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Examines the relationship between the orientation and moment arms of the human jaw muscles and normal craniofacial morphology. Characteristics of the jaw muscles of subjects with increased vertical craniofacial dimensions; Method used in defining the subjects' jaw muscle orientation; Use of magnetic resonance imaging in analyzing the craniofacial morphology of the subjects.

Objective: The aim of the present study is to identify a more reliable reference point in three-dimensional cephalometric analysis to replace the Porion point used in two-dimensional analysis, enhancing the accuracy of assessments. Methods: The methodology assessed potential alternative landmarks for three-dimensional cephalometric analysis. Utilizing a segmenting technique, anatomical landmarks were accurately pinpointed from the external acoustic meatus of 26 Cone Beam Computed Tomography (CBCT) scans. These landmarks were chosen for their clear and unambiguous detectability. To assess reproducibility, each landmark was replicated twice with a one-week interval by a master's student. Reproducibility was quantitatively evaluated by analyzing the absolute difference per axis. Results: Five possible candidate landmarks were identified: the most anterior, posterior, superior, and inferior points of the external acoustic meatus (EAM) and a notch delineating the epitympanic recess. The reproducibility of pinpointing these landmarks ranged from 0.56 mm to 2.2 mm. The absolute mean differences between measurements were 0.46 mm (SD 0.75) for the most anterior point, 0.36 mm (SD 0.44) for the most posterior point, 0.25 mm (SD 0.26) for the most superior point, 1.11 mm (SD 1.03) for the most inferior point, and 0.78 mm (SD 0.57) for the epitympanic notch. Conclusions: The most superior point of the EAM might successfully replace the Porion as an anatomical reference.

Objective: In this study, we thoroughly analyzed how balanced the left and right sides of the external acoustic meatus are. Despite previous research focusing on the consistency of various anatomical features and the shape of the external acoustic meatus, which are important for creating guidelines to assess changes in the skull, there hasn't been enough attention given to how symmetrical it is. Our aim was to fill this gap by providing a comprehensive examination of its bilateral symmetry, which is crucial for accurate evaluations in dentistry and medicine., Study Design: After importing 26 cone-beam computed tomography scans of patients into the ITK-SNAP 3D imaging software, a midsagittal plane was set up as the plane of symmetry for each patient. With this plane, we compared the positions of the most superior and inferior left and right points of the external acoustic meatus. We also compared the lengths and depths of the lines connecting the two points., Results: There were no statistically significant differences in the position, length, or depth of the external acoustic meatus between the right and left halves of the skull., Conclusion: Specific points on the skull, such as the highest (most superior MSP) and lowest (most inferior MIP) points, demonstrated a high degree of symmetry in the left and right halves. They demonstrated sufficient symmetry to establish a reliable reference plane. Along with the trajectory connecting them, these points can serve as viable alternatives to the Porion for three-dimensional imaging., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Masticatory muscle activation and temporomandibular joint (TMJ) load generated during asymmetrically loaded jaw closing are largely unknown. Two different strategies were developed to explain how the central nervous system (CNS) generates muscle activation patterns during motion: minimization of joint load (MJL) vs. minimization of muscle effort (MME). The aim of the present study was to investigate, experimentally, the neuromuscular strategy selected by the CNS to coordinate jaw closing in reaction to the application of an external asymmetric load. Masticatory muscle activation was measured with electromyography (EMG) and the minimum intra-articular distance (MID) was assessed by dynamic stereometry to infer joint loading. Ten healthy subjects performed jaw-closing movements against an asymmetric mandibular load set from 0.0 to 2.0 kg in 0.5-kg steps. Recordings were analyzed by exploratory and graphical statistical tools. Moreover, the observed differences in MID and EMG among the various mandibular loads were tested using non-parametric tests for repeated measures data. The ipsilateral-contralateral differences in MID and EMG of the anterior temporalis showed a significant increase (p < 0.001, p = 0.01) with increasing asymmetrical load with both joints being most heavily loaded at 1 kg. EMG signals of the masseter did not change significantly with increasing load. This study is the first to have analyzed the changes in the TMJ intra-articular space during asymmetrically loaded jaw-closing movements, not only three dimensionally and dynamically, but also combined with EMG. Asymmetrical load affected the TMJ space and masticatory muscle activation patterns, primarily resulting in an increased activation of the anterior temporalis muscle. This might suggest the involvement of a control mechanism to protect the joints from overloading. However, the results do not fully support the hypothesis of MJL nor the MME strategy., (© 2024. The Author(s).)

