INTRODUCTION
Optimal cleaning and shaping of root canal systems requires, among many things, the coincident integration and tangible application of numerous anatomical, clinical, and technique driven considerations. For example, the case must be diagnosed correctly; the clinical risk assessed; the technique, clinical supplies, and instruments selected; and all of the above used correctly and simultaneously to achieve the treatment objectives. This case study was written to evaluate all of the principle-driven clinical steps needed to treat the tooth shown in Figure 1, using controlled memory (CM) Ni-Ti; and to briefly review the current literature on this exciting and emerging technology.
Brief Historical Background and Literature Review of Controlled Memory Technology
The first generation of Ni-Ti was ground from Ni-Ti file blanks and not heat-treated. Such first-generation instruments are superelastic. Superelasticity denotes the ability of the file to deform (strain) from its original shape under a physical load (stress). Clinically, this is manifest as a Ni-Ti file rotating in a curved canal and returning to its original shape upon removal from the canal. In essence, the Ni-Ti undergoes a transformation (the instrument is “strained”) from its harder austenite crystalline phase configuration to its softer martensitic crystalline phase configuration while under such “stress.” When the stress is relieved, it returns to its original shape (austenite). Such behavior is termed “shape memory.” First-generation (nonheat-treated) Ni-Ti instruments can generally accommodate approximately an 8% strain before fracture. In contrast, CM instruments do not possess superelasticity and do not undergo the aforementioned transformation.
The second generation of Ni-Ti files is heat-treated, either in the bulk raw material stage before grinding or, alternatively, after grinding. CM instruments are a subset of this second generation of heat-treated instruments. CM technology was introduced in 2010 (D&S Dental). Heat treatment processes are proprietary.
Interestingly, there is a new file that is heat-treated only in the apical 10 mm of its cutting flutes, providing flexibility at its working end (Mani Silk). To the author’s knowledge, for all other current systems, heat treatment encompasses the entire instrument.
CM files are unique among the commercial products available at this time. While made of heat-treated Ni-Ti, they remain curved as they rotate around a curved canal. CM files do not regain their original shape after use. Hence, they have “controlled memory.” The literature suggests this CM feature reduces transportation and conserves tooth structure. The literature also states that CM files are 300% to 900% more resistant to cyclic fatigue and have a statistically significant greater flexibility than their first generation superelastic counterparts. Aside from flexibility, CM files have essentially equivalent torsional strength to nonheat-treated files. In the existing scientific literature published to date, there are no unfavorable reported findings on CM attributes. The current literature file on CM technology (in PDF form) is available by email from the author on request (see Editor’s Note).
Clinically, CM instruments feel “softer” during use and require minimal insertion pressure. Depending on the file design and file size, CM instruments will deform (stretch) during treatment yet continue to function. If deformed during canal shaping, they can be used (as recommended in this article) through the entire case and then either discarded or autoclaved. If, after autoclaving, they return to their original shape, they can be used again. If they do not return to their original shape, they should be discarded. Alternatively, they can be discarded after one use.
At the present time, CM technology exists commercially, among other forms, as MounceFiles (MF [MounceEndo]) and Typhoon (TP) Infinite Flex (CLINICIAN’S CHOICE).
CASE REPORT
Using CM Instruments
The clinical case described below is pictured in Figure 1. The patient’s medical history was noncontributory. Subjectively, the patient was asymptomatic.
Objectively, tooth No. 30 had mild bone loss, was within normal limits to percussion and palpation, had slight mobility, and no probing depths greater than 5 (distal and buccal furcation). No swelling was present. A small fistula was present on the buccal, from which no drainage could be expressed. Apical periodontitis was visible apically. Furcal bone loss was noted. The crown margins of No. 30 were open. Caries was visible at the distal. Cold testing was negative. All other cold testing in the quadrant was within normal limits.
The crown margin at the distal of No. 29 was open. The patient was informed and instructed to see the general dentist for a new crown on No. 29 after the endodontic treatment of No. 30. While a CBCT could have been taken in this clinical case, it was not deemed necessary due to the root morphology clearly visible in the 2-D radiograph.
