Influence of spacer and milling strategy on CAD/CAM ceramic crown fit and load-bearing capacity

This study assessed the influence of virtual spacer (70, 110, 150 m) and milling strategy (Standard vs. Veneer) on marginal and internal fit, and load-bearing capacity of CAD/CAM ceramic crowns.

Sixty composite resin abutments were scanned, and feldspathic ceramic crowns (CEREC Blocs) were fabricated. Micro-computed tomography evaluated marginal and internal fit on sagittal and axial planes. Crowns were bonded before monotonic load-bearing capacity testing. Data were analyzed using two-way ANOVA and Tukey's test (=5%).

Marginal fit showed no significant differences among milling strategies or spacer settings, and values for all groups were within the clinically accepted range (~100 to 150 m). The virtual spacer, but not the milling strategy, significantly influenced the internal fit at specific sites on both sagittal and axial planes. The 150 m spacer produced larger internal gaps compared to the 70 m setting at the affected sites. Load-bearing capacity (ranging from 924 N to 1297 N) showed no significant differences among any conditions tested.

The virtual spacer thickness influenced the internal fit of ceramic crowns at specific measurement sites, while the milling strategy did not. Neither factor significantly affected the immediate load-bearing capacity under monotonic loading. Marginal fit remained clinically acceptable across all conditions.