Relationships between the size, position, and angulation of human jaw muscles and unilateral first molar bite force

Human subjects commonly show large variations in bite force produced at the first molar teeth. To evaluate the role of muscle cross-sectional sizes and lever arms in bite-force production, we correlated these variables in 11 healthy adults. Axial and coronal images obtained by magnetic resonance were combined with conventional lateral cephalograms and dental cast data to reconstruct the craniomandibular morphology in each subject. The cross-sectional sizes of the right masseter and medial pterygoid muscles, their lever arms, and the bite-point lever arms were measured directly from these reconstructions. Physiological recordings of bite force were made in the region of the right first molar by means of a customized transducer aligned perpendicular to the functional occlusal plane. The average bite force for the sample as a whole was 189 +/- 78 N. The coefficients of variance were greater for bite forces, and for the cross-sectional sizes of the two muscles, than for their respective lever arms. Highly significant Pearson Product Moment correlation coefficients (p less than 0.005) were found between masseter and medial pterygoid cross-sectional size, and between the cross-sectional size of each muscle and bite force. No significant correlations (p greater than 0.1) were found between muscle or bite-point lever arms and bite force. Despite the fact that craniofacial spatial morphology may differ among subjects, jaw muscle size alone seems to explain most of the variation in bite force reported by ourselves and others.     

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.     

Maximal bite force and its association with signs and symptoms of TMD, occlusion, and body mass index in a cohort of young adults

The purpose of this population-based cohort was to measure maximal bite force (MBF) in the molar and incisal regions and to examine whether MBF was associated with TMD, gender, occlusion (in terms of overjet, overbite, and total number of occluding contacts), and body mass index (BMI). MBF in the molar and incisal regions was measured using a calibrated method in 384 (196 males, 188 females) and 357 (181 males, 176 females) subjects, respectively. Two attempts in each region (right molar, left molar, and incisal) were made in random order. The subjects completed a multiple-choice questionnaire including subjective symptoms of TMD and were subsequently clinically examined. Helkimo's clinical dysfunction index and BMI were calculated. The mean MBF value in the molar region was significantly higher in males (878 N, SD 194) than in females (690 N, SD 175) (p < 0.001). The incisal forces were 283 N (SD 95) and 226 N (SD 86) (p < 0.001), respectively. According to multiple linear regression, TMJ discomfort was significantly negatively associated with MBF in the molar region (p < 0.05) and overjet was significantly negatively associated with maximal incisal bite force (p < 0.05). No significant associations between MBFs and body mass were found. The results demonstrate that in a population-based cohort of young adults signs, and symptoms of TMD and studied occlusal factors, unlike body mass, associate independently with MBF.     

Maximal Bite Force and Its Association with Signs and Symptoms of TMD,Occlusion, and Body Mass Index in a Cohort of Young Adults

The purpose of this population-based cohort was to measure maximal bite force (MBF) in the molar and incisal regions and to examine whether MBF was associated with TMD, gender, occlusion (in terms of overjet, overbite, and total number of occluding contacts), and body mass index (BMI). MBF in the molar and incisal regions was measured using a calibrated method in 384 (196 males, 188 females) and 357 (181 males, 176 females) subjects, respectively. Two attempts in each region (right molar, left molar, and incisal) were made in random order. The subjects completed a multiple-choice questionnaire including subjective symptoms of TMD and were subsequently clinically examined. Helkimo's clinical dysfunction index and BMI were calculated. The mean MBF value in the molar region was significantly higher in males (878 N, SD 194) than in females (690 N, SD 175) (p<0.001). The incisal forces were 283 N (SD 95) and 226 N (SD 86) (p<0.001), respectively. According to multiple linear regression, TMJ discomfort was significantly negatively associated with MBF in the molar region (p<0.05) and overjet was significantly negatively associated with maximal incisal bite force (p<0.05). No significant associations between MBFs and body mass were found. The results demonstrate that in a population-based cohort of young adults signs, and symptoms of TMD and studied occlusal factors, unlike body mass, associate independently with MBF.     

