Assessment of multispecies biofilm growth on root canal dentin under different radiation therapy regimens.

OBJECTIVES: To assess the growth of a multispecies biofilm on root canal dentin under different radiotherapy regimens. MATERIALS AND METHODS: Sixty-three human root dentin cylinders were distributed into six groups. In three groups, no biofilm was formed (n = 3): NoRT) non-irradiated dentin; RT55) 55 Gy; and RT70) 70 Gy. In the other three groups (n = 18), a 21-day multispecies biofilm (Enterococcus faecalis, Streptococcus mutans, and Candida albicans) was formed in the canal: NoRT + Bio) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. The biofilm was quantified (CFUs/mL). Biofilm microstructure was assessed under SEM. Microbial penetration into dentinal tubules was assessed under CLSM. For the biofilm biomass and dentin microhardness pre- and after biofilm growth assessments, 45 bovine dentin specimens were distributed into three groups (n = 15): NoRT) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. RESULTS: Irradiated specimens (70 Gy) had higher quantity of microorganisms than non-irradiated (p = .010). There was gradual increase in biofilm biomass from non-irradiated to 55 Gy and 70 Gy (p < .001). Irradiated specimens had greater reduction in microhardness after biofilm growth. Irradiated dentin led to the growth of a more complex and irregular biofilm. There was microbial penetration into the dentinal tubules, regardless of the radiation regimen. CONCLUSION: Radiotherapy increased the number of microorganisms and biofilm biomass and reduced dentin microhardness. Microbial penetration into dentinal tubules was noticeable. CLINICAL RELEVANCE: Cumulative and potentially irreversible side effects of radiotherapy affect biofilm growth on root dentin. These changes could compromise the success of endodontic treatment in oncological patients undergoing head and neck radiotherapy.

Assessing push-out bond strength in re-irradiated teeth: Universal resin cement performance in self-etch and self-adhesive modes.

OBJECTIVES: To investigate the effect of cumulative doses of radiation on the pushout bond strength (BS) of a universal resin cement used in the self-etch (SE) and self-adhesive (SA) modes to the intraradicular dentin. MATERIALS AND METHODS: Forty-eight human teeth were distributed into three groups (n = 16) according to the radiation therapy dose (RT): NoRT (no-radiotherapy), 70RT (70 Gy), and 70 + 70RT (70 Gy + 70 Gy). The teeth were redistributed into two subgroups (n = 8), according to the adhesive mode: SE (NoRT-SE, 70RT-SE, and 70 + 70RT-SE) and SA (NoRT-SA, 70RT-SA, and 70 + 70RT-SA). Data were statistically compared after BS test (ANOVA, Tukey's post hoc test, and Fisher's exact test). RESULTS: In the SA mode, BS was significantly higher in nonirradiated teeth compared with 70RT and 70 + 70RT (p < 0.0001). There were no significant differences between SE and SA modes in nonirradiated teeth (p = 0.14). In the 70RT group, SE mode increased BS compared with SA mode (p < 0.0001). Most specimens had adhesive and mixed failures in SA and SE modes, respectively. CONCLUSIONS: The universal resin cement in the SE mode had greater BS to the irradiated dentin. When teeth were re-irradiated, the universal resin cement had similar performance in terms of BS, regardless of the adhesive approach. CLINICAL SIGNIFICANCE: There is no research establishing a correlation between radiotherapy and its impact on the BS of a universal resin cement used in SE and SA modes to intraradicular dentin.