Three-dimensional evaluation of the internal and marginal fit of multiunit implant-supported anterior fixed dental prostheses fabricated using different intraoral scanning protocols: An in vitro study

Statement of problem

The rapid advancement of intraoral scanners and the widespread adoption of dental implant scan bodies have streamlined the digital acquisition of implant position data and the subsequent fabrication of implant-supported prostheses. However, research on the fit of multiunit implant-supported fixed dental prostheses (FDPs) fabricated using a cast-free workflow is sparse.

Purpose

The purpose of this study was to evaluate the internal and marginal fit of 6-unit implant-supported FDPs fabricated from zirconia by using different intraoral scanning protocols and digital data superimposition and analysis techniques.

Material and methods

A definitive cast with implants placed in the maxillary right canine, right central incisor, and left canine positions was fabricated to simulate the partial edentulism of the 6 maxillary anterior teeth. Implant scan bodies were attached to the implants, and 10 consecutive intraoral scans were made. Custom abutments were designed based on one of the scan datasets, and 6-unit zirconia prostheses (n=10) were fabricated in a single-step cast-free workflow (Group IL). The designed custom abutments were then fabricated and tightened onto the definitive cast, followed by an additional set of 10 intraoral scans to fabricate another set of 6-unit zirconia prostheses (Group AL; n=10). The intraoral scan data were analyzed by using a cube-embedded implant scan body library and custom abutment dataset. Distances between each cube in the intraoral scan data were measured, and their ratios calculated relative to those obtained from tabletop scan data. Additionally, implant angulation was measured, and angular discrepancies between implant pairs were calculated. The fabricated prostheses were fitted onto the definitive cast, and internal and marginal gaps were assessed by using 3-dimensional data superimposition techniques. The data were analyzed by using a 2-way analysis of variance test (α=.05).

Results

The distance ratio in Group IL was significantly closer to the reference value than that in Group AL (P<.001). The angular discrepancy between implant positions was significantly smaller in Group IL than in Group AL (P<.001). The mean internal gap in Group AL was significantly greater than that in Group IL (P=.007). However, no significant difference was observed between the groups when comparing the marginal gaps of the zirconia prostheses (P>.05).

Conclusions

Zirconia prostheses fabricated through a single-step, cast-free workflow exhibited significantly smaller internal gaps than those fabricated through a 2-step process. However, the marginal fit of the zirconia prostheses did not significantly differ between the 2 scanning protocols.