AbstractObjectiveThe purpose of this experimental in vitro study was to assess the effect of having one or two intact axial walls on the improvement of the fracture resistance, and marginal and internal adaptation of computer‐aided design/computer‐aided manufacturer fabricated ceramic endocrowns.Materials and MethodsThirty‐six endodontically treated mandibular molars were divided into three groups (n= 12). Group A, represented teeth that all of their axial walls were reduced till they all had 3 mm height. In group B, the buccal wall had 5 mm height and the others were reduced to 3 mm. Specimens of the group C had 5‐mm‐height buccal and one 5 mm‐height proximal wall, with all other walls of 3 mm height. All teeth were scanned using intraoral scanner, and endocrowns were milled from zirconia lithium silicate ceramics blocks. The marginal and internal discrepancy of restorations were evaluated with the replica technique. Fracture resistance was also measured after cementation and modes of failure were observed. One‐way analysis of variance and Tukey HSD multiple comparisons were used to analyze the data (α= .5).ResultsSignificant differences were observed within the groups in terms of the axial discrepancy (p= .022); group A had significantly higher amounts of axial discrepancy compared to group B (p= .001) and group C (p= .003). Preservation of the intact axial walls did not result in a statistically significant decrease in marginal (p= .21) and pulpal (p= .31) discrepancy values. Also, concerning the fracture resistance no significant difference was observed among the groups (p= .51).ConclusionPreservation of at least one of the axial walls could reduce the amount of the axial discrepancy and, therefore, improves the adaptation of the restoration. However, based on this study, it did not improve fracture resistance.