COMPARATIVE ANALYSIS OF MARGINAL FIT AND FRACTURE RESISTANCE OF GRAPHENE, PEEK COPING-ZIRCONIA AND ZIRCONIA CROWNS MANUFACTURED USING CAD/CAM MILLING AND 3D PRINTING TECHNIQUE – AN IN VITRO RESEARCH

Background: Recent advances in restorative dentistry have introduced novel materials such as graphene-reinforced polymers, polyetheretherketone (PEEK), and zirconia, alongside evolving digital fabrication techniques. Vertical marginal fit and fracture resistance are critical to crown longevity, warranting comparison of additive (3D printing) versus subtractive (CAD/CAM milling) manufacturing.

Methods: This in vitro study evaluated 120 standardized typhodont mandibular premolars restored with full-coverage crowns of graphene-reinforced PMMA, PEEK copings veneered with zirconia, and monolithic zirconia, each fabricated by both CAD/CAM milling and 3D printing in a full factorial design (n = 20 per material per technique; 10 specimens each for marginal gap and fracture resistance evaluation). Vertical marginal gap was measured at three standardized points on SEM images of sectioned, gold sputter-coated specimens. Fracture resistance was assessed by axial compressive loading to failure in a universal testing machine. Normality was confirmed (Kolmogorov–Smirnov, Shapiro–Wilk); groups were compared using one-way ANOVA with post-hoc testing (α = 0.05).

Results: Monolithic zirconia crowns exhibited the highest fracture resistance and smallest marginal gaps, followed by PEEK-zirconia, while graphene-based crowns showed the lowest fracture resistance. Across all materials, 3D-printed crowns showed reduced marginal gaps and higher fracture resistance than CAD/CAM-milled crowns.

Conclusion: Within study limitations, 3D printing improved marginal adaptation and fracture resistance compared with CAD/CAM milling. Zirconia demonstrated the most favorable performance, followed by PEEK-zirconia, while graphene crowns showed comparatively lower mechanical performance.

Clinical Significance: 3D printing improves marginal fit and fracture resistance of metal-free crowns, particularly zirconia .