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

Comparative Evaluation of Three Access Cavity Preparation Techniques on Root Canal Instrumentation Using Micro-CT: An In Vitro Study

Background Access cavity preparation is a crucial step in nonsurgical root canal treatment. Recent advancements in access cavity designs focus on preserving maximum tooth structure while ensuring sufficient access to canal orifices for effective cleaning and shaping, resulting in minimally invasive procedures. However, there is limited information on the impact of three-dimensional (3D)-guided access cavity preparation in molars. A literature review found no prior studies comparing the effects of various access cavity preparation techniques on apical transportation, untouched surfaces, and debris formation within the canal. Objective The objective of this study is to compare and evaluate the effects of three different access cavity techniques on apical transportation, untouched surfaces, and debris formation within the root canal. Material and methods Thirty extracted permanent mandibular first molars were selected and randomly assigned to three groups for this study: Group I received 3D-printed static guided cavity preparation, Group II underwent conservative access cavity preparation, and Group III was subjected to traditional access cavity (TAC) preparation. The mesial canals in all samples were cleaned and shaped using TruNatomy files. Preoperative and postoperative micro-CT imaging was performed on each sample to assess the effects of the different access cavity preparation techniques on apical transportation, untouched surfaces, and debris formation within the root canal. Results The study found that Group I, which used 3D-printed static guided cavity preparation, exhibited significantly less apical transportation compared to Groups II and III, with mean differences of -0.1677 and -0.2079, respectively. Debris accumulation was similar across all groups, with mean values of 0.928 ± 0.824 for Group I, 0.751 ± 0.495 for Group II, and 0.938 ± 0.681 for Group III, indicating no significant impact of cavity preparation type on debris levels. For untouched canal surfaces, Group III (TAC preparation) had the fewest untouched surfaces, with mean differences of 3.0380 and 3.9020 compared to Groups II and I, respectively. Conclusions While TAC preparation reduces substantial tooth structure, it shows higher instrumentation efficacy and better cleaning of the root canal system. However, in complex cases where tooth structure preservation is crucial, guided access cavity preparation provides an effective balance between structural conservation and adequate canal access. This approach offers a tailored solution, optimizing treatment outcomes based on the specific clinical scenario.

Influence of sealer and supplementary approach on filling material removal during endodontic retreatment

Both root canal sealer-based and supplementary protocols may influence removal of filling material during endodontic retreatment. Mesial root canals of extracted mandibular molars were prepared using HyFlex EDM 25/.08, and filled with a calcium silicate sealer (Bio-C Sealer), or an epoxy resin (AH Plus), using the single cone technique (n = 12). Retreatment was performed using ProDesign Logic (PDL) RT and PDL 35/.05. The specimens were randomly divided into two experimental groups (n = 12), and the sealers were distributed similarly. A supplementary protocol was performed with PDL 50/.01 or XP-endo Finisher. Root canal transportation and volume, in addition to the remaining filling material percentage were evaluated using high-resolution (5 µm voxel size) micro-CT. Statistical analysis was performed using t-tests (α = 0.05). Root canals filled with AH Plus presented high residual filling material (p < 0.05). Both protocols decreased residual volume of filling material in the apical third (p < 0.05). PDL 50/.01 increased the apical root canal volume (p < 0.05). No difference was observed between the systems regarding canal transportation (p > 0.05). In conclusion, AH Plus is more difficult to remove from the apical third than Bio-C Sealer. PDL 50/.01 and XP-endo Finisher enabled greater removal of filling materials in the apical third, in the retreatment of curved root canals, without promoting apical transport.

Retreatment Strategies for Cases Containing Calcium Silicate-Based Root Canal Sealers: A Comprehensive Review

