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Introduction: The posterior palatal area is the most important area for retention of maxillary dentures and must be considered carefully during and after the reline. The purpose of this in vitro study was to compare the posterior palatal seal in relined complete dentures with two different methods.Materials & Methods: An average size of edentulous maxillary acrylic arch without undercuts was selected in this in vitro study. The alginate impression was made of this model ten times and was poured with a type IV gypsum product, and the casts of control groups were prepared. Then 10 definitive bases were created for each cast. For the experimental groups, one relief wax layer with a thickness of 2mm was put in post-dam area for relining processes. Then, 20 alginate impressions were made of this model. On definitive base, clear heat-cured acrylic bases were fabricated. In experimental groups, bases were divided into 2 groups of 10: first group was relined with heat-cured acrylic resin and another one was relined with cold cured acrylic resin. All of the bases were put in distilled water for two weeks and then each of them was placed on the definitive base. One code was considered for each model. The gap in posterior area between acrylic bases and arch was measured in five points (a-b-c-d-e: mid line, two points in hamular notch, and two points between midline and hamular notch) by two practicers in two different times (during two weeks) with light B×60 microscope. The data were analyzed by Tukey and Kruskal Wallis tests.Results: The results of this study indicated that there was a statistically significant difference in the amount of gap at point A between control (bases without reline) and experimental groups (P=0.047). At point D there was no significant difference between experimental groups, but a significant difference was detected between control group and bases relined with cold cure acryl (P<0.05).Conclusion: The results of this laboratory study indicated that there was no significant difference between relining methods with heat-cured and cold cured acryl reline method). So cold cured acryl could be recommended because it is more economic, easier and more time savory compared to heat-cured acryl.