Effect of gypsum separating media on the appearance of stone cast surfaces Tae Hyung Kim, DDS, a Tae Jun Ahn, DDS, b Reyes Enciso, MS, PhD, c and Alena Knezevic, DMD, MS, PhD d Ostrow School of Dentistry, University of Southern California, Los Angeles, Calif; School of Dental Medicine, University of Zagreb, Zagreb, Croatia Statement of problem. Several well-known parameters influence the appearance of the denture base surface, including proper isolation of the dental stone. There is lack of data describing the influence of this parameter on the appearance of the denture base surface. Purpose. The purpose of this study was to evaluate the effectiveness of 2 dental stone separating media on the surface of the denture base. Material and methods. A conventional flasking technique for fabricating a denture base was used. Twenty casts were poured with Type III yellow dental stone to produce 20 identical denture bases. Each cast was sectioned into halves. One half of the cast was treated with Al-Cote (control group) and the other half with Iso-K separating material. Once the denture base was finished, a single examiner, blinded to the experiment, visually compared the 2 surfaces of each cast (right and left part of the cast) under natural light to determine which surface was glossier. The McNemar test (.05 significance level) was used to compare the discordant pairs (20 discordant pairs). Results. Two pairs (10%) were glossier than the Iso-K treatment, and 18 pairs (90%) within the Iso-K treatment were glossier than the treatment with Al-Cote. A statistically significant difference was found between the 2 treatments (P<.001). The odds ratio was 9.00, with a 95% confidence interval of 2.155 to 79.981. Conclusions. When used according to the manufacturer’s instructions, denture surfaces treated with Iso-K appeared glossier than when treated with Al-Cote separating material. (J Prosthet Dent 2014;112:1001-1005) Clinical Implications When used according to the manufacturer’s instructions, the use of Iso-K improves the surface of a polymerized acrylic denture base. The compression-molding method is the standard procedure for heat- polymerized acrylic resin fabrication. In this procedure, acrylic resin is mol- ded against the gypsum cast surface, and if the cast surface has irregularities, similar discrepancies will be produced on the acrylic resin surface. 1 To achieve a clean acrylic resin surface, an ap- propriate separating medium must be applied to the stone cast. Two major complications can occur when an in- appropriate separating medium is used. First, if water passes from the stone into the denture base resin, it may influence This study was supported by USC Contract and Grant # 53-4303-6200. a Assistant Professor of Clinical Dentistry, Division of Restorative Science, Chair of Removable Section, Ostrow School of Dentistry of USC, University of Southern California, Los Angeles. b Assistant Professor of Clinical Dentistry, Division of Restorative Science, Ostrow School of Dentistry of USC, University of Southern California, Los Angeles. c Assistant Professor of Clinical Dentistry, Division of Dental Public Health and Pediatric Dentistry, Ostrow School of Dentistry of USC, University of Southern California, Los Angeles. d Clinical Assistant Professor, Division of Restorative Science, Ostrow School of Dentistry of USC, University of Southern California, Los Angeles. Kim et al