Three-dimensional processing deformation of three denture base materials Andreas Artopoulos, DDS, MSc,a Andrzej S. Juszczyk, LCGI, PhD,b Jose M. Rodriguez, DDS, MSc, MFDS, PhD,c Robert K. F. Clark, BDS, PhD, FDS,d and David R. Radford, AKC, BDS, PhD, MRDe King’s College London Dental Institute, London, UK; UCL Eastman Dental Institute, London, UK; Dental Academy, University of Portsmouth, Portsmouth, UK Statement of problem. Heat-polymerized polymethyl methacrylate denture bases deform during and after polymerization, and this deformation may affect the clinical performance of complete dentures. Purpose. The purpose of this study was to investigate the processing deformation of 3 denture base materials on a standardized anatomic model by using a contact scanner and surface matching software. Material and methods. Maxillary reproductions of a definitive cast were digitized by using a contact scanner. The casts were allocated to 4 groups, depending on the denture base material: compression molded (heat polymerized, polymethyl methacrylate based); injection molded (heat polymerized, polymethyl methacrylate based); manually adapted and light-polymerized (urethane dimethacrylate based); and manually adapted, compression molded, and light-polymerized (urethane dimethacrylate-based). The intaglio surfaces of denture bases fabricated on each replicate cast also were digitized by using the contact scanner. Surface-matching software was used to measure dimensional changes between each cast and its corresponding denture base. The Kruskal-Wallis analysis of variance based on ranks was used to assess differences in contraction, expansion, and overall change among groups. The Mann-Whitney U test was performed to determine differences among individual groups. Statistical significance was inferred when P1.5 mm could be attributed to artifact or processing errors. The nominal deviations (maximum-minimum accepted value of difference indicating lack of shape change) were set at
50 mm because the step-over distance and nominal pitch of the contact scanner used were

50 mm, which made differences in shape