Introduction. Obtaining a functional impression is an important stage in the process of manufacturing complete dentures. Proper matching of the impression material to the impression technique facilitates obtaining the optimal denture periphery, thereby providing suitable conditions for retaining the denture in the mouth. Aim. The objective of the study was to compare the reproducibility of the border of a functional impression of an edentulous mandible taken in a custom tray with wax or silicone impression materials with those obtained with tissue conditioning material placed on a patient’s own denture. Material and methods. 19 patients with edentulous mandibles and moderate atrophy of the alveolar process (Supple type I) were chosen for inclusion in the study. Custom trays were made and then tested in the patient’s mouth using the Herbst method. After the patient had worn this final denture for a minimum period of two weeks, Visco-gel tissue conditioner material was placed and the patient wore the denture for 24 hours, after which it was used to make a cast. All impressions obtained from the three materials were cast in dental stone (type III). The casts were levelled and sliced perpendicularly to the line of the alveolar process. 12 sections of each cast were obtained. Every slice was scanned at a resolution of 1000 dpi. The scanned pictures were processed with Microsoft Paint. The results were statistically analysed. Results. Wax impression material demonstrated the highest tendency for repeatable recording of the border of the impression. The tissue conditioner material showed significantly less repeatability. Conclusions. The use of an impression material which produces a functional, precise cast appeared to give better results as regards repeatability than a material formed only by the patient, in spite of being in situ for a long time during the forming.

Key words: functional impression, repeatability, scanning.