The role of the free-way space in the generation of muscle pain among denture-wearers.

Although the myofascial pain dysfunction syndrome has a multiple aetiology, faulty vertical dimension is a frequent cause of muscular pain among wearers of full dentures. Furthermore, it has been found that the restoration of a physiological free-way space in such cases, using a method which is based upon cephalometric analysis of the gonial angle, often leads to a dramatic remission of pain. The present investigation was prompted by curiosity as to what the underlying algogenic mechanisms in these cases might be; and how a change in the vertical dimension should so modify them as to result in the disappearance of the pain symptoms. The study is necessarily of a speculative nature, and makes use of two representative cases, one of which was adjudged to have too little free-way, and the other too much. Principles of neuromuscular physiology are applied in attempting to explain the clinical phenomena involved, as well as to find a reason for certain electro-myographic artefacts noted in one of the cases, which would appear to call into question the notion that muscular hyperactivity, per se, is responsible for muscular pain. Potgieter, Monteith & Kemp (1983) have presented an hypothesis that the amount of free-way space present in an individual is an expression of the contractile power of the masseter and medial pterygoid muscles. They have also devised a method whereby, through cephalometric analysis, the optimal amount of free-way may be determined for an edentulous patient during denture construction. Furthermore, they have stated that their method has proved particularly effective in the treatment of denture-wearers presenting with symptoms of the myofascial pain dysfunction syndrome. However, in the light of this syndrome's multifactorial aetiology one must assume that only those symptoms which are related to a faulty free-way space are at issue. The purpose of the present investigation is to examine the latter assertion; and by the application of the suggested method of cephalometric analysis to two representative cases, attempt to explain the phenomenon in terms of neuromuscular mechanisms. Of the two cases to be examined, one was found to have too much free-way, while the other had been provided with too little. Both had presented with symptoms of severe muscle pain.