C0093067x ove A. Peters

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The approach for ProTaper instruments differs from that for most other NiTi rotary files in that no traditional crown-down procedure is performed (Fig. 9-61).

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Size #10 and #15 hand files are precurved to match the canal curvature and then passively inserted into the coronal two thirds of a root canal as pathfinding files, which confirm the presence of a smooth, reproducible glide path. This step is essential for ProTaper shaping instruments, because they are mostly side-cutting and have fine, fragile tips.

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Shaping files S1 and S2 are then passively inserted into the scouted canal spaces, which have been filled with irrigant (preferably sodium hypochlorite). If necessary, the SX file can be used at this stage to relocate orifices or remove obstructing dentin. After each shaping file is used, the canals are reirrigated and a size #10 file is used to recapitulate to break up debris and move it into solution. This process is repeated until the depth of the pathfinding #10 or #15 file is reached.

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After irrigation the apical third is fully negotiated and enlarged to at least a size #15 K-file, and the working length is confirmed (see Fig. 9-61). Depending on the canal anatomy, the rest of the apical preparation can be done with engine-driven ProTaper shaping and finishing hand files. As an alternative, handles can be placed on these instruments (Fig. 9-62) so that they can be used for the balanced force technique.

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ProTapers S1 and S2 are then carried to the full working length, still in a floating, brushing motion. The working length should be confirmed after irrigation and recapitulation with a K-file, aided by an electronic apex locator and/or radiographs. Because of the progressive taper and more actively cutting flutes higher up in the ProTaper design, interferences in the middle and coronal thirds are removed at this stage.

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The preparation is finished with one or more of the ProTaper finishing files, used in a nonbrushing manner; because of their decreasing taper, these files will reach the working length passively. Recapitulation and irrigation conclude the procedures (see Fig. 9-61).

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Most cases requiring root canal therapy lend themselves to canal preparation with many different systems; depending on the individual anatomy and the clinician's strategy, various sequences may be used. Fig. 9-63 presents two cases that involved different problems and therefore were approached differently. Mesiobuccal roots of the maxillary molar can show substantial curvature; rotary instrumentation and/or hybrid techniques allow preservation of the curvature (Fig. 9-63, A) and optimal enlargement (Fig. 9-63, B). Often hand instruments other than ISO-normed files (see Fig. 9-62) are used in these cases to ensure a smooth, tapered shape or to eliminate ledges.

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Figure 9-56 Stepwise enlargement of mesial root canal systems in an extracted mandibular molar demonstrated with μCT reconstructions. The buccal canal (left) was prepared with a LightSpeed (LS) instrument, and the lingual canal (right) was shaped with a ProTaper (PT) instrument. A, Preoperative view from the mesial aspect. Note the additional middle canal branching from the lingual canal into the coronal third. B, Initial preparation and opening of the orifices, aided by ultrasonically powered instruments. C, First step of root canal preparation, up to LightSpeed size #20 and ProTaper shaping file S1. D, Further enlargement to LS size #30 and PT shaping file S2. E, Apical preparation to LS size #40 and PT finishing file F1. F, Additional enlargement to LS size #50 and PT finishing file F2. G, Superimposed μCT reconstructions comparing the initial canal geometry (in green) with the shape reached after use of the instruments shown in F. H, Final shape after step-back with LS instruments and PT finishing file F3. I, Superimposed μCT reconstructions comparing initial geometry and final shape. Note the slight ledge in the buccal canal after LS preparation and some straightening in the lingual canal after PT preparation.

Hybrid Techniques

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For some time some have suggested combining various NiTi preparation systems to address certain shortcomings of current instruments.57,304 Although many combinations are possible, the most popular and useful ones involve coronal preenlargement followed by different additional apical preparation sequences. However, clinicians must keep in mind that anatomic variations in each canal must be addressed individually with specific instrument sequences. Most important, oval canals extend deep into the apical area,276,312,315,316 and apical foramina in fact may be oval in most cases.41 Naturally, a rotating file can produce a round canal at best; therefore, a strategy must be devised for adequately shaping oval canals without overly weakening radicular structure (compare Figs. 9-43 and 9-45). One hybrid approach completely prepared 95% or more of all such canals and resulted in extremely wide apical sizes that may be difficult to achieve with most instrument systems140-143 (Box 9-5).

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Box 9-5 Benefits of Using a Combination of Instruments for Endodontic Therapy

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  • Instruments can be used in a manner that promotes their individual strengths and avoids their weaknesses (most important).

  • Hand instruments secure a patent glide path.

