Effects of repeated milling with a 1 mm small-diameter cutting tool on tool dimensions and on the surface characteristics and marginal adaptation of zirconia implant-supported restorations.
Journal
The Journal of prosthetic dentistry
ISSN
1097-6841
Date Issued
2026-02-11
Author(s)
Abstract
Limited information is available regarding the accuracy of computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia implant-supported restorations in relation to tool wear under standardized repeated milling conditions.
The purpose of this in vitro study was to evaluate the correlations of milling tool wear with changes in tool morphology and the external surface characteristics and marginal adaptation of zirconia implant restorations during repeated milling cycles.
A mandibular premolar implant-supported restoration was designed using a CAD software program. Zirconia restorations were repeatedly milled with a Ø1-mm cutting tool until 1 additional specimen was fabricated after the software program indicated tool replacement. Tool deterioration was quantified, and the cutting edge width measured 0.2 mm from the tool tip for each cycle. Pre- and post-processing scans of each restoration were superimposed with a surface-matching program to calculate deviations. Marginal discrepancies between the zirconia restoration and implant abutment were assessed by image analysis. The Kruskal-Wallis test was used for statistical comparisons; Spearman correlation coefficients (ρ) were calculated to assess relationships between tool wear and test variables (α=.05).
Progressive wear was observed on the milling tools. The cutting-edge width increased from 776.4 µm at 0% to 20% deterioration to 797.5 µm at 81% to 100% deterioration, indicating a strong correlation (r=.802). Digital superimposition revealed slight increases in surface deviations of the zirconia restorations with successive milling cycles. Marginal discrepancies substantially increased: horizontal gaps rose from 17.9 µm at 0% to 20% deterioration to 52.3 µm at 81% to 100% deterioration, also indicating a strong correlation (r=.664).
As milling cycles increased, tools became progressively wider and blunter. Although the external surfaces of zirconia implant-supported restorations remained largely consistent, marginal discrepancies increased significantly.
Type
journal article