Internal and marginal fit of digitally fabricated all-ceramic crowns with auxiliary retentive features on short clinical abutments: a micro-CT study.

Short clinical crowns/abutments (SCC) pose a challenge in achieving adequate retention. Auxiliary retentive features (ARF), such as grooves, are commonly employed to enhance retention. The marginal gap (MG) and internal fit (IF) of restorations are critical factors influencing clinical success. This study aimed to evaluate the MG, IF, and cement volume of digitally fabricated (computer-aided design (CAD) and computer-aided manufacturing (CAM)) all-ceramic crowns with and without grooves on SCC using micro-computed tomography (micro-CT). A mandibular second molar typodont tooth was prepared to simulate SCC. Four groups of crowns (n = 30 per group) were fabricated: Group 1: CAD/CAM zirconia without grooves, Group 2: CAD/CAM zirconia with grooves, Group 3: CAD/CAM lithium disilicate with grooves, Group 4: Conventional lithium disilicate with grooves. Crowns were cemented using resin cement. MG, IF, and cement volume were evaluated using micro-CT. Gap measurements were taken in two planes across seven zones (Z1 to Z7). Statistical analysis was performed using one-way ANOVA and post hoc Tukey tests. Significant differences in MG and IF were observed among the groups (p < 0.001). Group 1 exhibited the lowest MG and IF, followed by Group 3, Group 2, and Group 4. Group 4 showed the highest average marginal discrepancy (AMD) and average wall discrepancy (AWD) ((AMD: Z1 = 197.36 ± 10.56 µm; Z7 = 226.5 ± 8.24 µm), (AWD: Z2 = 150.05 ± 10.89 µm; Z6 = 169.38 ± 10.57 µm)), followed by Group 2 > Group 3 > Group 1. The greatest discrepancy at the cuspal area was observed in Group 2, followed by Group 3 > Group 1 > Group 4. In the central fossa, the maximum discrepancy was also noted in Group 2 (CFD = 194.48 ± 13.71 µm). No significant differences were found in total cement space volume among the groups. CAD/CAM crowns with grooves demonstrated clinically acceptable MG and IF values, with lithium disilicate crowns showing superior performance. These findings support the use of CAD/CAM technology for SCC restorations and underscore the importance of material selection and crown design for optimal clinical outcomes.