Effects of different stimulus locations on inhibitory responses in human jaw-closing muscles

The aim of this study was to examine the inhibitory responses in bilateral masseter and temporalis muscle activity when electrical stimulation with short or long duration was applied to six oro-facial locations. The exteroceptive suppression period (ES2) and inhibitory responses were recorded in the surface electromyogram (EMG) of bilateral masseter and temporalis muscles in 16 healthy subjects. Two stimulus durations (1 ms single pulse and 450 ms pulse train) adjusted to a perceived intensity of 7 (distinct painful) on a 0-10 Numerical Rating Scale (NRS) were applied to the following six oro-facial locations on the right side while the subject was biting at 50% of the maximal voluntary contraction: masseter muscle, temporalis muscle, temporomandibular joint, infraorbital nerve, supraorbital nerve, and mental nerve. The stimulus intensity required to reach an NRS score of 7 was significantly lower for 450 ms train stimuli than for 1 ms single stimuli (P<0·001). There were no significant differences in the magnitude of ES2 suppression among the six different locations (P>0·876) for the 1 ms single stimuli. There were significant decreases in Root-Mean-Square-EMG values in the 400-500 ms post-stimulus epoch compared with the pre-stimulus epoch (P<0·023) for 450 ms train stimuli, but there were no significant differences in the magnitude of inhibition among the six different locations (P<0·893). Short- and long-lasting electrical stimulation of various oro-facial locations induces similar bilateral inhibitory effects in the jaw-closing muscles but with different propensity which may reflect the somatotopic organisation of these responses.     

Maximal contraction force and endurance of human jaw-closing muscles in isometric clenching

Maximal unilateral bite force and endurance times from maximal bite force to the 75% and 50% levels of maximal values were recorded for 13 men and 15 women with bite openings of 10 and 14 mm. Measurements were made both from right and left molar regions and from the incisal region. Bite force values were significantly higher than previously measured in endurance tests by devices with unilateral housings. Men achieved greater bite force than women in the molar region in every trial. The general assumption that women's muscles are superior to those of men in static endurance when both are working at the same percentage of maximal voluntary contraction was not supported by this work for jaw-closing muscles. The endurance times to 75% and 50% levels of maximal bite force were shorter than could be expected from previous reports, and endurance times to the 50% level were even shorter than those reported for muscles of limbs.     

Effect of experimental pain on EMG-activity in human jaw-closing muscles in different jaw positions

We examined the effect of a standardized painful stimulus on the surface EMG-activity of the human jaw-closing muscles at rest and during two levels of jaw opening. Sixteen healthy women participated in two experimental sessions. In randomized order, hypertonic saline (HS: 5.8%) was infused into the left masseter muscle on one occasion, and isotonic saline (IS: 0.9%) on the other. The subjects scored the pain intensity continuously on a 0-10 visual analogue scale (VAS). The subjects were asked to hold the jaw in three different positions (rest, half-maximal, and maximal opening). Before, during, and after infusion, the EMG-activity was recorded from the masseter and temporalis muscles with the jaw in each of the three positions. HS induced significantly higher pain-levels than IS (mean VAS: HS: 5.2 ± 1.3, IS: 0.7 ± 0.2, P < 0.05). At rest, the EMG-activity in most of the jaw muscles increased significantly during both infusions (P < 0.05). At half-maximal opening, the EMG-activity in the infused muscle increased significantly with both HS and IS (P < 0.05). At maximal opening, the EMG-activity during infusion of HS decreased significantly in the right masseter and temporalis (P < 0.05). There was no significant difference in the position of the jaw at rest during infusions. However, the vertical opening distance was significantly decreased during infusion of HS at half-maximal and maximal opening (P < 0.05). Conclusions: It is concluded that experimental pain affects EMG-activity differentially in jaw-closing muscles in different opening positions of the jaw.     

Effect of transcutaneous electrical nerve stimulation on pain perception threshold and pain tolerance level of human teeth subjected to electrical stimulation

Abstract The effect of low current, sub-sensation transcutaneous electrical nerve stimulation on pain threshold and pain tolerance level of human teeth subjected to stimulation with an electrical pulp tester was studied. Electrodes were attached to the patients via a patch between the thumb and first finger and a damp cotton roll in the vestibule over the apex of the tooth to be tested. No significant differences between the values for the baseline, experimental and placebo pain perception thresholds were found. Nor were significant differences found between the average experimental and placebo values concerning pain tolerance level. However, in 1 individual the pain tolerance level was not reached at the highest level of stimulation from the electrical pulp tester.     

