7-year Clinical Evaluation of All-ceramic Crowns: Wear and Cracks Analysis

The long-term clinical performance of all-ceramic crowns on posterior teeth and the mechanism of failure are relatively unknown.  Objectives: This prospective study reports the results of clinical evaluation using USPHS criteria, wear and cracks analysis of three ceramic systems { IPS e.max Press (EP), Procera-AllCeram (PA) and metal ceramic (PFM)} over 7-year period.  Methods: A total of 90 posterior crowns were randomized into three groups equally in 48 patients. They were assessed over 7 years using modified USPHS criteria. Impressions were taken for Quantitative wear measurement. Recalls made at six-monthly intervals. The data were analyzed using Kruskal-Wallis non-parametric statistical test and subsidiary follow up Mann-Whitney was performed with Bonferroni correction. Crowns that developed cracks were removed and analyzed using Confocal Laser Scanning Microscope (CLSM) and SEM. Quantitative wear analysis was performed on contact and non-contact areas using 3D digitizer and data were statistically analyzed using Scheffe test.  Results: Out of 90 crowns, 81 were evaluated. USPHS evaluation showed visible roughness, wear and deformity in all crowns at the occlusal contact after 7 years. A number of PA showed chipping of the layering material. Three PA crown was rated Delta and removed due to fracture while four EP was 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 all the groups were significantly different. CLSM showed surface and subsurface cracking in both PA and EP.  SEM showed wear facets and surface cracks. Scheffe test (p>0.05) showed a significant difference in the amount of enamel worn by all types of restorations and vice-versa.  Conclusions: EP showed a comparable clinical performance with PA crowns and different mode of failure according to USPHS criteria with significantly improved wear resistance. Enamel opposing EP showed less wear compared to PA.