Cone Beam Computed Tomography in Orthodontics

Cone beam computed tomography (CBCT) is an important source of three‐dimensional volumetric data in clinical orthodontics. Due to the progress in the technology of CBCT, for orthodontic clinical diagnosis, treatment and follow‐up, CBCT supply much more reliable information compared to conventional radiography. The most justified indications for the use of CBCT in orthodontics are the existence of impacted and transposed teeth. For the management of the impacted teeth, CBCT enhances the ability to localize these teeth accurately and to assess root resorption of adjacent teeth. Patients with craniofacial anomalies like cleft palate cases, the abnormalities of the temporomandibular joint contributing malocclusion, evaluation of airway morphology in obstructive sleep apnea cases, patients needing maxillary expansion or planning orthognathic surgery in severe skeletal discrepancies are also listed among the indications of using CBCT in orthodontics. CBCT is useful in identifying optimal site location for temporary skeletal anchorage device. The use of CBCT for the assessment of treatment outcomes and evaluation of cervical vertebral maturation are still controversial issues. It should be kept in mind that before using CBCT, justification and evaluation of risks and benefits are needed. In order to minimize the radiation dose, the exam should include only the areas of interest

CORRELATION OF MONSON’S SPHERE AND SOME OTHER DENTOFACIAL VARIABLES TO TEMPOROMANDIBULAR JOINTS (TMJs) IN THE CHINESE POPULATION

Purpose: The purpose of this study was to investigate the correlation of Monson’s Sphere along with several dentofacial variables to the morphologic changes of condyles (condylar height in this case), as well as the possible mechanism that may govern this correlation. These variables are: the discrepancy of the mandibular and maxillary spheres, ANB (anterior-posterior relationship of the maxilla with the mandible), Bonwill’s Angle, Overbite, Overjet, the angle of mediolateral axes of two condyles and the distance between the two condyles. Materials and methods: CT (Computed Tomography) DICOM (Digital Imaging and Communications in Medicine) data of 54 Chinese patients were collected, including 43 females and 11 males aged from 11 to 49 years old. The coordinates of the dental, craniofacial and temporomandibular landmarks were measured through a DICOM viewer. A linear regression model was used to fit the sphere to the coordinates of the dental and temporomandibular landmarks. As well, condylar height and other variables were calculated from the coordinates of the landmarks. Pearson Correlation was performed to illustrate the bivariate correlation of the variables in couples. The difference among the groups categorized by the fixed factors including gender, age, ANB and so on, was tested by ANOVA, and the influence of multiple independent variables on dependent variables was examined. Results: From the data analysis, the mean radius of Monson’s Sphere in the maxilla is 92.42 mm and the mean radius in the mandible is 85.69 mm. Condylar height is correlated to the angle of the mediolateral axes of two condyles positively, and to Overjet, ANB and Bonwill’s angle in a negative way. The discrepancy of the two Monson’s spheres seems to have a linear correlation with both Overjet and Overbite, and the group with the lower values of condylar height are more likely to obtain a portfolio of the greater values of Overjet, Overbite and the discrepancy of the two spheres. Conclusion: The average radius of the mandible Monson’s Sphere is less than 100mm and the radii of only 3 out of 54 subjects are around 100 mm; however, the average distance between two submits of condyles is 100.87 mm. The group of Angle Classification Class II Division I seem to be the high-risk population with the feature of lower condylar height. This finding may pave the way for further research on the relationship between occlusion and temporomandibular joints. Note that since all the results and conclusions herein come from a specific set of populations (Chinese in particular), generalization to other populations may need to be applied with careful and informed consideration

Assessment of mandibular surface area changes in bruxers versus controls on panoramic radiographic images: A Case Control study

