key: cord-0934759-ed5jx5cd
authors: Hatzke, Matthew W.; Daigle, Francesca C.; Augsburger, Robert A.; Kesterke, Matthew J.; Jalali, Poorya
title: Retrograde Instrumentation of Surgically Resected Roots Using Controlled Memory Files: A Human Cadaver Study
date: 2020-06-15
journal: J Endod
DOI: 10.1016/j.joen.2020.05.023
sha: 98e4897f897dc42c8dc56b1a8a31b8e853315faa
doc_id: 934759
cord_uid: ed5jx5cd

INTRODUCTION: The purpose of this study is to evaluate the amount of residual obturation material of retroinstrumented surgically resected roots using controlled memory (CM) files and to evaluate the incidence of adverse treatment outcomes. METHODS: Thirty maxillary anterior teeth in human cadavers were selected and non-surgical root canal treatment was performed on these teeth. A standardized 4-mm osteotomy and a 3-mm root resection with as close to a zero-degree bevel as possible was made on each tooth. A microsurgical diamond tip was used to create a 1-2 mm starting point for each retropreparation. A 25/06 and 30/06 VTaper 2H (SS White, Lakewood, NJ) were bent at a about 90-degree angle to mimic the clinical and anatomical restrictions and used to create a retropreparation to a depth of 14-mm. Micro-CT scans were taken and analyzed for volume and percentage of residual obturation material at 5- and 10-mm. Additionally, the incidence of instrument separation and crack and ledge formation in the teeth were recorded. RESULTS: The median volume of residual obturation at 5- and 10-mm was 0.18 mm(3) (interquartile range of 0.36 mm(3)), and 1.97 mm(3) (interquartile range of 1.99 mm(3)) respectively. The overall incidence of file separation during retropreparation was 13.33% (4/30). Among the cases analyzed with micro-CT, none showed crack or ledge formation. CONCLUSIONS: Retroinstrumentation of surgically resected roots using controlled memory files cleans the canal effectively with relatively low adverse treatment outcomes. This novel technique, while limited in application, is a safe and effective way to achieve a deep, clean retropreparation.

Endodontic surgery is a viable treatment option to preserve the natural dentition. While every step in the procedure is important, one of the main challenges involved in surgical endodontics is the retrograde instrumentation of the root canal system. This critical step may affect the outcome of surgical treatment because the most common reason for nonsurgical and surgical endodontic failure is the persistence of intraradicular bacteria and their byproducts 1, 2 . The goal of retrograde instrumentation is to remove the obturation material, infected tissues, and irritants from the root canal system, and create a space that can be properly sealed 3 . Anything less undermines the biologic basis for successful endodontic treatment 4 . Throughout history, various retrograde instrumentation methods have been introduced and evaluated. Traditionally, the root end preparation was achieved by use of surgical burs in a handpiece. However, this technique has disadvantages including inadequate canal preparation, limited access, and risk of perforation of the palatal wall 5 . Additionally, the osteotomy may need to be enlarged greatly to allow sufficient access for the handpiece and bur.

One of the advancements in modern endodontic surgery was the introduction of surgical ultrasonic tips which allowed for more centered and deeper root end preparations. However, numerous studies have reported an increased incidence of cracks on resected roots after ultrasonic instrumentation [6] [7] [8] . Additionally, a majority of the ultrasonic tips can penetrate to only a depth of 3 mm into the canal. Indications for longer retropreparations include grossly and inadequately cleaned and obturated canals and missed canals. A recent randomized controlled trial evaluating the outcome of endodontic microsurgery revealed a 9 times greater chance of failure if the quality of the root filling was inadequate 9 . Although ultrasonic tips can be as long as 9 mm, they require a larger osteotomy or preparation of a key hole to accommodate the longer tip 10 . However, the diameter of an ideal osteotomy is recommended to be limited to 4mm 10 , and the removal of healthy facial or buccal bone may result in slower and incomplete healing 11 . Moreover, ultrasonic tips are very efficient in cutting dentin, and if not used carefully can result in root perforations, off axis preparation, and decreased residual dentin thickness. Therefore, there is a need for alternative techniques that allow for safe, deep retropreparations of the canal while preserving as much bone as possible.

