Abstract
Statement of problem
The inability to control die spacer thickness has been reported. However, little information
is available on the congruency between the computer-aided design parameters for die
spacer thickness and the actual printout.
Purpose
The purpose of this study was to evaluate the accuracy and precision of the die spacer
thickness achieved by combining computer-aided design and 3-dimensional printing technology.
Material and methods
An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared
tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone
models were produced from Type IV dental stone. The dies were randomly divided into
5 groups with assigned die spacer thicknesses of 25 μm, 45 μm, 65 μm, 85 μm, and 105
μm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D
Systems), were cemented onto their respective die-stone models with self-adhesive
resin cement and stored at room temperature until sectioning into halves in a buccolingual
direction. The internal gap was measured at 5 defined locations per side of the sectioned
die. Images of the printed resin coping/die-stone model internal gap dimensions were
obtained with an inverted bright field metallurgical microscope at ×100 magnification.
The acquired digital image was calibrated, and measurements were made using image
analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery
rate at 5% was used to adjust for multiple testing. Coefficient of variation was used
to determine the precision for each group and was evaluated statistically with the
Wald test (α=.05).
Results
The accuracy, expressed in terms of the mean differences between the prescribed die
spacer thickness and the measured internal gap (standard deviation), was 50 μm (11)
for the 25 μm group simulated die spacer thickness, 30 μm (10) for the 45 μm group,
15 μm (14) for the 65 μm group, 3 μm (23) for the 85 μm group, and -10 μm (32) for
the 105 μm group. The precision mean of the measurements, expressed as a coefficient
of variation, ranged between 14% and 33% for the 5 groups.
Conclusions
For the accuracy evaluation, statistically significant differences were found for
all the groups, except the group of 85 μm. For the precision assessment, the coefficient
of variation was above 10% for all groups, showing the printer’s inability to reproduce
the uniform internal gap within the same group.
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Article info
Publication history
Published online: March 19, 2015
Footnotes
Supported by an American Academy of Fixed Prosthodontics Stanley D. Tylman research grant (02600-74716) and the Marquette University School of Dentistry Student Research Fund.
Identification
Copyright
© 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