正畸与正颌联合治疗成人骨性反后咀嚼肌肌电变化

目的 :检查对比分析成人骨性反牙合正畸与正颌手术联合矫治前后的主要咀嚼肌肌电 ,揭示正畸与正颌手术联合矫治后咀嚼肌功能的变化规律。方法 :2 0名正畸与正颌手术联合治疗的成人骨性反牙合患者 ,利用肌电图仪测试治疗前后咬肌、颞肌前束、二腹肌前腹在功能活动中肌电变化。结果 :正畸与正颌手术联合矫治对咬肌、颞肌前束、二腹肌前腹的功能活动均有不同程度的影响 ,其中对咬肌的功能影响最明显。结论 :正畸与正颌手术联合治疗成人骨性反牙合 ,咀嚼肌的异常肌张力多数得到纠正 ,但咀嚼肌的功能未能得到满意的恢复 ,咀嚼肌的功能恢复是一个复杂而长期的过程 ,还需要较长的功能锻炼恢复期     

The influence of stimulus type and stimulus strength on the silent period in human masticatory muscles

The silent period in the jaw-closing muscles of nine healthy subjects was investigated. The stimulus types used were the open–close–clench movement (OCC), the mechanical chin tap and electrical skin stimulation. Irrespective of the jaw-closing speed for the OCC movements only the unmeasurable and single type silent periods were observed. Increasing the chin tap strength resulted in a decreasing percentage of single type silent periods and an increasing number of depressed, double and merged silent periods. The duration of the short and combined silent period was shorter for the OCC movements than for the chin taps. For the chin taps an increasing stimulus strength resulted in longer silent periods. Only the transition from hard to painful chin tap showed a slight, but significant decrease in short silent period duration. The beginning of the late inhibitory period, which could sometimes be evoked by electrical skin stimulation, coincided with the beginning of the second inhibitory phase of the chin-tap evoked double silent period. The long silent period as shown by one of the subjects cast doubt on the validity of the relationship between silent period duration and TMJ dysfunction.     

Skeletal muscle function and fibre types: the relationship between occlusal function and the phenotype of jaw-closing muscles in human

Mammalian skeletal muscle cells are composed of repeated sarcomeric units containing thick and thin filaments of myosin and actin, respectively. Excitation of the myosin ATPase enzyme is possible only with presence of Mg-ATP and Ca(2+). Skeletal muscle fibres may be classified into several types according to the isoform of myosin they contain. Nine isoforms of myosin heavy chain are known to exist in mammalian skeletal muscle including type I, IIA, IIB, IIX, IIM, alpha, neonatal, embryonic, and extra-ocular. Healthy adult human limb skeletal muscle contains type I, IIA, IIB, and IIX myosin heavy chains. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' myosin heavy chain. Adult human jaw-closing muscles, however, do not contain IIM myosin. Rather, they express type I, IIA, IIX (as in human limb muscle), and myosins typically expressed in developing or cardiac muscle. The morphology of human jaw-closing muscle fibres is also unusual in that the type II fibres are of smaller diameter that type I fibres, except in cases of increased function and hypertrophy. This paper describes the relationship of fibre types and motor unit function to changes in human occlusion and masticatory activity. Refereed Scientific Paper     

Influence of the thickness of soft tissues overlying human masseter and temporalis muscles on the electromyographic maximal voluntary contraction level

Skinfold measurements by means of calipers and the use of linear regression functions, representing relationships between maximal EMG activity and skinfold thickness, provide a simple and non-invasive procedure to diminish the influence of the thickness of the subcutaneous tissues overlying jaw-elevator muscles on electromyographic data of the maximal voluntary contraction (MVC) level. This method, which allows an improved comparison between different subject or muscle groups in terms of neuromuscular capacity, has been applied to MVC values from the masseter and the anterior temporal muscles (surface EMG) of 21 healthy males, 14 healthy females, and 14 females suffering from myogenous temporomandibular disorders (TMD). Non-corrected MVC values from both muscle groups were larger for the male controls than for the female controls. As the skinfold thickness was smaller for males than for females, these MVC levels did not differ significantly after correction for skinfold thickness. As the skinfold thickness was very similar for the female TMD patients and the controls, the correction method did not appreciably change the lower MVC values of the TMD patients.     

