Effect of packing types on the dimensional accuracy of denture base resin cured by the conventional cycle in relation to post-pressing times

Abstract

This study investigated the dimensional stability of denture bases influenced by packing methods, in relation to post-pressing times, in the Clássico acrylic resin which was prepared according to manufacturer recommendations. Forty maxillary wax bases were made and randomly assigned into 2 groups of 20 specimens each according to the conventional and RS system packing methods. In each method, the specimens were subdivided into immediate, 6, 12 and 24 h post-pressing times. The dough of the acrylic resin was packed in metallic flasks and processed in a water bath curing cycle at 74 masculine C for 9 h. After cooling at room temperature, the bases were removed from the flasks, finished and fixed on stone casts with instantaneous adhesive. The resin base-stone cast sets were transversally sectioned into 3 sections and the base-stone gap measured at 5 points in each section. The data were submitted to ANOVA and Tukey's test, which showed that the RS system had a smaller base distortion compared to conventional packing, with the exception of the 24-h post-pressing time. There was a statistically significant difference between the packing methods only in section C (posterior palatal zone). In the conventional packing method, the immediate and 6 h times demonstrated values with no statistically significant difference between them, as well as between the 12 and 24 h post-pressing times.

Effect of flask closure method and post‐pressing time on the upper denture base adaptation

“…The RS system and 6-h interaction resulted in the lowest base accuracy (Table 4). This result does not support the previous findings, in which the association of the RS system and post-pressing time-processed bases displayed improved accuracy to the stone cast 21,23 . It is possible that this observation is due to the differences between operators acting in different studies, which could cause different or modified effects on base adaptation.…”

“…This fact is probably due to the method conditions, in which the conventional clamp does not allow a similar pressure in all flasks for both resins. Consequently, the base adaptation would be due to other conjugated variables, such as post-pressing time 21 , the commercial acrylic resin 22 and flask closure methods 23 .…”

“…However, the distortion occurring in the base because of procedure techniques cannot be corrected easily following processing 19 . Some studies have shown that the base adaptation to the stone cast is unsatisfactory, as a result of the influence of a combination of several factors, such as the shape of the palate 20 , post‐pressing time 21 , acrylic resin manufacturer 22 , flask closure method 23,24 and flask cooling methods 25 .…”

“…The time between flask pressing and the initiation of the resin polymerisation is an important factor in denture base stability. The immediate post‐pressing time has been reported to show the most discrepancy in the denture base, when compared with longer post‐pressing times 21 . However, polymerisation shrinkage, thermal contraction due to flask cooling and strain resulting from stresses released after resin base/stone cast separation are associated factors that reduce the adaptation of the complete dentures 28–30 .…”

Effect of metallic flask closure and investment materials on the stability of the denture base resin

“…Denture base adaptation to the stone cast is not satisfactory, mainly in the midline regions of the central portion of the posterior border,4–9 and gap discrepancies in the adaptation are not easily corrected after complete denture processing 10. Denture base accuracy is also influenced by the types of PMMA polymers,5, 11, 12 depends upon the palate vault shape,13 stresses released,14–16 processing techniques of the dentures,17–24 and it is considered a critical and unresolved problem 25–31…”