External hexagon
Also known as: External hex, External hexagonal connection, Ext hex
An implant-abutment connection in which a hexagonal boss projects above the implant platform and engages a matching recess in the abutment, the two parts being held together by a screw.
Key facts
| Connection category | External connection. A 2020 review classifies implant-abutment geometries into two basic families, external connections with a hexagon on the implant platform and internal connections, the latter subdividing into internal hexagons, internal octagons and Morse taper (conical) designs.Verified spec[2] |
|---|---|
| Anti-rotation feature | A hexagonal boss standing proud of the implant platform.Verified spec[2] |
| Taper angle | None. The abutment meets the implant on a flat platform, so this is a butt joint and the screw alone holds it in preload. |
| Clinical evidence | A 2020 review reported screw-loosening rates for external hexagon connections of 6 to 48 per cent in the literature, and a lower microgap for internal connections than for external hexagons. A 2017 systematic review found that external hexagon implants failed to prevent microleakage under both static and dynamic loading, with microgaps of around 10 micrometres, against 2 to 3 micrometres for Morse taper designs.Verified spec[2][3] |
| Geographic availability | Nobel Biocare’s implant catalogue lists Branemark System and NobelZygoma 45 degree external hex implants under its external hex connection family.Manufacturer-reported[1] |
| Platform switching | Platform switching is possible with an external hexagon but is not inherent to it: the abutment simply has to be narrower than the implant shoulder. The original Branemark protocol matched them, which is why external hex implants are the usual comparator in platform-switching studies. |
Overview
The external hexagon is where implant dentistry started. It was designed as an engagement feature for the surgical driver rather than as a prosthetic joint, and it acquired its second job by accident when clinicians began screwing abutments onto it. Everything that has happened to implant connections since is, in effect, a response to its two structural weaknesses: the hexagon stands above the platform rather than inside it, so it is short and gives the abutment a small lever arm to resist, and the joint is flat, so nothing but screw preload holds the parts together. The comparative literature is consistent about the consequences - more screw loosening and larger microgaps than internal designs. None of that makes an existing external hex implant a problem: many have functioned for decades, and the design is still manufactured. But if someone offers a new implant on the basis that external hex is the original and therefore the proven design, that argument is running backwards.
Sources
Numbers match the citations beside each claim above.
Primary sources
- [1]Nobel Biocare implant catalogue — connection and surface filters — Nobel Biocare Services AG. Accessed 2026-07-21.
Clinical evidence
- [2]Review of the Mechanical Behavior of Different Implant-Abutment Connections — International Journal of Environmental Research and Public Health, via PubMed Central, 2020. Accessed 2026-07-21.
- [3]Microleakage at the Different Implant Abutment Interface: A Systematic Review — Journal of Clinical and Diagnostic Research, via PubMed Central, 2017. Accessed 2026-07-21.