Muscle function and craniofacial morphology: a clinical study in patients with myotonic dystrophy

The occlusal traits and the craniofacial morphology were studied in patients with an altered muscle function caused by myotonic dystrophy. Twenty-four adult patients were examined and compared with a matched group of healthy individuals. The condition of the masticatory muscles was evaluated by measuring the maximal bite force. The dental arches and the occlusal traits were analysed on dental casts. Lateral cephalograms were taken in the patients with myotonic dystrophy to study the craniofacial morphology. It was found that the patients suffering from myotonic dystrophy had weak masticatory muscles, which might be caused by the disease. A high prevalence of malocclusions (postnormal occlusion, anterior open bite and lateral cross bite) was found among these patients. Their craniofacial morphology showed a vertical aberration, characterized by a large angle between the mandibular and palatal planes and a steep mandible. These findings seem to be most pronounced in patients with an early onset of the disease and support the hypothesis that reduced muscle function may cause changes in the craniofacial morphology.     

Muscle and joint forces under variable equilibrium states of the mandible

It is well established that subjects without molars have reduced ability to comminute foods. However, epidemiological studies have indicated that the masticatory system is able to functionally adapt to the absence of posterior teeth. This supports the shortened dental arch concept which, as a prosthetic option, recommends no replacement of missing molars. Biomechanical modeling, however, indicates that using more anterior teeth will result in a larger temporomandibular joint load per unit of bite force. In contrast, changing bite from incisor to molar position increases the maximum possible bite force and reduces joint loads. There have been few attempts, however, to determine realistic joint loads and corresponding muscular effort during generation of occlusal forces similar to those used during chewing with intact or shortened dental arches. Therefore, joint and cumulative muscle loads generated by vertical bite forces of submaximum magnitude moving from canine to molar region, were calculated. Calculations were based on intraoral measurement of the feedback-controlled resultant bite force, simultaneous electromyograms, individual geometrical data of the skull, lines of action, and physiological cross-sectional areas of all jaw muscles. Compared to premolar and canine biting, bilateral and unilateral molar bites reduced cumulative muscle and joint loads in a range from 14% to 33% and 25% to 53%, respectively. During unilateral molar bites, the ipsilateral joints and contralateral muscles were about 20% less loaded than the opposing ones. In conclusion, unilateral or bilateral molar biting at chewing-like force ranges caused the least muscle and joint loading.     

A novel bite force recorder and maximal isometric bite force values for healthy young adults

Human bite forces have been studied with several types of equipment, and the maximal values reported have varied greatly. In the present study, a new bite force recorder was developed to measure human bite forces. When measuring maximal bite force, the mandible is, laterally and sagittally, almost in the intercuspal position, while the vertical opening of the jaws in the molar region is about 14 mm. Several teeth bite upon the housing. A quartz force transducer serves as a sensory unit. A microprocessor produces a numeric result, shown on a liquid crystal display (LCD). In order to adapt the sensor to be a part of a bite force recorder, we designed a unilateral housing of nonhardened tool steel. In laboratory calibration tests, a series of loads from 112.8 to 1691.5 N was used. The maximal bite forces of healthy undergraduate dental students, 15 men and 15 women, were investigated. The results for both genders remarkably exceeded the values previously reported for unilateral housings. The mean maximal bite force value in the molar region was 847 N for men and 597 N for women. The finding that pain or lack of muscular strength most often limited the clenching suggests that the actual masticatory potential was registered.     

Bite force and temporomandibular disorder in juvenile chronic arthritis

summary The aim of this study was to investigate the functional condition of the stomatognathic system in children suffering from juvenile chronic arthritis, with respect to bite force and temporomandibular disorder in relation to radiographic abnormalities of the mandibular condyle, occlusal factors and systemic disease parameters. Thirty-five children with juvenile chronic arthritis were compared to 89 healthy children with an Angle Class I occlusion and 62 children with an Angle Class II malocclusion. Subjective symptoms and clinical signs of temporomandibular disorder and radiographic mandibular condylar changes were more common in children with juvenile chronic arthritis than in the two comparison groups. Maximal molar and incisal bite forces and maximal molar bite force endurance times were also significantly reduced in children with juvenile chronic arthritis. It is concluded that the differences between the groups are caused mainly by the systemic inflammatory disease itself, but a functional influence of weakened masticatory muscles cannot be excluded.     

