Evaluation of root position during orthodontic treatment via multiple intraoral scans with automated registration technology.

INTRODUCTION: This study aimed to introduce a method for dynamically monitoring root position with intraoral scans using automated crown registration and root segmentation with artificial intelligence technology and to evaluate its accuracy using a novel semiautomatic root apical distance measurement procedure. METHODS: The sample consisted of 412 teeth from 16 patients whose intraoral scans and cone-beam computed tomography (CBCT) were obtained before and after treatment. Crowns from intraoral scans and roots segmented from CBCT with artificial intelligence technology before treatment were registered, integrated, and divided into individual teeth. With an automated registration program, the virtual root was constructed by crown registration before and after treatment. The distance deviation of the root position at the apex between the virtual root and the actual root, which served as a control, was measured and decomposed into the distance deviation in the mesiodistal and buccolingual directions. RESULTS: The shell deviation of crown registration between CBCT and oral scan before treatment was 0.19 ± 0.04 mm and 0.22 ± 0.04 mm in the maxilla and mandible, respectively. The apical root position distance deviations were 0.27 ± 0.12 mm in the maxilla and 0.31 ± 0.11 mm in the mandible. There was no significant difference between root position in mesiodistal and buccolingual directions. CONCLUSIONS: Applying automated crown registration and root segmentation with artificial intelligence technology in this study improved the accuracy and efficiency of monitoring root position. In addition, the innovative semiautomatic distance measurement procedure can more precisely distinguish the root position discrepancy.

Microcracks on the Rat Root Surface Induced by Orthodontic Force, Crack Extension Simulation, and Proteomics Study.

Root resorption is a common complication during orthodontic treatment. Microcracks occur on the root surface after an orthodontic force is applied and may be related to the root resorption caused by the orthodontic process. However, the mechanisms underlying root resorption induced by microcracks remain unclear. In this study, a rat orthodontic model was used to investigate the biological mechanisms of root resorption caused by microcracks. First, the first molar was loaded with 0.5-N orthodontic force for 7 days, and microcracks were observed on the root apex surface using a scanning electron microscope. Second, to describe the mechanical principle resulting in microcracks, a finite element model of rat orthodontics was established, which showed that a maximum stress on the root apex can cause microcrack extension. Third, after 7 days of loading in vivo, histological observation revealed that root resorption occurred in the stress concentration area and cementoclasts appeared in the resorption cavity. Finally, proteomics analysis of the root apex area, excluding the periodontal ligament, revealed that the NOX2, Aifm1, and MAPK signaling pathways were involved in the root resorption process. Microcrack extension on the root surface increases calcium ion concentrations, alters the proteins related to root resorption, and promotes cementoclast formation.

Biomechanical effects of corticotomy facilitated orthodontic anterior retraction: a 3-dimensional finite element analysis.

The objective of this study was to assess the biomechanical effects of different corticotomy designs used for orthodontic anterior retraction through finite element analysis. MATERIALS AND METHODS: A basic finite element model simulating retraction of anterior teeth was built reversely from CBCT films of an adult patient with protruded maxillary anterior teeth. Another thirteen FE models were created according to different corticotomy designs varied with site width and the extent of incision. The initial displacement, Von Mises stress and pressure stress of dento-alveolar structures was computerized and analyzed. RESULTS: Corticotomy can increase the initial displacement of anterior segment including teeth and surrounding alveolar bone, change the distribution of Von Mises stress in cancellous bone and the pressure stress in periodontal ligament of anterior teeth. When the incision was near the periphery of apical, the anterior segment showed the greatest displacement, the cancellous bone at either sockets or incision region showed the maximum stress. Bilateral incision combined with palatal incision showed approximate initial displacement and stress distribution with circumscribing incision. While the incision width increased, the biomechanical effects of corticotomy amplified. CONCLUSIONS: Varied corticotomy designs can change the biomechanical effects on dento-alveolar structures. The incision near the periphery of apical and bilateral incision combined with palatal incision may be the optimized design used for retraction of anterior teeth.

