Effects of occlusion modification on the remodelling of degenerative mandibular condylar processes.

OBJECTIVE: The temporomandibular joint (TMJ) displays a high remodelling capability in response to occlusion changes. The purpose of the current study was to investigate the responses of TMJ condyles of growing mice to the installation of a unilateral anterior crossbite (UAC) prosthesis and the replacement of the UAC prothesis with a bilateral anterior elevation (BAE) prosthesis. MATERIALS AND METHODS: C57BL/6J mice were randomly assigned to the blank control and experimental groups. In mice in the experimental groups, UAC was created, while in others, BAE was created after the creation of UAC or removal of UAC. Changes in TMJ condylar cartilage and subchondral bone were assessed. RESULTS: The degradation of condylar cartilage induced by UAC was reversed by BAE, as evaluated by cartilage histochemical changes, collagen II-positive area, collagen X-positive chondrocytes and expression levels of Adamts-5, Mmp13, Tnf-α and Il-1ß. Subchondral bone was assessed based on the subchondral bone volume, the number of TRAP-positive cells and the Opg/Rankl ratio. CONCLUSION: The growing mouse TMJ condyle displays a high remodelling capability, which can be degenerative or rehabilitative in response to the creation of UAC and the replacement of UAC with BAE. Early correction of occlusion is beneficial for the recovery of degenerative condyles.

Bilateral anterior elevation prosthesis boosts chondrocytes proliferation in mice mandibular condyle.

OBJECTIVE: We aimed to develop a mouse model predominating in a proliferative response in the articular cartilage of the temporomandibular joints. MATERIALS AND METHODS: Bilateral anterior elevation of occlusion was developed by installing metal tubes onto the incisors of mice with edge-to-edge relation to prevent tooth wear, leading to an increase in the vertical height of the dental occlusion with time. Morphological changes and expression changes in Cyclin D1, Aggrecan, and type II and type X collagen in the mandibular condylar cartilage were detected. In addition, cells were isolated from the mandibular condylar cartilage and exposed to cyclic tensile strain (CTS). RESULTS: Compared with age-matched controls, the tooth length was longer at 3 weeks, 7 weeks, and 11 weeks in BAE mice (p < 0.05), with increased condylar cartilage thickness, matrix amount, and cell number (p < 0.05). Compared with the deep zone cells, CTS stimulated the superficial zone cells to express a higher level of proliferating cell nuclear antigen, Cyclin D1, Aggrecan, and type II collagen but a lower level of type X collagen and alkaline phosphatase. CONCLUSION: Bilateral anterior elevation stimulated the proliferative response in the mandibular condylar cartilage, offering a new therapeutic strategy for cartilage degeneration.

Early growth response 1 reduction in peripheral blood involving condylar subchondral bone loss.

OBJECTIVES: To detect whether early growth response 1 (EGR1) in peripheral blood leucocytes (PBLs) indicates temporomandibular joint (TMJ) osteoarthritis (OA) lesions. MATERIALS AND METHODS: Egr1 mRNA expression levels in PBLs were detected in eight malocclusion patients without temporomandibular disorder (TMD) signs and 16 malocclusion patients with clinical TMD signs with (eight) or without (eight) imaging signs of TMJ OA. Twelve 6-week-old rats were randomized to a control group and a unilateral anterior crossbite (UAC) group and were sampled at 4 weeks. The Egr1 mRNA expression levels in PBLs and protein expression levels in different orofacial tissues were measured. RESULTS: Patients with TMD signs with/without TMJ OA diagnosis showed lower Egr1 mRNA expression levels in PBLs than patients without TMD signs. The lower Egr1 mRNA expression was also found in the PBLs of UAC rats, which were induced to exhibit early histo-morphological signs of TMJ OA lesions. In subchondral bone of UAC rats, EGR1 protein expression was decreased, co-localization of EGR1 with osterix or dentin matrix protein-1 was identified, and the number of EGR1 and osterix double-positive cells was reduced (all p < .05). CONCLUSION: Egr1 reduction in PBLs potentially indicates subchondral bone OA lesions at an early stage.