Main occluding area in partially edentulous patients: changes before and after implant treatment

The 'main occluding area', the location where food crushing occurs during the first stroke of mastication, is reported to be an important concept; however, it is currently limited to findings in individuals with normal dentition. The purpose of this study was to assess the changes in the location, area and bite force of the main occluding area before and after implant treatments. We enrolled 50 partially edentulous and 22 normally dentate subjects. To identify the location of the main occluding area, each subject was instructed to freely bite once on a dental stopping using the partially edentulous side or the normally dentate area. The location, occluding contact area and bite force of the main occluding area before and after the implant treatments were analysed. The main occluding area was located at a reproducible location in the partially edentulous and normally dentate subjects. This location was principally the first molar region, and for the partially edentulous patients with missing teeth in the molar regions, it moved from the premolar region to the first molar region after treatment. The occluding contact area and bite force for the main occluding area increased (P < 0·05) after the implant treatment in the partially edentulous patients with missing teeth in the molar regions. These results suggest that the main occluding area can be restored to the first molar region after implant treatment and may be an important factor in the assessment of prosthodontic treatment.     

Evaluation of molar and incisor bite force in indigenous compared with white population in Brazil

The purpose of this study was to determine maximum bite force in molar and incisor regions in young Brazilian indigenous individuals, who have had a natural diet since birth, and compare the sample with white Brazilian individuals. To do this, individuals were paired one-to-one (same weight, height, and Class I facial pattern). A secondary purpose was to elucidate the relation between bite force and gender in both populations. Eighty-two Brazilians took part in this study. Participants were aged between 18 and 28 years and were divided into two groups: 41 Xingu indigenous individuals and 41 white Brazilian individuals, with 28 men and 13 women in each group. The inclusion criteria were: having complete dentition; normal occlusion; no neurological, psychiatric or movement disorders; no reports of toothaches; having satisfactory periodontal health; absence of large facial skeletal alterations (typical Class II and Class III individuals); and no previous treatments using occlusal splints. To measure maximum bite force, a digital dynamometer model IDDK (Kratos-Equipamentos Industriais Ltda, Cotia, S?o Paulo, Brazil) was used, with a capacity of 1000N, adapted for oral conditions. Assessments were made in the first molar (right and left) and central incisive regions. Results reveal that mean maximum bite forces in indigenous individuals of the right molar is 421N, left molar 429N and incisor region is 194N and for white individuals of the right molar is 410N, left molar 422N and incisor region is 117N. Comparing indigenous with white individuals, maximal bite force showed a tendency of being greater in the indigenous group. It was observed that the incisor region showed statistical significance (p<0.0005) but no significance was observed in the molar region. Moreover, indigenous men showed the highest bite force values.     

Single tooth bite forces in healthy young adults

The assessment of bite forces on healthy single tooth appears essential for a correct quantification of the actual impact of single implant oral rehabilitations. In the present study, a new single tooth strain-gauge bite transducer was used in 52 healthy young adults (36 men, 16 women) with a complete permanent dentition. The influences of tooth position along the dental arch, of side, and of sex, on maximum bite force were assessed by an ANOVA. No significant left-right differences were found. On average, in both sexes the lowest bite force was recorded on the incisors (40-48% of maximum single tooth bite force), the largest force was recorded on the first molar. Bite forces were larger in men than in women (P < 0.002), and increased monotonically along the arch until the first or second permanent molar (P < 0.0001). The present data can be used as reference values for the comparison of dental forces in patients.     

Effect of face form on maximal molar bite force with natural dentition

Objective

The purpose of this study was to determine mean maximum bite force in adults with normal occlusion and to evaluate effect of face form on it.

