Unilateral Chewing Research Articles

Realization of Masticatory Movement by 3-Dimensional Simulation of the Temporomandibular Joint and the Masticatory Muscles

Masticatory muscles are closely involved in mastication, pronunciation, and swallowing, and it is therefore important to study the specific functions and dynamics of the mandibular and masticatory muscles. However, the shortness of muscle fibers and the diversity of movement directions make it difficult to study and simplify the dynamics of mastication. The purpose of this study was to use 3-dimensional (3D) simulation to observe the functions and movements of each of the masticatory muscles and the mandible while chewing. To simulate the masticatory movement, computed tomographic images were taken from a single Korean volunteer (30-year-old man), and skull image data were reconstructed in 3D (Mimics; Materialise, Leuven, Belgium). The 3D-reconstructed masticatory muscles were then attached to the 3D skull model. The masticatory movements were animated using Maya (Autodesk, San Rafael, CA) based on the mandibular motion path. During unilateral chewing, the mandible was found to move laterally toward the functional side by contracting the contralateral lateral pterygoid and ipsilateral temporalis muscles. During the initial mouth opening, only hinge movement was observed at the temporomandibular joint. During this period, the entire mandible rotated approximately 13 degrees toward the bicondylar horizontal plane. Continued movement of the mandible to full mouth opening occurred simultaneously with sliding and hinge movements, and the mandible rotated approximately 17 degrees toward the center of the mandibular ramus. The described approach can yield data for use in face animation and other simulation systems and for elucidating the functional components related to contraction and relaxation of muscles during mastication.

Association between occlusal curvature and masticatory movements with different test foods in human young adults with permanent dentitions

ObjectiveOcclusal curvatures such as the curve of Spee, curve of Wilson and Monsons's sphere exist in the human adult mandibular arch. A previous study showed that human young adults with flatter occlusal curvatures had higher ability of food comminution and mixing. The aim of this study was to clarify functional significance of occlusal curvatures in terms of masticatory movements. This study investigated the association between occlusal curvature and mandibular movements while chewing a variety of food items. DesignForty-six young adults with complete dentitions (mean age, 25.0 years) participated in the study. Sphere radius of occlusal curvature was determined by a three-dimensional analysis of the mandibular arch based on the Broadrick flag method. Mandibular movements during unilateral chewing of six test food items (chewing gum, cheese, kamaboko, boiled beef, gummy jelly and raw carrot) until the subjects felt ready to swallow were recorded using a six-degrees-of-freedom mandibular movement recording system, and 11 parameters for masticatory movements of a lower incisal point of the mandible were analysed. ResultsLinear regression analyses identified the sphere radius as a significant predictor for closing velocity in all test food items, occluding/cycle duration in 3 items, opening velocity, closing duration and chewing time in 2 items, and opening duration in 1 item (P<0.01). The results suggest that subjects with larger sphere radius (flatter occlusal curvature) in the mandibular arch could prepare food bolus effectively for swallowing. ConclusionOcclusal curvature seems to be associated with masticatory movements in young adults with permanent dentition.

Effects of thirty-times chewing per bite on secretion of glucagon-like peptide-1 in healthy volunteers and type 2 diabetic patients

Glucagon-like peptide 1 (GLP-1) is secreted from the small intestine to the blood in response to glucose intake during a meal; however, it is not known whether mastication affects GLP-1 secretion. Here, we examined the relationship between mastication and GLP-1 secretion, along with postprandial blood glucose and insulin concentrations. We compared the levels of blood glucose, serum insulin, and plasma active GLP-1 concentrations after young healthy volunteers ate a test meal either by usual eating (control) or in one of three specified ways: 1. unilateral chewing, 2. quick eating, 3. 30-times chewing per bite. Ten volunteers participated in each of the three groups. Plasma active GLP-1 concentrations did not change by unilateral chewing or quick eating, but did increase by the third method, without affecting the concentrations of blood glucose or serum insulin. Next, we tested whether 30-times chewing per bite increased plasma active GLP-1 concentrations in 15 patients with type 2 diabetes mellitus, but there was no difference in results between usual eating and 30-times chewing per bite. This is a pilot trial with a small number of subjects, but is the first study to investigate the relationships between various styles of mastication and the GLP-1 secretion in young healthy volunteers and type 2 diabetic patients.

