Effect of unilateral posterior crossbite on the electromyographic activity of human masticatory muscles

The impact of malocclusion on the prevalence of pain-related temporomandibular disorders in children and adolescents: a systematic review

Background

The connection between occlusion and temporomandibular disorders (TMD) remains a topic of discussion, and current research does not provide a definitive answer. Pain-related TMD are the most common types of TMD. They include myalgia, arthralgia, and headaches attributed to TMD. This systematic review aims to synthesize the current scientific evidence regarding impact of malocclusion on the prevalence of pain-related TMD in individuals under 18 years.

Methods

The study was based on a searching of the PubMed, Scopus, Embase, and Web of Science databases. Selection was limited to studies that explored the link between malocclusion and pain-related TMD in young individuals. The Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of the selected research. The certainty of evidence was assessed using the Grading Recommendations Assessment, Development and Evaluation (GRADE) approach. A visual representation of the screening and inclusion processes was created using a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagram. The information from the research was then summarized in a descriptive format.

Results

Out of 868 potentially relevant articles initially identified, 13 studies were selected based on the inclusion criteria. The majority of these studies were determined to be of moderate quality, according to the NOS assessment. The certainty of evidence was assessed as low, according to the GRADE approach. Most of the studies showed that malocclusion may be associated with TMD-pain signs/symptoms in children and adolescents. The most frequent relationship was found between the prevalence of pain-related TMD and posterior crossbite, Class II malocclusion, Class III malocclusion, and anterior open bite.

Conclusion

Certain types of malocclusion may have an impact on the prevalence of some TMD-pain signs and symptoms in young individuals. However, given the limited reliability of existing research and the inconsistencies observed across studies, additional well-structured, long-term investigations are necessary.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024570950.

Masseter muscle thickness before and after the correction of unilateral functional posterior crossbite in growing individuals: a prospective controlled clinical trial

OBJECTIVES

To evaluate whether unilateral functional posterior crossbite in growing children creates an asymmetry in masseter muscle thickness and whether this asymmetry is normalized after crossbite correction.

MATERIALS AND METHODS

Two groups of growing individuals were studied prospectively: (i) a treatment group: children with unilateral functional posterior crossbite, undergoing crossbite correction with maxillary expansion; and (ii) a control group: children without transversal malocclusions and orthodontic treatment. The thickness of the masseter muscles was measured bilaterally using ultrasonographic recordings at three time points: pre-treatment (T0); 9 months after (T1); and 30 months after posterior crossbite correction (T2); and at equivalent time points in the control group. Differences within and between the groups were evaluated using paired and unpaired t-tests respectively.

RESULTS

It was found that the thickness of the masseter muscles in patients with unilateral functional posterior crossbite was significantly thinner on the crossbite side (P = .013) by 0.5 mm. At T1, the masseter muscle of the treated crossbite side was thicker than that of the previous normal side (0.3 mm difference; P = .046) while this difference disappeared at T2 (P > .05).

LIMITATIONS

The lack of the inclusion of an untreated posterior crossbite group, and the heterogeneity in appliances used are the principal limitations of this study.

CONCLUSIONS

The masseter muscles in untreated individuals with unilateral functional posterior crossbite are thinner in the crossbite side than in the contralateral non-crossbite side. This muscular asymmetry however is eliminated some time after successful treatment of this malocclusion, possibly due to the bilateral symmetrization of the activity of the elevator masticatory muscles.

Comparative analysis of myoelectric activity and mandibular movement in healthy and nonpainful articular temporomandibular disorder subjects

OBJECTIVES

Temporomandibular disorders (TMDs) are one of the leading causes of craniofacial pain, and a high incidence of TMDs in young adults has been reported. Previous studies have used surface electromyography (sEMG) and mandibular kinematic analysis for TMDs diagnosis. This study aimed to provide normal reference values of sEMG and mandibular kinematics in Han Chinese adults, compare the sex differences and assess their diagnosis value on pain-free articular TMDs.

MATERIALS AND METHODS

This observational study recruited healthy young adults with individual normal occlusion and nonpainful articular TMDs patients with disc displacement. The sEMG signals of the anterior temporalis (TA), masseter (MM), and sternocleidomastoid and digastric were recorded in the mandibular postural positions (MPP) and during maximal voluntary clenching (MVC) with K7 electromyograph. Mandibular kinematics, including maximum opening and opening/closing velocities, were assessed by K7 kinesiograph.

RESULTS

The sEMG reference values ranged from 3.0 to 4.3 µV in the MPP (n = 90) in healthy subjects. The sEMG values during MVC, maximum opening, and opening velocity were significantly higher in males than in females. Also, these indices showed good diagnostic efficiency for pain-free articular TMDs (n = 26).

CONCLUSIONS

Reference values and sex differences in sEMG and mandibular kinematics in healthy subjects were determined. Compared with them, articular TMDs patients showed significantly lower myoelectric activity during maximal biting and restricted mouth opening range and velocity, which may assist in TMDs diagnosis.

CLINICAL RELEVANCE

By analyzing sEMG of masticatory muscle and mandibular kinematics data from healthy Han Chinese young adults and TMDs patients with disc displacement, this study evaluated the sex difference and their diagnosis value on nonpainful TMDs with disc displacement.

CLINICAL TRIAL REGISTRATION ID

NCT06372769.

Positional, morphologic, and volumetric differences in TMJ in unilateral posterior crossbites and controls: A retrospective CBCT study

OBJECTIVES

The objective of this study was to evaluate if there are any morphologic, positional, and volumetric differences in the temporomandibular joint (TMJ) of patients with unilateral posterior crossbite (UPC) compared to controls. Another objective was to analyse the discrepancy in the TMJ between the crossbite versus non-crossbite side in UPC versus right and left sides in controls. Additionally, this study aimed to evaluate the differences in the bone density at the masseteric insertion site at the angle of mandible in the UPC group and control group.

MATERIAL AND METHODS

One hundred and thirty-two CBCTs were analysed with 66 patients in UPC group and 66 patients in control group (non-crossbite). Temporomandibular joint spaces - Anterior joint space (AJS), Superior joint space (SJS), Posterior joint space (PJS), Medial joint space (MJS), Middle joint space (MiJS), and Lateral joint space (LJS) were measured. Additionally, bone density at angle of mandible and volume of mandibular condyle were evaluated. The measurements were compared between the groups as well as between the crossbite and non-crossbite sides within the UPC group and between right and left sides within the control group. Furthermore, the associations between UPC and changes in TMJ regarding joint space availability, bone density, condylar head volume, and the effects of sex and age were evaluated using regression analysis.