Catabolic changes of rat temporomandibular joint discs induced by unilateral anterior crossbite.

BACKGROUND: The temporomandibular joint (TMJ) disc plays a role in joint movement and in load absorbance and distribution. An experimental unilateral anterior crossbite (UAC) prosthesis induces mandibular condylar cartilage degeneration in rats. However, the changes in the articular disc are still unknown. OBJECTIVE: To describe changes in the TMJ discs of UAC rats. METHODS: The discs of fifty-four Sprague-Dawley rats, equally distributed into a UAC group and an age-matched sham-operated control group at 4, 12 and 20 weeks (n = 9), were evaluated by gross and histomorphological observation and by detection at the mRNA or protein expression levels of the markers related to the matrix elements. RESULTS: No macro- or micro-morphological differences were observed between groups. However, there were catabolic degradative changes at the molecular level in the UAC group, showing a significant reduction in the mRNA and/or protein expression levels of many molecules. The reduction became worse with time (P < 0.05). The reduced molecules included: (a) those related to the extracellular matrix, such as type I collagen, decorin and fibromodulin; (b) those related to chondrogenesis, such as type II collagen and aggrecan; and (c) those related to osteogenesis, such as alkaline phosphatase and runt-related transcription factor 2. The mRNA expression of vascular endothelial growth factor did not change. In contrast, fibronectin, which can promote wound healing, and its N-terminal fragment, which can induce cartilage degradation, were accumulated (P < 0.05). CONCLUSION: TMJ discs were stimulated to catabolic changes by the aberrant dental occlusion and seemed to go to inanimate with time.

Molecular changes in peripheral blood involving osteoarthritic joint remodelling.

Biomarkers of temporomandibular joint (TMJ) osteoarthritis (OA) remain unknown. The objective was to detect whether molecular biomarkers from peripheral blood leucocytes (PBLs) engage in TMJ OA lesions. Thirty-four six-week-old Sprague Dawley rats were used. The top upregulated gene ontology categories and gene-fold changes in PBLs were detected by a microarray analysis comparing rats that received 20-week unilateral anterior crossbite (UAC) treatment with age-matched controls (n = 4). Twenty weeks of UAC treatment had been reported to induce TMJ OA-like lesions. The other twenty-four rats were randomly placed in the UAC and control groups at 12- and 20-week time points (n = 6). The mRNA expression levels of the selected biomarkers derived from the microarray analysis and their protein expression in the alveolar bone and TMJ were detected. The microarray analysis indicated that the three most highly involved genes in PBLs were Egr1, Ephx1 and Il10, which were confirmed by real-time PCR detection. The increased protein expression levels of the three detected molecules were demonstrated in cartilage and subchondral bone (P < 0.05), and increased levels of EPHX1 were reported in discs (P < 0.05); however, increased levels were not present in the alveolar bone. Immunohistochemistry revealed the increased distribution of EGR1-positive, EXPH1-positive and IL10-positive cells predominantly in the osteochondral interface, with EXPH1 also present in TMJ discs. In conclusion, the increased mRNA expression of Egr1, Ephx1 and Il10 in PBLs may serve as potential biomarkers for developed osteoarthritic lesions relating to osteochondral interface hardness changes induced by dental biomechanical stimulation.

Enhancement of chondrocyte autophagy is an early response in the degenerative cartilage of the temporomandibular joint to biomechanical dental stimulation.

Autophagy is a cell protective mechanism for maintaining cellular homeostasis. The present study aimed to investigate whether autophagy is enhanced in the biomechanically induced degenerative cartilage of the temporomandibular joint (TMJ) and the potential role of mitogen-activated protein kinase kinase kinase kinase 3 (MAP4K3) and mammalian Target of rapamycin (mTOR) in this observation. To induce degenerative changes in the TMJs, rats were subjected to biomechanical dental stimulation by moving 4 molars away from their original position as we previously reported. The ultrastructure of autophagosome was observed by transmission electron microscopy. The number of lysosomes was analyzed by flow cytometry. The expression levels of Beclin1 and LC3 and the involvement of MAP4K3 activity were detected by immunohistochemistry, real-time PCR and western blot. The activity of the mTOR pathway indicated by p-mTOR and p-p70S6 K was assayed by western blot. TMJ degeneration, characterized by irregular cell arrangement and cell-free area, was induced in the experimental groups. Under transmission electron microscopy, we observed the presence of autophagosomes, small patches of condensed chromatin, abundant rough endoplasmic reticulum and Golgi apparatus. The number of lysosomes and the expression levels of Beclin1 and LC3 increased, while the activity of mTOR and the expression level of MAP4K3 decreased in the experimental groups. Cartilage in TMJ which was induced to be degenerative biomechanically exhibited autophagy accompanied by reduced mTOR and MAP4K3 activity.

