Biting

Abstract: One of the costly and welfare-reducing problems in modern pig production is tail biting. Tail biting is an abnormal behaviour, characterized by one pig's dental manipulation of another pig's tail. Tail biting can be classified into two groups: the pre-injury stage, before any wound on the tail is present, and the injury stage, where the tail is wounded and bleeding. Tail biting in the injury stage will reduce welfare of the bitten pig and the possible spread of infection is a health as well as welfare problem. The pigs that become tail biters may also suffer, because they are frustrated due to living in a stressful environment. This frustration may result in an excessive motivation for biting the tails of pen mates. This review aims to summarize recent research and theories in relation to tail biting.

Abstract: The mammalian mandible, and in particular the human mandible, is generally thought to function as a lever during biting. This notion, however, has not gone unchallenged. Various workers have suggested that the mandible does not function as a lever, and they base this proposition on essentially two assertions: (1) the resultant of the forces produced by the masticatory muscles always passes through the bite point; (2) the condylar neck and/or the temporomandibular joint is unsuited to withstand reaction forces during biting. A review of the electromyographic data and of the properties of the tissues of the temporomandibular joint do not support the non-lever hypothesis of mandibular function. In addition, an analysis of the strength of the condylar neck demonstrates that this structure is strong enough to withstand the expected reaction force during lever action. Ordinarily the human mandible and the forces that act upon it are analyzed solely in the lateral projection. Moments are then usually analyzed about the mandibular condyle; however, some workers have advocated taking moments about other points, e.g., the instantaneous center of rotation. Obviously it makes no difference as to what point is chosen since the moments about any point during equilibrium conditions are equal to zero. It is also useful to analyze the forces acting on the mandible in the frontal projection, particularly during unilateral biting. The electromyographic data suggest that during powerful unilateral molar biting the resultant adductor muscle force is passing between the bite point and the balancing (non-biting side) condyle. Therefore, in order for this system to be in equilibrium there must be a reaction force acting on the balancing condyle. This suggests that reaction forces are larger on the balancing side than on the working side, and possibly explains why individuals with a painful temporomandibular joint usually prefer to bite on the side of the diseased joint.

Abstract: Mandibular bone strain in the region immediately below the temporomandibular ligament was analyzed in adult and sub-adult Macaca fas-cicularis and mulatta. Following recovery from the general anesthetic, the monkeys were presented food objects, a wooden rod, or a specially designed bite-force transducer. Bone strain was recorded during incisal biting and mastication of food, and also during isometric biting of the rod and/or the transducer. The bone strain data suggest the following: The macaque TMJ is loaded by a compressive reaction force during the power stroke of mastication and incision of food, and during isometric molar and incisor biting. TMJ reaction forces are larger on the contralateral side during both mastication and isometric molar biting. Patterns of ipsilateral TMJ reaction force in macaques during isometric biting vary markedly in response to the position of the bite point. During biting along the premolars or first two molars a compressive reaction force acts about the ipsilateral TMJ; however, when the bite point is positioned along the M3, the ipsilateral TMJ has either very little compressive stress, no stress, or it is loaded in tension.