Influence of the vertical dimension in the treatment of myofascial pain-dysfunction syndrome

Occlusal splints constructed at three different vertical heights were used to study the influence of vertical dimension in the etiology of bruxism and MPD syndrome. The vertical dimension of least EMG activity was determined for each of 75 patients who were randomly divided into three groups according to the vertical dimension at which the occlusal splint was constructed. Group I occlusal splints were constructed at 1 mm from the occlusal vertical dimension, group II splints at 4.42 mm, and group III splints at 8.15 mm. Results showed a faster and more complete reduction in clinical symptoms for groups II and III than for group I. The temporary use of occlusal splints with a vertical height exceeding the physiologic rest position did not encourage a greater muscular tonus or hyperactivity of jaw muscles. It can be concluded that elongation of elevator muscles to or near the vertical dimension of least EMG activity by means of occlusal splints is more effective in producing neuromuscular relaxation.     

咬合板高度对TMD患者咀嚼肌肌电的影响

目的:研究不同高度的咬合板对颞下颌关节紊乱病(TMD)患者颞肌前束、咬肌肌电的影响。方法:73例TMD患者随机分为3组,戴用不同高度咬合板使咬合距离分别增加3mm、5mm、7mm,比较分析戴板前和戴板后即刻测量的双侧颞肌前束(TA)和咬肌(MM)肌电电位。结果:在静息及紧咬状态下,戴用不同高度咬合板即刻测量的TA及MM肌电电位均明显低于戴板前的测量值(P<0.05);紧咬状态下5mm和7mm咬合板对MM肌电电位的降低程度显著高于3mm组。结论:咬合板是治疗肌功能紊乱的有效方法。高度为5mm和7mm的咬合板降低咀嚼肌肌电的能力较3mm咬合板更强。     

[牙合]垫对牙齿重度磨耗患者口颌功能影响的临床研究

目的：研究殆垫对牙齿重度磨耗患者口颌功能的影响。方法：用殆垫恢复10例牙齿重度磨耗患者的垂直距离,分别检测治疗前、治疗后1个月、3个月、6个月的咬合平衡性、咬肌及颞肌前束的肌电幅值、颌位及殆的稳定性以及边缘运动的平滑度及对称性的变化。结果：①咬合平衡性、颌位及胎的稳定性以及边缘运动轨迹的平滑度及对称性在治疗后呈逐渐改善趋势,治疗6个月后80％的患者恢复正常;②治疗后各组的息止位肌电幅值均较治疗前显著降低（P〈0．05）,正中颌位紧咬时肌电幅值在治疗后3个月组和6个月组较治疗前显著增加（P〈O．05）。结论：通过6个月的治疗和观察,聆垫对重度磨耗患者的口颌功能的影响呈现持续改善趋势。     

Influence of group function and canine guidance on electromyographic activity of elevator muscles

A comparative EMG study was done between two types of occlusal guidances: group function and canine guidance. The purpose was to determine which of the two occlusal schemes causes a greater reduction in muscle activity and thereby a decrease in muscle tension in eccentric mandibular positions. Full-coverage occlusal splints were made for six test subjects with normal function of the stomatognathic system. Left- and right-side integrated EMG recordings were made of the masseter and temporal muscles during static (clenching) and dynamic (lateral excursion and clenching) maximal contractions. The results showed an EMG activity reduction of the elevator muscles with group function relative to their activity in centric occlusion. A more marked reduction was observed on the mediotrusive side, mainly in the temporal muscle. With canine guidance, the reduction in elevator muscle activity is much greater, more significant, and mainly in the temporal muscle of the mediotrusive side. The clinical implications of this study suggest the use of canine guidance in laterotrusion for therapy with full-coverage occlusal splints.     