Combined degenerative and regenerative remodeling responses of the mandibular condyle to experimentally induced disordered occlusion.

INTRODUCTION: The purposes of this research were to investigate the long-term responses of mandibular condylar cartilage to experimentally induced disordered occlusion and to evaluate changes in the expression of the SDF-1/CXCR4 axis. METHODS: Experimentally induced disordered occlusions were created in 8-week-old female Sprague-Dawley rats by orthodontic methods. After 24 weeks, remodeling of the mandibular condylar cartilage was assessed by hematoxylin and eosin staining. Protein and mRNA expression of SDF-1, CXCR4, MMP9, IL6, OPG, and RANKL were investigated by means of immunohistochemical staining and real-time polymerase chain reaction. RESULTS: Obvious cartilage degenerative remodeling responses were observed; they appeared as uneven distributions of cellular disposition, loss of cartilage surface integrity, and cell-free areas. Regenerative responses presenting as thickening of the whole and the calcified cartilage layers in the experimental group were also observed. Compared with the age-matched controls, the protein and mRNA levels of SDF-1, CXCR4, MMP9, IL6, and OPG, but not RANKL, were increased in the experimental group (all, P <0.05). In addition, the mRNA level of RANKL/OPG showed a decreasing trend in the experimental group compared with the age-matched controls (P = 0.052). CONCLUSIONS: This study demonstrated that long-term experimentally induced disordered occlusion leads to a combined response in degeneration and regeneration of mandibular cartilage, accompanied by active interaction of the SDF-1/CXCR4 axis and local upregulation of MMP9, IL6, and OPG.

Excess genistein suppresses the synthesis of extracellular matrix in female rat mandibular condylar cartilage.

AIM: To investigate the effect of excess genistein on the extracellular matrix in mandibular condylar cartilage of female rats in vivo. METHODS: Female SD rats were administered through oral gavage with genistein (50 mg/kg) or placebo daily for 6 weeks. The morphological changes of temporomandibular joints were studied with HE staining. The expression of cartilage matrix compounds (aggrecan and collagen type II), estrogen-related molecules (aromatase, estradiol, ERα and ERß) and proliferating cell nuclear antigen (PCNA) in mandibular condylar cartilage was detected using immunohistochemistry, ELISA and real-time PCR. RESULTS: The genistein treatment significantly reduced the thickness of the posterior and middle regions of mandibular condylar cartilage, and decreased the expression of collagen type II, aggrecan and PCNA. Compared with the control group, the estradiol content and expression levels of the key estradiol-synthesizing enzyme aromatase in the genistein-treatment group were significantly decreased. The genistein treatment significantly increased the expression of ERß, but decreased the expression of ERα. CONCLUSION: Excess genistein suppresses extracellular matrix synthesis and chondrocytes proliferation, resulting in thinner mandibular condylar cartilage. These effects may be detrimental to the ability of mandibular condylar cartilage to adapt to mechanical loads.

Changes of myelinated nerve and myelin basic protein expression in rats' periodontal ligaments after experimental tooth movement.

