Effect of 70 Gy tumor therapeutic radiation applied intermittently or directly on microcosm biofilm composition and dental hard tissues and its potential to cause dental caries.

OBJECTIVES

This study compared total (70 Gy, one session) and intermittent (35 sessions of 2 Gy) tumor radiation protocols on tooth morphology (n=5) using Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and on microcosm biofilm microbiota (n=12) through colony-forming unit (CFU) counts for Candida spp., total microorganisms, Streptococcus mutans, and total lactobacillus. It also assessed "radiation caries" development via Transverse Microradiography (TMR, n=12).

METHODS

Bovine enamel and root dentin were divided into three groups (n=17): total radiation (1); intermittent radiation (2); and no radiation-control (3). Biofilm was produced using saliva from irradiated (for 1 and 2) or non-irradiated patients (for 3) (n=3 donors) combined with McBain saliva with 0.2 % sucrose for 5 days. Data were analyzed using ANOVA/Tukey, t-test, and Kruskal-Wallis/Dunn's tests (p<0.05).

RESULTS

S. mutans and Candida spp. were observed on irradiated dentin compared to control, but these microorganisms were absent in enamel biofilm (S. mutans only in 50 % and 12.5 % of intermittent and total irradiated enamel). Total microorganisms and lactobacillus numbers were similar between groups, except for total microorganisms in irradiated enamel vs. control (p<0.037). No significant differences in mineral loss or lesion depth were detected between protocols or tissues (p>0.05). SEM-EDX revealed slight differences in magnesium (p=0.0439) and calcium (p=0.0216) content in intermittently irradiated dentin.

CONCLUSIONS

Despite increased cariogenic microorganisms in irradiated biofilm, no greater susceptibility to "radiation caries" was observed under this model.

CLINICAL SIGNIFICANCE: Although the radiotherapy alters oral microbiota and dental tissue morphology, these changes alone do not increase radiation-induced caries risk. Other factors, as salivary changes and diet, need to be better studied.