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A controlled trial was made using fifteen subjects and making 120 measurements with a caliper gauge between marks disposed on the upper lip and the point of the chin when maxillo-mandibular relationships were altered vertically by known amounts within a range of 6 mm. It was found that mean facial measurements could account for only half of the skeletal movement involved. The variability of soft tissue translation in relation to skeletal movement led to the conclusion that such facial measurements are inappropriate to clinical practice.

A longitudinal radiographic cephalometric and electromyographic investigation was performed on eighteen subjects provided with an immediate complete upper and a partial lower denture. The observation stages were: before final extractions and 7 weeks, 6 months and 1 year after denture insertion. The cephalometric analysis was based on measurements from lateral head films taken in centric occlusion. The EMG activity of the anterior temporal and masseter muscles was studied in postural position, light tapping and in maximal clench. The changes in jaw and occlusal relationships due to resorption of the edentulous maxillary ridge were slight, the mean decrease in occlusal vertical dimension during one year being 0.7 mm. The EMG clench activity at the pre-extraction stage, when the patients occluded on a residual anterior dentition, showed low mean values round 100 microV, and a further decrease was observed at the post-insertion stage. At the 1-year stage all muscles displayed significant increases to above the post-insertion level. The jaw muscle activity in light tapping and in postural position generally showed no significant mean changes during the observation period. The results indicate that preservation of a residual dentition in the lower jaw prevents marked changes in jaw and occlusal relationships and resulting changes in muscle activity.

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