Vertical dimension. Part 2: the changes in electrical activity of the cervical muscles upon varying the vertical dimension

This study was conducted in order to determine the effect of vertical dimension variation on the electromyographic (EMG) activity of the sternocleidomastoid and trapezius muscles. The study was performed on 15 healthy subjects. Basal tonic electromyographic (BT-EMG) recordings were performed by placing surface electrodes on the left sternocleidomastoid and trapezius muscles. BT EMG activity was recorded upon varying the vertical dimension every five millimeters from vertical dimension of occlusion to 45 millimeters of jaw opening (series 1), following the habitual opening path. Afterward, BT-EMG activity was recorded every millimeter from vertical dimension of occlusion to 4 mm, and then every two millimeters from four to ten millimeters (series 2). In series 1, a significant increase of BT-EMG activity was observed in both muscles (simple logarithmic regression analysis). In series 2, a significant increase was observed in the sternocleidomastoid muscle whereas trapezius muscle did not present a significant change. BT-EMG behavior of the sternocleidomastoid muscle in series 2 could be relevant when dentists increase vertical dimension by means of intermaxillary appliances during a short-term period. Moreover, these results add further information to the concept of the interrelatedness between the different components of the cranio cervical-mandibular system.     

The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension

The relation between BT-EMG activity and variations of VD (1 to 41 mm of interocclusal distance) was studied in the masseter, anterior temporal, and posterior temporal muscles of eight normal experimental subjects. EMG activity was recorded with surface electrodes, and the VD was measured with a specially designed device. Recordings were performed with dynamic variations (series A) and with static variations (series B) of VD. Series A shows a gradual decrease of EMG activity starting from the occlusal position, passing through a range of maximum reduction at a certain interocclusal distance, and gradually increasing to the highest values close to maximum jaw opening. Series B shows the same progression, although it points out the exact VD at which minimum basal EMG activity is observed in each muscle studied (10 mm for the masseter muscle, 13 mm for the anterior temporal muscle, and 16 mm for the posterior temporal muscle).     

无牙颌患者的咬合垂直距离与咀嚼肌肌电关系的实验研究

作者选择了颌关系正常、能合作的15名无牙颌受试者。在4kg咬合力作用下，在不同的咬合垂直距离时，测定了颞肌及嚼肌的肌电幅值，实验结果表明，在控制咬合力状态下，无牙颌患者的咀嚼肌肌电幅值随着垂直距离增加而逐渐下降，两者间呈非常显著性负相关关系；在肌电活动变化过程中，有一相对稳定区域，由此提示，为无牙颌患者重建的咬合垂直距离有一定生理范围，约1.0mm(后牙区测点）。     

Effect of occlusal splints on the electromyographic activities of masseter muscles during maximum clenching in patients with myofascial pain-dysfunction syndrome

Integrated EMG activities of masseter muscles during maximum voluntary isometric contraction with and without full-arch maxillary stabilization splints were observed in patients with MPD syndrome having occlusal interferences and in healthy subjects having no occlusal interferences. The masseter muscle activity was more significantly reduced in patients with MPD syndrome during maximum clenching with splints than in those patients without splints. In healthy subjects, such a significant difference could not be observed with and without splints. This finding suggests that the elimination of the occlusal interferences by means of occlusal splints could reduce the degree of sensory information from the periodontal receptors during nocturnal clenching or grinding. This could result in a decrease in masseter muscle activity giving rise to muscular relaxation.     

Changes in jaw relations and activity of masticatory muscles in patients with immediate complete upper dentures

A longitudinal radiographic cephalometric and electromyographic investigation was performed on eighteen subjects provided with an immediate complete upper and a partial lower denture. The observation stages were: before final extractions and 7 weeks, 6 months and 1 year after denture insertion. The cephalometric analysis was based on measurements from lateral head films taken in centric occlusion. The EMG activity of the anterior temporal and masseter muscles was studied in postural position, light tapping and in maximal clench. The changes in jaw and occlusal relationships due to resorption of the edentulous maxillary ridge were slight, the mean decrease in occlusal vertical dimension during one year being 0.7 mm. The EMG clench activity at the pre-extraction stage, when the patients occluded on a residual anterior dentition, showed low mean values round 100 microV, and a further decrease was observed at the post-insertion stage. At the 1-year stage all muscles displayed significant increases to above the post-insertion level. The jaw muscle activity in light tapping and in postural position generally showed no significant mean changes during the observation period. The results indicate that preservation of a residual dentition in the lower jaw prevents marked changes in jaw and occlusal relationships and resulting changes in muscle activity.     