Objective: To explore the relationship between the volumetric bone mineral density (vBMD), the thickness of the condylar cortex (T cortex ) and the hemimandibular volumes (V hemimandible ) of symmetrical and asymmetrical mandibles of children., Design: The data collection consisted of 92 archeological skeletal remains of children's mandibles between 1 and 12 years old. The mandibles were digitalized with a computed tomography (CT) scan, and three dimensional models were obtained. V hemimandible was calculated using the optimal symmetry plane. The volumes were used to calculate the asymmetry index (AI). Mandibles with an AI of ≥ 3% (N = 9) and a sample of the most symmetrical mandibles (N = 9) were selected for this research. Three groups were created: a symmetrical, an asymmetrical and a pooled group. Micro-CT was used to measure the vBMD and T cortex in four volumes of interest. The AI was calculated for these parameters as well., Results: Significant correlations were found between the vBMD and the T cortex in the pooled group (P < .01) and between the AI of the vBMD and the AI of the T cortex in the pooled (P < .01) and symmetrical group (P < .05). No significant correlations were found between the vBMD and the V hemimandible and between the respective AIs. Between the T cortex and the V hemimandible a significant correlation was found in the pooled and asymmetrical group., Conclusion: There is a relationship between the vBMD and the T cortex . The correlations between the T cortex and the V hemimandible are insufficient to draw firm conclusions. A relationship between the vBMD and V hemimandible was not confirmed in this study., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: Premature dental contact on the fractured side and a contralateral open bite are signs of a unilaterally fractured condyle of the temporomandibular joint (TMJ). The lateral pterygoid muscle pulls the condyle inwards, causing angulation of the fractured part and shortening of the ramus. This imbalance after fracture might change the load in both TMJs and consequently induce remodeling. The present study aimed to calculate this change in load. It is hypothesized to decrease on the fractured side and increase on the non-fractured side., Design: For these calculations, a finite element model (FEM) was used. In the FEM, shortening of the ramus varied from 2 mm to 16 mm; angulation, from 6.25° to 50°., Results: After fracture, load on the non-fractured side increased, but only at maximal mouth opening (MMO). Simultaneously, load on the fractured side decreased, at both timepoints, i.e., MMO and closed mouth. When comparing all simulations at those time points, i.e., from 2 mm and 6.25° to 16 mm and 50°, the load in the fractured condyle declines steadily. However, for both timepoints, a threshold stands out around 6 mm shortening and 18.75° angulation: visualization of the fractured condyle showed, apart from load on the condylar head, a second point of load more medial in the TMJ which was most evident in the 6 mm - 18.75° simulation., Conclusions: These findings could implicate that the balance between both TMJs is more difficult to restore after a fracture with more than 6 mm shortening and more than 18.75° angulation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: To explore the normal variation of asymmetry in mandibles of children in the age group of 1 to 12 years., Materials and Methods: The study group consisted of 92 cadaveric mandibles of children with a dental age of 1 to 12 years old in possession of ACTA (Academic Centre for Dentistry Amsterdam), Faculty of Dentistry, the Netherlands. 3D models of the mandibles were obtained from CT-scans and hemimandibular volumes of all mandibles were calculated. The condylar height, ramus height, mandibular body length and the gonial angle were bilaterally determined using a novel landmark-based method, and the degree of asymmetry was calculated., Results: No relationship was found between dental age and asymmetry of the studied parameters (P < .05). The highest degree of asymmetry was found in the ramus height, whereas the gonial angle presented the lowest degree of asymmetry. A positive correlation was found between the asymmetry of the hemimandibular volume vs the height of the ramus (P < .05) and the length of the mandibular body (P < .05). An inverse correlation was found between the asymmetry of the ramus height vs the condylar height (P < .05), mandibular body length (P < .05) and gonial angle (P < .05)., Conclusions: Mandibular asymmetries in children did occur (9.8% of the included mandibles presented with a relevant overall asymmetry of ≥3%) and were unrelated to age. The different segments of the mandible seem to compensate for each other, in order to maintain a functional equilibrium., (© 2023 The Authors. Orthodontics & Craniofacial Research published by John Wiley & Sons Ltd.)

Objectives: After a fracture of the condyle, the fractured ramus is often shortened, which causes premature dental contact on the fractured side and a contralateral open bite. The imbalance could change the load in the temporomandibular joints (TMJs). This change could lead to remodelling of the TMJs to compensate for the imbalance in the masticatory system. The load in the non-fractured condyle is expected to increase, and the load in the fractured condyle to decrease., Materials and Methods: These changes cannot be measured in a clinical situation. Therefore a finite element model (FEM) of the masticatory system was used. In the FEM a fractured right condyle with shortening of the ramus was induced, which varied from 2 to 16 mm., Results: Results show that, with a larger shortening of the ramus, the load in the fractured condyle decreases and the load in the non-fractured condyle increases. In the fractured condyle during closed mouth a major descent in load, hence a cut-off point, was visible between a shortening of 6 mm and 8 mm., Conclusions: In conclusion, the change of load could be associated with remodelling on both condyles due to shortening of the ramus., Clinical Relevance: The cut-off point implies that shortening over 6 mm could present more difficulty for the body to compensate., (© 2023. The Author(s).)

The aim of this systematic review was to gather the clinical and laboratory applications of CAD/CAM technology for preoperative planning, designing of an attachment system, and manufacturing of nasal prostheses. According to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, an electronic search was carried out. Only human clinical studies involving digital planning for the rehabilitation of facial defects were included. A total of 21 studies were included with 23 patients, which were virtually planned through different planning software. The most common preoperative data for digital planning were CT scans in nine cases, CBCT in six cases, and laser scans in six cases. The reported planning softwares were Mimics in six cases, Geomagic Studio software in six cases, ZBrush in four cases, and Freeform plus software in four cases. Ten surgical templates were designed and printed to place 36 implants after digital planning, while post-operative assessment was done in two cases to check the accuracy of planned implants. Digital 3D planning software was reported for presurgical planning and craniofacial implants placement, fabrication of molds, designing of implants, designing of retentive attachments, and printing of silicone prostheses. Digital technology has been claimed to reduce the clinical and laboratory time; however, the equipment cost is still one of the limitations.

Background/aims: There is a lack of data regarding the mechanical responses of the temporo-mandibular joints during an impact to the orofacial region. The aim of this study was to analyze the biomechanical effects of wearing a mouthguard (MG) on the impact response of the mandibular condyle and articular disk according to the type of occlusion. The hypothesis was that the MG would minimize the effect in those structures, regardless of the occlusion type., Methods: Using modeling software, a human skull with jaw, teeth and articular disk was created. The models were divided according to the occlusion type (Class I, II, or III) and the presence of a mouthguard (with or without). The geometries were exported to analysis software, and the materials were considered ideal. Fixation occurred at the base of the foramen magnum. The load (0-500N, 1s) was applied to the upper central incisors with a steel ball. Maximum principal stress and Von Mises results (MPa) were obtained in the mandibular condyle and articular disk. Minimum principal stress and maximum shear stresses were also recorded in the articular disk., Results: For both structures, the MG caused a decrease in stress concentration regardless of the occlusion and stress criteria. The condyle neck was the most tensile-stressed area while for the articular disk, both the superior and inferior surfaces were the most stressed areas. The highest stress peaks in the disk were found for compression followed by tensile and then shear stress., Conclusion: This biomechanical analysis of the effects of using a mouthguard exhibited considerably decreased stresses on the mandibular condyle and articular disk, regardless of the occlusion type., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The temporomandibular joint disc is a fibrocartilaginous structure, composed of collagen fibers, elastin fibers, and proteoglycans. Despite the crucial role of elastin fibers in load-bearing properties of connective tissues, its contribution in temporomandibular joint disc biomechanics has been disregarded. This study attempts to characterize the structural-functional contribution of elastin in the temporomandibular joint disc. Using elastase, we selectively perturbed the elastin fiber network in porcine temporomandibular joint discs and investigated the structural, compositional, and mechanical regional changes through: (a) analysis of collagen and elastin fibers by immunolabeling and transmission electron microscopy; (b) quantitative analysis of collagen tortuosity, cell shape, and disc volume; (c) biochemical quantification of collagen, glycosaminoglycan and elastin content; and (d) cyclic compression test. Following elastase treatment, microscopic examination revealed fragmentation of elastin fibers across the temporomandibular joint disc, with a more pronounced effect in the intermediate regions. Also, biochemical analyses of the intermediate regions showed significant depletion of elastin (50%), and substantial decrease in collagen (20%) and glycosaminoglycan (49%) content, likely due to non-specific activity of elastase. Degradation of elastin fibers affected the homeostatic configuration of the disc, reflected in its significant volume enlargement accompanied by remarkable reduction of collagen tortuosity and cell elongation. Mechanically, elastase treatment nearly doubled the maximal energy dissipation across the intermediate regions while the instantaneous modulus was not significantly affected. We conclude that elastin fibers contribute to the restoration and maintenance of the disc resting shape and actively interact with collagen fibers to provide mechanical resilience to the temporomandibular joint disc., (© 2020 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc.)

