Dr. Adams' Alabama Headache Blog

The effect of vertical dimension (VD) on maximizing isometric deltoid strength (IDS) has been researched in subjects with deep overbite. However, vertical dimension has been determined in these studies functionally using the Isometric Deltoid Press. In this study vertical dimension of occlusion was increased, 2, 4 and 6 mm using lower acrylic mouthplates. Twenty normal females, mean age 31 years, sat erect in a dental chair and were instructed to bite and either resist to their maximum ability a horizontal force applied to the forehead or a vertical downward force to the wrist of the first one then the other extended arm. This procedure was repeated in normal occlusion and while biting on mouthplates which raised the VD 2, 4 and 6mm. The order of testing was counterbalanced, with one investigator inserting the appliance while another performed the muscle testing. Horizontal and downward pressures were applied by a hand-held stain guage. Peake resistance was measured twice in each condition and averaged to produce a peak isometric strength (PIS). Mean strongest PIS for each site tested was compared to each subject's PIS while biting in habitual occlusion. PIS of cervical flexors with the elevated bite was significantly greater than that for habitual conclusion. PIS for right and left deltoids did not differ but mean deltoid PIS in the elevated condition was significantly greater than biting in habitual occlusion. In the peak condition, cervical flexors increased 24% and deltoids increased 30%. Strength was measures for habitual occlusion after all trialas were administered and were not found to differ from pre-experimental levels indicating that fatigue was not an important factor. In an earlier study, Hart et al was unable to show significant differences when the vertical dimension was raised gradually. However, his dependent variable was isokinetic strength. In earlier publications we have suggested that the strength phenomenon is more salient in isometric strength than isokinetic. Isometric strength of the cervical flexors and deltoids increase significantly when vertical dimension of occlusion is increased in deep overbite subjects.