Repeated clenching causes plasticity in corticomotor control of jaw muscles.

This study tested the effect of short-term tooth-clenching on corticomotor excitability of the masseter muscle using transcranial magnetic stimulation (TMS). Fifteen subjects with normal stomatognathic function participated. All subjects performed a tooth-clenching task (TCT) on five consecutive days. The TCT consisted of 10, 20, and 40% of maximum voluntary contraction in a randomized order within 1 h. All subjects underwent TMS in four sessions: pretask day 1 (baseline), post-task day 1, pretask day 5, and post-task day 5. Motor-evoked potentials (MEPs) from the masseter and the first dorsal interosseous (FDI) muscles were obtained using TMS in four sessions. Motor thresholds decreased, after the TCT, for the masseter muscle MEPs. Masseter muscle MEPs were dependent on stimulus intensity and on session, whereas FDI muscle MEPs were only dependent on stimulus intensity. Post-hoc Tukey tests demonstrated significantly higher masseter muscle MEPs post-task on day 5 with 80 and 90% stimulus intensity and above when compared with pre- and post-task day 1 values. Our results suggest that the performance of repeated TCTs can trigger neuroplastic changes in the corticomotor control of the jaw-closing muscles and that such neuroplastic changes may contribute to the mechanism underlying the clinical manifestations of tooth clenching.

Comparing the occlusal contact area of individual teeth during low-level clenching.

The aim of this study was to investigate the occlusal contact area (OCA) in individual teeth during low-level tooth clenching in 24 healthy participants. Before measurements were made, the 100% maximum voluntary contraction (MVC) was determined. At baseline, all subjects were instructed to close their mouth and touch the opposing teeth with minimal force. Occlusal contact was recorded during three jaw motor tasks (baseline, 20% MVC, and 40% MVC) using a blue silicone material. OCA thickness was determined from images and defined on five levels: level 1 (0-149 µm), level 2 (0-89 µm), level 3 (0-49 µm), level 4 (0-29 µm), and level 5 (0-4 µm). Premolar and molar OCAs increased significantly from baseline to 20% MVC and 40% MVC. The OCA of each anterior tooth did not change significantly with increasing clenching intensity at all levels. Our findings suggest that premolar and molar OCAs may be altered by low-intensity clenching, affecting the teeth and periodontal tissues.

Age-related associations between psychological characteristics and pain intensity among Japanese patients with temporomandibular disorder.

We investigated the relationship between pain intensity and psychosocial characteristics in patients with temporomandibular disorder (TMD). Participants with painful TMD, according to the Research Diagnostic Criteria for TMD (RDC/TMD), were recruited from our clinic and classified into six age groups: 15 to 24, 25 to 34, 35 to 44, 45 to 54, 55 to 64, and 65 to 85 years (Groups A through F, respectively). Self-reported present pain intensity and worst pain intensity during the past 6 months were ascertained using a numeric rating scale (0 to 10). Depression and somatization scores were evaluated using the RDC/TMD axis II questionnaire. Among women, worst pain intensity was significantly lower in Groups E and F than in Groups B and C (P < 0.05). In Groups A, C, and D, depression scores were significantly higher in women than in men (P < 0.05). Among women, depression score was significantly lower in Group F than in Groups A through C (P < 0.05). In Groups A through D, somatization scores were significantly higher for women than for men (P < 0.05). Depression score and TMD symptom severity appear to decrease with age in women.

Influence of visual feedback on force-EMG curves from spinally innervated versus trigeminally innervated muscles.

OBJECTIVE: We compared the influence of visual feedback between spinal and trigeminal muscle activity. DESIGN: Twelve subjects participated in two tasks: a finger pinch and a tooth clench task and performed a series of muscle activations with visual feedback as a training task and two series without visual feedback as pre- and post-training tasks. Five target force levels at 10%, 20%, 40%, 60% and 80% maximal voluntary contraction were performed in each series for both tasks. During all series electromyographic (EMG) activity and force were recorded. Target force-actual force and target force-EMG curves were compared with and without visual feedback for both tasks. The variability in each series was determined as the coefficient of variation (CV) from the EMG and force recordings. RESULTS: Although positive linear relationships were found between the target force level and the actual force value, and target force level and root mean square (RMS)-EMG amplitude from the tooth clenching task, the curves calculated from the finger pinch task were not completely linear. CVs of the actual force value and CVs of the RMS-EMG amplitude in both masseter and temporalis muscles were significantly influenced by visual feedback (P<0.001). However, the CVs of the RMS-EMG amplitude in right abductor pollicisbrevis and right first dorsal interosseous muscles were not significantly influenced by the three series. CONCLUSIONS: The influence of visual feedback was different between spinally innervated and trigeminally innervated muscles, and the specific mechanism of force execution from muscle activity appears to be different between the tasks.