RESULTS

It was observed that UPC group showed a greater condylar volume, than the control group. Additionally, a larger mean discrepancy was observed between the crossbite side and non-crossbite side within the UPC group concerning condylar volume than controls. Concerning age, condylar volume was observed to be larger in adults than children. Adults showed significantly greater bone density and condylar volume than adolescents. Concerning sex, it was observed that males showed a larger SJS (right), MiJS, LJS, and bone density at the mandibular angle than females.

CONCLUSION

There is a difference in the TMJ parameters particularly condylar volume in patients with UPC compared to controls.

Electromyographic Assessment of Muscle Activity in Children Undergoing Orthodontic Treatment-A Systematic Review

Background: Surface electromyography (sEMG) can provide an objective and quantitative image of the functional state of neuromuscular balance in the stomatognathic system. The objective of this systematic review is to examine current scientific evidence regarding the effects of orthodontic treatment on muscle electromyographic (EMG) activity in children. Methods: The search strategy included the PubMed, PubMed Central, Web of Science, Scopus, and Embase databases. The inclusion criteria were studies assessing EMG muscle activity in children undergoing orthodontic treatment compared with untreated children. The Cochrane risk-of-bias tool (RoB2) and the Newcastle-Ottawa Scale (NOS) were used to evaluate the quality of the studies. The quality of evidence assessment was performed using GRADE analysis. The PRISMA diagram visually represented the search strategy, as well as screening and inclusion process. Results: The search strategy identified 540 potential articles. Fourteen papers met the inclusion criteria. Six studies were judged at a low risk of bias. The certainty of evidence was rated as moderate to low, according to the GRADE criteria. Studies showed alterations in EMG muscle activity in children undergoing orthodontic treatment. Conclusions: Orthodontic treatment appears to affect muscle activity in children undergoing orthodontic treatment. However, the quality of evidence is low and, therefore, it is not possible to definitively state this effect. Further long-term studies are needed to confirm the findings of this review. Study protocol number in PROSPERO database: CRD42023491005.

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.

"Association between posterior unilateral functional crossbite and asymmetrical spinal flexion: A prospective study"

Background

Unilateral posterior crossbite (UPC) with functional shift is a malocclusion that may have the potential to affect the masticatory function and the flexibility of the spine due to intrinsic occlusal, structural and functional asymmetries sustained by marked asymmetrical muscular activation.

Research question

To investigate whether the presence of UPC with functional shift is associated with reverse chewing pattern and altered spine flexion.

Methods

Patients with UPC and a control group of patients with normal occlusion were recorded when chewing soft and hard boluses using a Kinesiograph (Myotronics-Noromed Inc., USA) and spine alignment was assessed with an electronic inclinometer Spinal Mouse® system (Idiag AG, Switzerland).

Results

There were 87 children with UPC in the patients' group among whom 38, with median (IQR) age 8.0 (7.3-9.3) years, had measurements before and after treatment. The UPC patients showed a higher percentage of anomalous/reverse chewing patterns on the crossbite side compared with a control group (p < 0.001). Moreover, a clear difference was observed between left and right flexion angles of the spine in the patients' group (p < 0.001 and p = 0.001, paired t-test) with the crossbite side being more flexible compared to the non-crossbite side. No such differences were seen in the control group, nor post-treatment for right and left crossbite (p = 0.44 and p = 0.15 respectively, paired t-test).

Significance

This study suggests an association between UPC, asymmetrical chewing patterns and asymmetrical flexion of the spine. These results may help improve understanding of any association between dental malocclusions and spine posture and hence aid diagnosis and treatment strategies.

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 malocclusion on jaw motor function and chewing in children: a systematic review

Objective

To investigate the effects of dental/skeletal malocclusion and orthodontic treatment on four main objective parameters of chewing and jaw function (maximum occlusal bite force [MOBF], masticatory muscle electromyography [EMG], jaw kinematics, and chewing efficiency/performance) in healthy children.

Materials and methods

Systematic searches were conducted in MEDLINE (OVID), Embase, and the Web of Science Core Collection. Studies that examined the four parameters in healthy children with malocclusions were included. The quality of studies and overall evidence were assessed using the Joanna Briggs Institute and GRADE tools, respectively.

Results

The searches identified 8192 studies; 57 were finally included. The quality of included studies was high in nine studies, moderate in twenty-three studies, and low in twenty-five studies. During the primary dentition, children with malocclusions showed similar MOBF and lower chewing efficiency compared to control subjects. During mixed/permanent dentition, children with malocclusion showed lower MOBF and EMG activity and chewing efficiency compared to control subjects. The jaw kinematics of children with unilateral posterior crossbite showed a larger jaw opening angle and a higher frequency of reverse chewing cycles compared to crossbite-free children. There was a low to moderate level of evidence on the effects of orthodontic treatment in restoring normal jaw function.

Conclusions

Based on the limitations of the studies included, it is not entirely possible to either support or deny the influence of dental/skeletal malocclusion traits on MOBF, EMG, jaw kinematics, and masticatory performance in healthy children. Furthermore, well-designed longitudinal studies may be needed to determine whether orthodontic treatments can improve chewing function in general.

Clinical relevance

Comprehensive orthodontic treatment, which includes evaluation and restoration of function, may or may not mitigate the effects of malocclusion and restore normal chewing function.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04356-y.

Evaluation of mandibular changes after rapid maxillary expansion: a CBCT study in youngsters with unilateral posterior crossbite using a surface-to-surface matching technique

OBJECTIVES

The purpose of this study was to evaluate mandibular asymmetry in youngsters with posterior unilateral crossbite (PUXB), through cone-beam computed tomography and reverse engineering technique, before and after rapid maxillary expansion (RME) treatment.

MATERIALS AND METHODS

Forty cone-beam computed tomography (CBCT) images were obtained from all patients at two time points, namely T0 acquired before the placement of a Hyrax expander and T1 after appliance removal. The CBCT scans were segmented and volume rendered into a surface there-dimensional (3D) mesh model. Thereafter, mandibular models were digitally registered by using a "best-fit" algorithm. Surface and volumetric changes, between T0 and T1, were compared by using Student's t tests.

