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UBC Theses and Dissertations

Marginal fit of lithium disilicate crowns : a three-dimensional analysis Mostafa, Nesrine


Objectives: To compare the marginal fit of lithium disilicate (LDS) crowns fabricated with digital impression and manufacturing (termed “DD”), digital impression and traditional pressed manufacturing (termed “DP”), and traditional impression and manufacturing (termed “TP”). Methods: Tooth #15 was prepared for all-ceramic crowns on an ivorine typodont. There were 45 LDS crowns fabricated using three techniques: DD, DP, and TP. Micro-computed tomography (micro-CT) was utilized to assess the 2D and 3D marginal fit of crowns in all three groups. The 2D vertical marginal gap (MG) measurements were done at 20 systematically selected points/crown while the 3D measurements represented the 3D volume of the gap measured circumferentially at the crown margin. Incidences of different marginal discrepancies were also recorded, including over-extension (OE), under-extension (UE), and porcelain chipping. Crowns with vertical MG>120 μm at more than five points were considered unacceptable and were rejected. The results were analyzed by one-way ANOVA with Scheffe post hoc test (α=0.05). Results: DD crowns demonstrated significantly smaller mean vertical MG (33.3±19.99 μm) compared to DP (54.08±32.34 μm) and TP (51.88±35.34 μm) crowns. Similarly, MG volume was significantly lower in DD group (3.32±0.58 mm³) compared to TP group (4.16±0.59 mm³). Interestingly, the mean MG volume for the DP group (3.55±0.78 mm³) was not significantly different from the other groups (DD and TP). The incidence of under-extension was higher in DP (6.25%) and TP (5.4%) than in DD (0.33%) group, while over-extension was more frequent in DD (37.67%) than in TP (28.85%) and DP (18.75%) groups. Overall, 4 out of 45 crowns fabricated were deemed unacceptable based on the vertical MG measurements (three in TP group and one in DP group) while all crowns in DD group were deemed acceptable. Conclusion: Digital impression and CAD/CAM manufacturing resulted in consistently better marginal fit and was associated with less manufacturing errors.

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