Temporomandibular disorder in the oral and maxillofacial fields

Temporomandibular disorder (TMD) is defined as orofacial pain and craniomandibular disorder. In short, it is a complex disorder related to temporomandibular joint (TMJ), masticatory muscle, and occlusion1. TMD is known as a multifactorial disease and is difficult to diagnose and treat because it has various clinical symptoms and etiology and the causal factor has yet to be defined2. In the past, irreversible treatments such as surgical, orthodontic, and prosthodontic therapy were performed according to only one theory, but many complications arose, with no good results. There are many etiologies of TMD. Researchers who point to disc displacement as a main reason are interested in manipulation therapy, anterior repositioning splint, and surgical therapy such as menis coplasty. On the other hand, researchers who focus on synovial pathology concentrate on joint injection, arthrocentesis, and arthroscopic surgery. Note, however, that TMD occurs for many reasons; hence the need to apply various treatment methods instead of using only one method. The incidence of TMD increases when joint is consistently overloaded. Psychological factor, oral parafunction such as clenching, bruxism, and unilateral chewing, malocclusion, and maxillofacial trauma cause trauma on TMJ directly or indirectly; thus causing TMD3. Many studies were conducted to identify the reason for and etiology of TMD4-9. Note, however, that they have yet to be discovered, and TMD is one of the uncovered areas in dentistry. An unknown field can be very interesting for researchers with its many themes to be researched. Therefore, TMD is an item to be researched actively by oral and maxillofacial surgeons. In the past when surgical treatment was carried out actively, many surgeons were interested, giving presentations in conferences and publishing many articles. When the indication of surgical therapy became very narrow and conservative, and semi-surgical treatments showed good results, however, surgeons lost interest. Nowadays, presentations on TMD in oral and maxillofacial surgery conferences or journals are very few and are on the decline. A specific treatment method for TMD is not yet established, and it is impossible to conclude that there is a particularly good method; hence the need to select non-invasive, reversible treatment first. If pain and dysfunction continue, and conservative treatment does not work, prosthodontic, orthodontic, semi-surgical, or surgical treatment should be considered. The purposes of TMD treatment are decrease of pain and inflammation, decrease of muscle's hyperactivity, prevention of mechanical overload on muscle and joint, and restoration of jaw function. There is a need to reestablish oral and maxillofacial surgeons' concept of TMD based on these recent treatments. In other words, to treat TMD, we must understand that non-surgical conservative treatments such as counseling, medication, physical therapy, or splint therapy are required, and that we should pay attention to them. Oral and maxillofacial surgeons who consider only surgical therapy cannot hope to treat TMD.

Relationship between the Preferred Chewing Side and the Angulation of Anterior Tooth Guidance

Objectives: The aim of this study was to evaluate a possible relationship between preferred chewing side (PCS) and the anterior guidance angle. Subjects and Methods: Forty dental nurses and technicians, aged 24-46 years, were each given a piece of chewing gum, which they chewed for about 3 min. At 7 regular intervals (every 15 s), they were interrupted by the principal investigator (P.L.) in order to observe on which side of their mouths they had the bolus of chewing gum. Moulds of their jaws were made and the position of the maxillary arch relative to temporomandibular joints was recorded with a facebow and transferred to a semi-adjustable articulator. After mounting the stone casts of each subject, a measure of the anterior guidance angle was taken with an adjustable incisal table. Results: Of the 40 subjects, 14 (35%) presented a PCS. Among the 14 subjects who preferred a chewing side, there was a correlation between the PCS and a low angulation of teeth constituting the anterior guidance on that side, but this correlation was statistically nonsignificant. Conclusion: In this study, we found that unilateral chewing creates uneven wear on the anterior teeth and changed the anterior guidance angulation.