Purpose: Determination of intra-oral surface areas might contribute to our understanding of the physiology of the oral cavity and oral diseases. In previous studies, the intra-oral surface area was determined using a laborious and technically challenging method. Our aim was to develop an easy and non-invasive method to determine the intra-oral surface areas., Methods: In this study, we used cone-beam computed tomography (CBCT) and digital analysis in 20 human cadavers to determine various intra-oral surface areas, based on digital segmentation. Next, we explored whether there was a relationship between various intra-oral surface areas and anthropometric measurements of the head using Pearson correlation coefficient., Results: Using CBCT and digital analysis, it was possible to determine various intra-oral surface areas. On average, the total intra-oral surface area was 173 ± 19 cm 2 . Moderate, statistical significant correlations were observed between (1) the length of the head and the palatal surface area, as well as (2) the depth of the head and the surface area of the tongue. These correlations suggest the feasibility of estimating intra-oral surface areas without relying on CBCT imaging., Conclusions: This study presents a technique for measuring the intra-oral surface areas by CBCT imaging in combination with digital analysis. The results of this study suggest that anthropometric measurements of the head might be used to estimate the surface areas of the palate and tongue.

In bone tissue engineering, prediction of forces induced to the native bone during normal functioning is important in the design, fabrication, and integration of a scaffold with the host. The aim of this study was to customize the mechanical properties of a layer-by-layer 3D-printed poly(ϵ-caprolactone) (PCL) scaffold estimated by finite element (FE) modeling in order to match the requirements of the defect, to prevent mechanical failure, and ensure optimal integration with the surrounding tissue. Forces and torques induced on the mandibular symphysis during jaw opening and closing were predicted by FE modeling. Based on the predicted forces, homogeneous-structured PCL scaffolds with 3 different void sizes (0.3, 0.6, and 0.9 mm) were designed and 3D-printed using an extrusion based 3D-bioprinter. In addition, 2 gradient-structured scaffolds were designed and 3D-printed. The first gradient scaffold contained 2 regions (0.3 mm and 0.6 mm void size in the upper and lower half, respectively), whereas the second gradient scaffold contained 3 regions (void sizes of 0.3, 0.6, and 0.9 mm in the upper, middle and lower third, respectively). Scaffolds were tested for their compressive and tensile strength in the upper and lower halves. The actual void size of the homogeneous scaffolds with designed void size of 0.3, 0.6, and 0.9 mm was 0.20, 0.59, and 0.95 mm, respectively. FE modeling showed that during opening and closing of the jaw, the highest force induced on the symphysis was a compressive force in the transverse direction. The compressive force was induced throughout the symphyseal line and reduced from top (362.5 N, compressive force) to bottom (107.5 N, tensile force) of the symphysis. Compressive and tensile strength of homogeneous scaffolds decreased by 1.4-fold to 3-fold with increasing scaffold void size. Both gradient scaffolds had higher compressive strength in the upper half (2 region-gradient scaffold: 4.9 MPa; 3 region-gradient scaffold: 4.1 MPa) compared with the lower half (2 region-gradient scaffold: 2.5 MPa; 3 region-gradient scaffold: 2.7 MPa) of the scaffold. 3D-printed PCL scaffolds had higher compressive strength in the scaffold layer-by-layer building direction compared with the side direction, and a very low tensile strength in the scaffold layer-by-layer building direction. Fluid shear stress and fluid pressure distribution in the gradient scaffolds were more homogeneous than in the 0.3 mm void size scaffold and similar to the 0.6 mm and 0.9 mm void size scaffolds. In conclusion, these data show that the mechanical properties of 3D-printed PCL scaffolds can be tailored based on the predicted forces on the mandibular symphysis. These 3D-printed PCL scaffolds had different mechanical properties in scaffold building direction compared with the side direction, which should be taken into account when placing the scaffold in the defect site. Our findings might have implications for improved performance and integration of scaffolds with native tissue., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The temporomandibular joint disc is a structure, characterized as heterogeneous fibrocartilage, and is composed of macromolecular biopolymers. Despite a large body of characterization studies, the contribution of matrix biopolymers on the dynamic viscoelastic behavior of the disc is poorly understood. Given the high permeability and low concentration of glycosaminoglycans in the disc, it has been suggested that poro-elastic behavior can be neglected and that the intrinsic viscoelastic nature of solid matrix plays a dominant role in governing its time-dependent behavior. This study attempts to quantify the contribution of collagen and elastin fibers to the viscoelastic properties of the disc. Using collagenase and elastase, we perturbed the collagen and elastin fibrillar network in porcine temporomandibular joint discs and investigated the changes of dynamic viscoelastic properties in five different regions of the disc. Following both treatments, the storage and loss moduli of these regions were reduced dramatically up to the point that the tissue was no longer mechanically heterogeneous. However, the proportion of changes in storage and loss moduli were different for each treatment, reflected in the decrease and increase of the loss tangent for collagenase and elastase treated discs, respectively. The reduction of storage and loss moduli of the disc correlated with a decrease of biopolymer length. The present study indicates that the compositional and structural changes of collagen and elastin fibers alter the viscoelastic properties of the disc consistent with polymer dynamics., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Nutrition of articular cartilage relies mainly on diffusion and convection of solutes through the interstitial fluid due to the lack of blood vessels. The diffusion is controlled by two factors: steric hindrance and electrostatic interactions between the solutes and the matrix components. Aging comes with changes in the cartilage structure and composition, which can influence the diffusion. In this study, we treated fibrocartilage of mandibular condyle with ribose to induce an aging-like effect by accumulating collagen crosslinks. The effect of steric hindrance or electrostatic forces on the diffusion was analyzed using either charged (Hexabrix) or uncharged (Visipaque) contrast agents. Osteochondral plugs from young equine mandibular condyles were treated with 500 mM ribose for 7 days. The effect of crosslinking on mechanical properties was then evaluated via dynamic indentation. Thereafter, the samples were exposed to contrast agents and imaged using contrast-enhanced computed tomography (CECT) at 18 different time points up to 48 h to measure their diffusion. Normalized concentration of contrast agents in the cartilage and contrast agent diffusion flux, as well as the content of crosslink level (pentosidine), water, collagen, and glycosaminoglycan (GAG) were determined. Ribose treatment significantly increased the pentosidine level (from 0.01 to 7.6 mmol/mol collagen), which resulted in an increase in tissue stiffness (~1.5 fold). Interestingly, the normalized concentration and diffusion flux did not change after the induction of an increased level of pentosidine either for Hexabrix or Visipaque. The results of this study strongly suggest that sugar-induced collagen crosslinking in TMJ condylar cartilage does not affect the diffusion properties., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Objective: Aging can cause an increase in the stiffness of hyaline cartilage as a consequence of increased protein crosslinks. By induction of crosslinking, a reduction in the diffusion of solutions into the hyaline cartilage has been observed. However, there is a lack of knowledge about the effects of aging on the biophysical and biochemical properties of the temporomandibular joint (TMJ) cartilage. Hence, the aim of this study was to examine the biophysical properties (thickness, stiffness, and diffusion) of the TMJ condylar cartilage of horses of different ages and their correlation with biochemical parameters., Materials and Methods: We measured the compressive stiffness of the condyles, after which the diffusion of two contrast agents into cartilage was measured using Contrast Enhanced Computed Tomography technique. Furthermore, the content of water, collagen, GAG, and pentosidine was analyzed., Results: Contrary to our expectations, the stiffness of the cartilage did not change with age (modulus remained around 0.7 MPa). The diffusion of the negatively charged contrast agent (Hexabrix) also did not alter. However, the diffusion of the uncharged contrast agent (Visipaque) decreased with aging. The flux was negatively correlated with the amount of collagen and crosslink level which increased with aging. Pentosidine, collagen, and GAG were positively correlated with age whereas thickness and water content showed negative correlations., Conclusion: Our data demonstrated that aging was not necessarily reflected in the biophysical properties of TMJ condylar cartilage. The combination of the changes happening due to aging resulted in different diffusive properties, depending on the nature of the solution., (Copyright © 2018 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Patients with hypermobility disorders of the jaw joint experience joint sounds and jerky movements of the jaw. In severe cases, a subluxation or luxation can occur. Clinically, hypermobility disorders should be differentiated from disc displacements. With biomechanical modelling, we previously identified the anterior slope angle of the eminence and the orientation of the jaw closers to potentially contribute to hypermobility disorders. Using cone-beam computed tomography (CBCT), we constructed patient-specific models of the masticatory system to incorporate these aspects. It is not known whether the clinical diagnosis of hypermobility disorders is associated with the prediction of hypermobility by a patient-specific biomechanical model. Fifteen patients and eleven controls, matched for gender and age, were enrolled in the study. Clinical diagnosis was performed according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) and additional testing to differentiate hypermobility from disc displacements. Forward simulations with patient-specific biomechanical models were performed for maximum opening and subsequent closing of the jaw. This predicted a hypermobility disorder (luxation) or a control (normal closing). We found no association between the clinical diagnosis and predictions of hypermobility disorders. The biomechanical models overestimated the number of patients, yielding a low specificity. The role of the collagenous structures remains unclear; therefore, the articular disc and the ligaments should be modelled in greater detail. This also holds for the fanned shape of the temporalis muscle. However, for the osseous structures, we determined post hoc that the anterior slope angle of the articular eminence is steeper in patients than in controls., (© 2018 The Authors. Journal of Oral Rehabilitation Published by John Wiley & Sons Ltd.)

