Objectives: Endodontic procedures might contribute to the development of vertical root fracture as well as other localized defects such as craze lines or incomplete cracks in root dentine. The objective of this study was to evaluate the maximum fracture resistance and the force produced by five different operators in lateral and vertical condensation during root canal filling. Methods: 74 human teeth, superior canines (SC) and inferior premolars (IPM) were selected. In order to determine the maximum fracture resistance during condensation, 24 teeth were submitted until failure to an axial compression load in a universal testing machine. Fifty teeth were used in order to measure the axial condensation force by means of a device developed to simulate clinical working conditions. Results: Fracture resistance mean values in kg were: SC = 14.96±2.65 and IPM = 7.56±1.05. Mean values of force applied by each of the five operator in Kg were, respectively: 2.49; 3.75; 2.24; 2.08 and 1.18. None of the operators achieved teeth's maximum fracture resistance during procedures. Conclusions: Different behaviors among five professionals monitored were observed for the same technique of root canal filling. The increase in strength during condensation had no radiographic improvement of root canal filling. During the root canal filling, lateral and especially vertical condensation, must be performed with reduced apical strength and pressure, avoiding excessive and unnecessary stress to root dentin.