Differences In Bite Force Research Articles

BITE FORCES AND EVOLUTIONARY ADAPTATIONS TO FEEDING ECOLOGY IN CARNIVORES

The Carnivora spans the largest ecological and body size diversity of any mammalian order, making it an ideal basis for studies of evolutionary ecology and functional morphology. For animals with different feeding ecologies, it may be expected that bite force represents an important evolutionary adaptation, but studies have been constrained by a lack of bite force data. In this study we present predictions of bite forces for 151 species of extant carnivores, comprising representatives from all eight families and the entire size and ecological spectrum within the order. We show that, when normalized for body size, bite forces differ significantly between the various feeding categories. At opposing extremes and independent of genealogy, consumers of tough fibrous plant material and carnivores preying on large prey both have high bite forces for their size, while bite force adjusted for body mass is low among specialized insectivores. Omnivores and carnivores preying on small prey have more moderate bite forces for their size. These findings indicate that differences in bite force represent important adaptations to and indicators of differing feeding ecologies throughout carnivoran evolution. Our results suggest that the incorporation of bite force data may assist in the construction of more robust evolutionary and palaeontological analyses of feeding ecology.

Masticatory muscle thickness, bite force, and occlusal contacts in young children with unilateral posterior crossbite

Few investigations have evaluated the characteristics of functional and structural malocclusion in young children. Thus, the aim of this study was to assess the ultrasonographic thickness of the masseter and anterior portion of the temporalis muscles, the maximum bite force, and the number of occlusal contacts in children with normal occlusion and unilateral crossbite, in the primary and early mixed dentition. Forty-nine children (26 males and 23 females) was divided into four groups: primary-normal occlusion (PNO), mean (PNO) age 58.67 months; primary-crossbite (PCB), mean age 60.50 months; mixed-normal occlusion (MNO), mean age 72.85 months; and mixed-crossbite (MCB), mean age 71.91 months. Thickness was evaluated with the muscles at rest and during maximal clenching, and comparison was made between the right and left side (normal occlusion), and between the normal and crossbite side (crossbite). The results were analysed using Pearson's correlation, paired and unpaired t-test, and Mann-Whitney ranked sum test. The anterior temporalis thickness at rest was statistically thicker for the crossbite side than the normal side in the MCB group (P = 0.0106). A statistical difference in bite force and the number of occlusal contacts was observed between the MNO and MCB groups, with greater values for the MNO subjects (P < 0.05). Masseter muscle thickness showed a positive correlation with bite force, but the anterior temporalis thickness in the PCB and MCB groups was not related to bite force. Masticatory muscle thickness and bite force did not present a significant correlation with occlusal contacts, weight, or height. It was concluded that functional and anatomical variables differ in the early mixed dentition in the presence of a malocclusion and early diagnosis and treatment planning should be considered.

Maximal bite force and EMG during bilateral and unilateral clenching

The observed maximal bite force is known to depend on the measuring method employed. Bite position, bite rise and unilateral or bilateral biting influence the observed bite force. The maximal bite force obtained when clenching unilaterally is smaller than the bite force summed for the two sides of a bilateral measurement (Bakke et al., 1989). We determined bite force and muscle activity of the masseter and temporal muscles during maximal voluntary contraction in a group of 81 dentate subjects. The bite force was measured between the first molars both bilaterally and unilaterally. The summed bite force obtained from the bilateral measurement was 569 ± 170 N. The bite force obtained for unilateral clenching was significantly lower: 430 ± 142 N. No significant differences in bite force between the right and left side for both the bilateral and unilateral measurements were observed. The muscle activity of the masseter and temporal muscles obtained from bilateral clenching did not differ significantly (masseter: 248 ± 149 μV and temporalis: 232 ± 105 μV). Also no significant differences were observed in muscle activity between the right and left side during bilateral clenching. We observed a significantly lower muscle activity in both masseter and temporalis for unilateral clenching as compared with bilateral clenching. The results of unilateral clenching showed no differences in muscle activity between the ipsi- and contralateral side for the masseter muscle (186 ± 127 μV). However, the muscle activity at the ipsilateral side of the temporal muscle (197 ± 127 μV) was significantly higher than at the contralateral side (150 ± 81 μV). We may conclude that bilateral clenching yields bite forces that are over 30% larger than those obtained during unilateral clenching. The muscle activity during unilateral clenching is symmetrical in the masseter muscles, but asymmetrical in the temporal muscles.

