Three-Dimensional Evaluation of Ideal Zygomatic Implant Trajectory Based on the 5.5 Rule: A Retrospective Cone Beam Computed Tomography Study

Background: Rehabilitation of the severely atrophic maxilla presents a persistent challenge in implant dentistry. Zygomatic implants (ZI) offer a predictable alternative to extensive bone grafting procedures, thereby reducing surgical morbidity and treatment duration. Nevertheless, successful outcomes depend on precise implant trajectory planning, and determining a pathway that maximises bone–implant contact (BIC) remains a critical clinical concern.

Aim: This study aims to evaluate the optimal trajectory for zygomatic implant placement that achieves maximum radiographic bone–implant contact (rBIC) using the proposed 5.5 rule.

Materials and Methods: A retrospective radiographic study was conducted using cone-beam computed tomography (CBCT) scans from 10 completely edentulous patients with severely atrophic maxillae, classified as Cawood and Howell Class V or VI. Virtual ZI were planned according to the proposed 5.5 rule, which designates Point A at the second premolar region tangent to the infraorbital foramen, Point B at the center of the zygomatic bone (ZB), and Point C at the outer cortical perforation point. Implant planning and measurements were performed using Blue Sky Plan® software. Radiographic bone–implant contact was assessed separately on the temporal and facial aspects of the ZB and expressed as the percentage of implant length engaged within the zygoma.

Results: The mean rBIC was 85.43% ± 6.43% on the temporal aspect and 88.80% ± 7.60% on the facial aspect, with an overall mean rBIC of 87%. Application of the 5.5 rule consistently guided implant placement through the central portion of the ZB, resulting in substantial bone engagement and a favorable implant trajectory.

Conclusion: The 5.5 rule offers a straightforward, reliable, and reproducible approach for planning zygomatic implant trajectories that maximise radiographic bone–implant contact. Further research involving larger patient cohorts and clinical follow-up is necessary to validate its effectiveness and long-term clinical applicability.

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