.

INTRODUCTION: In this study, we compared achieved and predicted crown movements of maxillary and mandibular first molars, canines, and central incisors in adults after 4 first premolar extraction treatment with Invisalign. METHODS: Seventeen adult patients who received 4 first premolar extraction treatment with Invisalign and completed the first series of aligners were included. Superimposition of pretreatment and actual posttreatment dental models was acquired using registrations of pretreatment and posttreatment craniofacial models on the basis of bone surfaces and registrations of craniofacial and dental models on the basis of dental crown surfaces, respectively. Superimposition of pretreatment and predicted posttreatment models was acquired from ClinCheck software. Achieved and predicted 3-dimensional crown movements of maxillary and mandibular first molars, canines, and central incisors were then compared using the paired t test. RESULTS: Relative to predicted changes, first molars achieved greater mesial displacement, mesial tipping, and buccal inclination in both the maxilla and mandible, greater intrusion in the maxilla, and greater mesial-lingual rotation and less constriction in the mandible. Canines achieved greater distal tipping in both the maxilla and mandible, less retraction in the maxilla, and greater lingual inclination and extrusion in the mandible. Central incisors achieved greater distal tipping and lingual inclination and extrusion in both the maxilla and mandible and less retraction in the maxilla. CONCLUSIONS: Tooth crown movements were not fully achieved as predicted following Invisalign treatment. Differences focused on mesial tipping, buccal inclination, mesial displacement, and intrusion of the first molars, as well as distal tipping, lingual inclination, insufficient retraction, and intrusion of the canines and central incisors.

Measuring orthodontic treatment impact: Description or judgment, challenge or result.

INTRODUCTION: Determination of improvement in orthodontic treatment may depend on the measurement method used and the purpose. METHODS: Improvement after orthodontic treatment (from T1 to T2 [beginning to end of treatment]) was assessed 3 ways from a set of 98 patient records: (1) calculated by subtracting judges' assessments at T2 from T1 for records presented in random order, (2) judged as a holistic impression viewing T1 and T2 records side by side, and (3) determined from proxies (American Board of Orthodontics Discrepancy Index, the American Board of Orthodontics Objective Grading System, and the Peer Assessment Rating index). RESULTS: High levels of intramethod consistency were observed, with intraclass correlation coefficient clustering around an intraclass correlation coefficient of 0.900, and distributions were normal. Calculated and judged improvements correlated at r = 0.606. Calculated or judged improvements were correlated at a lower level with proxies. Calculated improvement was significantly associated with "challenge" (T1) scores and judged improvement associated with "results" (T2) scores. Common method bias was observed, with higher correlations among similar indexes than among indexes at the same time that used various methods. Relative to differences in Peer Assessment Rating scores, calculated improvement overestimated low scores and underestimated high ones. The same effect, but statistically greater, was observed using direct judgment of improvement. CONCLUSIONS: These findings are consistent with decision science and measurement theory. In some circumstances, such as third-party reimbursement and research, operationally defined measures of occlusion are appropriate. In practice, the determination of occlusion and improvement are best performed by judgment that naturally corrects for biases in proxies and incorporates background information.

Analysis of correlation of 3-dimensional lip vermilion morphology and dentoskeletal forms in young Chinese adults on the basis of sex and skeletal patterns.

INTRODUCTION: The objective of this research was to evaluate the correlation between 3-dimensional (3D) lip vermilion (LV) morphology and skeletal patterns as well as incisor measurements in young Chinese adults. METHODS: In all, 240 young adults were enrolled; these included 80 patients each with skeletal Class I, Class II, and Class III malocclusions, respectively. Each sagittal skeletal pattern included 40 male and 40 female subjects. Twenty-two 3D LV measurements were obtained from 3D facial scans. Skeletal and incisor measurements were evaluated on lateral cephalograms. Correlation and regression analysis were performed between soft and hard tissue measurements. RESULTS: Six of 22 LV measurements showed significant differences between male and female subjects. The 3D LV morphology showed significant differences with respect to different skeletal patterns and sex. Adults with skeletal Class III malocclusion tended to have thinner upper vermilion and fuller lower vermilion than subjects with skeletal Class II and III malocclusion. The mandibular plane angle negatively correlated with the upper-lower vermilion midsagittal curve length and surface area ratio in adults with skeletal Class I and II malocclusion, yet the vertical facial skeletal type showed no correlation in adults with skeletal Class III malocclusion. The vermilion angle, central bow angle, vermilion height, vermilion midsagittal curve length, vermilion height and width ratio, and vermilion surface area showed a significant correlation with incisor measurements. Regression analysis found that the ANB angle was an important factor affecting the upper and lower vermilion midsagittal curve length and surface area ratio. Further, the vermilion height and height and width ratio were closely correlated with the interincisal (U1/L1) angle, whereas the central bow angle was closely correlated with the maxillary incisor torque. CONCLUSIONS: Most LV morphology variables were correlated to skeletal patterns and incisor measurements. Skeletal Class III malocclusion showed significant differences in vermilion morphology. Both the sagittal and vertical skeletal pattern have effects on vermilion proportion. The incisor torque was closely correlated to vermilion shape and central bow angle and might influence the vermilion esthetics. However, the proportion of the upper and lower vermilion was mainly affected by the ANB angle.

