Introduction: Orifice openers or orifice shapers are used to shape the coronal part of the root canals during endodontic treatment. Objectives: The aim of this work was to analyse the cutting efficiency of Quantec Series 2000 system orifice shapers by means of computerised tomography (CT). Materials and methods: Mandibular molars were selected, preoperative CT was performed and the cross-sections and surface area of the root canals were measured. Following access opening and preparation of the coronal part of the canals with Quantec Series 2000 orifice shapers, a further CT was obtained of all the teeth, the previous measurements were repeated and the two sets of measurements were compared. Results: Although the canals suffered modifications due to the action of the instruments, they remained centred and retained their original morphology; the changes were greater in the most coronal part of the canals. Conclusions: the orifice shapers of the system under study kept the canals centred on their original position, so they do not present great aggressiveness during endodontic treatment; the canals that were initially the widest were those that showed the greatest modification; the CT system employed in the study showed itself to be an effective, noninvasive system for studying the changes that had taken place inside the root canals.