Effect of different retraction and impression techniques on the marginal fit of crowns

Periodontal conditions in restored teeth are strongly influenced by the marginal fit of the restoration which is closely related to the quality of the impression. However, the influence of the retraction and impression technique on the outcome of the impression has only sparsely been investigated. Thus, it was the objective of this study to compare the marginal fit in fixed restorations using two modes of gingival retraction and two different impression techniques in an animal model.

To simulate clinical conditions, 6 teeth in each of 10 lower jaws of freshly slaughtered cows were prepared with subgingival finish lines. Two different retraction techniques were used to expose the finish line: retraction cords containing epinephrine (Surgident) and electro-surgery were applied contra-laterally at 3 teeth per quadrant. Two impressions per jaw were taken in a two-step putty-wash technique (TPW) and a one-step putty-wash technique (OPW), respectively. On the casts, measurement copings were fabricated and seated on the extracted original tooth. In each coping the marginal discrepancy was assessed at 8 reference marks. Since the data was normally distributed, results were subjected to parametric statistics (T-test; p=0.05).

Overall marginal discrepancies ranged between 0 and 200 microm. There was a small but not significant difference between electro-surgery and the retraction cords whereas TPW produced significantly better results than OPW (p<0.05).

Within the limits of the study it can be concluded that the use of gingival retraction cords as well as electro-surgery lead to acceptable results. The difference between TPW and OPW concerning the marginal discrepancies can be regarded as clinically insignificant.