Marginal adaptation of 3D-printed crowns: influence of preparation geometry and digitization workflow

BACKGROUND: This in vitro study evaluated the impact of different workflow and finish line design on the marginal adaptation of 3D printed resin matrix ceramic crowns. METHODS: Forty extracted mandibular molars were randomly allocated into two groups according to finish line design (n = 20); heavy chamfer 0.8 mm (H) and conservative chamfer 0.2 mm (C). Each main group was divided into 2 subgroups (n = 10) according to workflow; direct digital intraoral scanning workflow (D) and semi-digital workflow (S). Crowns were 3D printed from hybrid resin and cemented using adhesive resin cement. Marginal adaptation was evaluated for all groups using a stereomicroscope before cementation and after the combined cementation and artificial aging. Statistical analysis was performed with 3-way ANOVAs and post hoc Tukey test, (P < 0.05). RESULTS: Significant effects were found for finish line design, workflow, and the combined cementation and artificial aging (P < 0.05), with no significant interaction between finish line design and workflow (P = 0.552). Mean marginal gaps (µm) of test groups before cementation and after the combined cementation and aging protocol were: HD, (71.72 ± 4.82), (84.5 ± 2.75); CD, (82.16 ± 3.76), (97.32 ± 3.16); HS, (92.51 ± 3.64), (111.8 ± 3.37); and CS, (106.1 ± 3.57), (123.4 ± 2.58). All groups showed significant increases thereafter (P < 0.05). Heavy chamfer finish line and direct digital workflow each yielded significantly smaller marginal gap than conservative chamfer and semi-digital workflow at both time points (P < 0.05). CONCLUSIONS: Within the limitations of this in vitro study, finish line design and workflow type each independently influenced the marginal adaptation of 3D-printed resin matrix ceramic crowns. A heavy chamfer and a direct digital workflow were each associated with smaller marginal gaps.