RESULTS

A slight increase of 0.45 cm3 of the total mandibular volume was found at T1 when compared with T0 (p < 0.001). The mandibular hemi-volume on the crossbite side (CB) was slightly smaller than the non-crossbite side both at T0 and T1. However, the mean differences of hemi-volume from the CB (crossbite) and non-CB side between T0 and T1 show a decrease of 0.26 cm3 (p < 0.001). Findings for the surface-to-surface deviation analysis demonstrated a fine percentage of matching at T0 which slightly improved at T1 (p < 0.001).

CONCLUSIONS

Youngsters affected by PUXB showed a very slight and not statistically significant volumetric and morphological asymmetry between CB side and non-CB side at T0. However, the change in mean differences of 0.26 cm cannot be considered clinically relevant.

CLINICAL RELEVANCE

Mandibles in young PUXB patients exhibit only a very mild mandibular asymmetry. Although the statistically significant mean change found right after RME removal cannot be considered clinically relevant, a more consistent sample and a longer follow-up could be of interest in explaining the short-term findings.

The Prevalence of Temporomandibular Disorders and Dental Attrition Levels in Patients with Posterior Crossbite and/or Deep Bite: A Preliminary Prospective Study

Background

The prevalence of various temporomandibular disorders (TMD) and the severity of attrition in patients with either bilateral or unilateral deep bite and/or posterior crossbite has not been established, nor has the effect of one year of orthodontic treatment on TMD.

Methods

Of 310 patients presenting with suspected TMD, 160 were diagnosed with various TMD and 150 were TMD-free. Diagnosis was according to the Axis I of the Diagnostic Criteria for TMD. All participants underwent a dental examination, and 100 patients were reevaluated after one year of orthodontic treatment. Fisher's exact test and the proportion test with Bonferroni's correction were used for the categorical univariate analysis.

Results

There was a significant association (P < 0.001) between deep bite and dental attrition (wear), but not between crossbite and/or deep bite in patients diagnosed with either painful TMD or disc displacement. The risk of sustaining painful TMD when crossbite presented simultaneously on the anterior and the posterior dentition was 2.625-fold greater than when it presented with a normal bite, although this difference was not significant (P=0.286) due to the lack of statistical power. There was no significant sex-related association between the occurrence of either painful TMD or disc displacement. A reduction in TMD findings was demonstrated after one year of treatment, but no statistical power was reached due to the small sample size.

Conclusions

Deep bite may be related to dental wear but not to pain from TMD and/or disc displacement. Only crossbite that presents simultaneously on the anterior and the posterior dentition (mixed X-bite) may have some effect on the level of pain in TMD, but not on in the prevalence of disc displacement. Confirmation of these conclusions by well-designed studies on larger patient groups is warranted. There was a clinically significant improvement in TMD findings after one year of treatment.

Transverse Asymmetries of the Maxilla Even in Healthy and Apparently Symmetrical Subjects

In the formulation of an orthodontic treatment plan, the three-dimensional analysis of the dental arches represents a fundamental moment for the evaluation of all the morphological parameters necessary in order to have a correct and complete diagnosis. In this regard, the study of the dental arches on the horizontal plane is sometimes neglected or not thorough enough. When evaluating the transverse dimensions of the dental upper arche, the presence of an asymmetry is frequently found, and it means that an hemiarch is larger than the other. Furthermore, any variation in one of the three planes of space always involves an alteration also on the other two planes in order to have compensation. The morphology of a bone segment depends on various factors, mainly genetical, acquired and environmental. Regarding the environmental factors, the function determines the morphology, but this in turn determines the function. In the case of unilateral mastication, the upper maxilla will be asymmetrical, so growing patients will have compensation on other skull bones. From these considerations arises the need for a careful study of the horizontal plane of the maxilla in the presence of a malocclusion during diagnostic evaluations. These asymmetries, however, must be evaluated and quantified in the diagnostic phase in order to formulate a correct plan of treatment. The aim of this work is to demonstrate that there are almost always transverse asymmetries of the maxilla, albeit of a slight entity, even in healthy and apparently symmetrical subjects.

Evaluation of mandibular symmetry and morphology in adult patients with unilateral posterior crossbite: a CBCT study using a surface-to-surface matching technique

OBJECTIVES

To investigate mandibular morphology in adults affected by posterior unilateral crossbite (PUXB) and to evaluate the hemi mandibular volumes from the crossbite (CB) and non-CB sides of the same patients.

METHODS

Thirty-eight cone beam computed tomography (CBCT) images were consecutively recruited and the Digital Imaging and Communications in Medicine (DICOM)-formatted scans were volume rendered into a surface three-dimensional (3D) mesh model and volumes to obtain the 3D model of the mandibular bone. To achieve the surface point-to-point analysis of the mandibular models, a reverse engineering software was used. The same procedure was performed for an age-matched control group (19 CBCT images).

RESULTS

Total mandibular volume showed a difference of 2.46 cm3 between patients and controls, which was not statistically significant. A mean difference of 1.53 cm3 was found comparing the hemi mandibular volumes from the CB and non-CB sides of PUXB patients, this difference was statistically significant (P ≤ 0.01). Findings for the surface-to-surface deviation analysis, demonstrated a higher percentage of mismatch in patients PUXB, over 10% at 0.5 mm tolerance level.

LIMITATIONS

Limitations are related to the intrinsic surfaces matching methodology, that make difficult to evaluate discrepancies among different mandibular anatomical units.

CONCLUSION

Adult patients affected by PUXB show a greater mandibular structural asymmetry compared to controls because of a lower matching percentage obtained from the surface-to-surface matching technique.

IMPLICATIONS

Treatment of adult patients affected by PUXB should take into consideration the possibility of a mild mandibular asymmetry mainly localized at the condyle and gonial angle levels.

Impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency

BACKGROUND

Whether precise orthodontic detailing of occlusion impacts masticatory function is unknown. In this study, we aimed to assess the impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency.

MATERIALS AND METHODS

Fifty-four adults who completed orthodontic treatment were categorized into two groups using the American Board of Orthodontics (ABO) model grading system: one meeting ABO standards (ABO, N = 29), the other failing to meet them (non-ABO, N = 25). The electromyographic (EMG) signals of the anterior temporalis (AT) and superficial masseter muscles were recorded bilaterally during static (clenching) and dynamic (gum chewing) tests. Chewing efficiency was measured by calculating the median particle size (MPS) and broadness of particle distribution (BPD) after five chewing trials of experimental silicone food at a standardized chewing rate.

