Influence of preventive dental treatment on mutans streptococci counts in patients undergoing head and neck radiotherapy

ABSTRACT The aim of this study was to evaluate the influence of chlorhexidine gluconate, sodium fluoride and sodium iodine on mutans streptococci counts in saliva of irradiated patients. Material and Methods: Forty-five patients were separated into three experimental groups and received chlorhexidine (0.12%), sodium fluoride (0.5%) or sodium iodine (2%), which were used daily during radiotherapy and for 6 months after the conclusion of the treatment. In addition, a fourth group, composed by 15 additional oncologic patients, who did not receive the mouthwash or initial dental treatment, constituted the control group. Clinical evaluations were performed in the first visit to dental clinic, after initial dental treatment, immediately before radiotherapy, after radiotherapy and 30, 60, 90 days and 6 months after the conclusion of radiotherapy. After clinical examinations, samples of saliva were inoculated on SB20 selective agar and incubated under anaerobiosis, at 37°C for 48 h. Total mutans streptococci counts were also evaluated by using real-time PCR, through TaqMan system, with specific primers and probes for S. mutans and S. sobrinus. Results: All preventive protocols were able to reduce significantly mutans streptococci counts, but chlorhexidine gluconate was the most effective, and induced a significant amelioration of radiotherapy side effects, such as mucositis and candidosis. Conclusion: These results highlights the importance of the initial dental treatment for patients who will be subjected to radiotherapy for head and neck cancer treatment.


INTRODUCTION
Treatment of head and neck cancer (HNC) consists of surgery, radiotherapy (RT), and the association between them, besides the use of chemotherapy as an adjuvant in the treatment 14 .
However, radiotherapy has been associated with several side effects, such as mucositis, changes in salivary gland function, radiation caries and especially osteoradionecrosis of the jaws 2,23 .
These undesirable effects may affect treatment evolution and patient compliance with treatment.
The occurrence of these reactions depends on the radiation dose, volume of irradiated tissue, fraction size, fractionation scheme, type of ionizing radiation, location of the irradiated area and other concomitant treatments 23 . In addition, individual aspects including age, systemic status, oral hygiene habits, tobacco and alcohol consumption 2 also need to be considered.
The occurrence of radiation caries and mucositis is high as 40-100% of the irradiated patients 22,23 , producing extreme discomfort and compromising the acceptance 15 , continuity 21 and intensification of RT 7 . Salivary gland dysfunction induced by RT results in hyposalivation, which may change the oral microbiota to a highly cariogenic microbiota, decrease clearance of carbohydrates from diet and organic acids produced by microorganisms, reduce buffering capacity, and impair remineralization of the tooth structure 9,18 .
In addition, patients who have xerostomia may consume a diet of soft, carbohydrate-rich foods, which may further increase the susceptibility to dental caries. Taken together, these changes may lead to rampant caries after RT 6,20 . In Brazil, three preventive schemes are followed by most of the radiotherapy centers for prevention of radiation caries and osteoradionecrosis: chlorhexidine gluconate (0.12%), sodium fluoride (0.5%, aqueous solution) and sodium iodine (2% in hydrogen peroxide 10 v/v). However, there are no microbiological evidences that these protocols are effective when associated to the oral hygiene, especially in a population composed mainly by people with low socioeconomic level.
Thus, the aim of this study was to evaluate the influence of these preventive protocols associated to the improvement of oral hygiene standards on mutans streptococci counts in 60 patients submitted to radiotherapy for treatment of head and neck cancer. Prior to radiotherapy, patients were separated randomly into four different groups:

MATERIAL AND METhODS
Group I: patients were submitted to initial dental treatment (IDT), generally 3-4 weeks before RT, which consisted of extractions, restorations, scaling, and dental prophylaxis. The mean radiation dose received by the patients varied from 5.040 to 7.020 cGy, and the fractioning dose was 180 cGy. RT was carried out using a linear accelerator.

Clinical procedures
In groups I, II or III, clinical examinations were performed at the first contact with the patient, before any dental treatment or oral Influence of preventive dental treatment on mutans streptococci counts in patients undergoing head and neck radiotherapy hygiene instructions (stage 1), immediately after IDT (stage 2), before RT (stage 3), immediately after RT (stage 4), 30 days (stage 5), 60 days (stage 6), 90 days after RT (stage 7) and 6 months after RT (stage 8). The oral hygiene status was assessed using the plaque index (PI) 19 . In group IV, clinical examinations were performed just before RT, 3 weeks after the beginning of RT, immediately after, 30 days and 6 months after RT.

Collection of clinical samples, microbial isolation and enumeration
Whole resting saliva was collected from each patient before IDT, immediately after IDT, before RT, immediately after RT, 30, 60, 90 days and

real-time PCR
The presence and quantification of mutans

RESULTS
Unfortunately, out of the 60 patients initially examined, 10 did not conclude RT and 11 other patients were not in physical conditions to be submitted to final intra-oral examinations.
Oral manifestations associated to radiotherapy are presented in Table 1. Before RT, oral mucositis and dermatitis were not observed. erythematous candidosis was detected in one patient of group IV and xerostomia was reported by two patients (group II and group IV). After RT, mucositis, xerostomia, and dermatitis were widely disseminated, irrespective of the experimental group, and except for candidosis, there were no statistically significant differences between groups regarding these side effects of RT.
In Group IV, immediately after RT, candidosis was diagnosed both in its pseudomembranous   4 Group IV: patients did not receive initial dental treatment.   In relation to mutans streptococci counts, they were very high at baseline, but initial dental treatment as well as all preventive protocols used during the study were able to reduce acidogenic cocci. The mutans streptococci counts are shown in Table 2 At baseline, most patients of groups I, II and III were at high-risk for dental caries or presented microbial overgrowth on agar plates.
There was a slight caries risk reduction after IDT and this phenomenon was sustained during RT, except for group IV (Table 3). follow-up visits 6,9 . Therefore, patient care must be individualized with evaluation at regular intervals to determine the caries risk and evolution, in order to preserve adequate oral health status 9 . In this study, patients were instructed to maintain a monthly visit routine to the dental office and this regimen probably interfered with patients'

DISCUSSION
compliance, thus improving significantly the clinical outcome of the preventive protocols.
After RT, no single case of osteoradionecrosis was observed, probably due the time span between teeth extractions and the beginning of RT 23 in groups I, II and III, since wound healing during RT represents a high risk for the onset of osteoradionecrosis 1,12 . In group IV, due to lack of time for completion of the dental treatment, dental extractions were postponed indefinitely.
The occurrence of new caries in the experimental groups was much lower than initially expected and, in spite of the fact that no statistically significant findings were identified between caries experience and history of fluoride, iodine or chlorhexidine use, all preventive protocols were considered effective in the prevention of radiation caries and osteoradionecrosis.

CONCLUSIONS
Chlorhexidine was the most efficient mouthrinse to reduce mutans streptococci in the saliva of head and neck cancer patients undergoing radiotherapy treatment; it also ameliorated oral mucositis and eliminated oral candidosis in the experimental groups. The results evidenced the great importance of the dental team and initial dental treatment as a measure to reduce the severity and extension of radiotherapy side effects in the oral cavity.