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 chin tap force and bite force parameters on the duration of the electromyographic silent period

Controversy exists as to whether chin tap force and bite force affect the duration of the electromyographic silent period following the jaw jerk reflex during isometric contraction of the elevator muscles of the mandible. This study demonstrates that statistical trends exist showing increased silent period duration for increased tap forces and decreased silent period duration with increased bite forces.     

A standardized system for evoking masseteric silent periods with decreased variance

Masseteric silent periods have been evoked in a group of normal subjects under a standardized system and under nonstandardized conditions. In the designed system, head position, electrode placement, bite force, tap force, direction of tap, and surface zone of tap force delivery were controlled. Analysis of data confirmed the hypothesis that standardization of the procedure for eliciting the silent period results in measurements of duration with decreased standard deviations and variances. In the present study, under the standardized system the SPD range of standard deviations was between 1.37 and 3.68 (mean 2.97) and the range of variances was between 1.89 and 13.54 (mean 8.85). The recorded low variability suggests a high degree of reproducibility of the system. High reproducibility and low variability of measurements are necessary if an accurate measure of silent period duration is to be achieved and used in the interpretation of diagnostic findings for craniomandibular disorders.     

The effect of acrylic bite plane splints and their vertical dimension on jaw muscle silent period in healthy young adults

A significant question relative to treatment and disappearance of symptoms is raising the bite in combination with a maxillary bite plane splint in patients with TMJ muscle dysfunction. The objective of this research was to investigate the effect, if any, occlusal bite plane splints have on the latency and duration of the mention tap silent period and particularly whether the degree to which the bite is raised is of significance. Recordings were made in healthy young adults from both anterior temporal and masseteric muscles while subjects were clenching at their 70% maximum clenching effort. Placement of a splint significantly (P less than 0.05) prolonged the silent period duration (SPD). However, mean SPD values taken at two different vertical raised bites did not differ significantly (P greater than 0.05). The anterior temporal muscle SPD was less sensitive to a smaller change of vertical dimension than the masseteric SPD. Silent period latencies remained unchanged in all experimental conditions.     

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.     

Bite-opening Mechanics as Applied in the Begg Technique

Abstract

In the Begg Technique, factors controlling the anterior intrusive force provided by the archwire have yet to be fully clarified. The rationale for bite opening with very light forces, the effect of Class II elastics on intrusive force magnitude and the intrinsic quality of ‘Australian’ wire in bite opening are examined in this paper. A formula is presented which allows the intrusive force that archwires exert in different individuals to be predicted. The values derived from the formula were compared with case model measurements. It was found that the intrusive force of the archwire was affected by the length of the individual dental arch. The magnitude of this intrusive force was seen to increase gradually during the period of bite opening and appeared to be related to the use of Class II elastics. The study revealed factors which affected the magnitude of the intrusive force.     

Duration of the electromyographic silent period following the jaw-jerk reflex in human subjects.

During voluntary jaw clenching, a sharp tap to the menton of the mandible resulted in a transitory silent period (pause) in the electromyographic activity of the masseter and anterior temporalis muscles. Factors that could influence the duration of the silent period were studied, including direction and magnitude of the stimulus applied by the operator, the amount of muscular effort exerted by the subjects, and varying occlusal vertical dimensions. Decreased isometric muscle force resulted in statistically significant increases in silent period durations.     

Functional properties and regional differences of human masseter motor units related to three-dimensional bite force

The aim of this study was to estimate numerically the properties of masseter motor units (MUs) in relation to bite force magnitude and direction three-dimensionally and to confirm the hypothesis that the properties differ between different parts of the muscle by means of simultaneous recording of MU activity along with the MU location and three-dimensional (3D) bite force. The MU activity of the right masseter of four healthy men was recorded using a monopolar needle electrode in combination with a surface reference electrode. The location of the needle electrode was estimated stereotactically with the aid of magnetic resonance images and a reference plate. The magnitude and direction of the bite force was recorded with a custom-made 3D bite force transducer. The recorded bite force was displayed on a signal processor, which enabled the participant to adjust the direction and magnitude of the force. The activities of 65 masseter MUs were recorded. Each MU had specific ranges of bite force magnitude and direction (firing range: FR) and an optimum direction for recruitment (minimum firing threshold: MFT). There was a significant negative correlation between MFT and FR width. There were functional differences in MU properties between the superficial and deep masseter and between the superficial layer and deep layer in the superficial masseter. These results indicate that the contribution of human masseter motor units to bite force production is heterogeneous within the muscle.     

The effect of voluntary activity on the masseteric silent period duration

This study examined both TMJ and normal groups for any changes in the masseteric silent period with variation of the subjects' occlusal force. An analog meter was used to give each subject feedback on how hard the teeth were clenched together. Five silent periods were elicited at each of the four levels of occlusal force from 40% to 100% of maximum force.Results showed a small decrease in silent period duration for both groups when occlusal force was increased.     

