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 technologies, form comparison is still mainly limited to scalar measurements. The objective of this study was to test the potential use of a newly developed tensorial morphometric difference technique, the macroelement method, in a model restorative system where the processing and materials properties are known: duplication of a denture anchor in stone via polysulfide, addition silicone, and polyether impression materials. Nine machined landmarks were utilized to construct a nine-sided element for 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 results along boundary lines were equal to the traditional form difference measure of change in length/length of those lines. The macroelement method provided results which are superior to those of traditional methods in that both (1) the magnitude and direction of difference at any point on the structure could be determined, and (2) the graphical representation of the results provides an intuitive appreciation of how and where the forms differ. Therefore, since macroelement results: (1) compare well with known materials properties and traditional measures, and (2) have the above-stated advantages, tensorial techniques such as the macroelement method, used in conjunction with new digitizing technologies, can be used better to describe the kinematics of form difference. 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 suggest changes to be made in materials and/or techniques that would enable the desired size and shape to be obtained. [ABSTRACT FROM AUTHOR]