Internal fit and fracture resistance of different CAD‐CAM surveyed ceramic crowns: In vitro comparative analysis

Abstract

Abstract Purpose The success of removable partial dentures (RPDs) depends on well‐designed abutments or surveyed crowns. Advances in computer‐aided design and computer‐aided manufacturing (CAD‐CAM) technology have made all‐ceramic materials viable alternatives to traditional ceramo‐metal surveyed crowns, but their performance, particularly regarding internal fit and fracture resistance, requires further studies, especially with different rest seat preparations simulated on the abutment dies. This study evaluated the internal fit and fracture resistance of CAD‐CAM ceramic crowns with wide and narrow rest seat designs to assess their potential as surveyed crowns for RPDs. Materials and Methods Sixty mandibular premolar abutment dies were modified to simulate narrow and wide occlusal relief designs and were divided into six groups based on the design (wide/narrow) and material type: force‐absorbed hybrid ceramics (HC), zirconium lithium silicate (ZLS), and lithium disilicate glass‐ceramic (LDC). CAD‐CAM ceramic crowns were fabricated, milled, and analyzed for internal fit using Geomagic Control X software. Fracture resistance in newton (N) was tested using a universal testing machine. Scanning electron microscopy (SEM) was employed to examine fracture morphology. Statistical analyses included two‐way analysis of variance (ANOVA) and post hoc Tukey's test ( α = 0.05). Results The LDC group had the highest fracture resistance, while ZLS and HC showed no significant difference [ F (2) = 10.523, p < 0.001]. Internal fit did not significantly differ between materials [ F (2) = 0.381, p = 0.686], though LDC had a slightly larger internal gap. Rest seat design significantly affected both fracture resistance and internal fit [ F (1) = 68.581, p < 0.001; F (1) = 11.185, p = 0.002], with wide designs showing higher fracture resistance and narrow designs having larger internal gaps. SEM revealed crack propagation originating from rest seat bases, with longer crack lines observed in wide rest designs. Conclusion Rest seat design significantly influences the fracture resistance and internal fit of CAD‐CAM ceramic crowns. Wide rest seat designs provide superior fracture resistance compared to narrow designs, while narrow seats exhibit larger internal gaps, potentially compromising restoration longevity.