Electromyographic, Ultrasonographic, and Ultrasound Elastographic Evaluation of the Masseter Muscle in Class III Patients Before and After Orthognathic Surgery

Association between bilateral condylar resorption and reduced volumes of the craniofacial skeleton and masticatory muscles in adult patients: A retrospective study

Objectives

This retrospective cohort study aimed to analyze volumes of craniomaxillofacial bone and masticatory muscles of young adults with bilateral idiopathic condylar resorption.

Methods

This was a retrospective cohort study of 84 adults with bilateral idiopathic condylar resorption (BCR) and 48 adults with normal temporal-mandibular joint (TMJ) matched for age and sex (mean age, 23.2 ± 3.6 years). The volumes of craniomaxillofacial bone and masticatory muscles, as well as intercondylar angle were measured. Unpaired t-tests and Pearson correlation tests were applied to analyze the data. Multivariable linear regression models were used to estimate the association between bilateral condylar volume and volumes of craniomaxillofacial bone and masticatory muscles adjusted for age, sex, and disc status.

Results

Compared to the control group, the BCR group displayed significant decreased volumes of craniomaxillofacial bone (p < 0.001), craniomaxillofacial bone without mandible (p < 0.001), mandible (p < 0.001), mandible without mandibular condylar process (p < 0.001), bilateral masseter muscle (p < 0.001) and bilateral temporalis muscle (p < 0.001), as well as the intercondylar angle (p < 0.001). These variables were significantly correlated to the volume of mandibular condylar process (0.5< r < 0.8; p < 0.001). By linear regression analyses, significant associations were found for the bilateral condylar volume with craniomaxillofacial bone volume and mandible bone volume.

Conclusions

Young adults with BCR displayed smaller volumes of craniomaxillofacial skeleton and masticatory muscles, and smaller intercondylar angle than the normal patients. The craniofacial musculoskeletal volume and intercondylar angle are associated with mandibular condylar process volume.

Ultrasonographic evaluation of changes in the thickness, width, elasticity index and echogenic pattern of the masseter muscle after mandibular set-back surgery

INTRODUCTION

The masseter muscle is one of the structures that undergoes significant changes following jaw movements in orthognathic surgery. This study aims to investigate the effects of mandibular setback surgery, performed in patients with skeletal class III deformity, on the thickness, width, elasticity index, and echogenic pattern of the masseter muscle.

MATERIAL AND METHODS

This prospective case-control study enrolled patients with class III deformity who underwent mandibular setback surgery, while the control group consisted of class I patients. The predictor variable was the time measured at two different points: preoperative (T1) and postoperative 6 months (T2). The primary outcome variable focused on changes in the internal echogenic pattern of the masseter muscle. Secondary, tertiary, and quaternary outcome variables included changes in the thickness, width, and elasticity index of the masseter muscle, respectively. Gender, age, type of operation, and amount of movement were considered as covariates. Ultrasonography was employed to evaluate the outcome variables.

RESULTS

The study group comprised 31 patients, including 17 females (mean age 22.24 ± 3.52 years) and 14 males (mean age 23.14 ± 2.65 years). The control group consisted of 16 females (mean age 23.34 ± 1.22 years) and 15 males (mean age 23.12 ± 1.76 years). Masseter muscle thickness increased significantly after mandibular setback surgery (p = 0.015). However, there was no statistically significant difference in masseter muscle width before and after surgery (p = 0.627), nor in the elasticity index (p = 0.588). Furthermore, a statistically significant transformation from Type I to Type II was observed in the internal echogenic pattern of the muscle (p = 0.039). Additionally, there was no statistically significant correlation between the amount of mandibular movement performed and the changes in the masseter muscle.

CONCLUSIONS

Mandibular setback surgery leads to changes in both the physical and structural properties of the masseter muscle.

Electromyographic Evaluations of Masticatory Muscle Activity between Patients with Skeletal Class I and III Relationships

OBJECTIVE

 The aim of this study was to compare the muscle activity of the masseter muscle (MM) and anterior temporal muscle (TA) of patients with skeletal Class I and III during maximum voluntary clenching (MVC) at the intercuspal position (ICP) and during chewing.

MATERIALS AND METHODS

 Twenty patients were divided into Steiner's skeletal Class I and III groups. MM and TA activity during each task was measured by using surface electromyography. Averaged MM and TA activity during both tasks, symmetry of each muscle activity, synergy between ipsilateral MMs and TAs, and muscle effort were compared.

STATISTICAL ANALYSIS

 Means and standard deviations of intergroup variables were compared by an independent sample t-test for parametric evaluations or by the Mann-Whitney U test for nonparametric evaluations. A probability value of p less than 0.05 was considered significant.

RESULTS

 Averaged MM activity and muscle synergy during MVC at the ICP in skeletal Class III patients were lower than that in skeletal Class I patients. Neither symmetry nor muscle effort during both tasks was different.

CONCLUSION

 Masticatory muscle performance of skeletal Class III patients was inferior to that of skeletal Class I patients.

