Drs. Peet J. van der Vyver and Michael J. Scianamblo discuss the clinical guidelines for using Protaper Next instruments
Introduction
According to Bird, Chambers, and Peters (2009), rotary nickel-titanium (NiTi) instruments have become a standard tool for shaping root canal systems. These instruments provide the clinician with several advantages compared to conventional stainless steel instruments.
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They are more flexible, have increased cutting efficiency (Kim, et al., 2012; Peters, 2004; Walia, Brantley, Gerstein, 1988), can create centered preparations more rapidly (Short, Morgan, Baumgartner, 1997; Glossen, et al., 1995), and can produce tapered root canal preparations with a reduced tendency of canal transportation (Chen, Messer, 2002; Kim, et al., 2012).
However, nickel-titanium instruments appear to have a high risk of fracture (Arens, et al., 2003; Sattapan, et al., 2000) mainly because of flexural and torsional stresses during rotation in the root canal system (Berutti, et al., 2003; Parashos, Messer, 2006). When there is a wide area of contact between the cutting edge of the instrument and the canal wall during rotation, the instrument will be subjected to an increase in torsional stress (Peters, et al., 2004; Blum, et al., 1999). The preparation of a reproducible glide path can reduce the torsional stress on root canal instruments. A glide path is a smooth passage that extends from the canal orifice in the pulp chamber to its opening at the apex of the root (West, 2006). This will provide a continuous, uninterrupted pathway for the rotary nickel-titanium instrument to enter and to move freely to the root canal terminus.
The main purpose of a glide path is to create a root canal diameter the same size as, or ideally a size bigger than, the first rotary instrument introduced (Berutti, et al., 2004; Varela-Patio, et al., 2005; Berutti, et al., 2009). Another way to reduce torsional stress is to incorporate multiple progressive tapers to the instrument design, for example, the ProTaper® universal system (Dentsply/Maillefer). According to West (2001), the progressive taper allows for only small areas of dentin to be engaged. This design concept also contributes to maintaining the original canal curvature (Yun, Kim, 2003).
ProTaper Next
Recently, the ProTaper Next system (Dentsply/Maillefer) was launched into the dental market. (ProTaper NEXT® is only available in North America through DENTSPLY Tulsa Dental Specialties.) There are five instruments in the system, but most canals can be prepared by using only the first two instruments. This system also makes use of the multiple progressive taper concept. Each file presents with an increasing and decreasing percentage tapered design on a single file concept (Ruddle, Machtou, West, 2013). The design ensures that there is reduced contact between the cutting flutes of the instrument and the dentin wall, thus reducing the chance for taper lock (screw-in effect). At the same time, it also increases flexibility and cutting efficiency (Ruddle, 2001).
The first instrument in the system is ProTaper Next X1 (Figure 1), with a tip size of 0.17 mm and a 4% taper. This instrument is used after creation of a reproducible glide path by means of hand instruments or rotary PathFile™ instruments. This instrument is always followed by the second instrument, the ProTaper Next X2 (0.25 mm tip and 6% taper) (Figure 2). ProTaper Next X2 can be regarded as the first finishing file in the system, as it leaves the prepared root canal with adequate shape and taper for optimal irrigation and root canal obturation. ProTaper Next X1 and X2 have an increasing and decreasing percentage tapered design over the active portion of the instruments.
The last three finishing instruments are ProTaper Next X3 (0.30 mm tip with 7% taper) (Figure 4), ProTaper Next X4 (0.40 mm tip with 6% taper) (Figure 5) and ProTaper Next X5 (0.5 mm tip with 6% taper) (Figure 6). These instruments have a decreasing percentage taper from the tip to the shank. ProTaper Next X3, X4, and X5 can be used to either create more taper in a root canal or to prepare larger root canal systems.
Another benefit of this system is the fact that the instruments are manufactured from M-Wire and not traditional nickel-titanium alloy. Research by Johnson, et al., (2008) demonstrated that the M-Wire alloy could reduce cyclic fatigue by 400% compared to similar instruments manufactured from conventional nickel-titanium alloys. The added metallurgical benefit contributes toward more flexible instruments, increased safety, and protection against instrument fracture (Gutmann, Gao, 2012).
The last major advantage towards root canal preparation with the ProTaper Next system is the fact that most of the instruments present with a bilateral symmetrical rectangular cross section (Figure 6) with an offset from the central axis of rotation (except in the last 3 mm of the instrument, D0-D3). The exception is ProTaper X1 that has a square cross section in last 3 mm to give the instruments a bit more core strength in the narrow apical part.