BACKGROUND: Bruxism was the commonest of the many parafunctional activities of the masticatory system. Opinions on the causes of bruxism were numerous and widely varying. It can occur on sleep as well as wakefulness. Bruxism was for long considered a major cause of tooth wear. Other effects of bruxism may include tooth movement and tooth mobility, as well as changes in oral soft tissues and jaw bone. Since the exact etiology and manifestations are unclear it was difficult to diagnose Bruxism. In this study we evaluated the area change that can occur on the lower jaw bone in those with Bruxism and comparing the results with nonbruxers. AIMS AND OBJECTIVE: To determine the surface area changes of the mandible, condylar and coronoid processes in Bruxers from Panoramic radiographs and to compare and contrast the changes with age and gender matched controls. MATERIALS AND METHOD: The study was conducted in the department of Oral Medicine and Radiology. The total sample size was 40.The sample was divided in to two groups, Bruxers and nonbruxers with 20 subjects in each group. Healthy volunteers aged between 20- 30 years diagnosed with Bruxism and Healthy volunteers aged between 20- 30 years diagnosed without Bruxism were included in group II (Non Bruxers). Bruxchecker was made use of in confirming the Bruxism in Group I. The Orthopantomogram was used as the imaging modality for the study. The measurements were made with the help of a software, Image J. All the measurements were tabulated and statistical analysis was made using ANOVA (Post hoc) followed by Dunnet t-test and unpaired t-test. RESULTS AND DISCUSSION: The present study was conducted to assess the mandibular surface area changes in bruxers and nonbruxers. It was carried out on a study group comprising 20 healthy individuals as controls in comparison with 20 bruxers (10 males and 10 females).A comparison of the mandibular surface area as a whole and also condylar and coronoid processes individually were carried out. Significant results were obtained in case of condylar and coronoid processes between the two groups. The surface area of condylar process of Group I was found to be lower than that of Group II. The surface area of the right coronoid process of group I was found to be less when compared to that of group II but the values of the left coronoid process of group I was found to be more when compared with group II. The surface area of the mandible showed no significant difference between the groups. There was significant difference between the genders in case of mandible, condyle and coronoid. The surface area of mandible and condylar process was found to be lower in female when compared to male. The surface area of coronoid process was found to be more in case of females when compared to that of males in Group I. The results of our study show that while the overall surface area of bruxers remain unaffected when compared to controls, the condylar and coronoid process show significant change. The hitherto belief that the primary brunt of bruxism is borne by the masseter would require a revisit since alteration in tonicity of the masseter would reflect in surface area change of the mandible as a whole. An increase in the surface area of the coronoid process in bruxers was observed in our study which could be attributed to altered activity of the temporalis, a muscle largely responsible for the posture of the mandible. This could imply that bruxers show alteration in temporalis activity which would explain several clinical manifestations such as headache, neck pain, shoulder pain and altered posture and so on which we have observed in the clinical practice of neuromuscular dentistry. Further studies examining the activity of the temporalis and masseter would further corroborate our findings and for the basis for future research in this arena. Conclusion: This study is an original study that was carried out to assess the surface area changes in mandible and condylar and coronoid processes of Bruxers and nonbruxers. The results showed significant changes in the surface area of condylar and coronoid process in Bruxers when compared to the controls. This study was a step made to assess the bony changes in Bruxers which is seldom carried out by other researchers. We hope this study would be a stepping stone for the future studies in this field

