“ The historical sense involves a perception , not only of the pastness of the past , but of its presence . ” — T . S . Eliot , “ Four Quartets ” ENDODONTIC REBOOT Part One

Introduction Studies a ssessing the d iametr ic dimensions of apical anatomy repeatedly demonstrate that the bucco-lingual diameter is greater than the mesio-distal diameter— canals are predominantly ovoid throughout, not round (Figs. 1a and 1b). The technical flaw most inherent—the use of a round file of any design to clean an ovoid canal configuration —manifests as the failure to debride a substantial amount of the canal contents. A recent study showed that the mean (± standard deviation) of untreated areas ranged from 59.6 percent (±14.9, group PT/2) to 79.9 percent (±10.3, PT/1) for the total canal length and 65.2 percent to 74.7 percent for the apical canal portion, respectively (Fig. 2). In the 1960s, Dr. Herbert B. Schilder introduced two legacy concepts to the science of endodontics: The constricted envelope of motion for instrumentation (Fig. 3) and the use of hydraulics to enhance the rheology of the obturation material used to seal the root canal space and optimize its gravitometrics. Fig. 1a. This axial view of a mandibular molar demonstrates the ovoid eccentricity of the canals and existence of an isthmus connection between the MB and ML canals consistent with the findings of numerous studies. Dr. Gilberto Debelian received his DDS degree in 1987. In 1989, he completed the post-graduate program in endodontics at the University of Pennsylvania. In 1997, he received his PhD from the University of Oslo, Norway. Debelian now serves as an adjunct professor at the Department of Endodontics at UPenn and is in private practice in Oslo.