Achieving Dentin Conservation Through Modern Techniques and Instruments

Dentistry Today


Marcus Johnson, DDS
As endodontic techniques and practices continue to evolve and spawn new paradigm shifts lending to clinical demands of creative dentin-conservation designs, we also see the adaptation of the endodontic armamentarium. COLTENE recently introduced HyFlex Electrical Discharge Machining (EDM) rotary files (Figure 1), which are an upgrade in the well-established HyFlex Controlled Memory (CM) line of heat-treated rotary files. EDM uses spark erosion to harden the surface of the NiTi file. When combined with built-in shape memory, these enhancements have been specially designed to help clinicians in key areas, like dentin conservation, increased flexibility, fracture resistance, and canal debridement.1 These metallurgic properties aid in more nonconventional molar endodontic access designs, like the “truss” or “dual-access” as first outlined and described by Clark and Khademi.2 Modern access designs also call upon superior cutting from carbides and diamonds to exact proper line angles into the pulp chamber for minimally invasive preps, reducing prep time and allowing for detailed refinements that facilitate adaptability and strength of filling materials to effectively restore the access design.

Figure (1a.) The HyFlex EDM 25./12 orifice opener, 10./05 glidepath file, 20./05 preparation file, and 25~ HyFlex Onefile. (1b.) The EDM 20./05 preparation file highlights the controlled memory property.
Figure 2. Tooth No. 19 Dx: SIP/SAP.
Figure (3a.) Tooth No.19 “Dual-access” or “Truss” minimally invasive endo access design. (3b.) COLTENE Alpen Speedster Metal Cutter US No. 1558G and COLTENE Alpen diamond bur shape 856 for access prep.
Figure 4. KiS Tip 1D4 (Kerr) was activated ultrasonically to debride dentin bridge.
Figure 5. Dual access is restored. Figure 6. PO x-ray of obturation and sealed coronal anatomy.

Clinical Case Example
A 42-year-old female patient presented with a chief complaint of excruciating pain after suffering for months when an amalgam restoration was replaced with resin composite on tooth No. 19 for aesthetic concerns (Figure 2). Clinical and radiographic examinations were conducted. The chief complaint was reproduced, and RCT was recommended based on a diagnosis of symptomatic irreversible pulpitis/symptomatic apical periodontitis (SIP/SAP). After local anesthesia was achieved, isolation with a rubber dam was secured (Flexi Dam [COLTENE]). The access to the pulp chamber was leveraged from the occlusal surface to the roof of the pulp chamber by orienting a bur parallel to the long axis of the tooth in an oval shape buccolingually with an access bur (Alpen Speedster Metal Cutter US No. 1558G [COLTENE]). The bur was then placed over the distal pulpal horn, and access to the pulp chamber was gained in a similar fashion (Figure 3). A round-end, tapered diamond bur was used inside the pulp chamber at medium speed, creating a divergent wall in the access cavity (Alpen diamond bur shape 856 [COLTENE]). The canals were located and bathed in 6% sodium hypochlorite solution, and patency was gained with a 21-mm, precurved K-file, size No. 10 (Roydent). Subsequently, all canals were instrumented to a No. 15 K-file. Cervical preflare with the orifice opener was not employed in an effort to retain pericervical dentin (a critical zone, roughly 4 mm above crestal bone and extending 4 mm apical to crestal bone).2 The working length was measured using a CanalPro Apex Locator (COLTENE). A Glidepath was maintained with the 21-mm, 10/.05 rotary using 300 rpm of torque and 1.8 Ncm. The mesial canals finished with the 20./05 shaping file at 500 rpm/2.5 Ncm, while the distal canal was finished with the 25~ HyFlex Onefile (Figure 3). A brushing or sweeping motion of the files to aid against iatrogenic complications, like ledging, file separation, and perforation, was used in the canals with the CanalPro cordless rotary handpiece (COLTENE) (Figure 1). Irrigation protocol of NaOCl 6% for organic tissue removal and disinfection of all canals, followed by a one-minute rinse of EDTA for smear layer removal and a final rinse with NaOCl 6%, was done. Ultrasonic activation with the KiS Tip 1D4 (Kerr) allowed for tissue debridement underneath the dentin bridge (Figure 4). The canals were dried, matching gutta-percha points were seated with EndoSequence BC Sealer (Brasseler USA), check film was exposed, and gutta-percha was downpacked and backfilled to the canal orifice. Access cavities were primed (ONE COAT 7 UNIVERSAL [COLTENE]), filled incrementally (Fill-Up! shade A2), light cured, and occlusion adjusted. The postoperative radiograph was exposed (Figures 5 and 6). For more information, call COLTENE toll-free at (800) 221-3046 or visit


  1. Pirani C, Iacono F, Generali L, et al. HyFlex EDM: superficial features, metallurgical analysis and fatigue resistance of innovative electro discharge machined NiTi rotary instruments. Int Endod J. 2015 May 22 doi: 10.1111/iej.12470.
  2. Clark D, Khademi J. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am 2010;54:249-73.

Dr. Johnson is a Diplomate of the American Board of Endodontics. His practice, City Endodontics PLLC, is in Midtown Manhattan. He is the directing endodontic attending for the Interfaith Medical Center in Brooklyn and the VP of the New York State Association of Endodontists. He has lectured internationally and is the host of the Endo Voices podcast for the American Association of Endodontists, which aims to advance the art and science of endodontics and promote the highest standards of patient care. He can be reached at (212) 725-2573 or via email at