A Case Using Rotary Endodontics and Resin-Based Fillers
Richard Trushkowsky, DDS; and Anabella Oquendo, DDS
The use of rotary nickel-titanium files has allowed more centered canal preparations and fewer aberrations in the canal.
Sufficient shaping and cleaning of root canals are a prerequisite for long-term success. According to Schilder,1 root canal shape should meet these objectives: the root canal preparation should develop a continuously tapering funnel from the root apex to the coronal access cavity; the cross-sectional diameter of the preparation should be narrowed at every point apically and wider at each point as the access cavity is approached; the root canal preparation should flow with the shape of the original canal; the apical foramen should remain in its original position; and the apical foramen should be kept as small as possible.1 Instrumentation provides gross debridement and allows irrigants to mechanically flush the area, dissolve residual tissue, and eradicate any remaining bacteria.2 However, ledge formation, transportation of the apical foramen, and non-tapered hourglass-shaped preparation are problems that may occur especially during instrumentation of curved canals.3
Nickel-titanium (Ni-Ti) rotary-shaping techniques were developed more than a decade ago.2 These instruments were supposed to keep the original canal shape without deleterious effects because of their super-elastic behavior and shape-memory property. This is especially important in curved canals because excess straightening can modify the integrity of the canal.2 There are a great variety of rotary nickel-titanium (RNT) files and geometric designs available. The use of RNT has allowed more centered canal preparations and fewer aberrations in the canal. These instruments are usually used in a crown-down technique.4 Some of these are passive instruments with radial lands (ProFile; GT® Rotary System, DENTSPLY Tulsa, wwwtulsadental.com). The GT Rotary file possesses a more rounded tip, somewhat broader radial lands, and more flutes are present at the apical end. The radial land is designed to prevent the file from transporting the canal; however, the increased contact of the radial land creates a larger area of contact in the canal. This may, unfortunately, result in instrument fracture because of the increased friction and torque.
Active instruments such as FlexMaster (Vereinigte Dentalwerke, Munich, Germany), ProTaper (DENTSPLY Maillefer, https://www.dentsply.co.uk) and RaCe (FKG Dentaire, La Chaux-de-Fonds, Switzerland) provide a cleaner canal because they are more efficient in removing the smear layer, unlike instruments with radial lands that tend to burnish the canals. However, instruments such as the FlexMaster, which have a triangular cross-section, have a tendency to thread into the canals.
Fracture of RNT instruments has been a problem in endodontic practice because of the torsion and flexure these instruments undergo during their use. Torsional fatigue is caused by the tip of the instrument binding in the root canal as the file continues turning. If the elastic limit is surpassed, deformation will result in fracture. Flexural fatigue may occur in curved root canals because of the disproportionate tension-strain cycles in the area with the greatest curvature. The fatigue life of a NiTi rotary instrument depends on its dimension and to what extent it is flexed during instrumentation of a curved canal.5 The removal of coronal interferences and pre-flaring will reduce the stress on the instruments and reduce fracture. In addition, the concept of alternate rotation rather than continuous rotation may reduce the risk of fracture or deformation as a counter-clockwise motion will serve to disengage the tip of the instrument.6 An additional problem that may occur is incomplete preparation of buccal and lingual walls because some canals are long-oval or flat in cross-section. High-resolution micro-computed tomography (MCT) has been used to assess root canal preparation instruments. It has been demonstrated that the amount of prepared canal and the reduction of biofilm by mechanical means is frequently less than 60% of the canal surface.7 A newly developed self-adjusting file (ReDent-Nova, Ra'anana, Israel) has been designed in an attempt to overcome the shortcomings of traditional rotary files.8
The SafeSiders® system (Essential Dental Systems, https://www.edsdental.com) has a non-interrupted, flat-sided design that will create a reduction in engaging the dentin and also reduce the resistance of the instrument in the canal. The flat surface creates a reduced cross-sectional area that allows more flexibility and allows the instrument to negotiate curved canals more readily. The manufacturer claims that the reciprocating motion used for instrumentation results in a balanced force that allows the file to stay centered in the canal.