This design characteristic allows the instrument to experience a rotational phenomenon known as precession or swagger (Scianamblo, 2011). The benefits of this design characteristic include :
- It further reduces (in addition to the progressive tapered design) the engagement between the instrument and the dentin walls. This will contribute to a reduction in taper lock, screw-in effect, and stress on the file.
- Removal of debris in a coronal direction (Figure 7) because the off-center cross section allows for more space around the flutes of the instrument. This will lead to improved cutting efficiency, as the blades will stay in contact with the surrounding dentin walls. Root canal preparation is done in a very fast and effortless manner.
- The swaggering motion of the instrument initiates activation of the irrigation solution during canal preparation, improving debris removal.
- It reduces the risk of instrument fracture because there is less stress on the file and more efficient debris removal.
- Every instrument is capable of cutting a larger envelope of motion (larger canal preparation size) (Figure 6) compared to a similarly sized instrument with a symmetrical mass and axis of rotation. This allows the clinician to use fewer instruments to prepare a root canal to adequate shape and taper to allow for optimal irrigation and obturation.
- There is a smooth transition between the different sizes of instruments because the design ensures that the instrument sequence itself expands exponentially.
Clinical guidelines for ProTaper Next instruments
The clinical technique for ProTaper Next will be discussed by means of case reports. The first case report will outline the basic guidelines for the use of ProTaper Next instruments.
The patient, a 46-year-old male, presented with a previous emergency root canal treatment on his upper-left first premolar. A periapical radiograph showed evidence of three separate roots and large periapical lesion (Figure 8). According to the patient, the tooth was left open by his previous dentists that performed the emergency root canal treatment to allow for drainage.
Guideline one: Create straight-line access and remove triangles of dentin
It is very important to prepare an adequate access cavity that will ensure straight-line access into each root canal system. However, in the present clinical case there was still a dentin triangle obscuring direct access into the distobucaal root canal system (Figures 9A and 9B). The Start-X tip No. 3 (Dentsply/Maillefer) was used to remove some of this dentin on the pulp floor (Figure 10), allowing more direct access to the distobuccal root canal orifice.
A Micro-opener (Dentsply/Maillefer), size 10, 06% taper instrument was used to locate and enlarge the distobuccal and mesiobuccal canal orifices (Figure 11). For improved radicular access, the SX instrument (Dentsply/Maillefer) from the ProTaper Universal system was used (Figure 12A). The recommended method of use is to introduce the file into the coronal portion of the root canal, ensuring that the file is able to freely rotate. Restrictive dentin is then removed by using a backstroke, outward brushing motion. This step will also relocate the canal orifices more mesial or distal (away from furcal danger) and preflare the canal orifices, ensuring complete staight-line access into the root canal system (Figure 12b).
Guideline two: Negotiate canal to patency and create a reproducible glide path
The authors prefer to negotiate the root canal with size 08 or 10 K-files until apical patency is established (Figure 13A). Apical patency is the ability to pass small K-files 0.5 mm – 1 mm passively through the apical constriction, beyond the minor diameter without widening it (Buchanan, 1989). Length determination was done using a Propex Pixi Apex Locator (Dentsply/Maillefer). Predictable readings were achieved by using two size 10 K-files in the mesiobuccal and distobuccal root canals and a size 20 K-file in the larger palatal root canal and confirmed radiographically (Figure 13B).
After working length determination, a reproducible glide path should be established. According to West (2010), a glide path is a smooth passage that extends from the canal orifice in the pulp chamber to its opening at the root apex. Most authors recommend that the glide path should be the same size as, or ideally a size bigger, than the first rotary instrument that will be introduced into the root canal system (Berutti, et al., 2004; Varela-Patino, et al., 2005; Berutti, et al., 2009).
It is recommended to use the stainless steel K-files in vertical in and out motion with an amplitude of 1 mm and gradually increasing the amplitude as the dentin wall wears away and the file advances apically (West, 2006). West (2010) recommends a “super loose” size 10 K-file as the minimum requirement. To confirm that a reproducible glide path is present, the size 10 file is taken to full working length (Figure 14B). The file is then withdrawn 1 mm and should be able to slide back to working length by using light finger pressure. Thereafter, the file is withdrawn 2 mm and should be able to slide back to working length, using the same protocol. When the file can be withdrawn 4 mm to 5 mm and slide back to working length (Figure 14B), a reproducible glide path is confirmed (Van der Vyver, 2011).