Objective: Aging is accompanied by a series of changes in mature tissues that influence their properties and functions. Collagen, as one of the main extracellular components of cartilage, becomes highly crosslinked during aging. In this study, the aim was to examine whether a correlation exists between collagen crosslinking induced by artificial aging and mechanical properties of the temporomandibular joint (TMJ) condyle. To evaluate this hypothesis, collagen crosslinks were induced using ribose incubation., Methods: Porcine TMJ condyles were incubated for 7 days with different concentrations of ribose. The compressive modulus and stiffness ratio (incubated versus control) was determined after loading. Glycosaminoglycan and collagen content, and the number of crosslinks were analyzed. Tissue structure was visualized by microscopy using different staining methods., Results: Concomitant with an increasing concentration of ribose, an increase of collagen crosslinks was found. The number of crosslinks increased almost 50 fold after incubation with the highest concentration of ribose. Simultaneously, the stiffness ratio of the samples showed a significant increase after incubation with the ribose. Pearson correlation analyses showed a significant positive correlation between the overall stiffness ratio and the crosslink level; the higher the number of crosslinks the higher the stiffness., Conclusion: The present model, in which ribose was used to mimic certain aspects of age-related changes, can be employed as an in vitro model to study age-related mechanical changes in the TMJ condyle., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Purpose: Mandibular advancement devices are commonly used in the treatment of patients with mild to moderate obstructive sleep apnea (OSA). Designed to maintain the mandible in forced protrusion while being worn, mandibular advancement devices (MADs) are intended to increase the upper airway during sleep, thereby reducing OSA symptoms. Depending on the extent of mandibular protrusion, side effects including temporomandibular joint dysfunction are frequently reported. These are likely to reduce overall treatment success by affecting therapeutic adherence., Material and Methods: To investigate the biomechanical effects of an MAD on the temporomandibular joints, we used a biomechanical model of the human masticatory system. Alterations to the model were applied to mimic the effects of a titratable duoblock MAD. The extent of mandibular protrusion was simulated up to 10 mm in steps of 1 mm. Compression and shear stresses on the temporomandibular structures were predicted during an open-close maneuver and in neutral position., Results: As the extent of mandibular advancement increased, the mandibular condyle migrated anteriorly until passing the articular tubercle. Stress on the temporomandibular joint structures did not considerably increase in rest whatever the extent of mandibular advancement. However, closure of the jaw required extra muscle force as mandibular advancement increased., Conclusion: Results from this study suggest that temporomandibular dysfunction following MAD wearing might be related to altered muscle dynamics rather than changes due to increased stress in the temporomandibular joint itself., (Copyright © 2017 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Objectives: Against the background of a possibly compromised functional adaptation, the relationship between the height of the articular tubercle was analyzed as a function of the amount of divergence between the maxilla and the mandible., Design: These parameters were obtained retrospectively from orthopantomograms and lateral radiographs produced in a standard procedure before orthodontic treatment., Results: The height of the articular tubercle appeared to be significantly smaller in a group of patients with a dolichofacial morphology, with respect of those with an average (mesofacial) morphology. Furthermore, there was a significant correlation between the height of the articular tubercle and the mandibular angle., Conclusions: These results suggest that bone remodeling in selected parts of the orofacial skeleton can be compromised giving rise to an altered craniofacial morphology., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Purpose: The purpose of this study was to evaluate the influence of placement angle and force direction on the initial stability of orthodontic miniscrews using a three-dimensional finite element model that approximates the real interface between the screw and surrounding bone., Materials and Methods: Three-dimensional finite element models with 6-mm-long and 1.4-mm-diameter titanium miniscrews were used. Four insertion angles, ranging from 0 degrees (perpendicular to the bone surface) to 45 degrees, were examined. A load of 2 N was applied to the center of the screw head in four directions (upward, downward, and on the right and left sides)., Results: At the same insertion angle, the stresses on the miniscrews were highest in downward force applications, while they were the lowest in upward force applications. This means that with upward traction, stresses are more evenly distributed on the surface of the miniscrew. An analysis of the principal stress distribution in surrounding bone showed that compressive and tensile stresses increased with the angle of insertion up to 30 degrees. For larger insertion angles, the increase almost vanished., Conclusion: An obliquely inserted miniscrew and its surrounding tissues generally provide sufficient anchorage for 2 N of orthodontic loading, but care must be taken to avoid screw failure during placement and removal of obliquely placed miniscrews.