High-efficiency treatment with the use of traditional anchorage control for a patient with Class II malocclusion and severe overjet.

Patients with Class II malocclusion and severe overjet are often dissatisfied with their facial disharmony. Although temporary skeletal anchorage devices (TSADs) are now widely used in orthodontic treatment, traditional anchorage devices should not be overlooked as a treatment option. Proper design of traditional anchorage can achieve 3-dimensional control of incisors and molars as efficiently as TSADs in some patients with severe malocclusion. We used traditional anchorage devices, including a transpalatal arch and a Nance palatal arch, combined with a utility arch to treat an 11-year-old Chinese girl with a skeletal Class II malocclusion and severe overjet. The space was closed in 2 steps to protect molar anchorage. Facial improvement, especially smile esthetics, and Class I molar relationship and overjet correction were achieved in 17 months of treatment. Follow-up records 22 months after treatment show that the results remained stable.

A Novel Method to Quantify Longitudinal Orthodontic Bone Changes with In Vivo Micro-CT Data.

Orthodontic tooth movement (OTM) is the result of region-specific bone modeling under a load. Quantification of this change in the alveolar bone around a tooth is a basic requirement to understand the mechanism of orthodontics. The purpose of this study was to quantify subregional alveolar bone changes during orthodontic tooth movement with a novel method. In this study, 12 Sprague-Dawley (SD) rats were used as an orthodontic model, and one side of the first upper molar was used to simulate OTM. The alveolar bone around the mesial root was reconstructed from in vivo micro-CT images and separated from other parts of the alveolar bone with two semicylinder filters. The amount and rate of OTM, bone mineral density (BMD), and bone volume (BV) around the root were calculated and compared at 5 time points. The results showed that the amount of tooth movement, BMD, and BV can be evaluated dynamically with this method. The molar moved fastest during the first 3 days, and the rate decreased after day 14. BMD decreased from day 0 to day 14 and returned from day 14 to day 28. BV deceased from day 0 to day 7 and from day 14 to day 28. The method created in this study can be used to accurately quantify dynamic alveolar bone changes during OTM.

Biomechanical Effects of Various Bone-Implant Interfaces on the Stability of Orthodontic Miniscrews: A Finite Element Study.

INTRODUCTION: Osseointegration is required for prosthetic implant, but the various bone-implant interfaces of orthodontic miniscrews would be a great interest for the orthodontist. There is no clear consensus regarding the minimum amount of bone-implant osseointegration required for a stable miniscrew. The objective of this study was to investigate the influence of different bone-implant interfaces on the miniscrew and its surrounding tissue. METHODS: Using finite element analysis, an advanced approach representing the bone-implant interface is adopted herein, and different degrees of bone-implant osseointegration were implemented in the FE models. A total of 26 different FE analyses were performed. The stress/strain patterns were calculated and compared, and the displacement of miniscrews was also evaluated. RESULTS: The stress/strain distributions are changing with the various bone-implant interfaces. In the scenario of 0% osseointegration, a rather homogeneous distribution was predicted. After 15% osseointegration, the stress/strains were gradually concentrated on the cortical bone region. The miniscrew experienced the largest displacement under the no osseointegra condition. The maximum displacement decreases sharply from 0% to 3% and tends to become stable. CONCLUSION: From a biomechanical perspective, it can be suggested that orthodontic loading could be applied on miniscrews after about 15% osseointegration without any loss of stability.

Three-dimensional quantification of orthodontic root resorption with time-lapsed imaging of micro-computed tomography in a rodent model.