The reproducible glide path is then enlarged using rotary PathFiles (Dentsply/Maillefer). (PathFiles™ are only available in North America through DENTSPLY Tulsa Dental Specialties.) PathFile No. 1 (0.13 mm tip size) is taken to full working length operating at 300 rpm and 5 N/cm torque (Figure 15A). As soon as the file reaches working length, the authors recommend to brush lightly outwards against one side of the canal wall. The file is pushed back to working length and brushed outward against another part of the canal wall. This procedure is repeated four times (touching the canal wall in a mesial, distal, buccal, and lingual direction). PathFile No. 2 (0.16 mm tip size) is used following the same protocol (Figure 15B). When using ProTaper Next, it is only necessary (in most cases) to enlarge the glide path to the second PathFile (0.16 mm) as the first preparation instrument, the X1 of the ProTaper Next system has a tip size of ISO 17. However, it is recommended to use PathFile No. 3 (0.19 mm tip size) when dealing with challenging root canal systems.
Guideline three: ProTaper Next preparation sequence
ProTaper Next X1 (shaping instrument only)
Introduce sodium hypochlorite and the ProTaper Next X1 instrument into the root canal. The authors found that four scenarios can present itself when using ProTaper Next X1 instrument:
- Easy root canals
- More difficult and longer root canals
- Very long/severely curved root canals
- Larger diameter root canals and retreatment cases root canals where the use of ProTaper Next X1 is not necessary and canal preparation can be initiated with ProTaper Next X2, X3, X4, or X5.
The last two scenarios will be discussed later in this article. For easy canals (mesiobuccal root canal in this case report), allow the ProTaper Next X1 instrument (operating at 300 rpm and torque of 2.8N/cm) to slide down the glide path up to working length (Figure 16A). If this is possible, pull the instrument back to approximately 2-3 mm short of working length and incorporate a deliberate backstroke, outward brushing motion (away from any external root concavities) to create more space in the coronal aspect of the root canal (Figure 16B). Finally, take the file to full working length and “touch” the apex and brush outwards (coronally) with the file in the apical third of the root canal. This “touch-and-brush” sequence can be repeated up to 3 or 4 times (Figure 16C).
For more difficult and longer canals (distobuccal root canal in this case report), allow the ProTaper Next X1 to slide down the glide path until resistance is met (Figure 17A). Incorporate a deliberate backstroke, outward brushing motion in order to remove restrictive dentin at this level (away from any external root concavities). This motion will create more lateral space, enabling the file to slide a few more millimeters down the root canal towards working length (Figure 17B) (if the file ceases to progress apically, remove the file, clean the flutes, irrigate, recapitulate, and re-irrigate the canal before you progress with the shaping procedure). The above procedure is repeated until the file reaches full working length. Finally, take the file to full working length (Figure 17C) and the “touch-and-brush” sequence is done 3 to 4 times in order to complete canal preparation.
After the use of ProTaper Next X1, it is recommended to irrigate with sodium hypochlorite, recapitulate with a small patency file to dislodge cutting debris, and to re-irrigate to flush out all the dislodged debris from the root canal (Figure 18).
ProTaper Next X2 (first finishing instrument)
Use ProTaper Next X2 (25/06) to full working length, using the same protocol as previously described. However, it is recommended to use the “touch-and-brush” sequence in the apical part of the root canal only 2 to 3 times as a final step (Figure 19). Excessive “touch-and-brush” sequences in the apical part of the root canal can lead to transportation of the root canal. The root canal is again irrigated, recapitulated, and re-irrigated.
Gauging of apical foramen to determine if the preparation is complete
Introduce a size 25/02 NiTi hand file (Dentsply/Maillefer) to full working length (Figure 20). If the file is snug at working length, it means that the apical foramen is prepared to a size ISO 25, and the canal is adequately shaped.
The palatal root canal in the present case report was prepared with the ProTaper Next X1 and X2 according to the protocol previously outlined. In this case it was found that the 25/02 NiTi hand file was fitting loose at length, and it could be pushed past working length (Figure 21A) after canal preparation with the X2 instrument. This indicated that the apical foramen was still larger than 0.25 mm. In these situations, it is recommended to gauge the foramen with a size 30/02 NiTi hand file (Figure 21B). If the 30/02 file is snug at length, the shape is complete. If it is found that the 30/02 instrument fits tight, but short of the full working length (Figure 22A), it is recommended to continue canal preparation with the ProTaper Next X3 (30/07) (Figure 22B) and gauge again with the 30/02 NiTi hand instrument (Figure 22C).
Guideline four: Shaping recommendations for ProTaper Next X3, X4, and X5
ProTaper Next X3 (and X4 and X5 if necessary) is used in the same manner as ProTaper X1 or X2 with the exception that the apical preparation is done by using the “touch-and-brush” sequence only once or twice in the apical third of the root canal. Apical gauging is done according to the previously mentioned protocol using a size 30/02, 40/02, or 50/02 NiTi instruments.