Articular cartilage covers the temporomandibular joint (TMJ) and provides smooth and nearly frictionless articulation while distributing mechanical loads to the subchondral bone. The thickness of the cartilage is considered to be an indicator of the stage of development, maturation, aging, loading history, and disease. The aim of our study was to develop a method for ex vivo assessment of the thickness of the cartilage that covers the TMJ and to compare that with two other existing methods. Eight porcine TMJ condyles were used to measure cartilage thickness. Three different methods were employed: needle penetration, micro-computed tomography (micro-CT), and histology; the latter was considered the gold standard. Histology and micro-CT scanning results showed no significant differences between thicknesses throughout the condyle. Needle penetration produced significantly higher values than histology, in the lateral and anterior regions. All three methods showed the anterior region to be thinner than the other regions. We concluded that overestimated thickness by the needle penetration is caused by the penetration of the needle through the first layer of subchondral bone, in which mineralization is less than in deeper layers. Micro-CT scanning method was found to be a valid method to quantify the thickness of the cartilage, and has the advantage of being non-destructive., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Objective: The Temporomandibular Joint (TMJ) disc is a fibrocartilaginous structure located between the mandibular condyle and the temporal bone, facilitating smooth movements of the jaw. The load-bearing properties of its anisotropic collagenous network have been well characterized under tensile loading conditions. However, recently it has also been speculated that the collagen fibers may contribute dominantly in reinforcing the disc under compression. Therefore, in this study, the structural-functional role of collagen fibers in mechanical compressive properties of TMJ disc was investigated., Design: Intact porcine TMJ discs were enzymatically digested with collagenase to disrupt the collagenous network of the cartilage. The digested and non-digested articular discs were analyzed mechanically, biochemically and histologically in five various regions. These tests included: (1) cyclic compression tests, (2) biochemical quantification of collagen and glycosaminoglycan (GAG) content and (3) visualization of collagen fibers' alignment by polarized light microscopy (PLM)., Results: The instantaneous compressive moduli of the articular discs were reduced by as much as 50-90% depending on the region after the collagenase treatment. The energy dissipation properties of the digested discs showed a similar tendency. Biochemical analysis of the digested samples demonstrated an average of 14% and 35% loss in collagen and GAG, respectively. Despite the low reduction of collagen content the PLM images showed considerable perturbation of the collagenous network of the TMJ disc., Conclusions: The results indicated that even mild disruption of collagen fibers can lead to substantial mechanical softening of TMJ disc undermining its reinforcement and mechanical stability under compression., (Copyright © 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Patients with symptomatic hypermobility of the temporomandibular joint report problems with the closing movement of their jaw. Some are even unable to close their mouth opening wide (open lock). Clinical experience suggests that relaxing the jaw muscles or performing a jaw movement to one side (laterotrusion) might be a solution. The aim of our study was to assess the potential of these strategies for resolving an open lock and we hypothesised that both strategies work equally well in resolving open locks. We assessed the interplay of muscle forces, joint reaction forces and their moments during closing of mouth, following maximal mouth opening. We used a 3D biomechanical model of the masticatory system with a joint shape and muscle orientation that predispose for an open lock. In a forward dynamics approach, the effect of relaxation and laterotrusion strategies was assessed. Performing a laterotrusion movement was predicted to release an open lock for a steeper anterior slope of the articular eminence than relaxing the jaw-closing muscles, herewith we rejected our hypothesis. Both strategies could provide a net jaw closing moment, but only the laterotrusion strategy was able to provide a net posterior force for steeper anterior slope angles. For both strategies, the temporalis muscle appeared pivotal to retrieve the mandibular condyles to the glenoid fossa, due to its' more dorsally oriented working lines., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Objectives: To investigate the influence of unilateral disc displacement (DD) in the temporomandibular joint (TMJ) on the stress in the contralateral joint, with a normally-positioned disc, during clenching., Study Design: A finite element model of the TMJ was constructed based on MRI and 3D-CT of a single patient with a unilateral DD. A second model with bilateral normally-positioned discs served as a reference. The differences in stress distribution in various TMJ components during clenching were predicted with these models., Results: In the unaffected joint of the unilateral DD model, the largest von Mises stress at the start of clenching was predicted in the inferior surface of the disc and increased by 30% during clenching. In the connective tissue the largest stress (1.16 MPa) did not reduce during clenching, in contrast to the (unaffected) joints of the reference model. In the affected joint, the largest stress was predicted in the temporal cartilage throughout clenching. In the surrounding connective tissue, the largest stress (1.42 MPa) hardly changed during clenching indicating no, or negligible, stress relaxation., Conclusions: This suggested that a unilateral DD could affect the stresses in the unaffected (contralateral) joint during clenching, where it may lead to weakening of the tissues that keep the disc on the top of the condyle. The results may be helpful in counseling worried patients, since they give insight into possible future developments of the disorder., (Copyright © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

