Effects of time delay and tension system application after final flask closure on the vertical displacement of acrylic and porcelain teeth in maxillary complete dentures

Abstract

Background: The displacement of artificial teeth during complete denture construction presents major processingerrors in the occlusal vertical dimension which were verified at the previous trial denture stage. The aim of this studywas to assess the effect of delay in processing after final flask closure and tension application on the vertical acrylicand porcelain teeth displacement of complete dentures constructed from heat cured acrylic and the results werecompared with the conventional processing method.Materials and methods: forty samples of identical maxillary complete dentures were constructed from heatpolymerized acrylic resin. These samples were subdivided into the following experimental subgroups in which eachsubgroup contains 5 samples for both acrylic and porcelain teeth and as follows: 1. Conventional flasking techniqueand immediate processing. 2. Conventional flasking technique and 6 hours delay in processing. 3. flasking techniquewith tension system and immediate processing. 4. flasking technique with tension system and 6 hours delay inprocessing. Reference metal pins were attached to the middle of the buccal surface of the upper right canine andcenter of the buccal groove of the left first molar. And according to these reference points on the teeth anothermetallic Reference pins were fixed on the denture vestibules and at a distance of 7.5mm by straight lines and 6.5mmwhere placed between the metal pins and the vestibules in order to standardize the measurement. The distancebetween the right and left metal pins on the canine and molars and the corresponding metal pins on the buccalvestibules were measured during the wax up stage and after processing by using an optical travelling microscopewith an accuracy of 0.0005 mm. Means in (mm) were analyzed statistically by analysis of variance and thecomparative T-test and least significance test (LSD).Results: Significant reduction in vertical displacement of the teeth occurred in groups when 6 hours delay inprocessing were applied, but a significant improvement was also observed in groups with tension system applicationwhen compared with control group. On the other hand, there were a high significant reduction in the verticaldisplacement in groups with tension system and 6 hours delay in processing combination. While for the type ofartificial teeth data showed significant difference in the amount of vertical displacement of the teeth in groups withacrylic teeth when compared with porcelain teeth.Conclusions: The findings of this study showed that 6 hours delay in processing and tension system application wereeffective in reducing the vertical displacement of the artificial teeth during flasking. The maximum reduction in thedisplacement was observed in dentures constructed from acrylic teeth. On the other hand, significant decrease invertical displacement of the teeth was detected in dentures constructed from porcelain teeth.