Muscular and condylar response to rapid maxillary expansion. Part 1: Electromyographic study of anterior temporal and superficial masseter muscles

Measurement of surface electromyography activity during swallowing in paediatrics: a scoping literature review

Surface electromyography (sEMG) could be used for diagnostic and therapeutic purposes in various health conditions. For example, sEMG biofeedback is shown to be beneficial in adults with swallowing disorders (dysphagia), whereas there are no easily identifiable studies to support such evidence in paediatrics. The current review aimed to evaluate the feasibility of implementing sEMG during swallowing tasks in paediatric populations with various diagnoses. Additionally, the review aimed to describe findings in publications involving participants with cerebral palsy (CP) and dysphagia. Paediatric-related publications were sourced using English keywords and phrases across the following seven databases: PubMed, EMBASE, CINAHL, Web of Science, PsycINFO, and ProQuest Dissertations and Theses Global. The search included all available publications without language and date restrictions. Publications using sEMG during chewing tasks were also accepted in the review as chewing is considered to be part of the act of swallowing. The feasibility of measuring sEMG during swallowing in children with various health conditions was supported by 116 publications (n = 6 literature reviews) that met the inclusion criteria for the final full-text review. However, a few publications described some difficulties occurring directly during the sEMG data collection sessions. The review identified 15 publications involving 177 participants with CP who underwent sEMG while swallowing (n = 1 publication focused solely on the assessment of chewing). Ten publications described studies that recruited children with dysphagia. Children with CP who had dysphagia were recruited in five of these studies.

CONCLUSIONS

The acquisition of sEMG measurements while performing swallowing tasks was shown to be feasible in children with various diagnoses including those who have CP and dysphagia. Future studies should investigate the implementation of sEMG as a part of paediatric dysphagia therapy alongside biofeedback swallowing skill training.

WHAT IS KNOWN

• Surface electromyography (sEMG) could be implemented for diagnostic and therapeutic purposes in various health conditions. • Biofeedback using sEMG is beneficial in adults with swallowing disorders (dysphagia).

WHAT IS NEW

• Implementation of sEMG was shown to be feasible during swallowing tasks in paediatric populations with various diagnoses, including dysphagia and cerebral palsy. • The usage of sEMG biofeedback as a part of paediatric dysphagia management should be investigated in future studies.

Electrical stimulation prevents condyle and subchondral degeneration following the masseter atrophy

OBJECTIVE

There is a strong relationship between masticatory muscle atrophy and condyle degeneration. Although electrical stimulation (ES) is an effective treatment for muscle atrophy, its influence on the underlying condyle is unclear. This study aimed to investigate whether ES can prevent condyle degradation during the stage of masseter muscle atrophy.

MATERIALS AND METHODS

Six-week-old rats were randomly divided into the control, botulinum toxin (BTX), or BTX + ES group. BTX was injected into the bilateral masseters of rats to induce masseter atrophy. The left-side masseters without ES treatment were served as BTX group, and the right-side masseters received ES with different parameters (5 mA/10 Hz, 5 mA/50 Hz, 6 mA/10 Hz, 6 mA/50 Hz, 7 mA/10 Hz, and 7 mA/50 Hz) were served as BTX + ES groups. After 4 weeks, micro-CT and qualitative or quantitative analysis of osteogenesis, chondrogenesis, and angiogenesis-related genes in condyles were conducted.

RESULTS

ES, especially at 7 mA/50 Hz, significantly attenuated masseter atrophy, condyle degeneration, and subchondral bone loss. Moreover, the upregulation of related proteins, including collagen 1, osteocalcin, bone morphogenetic protein 2, collagen 2a, and vascular endothelial growth factor were observed.

CONCLUSION

ES partly rescued condylar degeneration and subchondral bone loss following masseter atrophy.

