FORM DIFFERENCE COMPUTATIONS IN RESTORATIVE DENTISTRY UTILIZING THE MACROELEMENT METHOD

The comparison between the size and shape (form) of two structures or the analysis of one object under differing conditions is important in restorative dentistry. Despite rapid advances in digitizing technologi es, form comparison is still mainly Limited to scalar measurements. Th e objective of this study was to test the potential use of a newly dev eloped tensorial morphometric difference technique, the macroelement m ethod, in a model restorative system where the processing and material s properties are known: duplication of a denture anchor in stone via p olysulfide, addition silicone, and polyether impression materials. Nin e machined landmarks were utilized to construct a nine-sided element f or macroelement analysis. Macroelement results compared well with the known impression materials properties of polymerization shrinkage and incomplete recovery in terms of: (1) larger die diameter, (2) smaller die (vertically), (3) horizontal direction of maximum expansion, and ( 4) vertical direction of maximum contraction. Also, macroelement resul ts along boundary lines were equal to the traditional form difference measure of change in length/length of those lines. The macroelement me thod provided results which are superior to those of traditional metho ds in that both (1) the magnitude and direction of difference at any p oint on the structure could be determined, and (2) the graphical repre sentation of the results provides an intuitive appreciation of how and where the forms differ. Therefore, since macroelement results: (1) co mpare well with known materials properties and traditional measures, a nd (2) have the above-stated advantages, tensorial techniques such as the macroelement method, used in conjunction with new digitizing techn ologies, can be used better to describe the kinematics of form differe nce. With the description of the kinematics provided by the technique, the dynamic cause of the form difference can be ascertained with the investigators' knowledge of materials. The investigators can then sugg est changes to be made in materials and/or techniques that would enabl e the desired size and shape to be obtained.