This review explores the field of retreatment strategies for cases filled with calcium silicate-based root canal sealers. Since the introduction of calcium silicate-based materials in dentistry, calcium silicate-based root canal sealers have become popular among dentists because of their biocompatibility, bioactivity, and sealing ability. Therefore, effective retreatment strategies are indispensable. This article aims to identify the challenges associated with the removal of calcium silicate-based sealers themselves and removal of gutta-percha with the sealers during retreatment, evaluate current techniques and materials, and provide future directions for research in this field. Regarding the strategies of removal of root canal sealers, calcium silicate-based sealers are still relatively new materials for clinicians compared with traditional sealers such as epoxy- or eugenol-based sealers. First, no clinically established solvents have been reported. Second, calcium silicate-based sealers are currently utilized by clinicians in either the cold sealer-based technique or the warm vertical condensation technique. Third, the setting process of calcium silicate-based sealers generates byproducts, primarily calcium hydroxide and secondarily hydroxyapatite, that could interact with dentine. Lastly, there is a lack of clinical studies evaluating the efficacy of retreatment protocols for teeth filled with calcium silicate-based sealers. Therefore, it is important to investigate the chemo-mechanical properties of calcium silicate-based sealers themselves and their reactions to solvents and/or mechanical instruments and identify the interfacial properties of calcium silicate-based sealers with respect to dentine and gutta-percha. In addition, researchers in the clinical field need to actively gather and report data on retreatments of teeth filled with calcium silicate-based sealers.

The Effect of Different Obturation Techniques Using Different Root Canal Sealers on the Residual Filling Material After Retreatment Procedures

BACKGROUND

This study aimed to compare the effect of different obturation techniques with root canal sealers on the residual filling material after retreatment using SEM.

MATERIAL AND METHOD

Sixty (60) single rooted mandibular premolars were selected and instrumented with rotary files using the Mtwo system up to file size 30/.05 taper. The samples were randomly divided to two groups based on the type of sealer and three sub-groups (n=10) based on the obturating technique used. The root fillings were removed using the PTUR system files and the specimens were longitudinally sectioned while digital images were obtained from the root canals with SEM. The time required to reach working lenght were recorded.

RESULTS

There was no difference in terms of the smear score when comparing both sealer and obturation technique groups in the apical third. Smear scores were significantly affected by the type of sealer and obturation technique in the medium and coronal thirds of root canals (p<0.05). Higher smear scores were obtained with GFB than AH Plus (p<0.05). The time required to reach working length with GFB was longer than AH Plus (p<0.05).

CONCLUSION

Residual filling material was observed in all samples, regardless of the root canal sealer or the obturation technique used. There was a significantly lower smear scores in the AH Plus groups as compared to the GFB.

Efficiency and complications in root canal retreatment using nickel titanium rotary file with continuous rotation, reciprocating, or adaptive motion in curved root canals: a laboratory investigation

BACKGROUND

It is currently unknown whether rotary file motion affects the best outcome of root canal retreatment. This experimental study compared the efficacy, efficiency, and complications of single-use NiTi rotary files using continuous rotation, reciprocating, and adaptive motions in root canal filling removal in curved root canals. Reciproc blue R25 was used with reciprocating motion (RB), VDW.ROTATE retreatment files with continuous rotation (VR), and ProTaper NEXT X2 with continuous rotation (PTNc) or adaptive motion (PTNa).

METHODS

Forty mesial root canals of extracted mandibular first and second molars with an angle of curvature between 20°-40° and a radius of curvature between 5 and 10 mm were collected. The specimens were instrumented and obturated with gutta-percha and AH Plus sealer using the continuous wave of condensation technique. The specimens were randomly divided into 4 retreatment groups (n = 10), RB, VR, PTNc, and PTNa. The percentage of root canal filling removal in each group was analyzed using Micro-Computed Tomography (µCT). The motor running time, total time, root canal complication, and instrument complication were recorded and statistically analyzed (p-value < 0.05).

RESULTS

The pre-operative root canal curvature and root canal filling volume were comparable among groups. The percentage of root canal filling removal from the whole canal in the PTNc, RB, PTNa, and VR group was 98%, 96%, 95%, and 93%, respectively. A significant difference was observed between the PTNc and VR groups for the whole canal and the apical-third part. The motor running time and total time were significantly different between the groups. Instrument fracture was observed at 40% in the VR and 20% in the PTNa group, but none in the RB and PTNc groups.

CONCLUSIONS

The ProTaper NEXT X2 with continuous rotation and RB files can be used with high efficacy and efficiency in curved root canal retreatment. Continuous rotation is more efficacious and efficient than adaptive motion when using the NiTi rotary file. Single file retreatment can be used in small canals with high efficacy, cost-effectiveness, and less time consumption.