Long-term evaluation of masseter muscle activity, dimensions, and elasticity after orthognathic surgery in skeletal class III patients

OBJECTIVE

To evaluate changes in the masseter muscle after orthognathic surgery using electromyography (EMG), ultrasonography (US), and ultrasound elastography (USE) in individuals with skeletal class III anomaly over long-term follow-up and compare with a control group.

MATERIALS AND METHODS

The study group included 29 patients with class III dentofacial deformities scheduled to undergo orthodontic treatment and orthognathic surgery. The control group included 20 individuals with dental class I occlusion. Assessment of the masseter muscles using EMG, US, and USE was performed before orthognathic surgery (T1) and at postoperative 3 months (T2) and 1 year (T3) in the study group, and at a single time point in the control group. All assessments were performed at rest and during maximum clenching. Masseter muscle activity, dimension, and hardness were analyzed.

RESULTS

Electromyographic activity of the masseter muscle during maximum clenching was increased at postoperative 1 year but did not reach control group values. On ultrasonography, the masseter muscle showed minimal changes in dimension at postoperative 1 year compared to preoperative values and remained below control group values. The postoperative increase in masseter muscle hardness at rest and during maximum clenching persisted at postoperative 1 year.

CONCLUSION

The results of this study suggest that after orthognathic surgery, additional interventions and much longer follow-up are needed to ensure better muscle adaptation to the new occlusion and skeletal morphology.

CLINICAL RELEVANCE

All assessment methods are useful for comprehensively evaluating changes in the masticatory muscles after orthognathic surgery.

Occlusal function and electromyographic activity of masticatory muscles in skeletal Class III patients with different patterns of mandibular asymmetry

BACKGROUND

Although jaw asymmetry is commonly seen in skeletal Class III patients, its correlation with occlusal function and masticatory muscle activity has not been fully elucidated.

OBJECTIVES

The purpose of this study was to investigate the occlusal function and masticatory muscle activity in skeletal Class III patients with various patterns of mandibular asymmetry.

METHODS

Forty-two patients and 10 normal participants were examined. The patients were categorised into three groups. Groups 1 and 2 exhibited menton and ramus deviation to the same side. Menton deviation was larger than ramus deviation in Group 1, whereas Group 2 showed the inverse relation. Group 3 patients showed menton and ramus deviation in opposite directions. Occlusal contact area (OCA), relative bite force (RBF), and temporalis anterior (TA) and masseter muscle (MM) activity at maximum clenching were measured using T-Scan Novus system and Bio-EMG-III. Statistical analysis was performed using the t-test, one-way analysis of variance with Bonferroni correction and Spearman correlation (α = .05).

RESULTS

Compared with normal participants, the patients had smaller OCA and greater asymmetry in the distribution of masticatory muscle activity. Greater ramus deviation was associated with smaller OCA in Group 1 but with larger OCA in Group 3. In Group 1, greater menton deviation was related to stronger TA activity on the non-deviation side. In Group 2, greater ramus deviation was related to stronger MM activity on the deviation side.

CONCLUSION

Deviation of the menton and ramus was individually related to OCA and masticatory muscle activity, and this relationship varied according to the pattern of mandibular asymmetry.

Ultrasonographic and electromyographic evaluation of three types of occlusal splints on masticatory muscle activity, thickness, and length in patients with bruxism

OBJECTIVE

To evaluate occlusal splint type differences in patients with bruxism.

METHODS

Seventeen controls and 51 patients were divided into three subgroups, each assigned to use a different occlusal splint (hard, soft, or semi-soft) for 3 months and assessed by ultrasonography and electromyography (EMG) before (BT) and 3 months after treatment (AT).

RESULTS

EMG values in all of the occlusal splint groups were significantly lower AT than BT (p < 0.05). BT and AT EMG values in the control group did not differ. Mean muscle thicknesses in bruxism patients was greater than in controls, and the greatest muscle thickness changes occurred with the hard occlusal splint (p < 0.05).

DISCUSSION

A decrease in EMG activity occurred with all three splint types and was most prominent in the hard occlusal splint group. Ultrasonographic measurements of muscle length and thickness should be used alongside EMG to measure muscle activity in bruxism patients.

Ultrasound Imaging in Dentistry: A Literature Overview

(1) Background: the frequency with which diagnostic tests are prescribed with exposure to ionizing radiation, a cause of biological damage, has been studied, and with much more attention, patients are subjected to these diagnostic tests for diagnosis and follow-up. This review aimed, given the recent developments of this technology, to evaluate the possible use of ultrasound in different branches of dentistry. The possibility of applying ionizing-radiation-free diagnostic exams in dentistry, overcoming the limits of this application, has led scientific research in this area to obtain interesting results that bode well for the future. (2) Methods: a search for articles on the application of ultrasounds in dentistry was performed using the PubMed electronic database. (3) Results: only 32 studies were included, and these clearly stated that this examination is widely usable and in great progress. (4) Conclusions: regarding the modern application techniques of this diagnostic test, it is essential to consider technological evolution as an objective to reduce the damage and side effects of necessary diagnostic tests. The use of ultrasound in dentistry can represent a valid radiation-free alternative, in certain contexts, to the other most used exams.