A study of spontaneous fulminant shock in a heart-lung-dog preparation: Wégria, R., Rojas, A. G., and Wiggers, C. J.: Am. J. Physiol. 138: 212, 1943

Abstract

Vertical dimension has been defined in relation to the clinical rest position of the mandible, the vertical dimension of occlusion, and the interocclusal space between the two. The physiologic rest position has been attributed to three possible mechanisms: postural tonicity of the muscles, myotatic (stretch) reflexes, and gravity-elasticity, and/or a combination of all three. There is general agreement that it varies due to head position and many other extrinsic and intrinsic stimuli.The myotatic (stretch) reflex is produced by stimulation of the stretch receptors in the elevator muscles producing a simple two-neuron reflex arc which causes reflex muscle contraction. Its function is to give proprioceptive information to the central nervous system concerning position and movement. The proprioception of mandibular position is determined for the most part by the joint receptors, muscle spindles, pressoreceptors (in the periodontal membrane), and exteroceptors in the oral mucosa.Minimal EMG activity has been demonstrated at the clinical rest position and slightly beyond, at an increased vertical dimension which eliminates the interocclusal space. However, experimental evidence has been shown with adult monkeys that long-term increases in the vertical dimension of occlusion result in intrusion of the posterior teeth with the return almost to the original vertical dimension of occlusion. Several clinical examples of intrusion of the posterior teeth were shown when long-standing occlusal splints were used. Since both occlusal adjustment and vertical dimension increases can cause a reduction in EMG activity, it is recommended that the treatment of TMJ dysfunction is best accomplished by occlusal correction.A treatment prosthesis is recommended for trismus and/or joint injury but it should be accomplished within the interocclusal space. Most treatment prostheses, except those for condylar repositioning, are utilized for the control of symptoms and do not treat the cause of TMJ dysfunction pain.