Skull Biomechanics and Simplified Cephalometric Lines for the Estimation of Muscular Lines of Action

Our study introduces a novel cephalometric analysis aimed at facilitating biomechanical simulations by elucidating the intricate relationship between craniofacial morphology and the size and inclination of the masseter muscle (MM) while incorporating muscle values. Our study analyzes the line of action of the MM drawn between the Gonion (Go) and Orbital (Or) points concerning dental and skeletal references (occlusal and Frankfort planes). A total of 510 pre-treatment lateral cephalometric tracings (217 males, 293 females, aged 6-50 years) and lateral Bolton standard tracings were examined. The key parameters investigated include (a) skeletal-cutaneous class (linear distance between projections of points A' and B' on the occlusal plane), (b) the angle between the perpendicular line to the occlusal plane and the Go-Or line at the molar occlusal point, and (c) the angle between the Go-Or line and the Frankfort plane. The assessment of anterior-posterior jaw discrepancy, measured as the skeletal-cutaneous class, ranged from -14.5 to 15.5 mm. Abnormal values were identified in two adolescents, showing no gender- or age-related patterns. The angle between the MM's line of action (Go-Or) and the normal to the occlusal plane averaged 39.3°, while the angle between Go-Or and Po-Or (Frankfort plane) averaged 41.99°. Age had an impact on these angles, with an average 3° decrease in adults and a 4° increase between ages 6 and 50. A weak relationship was observed between sagittal jaw discrepancy and the angle between Go-Or and the Frankfort plane, with about 20% of the variance explained by the anteroposterior maxillary-mandibular relationship. In conclusion, the study presents a cephalometric analysis of the relationship between craniofacial morphology and masseter muscle parameters. It finds that age influences the angles between key reference points, while the skeletal-cutaneous class does not exhibit age- or gender-specific trends. These findings can contribute to a better understanding of craniofacial biomechanics and aid in clinical orthodontic assessments and treatment planning.

In silico approach towards neuro-occlusal rehabilitation for the early correction of asymmetrical development in a unilateral crossbite patient

Neuro-occlusal rehabilitation (N.O.R.) is a discipline of the stomatognathic medicine that defends early treatments of functional malocclusions, such as unilateral crossbite, for the correction of craniofacial development, avoiding surgical procedures later in life. Nevertheless, N.O.R.'s advances have not been proved analytically yet due to the difficulties of evaluate the mechanical response after the treatment. This study aims to evaluate computationally the effect of N.O.R.'s treatments during childhood. Therefore, bilateral chewing and maximum intercuspation occlusion were modelled through a detailed finite element model of a paediatric craniofacial complex, before and after different selective grinding-alternatives. This model was subjected to the muscular forces derived from a musculoskeletal model and was validated by the occlusal contacts recorded experimentally. This approach yielded errors below 2% and reproduced successfully the occlusal, muscular, functional and mechanical imbalance before the therapies. Treatment strategies balanced the occlusal plane and reduced the periodontal overpressure (>4.7 kPa) and the mandibular over deformation (>0.002 ε) on the crossed side. Based on the principles of the mechanostat theory of bone remodelling and the pressure-tension theory of tooth movement, these findings could also demonstrate how N.O.R.'s treatments correct the malocclusion and the asymmetrical development of the craniofacial complex. Besides, N.O.R.'s treatments slightly modified the stress state and functions of the temporomandibular joints, facilitating the chewing by the unaccustomed side. These findings provide important biomechanical insights into the use of N.O.R.'s treatments for the correction of unilateral crossbite, but also encourage the application of computing methods in biomedical research and clinical practise.

Effects of orthodontic treatment on masticatory muscles activity: a meta-analysis

Context: A comprehensive meta-analysis was carried out to investigate the impact of orthodontics on masticatory muscles.Methods: A thorough search of various databases, including CNKI, Wan Fang, VIP, CBM, MEDLINE, PubMed, Cochrane Library, EMBASE, Web of Science, and Google Scholar, was performed to identify relevant studies on patients undergoing orthodontics or functional corrections. Six case-control studies were finally included in this analysis, which specifically examined the effect of orthodontic treatment on masticatory muscle function.Results: The results revealed that the mean masticatory muscle voltage in patients treated with orthodontics was found to be higher after treatment compared to before treatment [odds ratio (OR)=1.57, 95% confidence interval (CI) (0.57, 2.57), p = 0.002], which could potentially have an impact on masticatory muscle function, particularly in individuals with Class II Division 1 malocclusion.Conclusion: These findings contribute to our understanding of the effects of orthodontic interventions on masticatory muscles, further highlighting the importance of orthodontics in optimising masticatory function.