Effect of sustained contraction on motor unit action potentials and EMG power spectrum of human masticatory muscles

The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift.     

Trigeminal convergence from human teeth: influence of contralateral stimulation and stimulus frequency on the pain perception threshold

The arrangement of trigeminal nerve fibres and their secondary and subsequent neurones in the central nervous system is incompletely understood, but primary neurones from teeth pass to the trigeminal spinal nucleus on the same side. This means that stimulation of adjacent teeth on one side of the mouth could be associated with spatial summation in the trigeminal spinal nucleus, and this should reduce the intensity of stimulation required to reach the pain perception threshold. If the two teeth stimulated were on opposite sides of the mouth, no spatial summation would be possible at that level, so the pain perception threshold would be relatively higher. To test the hypothesis, electrical stimuli were applied to the teeth of human subjects who were able to indicate when the pain perception threshold was reached. This threshold was determined for single teeth and also for a series of teeth. The series started with an upper canine and extended tooth by tooth to the contralateral canine. The threshold value for two or more teeth was called the multiple value (M) and this was compared with the added individual values (A) for the same number of teeth. The $\text{M}\text{A}$ ratio thus obtained was not decisively affected by stimulation being extended to teeth across the midline.The investigation was made using two stimulation frequencies, 50 and 7 Hz. and the same result was obtained in each series. However, the peak current values were consistently higher when the lower frequency was used. This result had been predicted, and is explained by there being less opportunity for temporal summation at the synapses when using the lower frequency.     

Effect of cold pressor stimulation (4 degrees C) on human masseter muscle haemodynamics during and after sustained isometric contraction

The effect of cold pressor (CP) stimulation and sustained isometric contraction on the blood volume of the right masseter muscle was examined in seven healthy males, who performed 1 min of isometric jaw clenching at 50% of their maximum voluntary contraction without, with and again without a 4 degrees C CP stimulation. Total haemoglobin was measured in the masseter before, during and after the contraction task using near-infrared spectroscopy. CP stimulation during the isometric contraction diminished the magnitude of the contraction-induced decrease of blood volume when compared to the trials without CP stimulation. However, in the immediate post-contraction period (while the CP stimulation was still in place), no increase in blood volume above the usual post-contraction hyperaemia was evident. Once the CP stimulation had been removed, there was a clear decrease (faster return to baseline) in the vasodilation occurring in the post-contraction period. This diminished period of vasodilation occurred in spite of the fact that the vascular resistance (blood pressure) and heart rate were still substantially elevated by the CP effect during this same period. These data suggest that the strong CP stimulation produced a biphasic response. First, there was an early-onset strong vasodilation (during CP), which was followed by a period of diminished vasodilation, suggesting that an active, but delayed, vasoconstrictive drive may be induced by the CP stimulus.     

Effect of a nociceptive trigeminal inhibitory splint on electromyographic activity in jaw closing muscles during sleep

The nociceptive trigeminal inhibitory (NTI) splint has been claimed to decrease the electromyographic (EMG) activity of jaw-closing muscles and relieve symptoms of various types of temporomandibular disorders (TMD) and bruxism. The present study was designed to address the question about EMG-changes during sleep. Ten patients (age: 23-39 years) with a self-report of tooth-grinding during sleep were recruited. Patients were examined at baseline and after each treatment period with the use of the Research Diagnostic Criteria for TMD. A portable EMG-device was used to record EMG-activity from the masseter muscle during sleep. The patients received two 2-week splint treatments in a randomized cross-over fashion; an NTI splint and a standard flat occlusal splint (OS). EMG data were analysed according to published criteria. Using a 10% of maximum clenching EMG-activity cut-off threshold to determine the number of EMG-events h(-1) of sleep, the NTI splint was associated with a significant reduction (9.2 +/- 3.2 events h(-1)) compared with baseline EMG (19.3 +/- 4.0; anova: P = 0.004, Tukey post hoc: P = 0.006), whereas there were no differences between the OS (16.2 +/- 4.7) and baseline EMG (19.2 +/- 4.1; P = 0.716). There were no effects of either NTI or OS on clinical outcome measures (anovas: P > 0.194). This short-term study indicated a strong inhibitory effect on EMG-activity in jaw closing muscles during sleep of the NTI, but not the OS. However, the EMG-activity was not directly related to clinical outcome. Further studies will be needed to determine long-term effects and possible side effects of the NTI splint.     

