The effect of acute unilateral inflammation of the equine temporomandibular joint on the kinematics of mastication.
REASONS FOR PERFORMING STUDY
Diseases of the temporomandibular joint (TMJ) are well reported in man and some domestic animals other than the horse. The pathophysiology of equine TMJ disease and the effects of disease on the kinematics of mastication are unknown.


OBJECTIVES
To determine whether transient unilateral inflammation of the equine TMJ results in alterations in the masticatory cycle.


STUDY DESIGN
An experimental controlled study utilising 6 horses of various ages with normal dentition.


METHODS
Each horse was equipped with an optical motion tracking (kinematic) system. Horses were observed chewing grass hay over 3 min intervals. Regardless of the initial side of the power stroke in the masticatory cycle, lipopolysaccharide (LPS) was injected in the left TMJ in each horse and the horses were reassessed after 6 h.


RESULTS
Four horses developed effusion of the injected TMJs; 2 of these also began quidding. All horses injected on the original side of the power stroke switched sides while the 2 injected on the contralateral side did not. All horses developed reduced vertical pitch (vertical opening) of the mandible. Overall, rostrocaudal movement of the mandible did not change; however, the timing of this movement relative to the phase of the masticatory cycle did. Injection with LPS did not affect the amount of lateral movement of the mandible.


CONCLUSIONS
Injection of LPS into the TMJ significantly altered the masticatory cycle compared with baseline values representing avoidance behaviour due to inflammation of the joint, despite which the horses continued to eat using the contralateral mandible. Lipopolysaccharide administration also led to quidding and a loss of feed efficiency (in some individuals).
['Smyth|T T|TT|', 'Carmalt|J L|JL|', 'Treen|T T|TT|', 'Lanovaz|J L|JL|']
D000818:Animals D001696:Biomechanical Phenomena D006734:Horse Diseases D006736:Horses D007249:Inflammation D008070:Lipopolysaccharides D008409:Mastication D013704:Temporomandibular Joint D013705:Temporomandibular Joint Disorders
temporomandibular joint mastication horse dentition