RESULTS

Participants of the ABO group had a slightly more symmetric activation of the AT muscles during clenching (P = 0.016) and chewed a gum at a slower rate (P = 0.030). During the standardized chewing test with silicone food, ABO subjects had slightly greater EMG potentials at all muscle locations than non-ABO individuals (all P < 0.05). MPS and BDP did not differ significantly between groups (all P > 0.05).

LIMITATIONS

The severity of the initial malocclusion of the study participants was not in the statistical model as a potential confounder on the outcome measures.

CONCLUSIONS

Meeting ABO standards contributes to a slightly more balanced activation of the temporalis muscles during clenching and more efficient muscle recruitment during chewing but does not improve chewing efficiency.

Assessment of Masticatory Muscle Function in Patients with Bilateral Complete Cleft Lip and Palate and Posterior Crossbite by means of Electromyography

Aim

The aim of this study was to evaluate the electrical activity of the masticatory muscles in children with a bilateral complete cleft lip and palate (BCCLP) and posterior crossbite as well as in noncleft subjects with no malocclusion. Another purpose of the study was to examine the possible factors associated with this muscle activity.

Methods

The study included 52 children with mixed dentition and Class I occlusions (20 patients with nonsyndromic BCCLP and 32 subjects with no clefts). All the cleft patients had posterior crossbite. The surface electromyography (sEMG) was used to identify the electrical potentials of the temporalis and masseter muscles. The electromyographical (EMG) recordings were taken with a DAB-Bluetooth Instrument (zebris Medical GmbH, Germany) at rest and during maximum voluntary clenching (MVC). The relationships between muscle EMG activity and independent variables were identified through multivariate logistic regression analysis.

Results

The EMG activity of the temporalis muscles at rest was significantly higher in BCCLP patients with malocclusion in comparison with the noncleft subjects with normal occlusion. During MVC, significantly lower electrical potentials of the temporalis and masseter muscles were observed in cleft patients compared to the noncleft group. The presence of BCCLP, unilateral posterior crossbites, increased vertical overlap, and increased overjet are factors strongly associated with higher temporalis muscle EMG activity at rest.

Conclusion

The use of surface electromyography in imaging muscle function showed that children with BCCLP and posterior crossbite exhibited altered masticatory muscle potentials at rest and during clenching. The presence of unilateral posterior crossbites, increased vertical overlap, and increased overjet had a significant impact on temporalis muscle activity in cleft patients. This knowledge is important in the aspect of early and proper diagnosis and orthodontic treatment of malocclusions, thereby achieving correct occlusion and improvement in muscle function.

Relationship between Unilateral Posterior Crossbite and Human Static Body Posture

Background: We compared photogrammetry-assessed body posture between young adults with and without unilateral posterior crossbite (UPCB). Assessments were controlled by vision, mandibular position and sitting/standing position. In addition, we aimed to determine the relationship between UPCB laterality and the direction of body posture using photogrammetry and a static postural platform. Methods: Adults with natural dentition, with and without UPCB, were enrolled. Static body posture was assessed by photogrammetry based on horizontal acromial alignment and horizontal anterior-superior iliac spine (ASIS) alignment. Frontal photographs were taken with participants asked to open or close their eyes and hold their jaws at rest, at an intercuspal position, and at left or right lateral positions. Distribution of foot pressure was recorded using a static postural platform at different visual input and mandibular positions. General linear models with repeated measures were used to assess the effect of the various within- and between-subject factors. Results: In total, 36 adults (left UPCB = 12; Right UPCB = 6; controls = 18) participated. There were significant differences between the control and UPCB groups in horizontal alignment at the acromion (p = 0.035) and ASIS (p = 0.026) levels when controlled by visual input and mandibular position. No significant differences in horizontal alignment or foot pressure distribution were observed by laterality in the UPCB group. Conclusion: The presence of UPCB affects static body posture, but the side of crossbite is not related to the direction of effect on static body posture.

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.

The prevalence of posterior crossbite, deep bite, and sleep or awake bruxism in temporomandibular disorder (TMD) patients compared to a non-TMD population: A retrospective study

Objective: To assess the prevalence of posterior crossbite and/or deep bite among patients diagnosed with temporomandibular disorders (TMD) compared to a non-TMD population.Methods: Four hundred ninety-four patients were enrolled: 345 with TMD according to the diagnostic criteria for TMD and 149 without TMD (control group). The chi-square test was used for statistical analysis.Results: A statistically significant association was found between sleep and awake bruxism and painful TMDs (p < .001 for both), but not with disc displacement. There was no association between posterior crossbite and/or deep bite with either painful TMD or disc displacement.Conclusion: Within the study limitations, sleep bruxism and awake bruxism may be related to pain in the TMD, and the severity of a deep overbite and presence of a unilateral or bilateral posterior crossbite should not be considered risk factors or as having any effect on the pain associated with TMD and/or disc displacement.

Three-dimensional analysis of mandibular functional units in adult patients with unilateral posterior crossbite: A cone beam study with the use of mirroring and surface-to-surface matching techniques

OBJECTIVES

To use three-dimensional (3D) mirroring and surface-to-surface techniques to determine any differences in mandibular functional unit shape and morphology between the crossbite side and non-crossbite side in adult patients with posterior unilateral crossbite who had not received any corrective treatment for malocclusion.

MATERIALS AND METHODS

Cone-beam computed tomography (CBCT) records from 24 consecutive adult white patients (mean age, 27.5 years; range 22.6-39.7 years; 14 women and 10 men) seeking treatment for maxillary transverse deficiency were assessed in this study. The control group comprised CBCT scans from age- and sex-matched patients. Segmentation masks were generated to obtain 3D surface mesh models of the mandibles and analyze the six skeletal functional units, which were further analyzed with reverse engineering software.

RESULTS

Statistically significant differences in the mean surface distance when comparing the study sample and the control sample were found at the condylar process, mandibular ramus, angular process (P ≤ .0001), and alveolar process (P ≤ .01); no statistically significant differences were found for the coronoid process, the chin, and the mandibular body (P ≥ .5).

CONCLUSIONS

The condylar, angular, and alveolar processes plus the mandibular ramus appear to play a more dominant role than did the body, the coronoid, and the chin units in the asymmetry of the mandible in patients with unilateral crossbite.

