This study compared biomechanical properties (punch shear strength, toughness, hardness, and load to fracture) of 23 endodontically treated teeth (mean time since endodontic treatment: 10.1 yr) and their contralateral vital pairs. Analyses using paired t tests revealed no significant differences in punch shear strength, toughness, and load to fracture between the two groups. Vital dentin was 3.5% harder than dentin from contralateral endodontically treated teeth (p = 0.002). The similarity between the biomechanical properties of endodontically treated teeth and their contralateral vital pairs indicates that teeth do not become more brittle following endodontic treatment. Other factors may be more critical to failure of endodontically treated teeth.