OBJECTIVE: Despite various X-ray approaches have been widely used to monitor root resorption after orthodontic treatment, a non-invasive and accurate method is highly desirable for long-term follow up. The aim of this study was to build a non-invasive method to quantify longitudinal orthodontic root resorption with time-lapsed images of micro-computed tomography (micro-CT) in a rodent model. MATERIALS AND METHODS: Twenty male Sprague Dawley (SD) rats (aged 6-8 weeks, weighing 180-220 g) were used in this study. A 25 g orthodontic force generated by nickel-titanium coil spring was applied to the right maxillary first molar for each rat, while contralateral first molar was severed as a control. Micro-CT scan was performed at day 0 (before orthodontic load) and days 3, 7, 14, and 28 after orthodontic load. Resorption of mesial root of maxillary first molars at bilateral sides was calculated from micro-CT images with registration algorithm via reconstruction, superimposition and partition operations. RESULTS: Obvious resorption of mesial root of maxillary first molar can be detected at day 14 and day 28 at orthodontic side. Most of the resorption occurred in the apical region at distal side and cervical region at mesiolingual side. Desirable development of molar root of rats was identified from day 0 to day 28 at control side. The development of root concentrated on apical region. CONCLUSIONS: This non-invasive 3D quantification method with registration algorithm can be used in longitudinal study of root resorption. Obvious root resorption in rat molar can be observed three-dimensionally at day 14 and day 28 after orthodontic load. This indicates that registration algorithm combined with time-lapsed images provides clinic potential application in detection and quantification of root contour.

Biomechanical effects of corticotomy approaches on dentoalveolar structures during canine retraction: A 3-dimensional finite element analysis.

INTRODUCTION: Corticotomy has proven to be effective in facilitating orthodontic tooth movement. There is, however, no relevant study to compare the biomechanical effects of different corticotomy approaches on tooth movement. In this study, a series of corticotomy approaches was designed, and their impacts on dentoalveolar structures were evaluated during maxillary canine retraction with a 3-dimensional finite element method. METHODS: A basic 3-dimensional finite element model was constructed to simulate orthodontic retraction of the maxillary canines after extraction of the first premolars. Twenty-four corticotomy approach designs were simulated for variations of position and width of the corticotomy. Displacement of the canine, von Mises stresses in the canine root and trabecular bone, and strain in the canine periodontal ligament were calculated and compared under a distal retraction force directed to the miniscrew implants. RESULTS: A distal corticotomy cut and its combinations showed the most approximated biomechanical effects on dentoalveolar structures with a continuous circumscribing cut around the root of the canine. Mesiolabial and distopalatal cuts had a slight influence on dentoalveolar structures. Also, the effects decreased with the increase of distance between the corticotomy and the canine. No obvious alteration of displacement, von Mises stress, or strain could be observed among the models with different corticotomy widths. CONCLUSIONS: Corticotomies enable orthodontists to affect biomechanical responses of dentoalveolar structures during maxillary canine retraction. A distal corticotomy closer to the canine may be a better option in corticotomy-facilitated canine retraction.

[The relationship between sagittal upper airway size and surrounding skeletal structure with Delaire cephalometric analysis].

PURPOSE: To investigate the relationship between sagittal upper airway size and craniofacial characteristics in men with malocclusion in early permanent dentition,and to find out the factor that affect the pharyngeal airway size remarkably. METHODS: Seventy-four cephalometric films of non-snoring males with malocclusion aged from 11 to 16 years(mean 13 years) before treatment were collected and measured with Delaire cephalometric analysis,the results were assessed by SPSS13.0 software package,multiple regression analysis was used to examine the relationship between upper airway size and craniofacial characteristics variation. RESULTS: The size of nasopharyngeal space (PNS-ad) correlated negatively with the upper face height,the inclination of ramus plane,percentage of cranial height to cranial base length.The size of palatopharyngeal space(Ve-PVe) correlated negatively with the upper face height,percentage of cranial height to cranial base length.The size of hypopharyngeal space(Ph1-Ph2) correlated positively with the angle between cervical vertebrae tangent and cranial base, negatively mandibular plane angle, the length of mandibular body and percentage of cranial height to cranial base length. CONCLUSIONS: The sagittal upper airway size of non-snoring males with occlusion is significantly correlated to the craniofacial skeletal structures and head posture,the types of craniofacial growth and the skeletal structure around have remarkable effect on the upper airway space.