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A comparison of the marginal fit of crowns fabricated with digital and conventional methods
Jonathan Ng1, Dorin Ruse2, Chris Wyatt3
1Student, Graduate Prosthodontics Program, Faculty of Dentistry, The University of British Columbia, Vancouver, British Columbia, Canada.
Statement Of Problem:
Little evidence is available with regard to the marginal fit of crowns fabricated with digital impressions and computer-aided design/computer-aided manufacturing technology in comparison with crowns fabricated from conventional techniques.
Purpose:
The purpose of this study was to determine and compare the marginal fit of crowns fabricated with digital and conventional methods.
Material And Methods:
The maxillary right second premolar was prepared for a ceramic crown in a typodont. The typodont was then digitized with a laboratory scanner, and the digital file was used to mill a replica of the maxillary arch from a monolithic block of yttria-stabilized zirconia to serve as the master model. Digital impressions of the prepared maxillary right second premolar were recorded with a scanning unit. Scan files were exported as .STL files and sent by e-mail to a dental laboratory. The files were input into a digital design workflow for digital articulation, digital waxing, and design of the definitive crown. Fifteen crowns were produced by milling computer-aided designed lithium disilicate glass ceramic blocks with a 5-axis milling. Fifteen lithium disilicate glass ceramic crowns were produced with a conventional impression and a laboratory fabrication method. The original zirconia die was removed from the zirconia master model to evaluate the crown margins. Circumferential marginal gap measurements were made at 8 measurement locations: mescal, distal, buccal, palatal and associated line angles (mesiobuccal, mesiolingual, distobuccal, and distolingual). Measurements were made to determine the vertical component of the marginal gap according to the definition of marginal fit.
Results:
A total of 240 images (2 groups, 15 crowns per group, 8 sites per crown) were recorded and measured. The overall mean ±SD vertical gap measurement for the digitally made crowns was 48 ±25 μm, which was significantly smaller than that for the conventionally made crowns (74 ±47 μm).
Conclusion:
The fully digital fabrication method provided better margin fit than the conventional method.