Association between posterior crossbite and/or deep bite and temporomandibular disorders among Palestinian adolescents: A sex comparison

Objective: To assess the prevalence of temporomandibular disorders (TMDs) and posterior crossbite and/or deep bite and any possible association between them. Methods: One thousand-nineteen adolescents responded to a questionnaire regarding oral habits and TMD symptoms. Afterwards, they were diagnosed according to the Axis I of the DC/TMD and underwent a dental examination. The chi-square test was used for statistical analysis. Results: A significant association  was found between posterior crossbite and some TMD diagnosis, but no association was found between deep bite and TMD, nor between occlusal diagnosis and bruxism. TMDs were more prevalent in girls. There was a significant sex difference (more among females) in the prevalence of painful TMDs. Conclusion: Posterior crossbite in the adolescent population analyzed may be related to TMDs, in contrary to deep-bite. The presence of posterior crossbite may have different impact on TMD findings between the sexes.

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.

Electromyographic Analysis of Masticatory Muscles in Cleft Lip and Palate Children with Pain-Related Temporomandibular Disorders

Aim

The aim of this study was to assess the electrical activity of temporalis and masseter muscles in children with cleft lip and palate (CLP) and pain-related temporomandibular disorders (TMD-P).

Methods

The sample consisted of 31 CLP patients with a TMD-P (mean age 9.5 ± 1.8 years) and 32 CLP subjects with no TMD (mean age 9.2 ± 1.7 years). The children were assessed for the presence of temporomandibular disorders (TMD) using Axis I of the Research Diagnostic Criteria for TMD (RDC/TMD). Electromyographical (EMG) recordings were performed using a DAB-Bluetooth Instrument (Zebris Medical GmbH, Germany) in the mandibular rest position and during maximum voluntary contraction (MVC).

Results

The rest activity of the temporalis and masseter muscles was significantly higher in TMD-P group compared with non-TMD children. A significant decrease in temporalis muscle activity during MVC was observed in TMD-P patients. There was a significant increase in the Asymmetry Index for temporalis and masseter muscle rest activity in the TMD-P group.

Conclusion

Cleft children diagnosed with TMD-P have altered masticatory muscle activity, and this can affect their muscle function.

Gait and posture analysis in patients with maxillary transverse discrepancy, before and after RPE

AIM

The purpose of this study was to evaluate the effects of the rapid palatal expansion (RPE) on posture and gait analysis in subjects with maxillary transverse discrepancies.

MATERIAL AND METHODS

Forty-one patients between 6 and 12 years were divided into 3 groups: 10 control subjects (Cs), 16 patients with unilateral posterior crossbite (CbMono), 15 patients with maxillary transverse discrepancy and no crossbite (Nocb). Every subject underwent gait analysis and posturographic examination in order to evaluate the presence of balance alterations before (T0) and after (T4) RPE application. The examinations were performed through a six-cameras stereophotogrammetric system (60-120Hz, BTS S.p.A.) synchronized with two force plates (FP4060, Bertec Corp.). Romberg test was performed on a force plate, and the statokinesiogram and joint kinematics were evaluated. One-way Anova was performed among the variables after evidence of normal distribution (Levene's test for equality of variances) and Kruskal-Wallis test (P<0.05), in order to compare the three groups of subjects. While paired t-test was performed, or Kruskal-Wallis test, instead when comparing pre- and post-RPE application within the same group of subjects (P<0.05). Tamane T2 or Bonferroni correction was applied where needed.

RESULTS

The posturographic analysis reveal significant differences across the 3 population: 95% power frequency in medio-lateral and antero-posterior direction in T0, median frequency in medio-lateral direction in T0, mean power frequency in medio-lateral direction in T0. Significant differences were also registered in the three-dimensional joints kinematics variables, mainly between Cs and Cbmono in T0 and T4 and between Cbmono and Nocb in T4.

CONCLUSIONS

A detectable correlation between dental occlusion and body posture is shown in this study that confirms another benefit of the RPE. This was mainly revealed in the dynamic posture where modifications at the mandibular level affect the whole body.

Longitudinal effects of rapid maxillary expansion on masticatory muscles activity

BACKGROUND

To investigate the modifications induced by rapid maxillary expansion (RME) on the electromyographic (EMG) activities of the anterior temporal and superficial masseter muscles, in patients without pre-treatment EMG alterations.

MATERIAL AND METHODS

Twenty-one patients with unilateral posterior cross-bite selected from the orthodontic department of the University of L'Aquila (Italy), were enrolled. There was no control group in this study since each subject acted as a control of her/himself. Two surface EMG recordings were taken: T0 (before RME) and at T1 (3 month after the end of expansion). To verify the neuromuscular equilibrium, the EMG activities of both right and left masseter and anterior temporal muscles were recorded during a test of maximum clench. EMG indexes were compared by paired Student's t-test.

RESULTS

In both occasions, all indices showed a good symmetry between the right and left side masticatory muscles. No statistically significant differences were found between the two recordings.

CONCLUSIONS

In children without pre-treatment EMG alterations, no variations in standardized muscular activity after RME were found. The treatment did not alter the equilibrium of the masseter and temporal muscles. Key words:Rapid maxillary expansion, electromyography, masticatory muscles.

Electromyographic activity of the jaw muscles and mandibular kinematics in young adults with theoretically ideal dental occlusion: Reference values

Background

A necessary step to use neuromuscular analysis as diagnostic tool is to establish normal reference values for the physiological range in a healthy population. Surface electromyographic (sEMG) activity of the jaw muscles and mandibular kinematics were measured in young adults with theoretically ideal dental occlusion to determine normal reference values during different tasks. Differences between the sexes were evaluated.

Material and Methods

Forty young adults (20 men, 20 women; mean age 22.8 ± 3.9 years) with theoretically ideal dental occlusion were selected using very restrictive criteria. sEMG activity of the anterior temporalis (AT), posterior temporalis, masseter (MA), and suprahyoid muscles were evaluated in the rest position and during swallowing, mastication, and clenching. Mandibular kinematics in the rest position and during maximum excursions were assessed. Asymmetry, activity, and torque indices and MA/AT ratios were calculated.

Results

For all muscles, sEMG values were 1.01-3.57 µV at rest, 3.50-10.85 µV during swallowing, and 41.04-86.59 µV during mastication. During clenching, values were 230.08-243.55 µV for the AT and MA muscles. Mean total asymmetry, activity, and torque indices at rest were 20.34 %, -15.04 %, and 19.02 %, respectively; during clenching, these values were 6.14 %, -2.62 %, and 4.46 %. MA/AT ratios were near 1. Kinematic measurements during lateral excursion, protrusive and maximum opening were 7.54, 8.44, and 37.38 mm respectively; lateral mandibular shift was 1.41 mm; free way and lateral displacement at rest were 1.40 and 0.26 mm. Right MA activity during mastication and clenching was higher in men than women.

