Vertical dimension: A study of clinical rest position and jaw muscle activity

Abstract

A n understanding of factors which determine the position of the mandible with respect to the maxillae is critical for clinical dentistry. One of the more controversial aspects of jaw relation involves vertical rest position. Establishment of a correct vertical dimension of occlusion is of concern in several dental specialties. In the prosthodontic treatment of the edentulous patient, establishment of a correct vertical rest position is considered essential.” ’ Boucher et al.’ noted that if the vertical dimension is too great the patient may complain of soreness of the residual ridges, tightness of facial muscles, and clicking of the dentures during speech. If the vertical dimension is too small, the patient will look older as the lower half of the face is compressed, the cheeks and lips are slack, and the chin protrudes.’ For dentulous patients, Ramfjord and Ash’ have claimed that altering the vertical dimension of occlusion may result in traumatic occlusion. They also warn that altering the vertical dimension of occlusion can be a contributing factor in the progress of periodontal disease.’ Intruding upon the freeway space (interocclusal distance) is also believed to result in continuous hyperactivity of the masticatory muscles..’ Much of the controversy over the significance of clinical rest position stems from imprecise and inadequate definitions. Rest position, defined according to the Glossary of Prosthodontic Terms, is “the postural relation of the mandible to the maxillae when the patient is resting comfortably in the upright position and the condyles are in a neutral unstrained position in the glenoid fossae.“” One can easily see that this definition is inadequate. How is “postural position”