Aim To compare the shaping ability of four instrumentation systems in curved molar root canals, using computerized microtomography (micro‐CT). Methodology Forty mesial roots of mandibular molars were submitted first to radiographic examination to determine their curvature and then to a micro‐CT scan to analyse other initial morphological characteristics. The specimens were distributed into four experimental groups, according to the endodontic instrumentation system used (n = 10): Group R, Reciproc; Group PTN, ProTaper Next; Group WOG, WaveOne Gold; Group PDL, ProDesign Logic. After root canal instrumentation, the specimens were submitted to a second micro‐CT scan, and the pre‐ and postoperative data were examined to evaluate the following parameters: volume of dentine removed (DR), increase in root canal volume (VI), untouched root canal surface area (UA), volume of accumulated hard tissue debris (AD) and structure model index (SMI). The data observed for these parameters after instrumentation were analysed using generalized linear models. R software was used for the analyses, and the level of significance adopted was 5%. Results There were no significant differences among the instrumentation systems regarding the DR, VI, UA and AD parameters (P > 0.05). PTN and WOG systems were associated with greater increases in SMI than the PDL system (P < 0.05). Conclusions The four systems evaluated were similar regarding the parameters analysed, with the exception of the SMI, with the rate of variation of this parameter being greater after using the PTN and WOG systems than after using the PDL system. These results indicate that the four systems perform similarly in terms of their shaping ability, but that the PTN and WOG systems produced more rounded preparations than the PDL system.