Evaluation of Masticatory Muscles in Adult Patients with Maxillary Hypoplasia Treated with Surgically Assisted Rapid Maxillary Expansion (SARME): A Retrospective Study

Aim: The aim of the present study was to investigate modifications in electromyographic activity of temporal and masseter muscles before and after surgically assisted rapid maxillary expansion (SARME) in adult subjects. Materials and Methods: Data from 20 patients with unilateral posterior crossbite were selected retrospectively from the Orthodontics Department of the University of Genoa and the Department of Biomedical Surgical and Dental Sciences of the University of Milan, Fondazione IRCCS Ca’ Granda, Ospedale Maggiore Policlinico Milan. Inclusion criteria were set as skeletal class I; adult patients (age > 18); good general health; patients with a transverse maxillary deficiency with unilateral posterior crossbite and maxillary constriction ≥ 5 mm; Superficial electromyographic (EMG) examinations at T0 and T1. Exclusion criteria were smoking, metabolic bone diseases (e.g., hyperparathyroidism, vitamin C deficiency), chronic use of corticoids before or during treatment, parafunctional habits (e.g., bruxism), and temporomandibular joint dysfunction. The Shapiro−Wilk test was performed to check whether the data were normally distributed. Differences for each variable before and after SARME were analyzed with a paired t-test (p < 0.05). Results: The statistical analysis demonstrated no statistically significant differences between the EMG values taken before and after SARME regarding the standardized electrical activity of the masticatory muscles (masseter and anterior temporalis (p > 0.05)). Conclusions: Considering the specific conditions of this study, it can be concluded that SARME did not alter the EMG activity of the masseter and temporal muscles. The present study has shown that the masticatory musculature evaluated after approximately 8 months of therapy can adapt well to SARME.

Effects on Muscular Activity after Surgically Assisted Rapid Palatal Expansion: A Prospective Observational Study

The study aims to investigate the modifications in the temporalis and the masseter activity in adult patients before and after SARPE (Surgically Assisted Rapid Palatal Expansion) by measuring electromyographic and electrokinesographic activity. 24 adult patients with unilateral posterior crossbite on the right side were selected from the Orthodontic Department of the University of Milan. Three electromyographic and electrokinesographic surface readings were taken respectively before surgery (T0) and 8 months after surgery (T1). The electromyographic data of both right and left masseter and anterior temporalis muscles were recorded during multiple tests: standardized maximum voluntary contraction (MVC)s, after transcutaneous electrical nerve stimulation (TENS) and at rest. T0 and T1 values were compared with paired Student’s t-test (p < 0.05). Results: Significant differences were found in the activity of right masseter (p = 0.03) and right temporalis (p = 0.02) during clench, in the evaluation of right masseter at rest (p = 0.03), also the muscular activity of masseters at rest after TENS from T0 to T1 (pr = 0.04, pl = 0.04). No significant differences were found in the activity of left masseter (p = 0.41) and left temporalis (p = 0.39) during clench and MVC, in the evaluation of left masseter at rest (p = 0.57) and in the activity during MVC of right masseter (p = 0.41), left masseter (p = 0.34), right temporalis (p = 0.51) and left temporalis (p = 0.77). Results showed that the activity of the masseter and temporalis muscles increased significantly after SARPE during rest and clenching on the side where the cross-bite was treated.

Evaluation of Electromyographic Activity of Masticatory Muscles in Adults with Posterior Crossbite

Introduction

There is evidence that patients with posterior crossbite (PXB) have neuromuscular changes in the masticatory muscles. However, up to the present time, the relationship among these changes on the electromyographic activity of the masticatory muscles is still unclear.

Objective

To systematic review the available literature on the electromyographic activity of masticatory muscles in adults with PXB.

Methods

Between August 22 and September 9, 2020, we searched the following seven electronic databases: PubMed, EMBASE, Web of Science, Cochrane Library, SciELO, LILACS, and Scopus. No restrictions were applied regarding the language and year of publication. This systematic review was registered in the Prospective Register of Systematic Reviews (PROSPERO - CRD42020205057) database and conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. After data selection and extraction, the methodological quality of the selected studies was conducted independently by two reviewers, using two different evaluation tools.

