Jaw-neck motor strategy during jaw-opening with resistance load.

BACKGROUND: The jaw and neck motor systems have a close functional integration but the effect of resistance load to the mandible during jaw opening on the jaw-neck integration is not known. OBJECTIVES: To evaluate the effect of resistance load compared to no load on integrated jaw and neck motor function in individuals free from pain and dysfunction in the jaw and neck regions. METHODS: Jaw and head movements during continuous jaw opening were recorded with an optoelectronic system (MacReflex® ) in 26 pain-free individuals (14 women, 12 men, mean age 22 years). Jaw opening was performed with and without resistance load (1600 g) to the mandible. The relationship between jaw movement amplitude, head movement amplitude, head/jaw ratio (quotient of head and jaw movement amplitude) and resistance load were modelled using linear mixed-model analysis. A p-value <.05 was considered statistically significant. RESULTS: The expected head/jaw ratio mean was increased by 0.05 (95% CI: 0.03, 0.08, p < .001) with resistance load as compared to no load. This corresponds to an increase in expected mean by 55.6%. With resistance load, expected mean head movement amplitude increased by 1.4 mm (95% CI: 0.2, 2.5, p = .018), and expected mean jaw movement amplitude decreased by 3.7 mm (95% CI: -7.0, -0.5, p = .025). CONCLUSION: There is a compensation and adaptation of integrated jaw-neck motor function with an altered jaw-neck motor strategy during jaw opening with resistance load compared to no load. The head/jaw ratio demonstrates increased proportional involvement of the neck during increased load on the jaw system.

Jaw-neck motor function in the acute stage after whiplash trauma.

BACKGROUND: Jaw-neck motor function is affected in the chronic stage following whiplash trauma. It is not known whether motor function is affected also in the early stage after neck trauma. OBJECTIVES: To determine how jaw and head movement amplitudes and movement cycle times correlate with jaw and neck pain, and neck disability in the acute stage after whiplash trauma. METHODS: Jaw and head movements during jaw opening-closing were recorded with an optoelectronic system in 23 cases (4 men, 19 women, 18-66 years) within 1 month after whiplash trauma and compared with 27 controls without neck trauma (15 men, 12 women, 20-66 years). Jaw and head movement amplitudes, head/jaw ratio (quotient of head and jaw movement amplitude) and movement cycle times were evaluated in relation to jaw and neck pain (Numeric Rating Scale) and neck disability (Neck Disability Index). Analyses were performed with Mann-Whitney U test and Spearman's correlation. RESULTS: Compared with controls, cases showed smaller jaw movement amplitudes (P = .006) but no difference in head movement amplitudes, head/jaw ratios or movement cycle times. There were no significant correlations between movement amplitudes or cycle times and jaw and neck pain, and neck disability. Cases with high neck pain intensity had smaller jaw movement amplitudes compared to cases with low neck pain intensity (P = .024). CONCLUSION: The results suggest that jaw-neck motor function may be affected in the acute stage after whiplash trauma and more so in cases with higher neck pain intensity.

Work ability and productivity among dentists: associations with musculoskeletal pain, stress, and sleep.

PURPOSE: Work ability can be measured by the work ability index (WAI), and work-related questions measuring productivity loss in terms of quality and quantity of work. Dentists have high occupational risk of musculoskeletal pain and the exposure of ergonomic strain is already high during dental education. The aim was to evaluate work ability and productivity among dentists, and to identify gender differences and associations with sleep, stress, and reported frequent pain. METHODS: The study population comprised 187 dentists (123 women and 64 men) who had been working as dentists between 5 and 12 years. Participants completed a questionnaire regarding sleep, stress, presence of pain at different sites, work ability assessed by WAI, and productivity in terms of quality and quantity of work. RESULTS: Poor sleep quality and high level of stress were reported by 31% and 48.1% of participants, respectively, with no gender differences and no association with age. The prevalence of frequent pain ranged 6.4-46.5% with shoulders being the most prevalent site. Thirty-three percent reported reduced work ability. Poor sleep, high amount of stress, and multi-site pain were associated with decreased work ability. CONCLUSIONS: A high prevalence of pain was shown among dentists. Decreased work ability in terms of productivity loss was associated with poor sleep quality, high amount of stress, and multi-site pain. Preventive actions at the workplace should promote good musculoskeletal health, and measures taken, both individual and organizational, to minimize the risk of high, persistent stress and work-related pain.

Multimodal Sensory Stimulation of the Masseter Muscle Reduced Precision but Not Accuracy of Jaw-Opening Movements.

