Effect of scanned arch, level of impression, and impression technique on the accuracy of impressions for complete-arch implant-supported fixed dental prostheses.

Objectives: The long-term success of complete-arch implant-supported fixed dental prostheses (CAISFDPs) depends on impression accuracy, which may be influenced by the arch, impression level, and technique. This study investigated how these factors affect impression accuracy (trueness and precision) for CAISFDPs.

Methods: Maxillary and mandibular typodont models with 2 straight anterior and 2 tilted posterior implants (4.5 mm×12 mm) with or without multi-unit abutments (MUAs) were digitized using an industrial scanner (Artec Micro II). Impressions were made using digital and conventional techniques (n = 7). Scan trueness (3D deviation) was evaluated for each scan body using master model scans as the reference (Geomagic Control X), and precision was defined as the variance of deviations within each group.

Results: The scan trueness in mandible for scan bodies 46, 33, and 36 was affected by the interaction between impression level and technique (p < 0.05). For scan body 43, both factors independently influenced the trueness (p < 0.05). For maxilla, the impression technique affected the trueness at scan body 26, conventional impressions having higher trueness at multi-unit abutment level (MUA-L, p < 0.05). Mandibular MUA-L conventional impressions had lower trueness than maxillary conventional impressions at molar sites, while maxillary scans had lower trueness than mandibular scans at left molar site (p < 0.05). In the mandible, scan precision for scan body 46 was affected by the interaction between impression level and technique, scans having lower precision than conventional impressions at implant level (I-L, p < 0.05). In the maxilla, MUA-L scans of scan body 16 had lower precision than conventional impressions (p < 0.05).

Conclusions: The trueness and precision of digital scans and conventional impressions were comparable in both arches. Precision differences were minimal, however, conventional impressions tended to have higher precision.

Clinical Significance: The arch, impression level, and technique affected impression accuracy; MUA use may enhance digital scan trueness in the mandible.