After treatment of fractures in the neck of the mandible by means of immobilization of the dentition, often more or less severe manifestations of malocclusion remain. It was hypothesized that this is caused by an altered articulation in the jaw joint on the affected side. Furthermore, it was hypothesized that an anteriorly displaced condyle, as observed frequently as a side effect of the treatment, is caused by pull of the lateral pterygoid muscle, despite maxillomandibular fixation. Intervention experiments were performed in silico to test these hypotheses. With a biomechanical model of the human masticatory system alterations were applied mimicking a fractured mandibular neck and configurations that had been observed after healing. It was predicted that the altered articulation in the jaw joint caused asymmetrical jaw movements despite symmetrical muscle activation. The jaw was predicted to close with an open bite similar to clinical observations. The predicted laterodeviations, however, were not in accordance with clinical observations. Despite maxillo-mandibular fixation the lateral pterygoid muscle was able to pull the mandibular condyle out of its fossa in anterior direction. Consequently, despite some methodological limitations, in general the predictions corroborated the hypotheses., (Copyright © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Introduction: The primary aim of this study was to compare the precision of root canal length determination on cone-beam computed tomographic (CBCT) scans and periapical radiographs (PAs) with the actual root canal length. The secondary aim was to examine the influence of tooth type on root canal length measurements as assessed on CBCT scans and PAs., Methods: In total, 40 root canals of 33 teeth (molars, premolars, canines, and incisors) out of 5 dentate maxillas of human cadavers were included. Root canal length measurement was performed by a consensus panel (2 examiners) on CBCT scans (3D Accuitomo 170; J Morita, Kyoto, Japan) and digital PAs. After straight-line access opening, a #15 file was fixated in every root canal at the length measured on CBCT scans. All teeth were extracted, and the root canal containing the file was uncovered. Measurements made on images taken with a digital camera (AxioCam; Carl Zeiss, Sliedrecht, The Netherlands) linked to a stereozoom microscope (Stemi SV6, Carl Zeiss) were used as the actual root canal length., Results: When all roots were examined together, it was not clear which method is better for all types of teeth. For root canals of anterior teeth, there was no significant difference between the 2 methods. For root canals of posterior teeth, CBCT images gave results significantly closer to the actual root canal length in comparison with PAs (t value = -1.96; critical value is 1.74 with a significance level of 0.05)., Conclusions: Root canal length measurements of posterior maxillary teeth were more accurate when assessed by CBCT images than PAs., (Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Objectives: The temporomandibular joint (TMJ) is susceptive to the development of osteoarthritis (OA). More detailed knowledge of its development is essential to improve our insight into TMJ-OA. It is imperative to have a standardized reliable three-dimensional (3D) imaging method that allows for detailed assessment of both bone and cartilage in healthy and diseased joints. We aimed to determine the applicability of a contrast-enhanced microCT (µCT) technique for ex vivo research of mouse and human TMJs., Methods: Equilibrium partitioning of an ionic contrast agent via µCT (EPIC-µCT) was previously applied for cartilage assessment in the knee joint. The method was ex vivo, applied to the mouse TMJ and adapted for the human TMJ., Results: EPIC-µCT (30-min immersion time) was applied to mouse mandibular condyles, and 3D imaging revealed an average cartilage thickness of 110 ± 16 µm. These measurements via EPIC-µCT were similar to the histomorphometric measures (113 ± 19 µm). For human healthy OA-affected TMJ samples, the protocol was adjusted to an immersion time of 1 h. 3D imaging revealed a significant thicker cartilage layer in joints with early signs of OA compared with healthy joints (414.2 ± 122.6 and 239.7 ± 50.5 µm, respectively). A subsequent significant thinner layer was found in human joints with late signs of OA (197.4 ± 159.7 µm)., Conclusions: The EPIC-µCT technique is effective for the ex vivo assessment of 3D cartilage morphology in the mouse as well as human TMJ and allows bone-cartilage interaction research in TMJ-OA.

Objectives: The primary dental implant stability depends on the location of the implant in the jaw. This study analysed the architecture and mineralization of the trabecular bone at different jaw locations and thereby identified potential prognostic factors for implant failure. It has checked the hypotheses: (1) the mandible contains more compact and less mineralized trabecular bone than the maxilla and (2) within the mandible the trabecular bone is more compact and less mineralized in the anterior region., Methods: Alveolar bone specimens were produced from the cadavers of ten humans (7 males and 3 females; mean age: 73.7±12.5 years) and scanned with a high-resolution microCT system. Volumes of interest were chosen next to the roots of molars and incisors in both the maxilla and mandible. Several morphological parameters as well as the tissue mineral density were determined., Results: The alveolar bone specimens had a very high bone volume fraction (mean=0.31) with large differences (SD=0.17) between and within subjects. Yet several significant differences were found between the maxilla and the mandible. The bone volume fraction and trabecular thickness were significantly higher in the mandible than in the maxilla (p<0.01). But the tissue mineral density was not significantly different., Conclusions: A higher primary implant stability coincides with a higher bone volume fraction and degree of anisotropy Although local differences remain more important for implantology, the results suggest that the micro-structure also affects the implant stability. The tissue mineral density seems to have no predictive value., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Patients with hypermobility of the temporomandibular joint may have problems closing their mouth after opening widely. In the worst case, the mandibular condyles become trapped in front of the articular eminences and the jaw muscles cannot reposition them into the fossae (open lock). The difference in ease of closing the jaw between patients and non-patients is presently not well understood., Methods: Wide opening and subsequent jaw closing were simulated with a biomechanical model in a forward dynamics approach. The effect of anterior slope angle and orientation of jaw-closing muscles on condylar travel was determined., Findings: The mandibular condyles traveled anterior of the eminences and back into the fossae uneventfully with backwardly oriented jaw closers and eminences with a gentle anterior slope. However, combinations of relatively forward oriented jaw closers and a steep anterior slope caused the condyles to continue traveling anteriorly upon jaw-closing attempts, ending in an open lock position., Interpretation: Our results indicate that for the masticatory system to reach an open lock, various unfavorable combinations of jaw-closer orientation and anterior slope angle exist within normal physiological ranges. These findings could be relevant for maxillofacial surgeons, both for the diagnostic process and for clinical decisions, regarding patients suffering from open locks., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

This study analysed the effects of change of direction of masseter (MAS) and medial pterygoid muscles (MPM) and changes of moment arms of MAS, MPM and bite force on static and dynamic loading of the condyles after surgical mandibular advancement. Rotations of the condyles were assessed on axial MRIs. 16 adult patients with mandibular hypoplasia were studied. The mandibular plane angle (MPA) was <39° in Group I (n=8) and >39° in Group II (n=8). All mandibles were advanced with a bilateral sagittal split osteotomy (BSSO). In Group II, BSSO was combined with Le Fort I osteotomy. Pre and postoperative moment arms of MAS, MPM and bite force were used in a two-dimensional model to assess static loading of the condyles. Pre and postoperative data on muscle cross-sectional area, volume and direction were introduced in three-dimensional dynamic models of the masticatory system to assess the loading of the condyles during opening and closing. Postsurgically, small increases of static condylar loading were calculated. Dynamic loading decreased slightly. Minor rotations of the condyles were observed. The results do not support the idea that increased postoperative condylar loading is a serious cause for condylar resorption or relapse., (Copyright © 2012 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.)