Retrograde instrumentation with the use of hand files has been demonstrated, but only in select cases with sufficient bone destruction and access not restricted by anatomical factors 12 . Improvements in metallurgy and instrument design have provided an opportunity for the clinicians to explore innovative treatment options. Recently, rotary instruments made from controlled memory nickel-titanium (NiTi) alloys have been introduced into the market. These rotary files, unlike the traditional NiTi file systems, can be bent and retain their controlled memory 13 . This new technology has made the files very flexible and resistant to cyclic fatigue. In addition, the properties of these files may decrease the risk of some instrumentation errors such as transportation, ledging, or root perforation 14 . To the best of our knowledge, there is no study in the literature evaluating the feasibility of using rotary files in endodontic surgery. The purpose of this study is to evaluate the amount of residual obturation material of retroinstrumented surgically resected roots using controlled memory files and to evaluate the incidence of adverse treatment outcomes including file separation, root fracture/cracks, and root perforation.

Thirty maxillary anterior teeth within the maxillae of embalmed cadaver heads were used to maximize the replication of the clinical scenario. The inclusion criteria consisted of: intact teeth with minimal dental caries and/or restorations, absence of a periapical radiolucency, root length of at least 13 mm, and entire root within the maxillae. All cadaveric specimens were obtained through the Texas A&M College of Dentistry Anatomical Gift Program.

Preoperative radiographs were taken on each sample, with working length was established at 1 mm from the radiographic apex. Teeth were instrumented with serial preparation to a size 25/04. Copious irrigation with 3% NaOCl was used throughout and canals were dried with paper points. After drying the canals, the teeth were obturated with gutta percha and a resin sealer (2Seal easymiX, Roydent, Johnson City TN). Post-operative radiographs were taken from two angles to check for the presence of a dense and homogenous obturation with no radiographic voids. No restoration was placed in the access cavity. The samples were then stored in 100% humidity for 7 days to allow for complete setting of the sealer.

A soft tissue flap was raised with a periosteal elevator to mimic the clinical scenario. A standardized 4-mm osteotomy was made with a #4 round bur. Next, a 3-mm root resection with as close to a zero-degree bevel as possible was made with a Lindemann bur (Meisinger, Neuss, Germany) ( Figure 1 ). Post-operative radiographs were taken to evaluate the root resection and adjustments were made as necessary (Figure 1 , Left). A microsurgical ultrasonic diamond tip (Obtura Spartan, Earth City, MO) was used to make 1-2 mm starting point for the retropreparation. A new 25/06 and 30/06 VTaper 2H (SS White, Lakewood, NJ) were bent at about 90-degree angle to mimic the clinical and anatomical restrictions ( Figure 2 ). The two files were used in an alternating fashion to advance down the canal incrementally. The file was run at a speed of 600 rpm and 440 g-cm on a ProMark Endo Motor (ProMark, Dentsply Tulsa Dental). The file was advanced incrementally and cleaned with a sponge after each insertion. The file was first advanced to a depth of 10-mm, and if no adverse event occurred, the file was advanced to a depth of 14-mm. Post-operative radiographs were taken to have a 2-dimensional evaluation of the retropreparation (Figure 1 , Right). Copious irrigation with sterile saline was used to remove debris following retropreparation.

After retropreparation, each of the samples was scanned separately using the Micro-CT system (µCT 35; Scanco Medical, Bassersdorf, Switzerland). The scan settings were as follows: voxel size of 20 µm, 70 kV, 114 µA. The experimental teeth were removed atraumatically from the maxillae of the embalmed cadavers by sectioning through the surrounding bone. Teeth were subjected to micro-computed tomographic scans (micro-CT). Analysis of the percentage of remaining obturation material was calculated using Mimics Innovation Suite (v21, Materialise, Belgium).

Using threshold and region growing tools, two masks (residual obturation and empty canal) were created at 5-mm and 10-mm from the apex, and their corresponding volumes were calculated. The percentage of the residual obturation was calculated at each level (5-mm and 10-mm) using this formula: volume of residual obturation/ volume of residual obturation + volume of empty canal ( Figure 3 ).

Additionally, crack formation and ledge formation were assessed with this software by viewing the coronal, sagittal, and transaxial sections of each sample. Only the samples without file separation were scanned and analyzed with the micro-CT.

Only the samples in which file separation did not occur (26/30) were subject to micro-CT scans and analysis. Additionally, 2 samples not included due to poor image quality. In total, 24 samples were scanned and analyzed.

Among the 24 scanned specimens, volumetric analysis revealed a median percentage of residual obturation material to be 6.65% (interquartile range of 11.54%) and 28.41% (interquartile range of 28.47%) at 5-mm and 10-mm respectively (Table 1 ).

In terms of absolute volume of residual obturation material in mm 3 following the experimental protocol, the median volume and interquartile range at 5-mm was 0.18 mm 3 and 0.36 mm 3 , respectively. At 10-mm, the median volume was 1.97 mm 3 and the interquartile range was 1.99 mm 3 .

