Retentive properties of post and core systems.

An investigation was conducted in which different post and core systems were subjected to tensile, shear, and torque forces and their abilities to resist such forces were measured. The following conclusions can be drawn: (1) A post and core unit made of composite resin alone, without the additional retention provided by cemented posts or threaded pins, is the least retentive, and its use should be discouraged. (2) The retention of composite resin cores by four threaded pins compares favorably with other accepted techniques. (3) A round post retaining a composite resin core alone provides poor resistance to torque, but with the addition of threaded pins, its ability to resist displacement improves substantially. (4) The procedure in which composite resins are used to restore the coronal portion of pulpless teeth, with threaded pins and/or posts in the root canal, is reliable.