A nonvital pulpal diagnosis and periapical diagnosis of chronic apical periodontitis were made. The patient was given all available options (extraction and implant, extraction and bridge, extraction only, and endodontic therapy and placement of a new crown [due to the ill fitting existing crown]). The patient opted for endodontic therapy and a new crown.
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| Figure 1a. The preoperative radiograph of the highlighted case treated with controlled memory (CM) Ni-Ti (MounceEndo). | Figure 1b. The postoperative radiograph of the highlighted case treated with CM Ni-Ti. |
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| Figure 2. Mani Medium sized K-file. Medium sizes are 12, 17, 22, 27, 32, and 37. | Figure 3. The NSK ER-10 reciprocating handpiece (MounceEndo). |
Preoperative Case Evaluation
The goal of shaping procedures is to prepare a funnel with narrowing cross-sectional diameters of an appropriate taper and master apical diameter, leaving the canal and apical constriction in its original position without iatrogenic misadventure. In addition to the evaluation above, the case was assessed preoperatively for iatrogenic risk as well as a determination of the optimal treatment protocol to achieve the goals above.
The mesial root had moderate curvature and was radiographically calcified in the apical half. The pulp chamber was moderately calcified with a dramatic cervical dentinal triangle (CDT) at the mesial. Steps described below were taken to fully uncover the canal orifices and remove the CDT prior to insertion of hand files to avoid blockage and achieve patency. The fluting present on the distal aspect of the mesial root cautioned against preparing excessive taper in order to avoid strip perforation. A final taper of .06 and minimum apical diameter of 30 was sought preoperatively. It was assumed preoperatively that No. 30 had a minimum of 4 canals and possibly 6 (a third mesial canal and possibly a third distal canal).
The series of treatment steps used for this tooth (described below) is universally applicable to virtually all of the existing Ni-Ti instrumentation systems.
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| Figure 4. The CM MounceFile (MF) Assorted Pack containing, from left to right, the .08/25, .06/25, .04/25, .03/25, .02/25, and .03/30. | Figure 5. The Typhoon (TP) Crown Down Infinite Flex 4-pack: 35/.06, 30/.04, 25/.06, 20/.04 (CLINICIAN’S CHOICE). |
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| Figure 6. The E&Q Master cordless obturation device (Meta Biomed). |
Prior to access, the length of the tooth was estimated from the preoperative radiograph and an estimated working length (EWL) obtained. In this clinical case, the EWL was 22 mm in both roots.
Clinical Protocol: Instrumentation
The patient was anesthetized utilizing the STA Wand (Aseptico) via the placement of 2 inferior alveolar blocks (lidocaine 2% with 1:100,000 epinephrine) and one buccal infiltration with (articaine 4%, 1:200,000 epinephrine). After rubber dam placement and sealing of the rubber dam with OraSeal (Ultradent Products), straight-line access was obtained using Mani round burs (No. 4 FG) and diamonds (TR-13). After evacuation of all calcification from the pulp chamber with a No. 6 surgical length round bur under the microscope (Global Surgical), 4 canals were visualized. A viscous ethylenediaminetetraacetic acid (EDTA) gel (MD-ChelCream [Meta Biomed]) was placed after evacuation of the pulp chamber contents and prior to insertion of any hand files for lubrication and to emulsify the pulp and minimize blockage.
The isthmuses between the MB and ML, and DB and DL canals were explored with ultrasonics (Bonart P6 unit) and the TUFI No. 3 (San Diego Swiss) and Tun E1 (taper tip with diamond) ultrasonic tips (Engineered Endodontics). No additional canals were revealed.
The author routinely uses MF; alternatively, using CM technology, this case could have been treated with TP. For practical purposes, TP and MF are virtually identical with the exception that TP is triangular and MFs are square in cross section.
The .08/25 MF (orifice opener) was inserted into the coronal third to the point of resistance and brushed up and away from the furcation to remove the CDT and create a pathway for the insertion of subsequent canal negotiating hand files. Shaping the orifice in this manner allows large volumes of irrigant to be entered into the canal early in the shaping process, facilitating enhanced debris removal and reducing blockage.