Design

Twenty male and 20 female students with normal dentitions and between the ages of 19 and 27 participated in the study. A strain-gauge force transducer was developed to measure bite force and was calibrated with known loads. Three measurements were performed on each side of the dentition in the first molar region and mean values used for analysis. Face form was defined as square, tapering, square-tapering or oval and determined using digital photographs. Effect of gender and face form on bite force was statistically analysed using two-way ANOVA and Duncan tests.

Results

Mean maximum bite force and standard deviation (S.D.) in the sample population was 64.4 (24.0) kilograms (kg). In men, the mean was 73.6 (23.8) which was statistically higher than in women (53.0 (19.6) kg) (P < 0.05). Mean maximum bite force in subjects with square face form was 93.7 kg, which was significantly higher than in subjects with other facial forms (P < 0.05).

Conclusion

The results showed higher bite force in men and those with square face form. Square face form may contribute to higher bite force values by maintaining a higher mechanical advantage for muscles of mastication.     

Effect of biting speed and jaw separation on force used to incise food

Biting food too quickly might affect the control of jaw-closing muscles and the estimation of bite force. The objectives of this study were to compare the incisal bite forces used to cut food and the activity of masseter (MA) and anterior temporalis (AT) muscles between slow, habitual and fast biting speeds and also between small and large jaw openings. Twenty subjects were asked to use their incisors to cut through a 5 mm thick of chewing gum. In the first experiment, subjects bit at 10-mm incisal separation with slow, habitual and fast biting speeds, and in the second experiment, subjects bit with their habitual speed at 10- and 30-mm incisal separations. The activities in the MA and AT muscles were assessed with surface electromyography, and the bite force was recorded by a force sensor placed beneath the chewing gum. Peak bite forces and associated MA amplitudes were increased significantly as biting speed was increased (P's < .05). Anterior temporalis amplitude was significantly increased during fast biting compared to slow and habitual biting (P's < .001). At 30-mm incisal separation, both peak bite force and AT amplitude were significantly increased, whereas MA amplitude was significantly decreased, compared to those at 10-mm separation (P's < .05). Biting off food quickly with incisor teeth results in larger activities in both MA and AT muscles. In addition, biting a large piece of food resulted in increased activity of AT muscle. Both conditions could be injury stimulator for jaw muscles.     

Masticatory muscle fatigue: endurance times and spectral changes in the electromyogram during the production of sustained bite forces.

The purpose of this experiment was to determine if the characteristics of fatigue observed in the limb muscle system are also evident in the muscles of mastication, specifically, the masseter and temporalis. Surface electrodes were placed bilaterally over the masseter and temporalis muscles of 10 adults. Each subject was instructed to maintain maximal and six levels of submaximal incisal bite forces for as long as possible. The power density spectrum of the electromyographic signals for each muscle was calculated at the onset and failure of the task. The decrease in endurance time with an increase in bite force followed a pattern similar to that in limb muscles, and each muscle was characterized by a consistent reduction in the mean power frequency of the power density spectrum and a variable change in r.m.s. power. The variability of changes in r.m.s. power (which is inconsistent with changes found in the limb muscles) was explained in terms of either changes in motor-unit firing rate or the muscle's relative contribution to the generation of bite force. The analyses also demonstrated a curvilinear relationship between bite force and r.m.s. power, but no relationship between bite force and the mean power frequency of the power density spectrum.     

Occlusal force after mandibular advancement in adult rhesus monkeys

Maxillofacial surgery not only alters facial appearance and occlusion but also affects the morphology, physiology, and biomechanics of the craniofacial skeleton and the muscles of mastication. This study was performed to evaluate one aspect of craniofacial function--maximum stimulated bite force (BF)--after mandibular advancement. BF in the molar region was measured with a transducer during muscle stimulation in 63 rhesus monkeys that had been divided into two groups: a control group of various ages and sexes (n = 50); and an experimental sample of 13 monkeys that had undergone mandibular advancement via C-osteotomy at least one year prior to BF measurement. Biomechanical analysis of lateral cephalograms was performed to estimate the amount of the change in BF in the experimental group that could be attributed to alteration of craniofacial form. Regression analysis demonstrated a significant relation between molar bite force and weight in control animals (r = 0.94). In the monkeys that underwent surgery, BF values were an average of 16.7% less than those found for the control animals relative to body weight. However, the biomechanical analyses suggested a smaller and less variable BF loss in the operated monkeys (11.6%). These results indicate a greater and more variable change in BF following mandibular advancement than would be predicted on the basis of biomechanical considerations.     

