Contraindications
There are few absolute contraindications to implant dentistry. However, there are some systemic, behavioral, and anatomic considerations that should be assessed.
Particularly for mandibular (lower jaw) implants, in the vicinity of the mental foramen (MF), there must be sufficient alveolar bone above the mandibular canal also called the inferior alveolar canal or IAC (which acts as the conduit for the neurovascular bundle carrying the inferior alveolar nerve or IAN).
Failure to precisely locate the IAN and MF invites surgical insult by the drills and the implant itself. Such insult may cause irreparable damage to the nerve, often felt as a paresthesia (numbness) or dysesthesia (painful numbness) of the gum, lip and chin. This condition may persist for life and may be accompanied by unconscious drooling.
Uncontrolled Type II diabetes is a significant relative contraindication as healing following any type of surgical procedure is delayed due to poor peripheral blood circulation. Anatomic considerations include the volume and height of bone available. Often an ancillary procedure known as a block graft or sinus augmentation are needed to provide enough bone for successful implant placement.
There is new information about intravenous and oral bisphosphonates (taken for certain forms of breast cancer and osteoporosis, respectively) which may put patients at a higher risk of developing a delayed healing syndrome called osteonecrosis. Implants are contraindicated for some patients who take intravenous bisphosphonates.
The many millions of patients who take an oral bisphosphonate (such as Actonel, Fosamax and Boniva) may sometimes be advised to stop the administration prior to implant surgery, then resume several months later. However, current evidence suggests that this protocol may not be necessary. As of January 2008, an oral bisphosphonate study reported in the February 2008 Journal of Oral and Maxillofacial Surgery, reviewing 115 cases that included 468 implants, concluded "There is no evidence of bisphosphonate-associated osteonecrosis of the jaw in any of the patients evaluated in the clinic and those contacted by phone or e-mail reported no symptoms."
The American Dental Association had addressed bisphosphonates in an article entitled "Bisphosphonate medications and your oral health," In an Overview, the ADA stated "The risk of developing BON in patients on oral bisphosphonate therapy appears to be very low...". The ADA Council on Scientific Affairs also employed a panel of experts who issued recommendations for treatment of patients on oral bisphosphonates, published in June 2006. The overview may be read online at ada.org but it has now been superseded by a huge study—encompassing over 700,000 cases—entitled "Bisphosphonate Use and the Risk of Adverse Jaw Outcomes." Like the 2008 JOMS study, the ADA study exonerates oral bisphosphonates as a contraindication to dental implants.
Bruxism (tooth clenching or grinding) is another consideration which may reduce the prognosis for treatment. The forces generated during bruxism are particularly detrimental to implants while bone is healing; micromovements in the implant positioning are associated with increased rates of implant failure. Bruxism continues to pose a threat to implants throughout the life of the recipient. Natural teeth contain a periodontal ligament allowing each tooth to move and absorb shock in response to vertical and horizontal forces. Once replaced by dental implants, this ligament is lost and teeth are immovably anchored directly into the jaw bone. This problem can be minimized by wearing a custom made mouthguard (such an NTI appliance) at night.
Postoperatively, after implants have been placed, there are physical contraindications that prompt rapid action by the implantology team. Excessive or severe pain lasting more than three days is a warning sign, as is excessive bleeding. Constant numbness of the gingiva (gum), lip and chin—usually noticed after surgical anesthesia wears off—is another warning sign. In the latter case, which may be accompanied by severe constant pain, the standard of care calls for diagnosis to determine if the surgical procedure insulted the IAN. A 3D cone beam X-ray provides the necessary data, but even before this step a prudent implantologist may back out or completely remove an implant in an effort to restore nerve function because delay is usually ineffective. Depending upon the evidence visible with a 3D X-ray, patients may be referred to a specialist in nerve repair. In all cases, speed in diagnosis and treatment are necessary.
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