正颌手术后咀嚼肌改变的研究进展

正颌手术通过打破原有的颌骨系统,重建咬合平衡来达到改善面型和咀嚼功能的目的。随着现代医学的发展和人们观念的进步,正颌外科被越来越多的患者所接受,其疗效和安全性也得到了学术界的肯定,但是也有少部分术后恢复不佳甚至治疗失败的病例存在。颌面部解剖结构复杂,影响预后的因素较多,尤其正颌术后颌面部软组织的变化难以动态观察,至今其变化过程及机制尚不明确。本文就近年来正颌术后咀嚼肌改变的研究进展作一综述。     

Electromyographic analysis of the masticatory muscles of patients after complete rehabilitation of occlusion with protection by non-working side contacts

summary Surface electromography was used to study the function of the anterior temporal, surface masseter, deep masseter and anterior digastric muscles of 14 patients after complete rehabilitation of occlusion with fixed prostheses and/or removable partial prostheses. All patients had a balanced occlusion with protection by non-working side contacts during lateral excursion. Mean resting myoelectric activity was 2.5-3.8 μV, showing no hypertonia or muscular spasm. When patients clenched their teeth (i.e. exerted maximum voluntary occlusal force in centric occlusion), the anterior temporal muscles were the most active, followed by the surface masseters; the digastrics were significantly less active. During lateral displacements, the muscles exhibiting significantly higher potentials than the other muscles monitored were the working side anterior temporal muscle and the contralateral surface masseter. During mastication, the muscle that was most active in relation to its contralateral homologue was the working side surface masseter, the difference between the two being statistically significant.     

Electromyographic activity of human masticatory muscles in normal young people. Statistical evaluation of reference values for clinical applications

Electromyographic activity of anterior temporal and masseter muscles was measured in 92 young healthy men and women with sound dentitions during rest position, contact in centric occlusion and clench. Male and female mean potentials were similar except in clench, where males had higher electromyographic levels. Mean pooled electromyographic potentials were 1.9 μV (TA) and 1.4 μV (MM) during rest position, 6.5 μV (TA) and 2.8μV (MM) during contact in centric occlusion. Mean maximum voluntary clench potentials were 181.9μV (TA) and 216.2 μV (MM) in men, 161.7 μV (TA) and 156.8 μV (MM) in women. Examined muscles were more asymmetric at low electromyographic activity (rest and centric occlusion) with the temporal muscle less asymmetrical than the masseter. In females temporal muscle activity tended to dominate at every contraction level, while in males masseter activity was stronger in clench, and temporal activity in centric occlusion and in rest position.     

Electromyographic activity of the human masticatory muscles during submaximal clenching in the inter-cuspal position

The activity patterns of the masseter and the anterior temporal muscles were studied in twenty-one healthy male subjects while clenching at 10, 20, 30, 40 and 50% of the maximum clenching level. At low clenching levels the temporal muscle activity tended to dominate, at high levels the masseter muscle activity was stronger (P less than 0.001). The asymmetry in muscle activity also depended upon the clenching level (P less than 0.001), while at each level the masseter muscle asymmetry was greater than the temporal muscle asymmetry (P less than 0.05-P less than 0.025). By comparing the electromyographic activities of the left and right side within each subject it was found that the masseter muscle with the higher electromyographic activity tended to have the larger cross-sectional area (P less than 0.01) and at the 50% clenching level it tended to be on the side with the greater number of post-canine tooth contacts (P less than 0.001).     

