Real‐time three‐dimensional jaw tracking in temporomandibular disorders

When a dysfunction occurs in any component of the stomatognathic system, temporomandibular disorders (TMD) may originate. The aim of this study was to compare the deviations, displacement and the execution speed of mandibular movements among asymptomatic participants and those with TMD. Convenience sampling was used; forty participants diagnosed by clinical evaluation following the Research Diagnostic Criteria for Temporomandibular Disorders were divided into three groups: arthropathy (GART, 10 participants, 40% men), myopathy (GMYO, 10 participants, 30% men), and the control group (CG, 20 asymptomatic participants, 25% men). Participants were asked to perform the movements of free maximal mouth opening and closing, right and left lateral excursions, and protrusion with sliding teeth contacts. The mandibular trajectory was recorded using opto‐electronic devices tracking reflective markers placed in front of the ‘soft tissue pogonion point’. The movements were analysed on the following axis: x – medial‐lateral, y – vertical, z – antero‐posterior. Significative differences were found in CGxGART – unassisted maximal mouth opening and closing projection on y‐axis (OCY), CGxGMYO – unassisted maximal mouth opening and closing projection on x‐axis (OCX), and in the measures Opening lateral deviation on x‐axis (OLDX), closing lateral deviation on x‐axis (CLDX) and in the measures of speed for both. In regard to GARTxGMYO, a significative difference was found in Protrusion lateral deviation on x‐axis (PLDX) ‘Conover‐Iman Test of Multiple Comparisons Using Rank Sums’ using Bonferroni correction (P < 0·05). In conclusion, the total opening movements in individuals with TMD tended to have higher deviation than in those asymptomatic individuals and a reduction in the speed of movements.     

Implant-supported mandibular splinting affects temporomandibular joint biomechanics

Objectives: Mandibular functional movements lead to complex deformations of bony structures. The aim of this study was to test whether mandibular splinting influences condylar kinematics and temporomandibular joint (TMJ) loading patterns. Materials and methods: Six subjects were analyzed by means of dynamic stereometry during jaw opening–closing with mandibles unconstrained as well as splinted transversally by a cast metal bar fixed bilaterally to two implant pairs in the (pre)molar region. Statistical analysis was performed by means of ANOVAs for repeated measurements (significance level α=0.05). Results: Transversal splinting reduced mandibular deformation during jaw opening–closing as measured between two implants in the (pre)molar region on each side of the mandible significantly by 54%. Furthermore, splinting significantly reduced the distance between lateral condylar poles (average displacement vector magnitude of each pole: 0.84±0.36 mm; average mediolateral displacement component: 45±28% of the magnitude) and led to a medial displacement of their trajectories as well as a mediolateral displacement of stress‐field paths. Conclusions: During jaw opening–closing, splinting of the mandible leads to a significant reduction of mandibular deformation and intercondylar distance and to altered stress‐field paths, resulting in changed loading patterns of the TMJ structures. To cite this article:
Zaugg B, Hämmerle CHF, Palla S, Gallo LM. Implant‐supported mandibular splinting affects temporomandibular joint biomechanics.
Clin. Oral Impl. Res. 23 , 2012; 897–901
doi: 10.1111/j.1600‐0501.2011.02241.x     

Mandibular jaw movement capacity in 10-17-yr-old children and adolescents: normative values and the influence of gender, age, and temporomandibular disorders

The aims of this study were, first, to report normative values for jaw movements in Caucasian children and adolescents (maximum opening, laterotrusion, and protrusion) and, second, to investigate the influence of age, gender, and temporomandibular disorders (TMD) on jaw movement capacity. The population-based study included 1,011 randomly selected German children and adolescents, aged 10-17 yr. Case histories, as well as mandibular movements and the presence of TMD, were assessed according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). The mean +/- standard deviation for maximum opening was 50.6 +/- 6.4 mm, for laterotrusion to the right was 10.2 +/- 2.2 mm, for laterotrusion to the left was 10.6 +/- 2.3 mm, and for protrusion was 8.2 +/- 2.5 mm. Bivariable (t-test) and multivariable (linear regression) analyses showed that normative values for jaw opening capacity were influenced by age and gender. No influence on jaw movement capacity was seen when TMD were present. Based on the distribution of the measurements in the population (lowest decentile), the mandibular mobility of subjects with a maximum opening of < 43 mm and laterotrusive movements < 8 mm or protrusive movements < 5 mm might be considered as being limited. However, these limitations do not necessarily require treatment.     

