Objective: To investigate technical outcome and time efficiency, using ProTaper Universal (PTU) or ProTaper Next (PTN) rotary nickel titanium (NiTi) files, to prepare simulated canals, by undergraduate dental students. Methods: Sixty-six students were randomly assigned to two groups. Both groups prepared two endodontic blocks (n = 66) using PTU and PTN in crossover design. Preparation time was also recorded. The blocks were photographed under magnification and were assessed for procedural errors by two different observers. Data were recorded and analysed by descriptive statistics, generalised mixed model and analysis of variance (ANOVA) using SPSS. Results: The different file systems had a significant effect on the presence or absence of procedural errors, with a significance value of P 0.001. More successful preparation was achieved with PTN (89%) than PTU (37.5%). There were a total number of procedural errors of n = 58.The highest incidence of procedural errors by different file systems was transportation. The PTU showed 24 transportation errors out of a total of 51 errors and the PTN showed five transportation errors out of a total of seven. PTN demonstrated the quickest mean time of preparation with a P value of P 0.001. Conclusion: In the hands of novice operators, PTN showed a lower incidence of procedural errors and better time efficacy during instrumentation of simulated canals, compared with PTU. Palabras clave: procedural errors, ProTaper Universal, ProTaper Next, rotary