악관절의 해부학적 구조에 기반한 하악 움직임 경로의 생성

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2019. 2. 김명수.We introduce a new approach to the generation of mandible trajectories that can avoid collision between mandibular condyle and maxilla. This is used for analyzing occlusion and the development virtual articulator simulation technique to naturally move mandible following input from a user. Mandible movement has 6 degrees of freedom. However, articular disk, ligament, and muscle near temporomandibular joint constrain the condyle movement. As a result, Mandibular condyle moves from inside of mandibular fossa to below of articular tubercle through a specific trajectory. Therefore, we propose an effective condyle trajectory modeling method based on these features of the anatomical structure of a temporomandibular joint to show accurate mandible movement. By utilizing Bezier surfaces approximating components of both sides of temporomandibular joints, it constrains movable space of both condyles and expresses sequential mandible movement according to the location of those condyles. Mandible can be easily manipulated by simple user interface like virtual articulator, and it can present various movements such as protrusion, retrusion, and lateral movement. Also, the additional interface presents a space which is generated by one point of mandible located through all kinds of movements.본 논문에서는 환자의 치아 교합을 파악하기 위해 두개골 모델을 사용하여 하악 과두(mandibular condyle)의 충돌을 회피하면서 자연스럽게 움직이는 하악의 이동 경로를 생성하고, 사용자의 입력에 따라 하악 동작을 제어하는 가상 교합기 시뮬레이션 기법을 제시한다. 하악의 움직임은 한정된 공간에서 6-자유도(6-DOF)를 가지는 것으로 보이지만, 악관절(temporo-mandibular joint) 부근의 관절 원판(articular disk), 인대, 근육 등에 의해 하악 과두의 움직임이 크게 제한되어 있기 때문에 하악 과두는 상악의 관절 융기(articular tubercle)를 따라 일정한 경로 범위 이내에서만 움직인다. 이러한 악관절 해부학적 구조에 따라, 일반적인 과두의 움직임 경로를 효과적으로 모델링하고 하악의 움직임을 정확하게 나타내는 새로운 시뮬레이션 방법을 제안한다. 악관절 부근을 근사한 베지에 곡면을 이용하여 양측 과두의 움직임을 제한하고, 이에 따라 연속적으로 변화하는 하악의 위치와 방향을 구한다. 가상 교합기와 같이 간단한 사용자 인터페이스를 통해 과두의 움직임을 쉽게 조작할 수 있으며, 경로의 선택에 따라 전방 운동(protrusion), 후방 운동(retrusion), 측방 운동(lateral movement) 등을 다양하게 나타낼 수 있다. 이외에도, 생성된 경로에 따라 환자의 하악이 움직일 수 있는 공간을 나타내는 인터페이스를 제시한다.제 1 장 서론 1 1.1 연구의 배경 및 목적 1 1.2 관련 연구 3 1.3 논문의 구성 5 제 2 장 본론 6 2.1 예비지식 6 2.1.1 베지에 곡선과 베지에 곡면 6 2.1.2 사원수 7 2.2 하악의 움직임 9 2.3 교합기 13 2.4 과두의 움직임 경로 모델링 14 2.4.1 과두 경로 후보 14 2.4.2 접번축 위상과 하악 위치 결정 15 2.4.3 인터페이스 정의 16 2.4.4 과두 경로 후보 수정 16 2.5 시스템 구성 18 2.6 시뮬레이션 결과 20 2.6.1 전방 운동 20 2.6.2 측방 운동 22 2.6.3 하악 이동 가능 범위 시각화 23 제 3 장 결론 26 참고문헌 31 Abstract 32 감사의 글 34Maste

Explore the Dynamic Characteristics of Dental Structures: Modelling, Remodelling, Implantology and Optimisation

