###### Abstract  
Accurate assessment of dental student performance during preclinical operative mannequin courses is an essential milestone within the educational process. Training on novel, multicolored 3D-printed teeth resulted in higher performances of the students in comparison to training on standard, monochromatic plastic teeth. However, low reliability of students' grading using standard, monochromatic plastic teeth was reported. The aim of this study was to verify whether the use of 3D multicolored teeth can (1) provide better inter- and intra-examiner reliability, and (2) assess the effect of instructors' experience on their reliability. The novel tooth analogs consisted of digitally planned and 3D-printed plastic teeth containing green, yellow, and red stratifications according to increasing depths of preparation. Thirty-seven dental students performed three Class I preparations on the 3D-printed teeth, and these underwent blind evaluation by two examiners of varied experience at two timepoints. The data were compared with preparations done on conventional (monochromatic) plastic teeth. Results indicated excellent inter-examiner reliability on 3D-printed teeth (\(0.768<\text{ICC}<0.929\)), but only moderate reliability with conventional plastic teeth (\(0.314<\text{ICC}<0.672\)). The examiner having more experience was found to show higher intra-examiner reliability (ICC = 0.716 and 0.612 using 3D-printed teeth and conventional teeth, respectively) than the less experienced examiner (ICC = 0.481 and 0.095 using 3D-printed teeth and conventional teeth, respectively). The novel, multicolored 3D-printed teeth can provide more objective evaluation of cavity preparation compared with conventional plastic teeth. d 2021 28 June 2021 28 July 2021 28 July 2021 28 June 2021 28 July 20 to human subjectivity, compounded by a paucity of objective parameters. Studies have shown that the conventional clinical evaluating systems--\"glance and grade\", which provides an overall mark; and the \"analytical method\", which utilizes specific criteria and checklists--have low reliability and validity due to high inter- and intra-examiner variability [9; 10; 11]. [PERSON] et al. (2007) [9] concluded that both evaluation methods showed disagreement and high variability between examiners regarding the evaluation of operative dental procedures on plastic teeth. [PERSON] et al. (1996) [10] demonstrated that instructors grading preclinical operative procedures using a glance and grade method have a high degree of inter-examiner variability, and highlighted the need for a more comprehensive system of assessing preclinical performance. [PERSON] et al. (1973) [12] found not only inter-examiner variability, but also wide intra-examiner variation when the same instructor evaluated the same cavity preparation on a second occasion. These realizations, coupled with applied digital technologies, have prompted the development of more objective and reliable methods of teaching and evaluating outcomes [13; 14; 15]. For example, PrepCheck (Dentsply Sirona, Wals, Austria) makes use of CAD/CAM (computer-assisted design and computer-assisted manufacturing) technology by comparing scans of cavity preparations with a standardized \"master\" preparation [16]. In addition, the Dental Teacher system (KaVo Dental, Biberach, Germany) includes a 3D scanner, PC, and three software modules for preparation validation [15]. Studies of these newer methods of evaluation have shown them to be more effective than traditional methods, primarily in self-assessment and self-directed learning of manual skills [14]. Other studies have deduced that these methods do not improve student comprehension of the skills, because of the unrealistic goal of manually reproducing any preparation exactly according to predefined values [15; 17]. Therefore, obtaining an objective perspective for preparation evaluation remains a challenge. An attempt to attain this goal using a novel, 3D-printed tooth model composed of multicolored layers was recently introduced [18].