Results

6957 records were initially located after the search process. In the end, eight papers were selected. Most studies were classified as having average to low methodological quality and moderate to high risk of bias. Based on the available evidence, adult patients with PXB have electromyographic activity changes in the masticatory muscles when compared with individuals without PXB. Moreover, adult patients with unilateral posterior crossbite (UPXB) have asymmetrical electromyographic activity when the crossbite side is compared with the noncrossbite side.

Conclusion

Despite the lack of studies with high methodological quality, electromyographic evaluation of masticatory muscles should be considered in the diagnosis and in the orthodontic treatment plan of patients with PXB. Prospective studies with a higher sample size and follow-up time, conducted using a rigorous scientific methodology, are necessary to reach a more reliable conclusion.

Effect of Photobiomodulation on Relapse in an Experimental Rapid Maxillary Expansion Model in Rat

Rapid maxillary expansion (RME) is performed on transversely deficient maxilla. As all orthodontic treatments, retention is important in maintaining therapeutic outcomes. Fixed /removable retainers are used post-RME causing hygiene and compliance problems. Given photobiomodulation's positive effects on the quantity and quality of bone regeneration, its effect on post-RME relapse was studied. Thirty Sprague Dawley rats were randomly divided into group R, non-irradiated RME-treated (n = 12), group P, irradiated RME-treated (n = 12) and group C, non-RME non-irradiated (n = 6). A 1.5 mm metal ring inserted between maxillary incisors at days 0 and 15 was expanded until 1.5 mm space was obtained at day 30. In group P, Ga-Al-As diode laser (810 nm, 100 mW, 4J/cm² , 30 secs) was applied on days 0, 2, 4, 6, 8, 10, 12 and 14 as predictor variable. The relapse was measured as the space lost between incisors for 30 days after appliance removal (primary outcome variable) and compared with t-test. In week 2, space loss in group P was significantly lower (P < 0.05) than all other groups. The relapse during weeks 2 and 3 was significantly lower in group P than group R. However, no significant difference in relapse amount was found between groups during first and fourth week. There was a significant difference (P < 0.05) between groups in relapse rates (secondary outcome variable) but not in total relapse after 4 weeks. Photobiomodulation proved beneficial in resisting relapse in our study, and it is suggested to be continued until the end of expansion.

Longitudinal electromyographic changes in masseter and anterior temporalis muscle before and after temporomandibular joint arthroplasty in ankylosis patients

PURPOSE

The literature lacks evidence about activity of masseter and anterior temporalis muscles in temporomandibular joint ankylosis (TMJA) patients. The purpose of this study was to evaluate longitudinal electromyography (EMG) changes in masseter and anterior temporalis muscle before and after gap arthroplasty in unilateral TMJA patients. Specific aim was to investigate the EMG activity restoration to the level of non-ankylosed side after arthroplasty.

METHODS

The investigator implemented a prospective longitudinal study amongst TMJA patients treated with gap arthroplasty. EMG of masseter and anterior temporalis were recorded bilaterally on ankylosed and non-ankylosed side. EMG signals of masseter and anterior temporalis were recorded preoperatively and 1 week, 3 month and 6 month postoperatively at rest and at maximum voluntary clench (MVC).

RESULTS

The study sample was composed of 16 (male:female = 1:1.28) unilateral TMJA patients. The mean duration of ankylosis was 3.25 ± 1.18 years. The difference in EMG root-mean-square (RMS) values of ankylosed side when compared to the preoperative values of non-ankylosed side was found to be statistically significant (p < 0.001) preoperatively, 1 week and 3 month postoperatively, while it was statistically not significant (p > 0.99) at 6-month postoperatively.

CONCLUSION

The present study concludes that the TMJA patients have hyperactivity of masseter and anterior temporalis muscle. Restoring the function causes the muscle activity to progress to the values of normal side. EMG activity as measured on follow-up may be one of the predicting factor for re-ankylosis.

