Effect of multiple pouring on the accuracy of casts made using 3D-printed custom trays with different spacer thicknesses: A research study

Technique for Spacer Adaptation and Custom Tray Fabrication in Impression Making for Fixed Prosthodontics

The objective is to minimize the inaccuracies in two-step impressions by homogenizing the polymerization shrinkage of elastomeric impression material in fixed prosthesis fabrication. The objective is accomplished by the technique of spacer adaptation and custom tray fabrication for two-step impressions. The technique makes the use of two vacuum-adapted spacers, selected based on the viscosity of elastomeric impression, and a vacuum-adapted custom tray. The procedure of using the specially fabricated custom tray for impression making is also presented. Consistent thickness of the two different viscosities of impression material is maintained due to vacuum adaptation of the spacers. This homogenizes the polymerization shrinkage of the elastomeric material in different regions of impression, as uniform space is occupied by the material in the space created by the spacer. The procedure of vacuum adaption of the tray material also limits the dimensional change of the tray. The technique minimizes the inaccuracies of impression by homogenizing the polymerization shrinkage of the elastomeric impression, thus promising a well-fitting prosthesis.

Design parameters of polylactic acid custom trays manufactured by fused deposition modeling for partial edentulism: Consideration of the accuracy of the definitive cast

STATEMENT OF PROBLEM

The effects of design parameters of polylactic acid (PLA) custom trays manufactured by fused deposition modeling (FDM) on the accuracy of partially edentulous definitive casts have not been thoroughly explored.

PURPOSE

The purpose of this in vitro study was to explore the effects of the impression gap and base thickness of FDM-printed PLA custom trays on the accuracy of maxillary and mandibular definitive casts with Kennedy class II, modification I partial edentulism and to optimize these 2 design parameters.

MATERIAL AND METHODS

Custom trays with a 1-mm, 2-mm, or 3-mm impression gap and 1-mm, 1.5-mm, or 2-mm base thickness were designed on a pair of maxillary and mandibular resin casts and printed with PLA materials by using an FDM printer. Two-step silicone impressions were made by using these custom trays or stock metal trays on resin casts. Digital scans of definitive casts from these impressions were aligned one by one with those of resin casts. Three-dimensional deviations of the tooth area, mucosal area, and overall area were analyzed by using root mean square (RMS) as a metric. Two-way and 1-way analyses of variance with the RMSs as the dependent variable were carried out (α=.05).

RESULTS

The accuracy of definitive casts from custom trays with a 2.0-mm or 3.0-mm impression gap and 1.5-mm or 2.0-mm base thickness was significantly better than that of definitive casts from custom trays with a 1.0-mm impression gap or 1.0-mm base thickness and was not significantly different from that of definitive casts from stock metal trays.

CONCLUSIONS

Considering the accuracy of definitive casts, the optimal base thickness of FDM-printed PLA custom trays was 1.5 mm or 2.0 mm and the optimal impression gap was 2.0 mm or 3.0 mm for Kennedy class II, modification I partial edentulism.