Bilateral treatment of the masseter with botulinum toxin: Consequences for mastication, muscle force and the mandibular condyle.

BACKGROUND: Clinical use of botulinum neurotoxins (BoNTs) in masticatory muscles is usually bilateral, but most studies on the functional consequences of BoNT treatment have used unilaterally treated animals. OBJECTIVES: To test the hypothesis that bilateral BoNT treatment of the rabbit masseter hampers mastication and to assess its effects on bone density of the mandibular condyles. METHODS: Ten 5-month-old female rabbits received injections of BoNT into both masseter muscles and nine sham animals received saline. Body weight, incisor bite force during masseter tetany, and surface and fine-wire electromyography (EMG) of the masseter and medial pterygoid muscles were assessed at regular intervals. Half the sample was terminated after 4 weeks and the remainder after 12 weeks. Muscles were weighed and mandibular condyles were scanned with microCT to analyse bone density. RESULTS: BoNT rabbits lost weight and required a soft-food diet. Incisor occlusal force plummeted after BoNT injection and remained lower than the shams. The duration of masticatory cycles was increased in the BoNT rabbits for 5 weeks, with most of the increase due to the adductor burst. Masseteric EMG amplitude began to improve at Week 5, but remained low on the working side throughout the experiment. At the 12-week endpoint, masseter muscles were smaller in the BoNT rabbits. Medial pterygoid muscles did not compensate. Condylar bone density was reduced. CONCLUSION: Bilateral treatment of the rabbit masseter by BoNT severely affected chewing performance. Even after a 3-month recovery period, deficits remained in bite force, muscle size and condylar bone density.

The condylar capping for microvascular temporomandibular joint reconstruction: A preliminary study.

BACKGROUND: Defects of the temporomandibular joint (TMJ) are often difficult to be reconstructed in the correct dimensions and function. This preliminary study aims to describe a novel technique of condylar reconstruction with a microvascular flap in case of deforming arthrosis of the TMJ: condylar capping. PATIENTS AND METHODS: Four patients between 22 and 62 years old-three females and one male-with severe unilateral arthrosis of the TMJ underwent condylar capping. All patients had already had a failed conservative treatment, followed by arthroscopy with lysis and lavage and later open surgery with total or subtotal diskectomy combined with a condylar arthroplasty. Nevertheless, their pain was still at level six or more on a visual analogue scale. Moreover, they could eat only soft food. At this stage, they underwent condylar capping using an osteochondral lateral femoral condyle (LFC) flap. The surgical technique and the postoperative management are described in detail. Crucially the attachment of the lateral pterygoid muscle to the condylar neck was preserved in all cases. The patients were followed up clinically and by CT scan preoperatively, 6, and 12 months postoperatively. RESULTS: The mean height of the reconstructed neo-condyle was 6.0 mm, the mean width 16.2 mm, and the mean sagittal length 9.8 mm. The follow-up period ranged from 14 to 64 months. The procedures were uneventful for all patients, and the donor site morbidity was negligible. Twelve months later, the patients were all pain-free and able to have a regular diet. The TMJ and the knee had a normal range of movement and power. Postoperative imaging demonstrated bone healing and stable and anatomically correct condyle reconstruction. CONCLUSIONS: Based on the author's experience, the condylar capping with the LFC appears promising for reconstructing the condylar head in cases of severe osteoarthritis. Preserving the attachment of the lateral pterygoid muscle allows a complete restoration of the physiologic range of movement, including protrusion and laterotrusion of the mandible.

Influence of different treatment procedures on the temporomandibular joint after mandibular setback in skeletal class III - A retrospective study.