  • Tapered rotary instruments efficiently enlarge coronal canal areas.

  • Less tapered instruments allow additional apical enlargement.

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Figure 9-57 Preparation of a maxillary molar with LightSpeed (LS) instruments. After coronal enlargement with a tapered rotary instrument or GG drills (Figs. 9-47 and 9-50) and irrigation with NaOCl (1), the working length is determined with a small K-file, aided by an electronic apex locator. A patent glide path is secured by hand instrumentation up to a loosely fitting size #15 K-file (2). The canal size is gauged by hand-held LS instruments, and the first LS size to bind (FLSB) is selected. Apical instrumentation is then begun with engine-driven LS instruments, starting with the FLSB (4) up to the desired apical size (see text for further explanation).

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Figure 9-58 Finishing of LightSpeed preparations to allow obturation. With the canal system flooded (1), apical preparation (2) is continued until an LS instrument requires 12 pecks to reach the working length (WL). The next LS instrument (3) then is used to a point 4 mm short of the WL to prepare for LightSpeed's SimpliFill obturation system. Alternatively, canals may be flared for other root canal filling techniques by preparing with each subsequent instrument 1 mm shorter (5).

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Figure 9-59 ProFile instrumentation in a wider canal. In irrigated and flooded canals (1), a crown-down preparation is done with a sequence of #.06-tapered ProFile instruments (2). When the apical third is reached, the WL is determined and a glide path is secured (3). Apical preparation is then completed by continuing the crown-down sequence (4) up to the desired apical width at the WL. Several shaping waves may be required (5).

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Figure 9-60 Sequence of ProFile instruments used in constricted canals. After irrigation (1) and coronal preenlargement with orifice shapers (see Fig. 9-51), ProFile instruments size #25, #.06 taper; size #20, #.06 taper; and size #24, #.04 taper are used as crown-down instruments (2). After the WL has been determined and a glide path secured (3), apical preparation to the desired size begins (4). For additional taper, larger instruments may be used to a point short of the WL.

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Figure 9-61 Instrumentation of root canals with ProTaper instruments. After irrigation and scouting (1 and 2), the coronal thirds are enlarged with shaping files S1 and S2. Hand files then are used to determine the WL and to secure a glide path. Apical preparation is completed with S1 and S2. Finishing files are used to the desired apical width.

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Figure 9-62 Treatment performed with nickel-titanium rotary and hand instruments to eliminate instrument separation while maintaining biologic aims. A, Preoperative radiograph of tooth #15. B, Postoperative radiograph shows a significant curvature in the mesiobuccal canal and additional anatomy in the lingual root. C, Preoperative radiograph of teeth #14 and #15. Both teeth were diagnosed with irreversible pulpitis. D, Postoperative radiograph shows four canals in both of the treated maxillary molars. Note the wide apical preparation, particularly in the curved mesiobuccal canals. (A and B courtesy Dr. T. Clauder; C and D courtesy Dr. H. Walsch.)

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Figure 9-63 Instruments with increased taper that can be used by hand. A, ProTaper instruments with special handles attached to rotary instrument shanks. B, GT hand instruments.

Histologic slides (see Fig. 9-39) and μCT reconstructions (see Figs. 9-43, 9-45, and 9-56) show critical areas that were not mechanically prepared despite the use of various individual rotary techniques. The aim of hybridizing NiTi rotary techniques, therefore, is to increase apical size using a fast and safe clinical procedure.

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Various clinicians have used this type of hybrid procedure in their practices (see Figs. 9-2, 9-5, 9-15, and 9-62). The technique involves the use of a variety of instruments: GG drills and K-files for establishing straight-line access; ProTaper instruments for body shaping and apical preenlargement; NiTi K-files or LightSpeed instruments for apical widening; and various instruments for final smoothing.304

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After a precurved, stainless steel file has confirmed a smooth glide path into the coronal two thirds, irrigation and mechanical preparation with a sequence of ProTaper files open and preenlarge the apical third (Fig. 9-64). Once the working length has been established, the apical third is flooded with sodium hypochlorite and further enlarged with ProTaper finishing files F1 and F2. The F3 ProTaper finishing file is relatively inflexible, and because of its side-cutting action, it should be used with caution in curved canals (Fig. 9-65).

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The effectiveness of some hybrid techniques in enlarging canals recently was documented using superimposed root canal cross sections (Fig. 9-66). This approach can help identify insufficiently prepared areas and weakening of the radicular structure.

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Some hybrid systems seem to work better than others, but the deciding factors seem to be the root canal anatomy and an adequate preparation goal.

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