Evaluation of accuracy of various impression techniques and impression materials in recording multiple implants placed unilaterally in a partially edentulous mandible- An in vitro study.

Background: Various factors like implant angulation, type of impression material and tray type affects the implant impression accuracy. To date limited in-vitro studies were carried out on the implant impression accuracy of unilateral partially edentulous arches. The aim of this research was to evaluate the effects of 0o, 15o and 25o implant angulations on impression accuracy in simulated master casts of unilateral partially edentulous situation using different impression materials and tray selections.

Material and Methods: 30 replicas (N = 30) of a resin matrix (control) containing four implant analogues placed unilaterally from the midline till the region of second molar at an angulation of 00, 00, 150 and 250 to the vertical axis of the ridge respectively were obtained by using three impression techniques (stock metal tray, closed custom tray, and open nonsplinted custom tray) and two different impression materials (Polyvinyl-siloxane and polyether). Specific dimensions of the resultant casts were measured using coordinated measuring microscope. Mean linear changes were calculated and statistically analyzed using analysis of variance (ANOVA) and Tukey's post-hoc procedures ( p < 0.05).

Results: The casts obtained from all three impression techniques had significant differences in dimensions ( p <0.05) as compared to that of master model irrespective of impression materials. Comparing the techniques with regard to the parallel implants, no statistical significant difference ( p <0.05) was observed with custom tray techniques (closed/open). Whereas while comparing parallel versus non parallel, open tray technique showed superior accuracy compared to closed tray technique as the angulation increased more than 15 degrees.

Conclusions: The influence of material and technique appeared to be significant for highly non axial implant angulations ( p < 0.05), and increased angulation tended to decrease impression accuracy. The open tray technique was more accurate with highly nonaxially oriented implants for the small sample size investigated. Key words: Implant impressions, partially edentulous arch, angulated implants.