General risk
factors 		- Patient’s unrealistic expectations;
- Pre-existing altered sensation;
- Improper selection of site for implant placement;
- Anatomical and radiological risk factors related to mandibular vital structures;
- Female patients;
- Increased age of patients.
Intraoperative risk
factors 		- Protrusion through lingual or buccal plate;
- Perforation of mandibular canal;
- Direct mechanical injury (manifests by “sudden give” type of feeling);
- Extensive bleeding;
- Extrusion of preparative debris into canal;
- Slippage of the drill, implant placement deeper than planned, or bigger diameter implant placement;
- Excessive force using implant drill
(density and thickness of the bone surrounding the mandibular canal is not able to resist it);
- Repeated IAN blocks.
Postoperative risk
factors 		- The fact that the IAN is contained within the bony canal (compression, ischemia);
- Severity of injury;
- Interval between time of injury and diagnosis, treatment.

IAN = inferior alveolar nerve.