Bite performance in clariid fishes with hypertrophied jaw adductors as deduced by bite modeling.

Within clariid fishes several cranial morphologies can be discerned. Especially within anguilliform representatives an increase in the degree of hypertrophy of the jaw adductors occurs. The hypertrophy of the jaw adductors and skeletal modifications in the cranial elements have been linked to increased bite force. The functional significance of this supposed increase in bite force remains obscure. In this study, biomechanical modeling of the cranial apparatus in four clariid representatives showing a gradual increase in the hypertrophy of the jaw adductors (Clarias gariepinus, Clariallabes melas, Channallabes apus, and Gymnallabes typus) is used to investigate whether bite force actually increased. Static bite modeling shows that the apparent hypertrophy results in an increase in bite force. For a given head size, the largest bite forces are predicted for C. apus, the lowest ones for C. gariepinus, and intermediate values are calculated for the other species. In addition, also in absolute measures differences in bite force remain, with C. apus biting distinctly harder than C. gariepinus despite its smaller head size. This indicates that the hypertrophy of the jaw adductors is more than just a correlated response to the decrease in absolute head size. Further studies investigating the ecological relevance of this performance difference are needed.

Bite force in pre-orthodontic children with unilateral crossbite.

In the present study bite force was examined in pre-orthodontic children with unilateral posterior crossbite and compared with an age- and sex-matched control group. The sample comprised 52 children aged 7-13 years, 26 pre-orthodontic children with unilateral posterior crossbite (crossbite group), and 26 children with neutral occlusion (control group). Unilateral bite force was measured at the first molar by means of a pressure transducer. Furthermore, symptoms and signs of temporomandibular disorders (TMD) and number of teeth in contact in the intercuspal position (ICP) were recorded. In both groups, the maximum bite force increased significantly with age and with increasing stages of dental eruption, but the bite force in both sexes did not differ significantly. There were no significant differences in bite force between sides, but this was significantly smaller in the crossbite group than in the controls (P < 0.001). Regression analysis showed that stage of dental eruption (P < 0.001), number of teeth in occlusal contact (P < 0.01), and unilateral crossbite (P < 0.001) were the only variables significantly correlated with bite force. The number of teeth in contact was significantly smaller in the crossbite group than in the controls (P < 0.05) and the frequency of muscle tenderness was significantly higher in the crossbite group than in the controls (P < 0.05). These results suggest that differences in the muscle function associated with unilateral crossbite lead to a significantly smaller bite force in the crossbite group compared with controls and this difference did not diminish with age and development. These findings indicate that early treatment of unilateral posterior crossbite is advisable to optimize conditions for function.

Masticatory force and function in patients with hemispheric brain infarction and hemiplegia.

Recent functional animal studies have reported that the motor control of masticatory muscle function is bilaterally guided by both hemispheres, which may fundamentally differ from the cortical control of limb muscle function. In this study, we investigated whether unilateral cortical brain infarction induces different impairments in masticatory and upper limb motor performance. Evidence of the importance of both hemispheres in controlling masticatory movements would be greater if the masticatory function were shown to be unimpaired in patients with severe hemiplegia. The masticatory function of 16 patients with severe hemiparesis caused by brain infarction in the region of the middle cerebral artery was studied by means of interview, clinical examination, and bite-force measurements. Finger-thumb grip-force measurements and clinical examination of the upper limbs were also performed for evaluation of the effect of infarction on upper limb motor function. Localization of the infarction was confirmed with computer tomography and magnetic resonance imaging. The Scandinavian Stroke Scale demonstrated that each patient had a major unilateral cortical infarction which had caused a marked handicap with a serious impairment of upper limb function on the contralateral side. The clinical examination revealed no major signs of temporomandibular disorders, and the masticatory muscles, when examined by palpation, contracted symmetrically. None of the patients with unilateral brain infarction showed any differences in bite forces between the healthy and paralyzed sides. These results indicate that, in hemiparetic patients, great differences may exist between the motor performances of the masticatory and upper limb muscles. The present investigation clinically illustrates the importance of both hemispheres in the control of masticatory function and movements.