Variations in activities of human jaw muscles depend on tooth-tipping moments

Static mechanical analyses of the masticatory apparatus often assume that jaw muscle activity, as measured using electromyography (EMG), is linearly and constantly related to magnitude of bite force during biting, regardless of bite force-induced tooth-tipping moments. The objective of this study was to test the hypothesis that the relationship between EMG of the jaw muscles and bite force varies with the magnitude and sign of tooth-tipping moments. Seven healthy male subjects produced unilateral static occlusal forces at five biting positions, resulting in sequential changes from buccal (+) to lingual (-) tipping moments on the mandibular first molar. Jaw muscle activities were recorded bilaterally using surface (for temporalis and masseter muscles) and indwelling (for lateral pterygoid muscles) electrodes. Bite forces were recorded and controlled using custom devices. EMG versus bite force data were plotted and regression relationships were calculated for each subject, muscle and biting position. Linear regression analysis, analysis of variance and Bonferroni adjusted least significant difference tests were used to determine the effects of muscle, side (ipsilateral, contralateral) and biting position within subjects. It was found that the relationship between EMG and bite force for different tipping moments differed significantly within a subject and muscle. This was most common in the lateral pterygoid and temporalis muscles (all P25:1. In the masseter muscle, the EMG:bite force relationship for different tipping moments differed significantly in one subject (P<0.008); slopes varied up to 4.6:1. In conclusion, the relationship between EMG and bite force was linear. However, the slopes of the relationship changed significantly depending on sign (+, -) and magnitude of tipping moments acting on the molars.     

Regulation of bite force increase during splitting of food

The purpose of the study was to analyze how increases in the bite force, during the splitting of food morsels of different hardness, are modulated, and to evaluate the role of periodontal mechanoreceptors in this control. Fifteen subjects were instructed to hold and split food morsels of different hardness (peanuts and biscuits) between a pair of opposing central incisors before and during anesthesia of the teeth. The split occurred at an average bite force of 9 N for biscuits and at an average bite force of 18 N for peanuts. The duration of the split phase was longer, and the split force rate higher, for peanuts compared with biscuits. Furthermore, a steeper force trajectory was observed for the peanut. During anesthesia of the teeth, the duration of the split phase increased and the mean split force rate decreased for peanuts. Force trajectories for peanuts and biscuits were indistinguishable during anesthesia. The present results show that when higher bite forces are needed to split a morsel, both the duration and the rate of the bite force produced is increased. Furthermore, adaptation of the bite force rate to the hardness of the food is dependent on information from periodontal mechanoreceptors.     

Three-dimensional analyses of human bite-force magnitude and moment.

The effect of the three-dimensional orientation of occlusal force on maximal bite-force magnitude was examined in seven human subjects at three different unilateral anteroposterior bite positions (canine, second premolar and second molar). At each position, bite-force magnitude was registered in 17 precisely defined directions using a three-component force transducer and a feedback method. In addition, to assess the efficiency of transfer of muscle to bite force, for bites produced in the sagittal plane, moment-arm length was determined and the produced bite-force moment calculated. The results showed that the largest possible bite force was not always produced in a direction perpendicular to the occlusal plane. Generally, maximal bite force in medial and posterior directions was larger than that in, respectively, corresponding lateral and anterior directions. In each direction the produced force was larger at the posterior bite point than at the anterior bite point. The combined moment produced by the jaw muscles was largest for vertical bites, smallest for posteriorly directed bites and intermediate for anteriorly directed bites. In the case of vertically and anteriorly directed bites the produced moment did not vary significantly with the bite position. Hence, for these bite positions the jaw closing moment of the muscles must have kept constant. In the case of posteriorly directed bites the produced moment decreased when bite position changed from the anterior to the posterior side of the dentition. This indicated that jaw muscle activity had declined.     

Contribution of jaw muscle size and craniofacial morphology to human bite force magnitude

The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometrics and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalometric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.     

The silent period in the masseter and the anterior temporalis muscles in adult patients with mild or moderate mandibular dysfunction symptoms

The electromyographical silent period in the masseter and the anterior temporalis muscles during tooth tapping and jaw jerk were studied in patients with fairly mild temporomandibular joint dysfunction symptoms. The length of the silent periods in the patient group did not differ generally from that in a control group. During tooth tapping, however, patients with distinct muscular disorders had shorter silent period duration (7.7 ms) than patients with other symptoms or when compared with control subjects (10.5 and 11.3 ms, respectively). The duration returned to normal after correction of the muscular disorders. This finding suggests that the duration of the silent period is affected by the muscle condition. Patients with obvious muscular disorders of mild to moderate magnitude, thus, may show a shorter silent period duration during tooth tapping.     

The silent period duration of the masticatory muscles

This study was conducted to determine whether the reflex activity of the masticatory muscles is altered in prostheses wearers. The electromyographic silent period was measured on an oscilloscope screen. Thirty subjects were examined. Five subjects had natural dentitions. Twenty-five partially edentulous subjects wore removable prostheses. The silent period duration reached 18 to 21 ms on the masseter muscles and 20 to 22 ms on the temporal muscles. These values were not significantly different for subjects with and without teeth and in the control group. The duration of the silent period was the same for patients wearing prostheses and for subjects with natural teeth. This finding suggests that wearing a prosthesis does not change the normal activity of the masticatory muscles.     

