The Journal of Prosthetic Dentistry Suprono et al Clinical Implications The alternative materials performed best for the parameters tested. How- ever, they are more expensive than irreversible hydrocolloid impression materials, which may limit their acceptability as a replacement material. Statement of problem. Many new products have been introduced and marketed as alternatives to traditional irrevers- ible hydrocolloid materials. These alternative materials have the same structural formula as addition reaction silicone, also known as vinyl polysiloxane (VPS), impression materials. Currently, there is limited in vitro and in vivo research on these products, including on the effects of chemical disinfectants on the materials. Purpose. The purpose of this study was to compare the effects of a spray disinfecting technique on a traditional ir- reversible hydrocolloid and 3 new alternative impression materials in vitro. Material and methods. The tests were performed in accordance with the American National Standards Institute/ American Dental Association (ANSI/ADA) Specification Nos. 18 and 19. Under standardized conditions, 100 impres- sions were made of a ruled test block with an irreversible hydrocolloid and 3 alternative impression materials. Nondis- infected irreversible hydrocolloid was used as the control. The impressions were examined for surface detail reproduc- tion before and after disinfection with a chloramine-T product. Type III and Type V dental stone casts were evaluated for linear dimensional change and gypsum compatibility. Comparisons of linear dimensional change were analyzed with 2-way ANOVA of mean ranks with the Scheffé post hoc comparisons (α=.05). Data for surface detail reproduc- tion were analyzed with the Wilcoxon Signed-Rank procedure and gypsum compatibility with the Kruskal-Wallis Rank procedure (α=.05). Results. The alternative impression materials demonstrated significantly better outcomes with all 3 parameters tested. Disinfection with chloroamine-T did not have any effect on the 3 alternative impression materials. The irreversible hydrocolloid groups produced the most variability in the measurements of linear dimensional change. All of the tested materials were within the ADA’s acceptable limit of 1.0% for linear dimensional change, except for the disinfected ir- reversible hydrocolloid impression material. Conclusions. The alternative impression materials performed best for the parameters tested. Spray disinfection had no effect on the alternative impression materials. (J Prosthet Dent 2012;108:250-258) Effect of disinfection on irreversible hydrocolloid and alternative impression materials and the resultant gypsum casts Montry S. Suprono, DDS, MSD, a Mathew T. Kattadiyil, DDS, MDS, MS, b Charles J. Goodacre, DDS, MSD, c and Myron S. Winer, DDS d School of Dentistry, Loma Linda University, Loma Linda, Calif Presented at Loma Linda University School of Dentistry, in partial fulfillment of the requirements for the MSD degree, May 2011. a Assistant Professor, Department of Restorative Dentistry, LLU School of Dentistry, Loma Linda University; Assistant Professor, Western University School of Dentistry, Pomona, Calif; Private practice, Colton, Calif. b Program Director, Advanced Education in Prosthodontics, Department of Restorative Dentistry, LLU School of Dentistry, Loma Linda University. c Professor of Restorative Dentistry and Dean, LLU School of Dentistry, Loma Linda University. d Associate Professor, Advanced Education in Prosthodontics, Department of Restorative Dentistry, LLU School of Dentistry, Loma Linda University.