Abstract
OBJECTIVES: This study aimed to evaluate and compare the marginal adaptation and internal gap of implant-supported crowns fabricated from polyetheretherketone (PEEK) using CAD-CAM milling, heat pressing, and 3D printing, employing non-destructive micro-computed tomography (µCT). METHODS: This in-vitro study used thirty PEEK crowns (n = 10 per group) that were fabricated using CAD-CAM milling (MP), heat pressing (PP), and 3D printing (3DP) and seated on standardized zirconia abutments. Marginal and internal gaps were quantitatively assessed using high-resolution µCT scanning (voxel size: 9.2 μm) at 12 predetermined locations per crown in sagittal and coronal planes. Measurements included marginal gaps (mesial and distal), finish line gaps, and internal gaps at axial walls, occlusal surfaces, and internal line angles. Non-parametric statistical tests (Kruskal-Wallis and Dunn’s post hoc with FDR correction) were applied, with significance set at P < 0.05. RESULTS: All measurement sites showed statistically significant differences between the groups (P < 0.001), with large effect sizes. Milled crowns exhibited the smallest occlusal gaps and superior adaptation at the occlusal surface (P < 0.001), while 3D-printed crowns demonstrated the best adaptation along axial walls and internal angles. Pressed crowns consistently showed the largest marginal and internal gaps across most regions. All fabrication techniques demonstrated marginal gap values within the clinically acceptable threshold (< 120 μm); however, statistically significant differences were observed in both marginal and internal adaptation among the three groups (P < 0.001). CONCLUSIONS: Fabrication technique significantly affects the marginal adaptation and internal gap of implant-supported PEEK crowns. While milled crowns showed optimal occlusal adaptation, 3D-printed crowns provided the best internal conformity along axial surfaces. Pressed PEEK restorations exhibited the poorest adaptation. These findings underscore the importance of technique selection in optimizing clinical outcomes of PEEK-based implant prostheses. CLINICAL SIGNIFICANCE: Marginal adaptation and internal fit affect the biological and mechanical success of implant crowns. Milling and 3D printing showed better adaptation than heat pressing, supporting techniques that improve longevity and reduce complications. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12903-026-08150-8.