Group cognitive-behavioral intervention for patients with burning mouth syndrome.

This study was conducted to assess the psychological characteristics of, and determine the effectiveness of group cognitive-behavioral (CB) treatment for, patients with burning mouth syndrome (BMS). The baseline characteristics of 24 female patients (age 69.7 ± 5.9 years) and an identical number of healthy female control subjects (age 69.2 ± 5.5 years) were compared. The patient group had significantly higher anxiety scores (P < 0.05) at baseline. A brief group CB intervention was delivered in a small-group format. Two sessions were planned 6 months apart. A numeric rating scale (NRS) was used to assess pain intensity. Anxiety was evaluated using a state and trait anxiety inventories. Present pain intensity decreased after both the first and second sessions. The session effect was significant (P = 0.02), but no repeat effect was found (P = 0.19). The state anxiety inventory score also decreased after the second session. The session effect was significant (P < 0.01), as was the repeat effect (P < 0.01). The trait anxiety inventory score decreased after the second session, and the session effect was significant (P = 0.013), but the repeat effect was not (P = 0.93). The results suggest that a brief group CB intervention reduces pain intensity and anxiety in patients with BMS.

Influence of age and gender on trigeminal sensory function and magnetically evoked masseteric exteroceptive suppression reflex.

OBJECTIVE: The present study explored the effect of age and gender on trigeminal sensory function and masseteric exteroceptive suppression (ES) reflex responses. METHODS: Young healthy men (n = 12) and women (n = 12) (age: 23.5 ± 3.0 years) and older healthy men (n = 12) and women (n = 12) (age: 58.5 ± 5.2 years) participated. Sensory function was assessed on the skin overlying the mental foramen using mechanical stimuli. Surface EMG was recorded from the left masseter muscle to assess ES reflex responses evoked by a magnetic stimulus applied to the skin above the left mental nerve. RESULTS: The older group had significantly higher tactile detection thresholds. Early ES1 was present in all subjects. Onset latency of ES1 was significantly delayed in older subjects. ES2 was present in all young subjects, but only in 5 of the 12 men and 8 of the 12 women in the older group. Significant gender differences were found for sensory and pain thresholds to mechanical stimuli as well as for duration of ES. CONCLUSIONS: Ageing affects tactile detection thresholds, onset latency of ES1 responses, and appearance of ES2. The present results indicate that trigeminal sensory function and brainstem reflex responses differ between genders and age groups. These findings may have implications for assessment of craniofacial pain conditions.

Pain intensity and psychosocial characteristics of patients with burning mouth syndrome and trigeminal neuralgia.

This study compared pain intensity and psychosocial characteristics between patients with burning mouth syndrome (BMS) and those with trigeminal neuralgia (TN). Data from 282 patients with BMS and 83 patients with TN were analyzed. Patients reported duration of illness: duration ≤ 6 months was defined as acute illness and > 6 months as chronic illness. Present pain intensity and worst pain intensity during the past 6 months were reported using a 0-10 numeric rating scale (NRS). In addition, depression and somatization scores were evaluated on questionnaires. Patients with chronic BMS reported significantly higher pain intensity and had worse psychosocial characteristics than did those with acute BMS. Pain intensity was higher in TN patients than in BMS patients, although neither pain intensity nor psychosocial characteristics significantly differed between patients with acute and chronic illness. Logistic regression analysis of BMS and TN patients revealed that the odds ratio for worst pain was significantly lower for BMS patients than for TN patients and that the odds ratio for somatization score was 3.8 times higher in BMS patients. These findings suggest that BMS patients may require pain control targeting the central nervous system or psychosocial characteristics.