The properties of a structure can be both narrowly and broadly described. The mechanical properties, as a narrow sense of property, are those that are quantitative and can be directly measured through experiments. They can be used as a metric to compare the benefits of one material versus another. Examples include Young’s modulus, tensile strength, natural frequency, viscosity, etc. Those with a broader definition, can be hardly measured directly. This thesis aims to study the dynamic properties of dental complex through experiments, clinical trials and computational simulations, thereby bridging some gaps between the numerical study and clinical application. The natural frequency and mode shapes, of human maxilla model with different levels of integrities and properties of the periodontal ligament (PDL), are obtained through the complex modal analysis. It is shown that the comprehensiveness of a computational model significantly affects the characterisation of dynamic behaviours, with decreasing natural frequencies and changed mode shapes as a result of the models with higher extents of integrity and preciseness. It is also found that the PDL plays a very important role in quantifying natural frequencies. Meanwhile, damping properties and the heterogeneity of materials also have an influence on the dynamic properties of dental structures. The understanding of dynamic properties enables to further investigate how it can influence the response when applying an external stimulus. In a parallel preliminary clinical trial, 13 patients requiring bilateral maxillary premolar extractions were recruited and applied with mechanical vibrations of approximately 20 g and 50 Hz, using a split mouth design. It is found that both the space closure and canine distalisation of the vibration group are significantly faster and higher than those of the control group (p<0.05). The pressure within the PDL is computationally calculated to be higher with the vibration group for maxillary teeth for both linguo-buccal and mesial-distal directions. A further increased PDL response can be observed if increasing the frequency until reaching a local natural frequency. The vibration of 50 Hz or higher is thus approved to be a potential stimulus accelerating orthodontic treatment. The pivotal role of soft tissue the PDL is further studied by quantitatively establishing pressure thresholds regulating orthodontic tooth movement (OTM). The centre of resistance and moment to force ratio are also examined via simulation. Distally-directed tipping and translational forces, ranging from 7.5 g to 300 g, are exerted onto maxillary teeth. The hydrostatic stress is quantified from nonlinear finite element analysis (FEA) and compared with normal capillary and systolic blood pressure for driving the tissue remodelling. Localised and volume-averaged hydrostatic stress are introduced to describe OTM. By comparing with clinical results in past literature, the volume average of hydrostatic stress in PDL was proved to describe the process of OTM more indicatively. Global measurement of hydrostatic pressure in the PDL better characterised OTM, implying that OTM occurs only when the majority of PDL volume is critically stressed. The FEA results provide new insights into relevant orthodontic biomechanics and help establish optimal orthodontic force for a specific patient. Implant-supported fixed partial denture (FPD) with cantilever extension can transfer excessive load to the bone surrounding implants and stress/strain concentration which potentially leads to bone resorption. The immediate biomechanical response and long-term bone remodelling outcomes are examined. It is indicated that during the chewing cycles, the regions near implant necks and apexes experience high von Mises stress (VMS) and equivalent strain (EQS) than the middle regions in all configurations, with or without the cantilever. The patient-specific dynamic loading data and CT based mandibular model allow us to model the biomechanical responses more realistically. The results provide the data for clinical assessment of implant configuration to improve longevity and reliability of the implant-supported FPD restoration. On the other hand, the results show that the three-implant supported and distally cantilevered FPDs see noticeable and continuous bone apposition, mainly adjacent to the cervical and apical regions. The bridged and mesially cantilevered FPDs show bone resorption or no visible bone formation in some areas. Caution should be taken when selecting the FPD with cantilever due to the risk of overloading bone resorption. The position of FPD pontics plays a critical role in mechanobiological functionality and bone remodelling. As an important loading condition of dental biomechanics, the accurate assignment of masticatory loads has long been demanded. Methods involving different principles have been applied to acquire or assess the muscular co-activation during normal or unhealthy stomatognathic functioning. Their accuracy and capability of direct quantification, especially when using alone, are however questioned. We establish a clinically validated Sequential Kriging Optimisation (SKO) model, coupled with the FEM and in vivo occlusal records, to further the understanding of muscular functionality following a fibula free flap (FFF) surgery. The results, within the limitations of the current study, indicates the statistical advantage of agreeing occlusal measurements and hence the reliability of using the SKO model over the traditionally adopted optimality criteria. It is therefore speculated that mastication is not optimally controlled to a definite degree. It is also found that the maximum muscular capacity slightly decreases whereas the actual muscle forces fluctuate over the 28-month period

3D Innovations in Personalized Surgery

Current practice involves the use of 3D surgical planning and patient-specific solutions in multiple surgical areas of expertise. Patient-specific solutions have been endorsed for several years in numerous publications due to their associated benefits around accuracy, safety, and predictability of surgical outcome. The basis of 3D surgical planning is the use of high-quality medical images (e.g., CT, MRI, or PET-scans). The translation from 3D digital planning toward surgical applications was developed hand in hand with a rise in 3D printing applications of multiple biocompatible materials. These technical aspects of medical care require engineers’ or technical physicians’ expertise for optimal safe and effective implementation in daily clinical routines.The aim and scope of this Special Issue is high-tech solutions in personalized surgery, based on 3D technology and, more specifically, bone-related surgery. Full-papers or highly innovative technical notes or (systematic) reviews that relate to innovative personalized surgery are invited. This can include optimization of imaging for 3D VSP, optimization of 3D VSP workflow and its translation toward the surgical procedure, or optimization of personalized implants or devices in relation to bone surgery

Temporomandibular Joint Diseases: Diagnosis and Management

Temporomandibular Joint Diseases are common and dificult to treat. From diagnosis to treatment, our options are in a broad range. Keeping updated with new technologies is extremely important for researchers and health professionals

