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ePaper created 2018-05-16, 11:45:19 | version 1.38.0
ENDODONTIC REBOOT: Adaptive core debridement and disinfective finishing Drs. Gilberto Debelian, Oslo; Martin Trope, U.S., & Kenneth Serota, U.S. — Dr. Gilberto Debelian Fifty years ago, Dr. Herbert B. Schilder introduced two legacy concepts to the science of endodontics: the constricted envelope of motion for instrumentation and the use of hydraulics to enhance the rheology of the obturation material used to seal the root canal space and optimize its gravitometrics. These were radical inno- vations for their time and despite techno- logical and biological shortcomings of the armamentarium available, these innova- tions should have been technology- iterated and shortcomings in material and manufacturing evolution obviated; howev- er, until recently that has not proved to be the case in toto. In order to truly under- stand the inherent flaws, the clinician must recognize the totality of what is necessary to engender predictable clinical success in endodontics. Studies assessing the diametric dimen- sions of apical anatomy have repeatedly demonstrated that the buccolingual diameter is greater than the mesiodistal diameter; canals are predominantly ovoid throughout, not round (Figs. 1a & b).1–4 The technical flaw most inherent, the use of a round file of any design conformation to clean an ovoid canal configuration, mani fests as the failure to debride a sub- stantial amount of the canal contents. A recent study showed that the mean (± standard deviation) untreated areas ranged from 59.6% (± 14.9%) to 79.9% (± 10.3%) for the total canal length and 65.2% (18.7%) to 74.7% (17.2%) for the api- cal canal portion, respectively (Fig. 2).5 The evolution of nickel-titanium (NiTi) instrumentation manufacture has per- sisted with a round core blank, regardless of whether it was ground, twisted, nano- coated, heated or metallurgically refor- mulated. NiTi files are superelastic and able to self-center, avoid apical elliptici- zation and, with appropriate taper selec- tion, prevent thinning of the coronal and middle thirds of the root, resulting in weakening or strip perforation. They are, however, unable to cleanse most of the intracanal space effectively (Fig. 3). Moreover, regardless of design configu- rations with a variable tip or variable taper or multiple tapers on a single file, they were unable to adequately cleanse the isthmus confluence of many canals.6 A revolutionary design in file configuration, the Self-Adjusting File (SAF) System (ReDent Nova) was introduced to correct this deficiency by including a virtual core (Fig. 4). It showed significant promise in terms of the degree of debris removal in complicated intracanal anatomy such as the isthmus when compared with the widely accepted ProTaper system (Dentsply Maillefer); however, it failed to take hold as a true replacement for tradi- tional “round” rotary instrumentation systems.7–9 The manipulation of the metallurgical properties of NiTi by thermomechanical processing treatments has led to signifi- cant improvement on the clinical perfor- mance of the endodontic rotary files. The transition from the martensitic phase (soft phase) to the austenitic phase (stiff phase) is dependent on temperature and metal stress. The reversible transition between these two phases increase the safety and performance of these files during rotation. Unfortunately, fracture still occurs due to cyclic fatigue and torsional failure when the elastic limit is exceeded (Fig. 5a). The new generation of NiTi alloys have transformation temperatures much higher than those of conventional austenitic materials used in previous generations of rotary instruments and will transform at close to body temperature. A recent study of ProTaper Universal, HyFlex CM, TRUShape and Vortex Blue showed that a temperature increase to 37 °C, simulating body temperature, substantially decreased the fracture resistance of all instruments 34 — issue 2018 Endodontics Article