Assessment of Trueness and Internal Fit of Glass Ceramic Crowns Constructed by Four and Five-Axis Milling Machines (An In Vitro Study)

Document Type : Original Article

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Fixed Prosthodontics Department, Faculty of Dentistry, Cairo University

Abstract

Aim: This in-vitro study was conducted to assess the trueness and internal fit of glass ceramic crowns (Lithium disilicate: IPS e.max CAD) constructed by four and five-axis milling machines.
Methodology: A typodont model of mandibular 1st molar was prepared for full coverage crowns. With the intraoral scanner (primescan), the prepared model was digitally scanned and designed by CEREC software to fabricate 14 glass ceramic crowns (IPS e.max CAD).Group I: 4-axis (MX CL), and group II: 5-axis(MC X5) milling machines (n =7). The milled restorations were scanned then internal and external occlusal surfaces were superimposed onto the reference CAD model using software for difference analysis (Geomagic Control X, 3D systems, USA) to assess. A silicone replica technique was utilized to evaluate the internal gap. After testing for normality, Numerical data were presented as mean and standard deviation values. Data were statistically analyzed at a level of significance (P ≤ 0.05).
Results: Crowns produced by the MC X5 machine exhibited higher trueness than those produced by the MC XL machine (p <0.05). There were significant differences in trueness values between different crown areas (p< 0.001, 44.07±9.78 in the in-lab MC X5),) p < 0.001, 71.99±31.22 in the MC XL group). When comparing both groups regarding internal fit, the MC XL group had a significantly higher internal gap than the MC X5 group (p<0.05) for overall measurements and axial 2 which is the region between the axio-occlusal and the axial 1. Meanwhile, for the other measurements, there was no statistically significant difference (p>0.05).
Conclusions: The five-axis milling machine yielded higher trueness than the four-axis. Also, crowns produced by the four-axis milling machine had a significantly higher internal gap compared to those produced by the five-axis milling machine.

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Advanced Dental Journal
Volume 7, Issue 3
July 2025
Pages 435-447

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