Implant therapy is an elective treatment modality for the rehabilitation of partially and fully edentulous patients. The treatment should therefore not place an individual at risk or be carried out without consideration of possible contraindications. This module will define risk factors, both systemic and local, in relation to implant therapy as well as relative and absolute contraindications to implant placement.

After completing this ITI Academy Module, you should be able to: define the terms risk factor and contraindication in relation to implant therapy; identify the systemic risk factors associated with implant therapy; identify the local risk factors associated with implant therapy; and indicate relative versus absolute contraindications for implant therapy.

A risk factor is any attribute, characteristic, variable, or exposure of an individual that increases the likelihood of developing a disease, injury, or infection. Risk factors can further be divided into systemic risk factors and local risk factors.

Systemic risk factors affect multiple organs, systems, tissues, or the entire body. A local risk factor, on the other hand, originates in or is confined to one system or specific area of the body. In the context of implant therapy, examples of systemic risk factors are smoking and bleeding disorders, whereas a local risk factor would be one that is confined to the mouth of the patient, such as inadequate oral hygiene or local inflammatory processes.

A contraindication is defined as any condition of the patient that makes a surgical procedure inadvisable. Contraindications can be medical, psychological, or social. Contraindications for implant therapy can be divided into relative and absolute contraindications. The distinction between the two is not as clear as it might appear. However, a number of relative contraindications or one absolute contraindication will influence the treatment plan.

A relative contraindication is any medical reason, condition, clinical symptom, or circumstance that may or may not prevent implant therapy; it increases the risk of complications. An absolute contraindication is any medical reason, condition, clinical symptom, or circumstance that is so compelling or that carries such a high risk that under no reasonable circumstance is implant therapy advisable.

There are very few absolute contraindications to dental implant treatment; however, certain conditions may increase the risk of treatment failure or complications. The degree of systemic disease control may be more important than the nature of the disease or condition itself, and thus personalized medical control should be established prior to implant therapy. In many patients the functional benefits and improved quality of life from dental implants may outweigh the risks.

Definitions, Key Learning Points: A risk factor is any attribute, characteristic, variable, or exposure of an individual that increases the likelihood of developing a disease, injury, or infection. Risk factors can be divided into systemic and local. A contraindication is any condition of the patient (medical, psychological, or social) that makes a surgical procedure inadvisable. Contraindications can be divided into relative and absolute.

In the following slides, the systemic risk factors that should be identified prior to implant therapy will be described. Patients should be evaluated for these factors during a thorough medical history or anamnesis. These include immunodeficiency, immunosuppressive drugs, bleeding disorders, chemotherapy, irradiated bone, osteoporosis, poorly controlled diabetes, and a history of heavy smoking.

A patient with immunodeficiency is in a state in which their immune system's ability to fight infections is compromised or absent. These patients are said to be 'immunocompromised'. In developed countries, obesity, alcoholism, and drug use are common causes of poor immune function. However, malnutrition is the most common cause of immunodeficiency in developing countries.

Some medications present a risk for implant therapy, for example, the long-term use of corticosteroids for chronic conditions such as rheumatoid arthritis. Corticosteroid adverse effects include reduced bone density and immunosuppression. In consequence, the use of corticosteroids might compromise implant osseointegration and peri-implant healing. Moreover, patients on long-term steroid therapy may experience suppression of the adrenal cortex, which produces cortisol in response to trauma, infection, and surgery. These patients may require steroid supplementation during stressful procedures, which may include dental implant surgery. Patients that have received transplanted organs may be on long-term, high-dose immunosuppressive therapy. These medications increase the risk of postoperative infections.

Another systemic risk factor is bleeding disorders, both pathologic and medication-induced. The term 'bleeding disorders' describes a group of conditions caused by coagulopathy, a condition in which the blood's ability to clot is impaired. Patients may also have drug-induced anticoagulation. An anticoagulant is a substance that prevents clotting of blood. Patients may be prescribed anticoagulant medications for a variety of cardiovascular conditions or to prevent ischemic stroke. Patients with bleeding disorders or taking anticoagulant medications may experience prolonged or excessive bleeding, which may occur spontaneously or following an injury or medical and dental procedures.

Chemotherapy is the use of chemical agents in the treatment or control of a malignancy. Patients undergoing chemotherapy are considered to be at risk for developing postsurgical complications after implant placement due to a reduced wound-healing capacity. Furthermore, a number of chemotherapeutic agents contribute to significant clinical oral side effects, including xerostomia, alterations in taste, tooth sensitivity, gingival bleeding, mucosal ulcerations, hemorrhagic mucositis, and herpetic, bacterial, or fungal infections.

There is scientific evidence to show a higher failure rate of osseointegrated implants in irradiated patients. Radiotherapy may induce vascular fibrosis and thrombosis, with subsequent tissue breakdown and development of chronic nonhealing wounds. While the long-term risk may be higher failure rates, the immediate risk is osteoradionecrosis. Therefore, irradiated bone should be viewed as a risk factor for implant placement, and an adequate waiting period after radiotherapy is recommended; alternatively, a series of hyperbaric oxygen treatments can be prescribed before implant surgery to improve wound healing and osseointegration.

