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Background/objectives: The aim of this study was to evaluate large field of view (FoV) subjective image quality of three cone-beam computed tomography (CBCT) machines to assess the threshold for reliable diagnostic perceptibility when lowering exposure settings., Materials and Methods: One entire cadaver's head was scanned using three CBCT scanners. The largest available FoV of each device, imaging orthodontic relevant structures, was applied. CBCT datasets with different image quality based on standard to minimum scanning parameters were acquired. Five dentists evaluated the visibility of selected anatomical structures of the upper and lower jaw using a 5-point rating scale., Results: Image quality depends on parameters such as a minimum voxel size of 0.2 to 0.4mm or a minimum of 4mA. A reduction in number of images (scanning protocol) reduces image quality. Visualization of different anatomical structures for orthodontic treatment planning requires distinct scanning protocols to support adequate perception of these structures., Limitations: This study does not account for the evaluation of paediatric anatomical structures due to the availability of cadaver's head., Conclusions: CBCT scans performed for orthodontic purposes using a large FoV with reduced parameters (400 µm, 2 to 4 mA and low dose protocols) are acceptable for visualization of large anatomical structures. Further lowering these parameters will not be sufficient to view small anatomical structures. Orthodontic indications will have to define specific anatomical structures to choose adequate scanning protocols to reduce dose and ensure reliable diagnostic visibility., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The aim of this work was to predict the shape of the articular eminence in a patient with unilateral hypoplasia of the right mandibular ramus before and after distraction osteogenesis (DO). Using a patient-specific musculoskeletal model of the mandible the hypothesis that the observed differences in this patient in the left and right articular eminence inclinations were consistent with minimisation of joint loads was tested. Moreover, a prediction was made of the final shape of the articular eminence after DO when the expected remodelling has reached a steady state. The individual muscle forces and the average TMJ loading were computed for each combination of articular eminence angles both before and after DO. This exhaustive parameter study provides a full overview of average TMJ loading depending on the angles of the articular eminences. Before DO the parameter study resulted in different articular eminence inclinations between left and right sides consistent with patient data obtained from CT scans, indicating that in this patient the articular eminence shapes result from minimisation of joint loads. The simulation model predicts development of almost equal articular eminence shapes after DO. The same tendency was observed in cone beam CT scans (NewTom) of the patient taken 6.5 years after surgery.

Mandibular distraction osteogenesis will lead to a change in muscle coordination and load transfer to the temporomandibular joints (TMJ). The objective of this work is to present and validate a rigid-body musculo-skeletal model of the mandible based on inverse dynamics for calculation of the muscle activations, muscle forces and TMJ reaction forces for different types of clenching tasks and dynamic tasks. This approach is validated on a symmetric mandible model and an application will be presented where the TMJ reaction forces during unilateral clenching are estimated for a virtual distraction patient with a shortened left ramus. The mandible model consists of 2 rigid segments and has 4 degrees-of-freedom. The model was equipped with 24 hill-type musculotendon actuators. During the validation experiment one subject was asked to do several tasks while measuring EMG activity, bite force and kinematics. The bite force and kinematics were used as input for the simulations of the same tasks after which the estimated muscle activities were compared with the measured muscle activities. This resulted in an average correlation coefficient of 0.580 and an average of the Mean Absolute Error of 0.109. The virtual distraction model showed a large difference in the TMJ reaction forces between left and right compared with the symmetric model for the same loading case. The present work is a step in the direction of building patient-specific mandible models, which can assess the mechanical effects on the TMJ before mandibular distraction osteogenesis surgery.

Distraction osteogenesis has been accepted as an alternative treatment modality for hypoplastic mandibles. Knowledge about the changes occurring in the temporomandibular joint region during mandibular distraction osteogenesis is, however, limited and controversial. Stress distribution in the temporomandibular joint region during unilateral vertical mandibular ramus distraction was studied using a finite element model. The finite element model was based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the temporomandibular joint and mandible was analyzed quantitatively at different intervals of the vertical mandibular ramus elongation. During the distraction phase, the condyles, articular disks, and glenoid fossa regions were loaded with a differentiated stress pattern. The affected right condyle, disk, and fossa were submitted to increasing loads with increasing elongation compared with the contralateral temporomandibular joint. Loading on the unaffected left side shifted posteriorly and slightly laterally, because the left condyle was the center of rotation. The loading of the temporomandibular joint regions was low during the active distraction phase, although local areas were subjected to elevated peak stresses.

An approach was developed to evaluate the load transfer mechanism in the temporomandibular joint (TMJ) area before, during and after mandibular ramus elongation by distraction osteogenesis (DO). In a concerted approach using computer tomography, magnetic resonance imaging (MRI), and finite element analysis, three-dimensional numerical models based on a young male patient, with a dento-facial deformity were generated. The magnitude and direction of the muscle forces acting on the mandible were assessed using both values derived from the muscles volume and cross-section as retrieved from the MRI-scan data-sets and taken from the literature. The resistance of the soft tissue envelope towards elongation during the DO-phase was also included. The finite element analyses showed that before skeletal correction by DO the load transfer was asymmetrical with high peak stresses in the affected joint. Following ramus elongation a more symmetrical loading in TMJs was predicted. The reaction forces in the TMJs during DO were low.

The article presents the study on the three-dimensional (3D) evaluation of condylar and mandibular growth among patients with juvenile idiopathic arthritis (JIA) with unilateral temporomandibular joint who were treated with distraction splint. The cone-beam computed tomography (CBCT) scans and reconstruction of 3D models were conducted. The results were outlined and conclude on the effect of orthopedic functional treatment on condylar adaptation and modeling.