Impact of digital impression techniques on the adaption of ceramic partial crowns in vitro
Available online 6 February 2014
Abstract
Objectives
To investigate the effects digital impression procedures can have on the three-dimensional fit of ceramic partial crowns in vitro.
Methods
An
acrylic model of a mandibular first molar was prepared to receive a
partial coverage all-ceramic crown (mesio-occlusal-distal inlay
preparation with reduction of all cusps and rounded shoulder finish line
of buccal wall). Digital impressions were taken using iTero (ITE), cara
TRIOS (TRI), CEREC AC with Bluecam (CBC), and Lava COS (COS) systems,
before restorations were designed and machined from lithium disilicate
blanks. Both the preparation and the restorations were digitized using
an optical reference-scanner. Data were entered into quality inspection
software, which superimposed the records (best-fit-algorithm),
calculated fit-discrepancies for every pixel, and colour-coded the
results to aid visualization. Furthermore, mean quadratic deviations
(RMS) were computed and analysed statistically with a 1-way ANOVA.
Scheffé’s procedure was applied for multiple comparisons (n = 5,
α=0.05).
Results
Mean marginal
(internal) discrepancies were: ITE 90 (92) μm, TRI 128 (106) μm, CBC
146 (84) μm, and COS 109 (93) μm. Differences among impression systems
were statistically significant at p < 0.001 (p = 0.039).
Qualitatively, partial crowns were undersized especially around cusp
tips or the occluso-approximal isthmus. By contrast, potential
high-spots could be detected along the preparation finishline and at
central occlusal boxes.
Conclusions
Marginal and internal fit of milled lithium disilicate partial crowns depended on the employed digital impression technique.
Clinical
Significance. The investigated digital impression procedures
demonstrated significant fit discrepancies. However, all fabricated
restorations showed acceptable marginal and int
Comments