INTRODUCTION: Information about the effect of tooth movement on the myelinated nerve in the periodontal ligament is limited. In this study, we aimed to investigate what responses of the periodontal myelinated nerve can be evoked during experimental tooth movement. METHODS: In experimental-I group, the maxillary left and mandibular right third molars were moved distally. In experimental-II group, the maxillary left third molar but not the right one was moved, and the bilateral mandibular third molars were extracted. The ultrastructures of the myelinated nerve in the periodontal ligament of the bilateral maxillary third molars were observed under a transmission electron microscope. The expression of myelin basic protein was evaluated by immunohistochemistry. RESULTS: Degenerative ultrastructural changes of the myelinated nerve in the periodontal ligament were noticed mainly in the myelin sheath; these were observed earlier and were recoverable in the experimental-I group. In contrast, the ultrastructural changes of the myelinated nerve occurred mainly in the axons, were observed later, and were unrecoverable in the experimental-II group. A concomitant decrease of myelin basic protein expression was observed in both groups. CONCLUSIONS: Both experimental tooth movement and occlusal changes accompanying it caused changes of the myelinated nerve in the periodontal ligament.

Activation of the VpdmVGLUT1-VPM pathway contributes to anxiety-like behaviors induced by malocclusion.

Occlusal disharmony has a negative impact on emotion. The mesencephalic trigeminal nucleus (Vme) neurons are the primary afferent nuclei that convey proprioceptive information from proprioceptors and low-threshold mechanoreceptors in the periodontal ligament and jaw muscles in the cranio-oro-facial regions. The dorsomedial part of the principal sensory trigeminal nucleus (Vpdm) and the ventral posteromedial nucleus (VPM) of thalamus have been proven to be crucial relay stations in ascending pathway of proprioception. The VPM sends numerous projections to primary somatosensory areas (SI), which modulate emotion processing. The present study aimed to demonstrate the ascending trigeminal-thalamic-cortex pathway which would mediate malocclusion-induced negative emotion. Unilateral anterior crossbite (UAC) model created by disturbing the dental occlusion was applied. Tract-tracing techniques were used to identify the existence of Vme-Vpdm-VPM pathway and Vpdm-VPM-SI pathway. Chemogenetic and optogenetic methods were taken to modulate the activation of VpdmVGLUT1 neurons and the Vpdm-VPM pathway. Morphological evidence indicated the involvement of the Vme-Vpdm-VPM pathway, Vpdm-VPM-SI pathway and VpdmVGLUT1-VPM pathway in orofacial proprioception in wild-type mice and vesicular glutamate transporter 1 (VGLUT1): tdTomato mice, respectively. Furthermore, chemogenetic inhibition of VpdmVGLUT1 neurons and the Vpdm-VPM pathway alleviated anxiety-like behaviors in a unilateral anterior crossbite (UAC) model, whereas chemogenetic activation induced anxiety-like behaviors in controls and did not aggravate these behaviors in UAC mice. Finally, optogenetic inhibition of the VpdmVGLUT1-VPM pathway in VGLUT1-IRES-Cre mice reversed UAC-induced anxiety comorbidity. In conclusion, these results suggest that the VpdmVGLUT1-VPM neural pathway participates in the modulation of malocclusion-induced anxiety comorbidity. These findings provide new insights into the links between occlusion and emotion and deepen our understanding of the impact of occlusal disharmony on brain dysfunction.

A preliminary anatomical study on the association of condylar and occlusal asymmetry.

The aim of this study was to test the hypothesis that condylar and occlusion asymmetry are not associated. For each of 22 skulls, the asymmetry of condyles was graded by one examiner and the asymmetry of occlusion by another examiner, both blinded to each other's evaluation, as 0 = symmetrical, 1 = mild asymmetrical and 2 = severe asymmetrical. There were 18 condyles graded the same as to their occlusion, but in four, the grades differed by one degree. Nine were graded symmetrical, seven were mild, and six were graded severely asymmetrical condyles. The corresponding figures for occlusion were: 10 were graded symmetrical, seven were graded mildly asymmetrical, and five were graded severely asymmetrical occlusion. The relation between occlusion and condylar asymmetry was tested using Goodman-Kruskal's gamma and was found to be 0.970 (p < 0.001). The null hypothesis was not supported. The results indicate that asymmetry of occlusion and condyles are associated, which indicates the need for further studies on larger samples, and in vivo studies.

Masseter response to long-term experimentally induced anterior crossbite in Sprague-Dawley rats.