The aim of this study was to clarify the effects of three different orthognathic surgical procedures on the temporomandibular joint after mandibular setback. Conventional sagittal split ramus osteotomy (SSRO) with segmental fixation (conv-SSRO), intraoral vertical ramus osteotomy (IVRO), or SSRO without fixation followed by the physiological positioning strategy (nonfix-SSRO) was performed for mandibular setback. Temporomandibular joint disorder (TMD) symptoms were clinically assessed, and the condylar head angle was measured. In total, 129 patients participated. Preoperative TMD and treatment procedure were related to postoperative TMD. A menton deviation of 3.43 mm was the cutoff for the risk of postoperative TMD. The incidence rate of postoperative TMD in the conv-SSRO group was higher than that in the IVRO (p = 0.0197) and nonfix-SSRO (p = 0.0001) groups in asymmetric cases. There was no significant postoperative change in the temporomandibular joint space in each group. In symmetric and asymmetric cases, the condylar head was rotated inwards by 5.82 ± 4.75° (p < 0.0001) and 5.44 ± 3.10° (p < 0.0001), respectively, in the conv-SSRO group, and outwards by -7.98 ± 5.05° (p < 0.0001) and -8.32 ± 6.38° (p < 0.0001), respectively, in the IVRO group, but it was almost stable in the nonfix-SSRO group. Within the limitations of the study it seems that nonfix-SSRO should be preferred over conv-SSRO and IVRO whenever appropriate.

Características anatómicas-funcionales que orientan la posición del cóndilo en la fosa mandibular en una relación céntrica: una descripción narrativa / Anatomical functional characteristics that guide the condylar position in mandibular fossa a centric relation: narrative description

RESUMEN: La Relación Céntrica (RC) es un concepto que busca definir la posición ideal del cóndilo de la mandíbula en la fosa mandibular, siendo esta posición muy discutida en la literatura y ha ido cambiado con los avances en conocimiento y tecnología. Tomándose en la actualidad en consideración elementos anatómicos esenciales que son utilizados como guía para el clínico. La importancia de poder reconocer esta posición radica en la correcta ejecución tanto de procedimientos diagnósticos como de tratamiento en diversas áreas de la odontología. Existen elementos anatómicos de la articulación temporomandibular (ATM) que nos ayudarían a comprender mejor el concepto de RC, entre estos destacan que la condensación ósea de las superficies articulares funcionales y su recubrimiento por fibrocartílago; la porción media del disco articular, desprovista de vasos y nervios; el techo de la fosa mandibular que puede llegar a ser extremadamente delgado por lo cual no se consideraría un área para soportar carga; la prolongación posterior del disco articular (DA) que es altamente vascularizada e inervada. El DA se encuentra íntimamente relacionado con estructuras como el ligamento temporomandibular o lateral y la cabeza superior del músculo pterigoideo lateral que permitirían junto a los elementos anteriormente mencionados el adecuado funcionamiento de la ATM. El correcto aprendizaje y utilización de estos conceptos contribuirá a lograr un mejor ejercicio del desarrollo profesional de estudiantes y profesionales del área de la odontología.

SUMMARY: The Central Relation (CR) is a concept that defines the ideal position of the mandibular condyle in the mandibular fossa. The position has been the subject of much discussion in the literature, noting changes as advancements in knowledge and technology are achieved. Thus, certain essential anatomical elements that are used as a guide for the clinician, are taken into account. The importance of being able to identify this position lies in the correct execution of both diagnostic and treatment procedures in various areas of dentistry. There are anatomical elements of the temporomandibular joint (TMJ) that improve understanding of the CR concept. These include: Bone condensation of the functional articular surfaces and their fibrocartilage coating; the middle portion of the joint disc, devoid of vessels and nerves. The roof of the mandibular fossa can become extremely thin, so it would not be considered an area to support load; the posterior prolongation of the articular disc (AD) Which is highly vascularized and innervated. The AD is also closely related to structures such as the temporomandibular or lateral ligament and the superior head of the lateral pterygoid muscle. Along with the previously described elements, this would allow proper functioning of the TMJ. The correct learning and use of these concepts contributes to a better exercise in the professional development of students and professionals in the area of dentistry.

Evaluation of sagittal condylar guidance angles using computerized pantographic tracings, protrusive interocclusal records, and 3D-CBCT imaging techniques for oral rehabilitation.

