Barry Musikant

 RECENTLY  POSTED on DentalTown a research article that concluded that rotary NiTi instrumentation failed to shape the buccal and lingual extensions of ovoid canals. (The article was originally published in the November 2002 issue of the International Endodontic Journal.) If these ovoid canals are also curved, the degree of shaping is likely to be insufficient to allow enough irrigation to digest chemically the buccal and lingual extensions of tissue located there. Published research recommends a preparation to a minimum of 30 at the apex to create a space large enough for proper irrigation; evidently in the case of rotary NiTi such preparation is an absolute requirement in ovoid canals. However, instrumenting around significant curves with rotary NiTi exposes these instruments to an increased incidence of separation.
    My mentioning this drawback of rotary NiTi brought a response from a the DentalTown member who said that the SafeSiders® could do no better and that a single-point fill would certainly not drive the cement into the buccal and lingual recesses. I countered his assertions about the SafeSiders’ shaping by first stating that the asymmetric configuration of the SafeSiders allows the dentist to differentiate between a round and ovoid canal, something rotary NiTi in its present configurations cannot do. Knowing that a canal is ovoid tells a dentist that the canal must be shaped to a 30, at a minimum, and preferably wider so that the irrigants can get to the buccal and lingual extensions that the instruments are incapable of reaching. Unlike rotary NiTi, the stainless steel relieved reamers that compose the SafeSiders system are routinely prebent when they are required to negotiate an abrupt curve. Since separation is not an issue when either a reciprocating engine or a tight watchwinding motion is used, opening to the proper width to allow the efficient and effective use of the irrigants presents no problems.
    Although comparable instrument sizes for both systems leave buccal and lingual tissue remnants, the SafeSiders are designed to inform the dentist that he is, in fact, in an ovoid canal and then give him the ability to routinely widen the canal to a diameter sufficient for the irrigants to take over the job of debridement, including all the situations in which an ovoid canal is coupled to a significantly curved canal. By design, the SafeSiders give the dentist more information and have a greater ability to widen canals in an undistorted manner without any concern about their fracturing.
    I addressed the DentalTown member’s second point—that a single-point fill would certainly not drive the cement into the buccal and lingual recesses—with a series of x-rays that shows an intimate relationship between the canal walls and the cement, even when only one point is placed. However, I also made it very clear that in highly oval canals the EZ-Fill® obturation technique is not limited to a single point. Rather, in ovoid canals, after the first point is placed a spreader is placed into the canal space with a force never exceeding the weight of my hand to make room for one or more extra points. In this way, the cement is driven into an even more intimate relationship with the canal walls. While a single point works quite well in fairly round canals, extra well-coated points are routinely placed in ovoid canals. Figures 1 through 6 are x-rays of teeth shaped with SafeSiders and then filled with EZ-Fill epoxy-resin cement and a single prefitted point.

    What you see in these x-rays is a consistent adaptation of the cement to the walls of the canals. Observing the bucco-lingual configurations of these canals makes it obvious that they are ovoid canals. Please realize that these examples are limited to a single point at this stage. Yet, clinically, all these cases would receive one or more extra points, driving the cement into an even closer interface with the canal walls. The intimate fit is a result, first, of adequate shaping and, second, of chemical irrigation that digests any remaining tissue in the buccal and lingual extensions.
    To further explain the effectiveness of the EZ-Fill obturation, I borrowed some slides from a Polish dentist who made some useful observations about the bidirectional spiral used to apply the cement. Figures 7 through 10 show a side-by-side comparison of the bidirectional spiral and a Lentulo spiral. Please note that although both applicators drive the cement into lateral canals, the bidirectional spiral prevents the overextension of cement beyond the apex. Simple observation shows the cement tracking several millimeters into the lateral canals. Any applicator that can force cement several millimeters laterally will have no problem driving cement into the far shorter buccal and lingual extensions of an ovoid canal.

    Presently, I am preparing some samples of bicuspids with highly ovoid canals. Once they are shaped, debrided thoroughly with irrigation, and obturated, I will have the teeth sectioned along their length and photographed to show in cross-section both the thorough debridement that has occurred and the consistent interface between the gutta percha, cement, and the canal wall. I will then publish these results in the next newsletter. For those who want to see the results more quickly, I will be posting the documentation on DentalTown before the next newsletter is published.