A Rational Design Based On Critical Thinking

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The SafeSiders® endodontic instrumentation system differs from all other systems in that all the instruments are designed as reamers and all the instruments can be used either manually or in a 30-degree reciprocating handpiece (Figure 1).These differences lead to far greater efficiency and safety in shaping canals when compared to K-files and rotary NiTi. SafeSiders are designed as relieved reamers that have the following advantages over K-files:

  1. They have fewer and more vertically oriented flutes, allowing the instruments to cut more effectively when the traditional watch-winding motion is employed. For a blade to cut effectively, the angle of the blade must be more or less at right angles to the plane of motion. The SafeSiders incorporate a design that maximizes the cutting potential. K-files do not. Every horizontal stroke of a SafeSiders instrument removes dentin. K-files will remove dentin only on the pull stroke and then only selectively, to the outside wall of a curved canal. A flat side along the length of the SafeSiders reamer creates two vertical columns of chisels that enhance the instrument’s cutting ability while rendering it more flexible.
  2. The combination of the flat and fewer flutes (Figure 2) results in greater flexibility and less engagement along the length of the instrument. Greater vertical flute orientation produces superior cutting ability. Together they produce a superior tactile perception, giving the dentist the ability to differentiate between a tight canal and hitting an impediment. The former produces immediate tugback while the latter produces no immediate tugback. With immediate tugback, the dentist continues to negotiate apically. No immediate tugback tells the dentist to remove the instrument, bend it at the tip, and then negotiate around the impediment that the SafeSiders have given him the ability to detect.
  3. The asymmetrical design of the SafeSiders also gives the dentist the ability to distinguish between round and oval canals (Figure 3). Oval canals require a wider preparation with an emphasis on cleansing the walls that constitute the wider dimensions of the canal. The SafeSiders—whether used manually or in the 30-degree reciprocating handpiece—can be aggressively applied to these walls with no danger of instrument breakage or canal distortion. While the instruments stay centered on the down stroke, on the up stroke they may selectively lean against any wall that requires further shaping.

The SafeSiders can be used in the reciprocating handpiece because 30-degree reciprocation mimics the same safe motion that is used manually. In fact, 30-degree arcs of motion are generally less than those generated manually, making the instruments even less prone to torsional stress and cyclic fatigue. The research has clearly shown that any metal rotating around a curve is prone to stresses that can lead to breakage. The only rational reason for the continuing use of rotation would be that it provides a level of cleansing and canal shaping that cannot be matched in any other way. Again, research has demonstrated that SafeSiders used in reciprocation produce cleaner canals, as measured by the removal of the smear layer, than rotary NiTi systems do. In effect, the SafeSiders are safer and more effective.

Some other points to consider: Because SafeSiders instruments are not subject to the stresses of rotation, they can be used many times. Initially, they are significantly less expensive than rotary NiTi, and multiple usage reduces the cost to the dentist by more than 90 percent compared to the single use of rotary NiTi that manufacturers recommend. SafeSiders can be used effectively six to eight times before replacement. More importantly, overuse leads to a dull instrument, but not to breakage. SafeSiders are predominantly stainless steel. While somewhat stiffer than NiTi instruments, they can be prebent to conform to a curved canal (Figure 4). They are also capable of recording the curve of a canal. Once the curve has been recorded, a curved instrument conforms to the shape of the canal. An instrument made from a stiffer material would have the potential to distort a curved canal if it were used in rotation, but the tip of a SafeSiders instrument used in 30-degree reciprocation maintains a point contact within the center of the canal on the downstroke, preventing the apical distortion that would be expected if it were used in rotation. The relieved reamer design of the SafeSiders makes them highly flexible despite their stainless steel composition. Furthermore, users of stainless steel instruments need not concern themselves with “snapback,” a property of NiTi that compels the instrument to always seek a straight configuration, resulting in selective shaping to the outside wall that increases with the tip size and taper of the instrument. Instrument breakage and canal distortion are of increasing concern as larger rotary NiTi instruments are used, compromising the results that may be attained when using these vulnerable systems. These issues don’t affect users of SafeSiders, allowing the dentist to do what is biologically best for the tooth.

The system is based on a long process of critical thinking that results in the most rational system on the market today.

January - March 2011

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