Finish-line discrepancy in intraorally digitized abutments with and without gingival retraction and its association with the clinical marginal position of fixed dental prostheses

To investigate the influence of gingival retraction on preparation finish-line identification and to determine whether the resulting differences affect the clinical position of the restorative margins of fixed dental prostheses (FDP). Twenty posterior preparation sites for 3-unit tooth-supported FDPs in 13 patients were included. Each preparation site was intraorally scanned under two conditions: without gingival retraction (SG-I) and after placement of a gingival retraction cord (SG-II). Preparation finish lines were identified in dental CAD software, and model-free polymethyl methacrylate FDPs were fabricated from both digital records. After clinical evaluation and intraoral positioning of the restorations, the spatial relationship between the CAD-defined preparation finish lines and the corresponding restorative margins was assessed using a reverse-engineering approach. Root mean square values were compared between the two scanning conditions at a significance level of 0.05. A mean spatial discrepancy of 0.2873 mm (SD = 90.35 μm; range, 90–500 μm) was observed between the preparation finish lines identified from digital impressions obtained with and without gingival retraction. The mean discrepancy between the CAD-defined preparation finish line and the corresponding restorative margin was 0.1953 mm for SG-I and 0.1826 mm for SG-II, with no significant difference between the groups ( P =0.435). The intergroup difference in the discrepancy between the restorative margins positioned in situ and the preparation finish lines defined in the dental CAD software was also not significant ( P =0.956). Within the limitations of this clinical study, the spatial discrepancy in finish-line identification observed between intraoral scans obtained with and without gingival retraction did not significantly influence restorative margin position. These results should be interpreted within the specific clinical and digital workflow evaluated. ClinicalTrials.gov, NCT06447389, registered on 2 June 2024. Retrospectively registered.