PASS versus MBT™ for evaluation of anchorage control in three-dimensional measurements: a randomized controlled trial.

BACKGROUND: Growth and development might lead to anchorage loss during orthodontic treatment, such as the mesial drift of molars, the compensation characteristics of upper molars following mandibular growth, or the angulation of molars before treatment. Different anchorage reinforcement devices have been developed to prevent mechanical anchorage loss, but the anchorage loss resulting from physiological factors should also be taken into account. OBJECTIVE: To explore the efficacy of a new strategy to control physiologic anchorage compared with that of the conventional straight-wire appliance. TRIAL DESIGN: Randomized controlled trial (RCT). METHODS: Participants of Han ethnicity were randomized into the physiologic anchorage spee-wire system (PASS) group or McLaughlin-Bennett-Trevisi (MBT™) straight-wire group by minimization random allocation. The eligibility criteria were patients with a Class I or II molar relationship, permanent dentition (11-35 years old), fixed appliances involving the extraction of at least two upper first premolars, and medium or maximum anchorage requirements. Pre-treatment and post-treatment dental casts were scanned into digital casts and measured using a blinded method. Mesial displacements of the upper first molars were considered as the primary outcome for evaluating anchorage control. Measurements were taken for subgroups based on age. RESULTS: Data from 60 participants were analysed. The baseline characteristics were not significantly different between groups. Mesial displacement of the upper first molar (in mm) was 2.96 ± 1.52 in the PASS group and 2.70 ± 1.66 in the MBT group (P = 0.521). The variation in incisor torque was -6.94 ± 6.35 degree in the PASS group and -11.76 ± 7.65 degree in the MBT group (P = 0. 010). The incisor retraction (in mm) was 4.24 ± 1.99 and 5.67 ± 2.27 in the PASS and MBT groups, respectively (P = 0.012). Adverse effects were not documented in any patient. LIMITATION: The study was a single-centre study. CONCLUSIONS: Compared with the MBT group, the PASS group without additional anchorage devices could attain well anchorage control by considering the dentoalveolar compensation of anchor teeth. REGISTRATION: This RCT was registered at the Chinese Clinical Trial Registry (Chictr.org.cn) ChiCTR-TRC-13003260.

Evaluation of the Relationship Between Maxillary Sinus Wall and Maxillary Canines and Posterior Teeth Using Cone-Beam Computed Tomography.

BACKGROUND The proximity between the maxillary sinus and dental roots may impede orthodontic tooth movement. This study aimed to explore the relationship between the maxillary sinus wall (MSW) and maxillary canines and posterior teeth using cone-beam computed tomography (CBCT). MATERIAL AND METHODS CBCT images (317) were examined for whether the mesial, distal, buccal, and palatal surfaces of the examined root contacted the MSW, and the contact distance of each root surface with the MSW was measured. The effects of age and sex were analyzed using logistic regression and linear regression analyses. RESULTS The highest contact ratios with the MSW (ranging from 62.0% to 73.2%) were observed at the palatal root surfaces of the first molar mesiobuccal and distobuccal roots (1M MB and DB), the buccal root surface of the first molar palatal roots (1M P), and the mesial and buccal root surfaces of the second molars (2M), followed by the distal root surface of the second premolars (2PM) and the mesial root surfaces of the 1M MB and P (ranging from 49.2% to 59.3%). At these root surfaces, the contact ratios decreased with age (P<0.05), but the lowest still reached a range of 29.4% to 57.9% in the 30- to 47-year-old group. CONCLUSIONS The 2PM distal root surface, the 1M MB mesial and palatal root surfaces, the 1M DB palatal root surface, and the 1M P and 2M mesial and buccal root surfaces most frequently contacted the MSW. Clinicians should observe the contact of root surfaces with the MSW, even in aged patients.

The application and accuracy of feature matching on automated cephalometric superimposition.

BACKGROUND: The aim of this study was to establish a computer-aided automated method for cephalometric superimposition and to evaluate the accuracy of this method based on free-hand tracing. METHODS: Twenty-eight pairs of pre-treatment (T1) and post-treatment (T2) cephalograms were selected. Structural superimpositions of the anterior cranial base, maxilla and mandible were independently completed by three operators performing traditional hand tracing methods and by computerized automation using the feature matching algorithm. To quantitatively evaluate the differences between the two methods, the hand superimposed patterns were digitized. After automated and hand superimposition of T2 cephalograms to T1 cephalometric templates, landmark distances between paired automated and hand T2 cephalometric landmarks were measured. Differences in hand superimposition among the operators were also calculated. RESULTS: The T2 landmark differences in hand tracing between the operators ranged from 0.61 mm to 1.65 mm for the three types of superimposition. There were no significant differences in accuracy between hand and automated superimposition (p > 0.05). CONCLUSIONS: Computer-aided cephalometric superimposition provides comparably accurate results to those of traditional hand tracing and will provide a powerful tool for academic research.

Thickness change of masseter muscles and the surrounding soft tissues in female patients during orthodontic treatment: a retrospective study.