OBJECTIVE: The goal of registering the condylar guidance is to recreate the patient's occlusion as exactly as possible on the articulator, and is therefore essential for successful prosthodontic rehabilitation. Clinical, radiographic, and pantographic methods are used to determine sagittal condylar guidance angles (SCGAs). These methods generate different angles in the same patients. The present study is the first disquisition to evaluate and correlate SCGAs determined by the use of pantographic tracing (PT), protrusive records (PR), and radiographic (CBCT) techniques. MATERIALS AND METHODS: The condylar guidance was measured using PT, PR, and CBCT imaging techniques in 23 nonpatient participants aged between 18 and 30 years irrespective of sex. PT was recorded using Cadiax® Compact system, a computerized recorder of SCGAs. PR was obtained using polyvinyl siloxane bite registration material, transferred to a semiadjustable articulator (Denar Mark II, Whip Mix Corp., USA) using facebow transfer (Denar Mark II, Whip Mix Corp., USA) and CR records, to determine SCGAs. Images of the mid-facial region were obtained using CBCT scan for 3D reconstruction. The angle formed between Frankfort horizontal plane (FHP) and a line extending from the most supero-anterior point on the glenoid fossa to the most convex point on the apex of articular eminence (AE) was measured to obtain SCGAs. RESULTS: The mean left and right SCGAs were as follows: PT (34.42° and 33.93°, respectively), PR (32.14° and 31.82°), and CBCT (38.96° and 38.12°). The Pearson coefficients for the correlations with PT and PR on the left and right sides were 0.899 and 0.907, respectively, while it was 0.911 and 0.934, and 0.842 and 0.874 from PT and CBCT, and PR and CBCT, respectively. CONCLUSION: Strong correlations were found between SCGAs obtained using PT, PR, and CBCT techniques.

On the reinsertion of the lateral pterygoid tendon in total temporomandibular joint replacement surgery.

This report aims to present the concept of reestablishing lateral pterygoid muscle function during total temporomandibular joint (TMJ) replacement surgery. The key feature is a lattice structure (scaffold) located in the condylar neck of a titanium, three-dimensionally (3D)-printed mandibular component that houses morselized autologous bone from the resected condyle and osteogenic stem cells from iliac bone marrow aspirate, and to which the fibrous enthesis component (collagen attachments to a bone fragment) is fixed via suture cerclage prior to the development of the bony union. Five TMJs were replaced using enthesis reconstruction in three patients who were followed for 1 year and more. Laterotrusion to the contralateral side measured on average 6.4 mm preoperatively, 2.3 mm at 1 month, 3 mm at 3 months, 4 mm at 6 months, and at 1-1.5 years (62,5% of the preoperative laterotrusion/40% of a normal laterotrusion). Subjective normalization of mastication after 1 year was present in all patients. A successful reattachment of the enthesis to an alloplastic endoprosthesis suggests that patients will not only be able to open and close their mouths properly with reduced pain but will also be able to actually chew. The technique has potential applications in orthopedic alloplastic reconstruction.

Estimated functional space of centric condyle positions in temporomandibular joints of asymptomatic individuals using MRI.

Magnetic resonance imaging (MRI) studies on centric condyle positions lack 3D comparisons of guided and unguided methods, which are used for accomplishing centric relation reference positions. The purpose of this study was to describe the space, in which mandibular condyles are placed in vivo by dental intercuspation, Dawson's bimanual manipulation, and neuromuscular position. Twenty asymptomatic individuals aged 23 to 37 years underwent separate bite registrations using bimanual manipulation and the unguided neuromuscular technique. Subsequent 3-Tesla MRI scans of both temporomandibular joints yielded 3D data of the most superior condylar points at maximum intercuspation and both centric relation positions. We found concentric condyle positions in maximum intercuspation but considerable variation of condyle position after bimanual manipulation and neuromuscular technique. Their 95% predictive confidence ellipses overlapped substantially and created a space of reference positions. Its smallest volume averaged 2 mm3 for a minimal convex hull (95% confidence interval 1.1-3.2) and 3.5 mm3 for a minimal ellipsoid hull (95% confidence interval 1.8-5.4). Visualized in vivo by MRI, condyle positions at bimanual manipulation and neuromuscular position were not predictable and showed substantial variation in asymptomatic subjects. Clinicians should be aware of the functional space and its effect on dental intercuspation.