The supplementary use of XP-endo Finisher R after Reciproc enhances the removal of a bioceramic sealer in oval root canals

This study compared the performance of Reciproc and Reciproc Blue endodontic files in retreatment time and re-establishment of apical patency, plus removal of a bioceramic sealer from the canal surface with the supplementary use of the XP-endo Finisher R. Following preparation, slightly curved oval root canals in mandibular incisors were filled using a corresponding gutta-percha point and a bioceramic sealer. Apical patency achievement was assessed and the time required to reach the original working length was recorded. The samples were split longitudinally and were photographed to assess the material remaining on the canal walls. No significant differences were observed regarding patency achievement or retreatment times when comparing Reciproc and Reciproc Blue. Significant less material remained on the canal walls when Reciproc was followed by XP-endo compared with Reciproc alone, and when the data for Reciproc and Reciproc Blue were pooled.

Effect of Additional Apical Preparation on Retreatment of Curved Root Canals Filled with Different Sealers

OBJECTIVE

 This study assessed the influence of additional apical preparation on material removal during retreatment of curved root canals filled with different sealers.

MATERIALS AND METHODS

 Twelve mesial roots of mandibular molars with two separate canals and curvature between 25 and 35 degrees were selected. The working length was established 1-mm short of the apical foramen, and all the root canals were prepared using ProDesign R (PDR) 25/0.06. After preparation, the root canals were divided in two groups (n = 12) and filled by continuous wave condensation technique with NeoMTA Plus or AH Plus. All the root canals were retreated using rotary ProDesign Logic RT 25/0.08, reciprocating PDR 25/0.06 and apical preparation with PDR 35/0.05. Additional apical preparation was performed with ProDesign Logic (PDL) 50/0.01. The samples were scanned using a Skycan 1176 micro-computed tomography (micro-CT), voxel size 8.74 µm, before and after the retreatment procedures. Percentages of remaining filling material were evaluated.

STATISTICAL ANALYSIS

 The data were submitted to paired and unpaired t-tests (α = 0.05).

RESULTS

 Percentage of remaining filling material was similar between the root canals filled with NeoMTA Plus or AH Plus sealer after retreatment using PDR 35/0.05, and after additional apical preparation using PDL 50/0.01 (p > 0.05). However, PDL 50/0.01 significantly decreased the percentage of remaining filling material in the apical third after the additional apical preparation for both sealers (p < 0.05).

CONCLUSION

 NeoMTA Plus or AH Plus did not influence the retreatment of curved root canals. ProDesign Logic 50/0.01 promoted greater filling material removal in the apical third.

Apical transportation using Mtwo or Reciproc retreatment systems in severely curved canals: a micro-computed tomographic study

OBJECTIVE

To assess apical root canal transportation using Mtwo or Reciproc during retreatment of severely curved canals, using a multi-analytical approach.

METHODS

Forty mesial canals from mandibular molars (Vertucci type IV) were evaluated before and after endodontic retreatment to compare apical transportation with Mtwo retreatment or Reciproc. The systems were used on the same root but alternating the mesial canals. The analyses were performed by micro-computed tomography. Four evaluations were performed: (a) longitudinal transportation, (b) horizontal transportation, (c) variation in the angle of curvature of the canal, and (d) canal-root width ratio. Horizontal transportation and canal-root width ratio were evaluated in 1-, 3-, and 5-mm levels.

RESULTS

Longitudinal transportation occurred in all samples, with a mean of 0.13 mm for Mtwo and 0.17 mm for Reciproc. Horizontal transportation increased as distant from the apex was the evaluated level, in mean. However, the transport was not observed in all samples. The mean angle of curvature was 4.16 for Mtwo and 3.03 for Reciproc. Canal-root width decreased as distant from the apex was the evaluated level. No significant differences were observed considering all tested variables, independently of the retreatment system or evaluated level (p > 0.05).

CONCLUSION

Mtwo retreatment and Reciproc presented similar apical transportation (horizontal or vertical).

CLINICAL RELEVANCE

Both Mtwo retreatment and Reciproc systems could be considered safe regarding apical transportation.

Impact of minimally invasive endodontics procedures on the development of dentinal microcracks

INTRODUCTION

To evaluate the impact of root canal preparation in teeth with ultraconservative access cavities (UltraAC) on the development of dentinal microcracks using a non-destructive longitudinal micro-CT imaging experimental model. Root canal preparation in teeth with traditional access cavities (TradAC) was used as control.

