The Journal of Prosthetic Dentistry Pelaez-Vargas et al Statement of problem. One-step and incremental mixing procedures are currently used to produce dental ceramic pastes. In the ceramic industry, high quality is obtained using one-step mixing, but in dentistry, the best method has not been yet determined. Purpose. The purpose of this study is to evaluate the effects of 2 mixing techniques on the biaxial flexural strength and microstructure of dental porcelain. Material and methods. Feldspathic porcelain discs (2 x 15 mm in diameter) were produced and divided according to the ceramic paste preparation method, powder-liquid incremental mixing group (n=50) or one-step mixing, as a control group (n=50). Specimens were tested for biaxial flexural strength and characterized using porosimetry, relative humidity, SEM/EDS, XRD, and FT-IR analyses. Statistical analysis was conducted using Weibull statistics. The Weibull modulus, characteristic strength and relative humidity were compared between groups, using Student’s t-test and Mann-Whitney U test (α=.05). Results. The powder-liquid incremental mixing group showed significantly higher values (SD) of Weibull modulus (6.74 (0.70), P<.001) and characteristic strength (79.87 (2.01) MPa, P<.001) when compared to the one-step mix- ing group (4.94 (0.94) and 75.95 (2.61) MPa). Significantly lower mean (SD) relative humidity values (P=.009) were found for powder-liquid incremental mixing group (20% (0.5%)) compared to one-step mixing group (22% (1%)). XRD spectra showed that the one-step mixing group produced higher amounts of the amorphous phase. Conclusions. Specimens produced by the incremental mixing technique showed higher biaxial flexural strength than one-step mixing. (J Prosthet Dent 2011;105:308-314) The effect of slurry preparation methods on biaxial flexural strength of dental porcelain Alejandro Pelaez-Vargas, DDS, MSc, a Jaime A. Dussan, DDS, b Luis F. Restrepo-Tamayo, DDS, c Carlos Paucar, MSc, d Jorge A. Ferreira, MS, e and Fernando J. Monteiro, Eng. MSc, PhD f Institute of Biomedical Engineering, Porto, Portugal; University of Porto, Porto, Portugal; CES University, Medellin, Colombia; National University of Colombia, Medellin, Colombia; National Laboratory of Energy and Geology, S. Mamede Infesta, Portugal. Partially supported by scholarship No. E05D050652CO from AlBan Program (European Union) and scholarship No. FCT/SFRH/ BD/36220/2007 and Grant No. FCT/PTDC/CTM/100120/2008 from Portuguese Science and Technology Foundation (FCT, Por- tugal) Preliminary results were presented at IADR IADR/AADR/CADR 85th General Session and Exhibition, New Orleans. March 21-24, 2007. a PhD student. Institute of Biomedical Engineering (INEB - Instituto de Engenharia Biomédica) and Faculty of Engineering. Univer- sity of Porto (FEUP, Universidade do Porto). b Former Postgraduate Student. CES-LPH Research Group. Faculty of Dentistry. CES University (Universidad CES). c Assistant Professor. CES-LPH Research Group. Faculty of Dentistry. CES University (Universidad CES). d Associate Professor. Chemistry Department. Faculty of Sciences. National University of Colombia (Universidad Nacional de Colombia). e Researcher. National Laboratory for Energy and Geology (LNEG - Laboratorio Nacional de Energia e Geologia). f Full Professor. Institute of Biomedical Engineering (INEB - Instituto de Engenharia Biomédica) and Faculty of Engineering, Univer- sity of Porto (DEMM, FEUP, Universidade do Porto).