Impact of surface finishes on the flexural strength and fracture toughness of In-Ceram Zirconia Manal Manawi, DDS, PhD n Mutlu Ozcan, DDS, Dr.med.dent., PhD n Manal Madina, DDS, PhD n Cenk Cura, DDS, PhD Luiz Felipe Valandro, DDS, MSD, PhD A ll-ceramic dental materials are commonly used because of their superior biocom- patibility and optical properties compared to their metallic coun- terparts. However, their brittleness, in the form of microfractures, has hampered their wider use and lim- ited their application for extensive ixed dental prostheses (FDPs). 1,2 Inherent laws and defects that can propagate at a microscopic level sig- niicantly control the strength and mechanical properties of ceramics. 3 One such all-ceramic system, In-Ceram Alumina (Vident), has been developed. It is based on a slip-casting technique to build the framework of the FDPs ired to an open-pore microstructure. he material derives its strength through iniltration of the lanthanum glass to the microstructures of the open pores of this ceramic. 4 he high lexural strength of glass-iniltrated In-Ceram Alumina (400–605 MPa) has been further improved by adding 33% by weight zirco- nium oxide. 5,6 In-Ceram Zirconia (Vident) demonstrates a lexural strength of 750 MPa and fracture toughness that is two times higher than that of In-Ceram Alumina. 5,6 All-ceramic core materials are covered with suitable veneering ceramics, adequately glazed prior to cementation, and not intended to be exposed in the oral environ- ment. 7 Also, lately, monolithic zirconia FDPs are available that are not covered by a veneering ceramic, but only glazed or colored. Chipping of the veneering ceram- ics with zirconia core exposure has been commonly reported in clinical studies. 8,9 Because adhesion of resin- based materials for direct repair or retrieval of such reinforced ceramics is diicult, one clinical approach to such chipping is to smooth and polish the surface, depending on the size of the defect. 8,10 In fact, nonglazed ceramics have been shown to cause undesirable responses to the adjacent periodontal tissues, such as potentially increasing the wear of opposing teeth and increasing sus- ceptibility to plaque accumulation. 11 Moreover, surface roughness of all- ceramics might also inluence their mechanical properties. 12 Such clinical adjustments could initiate subcritical laws or larger defects. Under clinical Dental restorations made of zirconia are usually selectively adjusted chairside to eliminate occlusal or internal interferences that can impair the mechanical properties of ceramic framework material. Effects of polishing procedures on zirconia after chipping or simply glazing the monolithic zirconia restorations are not known. This study evaluated the effects of different surface treatment procedures—namely, glazing or grinding, finishing, and polishing regimens—on the flexural strength and fracture toughness of a zirconia core material. Forty zirconia specimens were prepared and divided into two main groups (n = 20) according to the type of surface treatment (glazed or ground, finished, and polished). Each group was further divided into two subgroups (n = 10) according to type of mechanical test (flexural strength and fracture toughness). The roughness measurements were performed before mechanical testing. Qualitative evaluation of representative specimens of each subgroup was performed using SEM. The surface roughness mean (μm; ± standard deviations) recorded for the glazed specimens (0.94 ± 0.2) was significantly lower than that of the finished and polished group (3.01 ± 0.1) ( P < 0.05). The glazed zirconia showed significantly higher flexural strength (385.4 ± 45.4 MPa) and fracture toughness (6.07 ± 1 MPa.m ½ ) values than the ground, finished, polished zirconia (302.4 ± 47.6 MPa and 2.14 ± 0.5 MPa.m ½ ) ( P = 0.002 and P < 0.001 for flexural strength and fracture toughness, respectively). A smooth topographic pattern after glazing could not be obtained after finishing and polishing. Grinding, finishing, and polishing markedly decreased the flexural strength and fracture toughness of zirconia compared to the glazed groups. Received: March 3, 2011 Final revisions: May 16, 2011 Accepted: August 1, 2011 Dental Materials 138 March/April 2012 General Dentistry www.agd.org