Newsletters for MDs

Radiation Therapy and the Prosthodontist

When the treatment protocol, for cancer of the head and neck, requires radiation therapy, there are several potential side effects in the oral cavity. On a simplistic level, radiation therapy is effective in killing tumor cells because it destroys cells which have a large nucleus. Unfortunately, salivary glands, in addition to tumor cells, have large nuclei. Radiation therapy may, therefore, result in an alteration in the quantity and/or quality of the saliva. Saliva both lubricates the mouth and prevents decay. Until proven otherwise, it must be assumed that all people who have received radiation therapy to the head and neck area, will have an alteration in the nature of their saliva.

The second effect of radiation is to decrease the size and number of blood vessels in the area of radiation. It is possible that this reduction in the amount of the blood supply to the irradiated bone and soft tissues may help reduce the nourishment to a quickly growing tumor. More importantly, the decrease in blood supply to the irradiated tissues (particularly bone), results in a decrease in the ability of these tissues to heal following injury, surgery, or infection. Post radiation infections of bone can be quite serious with prolonged healing time, occasionally resulting in osteoradionecrosis. The large sequestrums formed by osteoradionecrosis can potentially result in more significant bone loss than the original surgery.

Radiation induced changes in salivary function may result in a nasty, quickly developing, decay around the necks of the teeth (radiation induced caries). This decay is directly related to alterations in the quantity and quality of the saliva by the radiation therapy, not by the action of the radiation on the teeth. In fact, radiation therapy seems to have no clinically significant effects on either the hard or soft tissues of the teeth themselves. Many of today's drug therapies have a similar side effect of alterations in salivary flow. These people may also suddenly experience extensive dental caries.

Topical fluoride helps prevent the adherence of bacteria to the teeth, and, since bacteria cause decay, this therapy in conjunction with good oral hygiene, and frequent follow up, helps decrease the rate and significance of the radiation induced caries.. If all the salivary glands are affected by radiation, a dry mouth will develop. A severely dry mouth, xyrostomia, signals a potential increase in the amount of decay as well as generalized oral discomfort and alterations in perceived taste. There may also be a significant increase in sore spots associated with removable artificial devices due to the loss of lubrication.

The importance of radiation induced caries, as described above, is not the decay itself, but the potential of infection from either the pulp of the tooth (root canal), or periodontal disease (gum disease) or the trauma of a necessary extraction. The concern over osteoradionecrosis is the driving motivation for a dental consultation prior to radiation therapy.

Pre radiation dental clearance is a serious matter and must be done by someone with an understanding of the processes involved. Wholesale removal of all teeth prior to radiation is not an appropriate approach to preserve the patient's best quality of life. Routine pre-radiation clearance includes: Removal of teeth in the field of radiation that have a poor prognosis, elimination of periodontal and endodontic infections, targeting of existing decay for treatment ASAP, and the instruction of the patient in the reasons and techniques of proper oral hygiene and fluoride therapy. Always aware of the limited window for optimal radiation therapy following surgery, all pretreatment surgery is done immediately thus optimizing the timing for radiation therapy.

Pre-radiotherapy clearance, is not only an opportunity to prepare the oral cavity for therapy, and begin fluoride treatment. As a rehabilitative specialist, I represent a non-threatening practitioner who can go over the physical and psychological events related to surgery and/or radiation and chemotherapy. In essence, we function as a support group.

At approximately six months following radiation therapy, the level of salivary function is fairly well set. If xerostomia is going to be a factor in the patient's life, we will know it. At this point a determination of whether to continue fluoride therapy, and how frequent dental examinations should be done, can be made. Actual dental care may be done by the patient's general dentist, but determination of the level of care is a continuation of the original therapy. It is imperative that post radiation care include a dental evaluation a few weeks post radiotherapy, and at six months. If appropriate, I can then arrange for proper care and therefore the prevention of serious sequellae. As always, a well functioning team gives the patient the best possible results, with a minimum number of problems for the patient or the doctors involved.

The fear of inadequate blood supply and the resulting osteoradionecrosis following surgery, or implant failure, due to previous radiation therapy, has always been an impediment to the placement of dental implants. Dental implants placed in patients with previously irradiated bone has been accomplished in several medical centers on an experimental basis. In five and seven year studies the success rate has been demonstrated as twenty to thirty percent lower than implants placed in the same areas that have not been irradiated. Since the normal success rate is in excess of 90% this still gives approximately a 65% success rate for individual implants placed in radiated bone. More important than the success rate was the finding that failed implants did not routinely result in extensive loss of bone due to osteoradionecrosis. Instead, the failures seemed to follow the same course that failed implants in non radiated bone do. Failing implants demonstrated bone loss only in areas related to the implant rather than the feared generalized osteoradionecrosis. It should be noted, however, that the number of cases reported is small and can not therefore be assumed to represent universal results. Radiation therapy occurring after implants have been in place for several months, seems to have little effect on the success rate of the implants, but my experience has demonstrated an increase in minor complications.

In an attempt to increase the blood supply to the irradiated area, the use of hyperbaric oxygen has been fairly successful. Apparently, delivering high concentrations of oxygen under high pressure increases the oxygen levels in poorly vascularized areas (such as irradiated bone). This actually stimulates an increase in the number and size of the vessels in these areas. Logically this increase in blood supply should reduce the potential for either the surgical insult or an infection from causing a serious problem.

The placement of an implant demands adequate height and width of bone to allow the implant to exist in a healthy milieu of bone. When there isn’t adequate bone remaining to support the implant, bone augmentation is the possible. The width of the remaining bone can be increased, but height as alluded us to date, except in the area of the sinuses. Adding bone to the lower portion of the sinus effectively increases the height of the remaining dental ridge allowing implant placement in atrophic areas. When bony augmentation is done after radiation therapy, it is non-radiated bone and responds accordingly. The same is true with bone grafts placed as part of reconstructive surgery. If placed after the radiation therapy, the graft is capable of supporting dental implants without fear of osteoradionecrosis.

The bottom line on the use of dental implants for the support of maxillofacial devices is that they are an excellent adjunct, allowing rigid retention of the prosthetic devices. When possible the dental implants should be placed prior to radiation. Placement of dental implants in previously irradiated bone should only be done when the higher rate of failure is justified by the need for retention of the prosthesis. When dealing with heavily irradiated bone, hyperbaric oxygen treatment should be considered.

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