Biomechanical response of the human mandible to impacts of the chin

A scoping review of human skeletal kinematics research using biplane radiography

Biplane radiography has emerged as the gold standard for accurately measuring in vivo skeletal kinematics during physiological loading. The purpose of this scoping review was to map the extent, range, and nature of biplane radiography research on humans from 2004 through 2022. A literature search was performed using the terms biplane radiography, dual fluoroscopy, dynamic stereo X-ray, and biplane videoradiography. All articles referenced in included publications were also assessed for inclusion. A secondary search was then performed using the names of the most frequently appearing principal investigators among included papers. A total of 379 manuscripts were identified and included. The first studies published in 2004 focused on the native knee, followed by studies of the ankle joint complex in 2006, the shoulder in 2007, and the spine in 2008. Nearly half (180, 47.5%) of all manuscripts investigated knee kinematics. The average number of publications increased from 21.6 per year from 2012 to 2017 to 34.6 per year from 2017 to 2022. The average number of participants per study was 16, with a range from 1 to 101. A total of 90.2% of studies featured cohorts of 30 or less. The most prolific research groups for each joint were: Mass General Hospital (lumbar spine and knee), Henry Ford Hospital (shoulder), the University of Utah (ankle and hip), The University of Pittsburgh (cervical spine), and Brown University (hand/wrist/elbow). Future advancements in biplane radiography research are dependent upon increased availability of these imaging systems, standardization of data collection protocols, and the development of automated approaches to expedite data processing.

Factors predicting oral and maxillofacial fractures after falling and factors predicting the duration of treatment

BACKGROUND/AIM

The first objective of this study was to identify predictive factors for oral and maxillofacial fractures at the initial response to the patient. The second objective was to determine the factors influencing the incidence of treatment duration of more than 1 month using the information shown in the medical record.

MATERIALS AND METHODS

Hospital records from 2011 to 2019 were reviewed to identify patients who had sustained oral and maxillofacial injuries by falling or falling from a height. Patterns and types of oral and maxillofacial injury, injury severity, and background of the injury were collected from the hospital records. The variables independently associated with a treatment duration of more than 1 month were determined by logistic regression analysis.

RESULTS

In total, 282 patients (150 men, 132 women; median age, 17.5 years) were selected for analysis. Maxillofacial fractures were observed in 20.9% of patients (59/282); among these, mandibular fractures were the most common (47/59). Logistic regression analysis showed that age (odds ratio [OR], 1.026), nighttime occurrence (OR, 2.192), and upper face injury (OR, 20.704) were independent predictive factors for having a maxillofacial fracture. Additionally, the number of injured teeth (OR, 1.515) and the use of intermaxillary fixation (OR, 16.091) were independent predictors of treatment duration of more than 1 month.

CONCLUSIONS

These results may be useful in the initial management of maxillofacial injuries in terms of better-informing patients injured by falling their expected treatment duration and managing the psychological impacts of a long treatment duration.

Fracture Injury Risk of the Restrained Mandible to Anterior-Posterior Blunt Impacts

This study describes the results of anterior-posterior impacts conducted on the mandibles of 22 male postmortem human subjects (PMHSs). The objective of this study was to develop an injury criterion for the mandible based on blunt impact while the jaw was restrained. Previous studies have attempted to characterize the injury risk of blunt impact to the mandible; however, due to the translation of the mandible during impact and a limited number of fractured specimens, previous studies were not able to produce an injury criterion. Blunt impact to a restrained mandible is relevant to a wide array of helmeted individuals, including the military population and sports that require helmets with chinstraps. Therefore, in this study, specimens were positioned with restrained jaws and impacted using a monorail drop tower with a gravity-driven cylindrical impactor. Nineteen of 22 specimens sustained at least one fracture during testing. Injury cases had an average impact energy of 15.0 ± 5.7 J (11.1 ± 4.2 ft-lb) and a fracture force of 2684 ± 726 N (603 ± 163 lbf). Results were used to generate an impactor force based injury criterion through survival analysis. Risk of injury was modeled using a Weibull distribution and a 50% risk of injury was found to occur at approximately 2834 N (637 lbf). The developed injury risk curve can be used to characterize injury to the restrained mandible for future testing and research studies, especially in the development of maxillofacial protective equipment.

Maxillofacial Injuries in Cyclists: A Biomechanical Approach for the Analysis of Mechanisms of Mandible Fractures

PURPOSE

The investigators characterized the occurrence of maxillofacial injuries in cyclists and biomechanically analyzed the mechanisms of mandible fractures.

METHODS

We retrospectively analyzed injury data and performed biomechanical analyses with finite element models. Hospital records from 2011 through 2019 were reviewed to identify patients who had sustained oral and maxillofacial injuries while riding a bicycle. Patients with maxillofacial fractures were compared to those without. Logistic regression analysis was performed to identify which variables were independently associated with the occurrence of maxillofacial fractures. To reconstruct the injury scenario (one in which a person falls from a bicycle and contacts the road surface with their face), computer simulations using The Total Human Model for Safety model were performed.