측두하악장애 연구진단기준(RDC/TMD)를 이용한 측두하악장애의 근육성 동통과 관절성 동통 환자군의 비교

본 연구의 목적은 근육성 동통 및 관절성 동통을 가진 측두하악장애 환자를 대상으로 측두하악장애 연구진단기준(RDC/TMD) axis II 지수 및 관련 요소들을 비교하여 동통과 관련된 장애와 사회심리학적 상태 그리고 치료에 미치는 영향을 알아보는데 있다. 서울대학교 치과병원 구강내과를 내원한 측두하악장애로 진단되어진 252명의 환자들을 대상으로, 측두하악장애 연구진단 기준을 이용하여 근육성 동통군, 관절성 동통군, 근육성 동통과 관절성 동통을 모두 보이는 혼합형 동통군으로 분류한 뒤, 측두하악장애 연구진단기준 설문지를 이용하여 통증의 강도, 동통과 관련된 장애 일수, 만성통증척도, 우울 지수, 신체화 지수, 하악기능과 관련된 기능제한 등을 조사하였으며, 동통의 기간, 치료 기간 및 치료 효과 등 임상적 요소들과의 관계를 분석하여 다음과 같은 결과를 얻었다. 1. 연구대상자의 17.5%가 근육성 동통군, 31.0%에서 관절성 동통군, 51.6%가 혼합형 동통군으로 분류되었다. 성별 분포는 여성이 남성보다 높았으나 세 그룹간의 연령 및 성별은 통계적으로 유의한 차이를 보이지 않았다. 2. 측두하악장애 각 통증군의 사회심리학적 상태는 통계적으로 유의한 차이를 보여주었다(p<0.01). 관절성 동통군에 비해 혼합형 동통군에서 통증의 강도, 동통과 관련된 장애 일수, 만성통증척도가 높게 나타났으며(p<0.01), 우울 지수 및 신체화 지수는 관절성 동통군에 비해 근육성 동통군과 혼합형 동통군에서 유의하게 높게 나타났다(p<0.01). 3. 하악기능과 관련된 기능제한은 각 군간 통계적으로 유의한 차이를 보이지 않았으나 최대 개구량은 근육성 동통군 환자보다 관절성 동통군 환자에서 작게 나타났다(p<0.05). 4. 관절성 동통군 환자들은 다른 동통군의 환자들에 비하여 적은 수에서 만성 동통의 경향을 보였으며 (p<0.01), 혼합형 동통군의 환자들은 다른 동통군의 환자들에 비하여 상대적으로 낮은 치료 효과를 나타내었다(p<0.01). 5. 측두하악장애 환자의 치료 효과는 신체화 지수와 높은 관련성을 나타내었다. (<TEX>${\beta}$</TEX>=-0.251, p<0.05) The purposes of this study were to compare psychological profiles, to investigate the differences in the clinical characteristics, and to compare treatment outcomes between myogenous pain and arthrogenous pain subgroups of temporomandibular disorder (TMD) based on Research Diagnostic Criteria for Temporomandibular disorders (RDC/TMD). Two hundred and fifty two patients diagnosed as TMD were divided into three groups based on the RDC/TMD axis I diagnostic guidelines; myogenous pain group, arthrogenous pain group, and mixed pain (both myogenous pain and arthrogenous pain) group. RDC/TMD history questionnaire was administered to each patient and depression, somatization, jaw disability, pain intensity, disability days, and graded chronic pain scale were analyzed. Bruxism, clenching, insomnia, headache, and unilateral chewing were assessed in a standardized TMD dysfunction questionnaire and the duration of onset, chronicity of pain, treatment period, the effectiveness of the treatment, and improvement of symptoms also analyzed. Myogenous pain group had higher depression (p=0.002), and somatization scales (p<0.001) than the arthrogenous pain group. Mixed pain group showed higher pain intensity (p=0.008), disability days (p<0.001), graded chronic pain scale (p=0.005), somatization (p<0.001), and depression scores (p=0.002) than the arthrogenous pain group. Jaw disability did not show any significant differences among the three groups (p=0.058). Arthrogenous pain group reported more limitation of mouth opening than myogenous pain group (p=0.007). Duration of onset showed that the arthrogenous pain group had lowest prevalence of chronicity among three groups (p=0.002). Mixed pain group patients showed lowest symptom improvements among three groups (p=0.007). Multiple linear regression analysis results showed that the treatment effectiveness was significantly associated with somatization score (<TEX>${\beta}$</TEX>=-0.251, p=0.03).