下颌前突患者下颌支矢状劈开截骨术后髁突运动轨迹的改变

目的:研究双侧下颌支矢状劈开截骨术对下颌前突患者髁突运动轨迹的影响。方法:采用ARCUSdigma下颌三维运动轨迹描记仪,以髁突运动中心为参考点,研究30例正常受试者、14例下颌前突患者手术前后开口、前伸和左右侧向髁突运动的轨迹。用SPSSV11.0统计软件包进行配对t检验和成组t检验。结果:下颌前突患者术前、术后、正常组左侧髁突的运动轨迹与右侧基本相同,左侧髁突与右侧的开口、前伸和侧方运动范围无显著性差异(P>0.05)。术前组与正常组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均小于正常组(P<0.05);术后与正常组髁突运动轨迹接近,术后开口、前伸和侧方运动范围与正常组无统计学差异;术前与术后组髁突运动轨迹差别较大,术前开口、前伸和侧方运动范围均显著小于术后组(P<0.05)。结论:下颌前突患者手术后,随着术后正畸治疗及咬合自我调整,建立了正常的咬合引导关系,使下颌功能运动趋向正常。     

The medial pterygoid muscle: a stabiliser of horizontal jaw movement

There is limited information of the normal function of the human medial pterygoid muscle (MPt). The aims were to determine whether (i) the MPt is active throughout horizontal jaw movements with the teeth apart and (ii) whether single motor units (SMUs) are active during horizontal and opening–closing jaw movements. Intramuscular electrodes were placed in the right MPt of 18 participants who performed five teeth‐apart tasks: (i) postural position, (ii) ipsilateral (i.e. right) jaw movement, (iii) contralateral movement, (iv) protrusive movement and (v) opening–closing movement. Movement tasks were guided by a target and were divided into BEFORE, OUT, HOLDING, RETURN and AFTER phases according to the movement trajectories recorded by a jaw tracking system. Increased EMG activity was consistently found in the OUT, HOLDING and RETURN phases of the contralateral and protrusive movement tasks. An increased RETURN phase activity in the ipsilateral task indicates an important role for the MPt in the contralateral force vector. Of the 14 SMUs active in the opening–closing task, 64% were also active in at least one horizontal task. There were tonically active SMUs at the postural jaw position in 44% of participants. These new data point to an important role for the MPt in the fine control of low forces as required for stabilisation of vertical mandibular position not only to maintain postural position, but also throughout horizontal jaw movements with the teeth apart. These findings provide baseline information for future investigations of the possible role of this muscle in oro‐facial pain conditions.     

The human lateral pterygoid muscle: a review of some experimental aspects and possible clinical relevance