The 30/02 instrument was fitting snugly at working length in the palatal root canal in the present case report. The canals were obturated with ProTaper Next X2 gutta-percha points in the mesiobuccal and distobuccal root canals and a ProTaper Next X3 gutta-percha point (Dentsply/Maillefer) in the palatal root canal as master cones using the Calamus® Dual Obturation Unit (Dentsply/Maillefer). Figure 23 demonstrates the final result after canal obturation.
Preparation sequence for very long and curved root canals
In selected clinical cases, the clinician might find that ProTaper Next X1 does not progress to full working length even after a few coronal circumferential brushing motions. The authors then recommend to create more coronal shape by using ProTaper Next X1 followed by ProTaper Next X2 up to two-thirds of the canal length. This preparation sequence will create enough lateral space in the coronal two-thirds of the root canal to ensure that ProTaper Next X1 can now be taken to full working length without any difficulty.
Case report
The patient, a 50-year-old female, presents with pain on her mandibular rigth first molar with a history of a previous emergency root canal treatment. Clinical examination revealed a broken down and leaking temporary restoration possibly resulting in coronal leakage. A periapical radiograph revealed very long and curved mesial roots. Also visible on the radiograph was evidence of dentin triangles preventing straight-line access into the mesial root canals (Figure 24).
The defective temporary restoration and caries were removed before the tooth was restored with composite and a new access cavity prepared. Note the evidence of dentin triangles on the mesial aspect of the canal orifices (Figure 25, arrows). The dentin triangles were removed with a ProTaper SX instrument, ensuring straight-line access into all the root canals. Figure 26 shows the radiographic view of the length determination confirming straight-line access into the root canals.
As mentioned before, the clinical protocol for cases with very long and curved root canals would be to allow ProTaper Next X1 to progress to about two-thirds of the canal length (Figure 27A). This is followed by irrigation, recapitulation, and re-irrigation sequence with sodium hypochlorite. ProTaper Next X2 is then used in the same manner (with circumferential outstroke brushing motions) to the same length (Figure 27B). ProTaper Next X1 is then used again to progress with canal preparation to full working length (Figure 27C) using the “touch-and-brush” sequence as described before. ProTaper Next X2 is then taken to full working length (using the same protocol as described before) (Figure 27D) after irrigation, recapitulation, and re-irrigation of the root canal.
Canals were gauged according to the technique described before, and final preparation was done up to ProTaper Next X2 in the mesial root canals and up to ProTaper Next X3 in the distal root canal. GuttaCore™ verifiers were fitted (Figure 28A) to working length to confirm the size of obturators for each canal before the canals were obturated with corresponding GuttaCore obturators. Figure 28B shows the postoperative result after obturation.
Shaping recommendations for large diameter root canals or retreatment of root canals
If the first file to working length is a size 20 K-file and it is loose up to working length, the shaping procedure can be initiated by using ProTaper Next X2 (25/06). If the first files to length are a size 25/30, 30/35, or 40/45, and they are found to be loose in the canal up to working length, the shaping procedure can be initiated with ProTaper Next X3 (30/07), X4 (40/06), and X5 (50/06) respectively.
Case report
The patient, a 44-year-old female, presented with pain and discomfort on her maxillary right-central incisor. Radiographic examination revealed that the tooth was poorly root treated, and there was evidence of a large periapical area (Figure 29A). After removal of the previous gutta percha, it was possible to take a size 35 K-file to working length (Figure 29B).
Root canal preparation was initiated by preparing the root canal to working length with the ProTaper Next X4 (40/06) instrument (Figure 30A). Apical gauging with a 40/02 NiTi hand file revealed that the tip of the file was loose at length and able to travel past the predetermined working length (Figure 30B) and that a size 50/02 NiTi hand file was unable to reach full working length, penetrating to about 2 mm short of working length (Figure 30C). This indicated that the apical foramen size was between 0.40 mm and 0.50 mm. The root canal preparation was enlarged with a ProTaper Next X5 (50/06) (Figure 31A) and gauged again with a 50/02 hand NiTi file (Figure 5F). It was found that the 50/02 instrument fitted snug at working length (Figure 31B) indicated that the shape was complete. The prepared canal was obturated with a ProTaper Next X5 gutta-percha point (Dentsply/Maillefer) using Calamus Dual Obturation Unit (Dentsply/Maillefer). Figure 31C shows the final result after obturation.
Part 2 of this series will discuss the management of complex root canal systems with the ProTaper Next system (Dentsply/Maillefer).
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Gallery
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