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| Figures 7 to 9. Clinical cases performed with CM MF (courtesy of Dr. Mike Stevens, Billings, Mont). |
All CM file insertion was performed in the presence of sodium hypochlorite (NaOCl). The first hand file inserted in an effort to gain apical patency was a precurved Mani No. 6 hand K-file. Insertion was slow, passive, and intended to ascertain the curvature, calcification, and complexity of the canal.
Once the No. 6 stainless Mani hand K-file reached the EWL (apical patency was gained), the canal was enlarged slightly using a Mani No. 8 hand K-file. When the No. 8 Mani K-file reached the EWL, the iRoot (Meta Biomed) was used to obtain the first electronic determination of true working length (TWL). The length was verified with the Elements Diagnostic Unit (SybronEndo).
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| Figures 10 and 11. Clinical cases performed with CM TP instruments (courtesy of Dr. Peter Tawil, Chapel Hill, NC). |
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| Figure 12. Clinical cases performed with CM TP instruments (courtesy of Dr. Garrett Guess, San Diego, Calif). |
Sequentially, Nos. 10, 12 (medium size), 15, 17 (medium size), and 20 Mani K-files were reciprocated with the NSK ER-10 (MounceEndo) reciprocating handpiece to prepare the glide path. The canal was irrigated with NaOCl between each hand file size. When the No. 20 K file spun freely at the TWL, the canal was again measured electronically to verify the length (Figures 2 and 3).
While many equally valid Ni-Ti file systems could have been used in this case (including CM TP Infinite Flex), the MF Assorted pack (.06/25, .04/25, .03/25, .02/25) was inserted successively (using 500 to 700 rpm, 3 g-cm torque control powered by the AEU 27A endodontic motor [MounceEndo]) from larger tapers to smaller (crown down) until an .06 taper was prepared. Specifically, in this case, the .06/25 was inserted first, followed by the .04/25, .03/25, and .02/25, and the sequence repeated until the .06/25 reached the TWL. Alternatively, using TP, the Infinite Flex Crown Down pack (35/.06, 30/.04 , 25/.06, 20/.04) could have been used in the same manner to achieve the same result (Figures 4 and 5).
Once the basic shape of the canal was prepared as above, the master apical diameter was prepared using the .03/30 instrument from the MF Assorted pack. Alternatively, TP has larger apical sizes available for the same purpose.
After canal shaping to the above dimensions, .06/30, the canal was again copiously irrigated alternatively with NaOCl and liquid 17% EDTA (MD-Cleanser 17% EDTA [Meta Biomed]). The irrigation was activated using the .04/25, 21-mm Finishing Files (Engineered Endodontics).
Obturation
A .06/30 master cone coated with Adseal (Meta Biomed) was inserted to the TWL and the case obturated with the vertical compaction of warm gutta-percha via the E&Q Master cordless obturation device and Adseal Root Canal Sealer (both from Meta Biomed) (Figure 6).
After obturation, under the surgical microscope (Global Surgical), the preparation was microetched and the tooth built up under the rubber dam with Rock Core (both from Danville Materials). The patient was returned to the general practitioner for placement of the final crown restoration as well as the replacement of the existing crown on tooth No. 29. Additional clinical cases utilizing CM Ni-Ti are included in Figures 7 to 12 for comparison.
IN SUMMARY
This article has reviewed the literature and also demonstrated the clinical use of CM options for canal preparation in endodontics. Emphasis has been placed on sound clinical principles including straight-line access, achievement and maintenance of apical patency, use of a crown-down sequence, and avoidance of iatrogenic events.
Editor’s Note: To obtain the current literature file on CM technology mentioned in the article, please contact Dr. Mounce at richardmounce@mounceendo.com.
Dr. Mounce earned his DDS from Northwestern University in 1985. He completed his endodontics residency program at Oregon Health & Science University in 1991. He has lectured and written globally in the specialty and welcomes your questions and comments. He can be reached on Twitter: @MounceEndo, or via the website mounceendo.com.
Disclosure: Dr. Mounce is a paid consultant for Mani (with a contract) and is a vendor for Mani, Meta Biomed, and Aseptico. He has accepted honoraria in the past from Meta Biomed but is not contracted with them. He owns MounceEndo, LLC, marketing the rotary Ni-Ti MounceFile in Controlled Memory and Standard NiTi.
