Implant-soft tissue registration trueness across alignment protocols in intraoral photogrammetry

To evaluate the effect of implant-soft tissue alignment protocols on trueness of implant positions relative to soft-tissue scan using intraoral photogrammetry (IPG), comparing four coded scan body protocols with a cap scan body protocol.

A maxillary edentulous model with four parallel implant abutment analogs at canine and first molar positions was used. Reference scan data were obtained by scanning implant scan bodies with a desktop scanner. Five IPG groups (n=20/group) were evaluated: four coded scan body alignment protocols based on the positions of two coded scan bodies (anterior, posterior, diagonal, and hemi-arch) and one cap scan body protocol. Trueness was assessed by Euclidean linear and angular discrepancies between the experimental and reference scans for each implant scan body and overall. Higher discrepancies indicated lower trueness. Data were analyzed using the Kruskal-Wallis test with Bonferroni post-hoc comparisons (α=.05).

Overall Euclidean linear and angular discrepancies differed significantly among alignment protocols (p=0.044 and p<0.001, respectively). Diagonal alignment demonstrated the greatest linear and angular discrepancies. No significant differences in linear discrepancy were observed among the remaining protocols. Although cap alignment exhibited the lowest angular discrepancy, it did not significantly differ from posterior and hemi-arch alignments.

Implant-soft tissue alignment protocols significantly affected the trueness of implant positions relative to soft-tissue scan using IPG. The cap scan body protocol provided the most favorable trueness and relatively low dispersion of alignment errors. Among coded scan body protocols, posterior and hemi-arch alignments showed trueness comparable to the cap protocol, whereas diagonal alignment exhibited the lowest trueness.

For complete-arch implant scan using intraoral photogrammetry, cap scan bodies may be preferred because they demonstrated favorable trueness and relatively low dispersion of alignment discrepancies. When only coded scan bodies are used, posterior or hemi-arch alignment protocols may be preferred, whereas diagonal alignment appears less favorable because of greater alignment deviations.