The clinical notion that some disturbance to the activity of the lateral pterygoid muscle plays a role in the aetiology of temporomandibular disorders (TMD) is still widely accepted and influences management strategies. However, there is no rigorous scientific evidence to support this clinical notion and the role of the lateral pterygoid muscle in normal function is still controversial. The classically defined functions of each head of the muscle are that the superior head is active on closing, retrusion, and ipsilateral jaw movements, while the inferior head is active on opening, protrusion and contralateral jaw movements. However, recent data indicate that these concepts are too simplistic. For example, recent evidence suggests that parts of the superior head may also be active on opening, protrusion and contralateral jaw movements, and that the superior head may consist of three mediolaterally arranged functional zones. Given these complexities, the proposal that clicking and/or locking conditions arise in the temporomandibular joint through some form of lack of co-ordination between the two heads of the muscle needs re-evaluation. Despite earlier reports to the contrary, both heads of the lateral pterygoid muscle appear to be electrically silent at the postural or resting jaw position, and therefore appear to play no role in the anteroposterior positioning of the jaw at the postural position. An important role has also been demonstrated electromyographically for progressive changes in activity in the inferior head as the direction of horizontal jaw force shifts from one side to the other. This suggests an important role for the lateral pterygoid muscle in the generation of side-to-side and protrusive jaw forces. The lateral pterygoid muscle is likely therefore to play an important role in parafunctional excursive jaw movements and also possibly a role in influencing jaw position in patients where the maxillomandibular relationship records change from session to session. The above data provide new insights into the normal function of the lateral pterygoid muscle. The proposal that the lateral pterygoid muscle plays some role in the aetiology of TMD needs now to be rigorously tested.     

Concomitant mandibular and head-neck movementsduring jaw opening–closing in man

To test the hypothesis of a functional relationship between the human mandibular and cranio-cervical motor systems, head-neck movements during voluntary mandibular movements were studied in 10 healthy young adults, using a wireless optoelectronic system for three-dimensional (3D) movement recording. The subjects, unaware of the underlying aim of the study, were instructed to perform maximal jaw opening–closing tasks at fast and slow speed. Movements were quantified as 3D movement amplitudes. A consistent finding in all subjects was parallel and coordinated head-neck movements during both fast and slow jaw opening–closing tasks. Jaw opening was always accompanied by head-neck extension and jaw closing by head-neck flexion. Combined movement and electromyographic recordings showed concomitant neck muscle activity during head-neck movements, indicative of an active repositioning of the head. No differences in 3D movement amplitudes could be seen with respect to speed. The head movement was 50% of the mandibular movement during jaw opening, but significantly smaller (30–40%), during the jaw closing phase. In repeated tests, the 3D movement amplitudes of the concomitant head movements were less variable during slow jaw movement and during the jaw opening phase, than during fast and jaw closing movements, suggesting speed- and phase-related differences in the mechanisms controlling the integrated mandibular and head-neck motor acts. The present results give further support to the concept of a functional trigemino-cervical coupling during jaw activities in man.     

Correlation between facial morphology,mouth opening ability,and condylar movement during opening-closing jaw movements in female adults with normal occlusion

The aim of this study was to investigate the relationship between parameters of facial morphology, maximal voluntary mouth opening ability, and condylar movements in 21 adult females, aged between 20 and 24 years. The subjects had a normal occlusion without sign or symptoms of temporomandibular joint (TMJ) dysfunction. Mandibular movements were recorded using an opto-electric jaw movement recording system with six degrees of freedom under a series of maximal mouth opening-closing movements. Maximal jaw opening and coincident condylar movement were measured three-dimensionally. The mean values of the incisor and condylar path were 41.1 +/- 3.5 mm (range 35.6-50.9 mm) and 12.8 +/- 2.8 mm (range 8.1-19.2 mm), respectively. Although the positive correlation between maximal jaw opening and facial morphology was significant, none of the variables significantly differed between the value of the condylar path and facial morphology. The length of the path of maximum incisor movement and the condylar path during mandibular movement also did not correlate. Stepwise multiple regression analysis indicated a positive association between the maximal length of the incisor path and the cephalometric value of mandibular ramus inclination (R2 value was 0.369). The results of this study suggest that facial morphology size has a limited effect on maximal voluntary mandibular opening and condylar movements in normal adult female subjects.     