Among the total 30 specimens, the overall incidence of file separation during retropreparation was 13.33% (4/30). Three of the files separated at the junction of the cutting flutes and shank and one where a 4 mm segment of the file separated ( Figure 4 ). All 4 file separations (100%) were retrievable. Three files separated at the junctions of the cutting flutes and shank and were retrieved using a hemostat. One separated at 4 mm, which was irrigated out. (Table 2 ). In evaluating the 24 scanned samples, the incidence of crack formation was 0% (0/24) and the incidence of ledge formation was 0% (0/24) ( Table 2 ).

The goal of this study was to evaluate the amount of residual obturation material of retroinstrumented surgically resected roots using controlled memory files and to evaluate the incidence of adverse treatment outcomes. To the best of our knowledge, this is the first study to look at the feasibility of using rotary files in endodontic surgery. The rationale for the introduction of a novel retrograde instrumentation technique is biological. It is well documented that pathogenic bacteria and their byproducts are the main cause of endodontic failure and persistence of periapical disease 15 . Additionally, numerous studies have evaluated the efficacy of various techniques for gutta percha and obturation material removal during non-surgical retreatment procedures. The overwhelming consensus is that no instrumentation system or technique can effectively remove all obturation material [16] [17] [18] [19] [20] . The inability to completely remove all obturation material provides a potential etiology of future failure because bacteria and biofilm may persist in these untouched areas 21 .

With the high success rate of endodontic microsurgery, is there room for improvement? A recent long-term outcome study of endodontic surgery revealed a healing rate of 91.6% at 1year and a 91.4% healed rate at 5-years, respectively. However, at 10-years this rate dropped significantly to 81.5% 22 . Furthermore, von Arx et al 22 reported that maxillary incisors were one of 3 tooth groups that contributed to virtually all failures, with maxillary premolars and mandibular molars being the other tooth groups included in the failures. What could be contributing to these failures? Failure to thoroughly clean and debride the root canal system are the most significant potential reasons for failure following endodontic surgery 23 . Therefore, the proposed technique has a biological rationale. The success rate for surgery increases when nonsurgical orthograde retreatment is completed prior to the apical surgery 24 . This novel technique provides an avenue to effectively retreat the canal system in a retrograde fashion, removing more of the etiological factors of failure than a 3-mm retropreparation. Our hope is that this technique will contribute to an even higher and longer-term success rate in endodontic surgery. Therefore, the primary outcome measurement was the volume and percentage of residual obturation material in the canal following this novel technique. The results showed a median volume of residual obturation material of 0.18 mm 3 and 1.97 mm 3 at 5-mm and 10-mm, respectively. Additionally, the median percentage of residual obturation was 6.65% and 28.41% at 5-and 10-mm, respectively. Micro-CT analysis reported a 0% incidence of crack or ledge formation. Because this study represents a novel technique there is no direct comparison in terms of previous studies, methodologies, and results.

In traditional non-surgical retreatment, every attempt is made to remove as much of the previous obturation material as possible. A technique for achieving this objective is to use a rotary endodontic file that is larger than the existing preparation size 25 . However, this concept may not be applicable when rotary files are used for retropreparation. When the file is used in this technique, it will inevitably remove less material as the file progresses coronally because of the reverse taper of the file relative to the previously prepared canal. This explains this study's finding that more material remained at 10-mm from the apex compared with 5-mm from the apex. The potential drawback of enlarging the canal with rotary instruments is the increased risk of crack initiation or propagation 26 . While it has been known that no technique can completely remove the remaining obturation material [16] [17] [18] [19] [20] , every attempt should be made to clean the canal as well as possible to remove potential etiological factors for treatment failure.

The incidence of instrument separation was 13.33% (4/30) with all being retrievable using a hemostat. In orthograde endodontics treatment, a review of the literature indicates an incidence range of 1.3% to 10.0% 27 . However, in a retrospective study, of the 28 separated rotary nickel titanium instruments, 18 separated in retreatment cases whereas 10 separated during initial treatment 27 . Therefore, the chance of file separation maybe higher when removing existing filling materials. In this study, 2 separations occurred in lateral incisors and 2 in canines. The palatally inclined anatomic position of these teeth increased the amount of stress on these files and likely contributed to the separation. While the incidence of separation in this study is higher than previously reported file separation in orthograde endodontic treatment, the mere incidence of file separation alone may not be an outcome predictor. In this study, all the separated instruments were easily retrievable with a hemostat and therefore unlikely to affect the treatment outcome. Additionally, anecdotal evidence shows a relatively high incidence of ultrasonic instrument separation during retropreparation, which may be comparable to the incidence of file separation reported in this study.

