It is important to prevent the orofacial complications associatedwiTh cancer ' therapy, and this requires an oncological team that includes an experienced dental practitioner and hygienist (Scully and Epstein, 1996). This is particularly important in children, since orofacial complications are up to three times as -
common as in adults having similar treatment (Dreizen, 1990; Stalman et al,
1986). In relation to osteoradionecrosis, its prevention becomes even more important, since its investigation is rudimentary, medical treatment used alone has limited success, and surgical treatment is technically difficult and expensive.
Prosthetic techniques which shield normal tissue with lead, or pull it out of the radiation beam, should be employed wherever possible (Poole and
Flaxman, 1986; Levendag et al, 1990). Multiple fields should be used in
preference to single fields, and if possible, the major salivary glands should be excluded. Further advances in radiotherapy, like 3D CT planning, conformai and stereotactic therapy, should enable more normal tissue to be spared, by focusing the radiation on the tumour itself, therefore preventing the associated complications.
General measures to prevent the development of osteoradionecrosis are well established. Basically, all the factors mentioned as risk factors to the development of osteoradionecrosis as discussed earlier, can be accessed. The main concern is usually the dentition, and with good plaque control, intensive fluoride therapy, use of chlorhexidine and saline mouthwashes, it is likely that the motivated patients will derive years of service from their teeth in the
proposed irradiation field (Stamps et al; 1982). •
Most patients (97%) need some attention to oral health-care before starting radio- or chemotherapy for cancer (Lockhart and Clark, 1994). Not infrequently these patients have poor oral hygiene and care, and comply poorly with treatment. Dental and periodontal disease should therefore be treated
before cancer therapy and any oral infections controlled. Patients must achieve good oral hygiene levels before initiating treatment.
Even knowing that there are reports showing delays in wound healing after chlorhexidine rinses (Basetti and Kallemberger, 1980), the use of chlorhexidine and fluoride is highly recommended in the literature (Joyston-
Bechal et al, 1992; Scully and Epstein, 1996,). Chlorhexidine may reduce oral
mutans streptococci and lactobacilli (Epstein et ai, 1991). Dietary control and
topical fluoride therapy are essential and should be continued for life. Fluoride can reduce caries and can be used as gel containing 1% sodium fluoride
placed in carriers and applied for 5 min. per day (Daly et ai, 1972; Horiot et al,
1983). Sodium fluoride mouthrinses with chlorhexidine diacetate have also been recommended (Giertsen and Scheie, 1993).
The use of prevention protocols is most welcome. Jansma et al (1992)
published a very detailed protocol for prevention and treatment of oral sequelae resulting from head and neck radiation therapy. The protocol is particularly applicable in centres with a dental team, which should be involved at the time of initial diagnosis, so that a successful preventive regimen is an integral part of the overall cancer treatment regimen.
Despite all preventive measurements, some patients will present with decaying or periodontally involved teeth following radiotherapy. It is possible to perform conventional endodontic therapy at this stage without incurring an
increased risk of infection in the bone on the apical region (Cox, 1976; Seto et
al, 1985; Kielbassa et al, 1995). This would be a preventive measurement,
since an extraction is avoided.
9.1. Prophylactic hyperbaric oxygen
Hyperbaric oxygen has been suggested to be used to prevent osteoradionecrosis, mainly by using it before any planned extraction. Marx and Ames (1982) refined the HBO preventive treatment for extractions after radiotherapy for 20 preoperative and 10 postoperative dives, claiming a 91.6%
Chapter 2 - Literature Review - Section I - Osteoradionecrosis
success rate, which they noted was highly favourable compared with the 20% to 50% success rates reported without HBO (Obwegeser and Sailer, 1978;
Bedwineck etal, 1976).
