Comparison of two Preparation Designs of Shoulder and Chamfer on the Fracture Resistance of Feldespatic Crown Made with CAD/CAM

One of the most important evaluations of fixed restoration is their strength and resistance to fracture which has important role on their longevity and performance. The aim of this in vitro study was to evaluate the effect of two different preparation designs (shoulder and chamfer) on the fracture resistance of feldespatic crowns made with CAD/ CAM.
This study was undertaken using 20 machined stainless steel dies (10 samples for chamfer and 10 samples for shoulder) with 7 mm height, 5 mm diameter and 10´ axial walls canvergency in two finish line designs of 50´ chamfer (0.8 mm depth) and 90´ shoulde (1 mm depth). Twenty impressions were taken using a polyvinylsiloxane and poured with vacuum–mixed type 4 dental stone. Twenty first premolar feldespatic (cerec blocs) crowns were made with CAD/CAM. Each crown was cemented on its definitive stainless steel dye with clearfil SA luting and underwent a fracture test with a universal testing machine.
The mean value of fracture resistance for chamfer margins were 771.40 99.47 N and for the shoulder margins were 782.30129.40 N. The student’s t- test did not reveal a statistically significant different between two groups (P=0.835)
The results indicate that marginal design of the feldespatic crowns do not effect their fracture resistance and selection of finish line designs should be based on clinical condition of the restored tooth.