Neck motor unit activities induced by inputs from periodontal mechanoreceptors in rats

[Features of the formation of typical motor patterns of the craniocervical zone in functional disorders in the craniomandibular system]

OBJECTIVE

The aim of the study is to analyze the features of motor patterns formation in the craniocirvical zone with occlusal and functional disorders of the craniomandibular system.

MATERIALS AND METHODS

281 patients (201 women and 80 men) were examined at the age from 21 to 32 years. Two groups of individuals were identified based on the short Gambur test. The first group (I) included persons with intact dentition and without signs of functional disorders (n=30). The second group (II) included persons with intact dentition and dysfunction of the craniomandibular system (CMS) (n=30). All patients were examined by a digital analysis of the occlusal relationship. A digital method of capturing and reconstructing movement was used to assess the motor patterns of the craniocervical zone. Analysis of functional occlusion showed that the first contact in persons with functional impairment is predominantly localized on the molars region (χ²=44.1; df=11, p=0.00001).

RESULTS

In analysis of dynamic occlusion, the time exceed for reaching maximum intercuspation position significantly in group II instead of group I 0.127±0.072 sec and 0.261±0.091 sec (p<0.05). Disconnection time in group II was 0.443±0.096 sec, Which significantly differed from group I (p<0.05). Persons with CCM dysfunction head flexion was 11.00° [9.00°; 13.00°], which is significantly higher than in the comparison group 5.00° [5.00°; 5.50°]. In the transverse plane, an increase in the angle of lateroflexion in persons with functional impairments up to 11.00° [10.00°; 11.00°]. Correlation analysis showed the presence of a direct strong connection between the angle of flexion and the time of separation (r=0.76), as well as the time to reach the maximum intercuspation position (r=0.63).

CONCLUSION

Thus, functional disorders in the form of occlusal aberrations lead to changes in the cervical spine and head position through the formation of new motor patterns.

Splenius muscle activities induced by temporomandibular joint stimulation in rats

Recent studies show that temporomandibular joint disorders cause hyperalgesia and deficits in the postural control of cervical region. However, the effects of specific modalities of receptors in the temporomandibular joint area on these phenomena are still unclear. In this study, we investigated the neck muscle activities while natural mechanical stimulation was applied to the temporomandibular joint. Single motor unit activities were recorded bilaterally from the splenius muscles in 22 Wistar rats. Mechanical stimulation applied to the left temporomandibular joint elicited tonic discharges in the left or right splenius muscle. The mean threshold values for mechanical stimulation were 48.1 (+/-16.2 S.E.M.) and 54.1 mN (+/-16.3 S.E.M.) for left and right sides, respectively. It is suggested that the temporomandibular joint mechanoreceptors not only affect the motor unit activities of neck muscles, but also are concerned in the regulation of postural control of the head.

A new method for evaluating the threshold of periodontal ligament mechanoreceptor by slow speed mechanical stimulation

OBJECTIVES

This study aimed to establish a reliable method for detecting the threshold for perception of force applied to tooth and to report the basic properties of force threshold in the normal dentition subjects.

BACKGROUND

The perception of mechanical stimulation exerted to tooth is formed by input from periodontal ligament mechanoreceptors and intradental mechanoreceptors. Periodontal ligament mechanoreceptors respond to a wide range speed of stimulus, whereas intradental mechanoreceptors are activated only by a rapid stimulation. Reliable properties of perception have not been reported because of the difficulties to regulate velocity and degree of the stimulus.

METHODS

Eighteen healthy subjects were observed in this study (mean age: 27.2 +/- 5.7 years). A loading device to generate slow speed loading was fabricated and measured as follows: (i) the fluctuation of the force threshold within a day, (ii) day-to-day fluctuation, (iii) changes in the force threshold by a transient mechanical loading.

RESULTS

In the normal dentition, it was observed that the fluctuation within a day and day to day of the pressure sense showed no significant differences; however, a transient mechanical loading caused the sensitivity of the periodontal ligament to decrease significantly.

CONCLUSIONS

The device examining the force threshold resulted from periodontal ligament mechanoreceptors was useful in evaluating the sensitivity of the periodontal ligament.