OBJECTIVE: To detect the long-term response to unilateral anterior crossbite (UAC) in masticatory muscles and in molecular biomarkers of peripheral blood leukocytes. DESIGN: Fifty-six six-week-old Sprague-Dawley rats were used. The gene-fold changes in peripheral blood leukocytes were detected by the microarray analysis to compare the rats that received 20-week UAC treatment with age-matched controls (n = 4). Muscle atrophy-related gene Fbxo32 was selected based on the data of the microarray analysis verified by using real-time PCR. The remaining 36 rats were randomly separated in the UAC and control groups at 12 and 20 weeks (n = 12). The protein expression of Fbxo32 and the muscle injury and myogenesis-related markers, αB-crystallin and desmin, were detected in the masseter and lateral pterygoid muscles by western blot assay. RESULTS: In the 20-week UAC group, the masseter muscle weight was lower than that in the age-matched control group, and the expression level of Fbxo32 gene in peripheral blood leukocytes was increased according to the microarray analysis confirmed by real-time PCR detection. The increased protein expression levels of Fbxo32 were detected in the masseter in the 20-week UAC group, and the protein expression levels of desmin and αB-crystallin were decreased at this time point. No similar changes were detected in the lateral pterygoid muscle. CONCLUSIONS: Masseter atrophy is induced by long-term stimulation of UAC. The increased expression of the Fbxo32 gene in peripheral blood leukocytes may be a candidate biological marker of masseter atrophy.

Mandibular condylar cartilage response to moving 2 molars in rats.

INTRODUCTION: The purpose of this study was to investigate the responses of mandibular condylar cartilage to moving 2 molars in different combinations. METHODS: Rats were assigned to male and female control and experimental groups (each, n = 5). Elastic rubber bands were used to move medially the maxillary left and the mandibular right first molars in experimental group I. The same method was used to distally move the maxillary left and the mandibular right third molars, 2 mandibular third molars, and 2 maxillary third molars in experimental groups II, III, and IV, respectively. At the end of the eighth week, all condyles were examined histologically. The areas of histologic change as a percentage of total cartilage area were compared by using the Mann-Whitney U test. RESULTS: Cartilage degenerative remodeling was observed in experimental groups II, III, and IV. The percentage areas of degenerative remodeling were higher in female experimental groups II and III than in the female control group, and in female experimental group II than in female experimental group IV and male experimental group II (all, P <0.05). CONCLUSIONS: The mandibular condylar cartilage of female rats responded variously to different combinations of molar movement; the most obvious remodeling was observed in groups in which the maxillary left and mandibular right third molars were moved.

Injury responses of Sprague-Dawley rat jaw muscles to an experimental unilateral anterior crossbite prosthesis.

OBJECTIVE: Dental occlusion are frequently changed in clinic. Molecular responses in jaw muscles to aberrant dental occlusion are changes are attractive, yet remain are obscure. DESIGN: Unilateral anterior crossbite (UAC) prostheses were applied to Sprague-Dawley rats and then ceased after two weeks to detect the reactions of the masseter, a representative jaw elevator, and the lateral pterygoid muscle (LPM), a representative jaw depressor. RESULTS: Two weeks of UAC elicited mild injury of the two muscles. Myogenesis and protective reactions were detected as increases in αB-crystallin expression in the masseter after 3 days and in the LPM after 2 weeks, and increases in desmin expression in both muscles after 2 weeks. A switch in fibre types from IIb to IIx occurred in the LPM but not in the masseter. Inflammatory responses, shown by the infiltration of inflammatory cells and increases in TNF-α mRNA expression, and fibrosis responses, shown by increased mRNA expression of Type I and III collagens, appeared very mild in the two muscles. These responses were partially recovered by the cessation of UAC. During the whole process, no obvious changes were observed in mitochondrial function, as indicated by the levels of proliferator-activated receptor γ coactivator 1α, mitofusin-2 and voltage-dependent anion channel. CONCLUSIONS: UAC causes injury and very limited inflammatory and fibrosis adaption in the masseter and LPM. Both muscles respond with myogenesis and protective activity. The LPM responds also with muscle fibre isoform alternations. These alterations were partially recovered by the cessation of dental stimulation at an early stage.