Influence of occlusal stabilization splints and soft occlusal splints on the electromyographic pattern, in basal state and at the end of six weeks treatment in patients with bruxism

The aim of this study is to assess the electrical activity generated in temporal and masseter muscles during voluntary muscular contraction of patients with bruxism, as a result of the use of two types of occlusal splints (occlusal stabilization splint and soft occlusal splint) in which 2 groups of 8 patients were evaluated -12 women and four men aged 19 to 40 years, who used a single type of occlusal splint for 46 to 60 days. The splints were made from sheets of rigid acetate plus heat-cured acrylic (occlusal stabilization splint, control group) and sheets of flexible acetate (soft occlusal splint, experimental group). Two electromyographic tests (EMG) were performed on each patient; one before placing the splint and another at the end of the treatment. The statistical analysis used was computerized variance ANOVA analysis with F distribution (P < or = 0.025). In the control group, muscle electrical activity increased significantly in 5 patients and decreased slightly in 3. In the experimental group, there was considerable reduction of such activity in 6 patients and a slight increase in 2. There is a statistically significant difference (P < or = 0.025) between the muscle electrical activity generated in the control group and in the experimental group. The increase in muscle electrical activity in the control group may have been due to a neuromuscular recovery process; while the decrease in the experimental group might have been due to a negative or decremental process of muscular organization to prevent the recruitment of new motor units. Occlusal stabilization splints are therefore considered better than soft occlusal splints.     

Effects of a bite‐raising splint on the duration of the chewing cycle and the EMG activities of masticatory muscles during chewing in freely moving rabbits

Metal bite‐raising splints of 0.5 mm thickness were attached to the upper molar teeth on both sides of the jaw in rabbits. The effects of these splints on masticatory behaviour during the chewing of soft food (bread) by freely moving rabbits were investigated. We recorded electromyograms (EMGs) of the masseter and digastric muscles. The animals exhibited prolongation of the chewing cycle, decreased EMG activity of the masseter muscle and increased EMG activity of the digastric muscle during chewing after introduction of the bite‐raising splints. The effects of the splints on the activities of masticatory muscles were abolished by bilateral sectioning of the maxillary and inferior alveolar nerves. It seems likely that afferents from oral sensory receptors were responsible for the changes in masticatory behaviour after the introduction of the occlusal splint.     

咬合抬高对后牙重度磨耗患者咀嚼肌表面肌电值的影响

目的：探讨后牙重度磨耗患者咬合抬高后对咀嚼肌表面肌电反应的影响。方法：随机选取2012年1月至2014年1月在我北京航空总医院口腔诊疗中心就诊的,伴有双侧后牙重度磨耗的患者40名为受试对象,其中男性23名,女性17名,年龄40-50岁,治疗前及咬合抬高不同距离后分别进行咬肌及颞肌的肌电检查,并对结果采用多样本均数比较的单因素方差分析进行统计学处理。结果：切牙区颌间距离增加1mm时,双侧咬肌,双侧颞肌肌电值差异无统计学意义。切牙区颌间距离增加2mm时,左侧咬肌,右侧咬肌,左侧颞肌肌电值差异无统计学意义,右侧颞肌肌电值有所增加（17.08±3.27 VS 24.66±3.18,P〈0.05）。切牙区颌间距离增加3mm时,除右侧咬肌肌电值差异无统计学意义外（22.35±3.14 VS 27.74±4.26,P〉0.05）,左侧咬肌,左侧颞肌,右侧颞肌肌电值差异均有统计学意义。切牙区颌间距离增加4mm时,双侧咬肌,颞肌肌电值差异均有统计学意义。结论：切牙区颌间距离增加2mm时对咬肌和颞肌肌电值影响不大,切牙区颌间距离增加3mm会对咬肌和颞肌肌电值产生较大影响。     

Influence of Different Centric Functions on Electromyographic Activity of Elevator Muscles

This study compares eight different occlusal centric functions with splint contact on different teeth in order to determine their influence on mandibular elevator electromyographic (EMG) activity.

