Masseteric silent period in healthy young adults

The length of the silent period (SP) has been subject of extensive researches and its use has been established for the diagnosis of dysfunctional individuals. Because of its great variability we should be cautious about its assessment. This study is aimed to find the normal values taken in symptomless subjects using a commercial/medical recording system, designed for clinical use. Thirty-six readings of the SP have been taken causing a chin tap. The assessment of the motor dysfunction and the subsequent depressed activity gave the result of 32.37 ms (SD = 19.47, ranged from 15 to 110). This is slightly more extended than the results described by the majority of the Authors.     

The effect of the bite plane splint on the electromyographic silent period duration

An electromyographic study of the masseter and anterior part of the temporalis muscles was performed on ten patients presenting temporomandibular joint dysfunction symptoms. The EMG silent periods (SP) produced in the open-close-clench cycle and jaw-jerk reflex were compared for duration before and after treatment with an occlusal bite splint. Following use of the splint, there was a shortening of SP indicating the possible use of the duration of SP as a diagnostic measurement, and also as an indication of treatment effectiveness.     

The masseteric silent period following experimental bruxism in subjects wearing acrylic anterior bite planes

Masseteric silent periods were recorded in normal subjects who performed experimental bruxism whilst wearing an acrylic anterior bite plane. No significant increase of the silent period duration occurred. The results are compared with similar studies without the anterior bite plane.     

Influences of changing vertical dimension, occlusal contacts of bite plane and body position on masticatory muscle activities

The Bite plane therapy has been accepted to be useful for treatment of the patients with the stomatognathic dysfunction. The purpose of this study is to make clear the influences of changing the vertical dimension and occlusal contacts of the bite plane on masticatory muscle activities in order to improve the bite plane therapy. The full arch bite plane with an interincisal distance of 5 mm was fabricated for each one of 30 subjects without stomatognathic dysfunction. The EMG activities were recorded from the anterior part of the temporal muscles, the masseter muscles and the anterior belly of the digastric muscles bilaterally while the subject exerted tapping and maximal voluntary clenching in a postural position. Four kinds of experiments were performed as follows. In Exp. 1, integrated EMG activities of each muscle were compared with and without the bite plane. In Exp. 2, the influences of changing the vertical dimension of the bite plane (2.5 mm, 5 mm and 7.5 mm) were tested in 17 subjects. In Exp. 3, the influences of changing the location of occlusal contacts of the bite plane were studied in 12 subjects. In Exp. 4, the influence of changing the body positions on EMG activities and mandibular positions was compared in 30 subjects between the sitting and supine positions. Furthermore, the influence of the same factor was compared with and without the bite plane which was adjusted in each position. The results were summarized as follows: 1. Wearing the bite plane mainly reduced activities of the temporal muscles. 2. The bite plane with an interincisal distance of 5 mm was most effective in reducing activities of the temporal muscles. 3. Wearing the bite plane with anterior occlusal contacts reduced activities of the elevator muscles significantly. 4. Significant differences in activities of the temporal and digastric muscles were recognized between the two body positions when the bite plane was not applied. However, no significant difference was recognized when the bite plane was inserted. Furthermore, those differences were correlated with the difference in the antero-posterior mandibular displacement between the two body positions while the subject tapped the teeth. These results suggest the possibility to control masticatory muscle activities by applying the bite plane with the proper vertical dimension and occlusal contacts. In addition, it is necessary to take a suitable body position for the patient who has a difference in the mandibular displacement between the sitting and supine positions when applying the bite plane.     

