Accuracy of impressions of multiple implants in the Edentulous Arch: A systematic review

Background: Different clinical factors influence the accuracy of the completely edentulous implant impressions and there is no clear cut evidence on the materials and techniques best suited for the procedure. Objective: To analyse the data specific to complete arch implant impression accuracy and draw useful conclusions based on the evidence, for application in clinical practice. Materials and method: Relevant studies published between 1990 and December 2012, were included in the review. The articles were located through PubMed, and, manually through the references of peer reviewed literature. Papers examining implant impression accuracy in completely edentulous arches (3 or more implants) were selected for review. Clinical case reports, technique articles, abstracts and review papers were excluded. Results: Of the 34 studies selected for evaluation, 33 were in-vitro investigations and 1 was clinical. Ten studies compared between PVS (Polyvinyl siloxane) and PE (Polyether) and eight found them to be statistically equal, in terms of impression accuracy. The ‘splint effect’ was examined by 24 studies, and 10 of them failed to elicit any differences between splint and non-splint. 7 (>25%) studies showed implant splinting technique to be better than the non-splinting type. With regards to impression technique (pick up & transfer) evaluation, 13 studies were identified for investigating the differences. Among them, 6 favoured pick up over transfer and 5 found insignificant differences between the two techniques. The implant non-parallelism effect on the edentulous multiunit impression accuracy was examined by only two studies. Significant differences in accuracy was observed for 15º angulation.Conclusions: Majority of the evidence supports PVS and PE as the impression materials suitable for edentulous multi-implant situations with no clear choice between the two. Conflicting evidence exists on the most accurate impression technique (splint & non-splint; pick up & transfer) and no individual option could be selected over the other for recommendation. Inadequate research exists on several other factors possibly affecting the edentulous implant impression accuracy. There is lack of clinical research to support the in-vitro findings and the interpretation of the results must be done carefully.