BACKGROUND: Facial esthetics is a major concern of orthodontic patients. This study aims to evaluate orthodontic treatment-related thickness changes of the masseter muscles and surrounding soft tissues and the potential factors that would influence these changes during orthodontic treatment in female adults. METHODS: Forty-two female adult patients were included in this retrospective study and were divided into extraction (n = 22) and nonextraction (n = 20) groups. Pretreatment and posttreatment cone-beam computed tomography (CBCT) images were superimposed and reconstructed. The thickness changes of the masseter area of facial soft tissue (MAS), masseter muscles (MM) and surrounding fat tissue (FT) were measured. Pretreatment age, treatment duration, sagittal relationship (ANB), and vertical relationship (Frankfort-mandibular plane angle, FMA)-related MAS, MM and FT changes were compared between extraction and nonextraction groups. Spearman's correlation coefficient was calculated between the above variables. Regression analysis was conducted to confirm the causal relations of the variables. RESULTS: The thickness of MAS and MM significantly decreased in both groups, with larger decreases (> 1 mm) in the extraction group. There were strong correlations (r > 0.7) between the thickness decrease in MAS and MM in both groups and moderate correlations (r > 0.4) between MAS and FT in the nonextraction group. A significantly greater decrease of MAS and MM were found to be moderately correlated with a smaller FMA (r > 0.4) in the extraction group. Scatter plots and regression analysis confirmed these correlations. CONCLUSIONS: Masseter muscles and the surrounding soft tissue exhibited a significant decrease in thickness during orthodontic treatment in female adults. Low-angle patients experienced a greater decrease in soft tissue thickness in the masseter area in the extraction case. But the thickness changes were clinically very small in most patients.

The three-dimensional stable mandibular landmarks in patients between the ages of 12.5 and 17.1 years.

BACKGROUND: With the aid of implants, Björk identified two-dimensional mandibular stable structures in cephalograms during facial growth. However, we do not know what the three-dimensional stable structures are with certainty. The purpose of this study was to identify the most stable mandibular landmarks in growing patients using three-dimensional images. METHODS: The sample was comprised of two cone-beam computed tomography (CBCT) scans taken about 4.6 years apart in 20 growing patients between the ages of 12.5 (T1) and 17.1 years (T2). After head orientation, landmarks were located on the chin (Pog), internal symphysis (Points C, D and E), and mandibular canals, which included the mental foramina (MF and MFA) and mandibular foramina (MdF). The linear distance change between Point C and these landmarks was measured on each CBCT to test stability through time. The reliability of the suggested stable landmarks was also evaluated. RESULTS: The total distance changes between Point C and points D, E, Pog, MF, and MFA were all less than 1.0 mm from T1 to T2. The reliability measures of these landmarks, which were measured by the Cronbach alpha, were above 0.94 in all three dimensions for each landmark. From T1 to T2, the distance changes from Point C to the right and left mandibular foramina were 3.39 ± 3.29 mm and 3.03 ± 2.83 mm, respectively. CONCLUSIONS: During a growth period that averaged 4.6 years, ranging from 11.2 to 19.8 years old, the structures that appeared relatively stable and could be used in mandibular regional superimpositions included Pog, landmarks on the inferior part of the internal symphysis, and the mental foramen. The centers of the mandibular foramina and the starting points of the mandibular canal underwent significant changes in the transverse and sagittal dimensions.

3D assessment of mandibular skeletal effects produced by the Herbst appliance.

BACKGROUND: A functional appliance is commonly used to optimize the development of the facial skeleton in the treatment of Class II malocclusion. Recent three-dimensional(3D) image-based analysis offers numerous advantages in quantitative measurement and visualization in orthodontics. The aim of this study was to localize in 3D the skeletal effect produced by the Herbst appliance on the mandible using the geometric morphometric technique. METHODS: Twenty patients treated with a Herbst appliance and subsequent fixed appliances were included. Cone-beam computed tomography (CBCT) images were taken before treatment (T1), 8 weeks after Herbst appliance removal (T2), and after subsequent fixed appliance treatment (T3). Spatially dense morphometric techniques were used to establish the corresponding points of the mandible. The mandibular morphological changes from T1-T2, T2-T3, and T1-T3 were calculated for each patient by superimposing two mandibular models at two time points with robust Procrustes superimposition. These changes were then compared to the morphological changes estimated from normative mandibular growth curves over the same period. The proportion of cases exceeding the growth expression for controls was compared to a normal population using a one tailed binomial test. RESULTS: Approximately 1.5-2 mm greater condylar changes and 0.5 mm greater changes in the chin occurred from Tl to T2. This effect lasted until the completion of treatment (T1-T3), but there was no obvious skeletal effect during the orthodontic phase (T2-T3). Approximately 40-50% of the patient sample exceeded condylar growth by > 1.5 mm compared to untreated controls (p < .05). However, changes at the chin were not statistically significant. CONCLUSIONS: The principal skeletal effect of Herbst appliance treatment was additional increase in condylar length for about half of the sample. This inconsistency may relate to the degree of mandibular growth suppression associated with a specific malocclusion.