Digital evaluation of absolute marginal discrepancy: A comparison of ceramic crowns fabricated with conventional and digital techniques
Available online 5 April 2018
Research and Education
Abstract
Statement of problem
Marginal
discrepancy is key to evaluating the accuracy of fixed dental
prostheses. An improved method of evaluating marginal discrepancy is
needed.
Purpose
The purpose
of this in vitro study was to evaluate the absolute marginal
discrepancy of ceramic crowns fabricated using conventional and digital
methods with a digital method for the quantitative evaluation of
absolute marginal discrepancy. The novel method was based on
3-dimensional scanning, iterative closest point registration techniques,
and reverse engineering theory.
Material and methods
Six
standard tooth preparations for the right maxillary central incisor,
right maxillary second premolar, right maxillary second molar, left
mandibular lateral incisor, left mandibular first premolar, and left
mandibular first molar were selected. Ten conventional ceramic crowns
and 10 CEREC crowns were fabricated for each tooth preparation. A dental
cast scanner was used to obtain 3-dimensional data of the preparations
and ceramic crowns, and the data were compared with the “virtual
seating” iterative closest point technique. Reverse engineering software
used edge sharpening and other functional modules to extract the
margins of the preparations and crowns. Finally, quantitative evaluation
of the absolute marginal discrepancy of the ceramic crowns was obtained
from the 2-dimensional cross-sectional straight-line distance between
points on the margin of the ceramic crowns and the standard preparations
based on the circumferential function module along the long axis.
Results
The
absolute marginal discrepancy of the ceramic crowns fabricated using
conventional methods was 115 ±15.2 μm, and 110 ±14.3 μm for those
fabricated using the digital technique was. ANOVA showed no statistical
difference between the 2 methods or among ceramic crowns for different
teeth (P>.05).
Conclusions
The
digital quantitative evaluation method for the absolute marginal
discrepancy of ceramic crowns was established. The evaluations
determined that the absolute marginal discrepancies were within a
clinically acceptable range. This method is acceptable for the digital
evaluation of the accuracy of complete crowns.
Comments