Conclusions

Reference values for sEMG activity and mandibular kinematics were determined. Some muscular asymmetry and torque were observed.

Key words:Electromyography, masticatory muscles, kinesiography, jaw movements, normal dental occlusion, sexual dimorphism.

Unilateral Posterior Crossbite is Not Associated with TMJ Clicking in Young Adolescents

Unilateral posterior crossbite has been considered as a risk factor for temporomandibular joint clicking, with conflicting findings. The aim of this study was to investigate a possible association between unilateral posterior crossbite and temporomandibular disk displacement with reduction, by means of a survey carried out in young adolescents recruited from three schools. The sample included 1291 participants (708 males and 583 females) with a mean age of 12.3 yrs (range, 10.1–16.1 yrs), who underwent an orthodontic and functional examination performed by two independent examiners. Unilateral posterior crossbite was found in 157 participants (12.2%). Fifty-three participants (4.1%) were diagnosed as having disk displacement with reduction. Logistic regression analysis failed to reveal a significant association between unilateral posterior crossbite and disk displacement with reduction (odds ratio = 1.3; confidence limits = 0.6–2.9). Posterior unilateral crossbite does not appear to be a risk factor for temporomandibular joint clicking, at least in young adolescents.

Influence of orthodontic treatment on temporomandibular disorders. A systematic review

Objectives

The aim of this literature systematic review was to evaluate the possible association between malocclusions, orthodontic treatment and development of temporomandibular disorders. Material and Methods: A search was carried out on PubMed-Medline database from January 2000 to August 2013 using the keywords “orthodontics and temporomandibular disorders”, “orthodontics and facial pain” and “malocclusion and temporomandibular disorders”. Human studies included in the study were those assessing signs and symptoms of temporomandibular disorders in relation to orthodontic treatment.

Material and Methods

A search was carried out on PubMed-Medline database from January 2000 to August 2013 using the keywords “orthodontics and temporomandibular disorders”, “orthodontics and facial pain” and “malocclusion and temporomandibular disorders”. Human studies included in the study were those assessing signs and symptoms of temporomandibular disorders in relation to orthodontic treatment.

Results

The search strategy resulted in 61 articles. After selection according to the inclusion/exclusion criteria 9 articles qualified for the final analysis. The articles which linked orthodontics and development of temporomandibular disorders showed very discrepant results. Some indicated that orthodontic treatment could improve signs and symptoms of temporomandibular disorders, but none of them obtained statistically significant differences.

Conclusions

According to the authors examined, there is no evidence for a cause-effect relationship between orthodontic treatment and temporomandibular disorders, or that such treatment might improve or prevent them. More longitudinal studies are needed to verify any possible interrelationship.

Key words:Malocclusion and temporomandibular disorders, orthodontics and facial pain, orthodontics and temporomandibular disorders, temporomandibular disorders, temporomandibular dysfunction.

The electrical activity of the temporal and masseter muscles in patients with TMD and unilateral posterior crossbite

The aim of this study was to assess the influence of unilateral posterior crossbite on the electrical activity of the temporal and masseter muscles in patients with subjective symptoms of temporomandibular dysfunctions (TMD). The sample consisted of 50 patients (22 female and 28 male) aged 18.4 to 26.3 years (mean 20.84, SD 1.14) with subjective symptoms of TMD and unilateral posterior crossbite malocclusion and 100 patients without subjective symptoms of TMD and malocclusion (54 female and 46 male) aged between 18.4 and 28.7 years (mean 21.42, SD 1.06). The anamnestic interviews were conducted according to a three-point anamnestic index of temporomandibular dysfunction (Ai). Electromyographical (EMG) recordings were performed using a DAB-Bluetooth Instrument (Zebris Medical GmbH, Germany). Recordings were carried out in the mandibular rest position and during maximum voluntary contraction (MVC). Analysis of the results of the EMG recordings confirmed the influence of unilateral posterior crossbite on variations in spontaneous muscle activity in the mandibular rest position and maximum voluntary contraction. In addition, there was a significant increase in the Asymmetry Index (As) and Torque Coefficient (Tc), responsible for a laterodeviating effect on the mandible caused by unbalanced right and left masseter and temporal muscles.

Mandibular kinematic changes after unilateral cross-bite with lateral shift correction

The aim of this randomised prospective study was to evaluate the effects of slow maxillary expansion with expansion plates and Hyrax expanders on the kinematics of the mandible after cross-bite correction. Thirty children (15 boys and 15 girls), aged 7·1-11·8, with unilateral cross-bite and functional shift were divided into two groups: expansion plate (n = 15) and Hyrax expander (n = 15). Thirty children with normal occlusion (14 boys and 16 girls, aged 7·3-11·6) served as control group. The maximum vertical opening, lateral mandibular shift (from maximum vertical opening to maximum intercuspation, from rest position to maximum intercuspation and from maximum vertical opening to rest position) and lateral excursions were recorded before and 4 months after treatment. After treatment, the expansion plate group showed a greater lateral shift from rest position to maximum intercuspation than did the control group. The expansion plate patients also presented greater left/contralateral excursion than did the control group. Comparisons of changes after treatment in the cross-bite groups showed significant decreases in the lateral shift from the maximum vertical opening to maximum intercuspation and from the maximum vertical opening to rest position, a significant increase in the homolateral excursion and a significant decrease in the contralateral excursion in the Hyrax expander group, whereas no significant differences were found in the expansion plate group. In conclusion, the Hyrax expander showed better results than did the expansion plate. The Hyrax expander with acrylic occlusal covering significantly improved the mandibular lateral shift and normalised the range of lateral excursion.

Orthodontic intervention combined with myofunctional therapy increases electromyographic activity of masticatory muscles in patients with skeletal unilateral posterior crossbite

OBJECTIVE

The aim of this study was to evaluate the electromyographic activity of both the temporalis and masseter muscles and the mastication type of patients with skeletal unilateral posterior crossbite before and after orthodontic treatment and speech therapy.

METHODS

A total of 14 patients with skeletal unilateral posterior crossbite (eight females and six males), between 6-13 years of age, underwent electromyographic evaluation of their masseter and temporalis muscles in mandibular rest, habitual mastication and isometry. The subjects were assessed with regard to mastication type before and after orthodontic treatment and speech therapy. The data obtained during mandibular rest and habitual mastication were normalized in terms of the mean values of isometry. The Student's t-test was used for paired samples to compare the mean values of electromyographic activity (p < 0.05).

