Jaw muscle soreness after tooth-clenching depends on force level.

The effects of prolonged tooth-clenching on masticatory muscle pain have not been fully elucidated. We hypothesized that late-onset soreness may develop depending on the clenching force. Ten pain-free females were asked to endure sustained clenching tasks up to exhaustion in randomized sequences of 7.5%, 10%, 15%, 25%, and 40% of maximum clenching force. Perceived pain, fatigue, and pressure-pain thresholds of masseter and temporalis muscles were assessed before, immediately after, and one day after the tasks. Endurance times differed markedly among participants and force levels, ranging from 1.2 to 245.1 min. Masseter pressure-pain threshold decreased immediately after (-13.7%; p = 0.050) and one day after (-22.0%; p = 0.006) the 7.5% task. Temporalis pressure threshold decreased one day after the 7.5 % task (-14.6%; p = 0.003). It was concluded that prolonged low-level tooth-clenching in healthy young women induces a delayed soreness in the jaw elevator muscles.

The relation of mandibular laterotrusion with ipsilateral TMJ clicking.

The purpose of this study was to investigate the association of temporomandibular joint (TMJ) clicking with the types of canine guidance, the tracing patterns of mandibular laterotrusion and, especially, with the movements of the working side condyle. In a young subject group, the movements of left and right mandibular laterotrusion were measured at the incisal and the lateral pole point of the working side condyle. All samples were divided into one of two groups according to the mesial (M) or distal (D) canine guidance. They were also divided into protrusive laterotrusion (PL) or retrusive laterotrusion (RL) groups according to the tracing patterns. The incidence of clicking was 23.8% in all 84 TMJs. There was no significant difference between the M and the D groups. However, clicking occurrence was significantly higher in the RL than in the PL group (P<0.05). The condyles in clicking joints moved more posterior in ipsilateral laterotrusion than the condyles in non-clicking joints. The condyles in RL also moved more posterior than those in PL. It is suggested that the posterior movement of the working side condyle in RL has a strong relationship with the internal derangement of the TMJ. However, it is not related to the type of canine guidance.

The relation of canine guidance with laterotrusive movements at the incisal point and the working side condyle.

The effect of different types of canine guidance on the patterns of laterotrusive tracing at the incisal point and the relationship between the laterotrusive inclinations and the working side condylar movements were investigated in 42 young subjects. The subjects were divided into M and D groups according to their mesial and distal canine guidance, and were also divided into protrusive laterotrusion (PL) and retrusive laterotrusion (RL) groups according to their laterotrusive tracing patterns. No differences of laterotrusive inclinations and working side condylar movements were found between the M and D groups. The laterotrusive tracing pattern had no corresponding association with the type of canine guidance. In relation to the movements of the working side condyles, significant differences were found between the PL and RL groups. The condyles moved laterally and posteriorly in the RL group, but moved lateral and inferior in the PL one. The distance of condylar movement in the X direction was correlated with the horizontal and sagittal inclinations of laterotrusion. The results indicate that the movements of the working side condyle were affected functionally by the laterotrusion, but not by either the mesial or the distal type of canine guidance.

Ultrasonographic assessment of the swelling of the human masseter muscle after static and dynamic activity.

Work-related fatigue, pain and disorders in skeletal muscles have been related to prolonged static and dynamic activity. Such contractions have been shown to impair blood flow and increase muscle thickness and fluid. In the present study the effect of static and dynamic activity was evaluated from changes in masseter thickness as a measure of oedema, simultaneously with assessment of perceived pain/discomfort and cardiovascular responses. As static activity, fourteen young healthy women bit at 15% maximal voluntary contraction on bite-force transducers in the molar regions until exhaustion or 20 min at maximum (median endurance time 7.1 min). For dynamic activity, the same individuals chewed gum unilaterally until exhaustion or 40 min at maximum (all endured 40 min) with a cycle time of 725 ms, an average load of 9.3% of maximal electromyographic activity (maxEMG) and a peak mean voltage of 54.3% of maxEMG. Muscle thickness was measured by ultrasonography at the mid-portion of the ipsilateral masseter. Immediately after exercise, muscle thickness was significantly increased, more after static (14.0%) than dynamic (8.6%), and returned to pre-exercise values after 20-min recovery. Visual analogue scales (VAS) revealed the concomitant occurrence of pain (static 11.9 VAS%; dynamic 5.9 VAS%), and discomfort (static 8.1 VAS%; dynamic 5.9 VAS%), and both sensations decreased to pre-exercise values after 20-min recovery. Systolic blood pressure increased significantly, more during static (12.5%) than dynamic activity (4.3%), whereas heart rate rose significantly only during dynamic exercise (13.3%). Hence, activity was associated with muscular swelling and pain, and, despite the relatively small size of the masticatory muscles, also with general cardiovascular responses.

[Influence of tooth contacts on masseter and temporal muscle activity. 1. Total activity and its ratio to maximum biting activity in intercuspal position (IP ratio)].

14 natural dentitioned subjects with no signs of TMJ disorders, aged 19-58, were used in this study. They were divided into three groups according to their occlusal guidance. One is canine guidance group (CG group), the other is group function group (GF group), and the last is group having non-working side contacts (FB group). All subjects were asked to perform maximum biting in 1) intercuspal position (IP), 2) right lateral position (rLP), 3) left lateral position (lLP), 4) retruded position (RP), and 5) protruded position (PP). EMG recordings of right and left masseter, anterior and posterior temporal muscles from pairs of surface electrodes were taken in each occluded position. The results were as follows: 1) Total integrated EMG activity of FB group was approximately equal in any occluded position, whereas that of CG and GF group varied from position to position. 2) EMG patterns in rLP and lLP of CG group were obviously different from those of GF group. Ratio to maximum biting in IP of CG group in rLP and lLP were significantly small, approximately half of GF group.

[Effect of lingual surface inclination of maxillary canine on jaw muscle activity].

The effect of lingual surface inclination of the maxillary canine on the jaw muscle activity was investigated on five subjects. Several different metal maxillary canine risers were fabricated to change the lingual inclination. The EMG activity of the masseter and posterior temporal muscle was recorded bilaterally by means of bipolar surface electrodes simultaneously with the LED mandibular tracking device. On each subject the lateral gliding movements were carried out while maintaining the occlusal contact on the canine riser. The recorded muscle activity and mandibular gliding movements were analyzed quantitatively. During the lateral gliding, the working-side posterior temporal muscle was more active than the other three muscles. Steeper canine risers caused a reduction of the muscle activity when compared with the more flat guidance. In the gliding movement from maximum intercuspation, the temporal muscle showed more activity than the masseter muscle. However the relative relationships between the individual muscles as well as the working-side muscle and nonworking-side muscle remained unchanged with all canine risers. In the gliding movement into maximum intercuspation, the difference of the canine riser showed no consistent change in the muscle activity. In each subject, it was found that the canine riser with a moderate inclination was more comfortable to move the mandible, but no relationship between the EMG activity and his or her feeling was revealed.