Statement of problem. Numerous investigations have been done to determine the most accurate method to reproduce a dental arch. Investigations have used different definitive cast configurations, materials, and measuring techniques to evaluate dimensional change, leaving clinicians undecided as to the most accurate method to reproduce a dental arch. Purpose of study. The purpose of this investigation was to evaluate the effect of impression tray selection on accuracy of reproductions of a dental arch using a 3-dimensional optical digitizer. Materials and methods. Impressions were made of a stone cast of a dental arch using vinyl polysiloxane impression material in custom and stock impression trays (n=12). Custom trays, designed with full palatal coverage, were fabricated on a separate standard stone cast using 2 layers of pink baseplate wax as the spacer and tissue stops on 1 anterior tooth and both first molar teeth. Impressions were poured with type IV gypsum and allowed to set with the tray inverted (n=5) or not inverted (n=5). The standard cast and resulting casts were digitized using an optical digitizer. Custom software was used to align and process the 3-dimensional images created by the digitizer. Each image was superimposed onto the standard cast image, curves were created of the percent of points less than a defined distance between the 2 superimposed images, and the area under the curve was calculated. A weighted average area was calculated for each cast, and these values were analyzed using a 2-way ANOVA (α=.05). Results. The main effect of tray type, laboratory setting technique, and the interaction between these 2 characteristics was analyzed. None of these effects was significant. Conclusion. The differences in accuracy of reproductions of a dental arch, regardless of the impression and laboratory techniques, were not significant when evaluated using a 3-dimensional optical digitizer.