Validation of contralateral premolars as the substrate for endodontic comparison studies.

Contralateral premolar root canals were associated with similar changes in terms of volume, three-dimensional shape and degree of twisting from pre- to post-instrumentation. There was no difference between the CPR pairs pre- and post-instrumentation, and the study validates contralateral premolars as samples for root canal comparison studies. The null-hypothesis (H0 ) could not be rejected.