The influence of occlusion on jaw and neck muscle activity: a surface EMG study in healthy young adults

The electromyographic (EMG) characteristics of masseter, temporalis and sternocleidomastoid (SCM) muscles during maximum voluntary teeth clench were assessed in 27 male and 35 female healthy young adults. Subjects were divided into two groups: (i) 'complete' Angle Class I (bilateral, symmetric canine and molar Class I relationships), and (ii) 'partial' Angle Class I (one to three canine/molar Class I relationships, the remaining relationships were Class II or Class III). On average, standardized muscular symmetry ranged 80.7-87.9%. During maximum voluntary teeth clench, average co-contraction of SCM muscle was 13.7-23.5% of its maximum contraction. On average, all torque coefficients (potential lateral displacing component) were >90%, while all antero-posterior coefficients (relative activities of masseter and temporalis muscles) were >85%. The average integrated areas of the masseter and temporalis EMG potentials over time ranged 87.4-106.8 muV/muV s%. Standardized contractile muscular activities did not differ between 'complete' and 'partial' Angle Class I, and between sexes (two-way analysis of variance). A trend toward a larger intragroup variability in EMG indices was observed in the subjects with 'partial' Angle Class I than in those with 'complete' Angle Class I (significant difference for the temporalis muscle symmetry, P = 0.013, analysis of variance). In conclusion, the presence of a complete or partial Angle occlusal Class I did not seem to influence the standardized contractile activities of masseter, temporalis and SCM muscles during a maximum voluntary clench. Subjects with a 'complete' Angle Class I were somewhat a more homogenous group than subjects with 'partial' Angle Class I.     

The effect of bite force on the duration and latency of the menton tap silent period

The purpose of this research was to investigate the effect of bite force changes on the duration and latency of the menton tap silent period and particularly whether a decrease in bite force can increase the duration of the silent period to the extent which may be found in dysfunctional patients. The menton tap silent period was recorded from both anterior temporal and masseter muscles while the subject was clenching at different force levels. A bilaterally stable force transducer was used to monitor the clenching force. The results indicated no statistically significant differences in the mean durations and latencies of silent periods at different clenching forces. They suggest that duration and latency are not related to the degree of clenching force.     

Influence of the muscle tension on the masseteric silent period in children and adults

summary Three subject groups who have shown different biting forces were examined in order to investigate whether the physiological phenomenon that the duration of the silent period (SPD) of the masseter muscle would be influenced by background activities of the muscles. They were classified into child (CN, n = 10) and adult groups; the adult group was then further subdivided according to the strength of maximum biting force into a normal group (AN, n = 10) and a low biting force group with some symptoms (AS, n = 5). SPD was observed in maximum) and biting on a transducer (50N, 100N and maximum). With increase of muscle activities, SPD was significantly decreased in the AN and CN groups, whereas no significant changes were found in the AS group. When comparing SPDs among the three groups at the same voluntary effort, the AN group exhibited the shortest SPD followed by the CN and AS groups. The results suggest that SPD was positively influenced by the strength of the background activities of the muscles and that immaturity of the masseters in terms of muscle activity could affect the SPD.     

颈带口外弓与下颌多用途弓联合应用对牙颌骨垂直向的影响

目的:评估生长发育期骨性Ⅱ类1分类错(峆)患者,通过联合使用颈带口外弓与下颌多用途弓治疗后牙与骨的改变.方法:60例患者分为3组,第1组(n=20)只使用颈带口外弓治疗,第2组(n=20)使用颈带口外弓与下颌多用途弓联合治疗,第3组是未治疗的对照组(n=20).治疗前后牙和骨的改变通过头颅侧位片进行测量分析.采用SPSS15.0软件包对数据进行t检验.结果:治疗组前面高增加较对照组大,下颌支高度显著增加;下颌多用途弓引起下切牙压低且舌倾,下磨牙远中倾斜而来伸长;与对照组比较,颈带口外弓治疗后上磨牙伸长平均值不足1mm.结论:治疗组上颌突度显著减少;前面高较对照组显著增加,下颌支高度也显著增加,下颌平面无显著改变.治疗组上磨牙伸长小于1mm,可以认为没有临床意义.下颌多用途弓引起下切牙压低、舌倾;下磨牙远中倾斜,没有伸长.多用途弓并没有影响下颌的旋转.     