This study evaluated whether surgical mandibular advancement procedures induced a change in the direction and the moment arms of the masseter (MAS) and medial pterygoid (MPM) muscles. Sixteen adults participated in this study. The sample was divided in two groups: Group I (n=8) with a mandibular plane angle (mpa) <39° and Group II (n=8) with an mpa >39°. Group I patients were treated with a bilateral sagittal split osteotomy (BSSO). Those in Group II were treated with a BSSO combined with a Le Fort I osteotomy. Pre- and postoperative direction and moment arms of MAS and MPM were compared in these groups. Postsurgically, MAS and MPM in Group II showed a significantly more vertical direction in the sagittal plane. Changes of direction in the frontal plane and changes of moment arms were insignificant in both groups. This study demonstrated that bimaxillary surgery in patients with an mpa >39° leads to a significant change of direction of MAS and MPM in the sagittal plane., (Copyright © 2012 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.)

Objective: Increased friction due to impaired lubrication in the jaw joint has been considered as one of the possible causes for internal joint disorders. A very common internal disorder in the jaw joint is an anteriorly dislocated articular disc. This is generally considered to contribute to the onset of arthritic injuries. Increase of friction as caused by impairment of lubrication is suspected to be a possible cause for such a disorder., Method: The influence of friction was addressed by analysis of its effects on tensions and deformations of the cartilaginous structures in the jaw joint using computational biomechanical analysis. Jaw open-close movements were simulated while in one or two compartments of the right joint friction was applied in the articular contact. The left joint was treated as the healthy control., Results: The simulations predicted that friction primarily causes increased shear stress in the articular cartilage layers, but hardly in the articular disc., Conclusions: This suggests that impaired lubrication may facilitate deterioration of the cartilage-subchondral bone unit of the articular surfaces. The results further suggest that increased friction is not a plausible cause for turning a normally functioning articular disc into an anteriorly dislocated one., (Copyright © 2011 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Follistatin-like 1 (Fstl1) is a secreted protein of the BMP inhibitor class. During development, expression of Fstl1 is already found in cleavage stage embryos and becomes gradually restricted to mesenchymal elements of most organs during subsequent development. Knock down experiments in chicken and zebrafish demonstrated a role as a BMP antagonist in early development. To investigate the role of Fstl1 during mouse development, a conditional Fstl1 KO allele as well as a Fstl1-GFP reporter mouse were created. KO mice die at birth from respiratory distress and show multiple defects in lung development. Also, skeletal development is affected. Endochondral bone development, limb patterning as well as patterning of the axial skeleton are perturbed in the absence of Fstl1. Taken together, these observations show that Fstl1 is a crucial regulator in BMP signalling during mouse development.

Objective: Bruxism, the parafunctional habit of nocturnal grinding of the teeth and clenching, is associated with the onset of joint degeneration. Especially prolonged clenching is suggested to cause functional overloading in the temporomandibular joint (TMJ). In this study, the distributions of stresses in the cartilaginous TMJ disc and articular cartilage, were analysed during prolonged clenching. The purpose of this study was to examine if joint degradation due to prolonged clenching can be attributed to changes in stress concentration in the cartilaginous tissues., Design: Finite element model was developed on the basis of magnetic resonance images from a healthy volunteer. Condylar movements recorded during prolonged clenching were used as the loading condition for stress analysis., Results: At the onset of clenching (time=0s), the highest von Mises stresses were located in the middle and posterior areas (6.18MPa) of the inferior disc surface facing the condylar cartilage. The largest magnitude of the minimum principal stress (-6.72MPa) was found in the condylar cartilage. The stress concentrations were relieved towards the superior disc surface facing the temporal cartilage. On the surfaces of the temporal cartilage, relatively lower stresses were found. After 5-min clenching, both stress values induced in the TMJ components were reduced to 50-80% of the stress values at the onset of clenching, although the concomitant strains increased slightly during this period., Conclusions: It is suggested that both the condylar and temporal cartilage layers along with the TMJ disc, play an important role in stress distribution and transmission during prolonged clenching due to tissue expansion. Furthermore, our study suggests that a development of stress concentrations in the TMJ during prolonged clenching and risk factors for the initiation of TMJ degeneration could not be confirmed., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

In recent years, optical techniques based on diffusion approximation have demonstrated their ability to gain rich spectral information about bone. However, these methods normally assume homogeneity, while cancellous bone and marrow form a highly heterogeneous two-phase medium. This paper studies the limitations of this assumption, and quantifies the role of microstructure on long-range transport properties. The propagation of light pulses through trabecular bone is calculated by Monte Carlo simulation of the scattering and absorption in reconstructions of bone samples obtained from x-ray micro tomographic scans. The time-resolved responses are then fitted with the analytical response of a homogeneous material to obtain the apparent transport properties. These properties are used to test different homogenization equations that have been postulated in the past for heterogeneous tissues and to check their accuracy. The results show that nonlinearity and crosstalk between absorption and scattering are statistically significant, although their impact is relatively small. More importantly, we found that the weight of the components is not only affected by their volume fractions, but need to be corrected by other morphologic measures like trabecular spacing or connectivity density. These deviations from the homogeneous assumption are stronger for scattering than for absorption. In conclusion, the average optical properties of cancellous bone are strongly determined by its microstructure, meaning that optical techniques are a valid method for tissue evaluation, but careful consideration of structure-related perturbation sources is required.

