Statement of problem
The accuracy of impressions has been described in 1 or 2 dimensions, whereas it is
most desirable to evaluate the accuracy of impressions spatially, in 3 dimensions.
Purpose
The purpose of this study was to demonstrate the accuracy and reproducibility of a
3-dimensional (3-D) approach to assessing impression preciseness and to quantitatively
comparing the occlusal correctness of gypsum dies made with different impression materials.
Material and methods
By using an aluminum replica of a maxillary molar, single-step dual viscosity impressions
were made with 1 polyether/vinyl polysiloxane hybrid material (Identium), 1 vinyl
polysiloxane (Panasil), and 1 polyether (Impregum) (n=5). Corresponding dies were
made of Type IV gypsum and were optically digitized and aligned to the virtual reference
of the aluminum tooth. Accuracy was analyzed by computing mean quadratic deviations
between the virtual reference and the gypsum dies, while deviations of the dies among
one another determined the reproducibility of the method. The virtual reference was
adapted to create 15 occlusal contact points. The percentage of contact points deviating
within a ±10µm tolerance limit (PDP10 = Percentage of Deviating Points within ±10µm Tolerance) was set as the index for
assessing occlusal accuracy. Visual results for the difference from the reference
tooth were displayed with colors, whereas mean deviation values as well as mean PDP10 differences were analyzed with a 1-way ANOVA and Scheffé post hoc comparisons (α=.05).
Results
Objective characterization of accuracy showed smooth axial surfaces to be undersized,
whereas occlusal surfaces were accurate or enlarged when compared to the original
tooth. The accuracy of the gypsum replicas ranged between 3 and 6 µm, while reproducibility
results varied from 2 to 4 µm. Mean (SD) PDP10-values were: Panasil 91% (±11), Identium 77% (±4) and Impregum 29% (±3). One-way
ANOVA detected significant differences among the subjected impression materials (P<.001).
Conclusions
The accuracy and reproducibility of impressions were determined by 3-D analysis. Results
were presented as color images and the newly developed PDP10-index was successfully used to quantify spatial dimensions for complex occlusal anatomy.
Impression materials with high PDP10-values were shown to reproduce occlusal dimensions the most accurately.
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Article info
Footnotes
Supported in part by Kettenbach GmbH. Presented in part at the General Session of the International Association for Dental Research, Barcelona, Spain, July 2010.
Identification
Copyright
© 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