The variability of bite force measurement between sessions, in different positions within the dental arch

The effect of measuring bite force with different patterns of transducer on different occasions was studied. Maximum voluntary bite force was measured in eight volunteers. Three transducer positions, each with a different pattern of transducer, were used; between the anterior teeth, between the second premolar and the first molar on one side and between the second premolars and first molars on both sides. Visual feedback of force was provided. Two sets of five maximum clenches were recorded with a rest period in between. This sequence was repeated for each transducer and the experiment was repeated on three different days. The highest forces were measured with the bilateral posterior transducer (mean 580 N, s.d. 235) and the lowest on the anterior transducer (mean 286 N, s.d. 164). The standard deviations of the bite force mean values were used as an indication of the variability and were subjected to a non‐parametric anova (Kruskal–Wallis). The forces recorded with each transducer position were significantly different between the transducers ( P < 0·01) and the maximum bite force showed least variability when measured between the posterior teeth on one side only. There was little difference in bite force between the three different sessions ( P  ≥ 0·05) when measured in the same position within the dental arch, whichever of the three positions that may be.     

Bite force determination in children with primary dentition

The aim of this study was to determine the bite force with primary dentition in 30 children with normal occlusion (group I), cross bite (group II) and open bite (group III). The magnitude of the bite force was determined through a pressurized transmitter tube (pressure sensor MPX 5700 Motorola), which was connected to a converse analog/digital electronic circuit. The children bit the tube with maximum force three times successively for 5 s, with a 10 s interval among each bite, and the sign was sent directly to the computer. The highest value of the three, for each patient, was considered. Analysis of variance evaluated difference among the three groups. The means of maximum bite force were 213 17, 249 63 and 241 19 N for the groups, respectively, and there were no significant statistical differences among them (P > 0.05). The analysis of correlation showed that the weight, height and bite force presented weak positive correlation (r=0.24 and 0.23). It was concluded that in the studied groups the type of occlusion did not affect the maximum values of the bite force and body variables had a small influence in this magnitude.     

Bite force in children with bruxism

The bite force of 51 twelve-year-old bruxists was compared with that of a control group of the same age, in order to establish whether bruxism affects bite force and whether there is any connection between the degree of tooth abrasion and bite force. Criteria for bruxism were bruxo facets in the bite and, in the same children, teeth-grinding at the time of examination. No differences in bite force values for bruxists and non-bruxists were found for either very light bite or maximum bite. One group with dentine facets had a higher bite force value for very light bite than the children with enamel facets. Otherwise there was no difference between the various facet groups regarding the bite force produced.     

Mechanical capabilities of the human jaw muscles studied with a mathematical model

The human muscles of mastication have complex shapes with large attachment areas. This suggests a variety of bite force directions and magnitudes. The possible range of these and the concomitant joint force of each individual muscle were determined by a mathematical model describing static equilibrium conditions in the sagittal plane. The range of force directions for each muscle was defined by the action lines of the most anterior and most posterior (for the lateral pterygoid, most superior and most inferior) muscle fibre bundles. Calculations from the various directions of the reaction force in the temporomandibular joint demonstrated that each muscle can produce a unique variety of bite force directions. Except for the lateral pterygoid and posterior temporalis, the range and orientation of possible bite forces was closely related to the orientation of the joint force. In general, at the canine tooth the bite forces were directed more posteriorly than at the second molar. Within a muscle, distinct portions may produce considerably different bite force magnitudes; the largest bite forces are produced at horizontal and vertical joint force directions. The posterior portions of the deep masseter and temporalis muscles and the lateral pterygoid muscle have the largest mechanical advantage. In the majority of muscles the magnitude of the joint reaction force is smallest at an oblique joint force direction.     

Electromyographic heterogeneity in the human temporalis muscle

This study examined the possible existence of regional differences in activation of the temporalis muscle. Since the muscle is fan-shaped, its fibers pull in different directions. This suggests regional specialization for different motor tasks. EMG activity was registered by six bipolar fine-wire electrodes inserted anteroposteriorly across the muscle belly. Muscle signals were recorded during different static bite tasks for which both the direction and magnitude of bite force were specified. The results showed that the ratio of activities of the six muscle regions changed with the direction of bite force. This indicates a partitioning of the excitatory command to the muscle's motoneuron pool. Alteration in activity with changing bite-force direction was generally the smallest in the anterior-most region of the muscle, the largest in the posterior-most region, and the intermediate in the interjacent regions. Generally, all muscle regions exhibited the highest EMG activity when the bite force was in an approximately posterolateral direction. The muscle was activated uniformly only for bites in this preferential direction. Activity in the regions appeared to be scaled up or down in a linear way according to the desired bite-force level. The results indicate that the direction of pull of the muscle and the maximal force it can produce are not fixed, but depend on the direction of bite force.