The clinical performance of new all-ceramic systems on posterior teeth and the mechanism of failure are relatively unknown. Objectives: This study reports the results of prospective clinical evaluation and crack analysis of three ceramic systems {non-layered, experimental hot-pressed ceramic (EC)¹, Procera-AllCeram (PA)² and metal ceramic (PFM)³} over 54 months.  Methods: Ninety posterior crowns were randomized into three groups equally in 48 patients and assessed over 54 months using USPHS criteria.  Pressure film was used to analyse the distribution of force at the occlusal contact areas (OCA). The USPHS data were analyzed using the Kruskal-Wallis non-parametric statistical test and subsidiary follow up Mann-Whitney.  Crowns that developed cracks were removed and the surfaces were examined using Confocal Laser Scanning Microscope (CLSM) and SEM.  Results: Clinical evaluation showed visible roughness, wear and deformity in PA crowns at the region of OCA, whereas EC and PFM showed fewer changes.  Pressure analysis showed that each OCA is subjected to a different range of pressure points.  Two PA crown were rated Delta due to fracture and removed while two EC were rated Charlie and removed due to crack propagation.  Kruskal-Wallis showed a highly significant difference (p<0.0005) in alpha scores between the three crown systems. Mann-Whitney showed that all the groups were significantly different. CLSM examination showed a difference in crack depth with 50-60 μm deep subsurface cracking in PA crowns at the center of the OCA, with 10-40 μm depth in the EC at the margins of the OCA.  SEM showed surface cracks related to the OCA. Conclusions: EC showed a comparable clinical performance with PA crowns, but improved durability. Pressure analysis suggests that there was a correlation between the distribution of force at each OCA and crack propagation. The crack depth in the PA was higher than the EC.

1: Ivoclar-Vivadent, 2: NobelBiocare/Ducera, 3: Panadent/Ivoclar.