Objective: Measure the ECR of restorative materials. Identify key experimental variables that affect results such as indenter type and angle, and recommend best practices for edge chip testing.
Method: An edge chipping machine (Engineering Systems, Model CK 10, Nottingham, UK) was utilized to measure the ECR of a feldspathic dental porcelain using a rounded Rockwell C indenter, or alternatively, sharp conical indenters with varying tip angles (90o–140o). Edge toughness (Te) is equal to the slope of the line on a chipping force versus edge distance graph. Several other materials (three zirconias and a filled resin-matrix composite) were chipped in order to identify other factors that can have an effect on Te.
Result: The edge toughness for the dental porcelain was lower using the Rockwell C indenter (77.2±4.2 N/mm, one std. dev.) compared with the 120o conical indenter (137.5±4.9 N/mm). The Te values (N/mm) varied with indenter tip angle: 88.5±5.7 (90°), 116.2±8.4 (100o), 137.5±4.9 (120o), and 222.6±14.0 (140°). Te values for the three zirconias were similar to each other and ranged from 414-446 N/mm using a 120o sharp conical indenter.
Conclusion: Te can vary with the type of indenter, the indenter tip angle, and the edge distance range used. Other variables such as: specimen mounting, quality of edge, distance measurement method, and loading rate are also factors that can contribute to variation in Te results. It is essential that a well-defined testing methodology be used. Support: ADAF, NIST, and NIDCR Grant DE17983.
Keywords: Ceramics, Dental materials and Edge Chip
See more of: Dental Materials 3: Ceramic-based Materials and Cements