Implant-cemented Co-Cr frameworks produced by hard and soft milling: The impact of porcelain firing cycles on microstructure and fit accuracy.

Abstract

This study examines how porcelain firing cycles and fabrication methods impact the microstructure and the marginal and internal fit of implant-cemented Co-Cr frameworks. Two fabrication processes for Co-Cr specimens were used: hard milling or soft milling. Each type of framework was then allocated to use either as-fabricated or as porcelain-fired. The microstructural analysis employed x-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX). A total of ten Co-Cr frameworks were fabricated for each method, and discrepancies in margin and internal fit were evaluated using X-ray microtomography (micro-CT) before and after the porcelain firing. Statistical analysis was performed using two-way ANOVA and Tukey's multiple comparison tests (α = 0.05). The findings indicated a combination of γ-fcc and ε-hcp cobalt-based phases, with porcelain firing notably enhancing the ε-Co content, particularly among soft milled specimens. Soft milled specimens exhibited a diffuse presence of pores, while hard milled specimens revealed a random distribution of small pores. The soft milled specimens exhibited a significant reduction in discrepancies after the application of firing cycles. Although not statistically significant, the hard milled specimens also showed a trend toward reduced discrepancies post-firing. All subgroups maintained clinically acceptable marginal adaptation, with soft milled frameworks outperforming their hard milled counterparts in overall fit.