Death and proliferation of chondrocytes in the degraded mandibular condylar cartilage of rats induced by experimentally created disordered occlusion.

OBJECTIVE: To investigate the effect of experimentally created disordered occlusion (ECDO) on cell death and proliferation in rat mandibular condylar cartilage. METHODS: Sprague-Dawley rats were randomly assigned to experimental and control groups. In the experimental groups, ECDO was created by the dental orthodontic method. By means of histological evaluation, immunohistochemistry and TUNEL staining, we studied the histomorphological changes, the death and proliferation of chondrocytes. RESULTS: Time- and sex-related progressive histologic degradation was observed in the condylar cartilage of ECDO rats, accompanied with diminished chondrocyte proliferation in the female 12-week ECDO subgroup (P < 0.05). An increase in the number of apoptotic chondrocytes was seen in both the female 8- and 12-week ECDO subgroups and in the male ECDO 12-week subgroup (all P < 0.05), but not in the male ECDO 8-week subgroup (P > 0.05). CONCLUSION: ECDO induces degradation in the rat condylar cartilage accompanied by an increase in chondrocyte death.

Influence of changing occlusal support on jaw-closing muscle electromyographic activity in healthy men and women.

OBJECTIVES: To test whether changes in occlusal support differentially modulate masseter and anterior temporalis muscle electromyographic (EMG) activity during controlled maximal voluntary clenching. MATERIAL AND METHODS: Forty-seven healthy subjects (32 M and 15 F, 22.9+/-1.3 years) were recruited. Cotton-rolls were used to modify the occlusal contact relations and were positioned on the right, left, or both sides, and either in the molar or premolar regions, i.e. six different occlusal combinations. Surface EMG activity was recorded bilaterally from the masseter and anterior temporalis area and normalized with respect to maximal voluntary clenching in the intercuspal position. Analysis of variance and the paired t-test were used to test the data. RESULTS: Normalized EMG activity was influenced by changes in cotton-roll modified occlusal support, and there were differences between muscles (p<0.001). In general, EMG activity decreased in both muscles when occlusal support was moved from the molar to the premolar region. When occlusal support was moved from bilateral to unilateral contacts, EMG activity in the balancing-side anterior temporalis muscle and in bilateral masseter muscles decreased. Unilateral clenching on the molars, but not on the premolars, was associated with lower EMG activity in the balancing-side masseter and always associated with lower EMG activity in the balancing-side anterior temporalis compared to the working side (p<0.05). CONCLUSIONS: Masseter and anterior temporalis muscles respond differently to changes in occlusal support, which may have implications for stability of the mandible during intense clenching.

Malocclusion Generates Anxiety-Like Behavior Through a Putative Lateral Habenula-Mesencephalic Trigeminal Nucleus Pathway.

Malocclusion is an important risk factor for temporomandibular disorder (TMD), a series of disorders characterized by dysfunction in the orofacial region involving the temporomandibular joint (TMJ) and jaw muscles. We recently showed that experimental unilateral anterior crossbite (UAC) produced masseter hyperactivity through a circuit involving the periodontal proprioception, trigeminal mesencephalic nucleus (Vme), and trigeminal motor nucleus (Vmo). Anxiety is a common complication in patients with TMD. The lateral habenula (LHb) is involved in emotional modulation and has direct projections to the Vme. Therefore, the present research examined whether UAC facilitates excitatory input from the LHb to the Vme and, subsequently, anxiety-like behaviors in rats. The LHb activation was evaluated by the electrophysiological recording, assessment of vesicular glutamate transporter-2 (VGLUT2) mRNA expression, and measurement of anxiety-like behaviors. The effects of LHb activity on Vme were evaluated by electrophysiological recording from Vme neurons and local changes in VGLUT2 protein density. UAC produced anxiety in modeled rats and increased neuronal activity in the LHb. VGLUT2 mRNA expression was also increased in the LHb. Further, VGLUT2-positive boutons were observed in close apposite upon parvalbumin (PV)-labeled Vme neurons. VGLUT2 protein expression was also increased in the Vme. Significantly, injection of VGLUT2-targeted shRNA into the LHb reduced the expression of VGLUT2 protein in the Vme, attenuated UAC-associated anxiety-like behaviors, and attenuated electrophysiological changes in the Vme neurons. In conclusion, we show that UAC activates the LHb neurons as well as the periodontal proprioceptive pathway to provide excitatory input to the Vme and produce anxiety in rats. These findings provide a rationale for suppressing activity of the LHb to attenuate both the physical and psychological effects of TMD.