Alexithymia partly predicts pain,poor health and social difficulties in patients with temporomandibular disorders

Temporomandibular disorders (TMD) are functional diseases of the masticatory system; their symptoms are clicking, difficulty opening the mouth wide, ear pain, facial pain and headaches. The relationships among distress, emotional factors and TMD are well known. It was shown that patients with TMD have little awareness of their inner states and emotions, and it was found that those reporting oro‐facial pain presented higher alexithymia than did asymptomatic people. Other authors confirmed that alexithymia was higher in the painful TMD group than controls. This study was aimed to evaluate whether alexithymia and its components can be considered as predisposing factors for pain severity, poor health and greater social difficulties in patients with TMD. One hundred thirty‐three patients received a diagnosis of TMD and completed the 20‐item Toronto Alexithymia Scale. Multiple stepwise regressions showed that alexithymia and age explained 10% of the pain and 31% of poor health and also that alexithymia explained 7% of social difficulty. A direct comparison of patients with TMD based on alexithymia revealed a higher presence of pain in alexithymic patients with TMD than in those characterised by moderate or no alexithymia. In conclusion, alexithymia partly predicts pain, poor health and social difficulties in patients with TMD. Furthermore, alexithymic patients have more pain than those with moderate or low alexithymia.     

Efficacy of stabilisation splint therapy combined with non‐splint multimodal therapy for treating RDC/TMD axis I patients: a randomised controlled trial

Stabilisation splint therapy has long been thought to be effective for the management of temporomandibular disorders (TMD). However, the superiority of stabilisation splint therapy compared to other TMD treatments remains controversial. The aim of this study was to determine the efficacy of stabilisation splint therapy combined with non‐splint multimodal therapy for TMD. A total of 181 TMD participants were randomly allocated to a non‐splint multimodal therapy (NS) group (n = 85) or a non‐splint multimodal therapy plus stabilisation splint (NS+S) group (n = 96). Non‐splint multimodal therapy included self‐exercise of the jaw, cognitive–behavioural therapy, self‐management education and additional jaw manipulation. Three outcome measurements were used to assess treatment efficacy: mouth‐opening limitation, oro‐facial pain and temporomandibular joint sounds. A two‐factor repeated‐measures analysis of variance (anova ) was used to evaluate the efficacy of the two treatment modalities (NS vs. NS+S), and Scheffe's multiple comparison test was used to compare the treatment periods. Subgroup analyses were performed to disclose the splint effects for each TMD diagnostic group. All three parameters significantly decreased over time in both groups. However, there were no significant differences between the two treatment groups in the total comparison or subgroup analyses; an exception was the group with degenerative joint disease. No significant difference between the NS and NS+S treatment approaches was revealed in this study. Therefore, we conclude that the additional effects of stabilisation splint are not supported for patients with TMD during the application of multimodal therapy.     

Condylar movement analysis in subjects with clinically normal temporomandibular joints,utilizing an amorphous sensor

The purpose of this study was to determine the range of condylar movements in normal subjects, by the use of an amorphous sensor. The pair-matched sample consisted of 17 Caucasian males (aged 25.8 +/- 2.5 years) and 17 Caucasian females (aged 25.5 +/- 2.8 years) who had no subjective or objective symptoms related to temporomandibular joint (TMJ) sounds. Bilateral condylar and jaw movements were recorded simultaneously. The results showed that the typical condylar movement points plotted on the X-Y coordinates indicated a uniform or approximately straight line, that is X = Y. The mean +/- standard deviation (s.d.) for the maximum velocity of condylar movement during the opening and closing phases was 32.6 +/- 16.9 and 39.8 +/- 21.5 mm s-1, respectively. The mean +/- s.d. for the degree of jaw opening at the turning point of condylar movement was 36.9 +/- 21.7%. Significant correlations existed between any two measurements of maximum velocity of condylar movement. Moreover, significant correlations existed between the left and right sides in the degree of jaw opening at the turning point of condylar movement. These results suggest that a range of normal values of condylar movements can be developed when utilizing the amorphous sensor method.     