There has been a search for a root canal sealer that would simultaneously bond to the canal walls and to the filling material. The term "monoblock" has been used to describe the achievement of a gap-free root canal space filled with different materials that form a coherent mass that will improve the seal and increase the fracture resistance of the filled canals.9 New self-etching (third-generation) and self-adhesive (fourth-generation) root canal sealers are currently available.10 The self-etching primers incorporate the smear layers created by hand or rotary instruments. The acidic primers penetrate the smear layer and demineralize the superficial dentin. These materials must be sufficiently acidic to permit the penetration of thick smear layers.11 FibreFill™ R.C.S. and Resilon™ (Pentron Clinical Technologies,https://www.pentron.com) are examples of third-generation resin-based sealers. The monomers penetrate the conditioned dentin and micromechanical interlocking results in a hybrid layer formation. Resilon is a dimethacrylate-containing polycaprolactone-based thermoplastic filling material. Resilon can be used with either lateral or warm vertical-condensation techniques. The sealer Epiphany® (Pentron Clinical Technologies) is a methacrylate-based sealer. The fracture resistance of adhesive root-canal filling systems has been studied; Sagsen et al found no statistically significant difference in the fracture resistance between AH 26 and gutta-percha, Resilon and Epiphany. However, the fracture resistances of these experimental groups were much higher than the instrumented and not-filled groups.12
The fourth-generation materials are methacrylate resin-based sealers (eg, MetaSEAL™, Parkell Inc, https://www.parkell.com; RealSeal™ SE, SybronEndo, https://www.sybronendo.com). These materials have eliminated the separate etching/bonding step and the dentin adhesive primers are all incorporated in the resin-based sealer to make them adhere to the dentin.9 MetaSEAL is a dual-cured sealer containing an acidic monomer, 4-methacryloyloxyethyl trimellitate anhydride (4-META). This sealer bonds to both thermoplastic filling materials and to the radicular dentin. Hybrid layers are formed in both.
There has been some concern regarding the abilities of the self-etch and self-adhesives to hybridize intact radicular dentin. EDTA is recommended by the manufacturers as a final rinse to remove the smear layer and allow hybridization and copious resin tags. In addition, shrinkage stress associated with the narrow canal walls may potentially disrupt the contact between the sealer and the dentin.13 These shrinkage gaps may allow the ingress of microorganisms. Re-infection of the canal and seepage of tissue fluids at the apical end of the canal has to be prevented so that any remaining bacteria do not have access to nutritive material.14 The use of the single-cone technique also has been questioned. However, Tay and Pashley have found that bonds along the sealer/gutta-percha interface can be used successfully.15
Instrumentation of the Canal
SafeSiders® is a series of non-circular instruments with a non-interrupted, flat-sided architecture used in a reciprocating motion. The files can be used manually or with the Endo-Express® (Essential Dental Systems) reciprocating handpiece between 1,500 and 2,000 rpm. The handpiece is used with a firm pecking motion. If used manually, a wrist-watch winding motion is used to engage and disengage the dentin. Initially, a gray 08 or purple 10 SafeSider is used to negotiate to the apex. After the length is established, the white 15 and yellow 20 SafeSiders are used to the apex. The canal should always be irrigated with 5.25% NaOCL and instruments lubricated with EDTA; 2% chlorhexidine may also be beneficial to cleanse the canal. After the yellow 20 SafeSider, the Pleezer reamer in the kit is used to deepen and flare the canal. The flaring should not be at the expense of any furcation. The purpose of the flaring is to straighten the canal curve to permit more direct-line access to the apex. Usually, a firm pecking motion will allow the reamer to get within 6 mm of the apex. The canal is then instrumented to the apex with the red 25 and blue 30 SafeSider reamers. The orange 30/0.4 SafeSider NiTi reamer is used with a firm pecking motion to the apex. The NiTi instruments are best used in the Endo-Express reciprocation handpiece because the reciprocating motion helps to eliminate binding in the canal. Then, the green 35 SafeSider reamer is used to the apex. The black SafeSider is used 1 mm back from the apex, and the patency is confirmed with the yellow 20. The pink 25/.06 and possibly the brown 25/.08 SafeSider are used with a firm pecking motion to the apex. This creates an apical preparation of 25 and a 0.06-mm or 0.08-mm taper that should allow a firm fit of a medium gutta-percha point.
