Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy

Statement of problem. Several studies have attempted to determine the ideal combination of dental materials and laboratory techniques to produce the most accurate dental cast, Most have made use of 2-dimensional manual Measuring devices, which neglect to account for the dimensional changes that exist along a 3-dimensional surface. Purpose. The purpose of this study was to determine the effect of impression tray selection and cast formation techniques on the dimensional change of a dental cast with the use of new, 3-dimensioinal optical digitizing technology. Material and methods. Multiple impressions of a machined steel die that resembled a dental arch were made with custom and stock impression trays and vinyl polysiloxane impression material. The impressions were poured in type V artificial dental stone and allowed to set with the tray inverted or non-inverted. The steel master die and stone casts were digitized with the Steinbichler Cornet. 100 Optical Digitizer, which was developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. Three-dimensional images of the stone casts were aligned to the 3-dimensional image of the master die and analyzed with AnSur-NT software. Multiple measurements of the master die and stone casts were analyzed to determine the accuracy of the 3-dimensional technology and of the impression and cast fabrication techniques. Planar distances between the center of each crown preparation were measured, as were crown heights. Data were analyzed with analysis of variance (P<.05), and rout mean square error values were determined. Results. Casts were compared with a total of 45 significance tests, of which only 4 yielded P<.05. There was no pattern to these results, which suggests that they were false-positive findings. Conclusion. Results obtained with the use of new optical digitizing technology indicated that neither impression tray type nor cast formation technique affected the accuracy of final casts.