RESULTS

The masseters during habitual mastication presented higher electromyographic activity after both treatments (p = 0.0458). There was no significant difference between the contralateral masseters in terms of mandibular rest or habitual mastication before or after either treatment (p > 0.05). During habitual mastication, after the treatments, the temporalis muscle on the malocclusion side showed higher electromyographic activity than the contralateral side (p = 0.0263). Prior to therapy, all of the patients exhibited chronic unilateral mastication (n = 14) and 13 patients exhibited bilateral mastication after treatment.

CONCLUSIONS

Orthodontic intervention combined with myofunctional therapy in patients with skeletal unilateral posterior crossbite provided an increase in the electromyographic activity of the masseter and temporalis muscles during mandibular rest and habitual mastication, with predominantly bilateral mastication.

Malocclusion in early anatomically modern human: a reflection on the etiology of modern dental misalignment

Malocclusions are common in modern populations. Yet, as the study of occlusion requires an almost intact dentition in both the maxilla and mandible, searching for the ultimate cause of malocclusion is a challenge: relatively little ancient material is available for research on occlusal states. The Qafzeh 9 skull is unique, as its preserved dentition allowed us to investigate the presence and manifestations of malocclusion. The aim of this study was thus to examine the occlusal condition in the Qafzeh 9 specimen in light of modern knowledge regarding the etiology of malocclusion. We revealed a pathologic occlusion in the Qafzeh 9 skull that probably originated in the early developmental stage of the dentition, and was aggravated by forces applied by mastication. When arch continuity is interrupted due to misalignment of teeth as in this case, force transmission is not equal on both sides, causing intra-arch outcomes such as mesialization of the teeth, midline deviation, rotations and the aggravation of crowding. All are evident in the Qafzeh 9 skull: the midline deviates to the left; the incisors rotate mesio-buccally; the left segment is constricted; the left first molar is buccally positioned and the left premolars palatally tilted. The inter-arch evaluation revealed anterior cross bite with functional shift that might affect force transmission and bite force. In conclusion, the findings of the current study suggest that malocclusion of developmental origin was already present in early anatomically modern humans (AMH) (the present case being the oldest known case, dated to ca. 100,000 years); that there is no basis to the notion that early AMH had a better adjustment between teeth and jaw size; and that jaw-teeth size discrepancy could be found in prehistoric populations and is not a recent phenomenon.

Does orthodontic treatment provide a real functional improvement? a case control study

Background

Electromyographic analysis of the masticatory muscles provides useful data on the behavior of these muscles during stomatognathic system functioning and allows a functional assessment of orthodontic treatments. This study was undertaken to verify if achieving an Angle Class I bite through orthodontic treatment can lead to neuromuscular balance.

Methods

This study enrolled 30 patients (20 females, 10 males, mean age: 15.78 years) with an Angle Class II, division 1 malocclusion that was orthodontically treated. A group of 30 subjects (19 females, 11 males; mean age: 16.15 years), randomly selected among subjects with an Angle Class II, division 1 malocclusion that had not been orthodontically treated served as the Control group. Both groups were subjected to electromyography to study their neuromuscular characteristics. The Shapiro-Wilk's test revealed a non normal distribution, therefore we used a Friedman two way ANOVA by ranks test to compare differences of surface electromyography values between treated and untreated subjects at closed and open eyes condition.

Results

A statistically significant interaction between orthodontic treatment and open eyes conditions was detected for anterior temporal muscles. A significant imbalance of the anterior temporal muscles, which is indicative of an asymmetric electromyographic pattern, was also found.

Conclusions

The present data indicate that achieving a correct occlusal target does not necessarily correspond to a neuromuscular balance.

Neuromuscular dentistry: Occlusal diseases and posture

Neuromuscular dentistry has been a controversial topic in the field of dentistry and still remains debatable. The issue of good occlusion and sound health has been repeatedly discussed. Sometimes we get complains of sensitive teeth and sometimes of tired facial muscles on getting up in the morning. Owing to the intimate relation of masticatory apparatus with the cranium and cervico-scapular muscular system, the disorders in any system, draw attention from concerned clinicians involved in management, to develop an integrated treatment protocol for the suffering patients. There may be patients reporting to the dental clinics after an occlusal restoration or extraction, having pain in or around the temporomandibular joint, headache or neck pain. Although their esthetic demands must not be undermined during the course of treatment plan, whenever dental treatment of any sort is planned, occlusion/bite should be given prime importance. Very few dentist are able to diagnose the occlusal disease and of those who diagnose many people resort to aggressive treatment modalities. This paper aims to report the signs of occlusal disease, and discuss their association with TMDs and posture.

Influence of malocclusion on the development of masticatory function and mandibular growth

OBJECTIVE

To verify the hypothesis that appropriate acquisition of masticatory function and normal growth of the mandible are modified by malocclusion.

MATERIALS AND METHODS

Eighteen Jcl:ICR mice were divided into two groups. In one group we shifted the mandible laterally using an occlusal guidance appliance, creating a posterior crossbite at 5 weeks of age. The other group served as control. After 10 weeks, three-dimensional jaw movements and muscle activities were recorded simultaneously during mastication. Microcomputed tomography scans were obtained in vivo to evaluate morphometric changes in the mandible.

RESULTS

(1) The jaw movement pattern in the sagittal plane showed significantly less anteroposterior excursion in the malocclusion group during the late-closing phase (power phase). (2) Electromyography showed significantly less masseter activity in the malocclusion group. (3) The condylar width and mandibular bone mineral density (BMD) were significantly reduced in the malocclusion mice compared to the normal mice.

CONCLUSIONS

These findings suggest that optimization of the chewing pattern and acquisition of appropriate masticatory function is impeded by malocclusion. Altered mechanical loading to the mandible may cause significant reduction of condylar width and mandibular BMD.

Surface electromyographic evaluation of jaw muscles in children with unilateral crossbite and lateral shift in the early mixed dentition. Sexual dimorphism

OBJECTIVES

To examine the activity of jaw muscles at rest and during maximal voluntary clenching (MVC) in children with unilateral posterior crossbite (UPXB) and functional lateral shift in the early mixed dentition and to evaluate sex differences.