Effects of Rapid Palatal Expansion on Chewing Biomechanics in Children with Malocclusion: A Surface Electromyography Study

Malocclusion during childhood may affect both morphology and masticatory function and could greatly affect the subsequent growth and development of the jaws and face. The purpose of this study was to evaluate the efficiency of surface electromyography in describing the effects of the rapid palatal expansion (RPE) on Masseter (M) and Temporalis Anterior (T) muscles' activity in 53 children with different types of malocclusion: bilateral posterior crossbite (BPcb), underdeveloped maxillary complex without crossbite (NOcb) and unilateral posterior crossbite on the right (UPCBr) and on the left (UPCBl). The muscular activities during chewing tasks were assessed bilaterally before and after RPE application and three months after removal. Both the envelope's peak (µV) and its occurrence (% of chewing task) were extracted from the surface electromyography signal. Our results showed the presence of statistically significant differences (p < 0.05) on temporomandibular joint muscles, across different assessments, in all the tested populations of subjects. Surface electromyography demonstrated a relationship between the correction of a maxillary transverse discrepancy and the restoration of a muscle's activation patterns comparable to healthy subjects for both T and M.

Transverse Skeletal Effects of Rapid Maxillary Expansion in Pre and Post Pubertal Subjects: A Systematic Review

OBJECTIVE

The aim of this systematic review was to assess the transverse skeletal effects of rapid maxillary expansion (RME) in pre and post-pubertal subjects.

MATERIAL AND METHODS

Five databases were searched till May 2018; Pubmed, Cochrane, Scopus, Lilacs and Web of science in addition to the manual search of other sources. There were no language restrictions. Methodological Index for Non-Randomized Studies MINORS was used to assess the quality and risk of bias of the trials included.

RESULTS

Six studies were finally included in the qualitative analysis. A meta-analysis wasn't performed due to the heterogeneity of methodologies and outcomes. All of the included studies showed drawbacks in their structure yielding weak evidence. On the short term, RME caused an increase in the maxillary and lateral-nasal widths in pre-pubertal subjects by 3.4 mm and 3.3 mm, and by 2.8 and 2.2 mm respectively in post-pubertal subjects. Although statistically insignificant, the maxillary width increase was more than that of the post-pubertal subjects by 0.6 mm. Over the long term, expansion produced permanent increases in the transverse dimensions of both the dento-alveolar and skeletal components of the maxilla and circum-maxillary structures in pre-pubertal subjects. The post-pubertal subjects presented with a statistically significant increase only in the later-nasal width by 1.3 mm than the untreated controls with no permanent increase in the skeletal maxillary width.

CONCLUSION

The literature is very deficient regarding the use of skeletal age as a reference in the treatment of skeletal crossbites using RME. Only weak evidence exists supporting the increased maxillary and lateral-nasal widths after tooth-tissue borne RME in pre-pubertal subjects, with these effects being less in the post-pubertal ones.

Evaluation of masticatory muscle activity in patients with unilateral posterior crossbite before and after rapid maxillary expansion

Objectives

The relationship between unilateral posterior crossbite (UPCB) and the possible asymmetric activation of the jaw muscles in children is still under debate. This study aimed at evaluating the jaw muscle activity of children with UPCB before and after rapid maxillary expansion (RME) by means of surface electromyography and a standardized sampling protocol.

Subjects and methods

Twenty-nine children with UPCB (UPCB-group, mean age 9.6 ± 1.6 years) and 40 UPCB-free controls (Control-group, 10.5 ± 1.1) were recruited. The activity of the left and right anterior temporalis (AT) and superficial masseter muscles (MM) was recorded during maximum voluntary clenching and a chewing task (T0). In the UPCB-group, data were collected, also, after the correction of the UPCB with RME (T1) and 6 months later (T2), without any further treatment. Electromyographic indices comparing the activity of paired muscle were computed via software to estimate the extent of asymmetric AT and MM activity. Paired and unpaired t-test or Wilcoxon-signed rank and Mann-Whitney U test, ANOVA or Friedman test and chi-squared test were used in the statistical analysis.

Results

Both groups presented with asymmetric activity of the muscles, which did not differ between groups (T0, all P > 0.05). The treatment determined a decrease in muscular activity (T1, P = 0.040), and a more asymmetric pattern of muscle activation during chewing (T1, P = 0.040), which returned similar to baseline values at T2 (all P > 0.05).

