Dimensional Accuracy of Pickup Implant Impression: An In Vitro Comparison of Novel Modular Versus Standard Custom Trays

Purpose The purpose of this in vitro study was to evaluate the dimensional accuracy of pick-up impression technique using a Modular Individual Tray (MIT), and to compare it to the Standard individual Tray (ST) in multiple internal connection implants, considering both the role of materials and the geometrical misfits. Materials and Methods Since MIT relies on stiffness and elasticity of an acrylic Pattern Resin, a preliminary investigation on the dynamics of the resin volume contraction of this material during curing and polymerization process was carried out. Two series of specimens were tested to compare the accuracy of MIT (test group) to the ST (control group). The specimens were analyzed in three different steps during the impression procedure. Linear and angular displacements of the transfer copings were measured and compared between two groups. Experimental measurements were performed using a computerized coordinate measuring machine. Results Investigation of the curing dynamics of the acrylic Pattern Resin showed that the increase of the powder/liquid ratio speeds up the polymerizing process of the resin (less of 1/3 of the time required) and reduces the final volume contraction of 45%. This behavior showed a strong dependence by the physical properties of acrylic material and those linked to the powder/liquid ratio. However, the total shrinkage does not, in any case, exceed the elastic limits of the material hence it does not affect the coping’s stability. Test group measurements showed the reduction of linear errors of 55% and the angular one of 65%. The experimental investigation on the dimensional accuracy showed that the use of MIT technique could reduce the introduction of linear and angular misfits during all the phases of the implant impression procedure. Conclusions Linear and angular displacements of the transfer copings were significantly reduced in Modular Individual Tray group, which leads to a higher dimensional accuracy with respect to the Standard Tray group. MIT approach, in combination with thin and uniform amount of LS Pattern Resin in the pick-up impression technique, doesn’t showed significant permanent distortions in multiple misalignment internal connection implants, compared to the Standard Tray.