RESUMO
This study assessed canal preparation effects on disinfection and dentin preservation. Thirty mandibular incisors were paired into two experimental groups (n = 10). Following contamination, the initial microbial sample was collected. Instruments 30/0.03 (Group 1) and 30/0.05 (Group 2) were employed and a second sample was obtained. Canals were enlarged using instruments 40/0.03 and 40/0.05, respectively, and a third sample was collected. Final irrigation was performed, and sample S4 obtained. A final scan evaluated volume, surface area, unprepared areas, removed dentin and dentin thickness. Data were analysed using Student t-test, Mann-Whitney, Kruskal-Wallis and Dunn tests. A significant difference was observed between S1 and other time points (p < 0.05). Comparison between groups showed no differences in bacterial loads and in the percentage of microbial reduction (p > 0.05). Group 2 exhibited greater reduction in dentin thickness than group 1 in the mesial aspect of the root (p < 0.05). Instrument 30/0.03 might provide effective disinfection and safety during mandibular incisors canal preparation.