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.