Effect of Relining Method on Dimensional Accuracy of Posterior Palatal Seal. An In Vitro Study Yeongjeong Kim, DDS, DMD, 1 Konstantinos X. Michalakis, DDS, PhD, FACP, 2 & Hiroshi Hirayama, DDS, DMD, MS, FACP 3 1 Assistant Professor, Department of Prosthodontics and Operative Dentistry, Division of Graduate and Postgraduate Prosthodontics, Tufts University School of Dental Medicine, Boston, MA 2 Visiting Assistant Professor, Tufts University School of Dental Medicine, and private practice limited to prosthodontics, Athens, Greece 3 Professor, Director of Graduate and Postgraduate Prosthodontics, Tufts University School of Dental Medicine Keywords Denture reline; posterior palatal seal; autopolymerizing; heat-polymerizing. Correspondence Konstantinos X. Michalakis, 3, Greg. Palama Str., Thessaloniki 546 22, Greece. E-mail: kmichalakis@the.forthnet.gr Accepted October 14, 2006 doi: 10.1111/j.1532-849X.2007.00268.x Abstract Purpose: The posterior palatal seal contributes to the retention of the complete denture. Distortion of this area can occur during reline procedures. The purpose of this study was to evaluate the dimensional accuracy of various denture relining methods and materials on the maxillary posterior palatal seal area. Materials and Methods: A stainless steel cast was constructed from a maxillary edentulous cast. Fifty identical complete dentures were fabricated on 50 definitive casts made from the original metal cast. Five relining methods and materials were evaluated during this study, in regards to posterior palatal seal distortion: (I) labora- tory conventional heat-polymerizing method (Lucitone), (II) laboratory heat/pressure- polymerizing method (SR-Ivocap), (III) laboratory autopolymerizing method (Perm), (IV) chairside autopolymerizing method (Tokuso Rebase), and (V) chairside light- polymerizing method (Astron). The dimensional changes of the posterior palatal seal areas were determined by placing a low-viscosity silicone impression material between the metal cast and the tissue surface of the relined dentures. The silicone thickness was measured at five predetermined points, under a measuring microscope. Statistical analysis was performed using descriptive statistics, one-way analysis of variance, and Student-Newman-Keuls tests (α = 0.05). Results: The gap at the posterior palatal seal area ranged from 68.76 to 331.55 μm, when measured at the five predetermined points. Group IV exhibited the smallest mean gap (137.62 μm) and Group I revealed the largest mean discrepancy (192.35 μm). The different relining methods and materials presented statistically significant differences (p < 0.0001). Conclusion: The chairside autopolymerizing method exhibited smaller gap recordings than the rest of the tested complete denture relining methods. Complete dentures have been used extensively for the rehabili- tation of edentulous patients. The success of these restorations depends greatly on retention, support, and stability. 1−4 Due to the inevitable process of alveolar bone resorption, the complete denture may become loose and less retentive, resulting in sore- ness, loss of vertical dimension of occlusion, and poor function. Thus, complete dentures need to be relined or rebased to im- prove retention, stability, oral health, and esthetics. 5−9 Various denture relining procedures have been used in dentistry for years with different degrees of success. The posterior palatal seal is probably the most important area for retention and must be carefully considered during and after the reline procedures of a maxillary denture. Acrylic resin, which is used for reline procedures, has the disadvantage of polymerization shrinkage, regardless of the processing procedure. 10−12 Many reline materials and methods used have been specifically developed to minimize shrinkage and distortion. 13−25 The different procedures of denture relining use either auto- or heat-polymerizing acrylic resins, which are processed in the laboratory. Auto- or light-polymerizing resin materials have also been developed for clinical use. 26−28 The laboratory reline method has relatively good dimensional sta- bility and strength, but presents a major drawback: the patient has to be without the denture for a certain period of time. On the other hand, the chairside reline method seems to be conve- nient and easy and requires a short working time. Although the Journal of Prosthodontics 17 (2008) 211–218 c  2007 by The American College of Prosthodontists 211