Comparative Evaluation of the Marginal and Internal Fitness of Monolithic CAD/CAM Zirconia Crowns Fabricated from Different Conventional Impression Techniques and Digital Impression Using Silicone Replica Technique (An in vitro study)
Zainab T. Al-Atyaa and Manhal A. Majeed

Conservative Department of college, Dentistry, University of Baghdad, Baghdad-Iraq.

Corresponding Author E-Mail:

Abstract: The accuracy of fit is considered as one of the main factors in establishing the long-term functional success of the restoration, which is influenced by several factors, one of them is the impression technique. The objective of this in vitro study was to evaluate and compare the marginal and internal fitness of monolithic CAD/CAM zirconia crowns fabricated from four different conventional impression techniques and intra-oral digital impression using silicone replica technique. Two metal dies for a dentoform maxillary right first molar tooth were fabricated using lost wax technique: one for the dentoform before its preparation and the other one after preparation of the dentoform tooth to receive a monolithic zirconia crown. Impressions were then taken using vinyl polysiloxane impression material with four different conventional impression techniques (two-step putty/wash with and without spacer, one-step single and dual viscosity) and digital impression. All conventional impressions were poured with type IV gypsum product to produce thirty-two stone dies, which were then scanned extra-orally using in Eos X5 extra-oral scanner. Forty crowns were then designed and fabricated (eight crowns for each technique). Marginal and internal gaps were measured using silicone replica technique. The measurements were done using a digital microscope at twenty-one different measuring points for each specimen, which represented four different areas of measurement (margin, chamfer, axial and occlusal). The data were then analyzed using One-way ANOVA test and LSD test. The digital impression yielded the least mean marginal and internal gaps as compared with all conventional impression groups with statistically significant and highly significant differences. Among the four conventional impression groups, the results showed that the two-step putty/wash impression technique without spacer yielded the least mean marginal and internal gaps followed by the two-step putty/wash impression technique with spacer with statistically significant difference between them, while the one-step dual viscosity impression technique yielded the greatest mean marginal and internal gaps, but with statistically non-significant difference with the one-step single viscosity impression technique. As a conclusion, it is recommended to use intra-oral scanner, when available, to take a digital impression for the tooth preparation as it produced crowns with better marginal and internal fitness than conventional impression. Otherwise, the two-step putty/wash impression technique could be the next choice, which is preferred over both one-step impression techniques.

Keywords: Marginal Fitness; Internal Fitness; Monolithic Zirconia Crowns; CAD/CAM System; Silicone Replica Technique

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