Figure 1. Schematic representations of the various degrees of hard-tissue loss that the tested premolars might exhibit at completion of endodontic treatment. The darker area represents the missing structure in the conditions referred to as (A) 4 coronal walls retained (Group 1, N = 40), (B) 3 walls remaining (Group 2, N = 40), (C) 2 walls maintained (Group 3, N = 40), and (D) only 1 coronal wall preserved (Group 4, N = 40).