Conclusions

UPCB does not contribute to an asymmetric activation of AT and MM during functional tasks. The treatment of UPCB by RME did not determine a more symmetric activity of the assessed muscles.

Rapid maxillary expansion in the treatment of the functional posterior crossbite: joint noise and electromyographic activity analysis

Abstract Introduction The rapid maxillary expansion (RME) reduces the risk of developing structural and functional disorders in the stomatognathic system. Objective To examine the effects of the RME as a treatment for the posterior crossbite, related with the electromyographic activity of the masticatory muscles and the TMJ noises in a population of children. Material and method 13 girls and 7 boys, regardless of the type of malocclusion, with a mean age of 9 years old (± 3), were treated with RME. The electrovibratography analyzed the TMJ noise, and the electromyography analyzed the masticatory muscles before treatment (T0) and after three months of a short-term follow-up (T1). The comparisons of the affected and unaffected sides by the crossbite were performed using Mann-Whitney’s test, and to compare data before and after treatment the Wilcoxon’s test was used (level of significance: 5%). Result No significant differences were found in the parameters of joint noise in comparison to the sides affected and unaffected by the crossbite, in both T0 and T1 (p>0.05); only the side without the crossbite observed decrease in the peak amplitude of the joint noises after treatment. In the static electromyographic analysis, inter-side differences were observed before and after treatment, since the deliberate unilateral chewing showed greater asymmetry activity in T0 for both sides, which has been corrected after treatment, improving the functional chewing. Conclusion The proposed treatment did not lead to the occurrence of joint noises and improved the functional pattern of electromyographic activity during chewing at the end of treatment.

Expansion of permanent first molars with rapid maxillary expansion appliance anchored on primary second molars

Background

To evaluate how the amount of expansion of the primary second molars, the patient’s age, and the skeletal maturation stage influence the amount of expansion at the level of the permanent first molars.

Material and Methods

Fifty-five patients aged between 6 and 11 years with a cervical vertebral maturation stage of CS1 or CS2 were retrospectively selected. The intermolar width was measured before and after expansion to evaluate the amount of expansion achieved at the level of the primary second molars and the permanent first molars. Stepwise multiple linear regression was used to evaluate how the amount of primary molars expansion, the patient’s age, and the cervical vertebral maturation stage predict the amount of permanent molar expansion.

Results

A significant regression equation was found, and for every 1 mm of primary molar expansion, 0.91 mm of permanent molar expansion can be expected. An age between 6 and 11 years and the CS1 or CS2 skeletal maturation stage were not significant predictors of permanent molar expansion.

Conclusions

A rapid maxillary expansion appliance anchored on primary second molars is effective in expanding the permanent molars to correct a transverse maxillary deficiency in prepubertal patients, transferring the risks associated with the large forces used to the primary teeth.

Key words:Maxillary expansion, transversal deficiency, primary molars.

Evaluation of the effects of modified bonded rapid maxillary expansion on occlusal force distribution: A pilot study

Objective:

To evaluate the effects of modified bonded rapid maxillary expansion (RME) on occlusal force distribution.

Materials and Methods:

The sample included 12 patients (7 girls and 5 boys; mean age: 13.1 years) at the permanent dentition stage with bilateral posterior cross-bite. The patients were treated with a modified bonded RME appliance, activated twice a day. The study was terminated when the palatal cusps of the maxillary posterior teeth were occluding with the buccal cusps of the mandibular posterior teeth. The postretention period was 3 months. The T-Scan III device was used to analyze the percentages of occlusal force distribution, and records were taken at the pretreatment (T1), the postreatment (T2), and the postretention (T3) periods. Wilcoxon signed rank test was used for statistical analyses.

Results:

Incisors were most frequently without contact, followed by canines. The highest forces were seen in the second and first molar regions. A significant decrease was seen in total occlusal force during treatment (T1–T2); however, during retention, the force returned to its initial value, and no significant differences were found (T1–T3). No differences were found between right and left sides and in occlusal forces of the teeth in all time periods.

Conclusion:

The use of modified bonded RME decreases the total occlusal forces during the treatment period, but it does returns to its initial value after the postretention period.