Myoelectrical activity of clinical rest position and jaw muscle activity in young adults

summary Electromyographic activity of anterior temporal, superficial masseter, deep masseter and anterior digastric muscles was measured in 40 young healthy men and women during rest (at the beginning and the end of tests), clench, maximal opening, lateral displacement and CR manipulation. During initial rest position myoelectrical activity was 1.9 μV increasing to 2.1 μV at the end of tests (P = 0.08). During clench and maximal opening no significant differences between the sexes were found. The digastric muscle showed considerable activity during maximal opening, lateral displacement and CR manipulation.     

Effects of increased occlusal vertical dimension on daily activity and myosin heavy chain composition in rat jaw muscle

Mammalian skeletal muscles change their contractile-protein phenotype in response to mechanical loading and/or chronic electrical stimulation, implying that the phenotypic changes in masticatory muscles might result from new masticatory-loading conditions. To analyze the effects of increased occlusal vertical dimension (OVD) on daily activities and fibre-type compositions in jaw muscles, we measured the total duration of daily activity (duty time) and the myosin heavy chain (MyHC) compositions in the masseter and digastric muscles of freely moving control and bite-opened rats. In the control state, the duty time of the digastric muscle was higher than that of the masseter muscle at activity levels exceeding 5 and 20% of the day's peak activity. The opposite was true at activity levels exceeding 50 and 80% of the day's peak activity. The MyHCs consisted of a mixture of fast and slow types in the digastric muscle. The masseter consisted of mostly fast-type MyHC. The increment of OVD increased not only the duty time at activity levels exceeding 5, 20, 50 and 80% of the day’ peak activity in both muscles but also the proportion of MyHC IIa in the masseter muscle and MyHC I in the digastric muscle at the expense of that of MyHC IIb. These results suggest that the increment of OVD changes masseter and digastric muscles towards slower phenotypes by an increase in their daily activities.     

Effect of bite force on the masseteric electromyographic silent period in man

The duration of the masseteric EMG silent period as induced by tapping on the chin was measured at different levels of sustained bite force. Under both open bite and normal occlusion, the duration of the silent period was inversely related to the magnitude of the bite force. For bite force of the same magnitude, the value of the silent period remained relatively constant for the same subject in different trials (SEM ? 1 per cent), whereas the absolute values of the silent periods ranged far and wide for different individuals even under similar experimental conditions.     

Effect of bite openings and mandibular protrusion on genioglossus muscle activity in healthy adults with oral appliance

Oral appliance (OA) can effectively treat obstructive sleep apnea; however, numerous types of oral appliances and designs are variable and the precise mechanisms behind differences in treatment outcomes are uncertain. The objective of this study was to evaluate the effects of different degrees of mandibular position [4° of bite openings (BO): 2, 4, 8 and 12 mm; and protrusion (P): 0, 50%, MAX], for both the upright and supine positions: BO_{2 mm_}P_0%, BO_{4 mm_}P_0%, BO_{4 mm_}P_50%, BO_{4 mm_}P_MAX, BO_{8 mm_}P_0%, BO_{12 mm_}P_0%; with an OA on the: (1) activity of the genioglossus (GG) muscle by electromyogram, (2) inspiration by airflow sensor, and (3) recording mandibular movements (incisor and mandibular condyle point) in each position. Nine healthy male adults (age 27.5 ± 1.30 years) were recruited. The results show that GG muscle activity increased significantly from BO _4 mm_P_0% to BO_12 mm_P_0% during the supine position, and the strongest signal was found in BO_4 mm_P_MAX, compared to all of the other positions, and GG muscle activity in BO_4 mm_P_0% tended to be lower. From supine to upright position the inspiration increased significantly but GG muscle activity did not. These results might be a stimulus to augment a compensatory mechanism of GG muscle induced by OA, however, mainly in protrusion position. The increase of BO (2–12 mm) and even maximum protrusion might not negatively affect the temporomandibular joint.     