An in situ hybridization study of MMP-2, -9, -13, -14, TIMP-1, and -2 mRNA in fetal mouse mandibular condylar cartilage as compared with limb bud cartilage.

The main purpose of this in situ hybridization study was to investigate MMPs and TIMPs mRNA expression in developing mandibular condylar cartilage and limb bud cartilage. At E14.0, MMP-2, -14, TIMP-1 and -2 mRNAs were expressed in the periosteum of mandibular bone, and in the condylar anlage. At E15.0 MMP-2, -14, TIMP-1 and -2 mRNAs were expressed in the perichondrium of newly formed condylar cartilage and the periosteum of developing bone collar, whereas, expression of MMP-14 and TIMP-1 mRNAs were restricted to the inner layer of the periosteum/perichondrium. This expression patterns continued until E18.0. Further, from E13.0 to 14.0, in the developing tibial cartilage, MMP-2, -14, and TIMP-2 mRNAs were expressed in the periosteum/perichondrium, but weak MMP-14 and no TIMP-1 mRNA expression was recognized in the perichondrium. These results confirmed that the perichondrium of condylar cartilage has characteristics of periosteum, and suggested that MMPs and/or TIMPs are more actively involved in the development of condylar (secondary) cartilage than tibial (primary) cartilage. MMP-9-positive cells were observed in the bone collar of both types of cartilage, and they were consistent with osteoclasts/chondroclasts. MMP-13 mRNA expression was restricted to the chondrocytes of the lower hypertrophic cell zone in tibial cartilage at E14.0, indicating MMP-13 can be used as a marker for lower hypertrophic cell zone. It was also expressed in chondrocytes of newly formed condylar cartilage at E15.0, and continuously expressed in the lower hypertrophic cell zone until E18.0. These results confirmed that progenitor cells of condylar cartilage are rapidly differentiated into hypertrophic chondrocytes, which is a unique structural feature of secondary cartilage different from that of primary cartilage.

Integrity of Human Mandibular Angle After Block Graft Harvest from Mandibular Body.

PURPOSE: To examine human mandibular angle integrity alterations accompanying a mandibular body block graft harvest surgical procedure. MATERIALS AND METHODS: Hemimandibles from 24 human cadavers were resected and sorted into one of three groups by residual dental status. The height of each hemimandible body was obtained and recorded. Acrylic bone cement was utilized to mount the hemimandibles at the mandibular condyle. Using standard surgical instruments and techniques, cortical bone of the mandibular body buccal plate was resected from the right hemimandibles. Left hemimandibles were used as a control. Each hemimandible was secured in an Instron 5565 mechanical unit. With forces placed on and perpendicular to the occlusal plane, each hemimandible underwent sequential loading until osseous fracture occurred. Descriptive statistics between grouped data were compared and discussed in terms of mean, minimum, and maximum. The statistical relationship between the maximal load, gender, and mandibular body height were identified. RESULTS: Donor and control hemimandible maximal load mean values were 423.63 N and 957.90 N, respectively. A statistically significant difference was present between maximal loads of donor and control hemimandibles (P < .0001). Correlations of statistical significance were present between mandibular bone height and maximal load in the control hemimandibles (P = .009). Correlations of statistical significance were not found between mandibular bone height, displacement at maximal load, and maximal load in the grafted hemimandibles (P >.05). No statistically significant correlation between dental status and gender was found in the donor and control hemimandibles (P > .05). CONCLUSION: After subjected to a typical block graft harvest surgical procedure, the human mandible's integrity is significantly altered. Gender, dental status, and mandibular bone height do not correlate with maximal load,and thus integrity, of donor and control mandibles.

Impact of mounting methods in computerized axiography on assessment of condylar inclination.