Maxillary occlusal splints were built for eight subjects without craniomandibular dysfunction. Investigators divided each splint into three parts, in order to record different occlusal schemes in the same subject without varying the vertical dimension. EMG activity in the left masseter and anterior temporal muscles was registered during maximum voluntary clenching.

Results showed higher masseter activity with the splint than without, and anterior temporal activity was similar. There was a significant decrease of EMG activity with the anterior section of the splint. There were no significant differences between the remaining centric functions and clenching with the complete splint, except for the centric function with contralateral posterior contact, in which elevator activity was significantly reduced.

Results suggest that bilateral posterior occlusal stabilization is critical for maximum interocclusal force.     

Influence of Occlusal Splints on Bilateral Anterior Temporal EMG Activity during Swallowing of Saliva in Patients with Craniomandibular Dysfunction

A full-arch maxillary stabilization occlusal splint was made for each of 10 patients with craniomandibular dysfunction. These splints were divided into three sections (one anterior and two posterior). This procedure allowed variation in the anteroposterior centric localization of occlusal contacts, thus permitting the recording of the EMG effects produced by the different occlusal splint sections. The integrated EMG activity was recorded from the right and left anterior temporal muscles during swallowing of saliva in habitual occlusion and with the different occlusal splint sections inserted. EMG activity during swallowing of saliva was significantly lower with the different occlusal splints than in habitual occlusion. This supports the rationale for diurnal wear of the occlusal splint. No differences in EMG activity were found during swallowing of saliva when different sections of the occlusal splints were used. This fact points out the possibility for therapeutic use of different occlusal splints for improving swallowing function.     

Vertical dimension: A research and clinical analysis

Vertical dimension has been defined in relation to the clinical rest position of the mandible, the vertical dimension of occlusion, and the interocclusal space between the two. The physiologic rest position has been attributed to three possible mechanisms: postural tonicity of the muscles, myotatic (stretch) reflexes, and gravity-elasticity, and/or a combination of all three. There is general agreement that it varies due to head position and many other extrinsic and intrinsic stimuli.The myotatic (stretch) reflex is produced by stimulation of the stretch receptors in the elevator muscles producing a simple two-neuron reflex arc which causes reflex muscle contraction. Its function is to give proprioceptive information to the central nervous system concerning position and movement. The proprioception of mandibular position is determined for the most part by the joint receptors, muscle spindles, pressoreceptors (in the periodontal membrane), and exteroceptors in the oral mucosa.Minimal EMG activity has been demonstrated at the clinical rest position and slightly beyond, at an increased vertical dimension which eliminates the interocclusal space. However, experimental evidence has been shown with adult monkeys that long-term increases in the vertical dimension of occlusion result in intrusion of the posterior teeth with the return almost to the original vertical dimension of occlusion. Several clinical examples of intrusion of the posterior teeth were shown when long-standing occlusal splints were used. Since both occlusal adjustment and vertical dimension increases can cause a reduction in EMG activity, it is recommended that the treatment of TMJ dysfunction is best accomplished by occlusal correction.A treatment prosthesis is recommended for trismus and/or joint injury but it should be accomplished within the interocclusal space. Most treatment prostheses, except those for condylar repositioning, are utilized for the control of symptoms and do not treat the cause of TMJ dysfunction pain.     

