Effect of endodontic access preparation on resistance to crown-root fracture.
 This investigation involved the creation of coronal-radicular fractures in vitro and compared the fracture resistance of intact human mandibular molars, with molars after varied tooth preparation.
 Forty freshly extracted, non-carious, nonrestored human mandibular molars were randomly divided into four treatment groups.
 The molars were subjected to constantly increasing occlusal load until coronal-radicular fracture occurred.
 Tooth preparations significantly diminished resistance to coronal-radicular fracture.
