Microhardness Obtained with Two Ceramic Paste Preparation Methods

Introduction: Dental ceramics show low structural reliability in both laboratory and clinical conditions due to ceramic processing. The ceramic paste preparation is a fundamental phase in building up the restorations. Usually the dental laboratory techniques include either an incremental or a “one step” mixture of powder and liquid, but the industry uses the second method with the purpose of obtaining minor micro-defects in the final volume. Objectives: The aim of this study was to compare micro-hardness of ceramic discs produced using two different preparation methods as a measure of their surface micro-defects. Methods: 100 Vita-Omega 900 porcelain discs were produced and were divided according to ceramic paste preparation method in an incremental mixture group and one-step mixture group. The discs were polished and tested according to Vickers hardness under a 4.905 N load during 15 seconds. Results: Better resistance to indentation was found on the discs obtained by the incremental mixture method compared to one-step mixture method (p<0.05). But Weibull analysis shows that the one-step method allows for less variability of surface micro-defects in the final samples. Conclusions: Surface micro-defects inherent to processing are responsible for catastrophic failures of ceramic materials. It was found that better structural reliability of ceramic restorations might be achieved by using the one-step mixture preparation method. Acknowledgement: Program Alban, the European Union Program of High Level Scholarships for Latin America, scholarship No.E05D050652CO and CIDI, Universidad Pontificia Bolivariana, Convocatoria 2005.