Electromyographic activity of the masticatory and cervical muscles during resisted jaw opening movement

One of the relaxation techniques that have been used by physical therapists when treating patients with temporomandibular disorders, is the agonist contract-antagonist relax technique (AC). When the AC technique is applied, a submaximal resistance to the jaw opening movement is necessary to cause relaxation of the masticatory muscles. No information about the effect of this technique on masticatory or cervical muscles has been found in the literature. Thus, the aim of this study was to evaluate the electromyographic activity of the masseter and anterior temporalis and the upper trapezius and splenius capitis during resisted jaw opening movement. A convenience sample of 30 students was used. Electromyography activity of the superficial masseter, anterior temporalis, upper trapezius and splenius capitis was registered before, during and after the application of this resistive movement to jaw opening. A two-way anova with repeated measures analysis was used to analyse data. The level of significance was at alpha = 0.05. The EMG activity of both the masticatory muscles and the cervical muscles increased during and after the application of resisted jaw opening (P < 0.05). Based on the results obtained from this study, the behaviour of all muscles analysed (masseter, anterior temporalis, splenius capitis and upper trapezius) was similar. All muscles increased their activity when the resistance to the jaw opening movement was applied. Complex muscular interactions of the supra- and infrahyoid muscles (jaw openers), masticatory muscles, and cervical muscles may exist to stabilize the craniomandibular system during resisted jaw opening.     

Electromyographic biofeedback and rest position training of masticatory muscles in myofascial pain-dysfunction patients

Twenty-four women outpatients with myofascial pain-dysfunction were divided into three groups of eight. All received bilateral masseter electromyographic biofeedback training. One group received biofeedback only; one group received additional instructions and modeling to place their jaw in the "rest" position; and one group was given a prosthetic guide that spaced the incisors 6.8 mm apart. Two 15-minute training sessions were conducted at a 1-week interval, with posttreatment assessment 2 weeks later. The instruction and prosthesis groups obtained significantly greater electromyographic reductions in masseter activity and increases in mandibular range of motion compared with the biofeedback-only group. Subjects with pain obtained a significant reduction in therapist and self-report pain ratings. The results suggest that short-term biofeedback treatment may be meaningfully augmented by procedures that place the mandible in the rest position.     

Histological changes in masticatory muscles of mdx mice

Objective

Duchenne muscular dystrophy (DMD) patients have distorted dentofacial morphology that could be a result of changed force balance of masticatory muscles due to unequal dystrophic changes in various masticatory muscles. Skeletal muscles of DMD patients and those of murine model of DMD - mdx mice - are both characterized by Ca²⁺ induced muscle damage, muscle weakness and characteristic histological changes. Therefore, to determine the pathological changes in this animal model of DMD, we examined the masticatory muscles of the mdx mice for histological abnormalities including nuclei localization, fibre diameters, and collagen expression.

Design

Muscle sections from masseter (MAS), temporal (TEM), tongue (TON) and soleus (SOL) of mdx and control normal mice were stained with hemalaun/eosin or with Sirius Red and morphometrically analysed. Levels of collagen staining in normal and mdx muscles were measured using image analysis and the mean optical density (mod) was determined.

Results

Dystrophin deficient masticatory muscles contained 11-75% fibres with centralised nuclei. In mdx mice an increased mean fibre diameter was observed as compared to the age-matched control muscles (control vs. mdx; MAS: 33.44 ± 0.49 μm vs. 37.76 ± 0.68 μm, p < 0.005; TEM: 32.93 ± 0.4 μm vs. 42.93 ± 0.68 μm, p < 0.005; SOL: 33.15 ± 0.29 μm vs. 40.62 ± 0.55 μm, p < 0.005; TON: 13.44 ± 0.68 μm vs. 15.63 ± 0.18 μm, p < 0.005). Increased expression of collagen was found in MAS (mod control vs. mdx: 1.34 vs. 3.99, p < 0.005), TEM (mod control vs. mdx: 3.11 vs. 4.73, p < 0.01) and SOL (mod control vs. mdx: 2.36 vs. 3.49, p < 0.01).

Conclusion

Our findings revealed that mdx masticatory muscles are unequally affected by the disease process. The masticatory muscles of the mdx mice could present a useful model for further investigating the influence of dystrophin deficiency on muscles function.     

Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles

This study examined changes in masticatory function after botulinum toxin type A (BTX‐A) injection using objective and subjective tests during 12 weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M‐T group) were injected. Forty subjects were assigned into two groups; M group (n = 20) and the M‐T group (n = 20). The Meditoxin^® was used as BTX‐A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4 weeks and gradually recovered with time. Compared with the pre‐injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4 weeks after the injection (P < 0·05). When the results between M group and M‐T group were compared, scores of VAS and FIA were significantly different 4 weeks after the injection (P < 0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX‐A injection into the masticatory muscle after 4 and 8 weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12 weeks. Furthermore, after 8 weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.     