Brain Activity and Human Unilateral Chewing

Brain mechanisms underlying mastication have been studied in non-human mammals but less so in humans. We used functional magnetic resonance imaging (fMRI) to evaluate brain activity in humans during gum chewing. Chewing was associated with activations in the cerebellum, motor cortex and caudate, cingulate, and brainstem. We also divided the 25-second chew-blocks into 5 segments of equal 5-second durations and evaluated activations within and between each of the 5 segments. This analysis revealed activation clusters unique to the initial segment, which may indicate brain regions involved with initiating chewing. Several clusters were uniquely activated during the last segment as well, which may represent brain regions involved with anticipatory or motor events associated with the end of the chew-block. In conclusion, this study provided evidence for specific brain areas associated with chewing in humans and demonstrated that brain activation patterns may dynamically change over the course of chewing sequences.

Tooth surface loss and associated risk factors in northern saudi arabia.

Aim. To evaluate tooth surface loss (TSL) severity and associated risk factors in a representative sample of Saudi adults. Materials and Methods. Four hundred TSL patients (200 females and 200 males) participated in this study. Each patient completed a comprehensive questionnaire interview (using a modified Tooth wear Assessment Questionnaire) and then examined for the severity of TSL (using ordinal scale). Results. Seventy-five percent of participants demonstrated attrition, 90% had erosion, 15% had abrasion, and 95% had more than one type of TSL. The most common risk factors were consumption of acidic food/drinks (78%), parafunctional habits (70%), and unilateral chewing (50%). 77% of participants demonstrated grade 2 TSL. Males demonstrated greater TSL severity (P ≤ 0.05). Age, systemic disease, number of remaining teeth, acidic food/drinks, bruxism/parafunction, biting objects, facial pain/tenderness, sour taste, exposure to dust, unilateral chewing, using dental abrasives, and brushing frequency/technique had significant relationship with TSL severity (P ≤ 0.05). Conclusions. TSL has a multifactorial aetiology. Parafunction, gastrointestinal problems, and diet were the most common aetiological factors reflecting changes to stressful modern life-styles, eating/drinking habits, and behaviours. Gender didn't influence the aetiology of TSL; however males demonstrated more TSL severity. Patients' age had significant correlation to TSL severity.

Conventional vs. implant retained overlay dentures: a clinical trial of masseter and anterior temporalis electromyography

Abstract Background: Implant supported overlay dentures (ISODs) have been widely accepted among patients using conventional removable complete dentures (CRCDs). The present study aimed to comparatively study conventional and ISODs in terms of function and coordination of masticatory muscles using electromyograms.Materials and methods: Included were 10 patients with ISODs (each with 2 implants in the intercanine area). The mean wave range (MWR) and frequency (MWF) of masseter and temporalis were recorded with (ISOD) and without (CRCD) ball attachments while maximum clenching on cotton rolls (cotton roll clenching), maximum intercuspal clenching (clenching), and unilateral gum chewing (chewing) using electromyography. Data were analyzed in SPAW using t-paired for matched groups and independent sample t-tests for unmatched ones. Results: MWF differences were not statistically significant with or without attachments (p > 0.05). Without attachments in place, MWF of both masseter and temporalis muscles significantly decreased when patients clenched on cotton rolls (p = 0.01 and 0.02, respectively) and when chewing unilaterally (p = 0.01 both). With attachments present, the right and left temporalis muscles did not show identical mean wave ranges while chewing (p = 0.01). Without attachments, this disharmony was seen in the left and right masseter muscles (p = 0.03). MWR of masseter was higher in men while chewing with attachments (p = 0.02). Without attachments, MWR of temporalis was higher in women while cotton roll clenching (p = 0.03) and chewing (p = 0.02). Conclusion: These findings are seemingly in favor of improved masticatory function and coordination in edentulous patients with the application of ISODs.

