Fit accuracy of fully digital workflow custom-made post and core restorations.

Abstract

Objective: This study aimed to evaluate the internal fit accuracy of CAD/CAM-fabricated post-and- core restorations using three distinct digital workflows: Direct Intraoral Scanning (DS), Scan Body-aided Intraoral Scanning (SB), and Laboratory Scanning of Impressions (LS). The objective was to determine how scanning modality affects adaptation at the post- cement-die interface, with particular emphasis on apical fit and cement thickness distribution. Methods: Standardized 3D-printed resin dies, representing endodontically treated maxillary central incisor with post spaces prepared using 1.75 mm diameter parallel-sided drills (ParaPost size 7) to a depth of 8 mm, were used to eliminate anatomical variability. A total of 60 post-and-core restorations were fabricated across three groups (n = 20 per workflow). Cementation was performed under standardized pressure of 15 N applied vertically for 6 minutes using a universal testing machine (Instron, Norwood, MA, USA), with dual-cure resin cement. Internal fit was assessed via high-resolution micro-computed tomography (micro-CT), allowing non-destructive volumetric analysis of cement and post adaptation. Parameters measured included cement volume, post volume, regional cement thickness (coronal, middle, apical),apical gap and intra group analysis. Grayscale thresholding was calibrated using Fiji software for accurate segmentation. Results: The scanning technique had a statistically significant effect on internal fit accuracy (p < 0.001). The Lab Scanner (LS) group demonstrated the highest overall performance, with the lowest cement volume (7.32 ± 0.43 × 10⁷ µm³), highest post volume (3.89 ± 0.045 × 10⁸ µm³), and the smallest apical gap (190.3 ± 28.8 µm). The Scan Body (SB) group showed intermediate performance, with a cement volume of (9.49 ± 0.40 × 10⁷ µm³), post volume of (3.65 ± 0.043 × 10⁸ µm³), and apical gap of (279.5 ± 7.4 µm). The Direct Scanning (DS) group exhibited the lowest overall fit accuracy, with the highest cement volume (1.45 ± 0.056 × 108 µm³), the lowest post volume (3.15 ± 0.083 × 10⁸ µm³), and the largest apical gap (1747.8 ± 30.2 µm). Intra-group analysis revealed significant variation in adaptation across the coronal, middle, and apical thirds within each technique. Conclusions: Scanning modality plays a critical role in the internal adaptation of CAD/CAM post-and- core restorations. While laboratory scanning remains the most accurate under standardized conditions, the scan body technique was shown to be a clinically acceptable and efficient digital alternative when standardized properly. Direct intraoral scanning shows limited accuracy in capturing deep post spaces. Further research is needed to validate these findings across diverse anatomies, scanner systems, and clinical environments.