Comparison of marginal and internal fit of 10-unit fixed dental prostheses fabricated from cobalt chromium alloys or zirconia ceramics using digital workflows.

Abstract

Statement of problem: Long-span fixed dental prostheses (FDPs) can be challenging to fabricate with adequate marginal and internal fit. The performance of restorations fabricated from cobalt chromium or zirconia using a completely digital workflow requires further evaluation to ensure clinical acceptability.

Purpose: The purpose of this in vitro study was to evaluate and compare the marginal and internal fit of 10-unit FDPs fabricated from cobalt chromium or zirconia by using digital scanning and computer-aided design and computer-aided manufacturing (CAD-CAM).

Material and methods: Twenty-four complete arch digital scans of a typodont model with 6 prepared teeth were acquired to design and mill 12 cobalt chromium and 12 zirconia 10-unit FDP frameworks. For each framework, measurements from all 6 abutments and from both buccolingual and mesiodistal sections were pooled, yielding 1 mean value per measurement area per specimen. Marginal, chamfer, internal, and overall cement gaps were evaluated with the silicone replica technique. Trueness was defined as the difference between the measured gap and the preset cement spacer. Data were analyzed with 2-sample t tests on the pooled specimen means (α=.05).

Results: Mean gap measurements for cobalt chromium versus zirconia were (gap value ±standard deviation) as follows: marginal, 68.7 ±14.6 µm versus 53.3 ±11.8 µm; chamfer, 66.8 ±10.6 µm versus 58.1 ±10.8 µm; internal, 77.7 ±6.5 µm versus 95.8 ±9.4 µm; and overall cement gap, 74.2 ±8.2 µm versus 81.3 ±9.7 µm. The zirconia restorations exhibited a significantly smaller marginal gap (P=.01), whereas the cobalt chromium frameworks showed a significantly smaller internal gap (P<.001), with the chamfer gap being statistically similar (P=.061). Zirconia demonstrated significantly higher trueness in the marginal area (P=.01), while the internal gap trueness did not differ significantly between the 2 materials (difference 1.9 µm, P=.56). Both materials remained below the 120 µm clinical threshold for acceptable fit.

Conclusions: A digital workflow yielded precise, clinically acceptable fit for 10-unit restorations fabricated from both cobalt chromium and zirconia. Zirconia demonstrated significantly higher marginal trueness, whereas the internal gap trueness did not differ significantly between the 2 materials. Optimizing cement spacer settings and evaluating deviations from the planned spacer are crucial for an accurate assessment of fit.