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 > or = 0.05) when measured in the same position within the dental arch, whichever of the three positions that may be.

Effects of local anesthesia on bite force generation and electromyographic activity

Maximum voluntary bite force has been used to evaluate functional changes following orthognathic surgery. It has been proposed by others that maximum voluntary bite force may depend, in part, on sensory input from the dentition. However, results from previous studies have shown contradictory effects of local anesthesia on bite force following anesthetization of the dentition. The purpose of this study was to investigate the effects of drug-induced local anesthesia on the generation of first molar bite force and electromyographic (EMG) activity in adults. Twenty normal adults (3 women, 17 men) were evaluated. Electromyographic activity was monitored from four muscles of mastication bilaterally, and bite force was concurrently recorded at the right and left first molars. Maximal and submaximal bite forces were then measured after sequential unilateral anesthetization of the right mandible and maxilla with 2% lidocaine containing 1:100,000 epinephrine. No statistically significant differences in bite force or integrated EMG levels were observed between the unanesthetized and anesthetized sides, nor on the anesthetized side at different levels of anesthesia.

Bite force after temporomandibular joint surgery

Bitings were recorded bilaterally on 5 different submaximal and maximal force levels on 12 patients (7 women and 5 men) who had earlier been subjected to TMJ surgery (10 diskectomies and 2 condylectomies). The maximal bite force was relatively low for the recorded sample with mean values of 7.8 Kp and 8.3 Kp for operated and non-operated sides, respectively. The strongest forces were recorded after condylectomy. There was a wide range between the individual recordings on all levels and the differences increased with the force and were largest at maximal bite force level. No significant differences in bite force between operated and non-operated sides could be found for any of the force levels. The ability to discriminate between different force levels was better on the higher levels. The almost comparable results of the recordings of bite force on the operated and the non-operated sides may be an effect of functional interaction within the masticatory system and be an expression of the essentially improved function after the surgical treatment.

Bite Force as a Basis for Niche Differentiation Between Rain Forest Peccaries (Tayassu tajacu and T. pecari)

A lever model of jaw action indicates that the maximum bite force of white-lipped peccary (Tayassu pecari) should be at least 1.3 times that of collared peccary (T. taiacu) on food items of a given size. This prediction is consistent with the measured resistances of seeds and nuts that are eaten by the two species at a rain forest site in southeastern Peru. Such a difference in bite force, in association with differences in group size and digging ability, may be a basis for coexistence of the two species in Neotropical rain forests. THERE ARE TWO RECENT SPECIES OF PECCARY native to Neotropical rain forests: white-lipped peccary (Tayassu pecari) and collared peccary (T. tajacu). A third species, the newly discovered Chacoan peccary (Catagonus wagneri), is limited to the dry thorn forests of the South American Chaco (Wetzel et al. 1975; Wetzel 1977a, 1977b). The ranges of both T. tajacu and T. pecart extend southward into somewhat drier regions of South America, including the Chaco (Cabrera and Ypes 1940, Alston 1880, Wetzel 1977a). In the north, only T. tajacu occurs beyond the rain forests, as far as the Sonoran and Chihuahuan deserts of Mexico, Arizona, and Texas (Hall and

Maximal bite force with centric and eccentric load.

Premolar bite force was measured conventionally with a pressure transducer. During biting the tips of the buccal cusps made contact with the transducer. It was shown that the maximal bite force increased significantly if the eccentric load on the upper premolar was made centric and axial with respect to the transducer by covering the whole occlusal surface of the tooth with a plastic filling. Possible neurophysiological explanations of the difference in bite force are discussed. It is concluded that biting on a pressure transducer with an eccentric load cannot give a fair estimation of the true value of the maximal bite force during clenching in the position of intercuspidation.