A change of occlusal conditions after splint therapy for bruxers with and without pain in the masticatory muscles

Bruxism has been suggested as an initiating or perpetuating factor in a certain subgroup of temporomandibular disorders (TMD), however, the exact association between bruxism and TMD remains unclear. This study aimed to demonstrate the difference in responses between bruxism and a subgroup of TMD to a full-arch maxillary stabilization splint from the standpoint of an occlusal condition. This study was conducted to verify the null hypothesis that there were no differences between bruxer groups with and without myofascial pain (MFP) with respect to the changes in occlusal conditions after the use of a splint. Thirty bruxers with MFP and 30 without MFP participated. Occlusal conditions were examined before and after splint therapy, and occlusal changes following the use of a splint were compared between the two groups. The frequency of occlusal changes after splint therapy was significantly higher in the MFP bruxer group than the non-MFP bruxer group (p < 0.05) for the occlusal conditions investigated in the present study. However, no statistical differences were found with regard to each occlusal condition. This result may show the variety of splint effects and may demonstrate a heterogeneous aspect to bruxism and myofascial pain.     

Histological changes and changes in the myosin mRNA content of the porcine masticatory muscles after masseter treatment with botulinum toxin A

Objectives

Botulinum toxin A (Botox) is increasingly used for treatment of muscle hyperfunction. For a better understanding of the possible morphologic and chewing changes in patients induced by a therapy with Botox, muscle fiber and myosin heavy chain (MyHC) mRNA alterations were examined in this animal study.

Materials and methods

The investigation was carried out on 14-week-old pigs (seven treated animals, eight controls; calculated animal size with a power of 0.5). To initialise the total immobilisation of the right masseter, the Botox injection was distributed into ten areas. After a 56-day period, muscle tissue was taken from the left and right side of the masseter (three regions), temporal (two regions), medial pterygoid and geniohyoid muscles using a standardized method. The muscle fiber cross sections were examined immunohistochemically. Fiber staining was accomplished with antibodies to specific MyHC isoforms. The MyHC mRNA changes were analysed using real-time RT-PCR.

Results

Muscles adapt to such stress by changing fiber types and MyHC mRNA content. Paralysed masseters display atrophic changes while other masticatory muscles show hypertrophic changes. The results indicated that the typical distributions of type IIa und IIb fiber types in masticatory muscles were increased in the masseter muscles due to Botox application. On the other hand, the masseters without Botox in the treated group showed a significant increase of type I MyHC.

Conclusions

Application of Botox may lead to uncontrolled structural changes in affected and unaffected muscles.

Clinical relevance

Treatment of muscle hypertrophy with Botox may cause muscle imbalance.     

Electromyographic activity of masticatory muscles and mandibular movement during function in marginal mandibulectomy patients

The purpose of this study is to evaluate the masticatory muscle activity and mandibular movement during function in marginal mandibulectomy patients. Three marginal mandibulectomy patients and three healthy subjects participated in this study. The activities of the temporalis (TA) and masseter muscles (MM) on the normal and resected sides during maximum voluntary clenching (MVC) and gum chewing (Gch), and mandibular movement during Gch were analyzed. Paired t-test, Student's t-test and one-way ANOVA were performed at P < 0.05. For MVC, integrated EMG (iEMG) in patients was lower than in healthy subjects. When iEMG of each muscle activity in patients was compared, TA activity on the resected side was greater than that of MM. There were no differences between the normal and resected sides in TA or MM. For Gch, no differences in iEMG, burst or chewing time were found between patients and healthy subjects. MVC was greater than Gch in healthy subjects, but no difference was found in patients. The range of mandibular movement along the X axis in patients was greater than in healthy subjects. Within the limitations of this study, EMG activity in patients during MVC was remarkably lower than that in healthy subjects, and altered mandibular movement was observed.     

