Initial effects of reduced vertical dimension on the projection of the body's center of gravity on a standing surface - A pilot study

The aim of this article was to investigate how reduced vertical dimension (RVD) potentially affects the projection of the body's center of gravity (COP). Twelve subjects were treated with a properly fitting full denture in correct jaw relation and a duplicate test prosthesis, with a vertical dimension reduced by 7 mm, fabricated for each individual. Posturography was performed on standing subjects using the Zebris Pressure Distribution Measurement System. The subjects maintained random maximum clenching phases (15 s) under EMG monitoring of the masseter muscles. The effect of clenching on COP was documented in randomized order. Clenching was tested in correct maximum occlusion and significant RVD. Posturography was performed with the subjects' eyes open and closed. A statistically significant effect of clenching on COP with an RVD by 7 mm was only proven in the anteroposterior direction during clenching with eyes closed. Marked RVD can change the tone and/or posture of musculoskeletal organs outside the stomatognathic system; initial causality suggests a descending cause-and-effect chain. The experimentally induced effects were weak and only manifest when visual balance control was absent. Keywords: body's center of gravity, body posture, occlusion, posturography, vertical dimension