Comparison of marginal and internal fit of custom-made post and core restorations milled with 4-axis and 5-axis milling machines in Polyetheretherketone and composite.

OBJECTIVES

This study aimed to compare the effects of two milling systems (4-axis and 5-axis) and two materials - polyetheretherketone (PEEK) and computer-aided-design/computer-assisted-manufacturing (CAD/CAM) Composite- on the marginal and internal fit of custom-made post and core restorations.

MATERIALS AND METHODS

Eighteen single-rooted premolars were endodontically treated and prepared with a standardized post space of 10 mm. The teeth were scanned to receive post and core restorations, fabricated using the SHERAEco-mill 40 (4-axis) and SHERAEco-mill 50 (5-axis) milling machines (Shera Werkstoff-Technologie, Germany) and two materials-PEEK and Composite. Marginal and internal fit were measured using Geomagic Control X (3D Systems, Rock Hill, SC, USA), based on root mean square (RMS) values obtained from comparing the STL files of the design with the scanned, milled restorations. Data was analyzed with a two-way ANOVA and pairwise t-tests, with Bonferroni correction (p < 0.05).

RESULTS

Pairwise comparisons revealed significant differences in RMS values between milling machines, with 4-axis milled posts showing higher marginal (139.45±24.59 µm) and internal RMS values (135.04±8.68 µm) than 5-axis milled posts (104.14±10.51 µm and 116.22±9.89 µm, respectively). Higher significant RMS values in marginal surfaces were detected (118.60±16.7023.64 µm) for PEEK posts compared to (89.68±4.32 µm) for Composite posts milled with 5-axis. No significant differences were observed between materials for marginal or internal fit in 4-axis and internal fit in 5-axis.

CONCLUSIONS

This in vitro study findings demonstrated a superiority of 5-axis milling machines over 4-axis machines in achieving superior marginal and internal fit for post and core restorations, irrespective of the material utilized. While material selection did not significantly influence fit when employing 4-axis milling, a notable discrepancy emerged with 5-axis milling, where PEEK restorations exhibited poorer marginal fit compared to composite restorations.

CLINICAL SIGNIFICANCE

5-axis milling machines demonstrated superior performance in producing custom-made post and core restorations with enhanced marginal and internal fit compared to 4-axis machines. This improved fit can potentially enhance seating accuracy, minimize cement thickness and micro-gaps, and ultimately contribute to improved long-term clinical outcomes. Furthermore, the lack of significant differences in fit observed between PEEK and CAD/CAM composite materials with 4-axis milling provides clinicians with greater flexibility in material selection based on other clinically relevant factors, such as esthetics, mechanical properties, adhesive properties, and patient preferences.