Comparison of posterior occlusion between patients with anterior open bite and scissor deep bite.

Objective A minor alteration in the posterior occlusal height elicits a large transformation in the anterior vertical dimension. Thus, the present study was performed to determine whether a posterior cusp-to-cusp relation that increases the posterior vertical dimension contributes to an anterior open bite. Methods Study casts were examined from orthodontic patients aged 10 to 27 years, 21 with an open bite and 28 with a scissor deep bite. A logistic regression model was used to analyze the contribution of various factors to these two anterior occlusal patterns. The dental arch width and number of worn cusps were compared between the two groups. Results Patients with an open bite had a significantly higher incidence of a posterior buccal-lingual cusp-to-cusp relation, wider mandibular arch in the molar region, and larger numbers of worn maxillary buccal cusps and mandibular lingual cusps than patients with a scissor deep bite. Conclusions A posterior buccal-lingual cusp-to-cusp relation is associated with a larger anterior vertical dimension, such as that in patients with an open bite.

Vertical contact tightness of occlusion comparison between orofacial myalgia patients and asymptomatic controls: a pilot study.

OBJECTIVE: The association between occlusal contact and orofacial pain remains unclear. The aim of this study was to detect occlusal contact tightness by using a new method and to compare differences between patients and asymptomatic controls. METHODS: Fifteen female patients with orofacial myalgia and fifteen age- and sex-matched asymptomatic controls were enrolled. Occlusal contacts were recorded by making bite imprints. The numbers, sizes, and distributions of the contacts were detected by making photos of bite imprints after biting. The Mann-Whitney U test and ANOVA were used for statistical analysis. RESULTS: In myalgia patients, impact contacts at the molar regions were more frequent, larger in number and area size, and were distributed more on guiding cusps, compared with impact contacts in asymptomatic controls. CONCLUSION: Our new method revealed more prevalent and more severe impact contacts in orofacial myalgia patients, compared with asymptomatic controls.

Association Between Contact from an Overerupted Third Molar and Bilaterally Redistributed Electromyographic Activity of the Jaw Closing Muscles.

AIMS: To determine whether the facial side of an overerupted third molar and/or the side exhibiting symptoms of temporomandibular disorders (TMD) has an association with the bilateral distribution of occlusal contact number, occlusal force, or surface electromyographic (SEMG) activity of the anterior temporalis (TA) and masseter muscles. METHODS: Nineteen patients with unilateral TMD symptoms and one overerupted mandibular third molar were enrolled. Occlusal contacts and the SEMG activity of the anterior temporalis and masseter muscles were recorded simultaneously during maximal voluntary clenching (MVC) in the intercuspal position (ICP-MVC) and in the protrusive edge-to-edge position (Pro-MVC). The associations between the side of overeruption/TMD symptoms and the Δvalues of the differences between the right- and left-side values for the number of occlusal contacts, sectional force value (defined as the ratio of the anterior or posterior sectional arch bite force of the right or left side to the total arch force [SFV]), and SEMG activity of the temporalis and masseter muscles were analyzed. RESULTS: The overeruption side (P < .050), but not the symptomatic side (P > .050), showed an association with the Δvalues, with higher SFVs of the posterior arch and lower values for temporalis SEMG activity in the 100%, 75%, and 50% protrusive clenching positions and larger numbers of occlusal contacts in the posterior arch in the 100% and 75% protrusive clenching positions than the non-overeruption side. CONCLUSION: The pattern of occlusion, but not TMD symptoms, had an association with the number and distribution of the occlusal contacts, occlusal force, and temporalis SEMG activity.