Accuracy of the Index and Three Techniques for Abutment Impressions

Objectives: The present in vitro study compared the dimensional accuracy of a master cast (control group) with verification jig (Index) and 3 impression techniques (squared impression copings, squared impression copings splinted with autopolymerizing acrylic resin and squared impression copings with prolongations created from autopolymerizing acrylic resin in the vestibule-lingual direction).

Methods: An epoxy resin cast of a partially dentulous mandibular was fabricated with 6 abutment replicas, two passive implant frameworks and twenty-one identical custom impression trays were made with autopolymerizing acrylic resin. Polyether impression material (Impregum Soft medium consistency - 3M ESPE) was used for all impressions. Five groups: C- Control group (Master cast); I - Index ; NM group - nonmodified square impression copings; SR group - impression copings were splinted with acrylic resin and M group – Modified square impression copings (square impression copings with prolongations created from acrylic resin in the vestibulelingual direction with 7 casts each were formed, except the control group. The measurements were analyzed using software that received the images of a video camera coupled to a Leica microscope at x100 magnification. Data were analyzed with a 1-way analysis of variance at a <.05, followed by the Student Newman-Keuls test (a <.05).

Results: The mean values of abutment/framework interface gaps were: C group 32.3µm (±0.9 SD); I group 34,261µm (±2.5 SD); NM group 75.8µm (±2.7 SD); SR group 56.0µm (±3.0 SD); M group 37.9µm (±2.4 SD). SR group and NM group showed significant differences to each other and among all studied groups. Also significant difference was observed between C group and M group (P<.05).

Conclusion: Within the limitation of this in vitro study, the techniques of the Index or squared impression copings with prolongations were preferred methods for making implant-supported fixed restorations.