A functional integration between the trigeminal and craniocervical sensorimotor systems has been demonstrated, with simultaneous jaw and head-neck movements during jaw opening-closing. We previously showed that pain induction in the masseter muscle increased the relative contribution of the neck component of integrated jaw-neck movements. Induced pain or manipulation of proprioception by vibration did not affect accuracy during a jaw-opening task in men. It is not known how multimodal sensory stimulation, with a combination of pain induction and vibration, affects jaw-opening accuracy and precision. The aim was to investigate how jaw-neck movements, and specifically accuracy and precision of jaw-opening, are affected during concomitant nociceptive and proprioceptive stimulation of the masseter muscle. Twenty-one healthy men performed jaw-opening to a target position, defined as 75% of individual maximum jaw opening, during control (Ctr), vibration of masseter muscles (Vib), pain induction in the masseter (Pain), and concomitant vibration and pain induction in the masseter muscle (VibPain). Simultaneous jaw and head movements were recorded with an optoelectronic system and amplitudes calculated for each jaw opening-closing cycle. Accuracy of jaw movements was defined as the achievement of the target position. Precision of jaw movements was defined as the cycle-to-cycle variability from the mean of cycles 2-10 (coefficient of variation, CV). Differences between the trials were analyzed with Friedman's test, Dunn's test, and Benjamini-Hochberg correction. There were no significant differences between the trials for jaw movement amplitudes. For head movements, amplitudes for cycles 2-10 were larger during Pain compared to Ctr and Vib (both p = 0.034), and larger during VibPain compared to Ctr (p = 0.034) and Vib (p = 0.035). There were no differences in accuracy of jaw movements between the trials. For precision of jaw movements, the cycle-to-cycle variability was larger during VibPain compared to Ctr (p = 0.027) and Vib (p = 0.018). For integrated jaw-neck motor strategy, there was a difference between pain and non-pain trials, but no differences between unimodal and multimodal stimulation trials. For achievement of jaw-opening to a target position, the results show no effect on accuracy, but a reduced precision of jaw movements during combined proprioceptive and nociceptive multimodal stimulation.

Vibratory stimulus to the masseter muscle impairs the oral fine motor control during biting tasks.

PURPOSE: To investigated the effect of vibratory stimulus on masseter muscles during oral fine motor biting tasks. METHODS: Sixteen healthy individuals (age: 24.5 ± 2.4 years) participated in experiment I during which the participants were asked to "hold and split" half a roasted peanut placed on a force transducer with their front teeth. The participant performed ten series with ten trials of the "hold and split" behavioral task while vibratory stimulus was applied on the masseter muscle every alternate series. Further, fourteen participants participated (age: 25.2 ± 4.8 years) in experiment II during which they performed a series each of the behavioral task at baseline, an adjusted baseline without and with vibration as well as with and without visual feedback. Hold and split forces along with the variability of hold force and duration and force rate during the split were measured. RESULTS: The results of the study showed an increase in the magnitude of the hold force (P = 0.002), force rate during the split (P < 0.001) and a significant decrease in the duration of split (P < 0.001) due to the vibratory stimulus. However, there was no significant effect of the vibratory stimulus on the variability of hold forces (P = 0.879) or mean split force (P = 0.683) during the "hold and split" behavioral task. The results of experiment II also showed an increase in hold force due to the vibratory stimulus (P < 0.001). CONCLUSIONS: Vibratory stimulus to the masseter muscles impairs the oral force control during a standardized biting task and provide further insight into the sensorimotor regulation of the masticatory system.

The effect of supervised exercise on localized TMD pain and TMD pain associated with generalized pain.

OBJECTIVES: To evaluate the effect of a supervised exercise program in patients with localized/regional temporomandibular disorder (TMD) pain and with TMD associated with generalized pain. MATERIAL AND METHODS: Consecutively referred patients with localized/regional TMD pain (n = 56; 46 women and 10 men, mean age 44 years) and TMD associated with generalized pain (n = 21; 21 women, mean age 41 years) participated. Patients underwent a 10-session structured supervised exercise program over 10-20 weeks that included relaxation, and coordination and resistance training of the jaw and neck/shoulders. The outcomes were jaw pain intensity on the Numerical Rating Scale, endurance time for jaw opening and protrusion against resistance and chewing, and effect of pain on daily activities. RESULTS: After the exercise program, a reduction in jaw pain was reported by the local (p = .001) and general (p = .011) pain groups. There were no significant differences in jaw pain intensity between the groups, before (p = .062) or after treatment (p = .121). Endurance time increased for both groups for jaw opening/protrusion (both p < .001) and chewing (both p = .002). The effect of jaw pain on daily activities decreased after exercise compared to baseline for both the local (p < .001) and general (p = .008) pain groups. CONCLUSIONS: Supervised exercise can reduce TMD pain and increase capacity in patients with TMD. The results suggest that activation of the jaw motor system with exercise has a positive effect in patients with localized/regional TMD pain and TMD associated with generalized pain.

Does induced masseter muscle pain affect integrated jaw-neck movements similarly in men and women?