MATERIAL AND METHODS

The sample included 30 children (15 males, 15 females) aged 6 to 10 years old, with UPXB and functional mandibular lateral shift (≥1.5 mm) in the early mixed dentition. sEMG activity coming from the muscle areas (anterior temporalis [AT], posterior temporalis [PT], masseter [MA] and suprahyoid [SH]) were obtained from both the crossbite (XB) and noncrossbite (NONXB) sides at mandibular rest position. sEMG activity of the bilateral AT and MA muscles sides was obtained during MVC. Asymmetry and activity indexes were calculated for each muscle area at rest and during MVC; the MA/TA ratio during MVC was also determined.

RESULTS

At rest, no differences were found between sexes for any muscle areas or asymmetry and activity indexes. No differences were found between XB and NONXB sides. During MVC, however, significant sex differences were found in AT and MA activity, with higher sEMG values in males than in females, on both XB and NONXB sides. Asymmetry indexes, activity indexes and MA/AT ratios did not show significant differences between the sexes. Activity was symmetric both in males and in females.

CONCLUSIONS

At rest, no sex differences were found, but during MVC males showed higher activity than did females in both XB and NONXB AT and MA muscle areas. Muscular activity was symmetrical at rest and during MVC in both sexes. Sexual dimorphism should be considered in the diagnosis and treatment of UPXB and lateral shift in the early mixed dentition.

Dental occlusion, body posture and temporomandibular disorders: where we are now and where we are heading for

The aim of this investigation was to perform a review of the literature dealing with the issue of relationships between dental occlusion, body posture and temporomandibular disorders (TMD). A search of the available literature was performed to determine what the current evidence is regarding: (i) The physiology of the dental occlusion-body posture relationship, (ii) The relationship of these two topics with TMD and (iii) The validity of the available clinical and instrumental devices (surface electromyography, kinesiography and postural platforms) to measure the dental occlusion-body posture-TMD relationship. The available posturographic techniques and devices have not consistently found any association between body posture and dental occlusion. This outcome is most likely due to the many compensation mechanisms occurring within the neuromuscular system regulating body balance. Furthermore, the literature shows that TMD are not often related to specific occlusal conditions, and they also do not have any detectable relationships with head and body posture. The use of clinical and instrumental approaches for assessing body posture is not supported by the wide majority of the literature, mainly because of wide variations in the measurable variables of posture. In conclusion, there is no evidence for the existence of a predictable relationship between occlusal and postural features, and it is clear that the presence of TMD pain is not related with the existence of measurable occluso-postural abnormalities. Therefore, the use instruments and techniques aiming to measure purported occlusal, electromyographic, kinesiographic or posturographic abnormalities cannot be justified in the evidence-based TMD practice.

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.

Atividade elétrica do músculo masseter durante a deglutição de líquido em adultos jovens

OBJETIVO: Caracterizar a atividade elétrica muscular do masseter durante a deglutição de líquido em indivíduos adultos jovens saudáveis. MÉTODOS: A população constou de 14 voluntários considerados saudáveis seguindo os critérios de inclusão e exclusão estabelecidos para esta pesquisa. Foi realizada avaliação eletromiográfica do músculo masseter bilateralmente, durante o repouso e nas tarefas de deglutição de 14,5 ml, 20 ml e 100 ml de líquido. O sinal eletromiográfico foi normalizado pela máxima atividade voluntária resistida (MAVR), considerada como 100% de atividade elétrica muscular. RESULTADOS: No masseter direito, a maior média percentual foi encontrada na tarefa de deglutição de 20 ml e no masseter esquerdo na tarefa de 14,5 ml. No masseter direito ocorreu diferença entre as deglutições de 14,5 ml e 20 ml. No masseter esquerdo não houve diferença entre as tarefas de deglutição. CONCLUSÃO: A atividade elétrica muscular do masseter em adultos jovens saudáveis durante a deglutição de líquido pode ser influenciada pelo volume deglutido e apresenta diferentes respostas bilateralmente.

Characteristics of masticatory muscles in children with unilateral posterior crossbite

The aim of this study was to detect possible differences in the EMG (electromyography) activity, chewing rate (CR), cycle duration (CD) and preferred chewing side (PCS) between children with and without unilateral posterior crossbite. Thirty-seven children aged from 7 to 10 years were selected from the clinic of the Department of Pediatric Dentistry, Piracicaba Dental School, Brazil, and divided into two groups: unilateral posterior crossbite (UPCB group, n = 17), and normal occlusion (NOccl group, n = 20). The PCS was determined using a visual spot-checking method. The EMG activity was recorded during mastication, and two chewing sequences of 20 s were evaluated to establish each subject's CR (cycles/sec) and CD. UPCB and NOccl groups did not have a PCS. The EMG activity and the cycle characteristics did not differ between the groups. The correlations between CD, CR and EMG activity were statistically significant for the masseter and anterior temporalis muscles only in the NOccl group, in which there was also a significant correlation between the EMG activity of masseter and anterior temporalis. In conclusion, these findings suggest that although children with and without UPCB presented a bilateral masticatory pattern with similar CR and CD, balanced EMG activity of masseter and anterior temporalis muscles was observed only in the NOccl group. These results indicate that in children, UPCB can alter the coordination of masticatory muscles during mastication.

Clinical study of frontal chewing patterns in various crossbite malocclusions

INTRODUCTION

The purpose of this study was to clarify the frontal chewing patterns of various crossbite malocclusions.

METHODS

A mandibular kinesiograph was used to record the masticatory movements of 106 subjects (ages, 12-35 years) with crossbite malocclusion and 22 subjects (ages, 16-30 years) with normal occlusion. The chewing patterns were classified into 8 chewing types according to the cycle shape of the frontal incisor point movement. The crossbite subjects were divided into 5 groups by the anteroposterior position of the crossbite, and then the subjects with posterior crossbite were divided into 3 groups by the transverse position of the crossbite. The Mann-Whitney U test was used to compare the frequency of each chewing type between any crossbite group and the control group; and between the various crossbite groups.

RESULTS

In the crossbite groups, normal chewing occurred much less often than in subjects with normal occlusion. In the posterior crossbite group, reverse chewing was greater (P = 0.002), and normal chewing was less frequent (P = 0.001) compared with the anterior crossbite group. When accompanied by mandibular shift, mandibular prognathism, arch crossbite, in the crossbite or shift side, reverse type, and reverse-crossing type occurred more often than in contralateral side.

CONCLUSIONS

In the frontal plane, patients with posterior crossbite might have more abnormal chewing types than those with anterior crossbite, and posterior crossbite could contribute to the high frequency of reverse and reverse-crossing chewing types, especially when accompanied by mandibular shift, mandibular prognathism, or arch crossbite.