OBJECTIVE: Valid and reliable recording is a key requirement for accurately simulating individual jaw movements. METHODS: Horizontal condylar inclination (HCI) and Bennett's angle were measured using a digital jaw tracker (Cadiax® Compact 2) in 27 young adults. Three mounting methods (paraocclusal tray adapter, periocclusal tray adapter, and tray adapter with mandibular clamp) were tested. RESULTS: The mean values of the HCI differed by up to 10° between the mounting methods; however, the values for Bennett's angle did not differ substantially. While the intersession reliability of the Bennett's angle assessment did not depend on the mounting method, the reliability of the HCI assessment was only fair to good for the paraocclusal mounting method but poor for both periocclusal mounting methods. DISCUSSION: For attaching the tracing bow of jaw trackers to the mandible, a paraocclusal tray adapter should be applied, to achieve the most reliable results.

Aging does not change the compressive stiffness of mandibular condylar cartilage in horses.

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.

Part I: Development and Physiology of the Temporomandibular Joint.

PURPOSE OF REVIEW: Investigate the developmental physiology of the temporomandibular joint (TMJ), a unique articulation between the cranium and the mandible. RECENT FINDINGS: Principal regulatory factors for TMJ and disc development are Indian hedgehog (IHH) and bone morphogenetic protein (BMP-2). The mechanism is closely associated with ear morphogenesis. Secondary condylar cartilage emerges as a subperiosteal blastema on the medial surface of the posterior mandible. The condylar articular surface is immunoreactive for tenascin-C, so it is a modified fibrous periosteum with an underlying proliferative zone (cambrium layer) that differentiates into fibrocartilage. The latter cushions high loads and subsequently produces endochondral bone. The TMJ is a heavily loaded joint with three cushioning layers of fibrocartilage in the disc, as well as in subarticular zones in the fossa and mandibular condyle. The periosteal articular surface produces fibrocartilage to resist heavy loads, and has unique healing and adaptive properties for maintaining life support functions under adverse environmental conditions.

Part II: Temporomandibular Joint (TMJ)-Regeneration, Degeneration, and Adaptation.

PURPOSE OF REVIEW: Elucidate temporomandibular joint (TMJ) development and pathophysiology relative to regeneration, degeneration, and adaption. RECENT FINDINGS: The pharyngeal arch produces a highly conserved stomatognathic system that supports airway and masticatory function. An induced subperiosteal layer of fibrocartilage cushions TMJ functional and parafunctional loads. If the fibrocartilage disc is present, a fractured mandibular condyle (MC) regenerates near the eminence of the fossa via a blastema emanating from the medial periosteal surface of the ramus. TMJ degenerative joint disease (DJD) is a relatively painless osteoarthrosis, resulting in extensive sclerosis, disc destruction, and lytic lesions. Facial form and symmetry may be affected, but the residual bone is vital because distraction continues to lengthen the MC with anabolic bone modeling. Extensive TMJ adaptive, healing, and regenerative potential maintains optimal, life support functions over a lifetime. Unique aspects of TMJ development, function, and pathophysiology may be useful for innovative management of other joints.

A Morphometric and Cellular Analysis Method for the Murine Mandibular Condyle.

The temporomandibular joint (TMJ) has the capacity to adapt to external stimuli, and loading changes can affect the position of condyles, as well as the structural and cellular components of the mandibular condylar cartilage (MCC). This manuscript describes methods for analyzing these changes and a method for altering the loading of the TMJ in mice (i.e., compressive static TMJ loading). The structural evaluation illustrated here is a simple morphometric approach that uses the Digimizer software and is performed in radiographs of small bones. In addition, the analysis of cellular changes leading to alterations in collagen expression, bone remodeling, cell division, and proteoglycan distribution in the MCC is described. The quantification of these changes in histological sections - by counting the positive fluorescent pixels using image software and measuring the distance mapping and stained area with Digimizer - is also demonstrated. The methods shown here are not limited to the murine TMJ, but could be used on additional bones of small experimental animals and in other regions of endochondral ossification.

