A photogrammetric method for monitoring changes in the residual alveolar ridge form

Resorption of the residual alveolar ridge calls for regular attention to the fitting surface of a denture. In the case of distal extension partial dentures, changes which occur in less than a year may require attention. These changes are apparent, though difficult to measure using radiographic techniques. Stereophotogrammetry is a means of recording and measuring contours of land masses. A short focus non-metric camera was used in this study to produce stereoscopic paired pictures of four casts of the same partial dentition. Additional casts were made 2 and 12 months after a partial denture had been made. A stereophotogrammetric plotting instrument was used to map the alveolar ridge area of each cast. A prescribed area for each map was traced out and the volume above a reference height was calculated. The percentage error between the four columns for the pre-treatment casts was +/- 2%. A 10% loss of ridge volume was observed after wearing a partial denture for 2 months. The same area observed 12 months later revealed an 18% volume reduction. Short range stereophotogrammetry may be applied to study changes in alveolar ridge morphology which may result from wearing a partial denture.