Journal of Dental Research, Vol 75, 1464-1476, Copyright © 1996 by International & American Associations for Dental Research Online Journals
Form difference computations in restorative dentistry utilizing the macroelement method
M. E. McAlarney, C. B. Phillips and D. Song
Department of Prosthodontics, School of Dental and Oral Surgery, Columbia University, New York, NY 10032, USA.
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 restrative 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.
