Tuesday, January 15, 2013
In endodontics, pre-operatively assessing risk factors to avoid iatrogenic events is essential for clinical success. Read the case correctly, optimize the final result. Read the case incorrectly, compromise the final result.
This two part series was written to help clinicians chose their final taper in endodontic preparation (Part I) and avoid iatrogenic events, specifically perforation and canal transportation (Part II).
An ideal taper optimizes both obturation hydraulics and irrigation efficacy. A less than ideal taper can be catastrophic. For example, excessive taper risks perforation, often through overzealous shaping of the middle third. A less than ideal taper will not provide adequate irrigation into the apical third. In addition, excess dentin removal, even without perforation, leaves a root susceptible to vertical fracture and could make retreatment unfeasible.
Larger and less complex roots are candidates for a larger prepared final taper (.06 throughout the length of the root). Curved and complex roots are candidates for less prepared final taper (.04 taper throughout the length of the root).
It is worthwhile to review optimal canal shape and canal preparation goals. The goals of canal preparation are to:
- Maintain the original position of the canal/maintain the original position and size of the apical foramen
- Prepare a tapering funnel with narrowing cross sectional diameters. In essence to mimic the shape of a tornado
- Prepare a taper that is proportional to the external dimensions of the root that does not predispose the root to subsequent vertical root fracture
- Prepare a taper that allows cone fit with tug back and ideal obturation hydraulics during down pack with warm vertical obturation techniques (and warm techniques of all types)
- Prepare a taper that optimizes the necessary volume and space for activation of endodontic irrigants
Achieving these goals is multifactorial and requires a number of different skills, techniques, concepts and cognitions. These include, among many possible considerations:
Fig. 1: Three images of #19 demonstrating apical pathology, taken with a Planmeca ProMax, 3Ds.
1: Prior to making endodontic access, the case complexity must be evaluated. Complexity in this context means an anatomical evaluation determined subjectively and objectively as to the clinical risks and difficulty of the given case—including using cone beam technology for 3D imaging as needed.
Specifically, among many considerations, the length, curvature, maturity, calcification, number and dimensions of all roots must be assessed. Referral must always be considered when the case is too complex (Fig. 1).
2: Straight-line access is essential.
As an aside, it is worth mentioning that access through crowns and bridges is especially problematic and requires special mention. The desire to maintain the crown or bridge must be tempered with the reality that compromising the access to preserve the coronal restoration is counterproductive. If the clinician does not have full tactile and visual control over the orifice and instruments used, iatrogenic events will follow. In cases of limited opening or severe calcification, among other clinical challenges, it is usually indicated to remove the crown or bridge to give the clinician the required access to the orifice. Without such visual and tactile control, it is impossible to prepare the canal optimally (Fig. 2).
Fig. 2: #3 is a challenging non-vital case due to the tooth’s location, strategic value, the bridge, calcification and curvature.
3: Patency as a concept is integrally associated with achievement of the goals listed above. Specifically, once the orifice is enlarged (initiating canal preparation), every effort should be made to leave the canals open and negotiable. The more complex the root system, the more challenging this becomes.
In a severely calcified root canal system, literally, using an incorrect hand file, hand file size, or orifice opener in the wrong sequence can lead to canal blockage. While a comprehensive discussion of how such calcified canals are managed is beyond the scope of this article, it is relevant to mention that using a #6 hand K file (Mani K files) as the default file for negotiation of calcified canals as the first hand file entered into the orifice is the safest option. Alternatively, using a file specifically designed for small and calcified canals such as the Mani D finders is also invaluable (Figs. 3-4).
Fig. 3: Mani D finders
Fig. 4: Mani K files
Fig. 5: Clinical case with curvature and calcification prepared to a relatively ideal .06 taper and #30 tip size using the MounceFile rotary nickel titanium file system and the Mani files listed above.
Alternatively, if the orifice is wide open, and the canal easily negotiable—especially in vital cases—if the tissue present is propelled apically instead of being removed coronally, canal blockage can result and lead to a number of canal transportations including perforation, a situation which will be covered in Part II of this two part series. In any event, proper canal orifice management and initial canal negotiation are the gateway to subsequently obtaining the objectives above (Fig. 5).
Part I of this clinical article has specifically discussed optimal taper and canal shape in endodontics. Emphasis has been placed on determining the optimal final prepared taper before instrumentation commences. Part II will discuss specific techniques to achieve these goals.
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