Normal jaw opening-closing involves simultaneous jaw and head-neck movements. We previously showed that, in men, integrated jaw-neck movements during jaw function are altered by induced masseter muscle pain. The aim of this study was to investigate possible sex-related differences in integrated jaw-neck movements following experimental masseter muscle pain. We evaluated head-neck and jaw movements in 22 healthy women and 16 healthy men in a jaw opening-closing task. The participants performed one control trial and one trial with masseter muscle pain induced by injection of hypertonic saline. Jaw and head movements were registered using a three-dimensional optoelectronic recording system. There were no significant sex-related differences in jaw and head movement amplitudes. Head movement amplitudes were significantly greater in the pain trials for both men and women. The proportional involvement of the neck motor system during jaw movements increased in pain trials for 13 of 16 men and for 18 of 22 women. Thus, acute pain may alter integrated jaw-neck movements, although, given the similarities between men and women, this interaction between acute pain and motor behaviour does not explain sex differences in musculoskeletal pain in the jaw and neck regions.

Reciprocal influence on the incidence of symptoms in trigeminally and spinally innervated areas.

Temporomandibular disorders (TMD), headaches, and spinal pain show co-morbidity and may therefore influence each other. The hypothesis tested is that the presence of any of these conditions will increase the risk of onset of new symptoms within a 2-year period. The study population comprised 280 dental students, who were examined three times at 12-month intervals. The incidence was calculated for a 2-year period, based on subjects without the defined symptom at baseline. Each participant was classified into five different case-control groups, representing incidence cases or no incidence (controls) of: (1) nonpain TMD symptoms; (2) jaw pain; (3) headaches; (4) spinal pain; and (5) TMD pain. Presence of headaches and of spinal pain and signs and symptoms of TMD at baseline were used as independent variables in logistic regression analyses, controlling for age and sex. Incidence cases with TMD pain reported spinal pain at baseline significantly more often than the controls, and were mostly women. Incidence cases with headaches and incidence cases with jaw pain significantly more often had signs of TMD and reported spinal pain at baseline, compared to controls. Incidence cases with nonpain TMD symptoms or spinal pain significantly more often presented with signs of TMD at baseline. Our findings show that pain and dysfunction in trigeminally innervated areas and pain in spinally innervated areas mutually predict the onset of new symptoms in dental students, indicating common pathophysiological mechanisms and individual vulnerability. This may be of importance in risk assessment and treatment planning of individuals with musculoskeletal pain.

Does a dose-response relation exist between spinal pain and temporomandibular disorders?

BACKGROUND: The aim of this study was to test whether a reciprocal dose-response relation exists between frequency/severity of spinal pain and temporomandibular disorders (TMD). METHODS: A total of 616 subjects with varying severity of spinal pain or no spinal pain completed a questionnaire focusing on symptoms in the jaw, head and spinal region. A subset of the population (n = 266) were sampled regardless of presence or absence of spinal pain. We used two different designs, one with frequency/severity of spinal pain, and the other, with frequency/severity of TMD symptoms as independent variable. All 616 participants were allocated to four groups, one control group without spinal pain and three spinal pain groups. The subjects in the subset were allocated to one control group without TMD symptoms and three TMD groups. Odds ratios (ORs) were calculated for presence of frequent TMD symptoms in the separate spinal pain groups as well as for frequent spinal pain in the separate TMD groups. RESULTS: The analysis showed increasing ORs for TMD with increasing frequency/severity of spinal pain. We also found increasing ORs for spinal pain with increasing frequency/severity of TMD symptoms. CONCLUSION: This study shows a reciprocal dose-response-like relationship between spinal pain and TMD. The results indicate that these two conditions may share common risk factors or that they may influence each other. Studies on the temporal sequence between spinal pain and TMD are warranted.

Back pain in relation to musculoskeletal disorders in the jaw-face: a matched case-control study.

Back pain and temporomandibular disorders are both common conditions in the population with influence on the human motor system, but a possible co-morbidity between these conditions has not been fully investigated. The aim of this study was to test the hypothesis of an association between long-term back pain and pain and/or dysfunction in the jaw-face region. Back pain was defined as pain in the neck, shoulders and/or low back. The study-population comprised 96 cases with long-term back pain and 192 controls without back pain. We used a screening procedure, a questionnaire and a clinical examination of the jaw function. The questionnaire focused on location, frequency, duration, intensity and impact on daily life of symptoms in the jaw-face and back regions. The analysis was conducted on 16 strata, matched by age and sex for case vs. control, using Mantel-Haenszel estimates of matched odds ratio (OR) and 95% confidence interval (CI) as well as the corrected Mantel-Haenszel chi(2) test. The overall prevalence of frequent symptoms in the jaw-face region, as reported in the questionnaire, was 47% among cases and 12% among controls. The difference was statistically significant (P<0.0001) with a sevenfold odds ratio (CI: 3.9-13.7). Moderate to severe signs from the jaw region were clinically registered among 49% of the cases and 17% of the controls (P<0.0001, OR: 5.2, CI: 2.9-9.2). The results showed statistically significant associations between long-term back pain and musculoskeletal disorders in the jaw-face and indicate co-morbidity between these two conditions.