A new expandable NiTi file for residual canal debris removal

Drs. James Bahcall and Stephen Weeks discuss how to efficiently aid in the mechanical removal of residual canal debris

Residual canal debris is organic and/or inorganic material that remains on the dentinal wall after conventional endodontic chemomechanical canal preparation is complete.¹

This residual canal debris is also referred to in the literature as the smear layer. This organic and/or inorganic substance is derived from ground dentin, pulpal remnants, and in the cases of infected root canal systems, bacteria.²

A possible explanation for the residual canal debris after chemomechanical canal preparation is the fact that NiTi rotary files stay centered in the canal and, in turn, will not make contact with all the dentinal walls due to various invaginations and irregularities.³ An in vitro study by Chuste-Guillot demonstrated that whichever NiTi rotary file system a clinician uses to prepare an infected root canal system, the root dentin that remained was infected and not bacteria-free.⁴ Lin, et al., report that the major factors associated with endodontic failures are the persistence of bacterial infection in the canal space and/or the periradicular area.⁵

Another explanation of the presence of residual canal debris after canal instrumentation and irrigation may be due to a clinician not being vigilant in using EDTA (ethylenediaminetetraacetic acid) and sodium hypochlorite.⁶ Lastly, canal morphology can be complex, making it difficult for the chemomechanical canal preparation to be effective in removing all the canal debris.⁷

The three main factors in removing residual canal debris are irrigation activation plus mechanical and chemical debridement. Irrigation activation with an ultrasonic, polymer finishing file, polymer ultrasonic tip, positive pressure syringe, and negative pressure device have all demonstrated various abilities in removing residual canal debris.^7,8 The basis of irrigation activation is to create fluid motion and dentinal wall shear stress to enable the removal of residual canal debris from the dentinal walls. An in vitro study by Koch, et al.,⁹ found that the fluid shear stress observed from static position and cyclical axial motion of ultrasonic, a polymer finishing file, and positive pressure needle irrigation does not activate the irrigant powerfully enough to clinically remove residual canal debris alone after conventional endodontic chemomechanical treatment. They also reported that cavitation is not achieved during this type of irrigation activation, but rather non-inertial cavitation.

Mechanical removal of residual canal debris is performed through the physical contact of a file or irrigation activation instrument with the dentinal wall. Chemical removal of residual canal debris is achieved with the use of the sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA). The use of EDTA, as a chelating agent (removes calcium ions), in conjunction with NaOCl has been shown to aid in the removal of some, but not all of a canals residual debris.¹⁰

Although all three factors (irrigation activation plus mechanical and chemical debridement) can aid in removing residual canal debris, mechanical contact with the dentinal wall is the most direct and efficient method in the removal of dentinal wall residual debris.
Figure 1: XP-3D Finisher file (ISO #25)
Figure 2: XP-3D Finisher file in A-phase, allowing up to a hundredfold expansion. Permission for reprinting of image granted by Brassler USA ®Figure 3: XP-3D Finisher file is malleable at room temperature
Figure 4: Spraying Endo Ice ® over the XP-3D Finisher file casing

Clinical usage of the XP-3D Finisher™ file

The introduction of a new expandable NiTi file, the XP-3D Finisher™ file (Brasseler USA®) (Figure 1), offers an innovative instrument for mechanically cleaning the dentinal walls after chemomechanical canal preparation.

The XP-3D Finisher file comes in ISO #25 and #30 sizes with a zero degree taper. It is made of a proprietary alloy that, at room temperature, exists in a Martensitic phase (M-Phase) and at body temperature exists in an Austenitic phase (A-phase). In the M-phase, the file is straight.¹¹ In the A-phase, the file changes it shape to allow the instrument to expand its reach to 6 mm in diameter or hundredfold when the file tip is squeezed while in rotational motion¹² (Figure 2).

Since the XP-3D Finisher file is in the M-phase at room temperature, it is malleable (Figure 3), and therefore, a clinician may find it difficult to initially place into a canal. By using Endo-Ice™ (Coltene® Group, Altstätten, Switzerland, with American headquarters in Cuyahoga Falls, Ohio) and spraying it over the casing that the file comes in (Figure 4), it will cause the file to become stiffer, making it easier to guide into a canal. A dentist can also directly wipe the file out of the casing with an alcohol gauze, and it will provide the same stiffening effect as using Endo-Ice™.¹³

Prior to using the XP-3D Finisher file in a canal, set the working length, and make sure EDTA and/or NaOCl is in the canal. The optimal speed for the clinical usage of the XP-3D Finisher file is 800-1000 rpm with 1 Ncm of torque. It is recommended to be used as a single use file with up to four canals in one tooth.^11,12,14 The file should be used clinically by using slow and gentle 7 mm-8 mm lengthwise cyclical-axial movements to the full length of a canal while filing against the canal wall in a circumferential motion. After file usage, irrigate the canal with NaOCl and/or EDTA.¹¹

Regenerative endodontics

The XP-3D Finisher file can also be used for regenerative endodontic procedures. It can aid in canal preparation without further enlarging a canal. Just as it “scrapes” pulpal canal debris off the dentinal walls in conventional endodontic treatment, it will do the same in regenerative endodontic treatment. The file can also help stimulate apical bleeding in the apical region. After the removal of the calcium hydroxide or triple antibiotic paste at the second treatment appointment, the XP-3D Finisher file can be activated 1 mm outside the main canal portal of exit (POE) to stimulate bleeding within the canal.

Summary

The integration of the XP-3D Finisher file into your endodontic armamentarium will effectively and efficiently aid in the mechanical removal of residual canal debris. This file’s ability to expand makes it better able to adapt to the various canal morphologies. The XP-3D Finisher file is also effective in removing canal wall debris without enlarging the canal and stimulating apical bleeding in regenerative endodontic treatment.