Obtaining detailed information about a patient's medical history is mandatory before any surgical procedure such as implant therapy can be considered in a treatment plan. Special attention should be paid to patient-related factors that may affect bone healing. These factors can determine whether the patient is a suitable candidate for the planned procedure or if other treatment alternatives should be preferred. A systematic approach to receive the necessary preoperative information increases the likelihood that all relevant facets are elucidated. In addition, it will assist the clinician in identifying potential risk factors for the planned treatment and in revealing relative and absolute contraindications.

After completing this ITI Academy Module, you should be able to determine the general health condition of the patient and its relevance to oral surgery, identify relevant medical risk factors for implant therapy and distinguish between absolute and relative contraindications for implant therapy.

The American Society of Anesthesiologists has developed a physical status score system – the so-called ASA classification system, which is the most frequently used framework for medical risk assessment. It was developed to classify patients into risk classes before general anesthesia is administered, but is also used worldwide as an estimation tool for patient medical risk assessment in dental practice.

Using this system, the general health status of a potential implant patient may be classified into one of six classes with the following characteristics: ASA Physical Status 1 - the patient is a normal, healthy patient. ASA Physical Status 2 - the patient has a mild systemic disease. ASA Physical Status 3 - the patient has a severe systemic disease. ASA Physical Status 4 - the patient has a severe systemic disease that is a constant threat to life. ASA Physical Status 5 - the patient is moribund and is not expected to survive without the operation and ASA Physical Status 6 - the patient has been declared brain-dead and his organs are being removed for donor purposes.

In general, ASA 1 patients can undergo oral surgery without additional precautions. ASA 2 patients can usually also undergo oral surgery, provided their medical condition is well treated. Patients in this category include diabetics on oral hypoglycemic agents with good metabolic control, well-controlled asthmatic patients, well-controlled epileptic patients, and well-controlled mildly hypertensive patients on medication.

ASA 3 patients may be candidates for oral surgery. However, a consultation with the patient's physician is often indicated to make sure that the treatment of the medical condition is optimized. If this is not the case, elective oral surgery should be postponed. ASA 3 patients include well-controlled severely hypertensive patients on medication, well-controlled diabetic patients on insulin, patients with slight chronic obstructive pulmonary disease and patients with a history of myocardial infarction, cerebrovascular accident, or congestive heart failure more than 6 months ago.

ASA 4 patients are rarely candidates for elective oral surgery. In cases where, for example, an implant-supported dental prosthesis is essential for sufficient food-intake for the patient, hospital-based implant therapy may be considered. ASA category 4 includes patients with a history of unstable angina myocardial infarction, cerebrovascular accident, or congestive heart failure less than 6 months ago, patients with moderate to severe chronic obstructive pulmonary disease, and patients with uncontrolled hypertension, diabetes, or epilepsy. ASA 5 and 6 patients are not candidates for oral surgery and conservative alternatives should be chosen.

Estimation of General Health Condition, Key Learning Points: The ASA classification may be used to estimate the general health status of a patient. Medical conditions often do not preclude oral surgical procedures provided they are well-treated. Estimation of the general health status of a patient may assist the clinician in weighing surgical versus non-surgical treatment alternatives against each other.

A thorough medical history is mandatory prior to any implant treatment. A systematic approach to obtain the medical history is recommended since it will assist the clinician in identifying all relevant medical risk factors for implant therapy. A systematically obtained medical history addresses the general health status, a complete list of medication, any allergies, tobacco and alcohol consumption, and compliance. In the next section of this module we will discuss each of these issues separately.

