May 24-30, 2010United Kingdom Edition Microstructural replication – obturation S teven Covey is known for his book The Seven Habits of Highly Effective People. The habit most applicable to endodontics is the second one; Begin with the End in Mind. The implication of this vision in regard to idealising the final shape of the root canal system to ensure that the obturation represents a totality is profo- und. The root canal is negative space and as such recovery of its original unaffected form is the sine qua non of obturation or more descriptively – micro- structural replication. Perhaps the most significant example of negative space re- covery is Michelangelo’s statu- ary for the funerary of Pope Julius II. Four unfinished sculp- tures speak eloquently to this process: the figure was outl- ined on the front of the marble block and then Michelangelo worked steadily inwards from this side, in his own words ‘liberating the figure impriso- ned in the marble’. This is an exacting description of debri- dement and instrumentation of the root canal space prior to root filling after a myriad of patho- logic vectors have destroyed the dental pulp, and altered the morphology/topography of the system (Fig 12). Incomplete filling of the de- brided and sculpted root canal space is one of the major causes of endodontic failure (30) . Until recently, in vitro testing (dye leakage, fluid transport, bacte- rial penetration, glucose leak- age) was used to evaluate the sealing efficacy of endodontic filling materials and techniques by assessing the degree of pen- etration/absorbance of these tracers (31, 32, 33) . Unfortunately, leakage studies are limited stat- ic models that do not simulate the conditions found in the oral cavity (temperature changes, di- etary influences, salivary flow). Given the historic dominance of in vitro testing, the clinician must be cautious when extrap- olating study findings to the clinical situation, regardless of manufacturer’s claims (34) . This reliance on invalid testing pro- tocols diminishes the “mono- block” assertions applied to the new generation of adhesive ob- turating materials proposed as the “replacement material” for gutta-percha (35) . Gutta-percha was introduced to dentistry by Edwin Truman in 1847 (36) . The concept of thermo- labile vertical condensation of gutta-percha was originally de- scribed by Dr J R Blaney in 1927 (37) . The defining article on ob- turation remains Dr. Schilder’s classic on filling the root canal space in three dimensions pub- lished some 40 years later (38) . Logically, one cannot physically fill the root canal in two dimen- sions; however, one can fill the root canal space badly in three dimensions. This does not cri- tique Dr Schilder’s exposition, but it does demonstrate that words can easily be miscon- strued and alter perspective once they become, as Kipling said, ‘the most powerful drug of mankind’. Ironically, Schilder’s article came seven years prior to his treatise on cleaning and shaping the root canal system, which even to this day remains the iconic standard for the technical imperatives as- sociated with instrumentation. The Washington Study by In- gle indicated that 58 per cent of treatment failures were due to incomplete obturation (39) . The corollary is obvious; teeth that are poorly obturated are invari- ably poorly debrided and disin- fected. Procedural errors such as loss of working length, canal/ apical transportation, perfora- tions, loss of coronal seal and vertical root fractures have been shown to adversely affect the in- tegrity of the apical seal(40, 41) . The Toronto study evaluating success and failure of endodontic treat- ment at four to six years after completion of treatment showed that teeth treated with a flared canal preparation and vertical condensation of thermolabile gutta-percha had a higher suc- cess rate when compared with step-back canal preparation and lateral compaction. Highlight- ing the vertical condensation of warm gutta-percha obturation technique as a factor influencing success and failure simply con- firmed a perspective evident to most endodontists from years of clinical empiricism. There is a never-ending array of obturation materials, delivery systems and sealers appearing in the marketplace. Each is hall- marked by proprietary modifica- tions and each is heralded as the most significant iteration in ob- turation since the previous one; today, we practice with a sad tru- Flexibility is our Strength Untying the Gordian Knot; Part II Kenneth Serota continues his look at the Endodontic Implant Algorithm Fig 12 – The artist/clinician recognizes that negative space surrounding an object is equally important as the object itself. In the case of root canal therapy, the positive space is alterable, but must be created in balance with the encompassing negative space to ensure morphologic integrity. Fig 13 – While there is no meta-analysis to elucidate this concern, the incidence of fracture of the mesial root of mandibular molars has been shown to have a significant correlation to cuspal fracturing.

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