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.     

开(牙合)与颞下颌关节紊乱病

开患者的颜面形态、吞咽模式、咀嚼肌力平衡、下颌运动模式都有特殊之处,目前的研究对开与颞下颌关节紊乱病之间的相互促进作用和因果关系还不完全清楚。本文从开患者的颅面形态、咀嚼肌力、吞咽模式等几个方面对开和颞下颌关节紊乱病的相互关系进行综述。     

The effects of changes in bite pressure and mucosal stimulation on the perception of mandibular position in man

In edentulous subjects, the mandibular position (MP) was altered by adjustable hydraulic jacks attached to the denture base. The MP which they began to perceive as high (HMP) was shifted toward the closed position when the bite pressure against the incisal region was increased. Thus the perception of MP may be modulated by information concerning the distribution of bite pressure. The HMP also shifted toward the closed position when the incisal palatal region of the denture-supporting mucosa was subjected to increased mechanical stimulation, the distribution of the bite force being constant. Therefore, mechanoreceptors in the mucosa may be involved in the perception of MP by providing precise information as to the distribution of bite pressure.     

Prevalence of temporomandibular disorder syndrome (TMD) in university students--a third year report of the epidemiological study in Taiwan

A total of 2033 university students (1161 boys, 872 girls, ages ranged from 17 to 32 years) were examined according to an examination form. Pain and functional disorders of the head and neck muscles and TM joints, as well as the dental occlusal conditions were recorded. Questionnaires relating to personal history, oral habits, experience of pain and disorder, and psychoemotional status were also given and replied. It was found that 42.9% of the students had one or more signs of TMD, and girls suffered slightly more often. The prevalence was not as high as in junior college students, and was about the same as in teenagers reported in the previous two years. Occlusal factors like slide in centric, balancing side contact, dental restoration and molar guidance during protrusion were more often found in the TMD group, while missing teeth, incisal overlap, attrition and cross bite were not. About 34% of the students had a previous experience of TM joint pain and/or clicking while only 20% of them had such symptoms during the examination. More than 60% of the students having joint clicking were not aware of this symptom. The oral habit and bruxism were not found to be more often in the TMD group. Emotional factors such as Type A personality, emotion, stress, anger, etc. had a higher score in the TMD group while tension, anxiety, and competition did not. It could be concluded that TMD is a fairly common syndrome in the youth of Taiwan although not serious or treatment demanded. Psychoemotional factors are as important as dental factors in relation to the TMD symptomatology, if not more important.     

Maximal bite force and its association with signs and symptoms of craniomandibular disorders in young Finnish non-patients

Maximal bite force values and subjective symptoms and clinical signs of craniomandibular disorders (CMD) were recorded for a non-patient sample of 129 young adults, 56 men and 73 women. The signs and symptoms of CMD were classified on the basis of Helkimo's clinical dysfunction index. The two genders reported equally frequently subjective symptoms of CMD, but women had significantly more severe clinical signs of CMD than did men. Mean maximal bite force values for men were 909 N (SD, 177) in the molar region and 382 N (SD, 133) in the incisai region and thus significantly higher than corresponding figures for women, 777 N (SD, 168) in the molar, 325 N (SD, 116) in the incisai region, suggesting that separate evaluation of the genders would be advisable in future studies involving bite force assessments. Neither subjective symptoms nor clinical signs of CMD correlated significantly with maximal bite force values. The bite force values measured were in line with theoretical calculations.