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Title
Implant Distribution in the Edentulous Mandible: A CBCT-Based Analysis of Anterior–Posterior Spread and Cantilever Length
Background
Posterior implant placement in the edentulous mandible is frequently constrained by ridge resorption and proximity to the inferior alveolar nerve. These anatomical limitations restrict posterior implant positioning, reduce anterior–posterior (A–P) spread, and increase prosthetic cantilever length, potentially compromising biomechanical performance of full-arch implant-supported fixed prostheses.
Aim
To evaluate how different posterior implant distribution strategies influence A–P spread, cantilever length, implant length feasibility, and augmentation requirements in edentulous mandibles using CBCT-based virtual planning.
Materials and Methods
Fifty-six edentulous mandibles were analysed using CBCT-based virtual implant planning with a dual-scan technique. Each mandible was planned bilaterally using three configurations:
(1) axial inter-foraminal implants,
(2) distal-angulated inter-foraminal implants (30°), and
(3) axial distal-foraminal implants.
Primary outcomes included A–P spread area and cantilever length. Secondary outcomes included implant length feasibility and anatomical deficiency requiring augmentation.
Results
Distal-foraminal implant placement resulted in a marked increase in A–P spread area (182.9 mm²) and a substantial reduction in cantilever length (2.2 mm) compared with axial inter-foraminal (33.4 mm²; 18.4 mm) and distal-angulated inter-foraminal configurations (56.6 mm²; 14.8 mm) (p < 0.001).
Inter-foraminal configurations showed no severe anatomical deficiency, while severe deficiency was present in 40.2% of distal-foraminal sites. Longer implant lengths were feasible inter-foraminally (mode 14–16 mm), whereas distal-foraminal placement was predominantly limited to short implants (mode 6 mm).
Conclusion
Posterior implant distribution has a decisive impact on biomechanical parameters in edentulous mandibles. Axial distal-foraminal placement provides the most favourable A–P spread and minimal cantilever length when posterior anatomy permits. When posterior anatomy is limited, distal-angulated inter-foraminal placement offers a predictable and biomechanically advantageous alternative to conventional axial inter-foraminal implant placement.
Keywords
Edentulous mandible; full-arch implant rehabilitation; anterior–posterior spread; cantilever length; distal implants; tilted implants; CBCT; virtual implant planning; implant biomechanics; fixed complete dental prosthesis