Is inadequate osseointegration a concern in radiation-treated patients, if implants are treatment planned?
This question was submitted by a general dentist: Is inadequate osseointegration a concern in patients who have received radiation therapy for a head and neck malignancy if implants are treatment planned?
Dr. Jeff Chadwick, at Princess Margaret Hospital, Dental Oncology, Ocular, and Maxillofacial Prosthetics Group, provided a preliminary response to this question
Yes, however …
As with most questions related to this patient population, the answer is: “it depends.” Careful examination is a vital step in determining which restorative/prosthodontic approach best suits the individual. Examination also mandates a thorough review of their cancer diagnosis as well as the constituents and sequence of their treatment, including the type, duration, tissue volume and dose of radiation, use of concomitant chemotherapy or surgical management, as well as the usual detailed clinical and radiographic examination of current conditions.
The primary objectives of prosthetic rehabilitation in head-and-neck cancer patients are masticatory efficiency, intelligible speech, and optimal aesthetics. The relative importance to the patient of each factor, as well as the dentist’s ability to deliver them, should be confirmed and agreed upon by both patient and clinician before commencing any treatment. Frequently, these three goals are difficult to achieve in head and neck radiation-treated patients for a variety of reasons: persistent post-radiation xerostomia, tissue/muscle fibrosis altering extra oral and intra oral anatomy, and decreased vertical opening and general function. Lastly, the possibility of poor wound healing, and ultimately osteoradionecrosis (ORN), should cause the prudent practitioner to pause and reflect.
While the success of osseointegrated implants has made them the standard of care in the prosthetic rehabilitation of many clinical scenarios, placement of these fixtures in irradiated head and neck cancer patients is complicated by the several changes to the oral cavity that reduce their reliable placement (we may limit the discussion to those patients who have received either external beam or intensity-modulated radiation therapy [IMRT] for a head and neck malignancy). Specifically, as it relates to the successful placement of dental implants, one must exercise caution when osseous hypovascularity, hypocellularity, and hypoxia caused by radiation have become a concern..
The risk of ORN and the lack of osseointegration increase dramatically when the dosage of radiation is above 50 Gray (Gy) and most patients receive 70Gy to primary sites/involved lymph nodes with varying dosages of 20-50Gy to areas where microscopic disease may be present. The overall incidence of ORN with the use of IMRT has been reported to be anywhere between 0-6% and while this figure certainly appears low, the overarching issues is whether or not the benefit of implant placement offsets the risk of implant failure; and if the practitioner and patient want to risk the development of ORN.
The use of prophylactic hyperbaric oxygen (HBO) has been suggested to improve chances for success of implant placement in irradiated patients. Unfortunately, in many jurisdictions, wait-times for elective HBO therapy can be lengthy because it is reserved for patients with t medical conditions requiring its immediate use. In addition, depending on the literature that one consults, there is conflicting evidence for the use of this therapy for both prevention of ORN and increasing the likelihood of successful implant osseointegration.
The best way to avoid catastrophic results associated with the placement of implants is to consult the patient’s radiation oncologist to determine the dosage of radiation that was delivered to the proposed implant site. This information can be gleaned by consulting the original planning CT images and their treatment isodose curves (Figure 1). Isodose curves are essentially a “radiation dose contour map” and it is from these that one can determine the radiation dose delivered to the potential surgical site.
Lastly, it is important to remember that radiation delivery methods are not standardized across the country or across time, because there has been a secular trend to increase dose and add chemotherapy in modern times. Where, at one time, it would have been safe to use clinical clues, such as absence of facial hair or presence of skin pigmentation to act as a proxy for the radiation field, in the era of IMRT, these methods are no longer suitable.
Assuming that the patient and the practitioner agree on the goals of prosthetic treatment, commencing prosthetic rehabilitation with tooth/tissue-borne fixed or removable prostheses that do not rely on osseous healing may be a perfectly acceptable and successful alternative.
While the available literature shows a dearth of evidence-based guidelines surrounding implant osseointegratation and prosthetic rehabilitation in this patient population, up to this point, we have ignored the necessity for more frequent clinical and radiographic evaluations, which is the critical element of preventive care as well as the presence of significantly altered anatomy and innervation that may result from primary surgery for head and neck cancers. If there are important concerns, refer the patient his/her original treatment centre to visit their staff dentists (or a major treatment centre with a dental department/oral and maxillofacial prosthodontist).
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