Filling the Canal
A medium gutta-percha point is fitted to obtain a tight apical fit as indicated by tug-back. The bi-directional spiral is placed in a low-speed handpiece run at approximately 1,000 rpm in a clockwise direction. A rubber stopper is placed on the bi-directional spiral so that it stops 3 mm shy of the apex. The bi-directional file is coated with a thick layer of cement and then run in the canal at 1,000 rpm for approximately 5 seconds with a slow up-and-down motion for seven or eight strokes. The apical 10-mm to 12-mm of the prefitted gutta-percha is coated with the cement and inserted into the canal. Excess gutta-percha is seared with a hot instrument and the coronal access should be sealed with a resin-modified glass ionomer. In the examples shown in Figure 1, Figure 2, Figure 3, two maxillary premolars and a mandibular molar were instrumented and filled using the SafeSiders instrumentation and filled with gutta-percha and EZ-Fill Xpress (Essential Dental Systems).
Conclusion
The increased use of rotary endodontic instrumentation has demonstrated its advantages over the manual method. There is a lower incidence of formation deviation, better canal shaping, and reduction in preparation time. However, fracture of these instruments because of torsion and fracture that result from flexural changes do occur. The incidence of this happening is greatly reduced by strict adherence to the manufacturer's instructions. Single-cone and sealer may be used as an alternative to lateral condensation. This would minimize non-filled spreader tracks and potential dentin damage or vertical root fracture. Although an ideal root-canal filling material should prevent bacterial ingress into the canal, Resilon is susceptible to alkaline and enzymatic hydrolysis and polymer degradation may result in a lost seal.9
References
1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18(2):269-296.
2. Yoshimine Y, Ono M, Akamine A. The shaping effects of three nickel-titanium rotary instruments in simulated S-shaped canals. J Endod. 2005;31(5):373-375.
3. Khalilak Z, Alavi K, Akhlaghi NMZ, et al. Canal-centering ability of three rotary file systems in simulated curve canals: a comparative study. Indian J Dent Res. 2009;20(4):400-403.
4. Bergmans L, Van Cleynenbruegel J, Wevers M, et al. Mechanical root canal preparation with NiTi rotary instruments: rationale, performance and safety. Status report for the American Journal of Dentistry. Am J Dent. 2001;14(5):324-333.
5. Martins Rde C, Bahia MG, Buono VT. Geometric and dimensional characteristics of simulated curved canals prepared with proTaper instruments. J Appl Oral Sci. 2010;18(1):44-49.
6. Varela-Patino P, Ibanez-Párraga A, Rivas-Mundina B, et al. Alternating versus continuous rotation: a comparative study of the effect on instrument life. J Endod. 2010;36(1):157-159.
7. Peters OA, Schonenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed micro computed tomography. Int Endod J. 2001;34(3):221-230.
8. Peters OA, Boessler C, Paque F. Root canal preparation with a novel nickel-titanium instrument evaluated with micro-computed tomography: Canal surface preparation over time. J Endod. 2010;36(6):1068-1072.
9. Kim YK, Grandini S, Ames JM, et al. Critical review on methacrylate resin-based root canal sealers. J Endod. 2010;36(3):383-399.
10. Jainen A, Palamara JE, Messer HH. Push-out bond strengths of the dentine-sealer interface with and without a main cone. Int Endod J. 2007;40(11):882-890.
11. Kokkas AB, Boutsioukis AC, Vassiliadis LP, et al. The influence of the smear layer on dentinal tubule penetration depth by three different root canal sealers: an in vitro study. J Endod. 2004;30(2):100-102.
12. Sagsen B, Er O, Kahraman Y, et al. Resistance to fracture of roots filled with three different techniques. Int Endod J. 2007;40(1):31-35.
13. Davidson CL, de Gee AJ, Feilzer A. The competition between the composite-dentin bond strength and the polymerization contraction stress. J Dent Res. 1984;63(12):1396-1399.
14. Wu MK, van der Sluis LW, Ardila CN, et al. Fluid movement along the coronal two thirds of root canal fillings placed by three different gutta-percha techniques. Int Endod J. 2003;36(8):533-540.
15. Tay FR, Pahley DH. Monoblocks in endodontics: a hypothetical or a tangible goal. J Endod. 2007;33(4):391-398.
About the Authors
Richard Trushkowsky, DDS
Clinical Associate Professor
Department of Cariology and Comprehensive Care
Co-Director International Program in Advanced Interdisciplinary Dentistry
Associate Director Advanced Program in Esthetic Dentistry
New York University
College of Dentistry
New York, New York
Anabella Oquendo, DDS
Instructor Department of Cariology andComprehensive Care
Course Director
International Programin Advanced Interdisciplinary Dentistry
New York University
College of Dentistry
New York, New York