Osteoporosis is a condition characterized by generalized reduction in bone mass. Osteoporotic patients are at higher risk of periodontal disease, and patients with periodontitis are at higher risk of osteonecrosis of the jaw, or ONJ. In osteoporotic patients, periodontal intervention and disease prevention are imperative. Osteoporosis per se does not significantly increase the risk of complications; however, osteoporosis may be treated with antiresorptive medications, typically oral bisphosphonates or, less commonly, yearly intravenous bisphosphonates. These medications adversely affect the ability of the bone to remodel itself, so there is a small risk of compromised bone healing following implant placement if the patient has been in long-term treatment with oral bisphosphonates. In their 2014 position paper on medication-related osteonecrosis of the jaw, or MRONJ, the American Association of Oral and Maxillofacial Surgeons estimates that the risk of MRONJ following implant placement among patients exposed to oral bisphosphonates is similar to that following tooth extraction, or 0.5%.

Diabetes is a metabolic disorder characterized by high blood glucose levels that result from defects in the body's ability to produce and/or use insulin. Diabetes affects the whole body, and its oral effects include xerostomia, increased levels of salivary glucose, increased incidence of caries and periodontal disease. Questions remain as to the association of poor glycemic control and implant failure, although patients with poor glycemic control have been associated with an increased susceptibility to postoperative infections.

The literature implicates smoking as one of the prominent risk factors affecting the success rate of dental implants. Some studies report the failure rate of implants in smokers as being more than twice that in nonsmokers. Smoking is associated with significantly more marginal bone loss after implant placement and an increased incidence of peri-implantitis. Smoking is also associated with lower success rates for bone grafts. Heavy smoking has been shown to adversely affect the long-term prognosis of dental implants.

Systemic Risk Factors Associated with Implant Therapy, Key Learning Points: Implant candidates must be evaluated for systemic risk factors during a thorough medical history. Systemic risk factors include: immunodeficiencies, immunosuppressive drugs, bleeding disorders, chemotherapy, head and neck radiation, osteoporosis and bisphosphonate use, diabetes, and smoking.

The next series of slides will outline the local risk factors that should be identified prior to implant therapy. Patients should be evaluated for these factors during the medical and dental history and clinical examination. Local factors include poor oral hygiene, periodontal disease, oral mucosal diseases, and bruxism.

A general prerequisite for implant placement is that the patient must have adequate oral hygiene. The clinical image depicts an inadequate level of oral hygiene. There is substantial evidence that poor oral hygiene and microbial biofilms are associated with peri-implant disease and implant loss. A thorough assessment of the patient's ability to comply with a home care regime of oral hygiene procedures is crucial.

Periodontal disease refers to the inflammatory processes that occur in the tissues surrounding the teeth in response to the tooth-borne microbial biofilm. Induction of this inflammatory process results in loss of supporting alveolar bone, and, if left untreated, tooth loss. When periodontally diseased teeth are lost, the remaining alveolar bone height is significantly reduced. This may limit the available bone height for the placement of implants. Clinicians should exercise caution when considering the placement of implants in patients with a history of periodontal disease, because there is evidence suggesting that implants replacing teeth lost due to chronic periodontitis may have lower survival rates and more biological complications. Untreated or incompletely treated periodontal disease increases the risk of peri-implant disease and implant failure. There is evidence that periodontal pockets might serve as reservoirs of pathogens that can be transmitted to implants.

Diseases of the oral mucosa include Sjoegren syndrome, epidermolysis bullosa, and lichen planus. Studies have shown a high success rate for implants in patients affected by these diseases; however, the severity of these diseases and medical complications of the patient must be evaluated prior to implant placement, and long-term follow-up is essential to monitor the condition of the disease and of the implants. Moreover, diseases of the oral mucosa may compromise the patient's ability to maintain adequate oral hygiene.

Bruxism is a parafunctional activity that is characterized by involuntary grinding and clenching during sleep as well as during wakefulness, causing attrition or occlusal wear, periodontal trauma, and pain. Bruxism is considered a risk factor for excessive occlusal loading of dental implants and their prostheses, which may lead to mechanical failures such as screw loosening and screw and abutment fracture as well as technical complications such as prosthesis fracture or ceramic chipping.

Local Risk Factors Associated with Implant Therapy, Key Learning Points: Implant candidates must be evaluated for local risk factors during a thorough medical and dental history and clinical evaluation. Local risk factors include: poor oral hygiene, periodontal disease, oral mucosal diseases, and bruxism.

Contraindications to implant therapy remain controversial and evolve over time. The distinction between relative and absolute contraindications can be difficult. A relative contraindication in one patient may be considered to be an absolute contraindication in another patient if other conditions or risk factors exist. The most common relative contraindications will be covered in the following slides.

