Marginal Bone Loss and Peri-Implant Clinical Outcomes of Internal Hexagonal and Internal Conical Implant Abutment Connections: A Narrative Review.

The implant-abutment connection is the mechanical and biological interface between the implant and the prosthesis, and its geometry influences mechanical stability, sealing of the microgap, stress distribution, and the peri-implant tissue response. This narrative review compares internal hexagonal connections with internal conical connections, of which the Morse taper is a specific deep-cone, friction-locking type, focusing on marginal bone loss and peri-implant clinical outcomes, and distinguishes laboratory and mechanistic evidence from clinical evidence. Laboratory, finite element, and microbiological studies suggest that conical connections may reduce micromovement, microgap opening, and bacterial and endotoxin leakage and may transmit occlusal load more favorably than screw-retained internal hexagonal connections. Systematic reviews and meta-analyses report that internal connections, and conical connections in particular, are associated with lower short- to medium-term marginal bone loss, yet several randomized controlled trials, including a 2025 trial, show no significant difference between connection types in marginal bone loss, peri-implant tissue health, complications, or survival, and both designs achieve high survival. Clinical outcomes are strongly influenced by implant placement depth, abutment height, bone quality, soft-tissue phenotype, platform switching, loading protocol, prosthesis design, oral hygiene, smoking, systemic health, and follow-up duration. On current evidence, connection-specific clinical superiority has not been consistently established. Internal conical connections may be considered when marginal bone preservation, interface stability, and esthetic stability are priorities, whereas internal hexagonal connections may be preferred when prosthetic flexibility, indexed positioning, and retrievability are required. Connection selection should be individualized and guided by patient risk, site factors, prosthetic requirements, and the evidence for the specific implant system rather than by connection geometry alone.