The micro-CT analysis of this study revealed a 0% incidence of crack or ledge formation. This provides a potentially advantageous outcome when comparing controlled memory endodontic rotary instrumentation versus ultrasonic instruments for use in retroinstrumentation. Ultrasonic instruments have been shown to have an increased incidence of crack propagation following retropreparation in endodontic surgery 8, 28, 29 . The experimental procedure was performed with the teeth within the cadaver jaws, therefore, a true evaluation of transportation was not possible in this study because it was not feasible to take pre-operative micro-CT scans. Transportation maybe more likely with ultrasonic tips because they are very efficient in cutting dentin. It is reasonable to assume that ultrasonic tips, especially the longer instruments, could very quickly get off axis and may result in procedural errors.

While this study is the first to propose this novel technique, there are limitations within our study. First, a pre-operative scan was not possible because the experiment was designed to mimic a clinical scenario as much as possible. Second, there was no control group. It was not meaningful to have a control group because no other technique was similar to this. Third, this technique is only feasible on anterior teeth due to anatomical restrictions. Fourth, further studies are needed to evaluate the obturation and sealing ability of this novel retropreparation design. We discussed the idea of a reverse taper that this file creates relative to original canal morphology. We propose that future studies should evaluate the sealing ability of various techniques: a gutta percha cone and sealer, bioceramic material and sealer, and/or a combination of both.

Additionally, we wanted to comment further on 2 samples that we were unable include in the micro-CT analysis. One of the scans was blurry and appears to have been physically interrupted during the process and the other did not include the entire tooth. Multiple attempts were made to have these samples re-scanned. However, these attempts were unsuccessful and the 2020 COVID-19 pandemic closed access to the scanner. The decision was made to move forward with the data from the 24 micro-CT scans we had.

Retroinstrumentation of surgically resected roots using controlled memory files is able to clean the canal effectively with relatively low adverse treatment outcomes. This novel technique, while limited in application, is a safe and effective way to achieve a deep, clean retropreparation. 

A novel technique using controlled memory files for retrograde instrumentation in endodontic microsurgery maybe a viable technique that can safely and effectively debride the canal system and can achieve deep, clean retropreparations.

Aetiology of root canal treatment failure: why well-treated teeth can fail

A study of failures after endodontic surgery by radiographic, histologic and stereomicroscopic methods

Ultrasonic End Preparation

Surgical endodontics

Ultrasonics in endodontic surgery: a review of the literature

Ultrasonic root-end preparation Part 2, Microleakage of EBA root-end fillings

Effects of ultrasonic root-end cavity preparation on the root apex. Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Evaluation of cracks associated with ultrasonic root-end preparation

Outcome of endodontic microsurgery using mineral trioxide aggregate or Root Repair Material as root-end filling material: a randomized controlled trial with cone-beam computed tomographic evaluation

Microsurgery in Endodontics, 1 st

Correlation of bone defect dimensions with healing outcome one year after apical surgery

Retrograde instrumentation and obturation of the root canal space

Metallurgical characterization of controlled memory wire nickel-titanium rotary instruments

Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments

Coronal leakage as a cause of failure in root-canal therapy: a review

Micro-computed Tomographic Assessment of the Residual Filling Volume, Apical Transportation, and Crack Formation after Retreatment with Reciproc and Reciproc Blue Systems in Curved Root Canals

Efficacy of ProTaper NEXT compared with Reciproc in removing obturation material from severely curved root canals: a micro-computed tomography study

Removal of root canal fillings in curved canals using either reciprocating single-or rotary multiinstrument systems and a supplementary step with the XP-Endo Finisher

Comparison of hand and rotary instrumentation for removing gutta-percha from previously treated curved root canals: a microcomputed tomography study

Effectiveness of Gutta-percha/Sealer Removal during Retreatment of Extracted Human Molars Using the GentleWave System

What happens to unprepared root canal walls: a correlative analysis using micro-computed tomography and histology/scanning electron microscopy

A 10-year follow-up study of 119 teeth treated with apical surgery and root-end filling with mineral trioxide aggregate

A multivariate analysis of the influence of various factors upon healing after endodontic surgery

Treatment outcome in endodontics-The Toronto Study. Phases I and II: apical surgery

Comparison of the effectiveness of various rotary and reciprocating systems with different surface treatments to remove gutta-percha and an epoxy resin-based sealer from straight root canals

Incidence of apical crack initiation and propagation during the removal of root canal filling material with ProTaper and Mtwo rotary nickel-titanium retreatment instruments and hand files

Prevalence and management of instrument fracture in the postgraduate endodontic program at the Dental School of Athens: a five-year retrospective clinical study

Ultrasonic root-end preparation Part 2, Microleakage of EBA root-end fillings

Effects of ultrasonic root-end preparation on microcrack formation and leakage