Masseter length determines muscle spindle reflex excitability during jaw-closing movements

Evaluation of factors related to morphological masseter muscle changes after preoperative orthodontic treatment in female patients with skeletal class III dentofacial deformities

Background

The purpose of the current study was to investigate factors related to morphological changes in the masseter muscle after preoperative orthodontic treatment in patients with skeletal class III dentofacial deformities for analysis of muscle changes and malocclusions.

Methods

Twenty female patients with dentofacial deformities were included in the study. Computed tomography was performed before and after preoperative orthodontic treatment, and the lengths, widths, and cross-sectional areas of the masseter muscles were measured. Changes in these parameters were evaluated, and factors related to changes in masseter muscle area after preoperative orthodontic treatment were analyzed.

Results

The lengths, widths, and areas of masseter muscles were significantly smaller after preoperative orthodontic treatment. Smaller masseter muscle area was significantly associated with changes in overbite and pretreatment values of SNA angle.

Conclusions

Atrophy of the masseter muscle during preoperative orthodontic treatment was greater in patients with increased open bite due to improved dental compensation in patients with skeletal class III dentofacial deformities with maxillary retraction.

Can the subject reliably reproduce maximum voluntary contraction of temporalis and masseter muscles in surface EMG?

OBJECTIVE

To evaluate the repeatability of the surface EMG variables of myoelectric signals from the masseter and temporalis muscles according to three methods to induce maximum voluntary contraction (MVC) in healthy adults.

METHODS

Thirty healthy young subjects performed the following three MVC tasks three times each in three sessions on the same day without replacing surface electrodes: clenching the teeth (MVCIC) and biting down on two cotton rolls bilaterally with the posterior teeth (MVCBP) or first molars (MVCB6).

RESULTS

The intra-class correlation coefficient (ICC) of the amplitudes during the three MVC tasks ranged from 65 to 79%. The ICCs of the spectral variables ranged from 78 to 86%. The ICCs of the asymmetry index of the masseter ranged from 77 to 86%, and those of the activity index ranged from 68 to 90%.

CONCLUSION

The surface EMG measurements according to the three MVC methods exhibited good to excellent reproducibility.

Is scoliosis related to mastication muscle asymmetry and temporomandibular disorders? A cross-sectional study

OBJECTIVE

Patients with adolescent idiopathic scoliosis (AIS) may face motor control problems and health disability barriers during mandibular movements and chewing. However, studies investigating the extent of these disadvantages, and possible associated factors are quite limited in patients with AIS. This study was conducted to gain a deeper perspective on the effect of AIS on temporomandibular disorders (TMD) and to contribute to the small amount of data on this subject.

METHODS

Twenty-nine patients with AIS and 29 age- and sex-matched asymptomatic controls participated in this cross-sectional study. Cobb's method was used to measure scoliosis curves. In both groups, the volume of the masseter muscle was determined on magnetic resonance imaging, and Helkimo and Fonseca anamnestic indexes were used to evaluate temporomandibular joint (TMJ).

RESULTS

It was observed that the TMD symptoms were higher in the AIS group (22.6- Helkimo and 1.2 - Fonseca) than the asymptomatic group (13.6 - Helkimo and 0.7 - Fonseca). There was no significant asymmetry in masseter volume in patients with AIS, however the volume of the masseter muscles was smaller in the AIS group (R = 14.6/L = 13.6) compared to the control group (R = 16.1/L = 16.2).

CONCLUSIONS

The study results indicate that spinal curvatures affect the anatomical, biomechanical, and kinesiological features of the masticatory system, and individuals with AIS may experience more chewing problems than asymptomatic individuals. Examining musculoskeletal properties of masticatory system can provide information about the limitation of the TMJ in patients with AIS.

Craniofacial Morphology Affects Bite Force in Patients with Painful Temporomandibular Disorders

Craniofacial morphology affects masticatory performance in healthy dentate subjects, but little is known about its effects in patients with painful temporomandibular disorders (TMDs). Forty-eight female patients (mean age of 28±5.8 years) with painful TMDs underwent lateral cephalometric radiography. Using Ricketts' cephalometric analysis and the Vert method, subjects were assigned to three groups according to their craniofacial morphology: brachyfacial (n=22), mesofacial (n=13), and dolichofacial (n=13). Research diagnostic criteria for TMD were used to confirm the TMD diagnosis for each patient. Pain intensity was reported by each patient based on a visual analog scale (VAS). Maximum bite force (MBF) was measured with pressure sensors placed on the first molar site. Masticatory performance (MP) was assessed by chewing a silicone-based artificial material and determining the resulting particle size by the sieve method. Chewing ability (CA) was evaluated for seven food types and analyzed by a VAS questionnaire. Data were analyzed by one-way ANOVA followed by a Tukey-Kramer test (p<0.05). MBF differed in each group, with brachyfacial patients having the highest MBF values. There was no difference in MP among the groups. The groups differed only in their ability to chew one of the seven evaluated food types. In summary, craniofacial morphology affects the MBF without impairing MP or CA in patients with painful TMDs.