Effect of varying coping thickness on early load-to-fracture strength of Procera AllCeram copings cemented with 2 resin-modified glass-ionomer cements

Objectives: Clinical situations may dictate that Procera AllCeram copings (Nobel Biocare) be fabricated or adjusted to a 0.40-mm coping thickness rather than the standard 0.60 mm. The goal of the present study was to determine the relative strength of 0.40-mm aluminum oxide copings versus standard 0.60-mm aluminum oxide copings and ascertain the effect of luting agents on the load-to-fracture value of the copings. Method and Materials: Forty prefabricated grade 2 titanium dies, premilled to standardized dimensions of a mandibular molar, were scanned using Procera CAD/CAM. Twenty aluminum oxide copings were ordered in the standard 0.60 mm thickness and 20 in 0.40 mm. Two cements were selected. Ten copings of each thickness were cemented to the titanium dies with RelyX Luting (3M ESPE) and 10 of each thickness with Fuji Plus cement (GC). Immediately after cementation, copings were placed under 5-kg static load for 10 minutes and then stored for 1 week in a 100% humidity chamber. At the time of testing, the samples were inspected and placed in a jig to ensure uniform vertical force application. Samples were loaded to fracture at 0.5 mm/min using an Instron universal testing machine. Results were recorded and statistically analyzed using the unpaired Student's t test. Significance was determined at confidence level P = .05. Results: Mean load-to-fracture for the copings cemented with RelyX Luting was 451 N for 0.40-mm and 884 N for 0.60-mm copings, and for the copings cemented with Fuji Plus, 808 N and 1,701 N, respectively. Conclusions: Aluminum oxide copings of 0.60 mm showed significantly greater load-to-fracture values than 0.40 mm copings, regardless of the luting agent used. Within the independent comparisons, copings cemented with Fuji Plus exhibited higher load-to-fracture values than copings cemented with RelyX Luting cement. Palabras clave: aluminum oxide, coping thickness, Fuji Plus cement, load-to-fracture, luting agents, Procera AllCeram copings, RelyX Luting