In-vitro validation of a new method to assess the clinical accuracy of complete arch impressions.

OBJECTIVES: To develop and validate a new method to acquire reference distances. MATERIALS AND METHODS: A method to accurately register the intraoral position of precision balls was developed to generate reference values for the in-vivo assessment of impression accuracy and tested in vitro. Therefore, metal occlusal veneers with a special abutment carrying precision balls were provisionally attached to specific positions on the patient's dental arch (anatomical model with PMMA covered metal teeth). To register the precision ball positions, form-congruent counterparts were jointed to the abutments, adhesively fixed to a transfer aid, removed and digitized with a laboratory scanner. First, the distance determination using a transfer aid and a laboratory scanner was validated. Second, the process was tested for an anatomic situation. RESULTS: When measuring distances using a transfer aid and a laboratory scanner, distances could be detected with an accuracy of less than 5 mum. Using the new test setup on the anatomical model, the intraoral scanners more accurately reproduced scan volumes up to one quadrant, with deviations between the actual scan data sets/plaster models and the reference data set of < 52 mum for Primescan, < 82 mum for Omnicam, and < 125 mum for conventional impression. Longer distances tended to be more accurately represented by the conventional impression (Primescan < 304 mum; Omnicam < 328 mum; conventional impression < 164 mum). CONCLUSIONS: The developed method seems suitable for determining the clinical accuracy of conventional and digital complete arch impressions. CLINICAL RELEVANCE: For determining the clinical accuracy of conventional or digital impressions, reference values are crucial.