Enhanced Computerized Surgical Planning System in Craniomaxillofacial Surgery

In the field of craniomaxillofacial (CMF) surgery, surgical planning is an important and necessary procedure due to the complex nature of the craniofacial skeleton. Computed tomography (CT) has brought about a revolution in virtual diagnosis, surgical planning and simulation, and evaluation of treatment outcomes. It provides high-quality 3D image and model of skull for Computer-aided surgical planning system (CSPS). During the planning process, one of the essential steps is to reestablish the dental occlusion. In the first project, a new approach is presented to automatically and efficiently reestablish dental occlusion. It includes two steps. The first step is to initially position the models based on dental curves and a point matching technique. The second step is to reposition the models to the final desired occlusion based on iterative surface-based minimum distance mapping with collision constraints. With linearization of rotation matrix, the alignment is modeled by solving quadratic programming. The simulation was completed on 12 sets of digital dental models. Two sets of dental models were partially edentulous, and another two sets have first premolar extractions for orthodontic treatment. Two validation methods were applied to the articulated models. The results show that using the proposed method, the dental models can be successfully articulated with a small degree of deviations from the occlusion achieved with the gold-standard method. Low contrast resolution in CBCT image has become its major limitation in building skull model. Intensive hand-segmentation is required to reconstruct the skull model. Thin bone images are particularly affected by this limitation. In the second project, a novel segmentation approach is presented based on wavelet active shape model (WASM) for a particular interest in the outer surface of the anterior wall of maxilla. 19 CBCT datasets are used to conduct two experiments. This model-based segmentation approach is validated and compared with three different segmentation approaches. The results show that the performance of this model-based segmentation approach is better than those of the other approaches. It can achieve 0.25 +/- 0.2mm of surface error distance from the ground truth of the bone surface. Field of view (FOV) can be reduced in order to reduce unnecessary radiation dose in CBCT. This ROI imaging is common in most of the dentomaxillofacial imaging and orthodontic practices. However, a truncation effect is created due to the truncation of projection images and becomes one of the limitation in CBCT. In the third project, a method for small region of interest (ROI) imaging and reconstruction of the image of ROI in CBCT and two experiments for measurement of dosage are presented. The first experiment shows at least 60% and 70% of radiation dose can be reduced. It also demonstrates that the image quality was still acceptable with little variation of gray by using the traditional truncation correction approach for ROI imaging. The second experiment demonstrates that the images reconstructed by CBCT reconstruction algorithms without truncation correction can be degraded to unacceptable image quality

3-D Oropharyngeal Airway Analysis of Different Antero-Posterior and Vertical Craniofacial Skeletal Patterns in Children and Adolescents

Sleep apnea disorder has recently emerged as a significant public health issue. While the prevalence of obesity is on the rise among children, it is one of the main risk factors associated with apnea. Upper airway dimensions and morphology seem to be major components of obstructive sleep apnea (OSA) and can be affected by different craniofacial patterns. The purpose of this retrospective, cross-sectional pilot study is to correlate gender, Body Mass Index, risk for OSA, neck circumference, and 3-D oropharyngeal airway dimensions in children and adolescents with different antero-posterior (AP) and vertical craniofacial skeletal patterns. A total of 86 pre-orthodontic treatment records in the age group of 8-16 years were analyzed. 3-D volumetric skeletal tracing and oropharyngeal airway measurements were completed for each scan. Each subject was classified into AP Classes I, II, and III groups; vertical Normodivergent, Hypodivergent, and Hyperdivergent groups; and combined AP-vertical subgroups. Oropharyngeal airway measurements included the total oropharyngeal airway volume, minimum cross-section area, depth, width, and perimeter. Mean, standard deviation, and Pearson\u27s correlation coefficient were performed to evaluate the relationships among variables. There were one or more correlations, but not all, between gender, Body Mass Index, risk for OSA, neck circumference, and 3-D oropharyngeal airway dimensions in children and adolescents among the AP groups, vertical groups, and nine craniofacial subgroups (P \u3c 0.05 and P \u3c 0.01). This investigation aimed to determine whether patients with certain skeletal deficiencies are predisposed to upper airway obstruction. Early identification and management of airway problems in children and adolescents may prevent or minimize the sequelae and adverse dental implications of obstructive sleep apnea. Our small, young groups of sample were mainly in the healthy weight category with normal size neck circumference. Therefore, this limited our overall findings. Currently, sleep disorders are not well researched and understood. Long-term goal of our study is to further investigate this study in larger sample size taken into considerations predisposing factors (i.e. abnormal neural regulation and intrinsic muscle weakness) and pathologic conditions (allergies, polyps, and tumors). The physiology of the airway, influenced by these confounding factors, has an essential role in determining whether patients with certain skeletal deficiencies are predisposed to upper airway obstruction. Sleep apnea is a complex phenomenon that warrants further research regarding the physiology and anatomy of the airway and craniofacial structures

Segmentation of the Oral and Facial Regions from Imaging Modalities with Reduced or No Ionizing Radiation

Ph.DDOCTOR OF PHILOSOPH