Maximum voluntary clenching and unilateral chewing in patients with mild-moderate TMD

Temporomandibular disorders (TMD) consist of a number of clinical problems that involve the masticatory muscles, the temporomandibular joint and associated structures. The aim of the study was to quantitatively compare electromyographic (EMG) parameters of patients with mild-moderate TMD and healthy subjects. Twenty patients with mild-moderate TMD (5 men, 15 women, 22–56 y) and 19 healthy subjects (9 men, 10 women, 21–49 y) were analyzed. sEMG of the left and right masseter and temporalis anterior muscles was recorded using a wireless device (TMJoint, BTS, Italy). Each subject performed a 5 s-maximum voluntary contraction (MVC) with the teeth in intercuspal position (CLENCH), and one with two 10 mm-thick cotton rolls positioned on the mandibular second premolars/first molars (COT). EMG activity was further recorded during unilateral, right and left, gum chewing. EMG potentials of both MVC and chewing were standardized as percentages of the potentials obtained during COT recording [1]. During MVC, EMG activities were less symmetric and had a larger torque component in TMD patients than in healthy subjects (muscular asymmetry: 10.4±9.1% vs 4.4±4.2%, Student’s t-test, p=0.013; torque: 9.8±10.9% vs 4.4±4.0%, p=0.047). During chewing, all healthy subjects had a good coordination between masseter and temporalis contractions, with a prevalent activity of the working-side muscles. Among TMD patients, instead, 9 subjects performed at least one of their unilateral chewing tests with an altered muscular coordination. EMG activity of TMD patients was less coordinated than that of healthy subjects, with a larger variability between chewing cycles (Hotelling’s ellipse area: 2275±2734% vs 1010±845%, Student’s t-test, p=0.061). sEMG analysis could be a useful tool to detect functionally altered stomatognathic muscular coordination. Dote ricerca: FSE, Regione Lombardia

Endurance to physical strain in patients with temporomandibular disorders: a case-control study

Objective. The hypothesis tested was whether patients with temporomandibular disorders (TMD) have an impaired endurance to motor tasks, under physical strain. Material and methods. The study population included 81 cases with TMD and 75 controls. After giving their informed consent, the participants filled out a questionnaire and performed five endurance trials. Each trial was measured in seconds from start to termination. The tests included: (a) holding the arm in a straight out position with a 2 kg weight in the hand, (b) lifting and lowering the arm with a 2 kg weight in the hand, (c) opening and closing the mandible repeatedly against a resistance of 1.6 kg during the jaw-opening phase, (d) protruding and retracting the mandible repeatedly against a resistance of 1.6 kg during the protruding phase and (e) unilateral chewing of three pieces of chewing gum. Analysis of differences between cases and controls for endurance were evaluated with Mann-Whitney U-test. A p-value < 0.05 was considered statistically significant. Results. The cases had statistically significantly (p < 0.0001) lower endurance time than controls for all tests. Conclusions. Patients with TMD compared to those without signs and symptoms of TMD have an impaired capacity to endure motor tasks that involve physical demand of the jaw muscles and shoulder girdle muscles.

Long-term training effects on masticatory muscles

Neuromuscular adaptations during skill acquisition have been extensively investigated for skeletal muscles. Motor rehabilitation is the main target for application of motor training. Such measures are also relevant for the musculature of the jaw, but few data are available for motor adaptation of the masticatory system. The objective of this study was to evaluate and compare long-term training effects of different motor tasks on masseter and temporal muscles. In 20 healthy subjects, the electromyographic response to unilateral and bilateral maximum voluntary tooth clenching, balancing the mandible on a hydrostatic system under force-feedback-controlled conditions, and unilateral chewing was investigated in an initial session and then in two follow-up sessions separated by 2 and 10 weeks from baseline. Motor tasks were repeated three times for chewing, nine times for maximum biting (MB) and 24 times for the coordination tasks (CT). The sequences of the various motor tasks were applied once in the first session and twice in the second and third sessions. No effects of training were observed for MB tasks except for MB in intercuspation, for which significant yet transient avoidance behaviour occurred in the second session. No significant effects were found for chewing tests. For the CT, however, a robust significant long-term training effect was detected which reduced the electric muscle activity in session 2 by approximately 20% and in session 3 by approximately 40% compared with the initial measurements. The study showed that the masticatory muscles are remarkably prone to motor adaptation if demanding CT must be accomplished.

