It has been established that the centre of the hard palate does not change after tooth loss and can be used as a reference area from which changes in the alveolar bone may be measured. A mechanical instrument was made for this purpose but, although giving reproducible results, the technique was tedious and time-consuming. The present equipment enables enlarged tracings to be produced of dental casts along any predetermined contours on anXY recorder and bone loss evaluated by changes in the height and thickness of the alveolar ridge. The instrument may be used for examining the change in shape of either metal or plastic denture bases at various stages during fabrication.