RESULTS

The hospital records of 94 patients (62 men, 32 women; 26.1 ± 17.3 years of age) who sustained oral and maxillofacial injuries while riding a bicycle were reviewed. Twenty patients (21.3%) sustained maxillofacial fractures; mandible fractures were most common (16 patients). Patients with maxillofacial fractures were significantly older and had higher severity injuries; however, logistic regression analysis showed that only age was an independent predictor of the occurrence of maxillofacial fracture (odds ratio, 1.03; P = .025). In simulations, higher von Mises stresses were found in the mandible when the cyclist fell with the neck extended and the body horizontal, and consequently, the center of mandibular body strikes the road surface. Contact forces were approximately 8 kN. High tensile stresses occurred laterally and high compressive stresses occurred medially in the mandibular ramus, which indicated that the mandibular ramus deformed in the transverse plane.

CONCLUSION

Biomechanical analyses show that mandible fractures can occur when a cyclist falls from a bicycle and their lower face strikes the road's surface.

Finite element investigation of human maxillary incisor under traumatic loading: Static vs dynamic analysis

BACKGROUND AND OBJECTIVE

Traumatic loading is the main form of injury sustained in dental injuries. In spite of the prevalence of dental trauma, little information is available on traumatic dental damage and the evaluation of tooth behavior under traumatic loading. Due to the short period of traumatic loading, at first sight, a dynamic analysis needs to be performed to investigate the dental trauma. However, it was hypothesized that dental traumatic loading could be regarded as quasi-static loading. Thus, the aim of the present study was to examine this hypothesis.

METHODS

Static and dynamic analyses of the human maxillary incisor were carried out under traumatic loading using a 3D finite element method. Also, modal analysis of the tooth model was performed in order to evaluate the assumption of the dental traumatic loading as a quasi-static one.

RESULTS

It was revealed that the static analysis of dental trauma is preferred to the dynamic analysis when investigating dental trauma, mainly due to its lower computational cost. In fact, it was shown that including the inertia of the tooth structure does not influence the results of the dental trauma simulation. Furthermore, according to the modal analysis of the tooth structure, it was found that the mechanical properties and geometry of the periodontal ligament play significant roles in the classification of dental traumatic loading as a quasi-static one, in addition to the time duration of the applied load.

CONCLUSIONS

This paper provides important biomechanical insights into the classification of dental loading as quasi-static, transient or impact loading in future dental studies.

Decreased Temporomandibular Joint Range of Motion in a Model of Early Osteoarthritis in the Rabbit

PURPOSE

Analysis of mandibular biomechanics could help with understanding the mechanisms of temporomandibular joint (TMJ) disorders (TMJDs), such as osteoarthritis (TMJ-OA), by investigating the effects of injury or disease on TMJ movement. The objective of the present study was to determine the functional kinematic implications of mild TMJ-OA degeneration caused by altered occlusion from unilateral splints in the rabbit.

MATERIALS AND METHODS

Altered occlusion of the TMJ was mechanically induced in rabbits by way of a unilateral molar dental splint (n = 3). TMJ motion was assessed using 3-dimensional (3D) skeletal kinematics twice, once before and once after 6 weeks of splint placement with the splints removed, after allowing 3 days of recovery. The relative motion of the condyle to the fossa and the distance between the incisors were tracked.

RESULTS

An overall decrease in the range of joint movement was observed at the incisors and in the joint space between the condyle and fossa. The incisor movement decreased from 7.0 ± 0.5 mm to 6.2 ± 0.5 mm right to left, from 5.5 ± 2.2 mm to 4.6 ± 0.8 mm anterior to posterior, and from 13.3 ± 1.8 mm to 11.6 ± 1.4 mm superior to inferior (P < .05). The total magnitude of the maximum distance between the points on the condyle and fossa decreased from 3.6 ± 0.8 mm to 3.1 ± 0.6 mm for the working condyle and 2.8 ± 0.4 mm to 2.5 ± 0.4 mm for the balancing condyle (P < .05). The largest decreases were seen in the anteroposterior direction for both condyles.

CONCLUSION

Determining the changes in condylar movement might lead to a better understanding of the early predictors in the development of TMJ-OA and determining when the symptoms become a chronic, irreversible problem.

The Comprehensive AOCMF Classification System: Mandible Fractures- Level 2 Tutorial

This tutorial outlines the details of the AOCMF image-based classification system for fractures of the mandible at the precision level 2 allowing description of their topographical distribution. A short introduction about the anatomy is made. Mandibular fractures are classified by the anatomic regions involved. For this purpose, the mandible is delineated into an array of nine regions identified by letters: the symphysis/parasymphysis region anteriorly, two body regions on each lateral side, combined angle and ascending ramus regions, and finally the condylar and coronoid processes. A precise definition of the demarcation lines between these regions is given for the unambiguous allocation of fractures. Four transition zones allow an accurate topographic assignment if fractures end up in or run across the borders of anatomic regions. These zones are defined between angle/ramus and body, and between body and symphysis/parasymphysis. A fracture is classified as "confined" as long as it is located within a region, in contrast to a fracture being "nonconfined" when it extents to an adjoining region. Illustrations and case examples of mandible fractures are presented to become familiar with the classification procedure in daily routine.