髁突运动中心大张口轨迹与关节窝形态的关系及临床应用探讨

目的　探讨髁突运动中心大张口轨迹与关节窝形态的关系 ,对TMD患者髁突运动中心轨迹特征进行初步研究。方法　利用自行开发的髁突运动中心轨迹显示分析系统 ,分别以运动中心、终末绞链轴点作为参考点 ,观察 10名健康人和 7例临床检查怀疑盘前移位的TMD患者大张口轨迹 ,与磁共振成像得到的相应关节窝形态及关节盘位置诊断结果进行比较。结果　健康人左右侧运动中心轨迹与关节窝形态曲线重合率分别为 80 % (8/ 10 )和 90 % (9/ 10 ) ;终末绞链轴点轨迹与关节窝形态重合率均为 0 (0 / 10 )。TMD患者中 ,11侧盘前移位关节 ,除 1侧可复性盘前移位关节外 ,髁突运动中心轨迹均与正常的轨迹明显不同 ,出现各种改变 ;3侧正常盘位关节 ,髁突运动中心轨迹均与健康人的轨迹相似。结论　运动中心轨迹较终末绞链轴点个体稳定 ,可认为是较理想的研究髁突运动轨迹的参考点     

健康人髁突运动中心前伸和大张口轨迹特征的研究

目的 探讨髁突参考点选择不同对髁突运动轨迹形态的影响。方法 利用自行开发的髁突运动中心轨迹显示分析系统，分别以运动中心，终末绞链轴点作为参考点，研究30名健康人下颌前伸和大张口时髁突运动的矢状面轨迹。结果 运动中心位于终末绞链轴点的前上方，二者轨迹不同。健康人的髁突运动中心大张口迹轨，为一斜向前下方的平滑曲线，形态稳定，没有轨迹异常特征出现且左右侧对称，大张口运动轨迹起止点连线距离与前伸运动轨迹起止点连线距离的比值大于1．5。而终末绞链轴点大张口轨迹左右侧不对称，形态不稳定，会出现不规则形状，大张口运动轨起止点连线距离与前伸运动轨迹起止点连线距离的比值较小。结论 对于同一健康个体，运动中心轨迹较终末绞链轴点轨迹更恒定。     

Pharmacological treatment of oro‐facial pain – health technology assessment including a systematic review with network meta‐analysis

This health technology assessment evaluated the efficacy of pharmacological treatment in patients with oro‐facial pain. Randomised controlled trials were included if they reported pharmacological treatment in patients ≥18 years with chronic (≥3 months) oro‐facial pain. Patients were divided into subgroups: TMD‐muscle [temporomandibular disorders (TMD) mainly associated with myalgia]; TMD‐joint (TMD mainly associated with temporomandibular joint pain); and burning mouth syndrome (BMS). The primary outcome was pain intensity reduction after pharmacological treatment. The scientific quality of the evidence was rated according to GRADE. An electronic search in PubMed, Cochrane Library, and EMBASE from database inception to 1 March 2017 combined with a handsearch identified 1552 articles. After screening of abstracts, 178 articles were reviewed in full text and 57 studies met the inclusion criteria. After risk of bias assessment, 41 articles remained: 15 studies on 790 patients classified as TMD‐joint, nine on 375 patients classified as TMD‐muscle and 17 on 868 patients with BMS. Of these, eight studies on TMD‐muscle, and five on BMS were included in separate network meta‐analysis. The narrative synthesis suggests that NSAIDs as well as corticosteroid and hyaluronate injections are effective treatments for TMD‐joint pain. The network meta‐analysis showed that clonazepam and capsaicin reduced pain intensity in BMS, and the muscle relaxant cyclobenzaprine, for the TMD‐muscle group. In conclusion, based on a limited number of studies, evidence provided with network meta‐analysis showed that clonazepam and capsaicin are effective in treatment of BMS and that the muscle relaxant cyclobenzaprine has a positive treatment effect for TMD‐muscle pain.     

