Clinical quality and efficiency of monolithic glass ceramic crowns in the posterior area: digital compared with conventional workflows

Purpose: The aim of this clinical study was to test whether or not digital workflows for the fabrication of crowns render different clinical outcomes from the conventional pathway with respect to (1) crown quality, and (2) time efficiency. Material and methods: For each of the 10 patients in need of one tooth-supported crown, five monolithic crowns were produced out of lithium disilicate reinforced glass ceramic. Four different optical impression and associated computer-aided design/computer-aided manufacturing (CAD/ CAM) systems were used for crown fabrication (digital workflows): (1) Lava C.O.S. scanner and Lava C.O.S. and CARES CAD software, centralized CAM (group L); (2) Cadent iTero scanner, CARES CAD software and centralized CAM (group iT); (3) Cerec Bluecam, Cerec Connect CAD software, followed by laboratory-based CAM (group CiL); and (4) centralized CAM (group CiD). The conventional crown (group K) was fabricated based on a conventional silicone impression followed by a conventional wax-up and heat press technique. The examiners were blinded and evaluated the crowns clinically at the bisque-bake stage (initial try-in), and subsequently after finalization by a dental technician (final try-in). For the assessment of crown quality, modified United States Public Health Service (USPHS) criteria were used. Treatment times were recorded for clinical evaluation and adjustment. The quality ratings were analyzed descriptively. For both the continuous and ordinal outcomes, the non-parametric paired Wilcoxon test was applied, together with an appropriate Bonferroni correction to evaluate the differences between treatment groups. The results of the statistical analysis were interpreted globally at the significance level P = 0.05. Results: The clinical evaluation during the initial and final try-ins demonstrated similar clinical outcome measures for crowns generated with the four digital workflows and the conventional workflow. No statistically significant differences of crown quality in any state were found between groups (P > 0.005). The total clinical treatment times measured were: 456 +/- 240 s for L; 655 +/- 374 s for iT; 783 +/- 403 s for CiL; 556 +/- 285 s for CiD; and 833 +/- 451 s for K. No statistically significant differences in treatment times were found between the groups (P > 0.05). Conclusions: Within the limitations of the present study, the monolithic ceramic crowns resulting from the four different CAD/CAM systems did not differ from the conventionally produced crowns with respect to the clinical quality rating and the treatment time efficiency.