Kinematics of the human masticatory system during opening and closing of the jaw have been reported widely. Evidence has been provided that the opening and closing movement of the jaw differ from one another. However, different approaches of movement registration yield divergent expectations with regard to a difference in loading of the temporomandibular joint between these movements. Because of these diverging expectations, it was hypothesized that joint loading is equal during opening and closing. This hypothesis was tested by predicting loading of the temporomandibular joint during an unloaded opening and closing movement of the jaw by means of a three-dimensional biomechanical model of the human masticatory system. Model predictions showed that the joint reaction forces were markedly higher during opening than during closing. The predicted opening trace of the centre of the mandibular condyle was located cranially of the closing trace, with a maximum difference between the traces of 0.45 mm. The hypothesis, postulating similarity of joint loading during unloaded opening and closing of the jaw, therefore, was rejected. Sensitivity analysis showed that the reported differences were not affected in a qualitative sense by muscular activation levels, the thickness of the cartilaginous layers within the temporomandibular joint or the gross morphology of the model. Our predictions indicate that the TMJ is loaded more heavily during unloaded jaw opening than during unloaded jaw closing., (Copyright 2010. Published by Elsevier Ltd.)

Long-term in-vivo recordings of habitual bone strain in freely moving animals are needed to better understand the everyday mechanical loading environment responsible for bone-tissue maintenance. However, wireless methods to make such recordings are scarce. We report on the successful customisation of a commercially available voltage transmitter hooked-up to a strain-gauge rosette, its subcutaneous implantation in rabbits, and the quality of the implant's strain-gauge recordings. Continuous wireless recordings of a completely operational strain-gauge rosette glued to the mandibular surface of a freely moving rabbit could be made up to 33h. The resolution of the system was 1.5 microstrains/bit. The noise in the signal was 4.5 microstrains. To facilitate the automatic counting of bone-strain events in the retrieved data, and to calculate their peak amplitude, a novel approach is presented. The described technique enables the quantification of the daily bone-strain history defining the architecture and composition of bone tissue, and can help to further elucidate the strain parameters which influence bone tissue., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Daily mechanical loading strongly influences the architecture and composition of bone tissue. Throughout the day, the amplitudes, rates, frequencies, and the dispersion over time of these loads vary. Nevertheless, most experimental and descriptive studies on the aforementioned relationship consider only cyclic loading and, in addition, focus on weight-bearing bones. A more complete assessment of the daily loading of bone might lead to a better understanding of the natural everyday stimulus for bone maintenance or adaptive responses. In the present study, we measured the daily habitual strain history of the non-weight-bearing mandible bone in the rabbit. Long-term continuous strain recordings were made using an implantable telemetry device able to read out bone-bonded strain gauges. The lateral surface of the rabbit mandibular corpus was chosen as the bone surface of interest. During the recordings, which lasted up to 33 h, the rabbits (N=7) were able to move unrestrictedly in their cages, performing their habitual behaviours. Analysis of the recordings revealed that the measured bone surface was subjected to 2.9 (+/-1.4)x10(3) strain events per hour of which 1.8 (+/-1.0)x10(3) had amplitudes < or =10 microstrains (muvarepsilon). Larger strain amplitudes occurred less often and principal strains fell within the range of -517 (+/-118) muvarepsilon to 298 (+/-81) muvarepsilon. Strain rates never exceeded 10,000 muvarepsilon/s and only 8.9% (+/-7.2%) of the habitual strain rates were higher than 1000 muvarepsilon/s. Strain frequency spectra displayed clear peaks at 4-5 and 9 Hz. The wirelessly recorded daily strain history of the rabbit mandible featured peak strain amplitudes resembling those of other mammalian mandibles, but much smaller than those found in many long-bone strain measurements., (Copyright (c) 2009 Elsevier Inc. All rights reserved.)

The human masticatory system consists of a mandible which is able to move with respect to the skull at its bilateral temporomandibular joint (TMJ) through contractions of the masticatory muscles. Like other synovial joints, the TMJ is loaded mechanically during function. The articular surface of the mandibular condyle is covered with cartilage that is composed mainly of collagen fibers and proteoglycans. This construction results in a viscoelastic response to loading and enables the cartilage to play an important role as a stress absorber during function. To understand its mechanical functions properly, and to assess its limitations, detailed information about the viscoelastic behavior of the mandibular condylar cartilage is required. The purpose of this paper is to review the fundamental concepts of the biomechanical behavior of the mandibular condylar cartilage. This review consists of four parts. Part 1 is a brief introduction of the structure and function of the mandibular condylar cartilage. In Part 2, the biochemical composition of the mandibular condylar cartilage is summarized. Part 3 explores the biomechanical properties of the mandibular condylar cartilage. Finally, Part 4 relates this behavior to the breakdown mechanism of the mandibular condylar cartilage which is associated with the progression of osteoarthritis in the TMJ.

The direction of the first principal stress in the articular disc of the temporomandibular joint was predicted with a biomechanical model of the human masticatory system. The results were compared with the orientation of its collagen fibers. Furthermore, the effect of an active pull of the superior lateral pterygoid muscle, which is directly attached to the articular disc, was studied. It was hypothesized that the markedly antero-posterior direction of the collagen fibers would be reflected in the direction of the tensile stresses in the disc and that active pull of the superior lateral pterygoid muscle would augment these tensions. It was found that the tensile patterns were extremely dependent on the stage of movement and on the mandibular position. They differed between the superior and inferior layers of the disc. The hypothesis could only be confirmed for the anterior and middle portions of the disc. The predicted tensile principal stresses in the posterior part of the disc alternated between antero-posterior and medio-lateral directions.

Background: The purpose of this study was to investigate the effects of low-intensity pulsed ultrasound (LIPUS) stimulation on the proliferation and differentiation of cementoblast lineage cells., Methods: An immortalized human periodontal ligament cell line (HPL) showing immature cementoblastic differentiation was used. Cultured HPL cells were subjected to LIPUS exposure (frequency = 1 MHz; pulsed 1:4; intensity = 30 mW/cm(2)) or sham exposure for 15 minutes per day. Expression levels of alkaline phosphatase (ALP), type I collagen (Col-I), runt-related gene 2 (Runx2), bone sialoprotein (BSP), osteocalcin (OCN), and osteopontin (OPN) mRNA were analyzed with real-time polymerase chain reaction analysis. Furthermore, ALP activity, collagen synthesis, and protein level of Runx2 were examined after 6 days of LIPUS exposure., Results: mRNA and protein levels of ALP, Col-I, and Runx2 were significantly increased by LIPUS exposure compared to controls, whereas BSP, OCN, and OPN mRNA expression could not be detected in HPL cells, irrespective of LIPUS exposure., Conclusion: LIPUS enhanced ALP activity, collagen synthesis, and Runx2 expression of HPL cells, which provides important insight into the promotion of early cementoblastic differentiation of immature cementoblasts.