The role of rapid maxillary expansion in the promotion of oral and general health

Rapid maxillary expansion (RME) is an effective orthopedic procedure that can be used to address problems concerned with the growth of the midface. This procedure also may produce positive side effects on the general health of the patient. The aim of the present consensus paper was to identify and evaluate studies on the changes in airway dimensions and muscular function produced by RME in growing patients. A total of 331 references were retrieved from a database search (PubMed). The widening of the nasal cavity base after midpalatal suture opening in growing patients allows the reduction in nasal airway resistance with an improvement of the respiratory pattern. The effects of RME on the upper airway, however, have been described as limited and local, and these effects become diminished farther down the airway, possibly as a result of soft-tissue adaptation. Moreover, limited information is available about the long-term stability of the airway changes produced by RME. Several studies have shown that maxillary constriction may play a role in the etiology of more severe breathing disorders such as obstructive sleep apnea (OSA) in growing subjects. Early orthodontic treatment with RME is able to reduce the symptoms of OSA and improve polysomnographic variables. Finally, early orthopedic treatment with RME also is beneficial to avoid the development of facial skeletal asymmetry resulting from functional crossbites that otherwise may lead to functional and structural disorders of the stomatognathic system later in life.

Longitudinal evaluation of sEMG of masticatory muscles and kinematics of mandible changes in children treated for unilateral cross-bite

The aim of this study was to evaluate masticatory muscle activity and kinematics of mandible changes in children with unilateral posterior cross-bite (UPXB) after orthodontic treatment, and one year after retention. Twenty-five children with UPXB and functional mandibular shift were evaluated before treatment (mean age 12.5years), after treatment (mean age 14.9years), and one year after retention (mean age 16.8years). The same data were collected in a control group of thirty age-matched normocclusive children. Simultaneous bilateral surface electromyographic (sEMG) activity from anterior temporalis (AT), posterior temporalis (PT), masseter (MA), and supra-hyoid (SH) muscle areas were evaluated at rest, during swallowing, mastication and clenching. Kinematic records of rest position, mandibular lateral shift, swallowing and mastication were analyzed. Results showed a lateral shift of the mandible present at rest. During swallowing, sEMG activity of SH predominated before and post-treatment and retention. High frequency of immature swallowing was maintained post-treatment and retention. During mastication, MA activity increased significantly and its asymmetry was corrected post-treatment. During clenching, cross-bite side AT and MA activity increased significantly posttreatment and remained stable after retention, and MA/AT ratio reversed. These findings reinforce the advantages of treating children with UPXB and functional shift as early as possible.

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

INTRODUCTION

The masticatory muscles are considered to be important determinants of facial form, but little is known of the muscle spindle reflex characteristics and their relationship, if any, to face height. The aim of this study was to determine whether spindle reflexes, evoked by mechanical stimulation of an incisor and recorded on the masseter muscle, correlated with different facial patterns.

METHODS

Twenty-eight adult volunteers (16 women; ages, 19-38 years) underwent 2-N tap stimuli to their maxillary left central incisor during simulated mastication. Reflexes were recorded during local anesthesia of the stimulated tooth to eliminate the contribution from periodontal mechanoreceptors. Surface electromyograms of the reflex responses of the jaw muscles to these taps were recorded via bipolar electrodes on the masseter muscle and interpreted by using spike-triggered averaging of the surface electromyograms. Lateral cephalometric analysis was carried out with software (version 10.5, Dolphin, Los Angeles, Calif; and Mona Lisa, Canberra, Australia).

RESULTS

Two-newton tooth taps produced principally excitatory reflex responses beginning at 17 ms poststimulus. Correlation analysis showed a significant relationship between these muscle spindle reflexes and facial heights: specifically, shorter face heights were associated with stronger spindle reflexes. This correlation was strongest between the derived measure of masseter length and the spindle reflex strength during jaw closure (r = -0.49, P = 0.008).

CONCLUSIONS

These results suggest that a similar muscle spindle stimulus will generate a stronger reflex activation in the jaw muscles of patients with shorter faces compared with those with longer faces. This finding might help to explain the higher incidence of clenching or bruxism in those with short faces and also might, in the future, influence the design of orthodontic appliances and dental prostheses.