Uncontrolled disease: Chronic diseases which are not under control can reduce the healing ability of the body. For example, if diabetes is not under control, the patient is not a good candidate for implants, because healing will be impaired. However, if your diabetes is well under control then you can get an implant. Similarly, leukemia and hyperparathyroidism can also affect the success of a dental implant. People undergoing chemotherapy should postpone getting an implant.
Chronic illnesses: chronic illnesses such as liver and kidney problems, tumors and auto-immune diseases are also an absolute contra-indication for getting implants. You should seek treatment for your medical illness first, and when you are healthy again you should visit your dentist for re-evaluation.
Poor oral hygiene: dental implants are bound to fail if you do not maintain optimal oral hygiene. Therefore, I will not consider giving dental implants to a patient who is unable to maintain dental hygiene. At least not till his or her oral health has attained a satisfactory level.
Pregnancy: Pregnant females should not have dental implants in the first three months, although it is best to postpone the operation till after the baby has been delivered.
Psychiatric disorders: People with psychiatric or emotional stresses should be considered very carefully before being treated for an implant, because it can place extra psychological stress on the patient.
Lack of muscular coordination: Implants do not need as much care as do conventional dentures, but they still need regular oral hygiene. People who cannot for some reason, manage this should not invest in the expensive treatment.