METHODS

Forty mandibular molars were scanned in a micro-CT device, anatomically matched, and distributed into 4 groups according to the type of access cavity and instrumentation system: traditional/Reciproc (TradAC/RC); traditional/XP-endo Shaper (TradAC/XP); ultraconservative/Reciproc (UltraAC/RC) and ultraconservative/XP-endo Shaper (UltraAC/XP). After root canal preparation, the teeth were rescanned. After reconstruction and co-registration procedures, the images were screened from the furcation level to the apex to identify the presence of dentinal microcracks.

RESULTS

From a total of 15340 cross-section images, 19.65% (3014 slices) had some dentinal microcrack. The qualitative analysis demonstrated the presence of some dentinal microcrack in 11%, 33%, 19%, and 15% of the images of cross-sections in TradAC/RC, TradAC/XP, UltraAC/RC, and UltraAC/XP groups, respectively. All dentinal microcracks observed after root canal preparation were already present in the corresponding images before canal instrumentation. Therefore, no new microcracks were detected, regardless of the access cavity and root canal instrumentation system.

CONCLUSIONS

Root canal preparation with Reciproc or XP-Endo Shaper under traditional or ultraconservative access cavities did not create dentinal microcracks in extracted mandibular molars.

Sonic irrigation for removal of calcium hydroxide in the apical root canal: A micro-CT and light-coupled tracking analysis

Objective

This study aimed to evaluate the efficacy of three sonic irrigation systems for removal of calcium hydroxide dressing from the apical root canal.

Materials and methods

A total of 96 single-rooted teeth in three categories of root canal curvatures (straight: 0–5°, moderate: 6–20°, and severe: > 20°) were allocated to four groups: conventional needle irrigation, EndoActivator, EQ-S, and Vibringe. The root canals were instrumented using Protaper NEXT and filled with calcium hydroxide. After removal of calcium hydroxide, the remaining volume of calcium hydroxide was measured by micro-CT analysis. Data were compared among root canal curvatures and irrigation systems using the Kruskal-Wallis test and Mann-Whitney test (p < .05). The oscillating range of each irrigation system was measured using light-coupled motion tracking.

Results

The volumes of calcium hydroxide remaining in the canals with severe curvature were significantly higher than in those of straight curvature (p < .05). In the canals of moderate or severe curvature, EQ-S showed the highest removal percentage, followed by EndoActivator, Vibringe, and needle irrigation (p < .05). Light-coupled tracking showed the largest oscillating range in EQ-S (p < .05).

Conclusions

Sonically activated irrigation systems with a flexible tip can be beneficial for calcium hydroxide intracanal dressing removal in the curved apical canals.

Noncontact 3D evaluation of surface topography of reciprocating instruments after retreatment procedures

This study evaluated the Reciproc R25 and Pro-R 25 instruments in unused condition, after one and a second use in endodontic retreatment employing a noncontact 3D light interferometer profiler, scanning electron microscopy (SEM) and cyclic fatigue tests. Twenty single-root teeth were instrumented with Reciproc R25 and filled with gutta-percha and sealer. A 3D profiler with a 20x objective using the Mx™ software was used to evaluate the cutting blade surfaces of Reciproc R25 and Pro-R 25 (n=5 per group) in unused condition, after the first and second uses in retreatment procedures. After retreatment, SEM was used to evaluate the topographic features of the used instruments. Cyclic fatigue tests were performed to compare new to used instruments. One-way ANOVA followed by Tukey test was used to compare the tested instruments before and after the first and second uses. Student t-test was used to compare the different instruments and for cyclic fatigue evaluation. No significant differences were observed in the cutting blade surfaces of Reciproc and Pro-R before and after one and two uses (p>0.05). Reciproc without use showed higher Sa and Sq when compared to Pro-R without use (p<0.05). No differences were observed between Reciproc and Pro-R after one and two uses (p>0.05). New and unused Reciproc showed longer time to fracture than Pro-R instruments (p<0.05), and only Pro-R showed differences between new and used instruments (p<0.05). Retreatment procedures with Reciproc and Pro-R did not change the surface topography of instruments. Reciproc had greater resistance to cyclic fatigue compared with Pro-R.

Fracture incidence of Reciproc instruments during root canal retreatment performed by postgraduate students: a cross-sectional retrospective clinical study

Objectives

To evaluate the fracture incidence of Reciproc R25 instruments (VDW) used during non-surgical root canal retreatments performed by students in a postgraduate endodontic program.