Marx et ai (1985) performed a randomised, prospective clinical trial using
HBO and penicillin in previously irradiated jaws. They demonstrated that prophylactic HBO improved extraction wound healing when compared with antibiotics. However, they had very high levels of osteoradionecrosis following extraction in both groups - 5.4% for the hyperbaric group and 29.9% for the antibiotics group. It is interesting to note that they did not perform an alveolectomy and primary closure was not attempted.
However, some authors question the benefits of hyperbaric oxygen in the prevention of osteoradionecrosis and do not use HBO before extractions
(Maxymiw et al, 1991). These authors extracted 449 teeth in 72 post-irradiated
patients, and the only preventive measure was the use of low-epinephrine or epinephrine-free, non-lignocaine local anaesthetics, and conservative surgical techniques. In a follow-up ranging from 68 days to 19.3 years (median 4.8 years), no instances of ORN occurred as a result of dental extraction.
Epstein et al (1987) mentioned that due to the low incidence of
osteoradionecrosis in patients after dental extractions, prophylactic use of hyperbaric oxygen can not be justified. This was reaffirmed by daym an (1997), who performed a review of the literature, regarding the use of HBO for the prevention of osteoradionecrosis after dental extractions. He observed that the true loss of continuity of mandibles that develop osteoradionecrosis after dental extractions varies greatly between small series, but in aggregate review is quite low. Even if one were to disallow any contribution of spontaneous osteoradionecrosis to the reported post-extraction osteoradionecrosis rate, the loss of continuity rate would still be 2.5%. If one were to treat all of these at-risk mandibles with HBO before extractions, the loss of continuity rate might be reduced to 0.5% if HBO were 80% effective, which may be an overly optimistic assessment. The cost to treat 100 patients with HBO to prevent two cases of loss of continuity would be approximately 1.5 million dollars (data courtesy
Hyperbaric Unit, Henry Ford Hospital, Detroit, Ml). Although it would be very desirable to eliminate osteoradionecrosis after extractions, the cost of treating 98 patients who would not have benefited, may well be insupportable, daym an (1997) therefore concludes that these data do not support the mandatory use of HBO before removing teeth in irradiated mandibles, particularly when one considers that in the most recent reports of osteoradionecrosis after dental
extractions the rate was only 2.1% (Marciani and Ownby, 1986; Makkonen et
al, 1987; Maxymiw ef a/, 1991; Widmark ef a/, 1989; Brunton, 1994).
Hyperbaric oxygen therapy has also been advocated to be used before the placement of dental implants in irradiated mandibles. The literature is very controversial in this subject. Those in favour of its use claim success rates of implants up to 100%, and only 57.9 to 64.7% without HBO (reviewed by Larsen, 1997). He suggested the use of a protocol similar to that used for extractions, with 20 dives before and 10 after implant surgery. As an example,
Granstrom et ai (1992) showed an implant failure of 58% before the introduction
of HBO, and of 2.6% after, in the maxilla and orbit. Keller (1997) reviewed the literature against the use of HBO, which showed also good success rates, ranging from 74 to 100%.He suggests that the risk of developing osteoradionecrosis is very low, and that with increased healing time the implants will osseointeg rate well. The costs and risks involved in the use of HBO, and the low incidence of complications without its use do not justify its routine use (Keller, 1997).
9.2. Prophylactic ultrasound
Ultrasound therapy seems to be an extremely useful tool in the prevention of osteoradionecrosis. It has been shown to be very effective in the treatment of osteoradionecrosis (Harris, 1992), but until now, no one has used it to prevent it. We think that a preventive protocol using 20 sessions of ultrasound before extractions or implant surgery, followed by further 20 sessions would be very useful (Reher and Harris, 1997). Ultrasound is readily available in all hospitals and very inexpensive. The cost to treat only one patient with the HBO
Chapter 2 - Literature Review - Section I - Osteoradionecrosis
prevention quoted by daym an (1997), would purchase at least 5 ultrasound machines.
This section will give an overview of the current literature related to angiogenesis. It has been divided into the following:
1. Mechanisms of blood vessel formation