Electromyographic study of masticatory dysfunction in patients with unilateral cleft lip and palate and reversed occlusion

Masticatory dysfunction in patients with unilateral cleft lip and palate was studied on the basis of electromyograms of the masticatory muscles. The purpose of the study was to elucidate the origin of the dysfunction by means of comparisons among electromyograms of masticatory muscles in cases of normal occlusion, reversed occlusion and reversed occlusion caused by unilateral cleft lip and palate. Subjects were 10 cases of normal occlusion (10y2m-11y10m), 10 cases of reversed occlusion (7y2m-11y2m) and 20 cases of unilateral cleft lip and palate (8y0m-14y3m). In each subject, electromyograms of the masseter and anterior venters of the temporal muscles at the isometric-contraction phase were recorded by means of the surface-electrode method with mandible loads of 1-5 kg. The electromyograms were analyzed quantitatively by means of an electromyographic device called a Turn Counter. Relations between loads and amplitude as well as numbers of turns were examined. At the same time maximum masticatory pressure and occlusal contact points were measured and then examined in comparison with electromyographic findings. Results: 1. Correlation coefficients between loads and amplitudes as well as numbers of turns decreased among the groups in this order: normal occlusion, reversed occlusion and cleft-caused reversed occlusion. Significant differences were observed between the normal-occlusive group and the reversed and cleft-caused reversed-occlusive groups. 2. No. difference was observed between the normal-occlusive and reversed-occlusive groups in terms of correlation coefficients between total sums of amplitudes and turns of the 4 masseter muscles (right and left masseters and anterior venters of the temporal muscles) and loads. Correlation coefficients in the cleft group were significantly smaller than those in the other 2 groups. 3. Because of great differences in regression coefficient among individuals, no synergic contraction pattern of the 4 mastication muscles (right and left masseter and temporal muscles) could be specified. 4. The A/T ratio of masseters in the cleft group was significantly smaller than those in the normal- and reversed-occlusive groups. 5. Under maximum load, the activity ratio of the 4 masseter and temporal muscles was 1:1 in the normal- and reversed-occlusive groups, whereas temporal-muscle activity predominated over masseter-muscle activity in the cleft group. 6. Maximum masticatory pressure decreased in the order: normal-occlusive, reversed-occlusive, and cleft caused occlusive. No correlation with electromyographic findings was observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electromyographic analysis of masticatory and neck muscles in subjects with natural dentition, teeth-supported and implant-supported prostheses

Objectives: To compare the electromyographic (EMG) characteristics of masticatory and neck muscles in patients with natural dentition, teeth‐supported prostheses and implant‐supported prostheses. Materials and methods: Twenty‐five subjects aged 40–80 years were examined. Five patients had maxillary and mandibular implant‐supported fixed prostheses; five patients had mandibular implant‐supported fixed prosthesis and maxillary removable complete denture; seven patients had implant‐supported fixed prosthesis (one arch) and natural dentition or full‐arch tooth‐fixed prosthesis (one arch); and eight control subjects had natural dentition or single tooth‐fixed prostheses. Surface EMG of masseter, temporal and sternocleidomastoid muscles was performed during maximum teeth clenching and unilateral gum chewing. Interarch dental contacts were assessed with shim stocks. Results: All groups had similar interarch dental contacts (P>0.05). During clenching, patients with maxillary and mandibular implant‐supported fixed prostheses had unbalanced standardized masseter and temporalis anterior activities (74%), with significantly larger values found in the other patients and control subjects (all mean values larger than 86%, P=0.017). All patients chewed with significantly larger muscular potentials than control subjects (on average, 1434–2100 μV s vs. 980 μV s, P=0.04), and had altered muscular patterns (left side, P=0.021). The patients with one arch with natural dentition/tooth fixed prostheses had chewing muscular patterns similar to the control subjects. Conclusions: Clenching with the analyzed prostheses was performed with a relative increment of temporalis activity. Neuromuscular coordination during chewing was larger in patients who maintained their teeth or dental roots, independently from the number of dental contacts.