Bite Force Data Research Articles

顎関節負荷の調節メカニズムの静力学的解析 : 咬合点の違いによる咀嚼筋協調活動の変化

Masticatory or bite forces applied to the teeth are known to generate compressive forces in the temporomandibular joint (TMJ), which are referred to as "TMJ loading." Normal TMJs are both tolerant and adaptable to a certain amount of loading, but excessive loading is believed to be one of the causes of TMJ dysfunctions. Thus TMJ loading can be considered to be controlled to a certain extent by the stomatognathic system, so as not to exceed a certain limit. In an attempt to clarify that control mechanism during biting, we previously analyzed TMJ loading using a two-dimensional static jaw model and then proved, by computer simulation, that the TMJ loading is minimized when the load vector points in a certain direction. This minimization can be achieved merely by coordinating the activities of the masseter and the temporalis. We then analyzed the modification of such coordinated activities of masticatory muscles by changing the bite point and validated the jaw model by comparing our simulation results with somatometric data. Our jaw model comprises two rigid bodies, the upper and lower jaws, and a spring-element model of the articular disk, including masticatory muscles as follows: 1) the masseter, including the internal pterygoid; 2) the temporalis; and 3) the lateral pterygoid, all of which function dominantly during biting. Bite force is assumed to be applied to a single point on the occlusal plane. Muscle forces applied to our model were determined by referring to morphological and electromyographic data reported previously. First, we carried out experiments in order to obtain masseter and temporalis forces minimizing TMJ loading under various locations of bite point on the occlusal plane. Simulation results indicated that 1) the location of the bite point solely affects the activity of the masseter under the condition that the magnitude and direction of bite force are both constant and TMJ loading is minimized; and 2) the activity balance between the masseter and the temporalis minimizing TMJ loading is sensitive to the direction of bite force. Comparison of our simulation results with EMG data for the masseter and temporalis and biteforce data demonstrated that our results almost coincided with somatometric data for biting at the canine or the premolar, and for biting weakly at the first molar. This strongly suggests that minimization of TMJ loading is actually realized by the stomatognathic system under certain bite conditions.

Sexual dimorphism of head size in Gallotia galloti: testing the niche divergence hypothesis by functional analyses

1. Two often cited hypotheses explaining sexual head size dimorphism in lizards are: sexual selection acting on structures important in intrasexual competition, and reduction of intersexual competition through food niche separation. 2. In this study some implicit assumptions of the latter hypothesis were tested, namely that an increase in gape distance and bite force should accompany the observed increase in head size. These assumptions are tested by recording bite forces, in vivo, for lizards of the species Gallotia galloti. In this species, male lizards have significantly larger heads than female conspecifics of similar snout–vent length. 3. Additionally, the average force needed to crush several potential prey species was determined experimentally and compared with the bite force data. This comparison clearly illustrates that animals of both sexes can bite much harder than required for most insect food items, which does not support the niche divergence hypothesis. The apparent ‘excess’ bite force in both sexes might be related to the partially herbivorous diet of the animals. 4. To unravel the origin of differences between sexes in bite capacity, the crushing phase of biting was modelled. The results of this model show different strategies in allocation of muscle tissue between both sexes. The origin of this difference is discussed and a possible evolutionary pathway of the development of the sexual dimorphism in the species is provided.

In vivo forces on dental implants: Hard-wiring and telemetry methods

Methods are presented for measuring vertical force components on bridged titanium dental implants in dog mandibles. These methods have included custom-made strain-gauge transducers, plus hard-wiring and telemetric schemes for data collection. The essential components of the measurement system are described, and typical bite force data are illustrated.