5-氮杂-2'-脱氧胞苷对涎腺腺样囊性癌细胞系细胞MGMT和hMLH1基因表达的影响

目的 观察5-氮杂-2’-脱氧胞苷(5-aza-2-deoxycytidine,5-Aza-CdR)对体外培养人涎腺腺样囊性癌(salivary adenoid cystic carcinoma,SACC)细胞系细胞O6-甲基鸟嘌呤-DNA甲基转移酶(O6-methylguanine-DNA methyhransferase,MGMT)和人类mutL同源物1(homo sapiens mutL homolog 1,hMLH1)基因表达的影响,探讨DNA甲基转移酶抑制剂应用于SACC治疗的可行性及机制.方法 用不同浓度5-Aza-CdR分别处理体外培养SACC-83和SACC-LM细胞作为药物处理组,以药物处理浓度0 μmol/L为对照组.甲基噻唑基四唑法确定5-Aza-CdR的半数抑制浓度(half maximal inhibitory concentration of a substance,IC50);实时聚合酶链反应和反转录聚合酶链反应检测用药后细胞中MGMT和hMLH1 mRNA表达水平.结果 药物处理细胞24 h后细胞形态发生变化,并且随时间延长变化愈加显著.5-Aza-CdR对SACC-83和SACC-LM细胞的IC50分别为(11.816±0.023)、(5.751± 0.049) μmol/L.经5-Aza-CdR处理后,SACC-83和SACC-LM细胞中MGMT和hMLH1 mRNA表达增高1～5倍,MGMT和hMLH1在药物处理组与对照组之间的表达差异有统计学意义(P＜0.01).结论 5-Aza-CdR可改变细胞形态,上调MGMT和hMLH1 mRNA的表达,其机制可能与5-Aza-CdR反转MGMT、hMLH1基因DNA启动子区高甲基化状态有关.     

Effect of acetaminophen, ibuprofen and methylprednisolone on different parameters of human osteoblast-like cells

Anti-inflammatories are divided between steroidal and non-steroidal drugs according to their chemical nature. They are frequently used in combination to achieve analgesia and reduce inflammation after surgery, especially when bone tissue is affected. However, their effects on bone level are not well known, and results of the scant studies in humans have been contradictory.

Objective

To study the short-term effect of ibuprofen, acetaminophen and methylprednisolone at therapeutic doses on different cell parameters of human osteoblasts in culture.

Design

Osteoblasts were derived from samples of human bone sections obtained during third molar surgery. Cell lines were incubated in culture medium with different concentrations of anti-inflammatories (5 or 25 μM of ibuprofen or acetaminophen, 10⁻⁶ or 10⁻⁸ M of methylprednisolone) for 24 or 48 h. Flow cytometry was used to study proliferation, antigenic profile, phagocytic activity and cell cycle.

Results

All three anti-inflammatories inhibited osteoblastic proliferation, but no significant cell cycle changes were observed. The drugs had no effect on antigenic profile or phagocytic capacity.

Conclusion

These results suggest that ibuprofen, acetaminophen and methylprednisolone at therapeutic doses reduce osteoblast growth without affecting other cell parameters, such as antigenic profile or cell cycle. Use of these drugs should be reconsidered in clinical situations that require a rapid healing of bone defects.     

Spectral analysis of the electromyogram: A microcomputer system for use in the clinic and laboratory

The electromyographic activity (EMG) of the jaw musculature is of interest in relation to the diagnosis of certain facial pain conditions in which muscle hyperactivity has been implicated. The mean power frequency of the EMG is of special relevance; it is known to be sensitive to experimentally induced fatigue which has been studied as a pathophysiological model of the temporomandibular joint pain dysfunction syndrome. An inexpensive microcomputer-based system is described which is suitable for performing spectral analysis in laboratory experiments and in the clinical situation.     

