Marginal Fitness of Monolithic Zirconia Crowns Fabricated from Direct Digital Scanning, Impression Scanning and Indirect Digital Scanning Using Different Impression Materials

Aim: To evaluate and compare the marginal fitness of zirconia crowns fabricated from direct digital scanning, scanning of conventional impressions made with different impression materials and indirect scanning of the resulting stone dies using an extra-oral scanner.

A metal die for a prepared maxillary right first molar was used as a master model for this study. A total of fifty-six zirconia crowns were then fabricated using CAD/CAM system according to the following sample grouping: Group I: Crowns fabricated from direct digital scanning of the metal die (8 crowns), Group II: Crowns fabricated from scanning of the conventional impression, which was further subdivided into three subgroups of 8 crowns according to the type of impression material used: (Subgroup IIA: condensation silicone, Subgroup IIB: PVS and Subgroup IIC: VPES). Group III: Crowns fabricated from scanning of the stone dies obtained from pouring of the conventional impression, which was also subdivided into three subgroups of 8 crowns as for Group II. The marginal gap of each crown was then measured using digital microscope at a magnification of 230x. The recorded measurements were then subjected to statistical analysis using One-way ANOVA test, Dunnett's test, Tukey's HSD test and Holm-Bonferonni test at a level of significance of 0.05.

The results of this study showed that the lowest mean value of marginal gap was recorded by crowns fabricated using direct digital scanning (Group I) with statistically highly significant differences when compared with other groups. On the other hand, the highest mean value of marginal gap was recorded by crowns fabricated from scanning of stone dies obtained from pouring of condensation silicone impressions (Group IIIA).

Conclusions: The mean values of marginal gap of zirconia crowns of all groups are within the clinically acceptable limit of 120 μm except those of crowns fabricated using condensation silicone impression material. Crowns fabricated by direct digital scanning showed better marginal fitness than crowns fabricated by the indirect method which showed more discrepancy.