When evaluating the general health status of the patient, information about preexisting diseases should be gained, since this assists the surgeon in evaluating conditions that could influence bone healing. Candidates for dental implant therapy should be free of any condition affecting the local bone healing. Patients that have received high-dose head and neck irradiation are at high risk of developing osteoradionecrosis if implants are placed within the field of radiation. If implant therapy is considered in irradiated patients, the field and dose of radiation should be available and the hospital unit responsible for the oncological treatment and the local maxillofacial department should be consulted. Radiation treatment of oro-pharyngal cancers usually implies 33 to 34 doses of 2 Gray each yielding an accumulated dose of 66 to 68 Gray. The risk of developing osteoradionecrosis has been demonstrated to increase when the accumulated dose of irradiation exceeds 45 Gray. Intensity-modulated radiation therapy may reduce the effective dose of irradiation to the tooth-bearing areas thereby making implant treatment possible. It is, however, still mandatory to possess complete information about the radiation therapy and it is advisable to consult the local maxillofacial service before implant therapy is considered.

Candidates for dental implant therapy should be free of any condition affecting general normal bone healing including any conditions predisposing to postoperative infectious complications. Diabetic patients with poor glycemic control, which means uncontrolled diabetes, have been associated with increased susceptibility to postoperative infections and should only be treated with great caution. In contrast, well-controlled diabetes has not been associated with an increased risk of complications. Patients that have received transplanted organs and some rheumatic patients may be in long-term, high-dose immunosuppressive therapy, which increases the risk of postoperative infections. In theory, systemic conditions influencing bone metabolism, like osteoporosis, should affect the prognosis of implant therapy. However, systematic reviews have failed to substantiate such relation. It is, therefore, debated whether patients suffering from osteoporosis are at increased risk of implant failure compared with non-osteoporotic patients. Today it is believed that the presence of osteoporosis per se does NOT significantly increase the risk of complications after placing implants. However, osteoporotic patients in long-term treatment with antiresorptive medication - like oral bisphosphonates - may be at increased risk for healing complications.

There is virtually no scientific data documenting implant therapy in patients suffering from neuro-psychiatric disorders. A few published cases have demonstrated that implant therapy may be successful in patients suffering from Down Syndrome, autism, Huntington's disease and schizophrenia. Therefore, these diseases do not by themselves constitute contraindications, but they may pose problems with compliance. Therefore, it is of great importance to evaluate whether a patient with a neuro-psychiatric diagnosis will be able to comply with the postoperative instructions and maintain sufficient oral hygiene.

A complete list of medication should be obtained well ahead of the planned surgical procedure. Such a list enables the surgeon to evaluate if one or more of the drugs constitute contraindications to the planned treatment or if they should be adjusted in the peri-operative period. Special attention should be paid to medication that affects local or general bone healing, medication that may increase the complexity of the planned surgical procedure, and medication with possible interactions with drugs prescribed for the peri-operative period.

Medication that affects local and general bone healing includes high-dose antiresorptive agents administered against myelomatosis or bone metastases from other malignant conditions. Due to the accumulation of these drugs in bone tissue and a halftime of more than ten years, bone healing should be expected to be compromised for the whole life in these patients. There may be a marginally increased risk of dental implant failure in osteoporotic patients on antiresorptive medication. This risk is expected to increase with the duration of the medication. Several experimental studies have shown that chemotherapy and immunosuppressive agents like cyclosporine reduce normal bone healing around dental implants. However, no clinical data is available regarding implant placement in these patients taking these kinds of medication. Despite the lack of clinical evidence, chemotherapy and immunosuppressive agents including long-term high-dose systemic corticosteroids are believed to increase the risk of postoperative complications and implant failure. It is, therefore, advised to prefer other treatment alternatives than implants and bone augmentation procedures until clinical data support this treatment option. Patients previously treated with these agents do not seem to be at increased risk for implant failure provided that their immune system has recovered completely as documented by blood samples.

