Fracture-toughness measurement of dental ceramics using the indentation fracture method with different formulas

This study examined fracture toughness (K-IC) measurements obtained using the indentation fracture (IF) method with a view to improving their reliability. The K-IC values of five dental ceramics were measured using the IF method with five different formulas, and the single-edge precracked beam (SEPB) method was used as a control. The elastic moduli of the dental ceramics were evaluated by dynamic hardness test. Load conditions of the dental ceramics that produced a median/radial crack for the IF method formulas were investigated. Based on the resultant c/a and P/c(1.5) values, the indentation load (P) required for median/radial crack occurrence varied greatly from 29.4 to 196 N depending on the ceramic used. Among the five formulas, none of the K-IC values obtained by the IF method with Miyoshi's formula differed significantly (p > 0.05) from the values obtained-using SEPB method. These results suggested that, after an appropriate indentation load is determined, reliable K-IC values for small dental ceramic specimens can be easily obtained using the IF method if Miyoshi's formula is used in combination with the dynamic hardness test.