Effects of a functional appliance on masticatory muscles of young adults suffering from muscle-related temporomandibular disorders.
TL;DR: The results show that the FGB-D corrects the torque index and thus the lateral displacement of the mandible.
Abstract: The aim of this study was to investigate the effects of an original orthodontic functional appliance [function generating bite for deep bite correction (FGB-D)] on masticatory muscle activity in subjects suffering from muscle-related temporomandibular disorders (TMD). Electromyographic (EMG) analysis was performed on 33 young adults (nine men, 24 women) to evaluate the contractile symmetry of the right and left masseter and anterior temporalis muscles. The subjects were divided into three groups: a muscle-related TMD group requiring orthodontic treatment for deep bite correction (three men, eight women) and treated with FGB-D; a muscle-related TMD group not requiring orthodontic treatment (three men, eight women) and treated with a Michigan occlusal splint; and a TMD-free group (three men, eight women) as a control group. Records were made by surface EMG of maximum voluntary teeth clenching, with and without the functional appliance or occlusal splint in place, before and after 12 months of therapy. A torque index was derived from the surface EMG recordings to estimate lateral displacement of the mandible. The results show that the FGB-D corrects the torque index and thus the lateral displacement of the mandible.
Summary (2 min read)
- The lack of standardized diagnostic criteria was a critical obstacle towards a further understanding of temporomandibular disorders (TMD).
- According to RDC, TMD can be classified into three major groups: (1) muscle conditions, (2) disc displacements, and (3) arthralgia, arthritis, and arthrosis, on the basis of a simple physical examination and case history.
- Quantitative surface electromyography (sEMG) of masticatory muscles is a reliable technique for the assessment of TMD patients (3, 4).
- The treatment of TMD by interocclusal devices followed ª 2004 Blackwell Publishing Ltd 524 Journal of Oral Rehabilitation 2004 31; 524–529 two paths: occlusal splints and functional orthopedic appliances.
- This kind of appliance with metallic bite planes acts simultaneously as an orthodontic corrector (9, 13–16) and as an occlusal splint.
- Three groups of 11 subjects each (three men, eight women in each group) were selected for this study.
- The first group (F – functional, mean age 25Æ4 6Æ3 years) was suffering from muscle-related TMD requiring orthodontic treatment for deep bite correction.
- This group was treated with a Michigan occlusal splint (17).
- During the 12 months of therapy the patients were treated by expert operators.
- All subjects gave their written informed consent.
- The superficial bundle of the right and left masseter muscles (MM) and the right and left temporalis anterior muscles were studied.
- Before electrode placement, the skin was carefully cleansed with abrasive paste to reduce electrode impedance, and recordings were made after 5 min to allow absorption of the conductive gel by the skin.
- Surface EMG recordings were obtained from four channels of the eight-channel electromyograph FREELY†.
- The signals were assessed as the root mean square (RMS) of the amplitude.
- Surface EMG recordings were obtained during two sessions: before treatment began (T0) and after 12 months of active treatment, with and without (T1w and T1wo, respectively) appliance/splint in place.
- The control group was monitored at the same time.
- In the first session (T0) the subjects were asked to perform maximum voluntary clenching (MVC) (‘clench as hard as possible’) in the intercuspal position.
- At each session, a first recording for the standardization of EMG potentials was made as follows.
- The most important characteristic, for the FGB-D (Fig. 1), is the presence of anterior and posterior metallic bite planes, which disengage the mandible from occlusion.
- The direction of the forces of the masseter and temporalis anterior muscles may produce a lateral deviation of the mandible.
- Indices were calculated automatically for each test by EMA software.
- Mean values and standard deviations were calculated for the torque indices, and also for the positive and negative values taken separately.
- Torque indices before and after therapy were compared using Student’s t-test for paired data.
- The data were also analysed using one-way repeated measurement analysis of variance , followed by post hoc Tukey–Kramer multiple comparisons test when required.
- Absolute mean values and standard deviations of torque indices are reported in Table 1.
- The appliance and a schematic representation of the FGB-D in place.
- (1) anterior metallic bite planes; (2) posterior metallic bite plane.
- In healthy subjects, a mandibular rotation on the horizontal axis may be counterbalanced by the actions of ligaments and other jaw muscles forces.
- Inui et al. (23) reported that facial asymmetry, if present, was characterized as a mandibular lateral displacement and a canted frontal occlusal plane ascending towards the displaced side of the mandible in TMD patients.
- An important issue is whether orthodontic therapy aimed at correcting the occlusion will affect the neuromuscular system.
- The torque index proposed by Ferrario et al. (21) may be helpful in these studies because it indicates the presence of resultant muscular forces with a laterodeviating effect on the mandible.
- Further investigation is necessary before the authors can fully understand the mechanism of its involvement.
- The main conclusions of this study are: (1) Quantitative sEMG of masticatory muscles cannot distinguish healthy subjects from those with musclerelated TMD (group H versus group S); (2) Deep bite seems to be related to a high torque index and then to a lateral displacement of the mandible; (3) The FGB-D reduces the torque index.
- These findings suggest that FGB-D may be useful in muscle-related TMD patients requiring orthodontic treatment for dental deep bite correction.
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..., USA) in accordance with previous reports [11,27]....
Cites background from "Effects of a functional appliance o..."
...The investigation of the adaptation process to a new denture is relevant to understand the control of muscles during maximal voluntary clenching and may provide essential information for the diagnosis of dysfunctions of the masticatory system (9, 10)....
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Q1. What are the contributions in "Effects of a functional appliance on masticatory muscles of young adults suffering from muscle-related temporomandibular disorders" ?
The aim of this study was to investigate the effects of an original orthodontic functional appliance [ function generating bite for deep bite correction ( FGB-D ) ] on masticatory muscle activity in subjects suffering from muscle-related temporomandibular disorders ( TMD ).