Biomechanics of differences in lower facial height

A two-dimensional model which allows calculation of mechanical advantage of the human temporalis and masseter muscles is presented. The model is manipulated to demonstrate how selected differences in facial morphology affect the mechanical advantage of the muscles. The model is then used to evaluate the differences in mechanical advantage between patients with the long face syndrome and those with the short face syndrome. Differences in facial morphology between these two groups result in significant differences in the mechanical advantages of their muscles. Mechanical advantage may, in part, explain observed differences in bite force between the two groups. The model suggests that some surgical procedures used to correct facial disharmonies may have a significant effect on the mechanical advantage of the jaw muscles.

Bite force and oral function in complete denture wearers

Oral function was evaluated in complete denture wearers by using a questionnaire, clinical examination and bite force measurements. Ten patients with satisifactory and ten with unsatisfactory dentures were studied and six of the latter patients were reexamined 1 year after the insertion of new dentures. The bite force values were compared with those obtained in ten dentate controls. No significant differences in bite force were found between the satisfactory and unsatisfactory denture groups. Individual values varied much in both groups. The six patients re-examined were satisfied with their new dentures and thought they had improved chewing but no significant increase of bite force was found. The maximal bite force was 5-6 times greater in the dentate subjects than in the denture wearers. Edentulous persons are very handicapped in masticatory function and even clinically satisfactory complete dentures are poor substitutes for natural teeth.

Bite force and state of dentition

The maximal bite force and the strength of the finger-thumb grip of 125 Skolt Lapps, aged 15 to 65, was measured with a specially devised apparatus. The bite force was measured with the biting fork placed between the first molars and between the incisors, respectively. The finger-thumb grip was measured by letting the subject press the prongs of the fork between the thumb and forefinger of each hand as hard as possible. The range of inter-individual variation of the maximal bite force and finger-thumb grip was great. The mean values were higher for the males than for the females. In the males the maximal bite force thus measured in the molar region was 39 kg (382 N) and 18 kg (176 N) in the incisor region. The corresponding values for the females were 22 kg (216 N) and 11 kg (108 N). The finger-thumb grip strength for males was, on the average, 10 kg (98 N); that of the females, 7 KG (69 N). The average difference in bite force between the men and the women was larger in the group with natural teeth than in the one with complete dentures. The values found for the bite force decreased with increasing age, especially for the females. Most of this reduction with increasing age was probably due to the age-dependent deterioration of the dentition. In both sexes the bite force was notably smaller among the denture wearers than among the dentate persons. The number of natural teeth varied closely with the bite force, i.e. the greater number of natural teeth the greater the bite force.

Bite force in patients with functional disturbances of the masticatory system

In thirty patients (24 women and 6 men) treated because of dysfunction of the masticatory system at the department of Stomatognathic Physiology, University of Gothenburg, bite force was registered before, during and after treatment had been completed. In the controls, thirty-six dental students and trainee dental nurses, with no dysfunction of the masticatory system, bite force was registered on two occasions. Bite force was measured between the first molars on each side and between the central incisors. Also finger force was registered. The force measurements were made at five different levels, increasing from very weak to maximum force. Repeated tests of bite force in the control group, made at intervals of about 1 week, gave almost identical results. Bite force in the patient group was lower than in the control group at the first registration but increased with palliation of the symptoms during treatment. There was no significant difference in bite force between the affected and the unaffected side.

Isometric bite force in children and its relation to body build and general muscle force.

Bite force, muscle strength in various muscle groups and body build (skeletal dimensions) were examined in 12 year old children, 37 boys and 42 girls. There were no statistically significant differences in bite force between boys and girls, and only small differences between the children and adults (20-30 years of age) who had been examined earlier with the same technique. In the children, maximum bite force covariated slightly with muscular force and skeletal dimension (r = 0.24 – 0.28, P<0.05), while no statistically significant correlation was found in similarly examined adults. It is suggested that masticatory training is important for bite force while factors relating to body build seem less important.