Fracture Toughness of Esthetic Pressed and Milled Restorative Materials

As the dental profession shifts towards monolithic restorative materials, it is necessary to establish a clear understanding of the materials available and how they should be used clinically. The purpose of this investigation is to document the fracture toughness of a number of esthetic indirect restorative materials on the market and to provide recommendations for their application based on existing clinical and laboratory data sets.

Fifty-six monolithic esthetic restorative materials were tested for fracture toughness. Monolithic zirconia materials were tested using the Single Edge Pre-Cracked Beam (SEPB) method, while glass ceramics and resin-ceramic hybrids were tested using the Single Edge V-Notch method (SEVN).

Fracture toughness values for monolithic zirconia correlated inversely with increasing yttria content. 3 mol % yttria-stabilized tetragonal zirconia polycrystal (3Y -MZ) had the highest fracture toughness range (5.55 - 5.64 MPa√m), followed by 4Y -MZ (4.02 - 4.15 MPa√m) and 5Y -MZ (2.43 - 2.70 MPa√m). For some 4Y -MZ and 5Y -MZ products, there was not a significant difference in toughness (p <0.05). Several lithium-based glass ceramics (LBC) had a similar fracture toughness (range of 2.46 - 2.68 MPa√m) to 5Y -MZ (p <0.05). Most LBCs had a fracture toughness range of 1.53 - 2.04 MPa√m, higher than that of other glass ceramics but less than that of 5Y -MZ (p<0.05). Results for resin-ceramic hybrids varied from 1.15 - 2.05 MPa√m, with none reaching the fracture toughness of the higher LBCs or 5Y -MZ (p <0.05).

Clinicians should be aware of the fracture toughness of the materials they use and adjust their preparation parameters accordingly. As fracture toughness decreases, thickness of the resultant restoration should be increased to accommodate the decrease in fracture resistance.