Neuromuscular control of balancing side contacts in unilateral biting and chewing

When jaw gape in unilateral biting or chewing narrows, the working/balancing side activity ratio (W/B ratio) of masseter muscles increases due to decrease of balancing side (BS) activity. This was interpreted as a neuromuscular strategy to delimit the impact of BS contacts during chewing. To test this hypothesis, we studied whether W/B ratios are associated with incidence of BS tooth contacts. In 40 healthy subjects, bilateral masseter activity was recorded during unilateral biting with different jaw gapes and during various chewing tasks. Biting was performed with absence and with deliberate avoidance or generation of BS tooth contacts. Subjects were divided into three groups according to jaw gapes of 2, 1, and 0.5mm for which BS contact was first noticed in strong biting. The smaller this gape was, the higher were the mean W/B ratios. In biting with contact avoidance, the W/B ratios in each group increased with decreasing gape. In biting with generation of BS contacts, W/B ratios were smaller than with contact avoidance. W/B ratios in chewing with minimum interocclusal distances below 0.5mm were bigger than in biting with contact generation and were mostly bigger than in biting with contact avoidance. The findings confirm that increasing the masseter W/B ratio is a neuromuscular measure suitable to avoid BS contacts and support the idea that motor control uses jaw gape-related activation to limit the impact of BS contacts. Clarification of this protection mechanism might contribute to uncover the etiology of functional disorders and occlusal malfunctions.

The effect of various jaw motor tasks on body sway

Alterations of body sway caused by isometric contractions of the jaw muscles have been reported previously. The objective of this study was to test if motor tasks of the masticatory system with different control demands affect body posture differently during quiet stance. Position and sway displacements of the center of foot pressure (COP) were measured for 20 healthy subjects who either kept the mandible at rest or performed unilateral and bilateral maximum voluntary teeth clenching, feedback-controlled biting tasks at submaximum bite forces, or unilateral chewing. Two weeks later the measurements were repeated. Compared with quiet stance, the COP results revealed significant changes during the feedback-controlled biting tasks. Robust sway reduction and anterior displacement of the COP were observed under these conditions. Body oscillations were not significantly affected by maximum bites or by unilateral chewing. For most of the variables investigated there were no significant differences between unilateral and bilateral biting. Robust sway reduction during feedback-controlled biting tasks in healthy subjects involved a stiffening phenomenon that was attributed to the common physiological repertoire of posture control, and might optimize the stability of posture under these conditions.

Prevalence of Chewing Side Preference in the Deciduous, Mixed and Permanent Dentitions

This study evaluated the prevalence of the chewing side preference (CSP) in the deciduous, mixed and permanent dentitions. Three-hundred subjects were divided in three groups (n = 100): Group 1 - children with deciduous dentition; group 2-children with mixed dentition; group 3 - subjects with permanent dentition. The CSP was determined using a direct method (visual observation) developed by McDonnell et al. (2004). Descriptive statistic was used to observe the prevalence of CSP. The Pearson's Chi-square was used to investigate signicant associations between gender, presence of CSP and preferred side (right/left). Eighty-seven percent of group 1 had a CSP. Eighty-two percent of group 2 had a CSP. Seventy-six percent of group 3 had a CSP. There was no statistically significant association between presence of CSP and gender in all groups. There was no statistically significant association between preferred side (right/left) and gender in all groups. There is a higher prevalence of subjects in deciduous, mixed and permanent dentition that presented chewing side preference. The early diagnosis of the presence of chewing side preference can prevent the unilateral chewing pattern with prophylactic therapy applied to the first teeth (deciduous).

The effect of denture stability on bite force and muscular effort

This study tested the hypothesis that denture instability limits the amount of voluntary muscular effort generated by denture wearers. Seventeen edentulous subjects (seven men, 10 women; mean age 60·3 ± 13·0 years) with newly acquired implant-retained mandibular overdentures and a conventional maxillary denture participated. Maximum bite forces and corresponding electromyographic (EMG) activity from the temporalis and masseter muscles (bilaterally) were recorded under two experimental conditions: (i) Unilateral premolar and molar bites without additional support, and (ii) premolar and molar bites with bite block support on the opposite side. In addition, EMG values alone were recorded during maximum clenching without any transducer between the upper and lower dentures. The level of muscular effort was significantly higher with greater denture support. These results indicate that denture instability probably prevents denture wearers from using the full potential of their jaw muscles, especially during unilateral biting and chewing, even with two implants supporting the mandibular dentures.