Functional analysis of the rabbit temporomandibular joint using dynamic biplane imaging

The dynamic function of the rabbit temporomandibular joint (TMJ) was analyzed through non-invasive, three-dimensional skeletal kinematics, providing essential knowledge for understanding normal joint motion. The objective of this study was to evaluate and determine repeatable measurements of rabbit TMJ kinematics. Maximal distances, as well as paths were traced and analyzed for the incisors and for the condyle-fossa relationship. From one rabbit to another, the rotations and translations of both the incisors and the condyle relative to the fossa contained multiple clear, repeatable patterns. The slope of the superior/inferior incisor distance with respect to the rotation about the transverse axis was repeatable to 0.14 mm/deg and the right/left incisor distance with respect to the rotation about the vertical axis was repeatable to 0.03 mm/deg. The slope of the superior/inferior condylar translation with respect to the rotational movement about the transverse axis showed a consistent relationship to within 0.05 mm/deg. The maximal translations of the incisors and condyles were also consistent within and between rabbits. With an understanding of the normal mechanics of the TMJ, kinematics can be used to compare and understand TMJ injury and degeneration models.

Development and validation of a distal radius finite element model to simulate impact loading indicative of a forward fall

The purpose of this work was to develop and validate a finite element model of the distal radius to simulate impact loading. Eight-node hexahedral meshes of the bone and impactor components were created. Three separate impact events were simulated by altering the impact velocity assigned to the model projectile (pre-fracture, crack and fracture). Impact forces and maximum and minimum principal strains were calculated and used in the validation process by comparing with previously collected experimental data. Three measures of mesh quality (Jacobians, aspect ratios and orthogonality) and four validation methods (validation metric, error assessment, fracture comparisons and ensemble averages) assessed the model. The element Jacobians, aspect ratios and orthogonality measures ranged from 0.08 to 12, 1.1 to 26 and -70° to 80°, respectively. The force and strain validation metric ranged from 0.10 to 0.54 and 0.35 to 0.67, respectively. The estimated peak axial force was found to be a maximum of 28.5% greater than the experimental (crack) force, and all forces fell within ±2 standard deviation of the mean experimental fracture forces. The predicted strains were found to differ by a mean of 33% across all impact events, and the model was found to accurately predict the location and severity of bone damage. Overall, the model presented here is a valid representation of the distal radius subjected to impact.

Analysis and design of rolling-contact joints for evaluating bone plate performance

An apparatus for testing maxillofacial bone plates has been designed using a rolling contact joint. First, a free-body representation of the fracture fixation techniques utilizing bone plates is used to illustrate how rolling contact joints accurately simulate in vivo biomechanics. Next, a deterministic description of machine functional requirements is given, and is then used to drive the subsequent selection and design of machine elements. Hertz contact stress and fatigue analysis for two elements are used to ensure that the machine will both withstand loads required to deform different plates, and maintain a high cycle lifetime for testing large numbers of plates. Additionally, clinically relevant deformations are presented to illustrate how stiffness is affected after a deformation is applied, and to highlight improvements made by the machine over current testing standards, which do not adequately re-create in vivo loading conditions. The machine performed as expected and allowed for analysis of bone plates in both deformed and un-deformed configurations to be conducted. Data for deformation experiments is presented to show that the rolling-contact testing machine leads to improved loading configurations, and thus a more accurate description of plate performance. A machine for evaluation of maxillofacial bone plates has been designed, manufactured, and used to accurately simulate in vivo loading conditions to more effectively evaluate the performance of both new and existing bone plates.

Effect of mouthguards on head responses and mandible forces in football helmet impacts

The potential for mouthguards to change the risk of concussion was studied in football helmet impacts. The Hybrid III head was modified with an articulating mandible, dentition, and compliant temporomandibular joints (TMJ). It was instrumented for triaxial head acceleration and triaxial force at the TMJs and upper dentition. Mandible force and displacement were validated against cadaver impacts to the chin. In phase 1, one of five mouthguards significantly lowered HIC in 6.7 m/s impacts (p = 0.025) from the no mouthguard condition but not in 9.5 m/s tests. In phase 2, eight mouthguards increased HIC from +1 to +17% in facemask impacts that loaded the chinstraps and mandible; one was statistically higher (p = 0.018). Peak head acceleration was +1 to +15% higher with six mouthguards and 2-3% lower with two others. The differences were not statistically significant. Five of eight mouthguards significantly reduced forces on the upper dentition by 40.8-63.9%. Mouthguards tested in this study with the Hybrid III articulating mandible lowered forces on the dentition and TMJ, but generally did not influence HIC or concussion risks.