Displacement of implant components from impressions to definitive casts

Four possible displacements of implant components from a patient model to a definitive cast were assessed to suggest a standard method of comparing the accuracies of implant impression techniques.

Two techniques for impression making were assessed: a nonsplinted open-tray technique and a light-curing resin splinted open-tray technique. A mandibular model with 5 parallel implants was fabricated. Five definitive casts were fabricated per technique. Using a computerized coordinate measuring machine, 5 part coordinate systems were established, and 7 sets of data were obtained for each sample. From the data, the amount of displacement while connecting components and the linear and angular displacement of components during impression making and cast fabrication were calculated. The Mann-Whitney test was used to determine significant differences between the impression techniques (P < .05).

The average displacements while connecting impression copings and abutment replicas were 31.3 and 30.4 microm, respectively. Less displacement occurred in the nonsplinted group compared to the splinted group during impression making (P = .001) but greater displacement occurred in that group during definitive cast fabrication (P = .015).

In contrast to previous studies, the current study excluded displacement resulting from component connection, because displacement from that source has no relation to impression technique and cannot be controlled.

Connecting a component produced as great a displacement as that resulting solely from a impression or cast fabrication. The nonsplinted group was more accurate during impression making but less accurate during cast fabrication.