Intake of some drugs may warrant additional caution during and after the surgical procedure. This may be the case in patients receiving antithrombotic or anticlotting treatment. The risk of excessive bleeding during and after standard implant placement is normally considered low. In general, antithrombotic treatment should not be discontinued since the risk of severe bleeding most often is much lower than the risk of a thromboembolic event. However, the surgeon should make sure that the antithrombotic treatment is well adjusted and within the therapeutic range. If the surgical procedure is expected to be complex and the risk of bleeding elevated - as in major bone augmentation procedures - it may be indicated to discontinue the medication or to reduce the dose from therapeutic levels to prophylactic levels. Adjustment of the patient's medication should always be done in agreement with the patient's physician.

Finally, the surgeon must make sure that there are no interactions between the patient's regular medication and medication prescribed in relation to the planned surgical procedure. Again, special attention should be paid to patients taking antithrombotic medication in the form of Vitamin K antagonists because of severe interactions with antibiotics and painkillers. For example especially metronidazole but also non-steroidal anti-inflammatory drugs may dramatically increase the risk of bleeding in patients taking Vitamin K antagonists.

Allergies are rarely a problem related to the implant material and the surgical procedures themselves. However, some patients may have allergies towards the medication prescribed pre- and post-operatively. This is mainly the case with antibiotics and painkillers.

Smoking is a risk factor for implants placed in native bone as well as for implants placed in the augmented bone. Although smoking should not be considered an absolute contraindication for implant therapy, the patient should be informed about the increased risk of implant loss and peri-implant disease and should be motivated for cessation or at least dose-reduction. Alcohol consumption has not been significantly linked to a negative impact on implant success and survival, but the main problem with alcoholism and implant therapy is probably related to compounding factors such as malnutrition, poor oral hygiene and compliance. Therefore, patients with any kind of abuse issue should be evaluated extremely carefully, and alternatives to implant therapy should usually be preferred.

Patients who are not able to comply with postoperative instructions should not be considered for implant therapy. Compliance can be difficult to determine during a single pre-operative examination. However, an indicator may be insufficient oral hygiene. Thus, if the patient presents with inadequate oral hygiene it is highly recommended to go through a hygiene phase before implant treatment is considered.

Risk Factors for Implant Therapy, Key Learning Points: A systematic and complete medical history is mandatory before any implant treatment. Preexisting medical conditions that could influence bone healing or interfere with patient compliance should be revealed. Medication that influences bone healing, affects the surgical procedure, or interacts with medication prescribed during implant treatment should be recorded. Allergies towards materials or medication used during the planned implant treatment should be excluded. Use of tobacco and/or alcohol should be recorded. The patient's ability to comply with intra- and post-operative precautions should be ensured.

In the next section of the module we focus on absolute and relative contraindications to implant therapy. An absolute contraindication to implant therapy is defined as a medical, psychological or clinical condition or factor that under no reasonable circumstance makes implant therapy advisable. A relative contraindication to implant therapy, on the other hand, is a medical, psychological or clinical condition or factor that increases the risk of complications, but which may be outweighed by the benefit of the implant therapy for the patient. Absolute and relative contraindications may be revealed during any part of the preoperative systematic examination. As the evidence behind implant therapy in medically compromised patients is limited, there is often a wide gray area between absolute and relative contraindications. The patient should always be informed about any increased risk for implant failure, intra-operative, or postoperative complications.

Implant therapy has the potential to improve the quality of life considerably. Therefore it may also be a part of treating general diseases where ill-fitting dental prostheses or lack of self confidence are a part of the problem. However, implant treatment in terminally ill patients, like ASA 5 and 6 patients, is contraindicated. Implant therapy is also contraindicated in patients that have received high-dose radiation therapy in the area where implants could have been indicated. Patients in ASA categories 2, 3 and 4 can receive dental implants if their medical condition is well-treated and controlled. Many medical conditions may contraindicate implant therapy if insufficiently treated. It is therefore of utmost importance to make sure that all medical conditions are well controlled before implant therapy is initiated. A conference with the patient's physician is often indicated to make sure that the general condition of the patient is optimized. Diabetics with poor glycemic control are at increased risk of severe healing complications that may outweigh the potential benefit of the implant therapy. Therefore, poorly-controlled diabetics should only be considered for implant therapy with great caution. However, due to inconsistent clinical scientific data, implant placement is not considered an absolute contraindication in these patients.

