Objective: To verify the presence or absence of microorganisms in resin composite samples (RCS), photoacti vated or not, and on the surfaces of RC cartridges (RCC) during clinical use in three dental offi ces (A, B, C) at the city of Fortaleza, CE, Brazil. Method: The following groups were formed in the three dental offi ces, according to the substrates analyzed for contaminati on: G1 (control, n= 10) -non-photoacti vated RCS, G2 (n= 10) -RCS photoacti vated with LED, G3 (n= 10) -RCS photoacti vated with halogen light, G4 (n= 15) -RCC aft er clinical use. In the dental offi ces B and C, an additi onal G5 (n= 5, control) was composed of RCC disinfected with alcohol 70 aft er clinical use. A total of 145 specimens were obtained. Swabs were used for sample collecti on in G4 and G5. In G1 to G3, 2-mm-thick increments of RC were obtained and photoacti vated or not for 20 seconds with a LED or halogen light source. The samples were then placed in test tubes with BHI broth and maintained under refrigerati on unti l incubati on in microaerophilia. Results: Contaminati on was found in 46.9% of the samples; G4 and G5 had 100% of contaminated samples (mean McFarland value of 7.0 +/- 3.02). There was no stati sti cally signifi cant diff erence in the frequency of contaminati on among the dental offi ces A, B and C, in all groups, aft er analysis by the chi-square and Kruskal-Wallis tests (p= 0.367 and p= 0.090). There was no stati sti cally signifi cant diff erence between G1 and G2 and G3 aft er analysis by the Mann-Whitney test (p= 0.396) nor between G2 and G3 (p= 0.487) aft er analysis by the Pearson's chi-square test. Cocci (isolated or arranged in pairs, chains or clusters), bacilli (isolated or arranged in pairs or chains) and yeast were identi fied. Conclusion: Microorganisms were detected on the RC samples and on the surfaces of the RC cartridges in the three dental offi ces evaluated in this study.