Validity of the 'protocol of oro-facial myofunctional evaluation with scores' for young and adult subjects

Summary The aims of this study were to analyse the validity, sensitivity and specificity of the protocol of oro‐facial myofunctional evaluation with scores (OMES) for oro‐facial myofunctional disorder (OMD) diagnosis in young and adult subjects. Eighty subjects were examined. The OMES was validated against the Nordic Orofacial Test‐Screening (NOT‐S) protocol (criterion validity) (Spearman correlation test). The construct validity was tested by analysis of the ability of the OMES (i) to differentiate healthy subjects (n = 22) from temporomandibular disorder (TMD) patients (n = 22), which frequently have OMD (Mann–Whitney test) and (ii) to measure the changes that occurred in a subgroup with TMD between the period before and after oro‐facial myofunctional therapy (T group, n = 15) (Wilcoxon test). Two speech therapists trained with the OMES participated as examiners (E). There was a statistically significant correlation between the OMES and NOT‐S protocols, which was negative because the two scales are inverse (r = ?0·86, P < 0·01). There was a significant difference between the healthy and TMD subjects regarding the oro‐facial myofunctional status (OMES total score, P = 0·003). After therapy, the T group showed improvement in the oro‐facial myofunctional status (OMES total score, P = 0·001). Inter‐ and intra‐examiner agreement was moderate, and the reliability coefficients ranged from good to excellent. The OMES protocol presented mean sensitivity and specificity = 0·80, positive predictive value = 0·76 and negative predictive value = 0·84. Conclusion: The OMES protocol is valid and reliable for clinical evaluation of young and adult subjects, among them patients with TMD.     

Short-term efficacy of physical therapy compared to splint therapy in treatment of arthrogenous TMD

A prospective randomized study was carried out to evaluate the efficacy of physical therapy in addition to splint therapy on treatment outcome in patients with temporomandibular disorders (TMD) with respect to objective and subjective parameters. Twenty-six patients suffering from an arthrogenic TMD and exhibiting a painfully restricted jaw opening were randomized in two groups. Thirteen patients were treated solely with Michigan splint (group I), 13 patients received supplementary physical therapy (group II). Before treatment a clinical examination and electronic recording of jaw movements were performed and subjective pain level was evaluated by visual analogue scales. After 3 months of therapy maintenance of improvement was evaluated. Within treatment groups comparison of data before and after treatment was analysed using Wilcoxon test. Groups were compared by Mann-Withney-U test. A P-value < 0.05 was considered significant. Compared with the baseline, in both groups mandibular movement capacity increased significantly after treatment, whereas subjective pain decreased significantly (P < 0.05). Active jaw opening increased from 28.6 +/- 5.8 to 35.9 +/- 4.8 mm in group I and from 30.1 +/- 5.4 to 40.8 +/- 4.1 mm in group II. After therapy the difference of active jaw opening between groups was significant (P < 0.05). Physical therapy also gave a supplementary improvement of protrusive mandibular movement capacity during electronic registration and subjective pain level. For none of these parameters this difference between groups was significant. Physical therapy seems to have a positive effect on treatment outcome of patients with TMD.     

A Model of Mandibular Movements During Speech: Normative Pilot Study for the Brazilian Portuguese Language

Abstract

The precision of speech articulation is related to the possibility and freedom of the mandibular movements, modifying the spaces in order to allow the different articulatory positions of each sound. Electrognathography allows the objective delineation and registration of the mandibular movements, determining the level of opening, translations and velocity of these movements. Its use is a resource that can establish quantitative diagnostic parameters. The aim of this study was to verify the amplitude, velocity and characterization of the mandibular movements during speech using computerized electrognathography. Participants were 40 adults, male and female, with no temporomandibular disorders; with no missing teeth; with no dental occlusion alterations or dentofacial deformities; with no dental prostheses; and with no communication, neurological or cognitive deficits. The mandibular movements were observed during the sequential naming of pictures containing all the phonemes of the Brazilian Portuguese language. The registrations were obtained using electrognathography (BioENG – BioPak system), assessing the spatial position, course and velocity of the mandibular movements. The mean values of velocity were: 88.65 mm/sec during opening and 89.90mm/sec during closing. The mean values of amplitude were: sagittal opening: 12.77 mm, frontal opening: 11.21 mm, protrusion: 1.22 mm; retrusion 5.67 mm; translations to the right: 1.49 mm and to the left: 1.59 mm. The velocity of opening is directly related to that of closing. The amplitude of opening demonstrates a direct correlation with the velocity of opening and closing. All participants presented lateral translations during the course of the jaw. The assessment of speech in normal individuals is characterized by: discreet mandibular movements with an anteroposterior component and lateral translations. This study allowed for the delineation of a profile of the mandibular movements during speech in asymptomatic individuals.     