Correlation between numbers of cells in human dental pulp and age: Implications for age estimation

ObjectiveThe aim of this study was to investigate correlations between dental pulp cell count of odontoblasts, subodontoblasts and fibroblasts and age, within different age groups. Formulation of regression equations using the dental pulp cell count for predicting age was attempted.DesignEighty-one extracted teeth were grouped into two age groups (6–25 years, 26–80 years). The teeth were demineralized and histological sections were prepared for cell count. Regression equations were generated from regression analysis of cell count and tested for age estimation.ResultsThe number of dental pulp cells were found to increase until around the third decade of life and following this, the odontoblasts and subodontoblasts cell numbers began to decline while the fibroblasts seemed to remain almost stationary. The Pearson correlation test revealed a significant positive correlation between the cell number for all type of cells and age in the 6–25 years group (r = +0.791 for odontoblasts, r = +0.600 for subodontoblasts and r = +0.680 for fibroblasts). In the 26–80 years age group, a significant negative correlation of the odontoblasts (r = −0.777) and subodontoblasts (r = −0.715) with age was observed but for fibroblasts, the correlation value was negligible (r = −0.165). Regression equations generated using odontoblasts and subodontoblasts cell number were applicable for age estimation. The standard error of estimates (SEEs) were around ± 5 years for 6–25 years and ± 8 years for 26–80 years age groups. The mean values of the estimated and chronological ages were not significantly different.ConclusionsA significant correlation between the cell count of odontoblasts and subodontoblasts with age was demonstrated. Regression equations using odontoblasts and subodontoblasts cell number can be used to predict age with some limitations.     

Effects of prolonged gum chewing on pain and fatigue in human jaw muscles

Gum chewing has been accepted as an adjunct to oral hygiene, as salivary stimulant and vehicle for various agents, as well as for jaw muscle training. The aim of this study was to investigate the effects of prolonged gum chewing on pain, fatigue and pressure tenderness of the masticatory muscles. Fifteen women without temporomandibular disorders (TMD) were requested to perform one of the following chewing tasks in three separate sessions: chewing a very hard gum, chewing a soft gum, and empty-chewing with no bolus. Unilateral chewing of gum or empty chewing was performed for 40 min at a constant rate of 80 cycles/min. In each session, perceived muscle pain and masticatory fatigue were rated on visual analog scales (VAS) before, throughout, and after the chewing task. Pressure pain thresholds (PPTs) of masseter and anterior temporalis muscles were assessed before and immediately after the chewing tasks, and again after 24 h. The VAS scores for pain and fatigue significantly increased only during the hard gum chewing, and after 10 min of recovery VAS scores had decreased again, almost to their baseline values. No significant changes were found for PPTs either after hard or soft gum chewing. The findings indicate that the jaw muscles recover quickly from prolonged chewing activity in subjects without TMD.     

The effects of stimulus polarity and electrode area on the threshold to monopolar stimulation of teeth in human subjects, with some preliminary observations on the use of a bipolar pulp tester

No consistent relationship was found between the threshold to electrical stimulation of human teeth and the area of electrode contact. The different patterns observed can be accounted for on the basis of different sites of initiation of nerve impulses. In some cases, the threshold increased progressively as the area of the electrode was increased and in these cases it appears that nerves were being stimulated in the dentine or superficial layers of the pulp. Bipolar stimulation gave thresholds which were similar to those obtained with monopolar cathodal stimulation and lower than those with monopolar anodal stimulation.     

Effect of salivary stimulation on erosion of human and bovine enamel subjected or not to subsequent abrasion: an in situ/ex vivo study

This in situ/ex vivo study evaluated whether saliva stimulated by chewing gum could prevent or reduce the wear and the percent change in microhardness (%SMH) of bovine and human enamel submitted to erosion followed by brushing abrasion immediately or after 1 h. During 2 experimental 7-day crossover phases, 9 previously selected volunteers wore intraoral palatal devices, with 12 enamel specimens (6 human and 6 bovine). In the first phase, the volunteers immersed the device for 5 min in 150 ml of cola drink, 4 times per day (at 8, 12, 16 and 20 h). Immediately after the immersions, no treatment was performed in 4 specimens, 4 other specimens were immediately brushed (0 min) using a fluoride dentifrice, and the device was replaced into the mouth. After 60 min, the remaining 4 specimens were brushed. In the second phase, the procedures were repeated, but after the immersions, the volunteers stimulated the salivary flow rate by chewing a sugar-free gum for 30 min. Changes in wear and %SMH were measured. ANOVA and Tukey's test showed statistical differences (p<0.05) for the following comparisons. The chewing gum promoted less wear and %SMH. A decreasing %SMH and an increasing enamel wear were observed in the following conditions: erosion only, 60 min and 0 min. The human enamel presented greater %SMH and less wear compared to bovine enamel. The data suggest that the salivary stimulation after an erosive or erosive/abrasive attack can reduce the dental wear and the %SMH.