Endosseous implants are not recommended for patients below the age of 16 because of the potential for further growth of the jaws; the implant is ankylosed in the bone, and therefore it will become sub-merged as the jaws grow. There is no absolute upper age limit for endosseous implants. A patient's medical history will determine their suitability for endosseous implants. For example, a poorly controlled diabetic is at risk of infection and soft-tissue breakdown around an implant, which may contraindicate implant surgery. The patient may have a history of psychosis, or there may be an ongoing history of drug or alcohol abuse. Such patients are unsuitable for implant surgery. Referral for a specialist opinion is recommended if there is doubt about the suitability of a patient with medical problems for implant surgery.

Poor oral hygiene will compromise implant provision because of peri-implant inflammatory disease (which is destructive in a manner similar to periodontitis). Patient education can effectively improve oral hygiene status in some patients. A patient must demonstrate consistency in maintaining their oral hygiene over several months; only then can implants become a feasible option. Smoking is a relative contraindication, because some smokers are at increased risk of losing the implant through inflammation of the peri-implant mucosa, and increased resorption of peri-implant bone. This manifests clinically as an increase in the bleeding index, the peri-implant pocket depth, the degree of peri-implant mucosal inflammation and radiographic evidence of bone resorption mesial and distal to the implant. There is emerging evidence of an increased risk for implant loss in patients on bisphosphonates, though the risk for patients on oral bisphosphonates seems to be less than for patients having intravenous doses