Occlusal dysfunction and stress

A dysfunctional occlusal relationship was produced in six Macaca irus monkeys by insertion of occlusal splints which raised the vertical dimension of occlusion by 3–4 mm and incorporated interferences into the occlusion. Cortisol levels of plasma and 24 h urine samples were measured by competitive protein-binding analysis. After insertion of the splints there was an immediate, approximately two-fold rise of the mean 24 h urinary cortisol excretion rate and a significant decrease of urinary volume and body weight. The plasma cortisol level did not rise significantly. During the 3 weeks experimental period the teeth showed increasing mobility and occlusal wear facets developed on the splints. Urinary cortisol excretion rates were significantly elevated throughout the experimental period. Urinary cortisol levels declined to basal values when the splints were removed. This animal model produces experimental evidence in support of the hypothesis that a dysfunctional occlusal relationship may result in bruxism associated with emotional stress.     

Influence of altered occlusal guidance on masticatory muscle activity during clenching

This study investigated the influence of experimentally altered occlusal guidance on masticatory muscle activity. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid on the second molar and the non-working side second molar to simulate a canine-protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern revealed to have statistically significant effects on EMG activity. As the most characteristic change, EMG activity in the anterior temporalis significantly increased in the simulated group function occlusion and the simulated bilateral balanced occlusion compared with the simulated cuspid protected occlusion. The increased teeth contacts to the posterior region altered the unilateral pattern of the anterior temporalis activity to the bilateral pattern, while that of masseter activity remained unchanged.     

Influence of occlusal vertical dimension on the masticatory performance during chewing with maxillary splints

Changing the occlusal vertical dimension is a common procedure in restorative dentistry, during treatment of patients with cranio-mandibular disorders, and during orthodontic and orthognathic treatment. The treatment may alter the length of the main jaw elevator muscles and the position of the mandibular head in the fossa temporalis. These changes may influence the bite forces that are generated during chewing and thus may affect the masticatory function. We measured the objective masticatory function, defined as masticatory performance, by determining an individual's capacity to pulverize a test food. The immediate influence of the increase in the occlusal vertical dimension on the masticatory performance was determined using three anatomical maxillary splints in a group of seven dentate subjects. The splints gave an increase in the occlusal vertical dimension of 2, 4 and 6 mm, respectively. Before we started the experiments the subjects practiced chewing with the splints during about 5 min. No significant differences were observed in masticatory performance among the conditions without and with the three splints. Thus, an increase in the occlusal vertical dimension up to 6 mm did not have a significant effect on the masticatory performance. Maxillary splints may be used to study the effect of occlusal factors on the chewing process by manipulating tooth shape and occlusal area of the splint.     

The immediate effects of a stabilization splint on the muscular symmetry in the masseter and anterior temporal muscles of patients with a craniomandibular disorder

In 36 myogenous craniomandibular disorder patients, the immediate effects of a stabilization splint on the symmetry in the activities of the masseter and anterior temporal muscles during submaximal clenching at five clenching levels were investigated electromyographically. After the adjustment of the splint necessary at the time of delivery, 20 splints remained free from occlusal interferences throughout the treatment period and thus needed no further adjustment. These splints caused an immediate improvement in masseter muscle symmetry at the time of delivery (p less than 0.01). However, 16 splints needed further adjustment for occlusal interferences at the first recall, 2 weeks after delivery of the splint. These splints resulted in a small but statistically significant worsening in masseter muscle symmetry at the 10% clenching level (p less than 0.01). No such response was found for temporal muscle activity. The immediate changes in masseter muscle activity suggest that muscular symmetry is an objective basis in the evaluation of the treatment provided.     

The influence of altered occlusal guidance on condylar displacement

This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26.5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P < 0.001 and P < 0.001, respectively). When compared to the simulated group function occlusion, the simulated canine protected occlusion and balancing contact caused statistically significant smaller superior displacements of the non-working side condyle, which suggests that they may result in reduced temporomandibular joint (TMJ) loading. Furthermore, the simulated canine protected occlusion was associated with the lowest EMG activity, which suggests that this occlusal pattern has the capacity to reduce the level of parafunctional activity.