Research and Education Evaluation of the fit of zirconia copings fabricated by direct and indirect digital impression procedures
The Journal of Prosthetic Dentistry
Available online 7 February 2018
Statement of problem
Intraoral scanners are effective for direct digital impression when dental restorations are fabricated using computer-aided design
and computer-aided manufacturing (CAD-CAM); however, if the abutment
tooth cannot be dried completely or the prepared margin is placed
subgingivally, accurate digital images cannot always be guaranteed.
Purpose
The purpose of this in vitro
study was to compare the internal and marginal discrepancies of
zirconia copings fabricated directly using an intraoral scanner with
those fabricated indirectly with impression scanning.
Material and methods
Forty-five
resin dies fabricated with a 3-dimensional (3D) printer were divided
into 3 groups: direct scanning (DS), impression scanning (IMP), and
lost-wax casting (LW). For the DS group, a resin die was scanned with an
intraoral scanner (Trios; 3Shape), whereas for the IMP group,
impressions made with polyether were scanned with a cast scanner (D700;
3Shape). The zirconia copings were fabricated in the same way in the DS
and IMP groups. For the LW group, impressions were made in the same way
as in the IMP group, and Ni-Cr alloy copings were fabricated using LW.
The marginal and internal discrepancies of the copings were measured by
cementing them onto resin dies, embedding them in acrylic resin, and
sectioning them in a buccolingual direction. The cement layer was
measured, and the Kruskal-Wallis test was used to detect significant
differences (α=.05). A nonparametric Friedman test was also performed to
compare the measurements of each group by location (α=.05).
Results
The
mean marginal discrepancies in the DS, IMP, and LW groups were 18.1
±9.8, 23.2 ±17.2, and 32.3 ±18.6 μm (mean ±standard deviation),
respectively. The mean internal discrepancies of the DS, IMP, and LW
groups in the axial area were 38.0 ±9.1, 47.0 ±16.3, and 36.5 ±15.8 μm,
and those in the occlusal area were 36.7 ±16.9, 33.4 ±21.6, and 44.5
±31.9 μm, respectively. No statistically significant differences were
found in marginal or internal discrepancies among groups (P>.05).
Conclusions
Within
the limitations of this study, the zirconia copings fabricated with
CAD-CAM using different digitization methods and Ni-Cr copings
fabricated using the lost-wax technique and casting produced clinically
acceptable marginal and internal discrepancies. No significant
differences were found among the DS, IMP, and LW groups.
Comments