Analysis of masticatory muscle coordination during unilateral single-tooth clenching using muscle functional magnetic resonance imaging.

In a previous study, we used muscle functional magnetic resonance imaging to show that the anterior movement of the occlusal point increased the activity of the superior head of the ipsilateral lateral pterygoid muscle (ipsilateral SHLP) during unilateral single-tooth clenching. The purpose of this study was to verify the hypothesis that the increased activity of the ipsilateral SHLP described above serves to antagonise the occlusal force acting on the condyle. In total, 9 healthy volunteers were requested to perform left unilateral clenching at the first molar or first premolar region for 1 minute at 20% or 40% maximum voluntary clenching force. Changes in the mean proton transverse relaxation time (∆T2) were examined from the magnetic resonance images obtained before and after each clenching act as an index of the activity in all masticatory muscles. Correlation analyses of the mean ΔT2 for each volume of interest were performed with the first molar or premolar clenches to analyse the correlation between the activities in each muscle. A statistically significant correlation was exhibited between the ipsilateral temporal and ipsilateral SHLP (r = .651, P = .003) during first premolar clenching. However, no significant correlations were observed in the ipsilateral SHLP during first molar clenching. The results of this study suggest that the ipsilateral SHLP may contribute to the pulling of the mandibular condyle forward against the occlusal force generated by the ipsilateral temporal muscle.

The correlation between direction and amount of retrusive movement and condyle position and joint space.

OBJECTIVE: The direction and amount of retrusive movement may be correlated with the amount of joint space and the maximum intercuspal position of the condyle. The aim of this study was to identify any such correlation using an ultrasonic jaw motion analyzer and digital volumetric tomographic (DVT) scans. METHODS: Thirty-five dental students were selected as subjects. DVT scans were obtained using a next-generation i-CAT CBCT unit, and the direction and amount of retrusive movement were measured with a 3-D analyzer. RESULTS: Spearman Rho correlation tests showed no correlation between the amount of retrusive movement and the condyle position and joint space on either the right or left side. DISCUSSION: There is sufficient reason to suggest that retrusive movement of the condyle does not occur in isolation but is influenced by glenoid fossa bone morphology.

Physiological positioning strategy alters condylar position after mandibular ramus sagittal split osteotomies for mandibular prognathism.

OBJECTIVE: The aim of this study was to elucidate the physiological position of the proximal segment for postoperative jaw movement in patients with mandibular prognathism. METHODS: Twenty-two patients with mandibular prognathism were treated by orthognathic surgery using bilateral mandibular sagittal split ramus osteotomies (SSRO) with a physiological positioning strategy. The skeletal stability was assessed, and the movement of the proximal segment was evaluated by cephalography and computed tomography performed preoperatively, immediately postoperatively, and one year postoperatively. RESULTS: The patients were divided into two groups: the stable group (SNB relapse <1.5°) and the relapse group (SNB relapse ≥1.5°). In the stable group at one year postoperatively, the average SNB relapse was only 0.29° (7%), the condylar head had moved posteriorly by 0.75 mm, and the proximal segment had rotated counterclockwise by 1.2°. CONCLUSION: This new physiological positioning strategy improves the position of the condyle compared with the preoperative position in patients with mandibular prognathism.

The different effects of intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO) on mandibular border movement.

OBJECTIVES: This study investigated the different effects of intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO) on mandibular border movement. METHODS: The participants included 22 patients receiving IVRO and 22 patients receiving SSRO who were treated at Okayama University Hospital. Their mandibular border movement was evaluated in three dimensions with 6° of freedom using an optical recording system. RESULTS: A strong correlation between condylar and lower incisor movement was observed during maximum jaw protrusion and laterotrusion. Significant improvements in condylar and lower incisor movement were detected after orthognathic surgery during maximum jaw protrusion and laterotrusion in the IVRO group and during maximum jaw protrusion in the SSRO group. DISCUSSION: IVRO likely achieves greater improvement in jaw movement than SSRO. Therefore, the application of IVRO could be considered in the treatment of patients with jaw deformities featuring temporomandibular joint problems.