The evaluation of pre-clinical technical achievement in fixed prosthodontics cannot be objective when using visual examination of dental preparations. This is, however, still the main method used in dental schools. The present study introduces a new method, based on a mathematical formula, to reduce the problem. The idea emerged when using the Kavo PrepAssistant® system (software version 1.05). This system is a 3D-scanner with software that can quantify geometrical differences between an instructor and student dental preparation in model teeth. Therefore, a mathematical formula was created, integrating selected clinically relevant geometric characteristics of dental preparations measured by the system. In this new formula, 70% of the evaluation parameters were computer analysed, whilst 30% were visually evaluated. This new method was compared with the traditional visual evaluation system during a pre-clinical practical examination, with the participation of 25 students. Using both methods to evaluate the 25 preparations, results showed similar grading for both methods (K–S test = 0.16; P < 0.05). Although this method does not provide overall clinical evaluation of student performance these results suggest that it can be helpful accessing technical achievement. In this method, the student has the guarantee that 70% of his/her grade results from an objective computer evaluation, with the possibility to visualise the mistakes with the software. It also reduces problems related to the calibration between different examiners. The Kavo PrepAssistant® is a powerful tool in pre-clinical teaching, but has some drawbacks. It has to be developed towards the actual needs of pre-clinical departments, in order to achieve its full potential, as described in this study.