Materials and Methods

From the analysis of clinical record cards and periapical radiographs of root canal retreatments performed by postgraduate students using the Reciproc R25, a total of 1,016 teeth (2,544 root canals) were selected. The instruments were discarded after a single use. The general incidence of instrument fractures and its frequency was analyzed considering the group of teeth and the root thirds where the fractures occurred. Statistical analysis was performed using the χ² test (p < 0.01).

Results

Seven instruments were separated during the procedures. The percentage of fracture in relation to the number of instrumented canals was 0.27% and 0.68% in relation to the number of instrumented teeth. Four fractures occurred in maxillary molars, 1 in a mandibular molar, 1 in a mandibular premolar and 1 in a maxillary incisor. A greater number of fractures was observed in molars when compared with the number of fractures observed in the other dental groups (p < 0.01). Considering all of the instrument fractures, 71.43% were located in the apical third and 28.57% in the middle third (p < 0.01). One instrument fragment was removed, one bypassed, while in 5 cases, the instrument fragment remained inside the root canal.

Conclusions

The use of Reciproc R25 instruments in root canal retreatments carried out by postgraduate students was associated with a low incidence of fractures.

The efficacy of different instruments combined with Nd:YAP in endodontic retreatment

BACKGROUND

To evaluate the efficiency of endodontic retreatment using different instruments and observe whether the Nd:YAP laser can assist.

METHODS

Eighty premolars were selected, of which the root canals were prepared, and were filled with both gutta-percha and AH plus. The teeth were randomly divided into eight groups, respectively using and not using the Nd:YAP laser with the use of H files, Reciproc files, Mtwo R files, and Mtwo R + H files to remove the root-canal filling material. The retreatment time of each sample was recorded, and the amount of residual gutta-percha was calculated by Image J.

RESULTS

(I) In the four no-Nd:YAP laser groups, the Mtwo R group and Reciproc group took the least time, and there was no statistical difference between them (P>0.05). The Mtwo R + H file group took longer than the Mtwo R group and Reciproc group (P<0.05). The H file group took the longest time (P<0.05). (II) In the Nd:YAP laser group, the H file group took the longest time (P<0.05), and there were no significant statistical difference between the other three groups (P>0.05). (III) The Nd:YAP laser groups took a longer time than the no-Nd:YAP laser groups (P<0.05). (IV) All of the groups had residues. (V) The residues in the Mtwo R + H files group and the Reciproc group were the least among the four groups (P<0.05), and the residues in the Mtwo R group were the most (P<0.05). (VI) The residues in the Mtwo R and H file groups of the Nd:YAP laser groups were less than those of the no-Nd:YAP laser groups (P<0.05), and the residues in the Reciproc and the Mtwo R + H file groups of the Nd:YAP laser group showed no statistical difference with that of the no-Nd:YAP laser group (P>0.05).

CONCLUSIONS

None of the experimental methods could altogether remove the root-filling material. The Nd:YAP laser could assist, but the procedure still took a long time and the efficiency of endodontic retreatment was limited. Using the Mtwo R + H or Reciproc file was the most efficient.

Is canal overinstrumentation able to produce apical root dentinal microcracks in extracted teeth?

AIM

To assess the impact of mechanical overinstrumentation of root canals in extracted teeth on the development of dentinal microcracks in the apical portion of the root by means of micro-computed tomographic (micro-CT) analysis. Root canal preparation short of the canal terminus and at the apical foramen (AF) were used as controls.

METHODOLOGY

Twenty 2-rooted maxillary premolars with two canals were selected, scanned in a micro-CT device and the root canals prepared sequentially using Reciproc M-Wire R25 instruments to working lengths: 1 mm short of the AF (AF - 1 mm), at the AF (AF), and overinstrumentation (AF + 1 mm). A micro-CT scan of each specimen was performed after each time point. After reconstruction and co-registration procedures, the images were screened from the cementoenamel junction to the apex (n = 55 352) to identify the presence of dentinal microcracks in the apical third of the root.

