Fig. 1

a Standardized acrylic bloc designed for preclinical restorative training. Only the O and S figures were assessed in the present study. b Preparation precision assessment based on side view photographs of the O figure: the evenness and the accuracy of depth of the cavities were evaluated by taking length measurements. The internal angles (α, β, γ, and δ) of the axial walls of the preparation were measured to assess the compliance with the required angles. c Preparation precision assessment based on top view photographs of the S figure: the parameter overpreparation and the parameter underpreparation quantified the area (red) outside the borderline and the area (yellow) inside the borderline of the S figure, respectively