Experimental Investigation of CAD/CAM-Fabricated Lithium Disilicate Fixed Dental Crowns: Influence of Design Parameters and Ageing on Adaptation and Surface Integrity

Computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have significantly transformed fixed dental prosthesis fabrication by improving precision, repeatability, and clinical efficiency. The present study experimentally investigates the influence of critical design parameters—finish line geometry, convergence angle, and cement layer thickness—on the marginal and internal adaptation of lithium disilicate glass-ceramic (LDGC) fixed dental crowns. A structured design of experiments based on the Taguchi method was employed to systematically evaluate the selected parameters while maintaining clinically relevant constraints. Monolithic LDGC crowns were fabricated using a standardized CAD/CAM workflow, ensuring uniformity across all specimens. Marginal discrepancy (MD), absolute marginal discrepancy (AMD), and internal discrepancy (ID) were quantified non-destructively using synchrotron radiation X-ray micro-computed tomography (SR-µ-CT). In addition, the long-term surface integrity of the crowns was assessed through surface roughness and micro-hardness measurements under simulated thermal-pH ageing cycles up to 40,000 cycles. The results revealed that geometric design parameters significantly affect crown adaptation, with finish line type and cement layer thickness playing dominant roles. Ageing cycles led to a progressive increase in surface roughness and a corresponding reduction in micro-hardness, attributed to thermochemical degradation of the glass-ceramic matrix. The study demonstrates that optimized CAD/CAM design control combined with appropriate parameter selection can enhance the clinical performance and longevity of LDGC fixed dental crowns.