Prevalence of unilateral chewing habit in orthodontic patients

Prevalence of unilateral chewing habit in orthodontic patients

Immediate effect of an elastomeric oral appliance on the neuromuscular coordination of masticatory muscles: a pilot study in healthy subjects

To compare the electromyographic characteristics of masticatory muscles with and without a new elastomeric oral device proposed for masticatory muscle training, 10 healthy subjects aged 23 to 32 were examined. Surface electromyography of masseter and temporal muscles was performed during maximum teeth clenching without and with the device and during unilateral chewing with either gum or the device. During clenching, a significant increment of the overall muscular activity was promoted by the occlusal device in comparison with the intercuspal teeth clenching (P=0·05). Muscular standardised activity during device chewing was significantly higher than that during gum chewing (P=0·005), and it was more evenly distributed between working and balancing sides (P=0·023 right side, P=0·039 left side), and between masseter and temporal muscles (right side test, P=0·014). No significant differences were found for the global neuromuscular co-ordination, the masticatory symmetry and the chewing frequency. Clenching and chewing with the analysed occlusal prostheses was performed with a relative increment of muscular activity. These findings may be the basis for the training effect proposed for this device.

Cardiovascular and muscle activity during chewing in whiplash-associated disorders (WAD)

Objective The present study aimed to elucidate possible physiological mechanisms behind impaired endurance during chewing as previously reported in WAD. We tested the hypothesis of a stronger autonomic reaction in WAD than in healthy subjects in response to dynamic loading of the jaw–neck motor system. Design Cardiovascular reactivity, muscle fatigue indicies of EMG, and perceptions of fatigue, exhaustion and pain were assessed during standardised chewing. Twenty-one WAD subjects and a gender/age matched control group participated. Baseline recordings were followed by two sessions of alternating unilateral chewing of a bolus of gum with each session followed by a rest period. Results More than half of the WAD subjects terminated the test prematurely due to exhaustion and pain. In line with our hypothesis the chewing evoked an increased autonomic response in WAD exhibited as a higher increase in heart rate as compared to controls. Furthermore, we saw consistently higher values of arterial blood pressure for WAD than for controls across all stages of the experiment. Masseter EMG did not indicate muscle fatigue nor were there group differences in amplitude and mean power frequency. Pain in the WAD group increased during the first session and remained increased, whereas no pain was reported for the controls. Conclusion More intense response to chewing in WAD might indicate pronounced vulnerability to dynamic loading of the jaw–neck motor system with increased autonomic reactivity to the test. Premature termination and autonomic involvement without EMG signs of muscle fatigue may indicate central mechanisms behind insufficient endurance during chewing.

Indications for jaw gape‐related control of relative muscle activation in sequent chewing strokes

Jaw muscle activity ratios in unilateral isometric biting differ from ratios of unilateral chewing but approach the latter if the jaw gape in biting is made as small as the minimum interocclusal distance (MID) of chewing. Especially, the masseter working/balancing side ratio (W/B-ratio) becomes as asymmetric as in chewing, because of reduction in balancing side (BS) masseter activity. This behaviour of ratios might reflect a 'chewing-specific' motor strategy induced when isometric biting is performed with a 'chewing-like' gape. If this hypothesis applies, activity ratios should be associated with MIDs of sequent chewing strokes in a similar manner as with incremented jaw gapes in isometric biting. To test this prediction, bilateral surface electromyograms of masseter and anterior temporalis muscles and incisor movements were recorded during unilateral chewing in 52 subjects. W/B-ratios of masseter and temporalis activities and temporalis/masseter-ratios on both sides were calculated. The ratios were related to MIDs of consecutive chewing cycles. Three of the four ratios were associated with masticatory MID in the same manner as with jaw gape in isometric biting. In particular with decreasing MID, the masseter W/B-ratio increased from 1.5 to 2.2 (P < 0.01). This increase in asymmetry was attributed to a stronger decrease in masseter activity on the BS than on the working side. We conclude that relative jaw muscle activation is associated with interocclusal distance in a similar way in isometric biting and in chewing. This analogy supports the idea of a common jaw gape-related neuromuscular strategy facilitated by afferent signalling of interocclusal distance.