UBC Theses and Dissertations
Micro-CT measurement of the internal fit of lithium disilicate crowns David, Alfaro
The introduction of digital impressions into the field of dentistry has begun the era of entirely computer assisted crown fabrication. The aim of this study was to assess the internal fit of lithium disilicate crowns fabricated using this novel impression technology and to compare their fit to the fit of crowns obtained by traditional elastomeric impressions. Thus, 15 lithium disilicate crowns were fabricated using an entirely digital workflow (impression and fabrication), 15 lithium disilicate crowns were fabricated manually from digital impressions, and 15 lithium disilicate crowns were fabricated using a “traditional” manual process. For the fabrication of the crowns, tooth #15 was prepared for an all-ceramic restoration on an ivorine typodont, which in turn was digitized and a replica milled in zirconia. This master zirconia model and die were then utilized for the impression procedures. Duplicate dies of the master zirconia die were made in polyurethane, enabling the internal fit of each crown to be evaluated via micro CT analysis, due to the contrast in radioopacity between the ceramic, die and internal space. The total volume of the internal space (gap), the mean and maximum thickness of the gap, and the percentage of the gap that was at or below 120um thickness were calculated and evaluated statistically via one-way ANOVA, with post-hoc Scheffé analysis. The results demonstrated that the lithium disilicate crowns fabricated from digital impressions resulted in a smaller internal space, and therefore more intimate fit, in comparison to the lithium disilicate crowns fabricated via the traditional manual approach. Three-dimensional renderings of the internal space were also created, allowing for a descriptive analysis of the distribution of this internal space.
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