Effect of tray relief amount and impression material type on dimensional accuracy of complete denture impressions

The purpose of this study was to evaluate the combined effects of tray relief amount and impression materials on the three-dimensional (3D) accuracy of complete denture impressions.

A fully edentulous maxillary cast and corresponding custom trays were digitally designed with a uniform 1.0 mm relief, and additional midpalatal relief of 0, 1.5, and 3 mm was incorporated. Impressions were made using four elastomeric impression materials and poured with Type IV dental stone. 3D surface deviation analysis was performed, and the average deviation and maximum absolute deviation (MAD) were calculated.

Across all impression materials, both the average deviation and the MAD increased as the midpalatal relief amount increased from 0 to 1.5 and 3 mm. Significant differences among the three relief conditions were confirmed for all materials (p < 0.05), and the post hoc test showed that every material exhibited a significant increase between the 0 and 3 mm conditions. Across all relief levels, no significant differences in average deviation were observed among the four materials. For MAD, a material-dependent difference was identified only at the 1.5 mm relief condition (p < 0.001).

The results demonstrated that polymerization shrinkage of elastomeric impression materials can produce localized microrelief within relieved regions of edentulous impressions, resulting in polymerization-induced microrelief. Both the relief amount and the material type influenced the magnitude of shrinkage-related dimensional change, suggesting that the interaction between tray relief and material behavior affects impression accuracy in edentulous patients.