Insufficient bone volume at the planned implant site is nowadays considered to be only a relative contraindication because a number of different bone reconstructive techniques have been developed for ridge augmentation prior to or simultaneously with implant placement. Surgical augmentation can be performed to correct both vertical and horizontal ridge deficiencies.

Periodontitis allows for possible cross-infection to implants. Active periodontitis sites may act as reservoirs of pathogenic organisms that may infect implant sites. It is also important to note that patient susceptibility does not change simply because teeth have been removed, and therefore risks to outcome of implant therapy should be carefully weighed.

As a rule retained roots should be removed prior to implant placement. The exception would be cases where the gingival and bone health around the root are sound. In such cases, root removal at the time of implant placement can be considered.

Implants should be placed in non-infected sites. Infection may compromise osseointegration of the implant. Furthermore, chronic endodontic infections result in inflammatory bone resorption, and after healing the residual bone volume may be insufficient to house an implant. Teeth adjacent to the planned implant site should also be assessed for endodontic pathology and other infections that could jeopardize a planned implant.

Alcohol and drug abuse can have an effect on the success of implant therapy. Alcoholism increases the likelihood that nutritional intake will be poor, and the resulting deficit of vitamins and minerals can reduce the body's ability to heal. Furthermore, alcohol or drug abuse may interfere with prescribed preoperative or postoperative medications. Such patients also can be inconsistent with regard to compliance with postoperative instructions and their home care regime.

There are many individuals living with mental or psychological conditions. When seeing these patients, the dentist may be confronted with behaviors that may interfere with the safe and efficient delivery of implant therapy. Such disorders may also pose problems with compliance. Therefore, it is of great importance to evaluate whether a patient who has been diagnosed with a psychological or mental disorder will be able to comply with postoperative instructions and maintain sufficient oral hygiene.

Implants should not be placed in children and adolescents who have not yet reached their full skeletal maturity. Dental implants, similar to ankylosed teeth, do not erupt or migrate during dentoalveolar development. If implant placement is not deferred until substantial craniofacial growth has ceased, the implant prostheses may become infraoccluded. Both dental age and skeletal maturation should be used to assess growth and development. On the other hand, advanced age itself is not a contraindication. However, elderly patients often present a number of general health problems that might contraindicate surgery.

The next few slides will describe absolute contraindications to implant placement. It is important to remember that there may be a wide grey area between absolute and relative contraindications, because the evidence supporting implant therapy in medically compromised patients is limited. The American Society of Anesthesiologists has developed the ASA classification system for medical risk assessment. Patients classified as ASA 5 are moribund or near death, and patients classified as ASA 6 are brain-dead.

Medication-related osteonecrosis of the jaws, or MRONJ, is a relatively rare but potentially serious complication of treatment with bisphosphonates. Intravenous bisphosphonates and other IV antiresorptive drugs are primarily used in the treatment of cancer-related conditions such as bone metastases. In their 2014 position paper, the American Association of Oral and Maxillofacial Surgeons reported that 1.6% to 14.8% of cancer patients exposed to IV bisphosphonates develop MRONJ following tooth extraction. The risk of developing MRONJ among patients exposed to antiresorptive drugs for dental implant placement is unknown but considered to be comparable to the risk associated with tooth extraction. Therefore, patients currently being treated with high-dose intravenous bisphosphonates are not candidates for implant therapy.

Implant therapy is also contraindicated in patients who have received high-dose radiation at the area where implants could have been indicated. Patients undergoing active chemotherapy or in treatment with high-dose immunosuppressive agents like cyclosporine are also not candidates for elective procedures such as implant therapy. Certain serious systemic or life-threatening diseases are incompatible with implant placement, particularly osseous disorders like osteomalacia and osteogenesis imperfecta. An allergy to titanium or titanium alloys used to manufacture dental implants is extremely rare, but if an allergy is suspected further testing is required. Finally, implants should not be placed when there is doubt as to the patient's ability or willingness to comply with preoperative, intraoperative, or postoperative instructions, whether the suspected lack of compliance is due to physical, mental, or emotional abilities or as the result of drug or alcohol abuse.

Relative Versus Absolute Contraindications to Implant Therapy, Key Learning Points: Implant candidates must be evaluated for contraindications. Contraindications to implant therapy remain controversial and evolve over time. Relative contraindications include: insufficient bone volume, periodontitis, retained roots, local infection, drug or alcohol abuse, psychological or mental disorders, and age. Absolute contraindications include: serious systemic diseases and the current use of intravenous bisphosphonate therapy.

General Risk Factors and Contraindications for Implant Therapy, Module Summary: It is important to know the difference between risk factors and contraindications to implant therapy and to identify these from the outset to avoid complications. An important aspect of implant therapy is to detect at-risk patients at the outset, because patients often have more than one risk factor that impacts on the treatment protocol and the prognosis for treatment outcome. Another important aspect of implant therapy is to detect relative and absolute contraindications prior to treatment, because a number of relative contraindications or one absolute contraindication must lead to a re-evaluation of the original treatment plan.