拔除第二双尖牙矫正病例(牙合)颌面的垂直向变化

目的　评价安氏 I类错畸形患者,特别是下颌平面角较大的患者拔除第二双尖牙矫正后颌面的垂直向变化,尤其是下颌平面的旋转变化。方法　24 例覆正常或较浅且下颌平面角大于均值的安氏 I类错患者(骨性与牙性均为 I类)拔除第二双尖牙,应用直丝弓技术完成矫治,25 例符合同样标准的患者由不拔牙矫正完成。对所有病例治疗前后的头颅侧位片进行描图和手工测量,比较拔牙组与非拔牙组颌面垂直向的变化。结果　对拔牙和非拔牙两组患者的头影测量结果进行的统计学比较发现,除下磨牙的伸长量拔牙组大于非拔牙组外,两组患者间颌面垂直向的变化并无统计学意义的差别。结论　第二双尖牙的拔除并不一定意味着下颌平面角的减小,对于高角前牙开倾向病例选择拔除第二双尖牙后,在矫正过程中仍需注意对后牙的垂直向控制。     

The effects of isometric exercise on maximum voluntary bite forces and jaw muscle strength and endurance

The effects of training and exercise on the strength and endurance of limb muscles has been investigated extensively, but the response of the jaw muscles to exercise remains poorly known. The purpose of this study was to determine whether short-term isometric training increases strength and endurance of the superficial masseter and anterior temporalis muscles. Maximum and submaximum voluntary bite forces and corresponding electromyographic (EMG) activity were measured in 28 young adults, randomly divided into exercise and non-exercise (control) groups. Subjects in the exercise group performed isometric clenches against a soft maxillary splint for five 1-min sessions per day over a 6-week period. After exercise, subjects increased their maximum bite forces by 37%, but control subjects' bite forces also increased by 25%. After exercise, EMG levels per unit of bite force generally decreased, but similar decreases were also seen in the non-exercised controls. Masseter muscle activity levels during standardized 10-kg bites decreased after 6 weeks of exercise. Fatigue resistance increased significantly with exercise but did not differ significantly from control values after 6 weeks of exercise. The results of this study indicate that increases in maximum bite force can be easily produced with training, but that actual strengthening of the jaw muscles is more difficult to achieve.     

The effect of first premolar extraction on vertical dimension.

The purpose of this study was to evaluate the vertical changes occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extractions. Records of 40 Class I nonextraction cases (24 girls, 16 boys) and 40 Class I maxillary and mandibular first premolar extraction cases (23 girls, 17 boys) were obtained. The pretreatment and posttreatment cephalograms were digitized, and 6 linear and 8 angular cephalometric measurements were selected to evaluate vertical changes. Evaluation of the treatment results of the extraction and nonextraction cases showed that the vertical changes occurring after the extraction of maxillary and mandibular first premolars were not different than those occurring in the nonextraction cases.     

The effect of increasing occlusal vertical dimension on face height

PURPOSE: This study evaluated the effect of increasing occlusal vertical dimension (OVD) on the face height in completely dentate young adults. MATERIALS AND METHODS: Faces of 22 subjects were photographed in a standardized manner in an anterior view. Sequential photographs were taken at intercuspation and clinical rest position, with four complete arch maxillary occlusal overlays increasing OVD in interincisal increments of 2, 4, 6, and 8 mm. Objective measurements were made from the photographs using facial reference markers. Ten observers made subjective evaluations of the resulting changes in face height using the sequential photographs randomly presented. RESULTS: Measurements of the facial markers showed that on increasing OVD, a corresponding change in lower face height was 50% of the interincisal increase in intercuspation and 40% for clinical rest position. ANOVA for repeated measures showed a statistically significant effect of the intraoral increase in OVD on lower face height. However, subjective results showed that observers were not capable of detecting changes in face height caused by an intraoral increase in OVD (2 to 6 mm intrinsically). ANOVA for the difference between dentists and nondentists showed a minimal, but significant, difference between the two groups, with dentists erring slightly less. CONCLUSION: Attempts to alter face height by changing OVD within the range of 2 to 6 mm for esthetic reasons may not be visually distinguishable.