Clinical acceptance of single-unit crowns and its association with impression and tissue displacement techniques: Findings from the National Dental Practice-Based Research Network
The Journal of Prosthetic Dentistry
Available online 4 October 2019
Abstract
Statement of problem
The
definitive impression for a single-unit crown involves many material
and technique factors that may affect the success of the crown.
Purpose
The
purpose of this prospective cohort study was to determine whether
impression technique (tray selection), impression material, or tissue
displacement technique are associated with the clinical acceptability of
the crown (CAC).
Material and methods
Dentists
in the National Dental Practice-Based Research Network documented
details of the preparation, impression, and delivery of 3730 consecutive
single-unit crowns. Mixed-effects logistic regression analyses were
performed to evaluate associations between impression techniques and
materials and the CAC and to assess associations between the presence of
a subgingival margin with the displacement technique and the outcome
variables CAC and number of impressions required.
Results
Of
the 3730 crowns, 3589 (96.2%) were deemed clinically acceptable. A
significant difference in the CAC was found with different impression
techniques (P<.001) and different impression materials (P<.001).
The percentage of the CAC for digital scans was 99.5%, 95.8% for
dual-arch trays, 95.2% for quadrant trays, and 94.0% for complete-arch
impression trays. Although no statistically significant difference was
found in the CAC produced with dual-arch trays without both mesial and
distal contacts, crowns fabricated under these conditions were less
likely to achieve excellent occlusion. The percentage of the CAC for
digital scans was 99.5%, 97.0% for polyether impressions, 95.5% for
polyvinyl siloxane impressions, and 90.5% for other impression
materials. Accounting for the location of the margin, the use of a
dual-cord displacement technique was significantly associated with lower
rates of requiring more than 1 impression (P=.015, odds ratio=1.43).
Conclusions
Dual-arch
trays produced clinically acceptable crowns; however, if the prepared
tooth was unbounded, the occlusal fit was more likely to have been
compromised. Digital scans produced a slightly higher rate of CAC than
conventional impression materials. The use of a dual-cord technique was
associated with a decreased need to remake impressions when the margins
were subgingival.
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