![]() The types of instruments used to create the taper of the canal can influence (for better or worse) the final ideal prepared taper. Three dimensionally narrow roots are especially at risk as are highly fluted ones. Pre-operatively assessing the risk of strip perforation and excessive dentin removal given the anatomy at hand using GG drills, Peezo Reamers and RNT orifice openers. Preparation of an ideal taper in any given root is a function of a number of different parameters. Especially so in non-vital cases as asepsis in vital cases is simpler to achieve (keeping bacteria out of the tooth) than disinfection (removing bacteria from the canal system). To maximize success then, the taper and the master apical diameter must be optimized. This second finding is interrelated to the first in that ideally shaping and cleaning is a combination of both preparing the correct taper and master apical diameter. The second evidence for this concept in the endodontic literature is the fact that non-vital teeth with apical pathology do not heal at the same rate as vital cases. In essence, bigger is better with regard to canal preparation as long as the preparation does not risk or cause iatrogenic events. ![]() ![]() Studies have found that canals prepared to a #50 ISO diameter for example are cleaner than canals prepared to a #30 ISO diameter. One is the fact that larger apical diameters result in cleaner canals. The validity of this concept is found in two places in the endodontic literature. Conceptually, a correctly prepared taper provides a means for the irrigating solutions to reach the apical regions of the tooth that would otherwise remain untouched. While RNT shaping files can remove pulp and bacteria, the true measure of canal disinfection is the penetration of irrigants into the apical regions of the roots. It is simple to achieve cone and/or obturator fit at the MC in a canal shaped to an ideal taper and master apical diameter. If the quantity of sealer and/or placement of the master cone are ideal, it is unnecessary to back the master cone or obturator away from the MC. In our hands, master cones and obturators are taken to the MC and not placed short for “safety” to minimize the extrusion of sealer and obturating material. In addition, transported canals should be viewed in the context of whether the completion of the root canal can be achieved with a coronal and apical seal and/or whether the completed long term result risks vertical root fracture or perforation, usually at the midroot. To shape a canal which is non-negotiable risks perforation, instrument fracture, further blockage and a host of other iatrogenic events. Efforts to shape the canal should not cease until the canal is made negotiable and patent or the canal cannot be made negotiable. While a comprehensive discussion of each of these canal types is beyond the scope of this article, suffice it to say that if a canal is non negotiable, the clinician should work with small hand files for as long as it takes to make the canal negotiable and ultimately patent at the MC. Canals, in the most general terms, fall into four categories, negotiable, non-negotiable, transported and non-transported. For instrumentation, this means that the MC is left at its original position and size and that the tip of shaping instrument (rotary nickel titanium (RNT) file tip) goes up to but not beyond the MC.īreaking down the stages of instrumentation even further, the achievement of straight line access and removal of the cervical dentinal triangle are absolutely essential to gain tactile and visual control over the orifice and hence all shaping procedures that occur beneath the orifice to the position of the MC. We instrument, irrigate and obturate to the MC in both vital and necrotic cases. ![]() With regard to working length, while there is some divergence of opinion among clinicians, the natural termination point for endodontic cleanings, shaping and obturation is the minor constriction (MC) of the apical foramen. Several parameters should be considered in shaping root canal spaces, these include choosing the correct: ![]()
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