Patients in treatment or previously treated with high-dose antiresorptive agents against myelomatosis or bone metastases are not candidates for implant therapy. The same is true for patients in active chemotherapy and in treatment with high-dose immunosuppressive agents like cyclosporine. However, some patients who are in low-dose treatment with immunosuppressive agents may receive implants after consulting the patient's physician. The risk of post-operative complications may be increased in osteoporotic patients in long-term low-dose treatment with antiresorptive agents, patients in long-term high-dose treatment with corticosteroids, and patients in long-term high-dose treatment with non-steroidal anti-inflammatory drugs which are abbreviated as NSAIDs. Alternatives to implant therapy should be considered and the patient should be well informed about this increased risk. Before placing implants in patients on antithrombotic medication, it is mandatory to know the specific medication and to be sure that the treatment is well controlled. For patients on temporary antithrombotic treatment after myocardial infarction and other thromboembolytic events, it might be advantageous to postpone the implant placement until this medication has stopped. Due to severe interactions, patients taking Vitamin K antagonists should NEVER receive antibiotics in form of macrolides or metronidazole, analgesics in form of non-steroidal anti-inflammatory drugs and antimycotic drugs from the imidazole group.

Allergy to titanium or titanium alloys used as bulk material for dental implants is extremely rare. Whenever in doubt, the patient should be referred to a specialist for further testing. Allergies may also exist towards drugs or agents used during or after surgery such as local anesthetics, pain killers, or antibiotics. Alternatives usually exist, which may be identified by consulting the patient's physician or a specialist.

Abuse of alcohol or any other euphorizing substances is related to a significant lack of compliance and is considered an absolute contraindication to implant therapy. A moderate intake of alcohol, which may be defined as an amount below maximum intake recommended by the local health authorities has not been documented to affect implant failure rate or the rate of postoperative complications. Heavy smoking, which generally is defined as more than ten cigarettes per day, is documented to reduce implant survival and increase complications including peri-implant disease. The patient should be informed about the increased risk and supported in stopping or at least reducing this habit.

If the preoperative evaluation gives reason to doubt whether the patient will be able to comply with intra- and postoperative instructions including oral hygiene, alternatives to implant therapy should be preferred. Whenever in doubt, a thorough hygiene phase should be instituted and the result thoroughly evaluated before implant therapy is considered. Insufficient oral hygiene may have many causes. But the patient should demonstrate willingness and technical ability to attain optimal oral hygiene before implant placement is scheduled.

Absolute and Relative Contraindications, Key Learning Points: There are few absolute contraindications to implant therapy. These include: ASA 5 & 6 patients, full-dose head and neck irradiation, current or previous high-dose antiresorptive medications, ongoing chemotherapy, high-dose immunosuppressive therapy, allergy to implant material, abuse of euphorizing substances, and lack of compliance. However, some medical conditions may turn into absolute contraindications if they are not sufficiently treated. Relative contraindications may disappear if they are sufficiently treated. When relative contraindications are identified during the systematic preoperative evaluation, the patient should be informed about the potentially increased risk for implant failure, intraoperative and postoperative complications.

Patient Medical Factors, Module Summary: A thorough systematic medical history is mandatory before any implant treatment to assess the general health status of the patient, and to identify potential risk factors, absolute and relative contraindications. Risk factors are medical conditions or habits that might compromise treatment outcome of the implant therapy or increase the risk of intra- or postoperative complications. These should be revealed and recorded preoperatively. If absolute contraindications are identified, alternatives to implant therapy should be looked for; when relative contraindications are identified, the medical condition should be optimized or the detrimental habit if possible stopped or reduced. Hereafter the situation should be reevaluated and the patient informed about potential risks related to implant treatment as well as about possible alternatives.