Functional and radiographic long-term results after bad split in orthognathic surgery

Bilateral sagittal split osteotomy (BSSO) is a standard procedure in orthognathic surgery. The aim of the present study was to perform a matched pair analysis (bad sagittal split versus regular sagittal split) regarding the functional and radiographic long-term results after BSSO. Of 110 cases of mandibular hypoplasy treated with BSSO, 7 cases of bad sagittal splits (Group A) were selected, clinically examined and matched to 7 cases where no bad split occurred (Group B). The Research Diagnostic Criteria for Temporo Mandibular Disorders (RDC/TMD), condylar morphology scale (CMS) and ramus height measurements using orthopantomograms were carried out in the follow-up period to observe the clinical and functional status and condylar resorbtion or remodelling. The mean follow-up time was 28.6 months. The RDC/TMD examination did not show a higher incidence of temporomandibular dysfunction, including pain or clicking in the bad split group. Patients without a bad split showed statistically significant (p<0.05) better mouth opening. The CMS measurements were comparable in both groups. When compared with regular splits, bad splits, if treated in an appropriate manner, have a good chance of functional success, although, some mandibular movements can be compromised.     

Increased sternocleidomastoid,but not trapezius,muscle activity in response to increased chewing load

Previous findings, during chewing, that boluses of larger size and harder texture result in larger amplitudes of both mandibular and head–neck movements suggest a relationship between increased chewing load and incremental recruitment of jaw and neck muscles. The present report evaluated jaw (masseter and digastric) and neck [sternocleidomastoid (SCM) and trapezius] muscle activity during the chewing of test foods of different sizes and textures by 10 healthy subjects. Muscle activity was recorded by surface electromyography and simultaneous mandibular and head movements were recorded using an optoelectronic technique. Each subject performed continuous jaw‐opening/jaw‐closing movements whilst chewing small and large boluses of chewing gum and rubber silicone (Optosil). For jaw opening/jaw closing without a bolus, SCM activity was recorded for jaw opening concomitantly with digastric activity. During chewing, SCM activity was recorded for jaw closing concomitantly with masseter activity. Trapezius activity was present in some, but not all, cycles. For the masseter and SCM muscles, higher activity was seen with larger test foods, suggesting increased demand and recruitment of these muscles in response to an increased chewing load. This result reinforces the previous notion of a close functional connection between the jaw and the neck motor systems in jaw actions and has scientific and clinical significance for studying jaw function and dysfunction.     

Precision of jaw‐closing movements for different jaw gaps

Jaw‐closing movements are basic components of physiological motor actions precisely achieving intercuspation without significant interference. The main purpose of this study was to test the hypothesis that, despite an imperfect intercuspal position, the precision of jaw‐closing movements fluctuates within the range of physiological closing movements indispensable for meeting intercuspation without significant interference. For 35 healthy subjects, condylar and incisal point positions for fast and slow jaw‐closing, interrupted at different jaw gaps by the use of frontal occlusal plateaus, were compared with uninterrupted physiological jaw closing, with identical jaw gaps, using a telemetric system for measuring jaw position. Examiner‐guided centric relation served as a clinically relevant reference position. For jaw gaps ≤4 mm, no significant horizontal or vertical displacement differences were observed for the incisal or condylar points among physiological, fast, and slow jaw‐closing. However, the jaw positions under these three closing conditions differed significantly from guided centric relation for nearly all experimental jaw gaps. The findings provide evidence of stringent neuromuscular control of jaw‐closing movements in the vicinity of intercuspation. These results might be of clinical relevance to occlusal intervention with different objectives.