Adjustment Efficiency and Internal Fit of Screw-Retained Zirconia Crowns on Additively Manufactured Dental Casts: An In Vitro Study on the Effect of Printing Layer Thickness and Digital Implant Analog Design.

Purpose

To evaluate how the layer thickness of additively manufactured casts and implant analog design influence the adjustment efficiency and internal fit of screw-retained zirconia crowns, compared with those adjusted on conventional stone casts.

Materials And Methods

A master mandibular model with an implant and its antagonist were digitized to additively manufacture implant casts with 50 µm or 100 µm layer thicknesses and either proprietary friction-retained (S) or third-party screw-retained (N) analogs (S-50, S-100, N-50, N-100), along with their corresponding maxillary casts. Conventional stone casts (CNV) served as the control (n = 10). Screw-retained zirconia crowns were fabricated for each cast, and the duration of interproximal and occlusal contact adjustments was recorded. Crown fit on the master model was evaluated using the triple-scan protocol, followed by a qualitative assessment of interproximal and occlusal contacts. Crowns with heavy contacts were readjusted and timed, then reevaluated to determine whether interproximal adjustments affected the fit. Comparisons among resin casts were performed using a generalized linear model with Bonferroni-adjusted post hoc tests, while comparisons with CNV casts were made with 1-way analysis of variance and Dunnett's tests. Qualitative contact data were analyzed using the chi-square test (α = .05).

Results

Crowns on 50 µm-layer casts needed less adjustment and exhibited smaller gaps than those on 100 µm-layer casts; S analogs led to smaller gaps (P ≤ .010). Compared to CNV, 50 µm-layer casts led to lower adjustment duration and S-50 led to lower internal gaps (P ≤ .020). Only mesial interproximal contacts differed significantly on the master model (P = .001); crowns from S analog casts showed normal contacts, while at least 50% those from other casts had light contacts. At least 50% of the crowns exhibited normal distal contacts, and those with heavy contacts (3 on the mesial and 16 on the distal side) showed improved fit after adjustment. No occlusal adjustments were required on the master model.

Conclusions

Reduced printing layer thickness and the use of proprietary friction-retained analogs improved the adjustment efficiency and internal adaptation of screw-retained zirconia crowns.