RESULTS

After the analyses of 55 352 slices, dentinal microcracks were visualized in 12.45% of the images (6892 slices), with 5.73% (3174 slices) in the cervical, 3.57% (1976 slices) in the middle and 3.15% (1740 slices) in the apical third. All dentinal microcracks observed at all time points (AF - 1 mm, AF and AF + 1 mm) were already present in the corresponding images before canal instrumentation. Therefore, no new microcracks were detected, regardless of the working length used for canal instrumentation.

CONCLUSION

Reciprocating root canal preparation either short, at or beyond the AF (overinstrumentation) did not create dentinal microcracks in the roots of extracted 2-rooted maxillary premolars.

Microcomputed tomographic evaluation of shaping ability of two thermo mechanically treated single-file systems in severely curved roots

Context:

Canal shaping abilities such as canal transportation, centering ability, and preparation time are important and have to be considered before using any Nickel–Titanium file system.

Aim:

This in vitro study aimed to evaluate and compare the amount of canal transportation, centering ability, and time required for the shaping of severely curved canals with WaveOne Gold (WOG) Primary Reciprocating file and One Curve (OC) Rotary file using the micro computed tomography (μCT).

Materials and Methods:

Thirty intact mesial roots of extracted human mandibular first molars having severe curvature (25°–35°) were selected. Samples were divided into two groups. Samples in Group I and II were shaped with WOG primary reciprocating files and OC rotary files, respectively, to the working length. Time required to prepare each canal was recorded. μCT pre- and post-instrumentation scans of all samples were taken. The cross-sectional images at 3, 6, and 9 mm from the radiographic apex were selected for analysis. Statistical analysis was performed using the Kruskal–Wallis and unpaired t-test.

Results:

At 3 mm, OC showed statistically lower canal transportation with mean value (0.17 ± 0.10) than WOG (0.55 ± 0.42). Furthermore, OC showed statistically significant better centering ability (0.59 ± 0.25) than WOG (0.39 ± 0.20) at 3 mm level. However, the differences between both instruments were not statistical significant at 6 and 9 mm level for canal transportation and centering ratio. WOG reciprocating file required less time for canal preparation than OC file.

Conclusions:

OC rotary file showed less canal transportation and better canal centring ability than WOG file, during the preparation of severely curved canals. However, WOG required less time for canal preparation.

Micro-CT analysis of dentinal microcracks on root canals filled with a bioceramic sealer and retreated with reciprocating instruments

This study aimed to analyze the potential occurrence of dentinal defects after the removal of a root canal filling with two different sealers using Reciproc (RC) or Reciproc Blue (RB). The mesial roots of 60 mandibular molars with a Vertucci type IV configuration were selected. The samples were initially instrumented with Reciproc (R25) and then divided into the following four experimental groups according to the endodontic sealer and retreatment instrument (n = 15): BC Sealer/Reciproc (BCRC); BC Sealer/Reciproc Blue (BCRB); AH Plus/Reciproc (AHRC); and AH Plus/Reciproc Blue (AHRB). Then, the samples were scanned under micro-CT after obturation and removal of the filling material. Two analyses were conducted. First, an evaluation was performed on all the axial images, and another analysis evaluated each millimeter of the 10 mm from the apex. Dentinal defects were observed in all the samples. All of the identified defects in the images after filling material removal were present in the corresponding images after obturation. The use of AH Plus and EndoSequence BC Sealer, and filling material removal using RC and RB instruments did not induce dentinal defects.

The potential effect of instrumentation with different nickel titanium rotary systems on dentinal crack formation-An in vitro study

The potential mechanical impact of different rotary systems used for root canal preparation has been a matter of debate for long. The aim of this study was to explore the incidence of dentinal cracks after root canal instrumentation with various rotary systems, in vitro. One hundred and eighty intact lower central incisors were selected and randomly divided into fourteen treatment groups (n = 12/group) and a control group (n = 12). After decoronation, the root canals were instrumented with fourteen different rotary systems (E3, E3 azure, NT2, Hyflex CM, Hyflex EDM, 2Shape, OneCurve, ProTaper Next, ProTaper Gold, WaveOne Gold, Mtwo, Reciproc Blue, TF adaptive, K3XF). All roots were horizontally sectioned at 3, 6, and 9 mm from the apex with a low-speed saw under water-cooling. The slices were then examined under stereomicroscope for dentinal cracks. No cracks were found in the control group. Cracks were found in all treatment groups, predominantly in the 3 mm slices. There was no statistically significant difference in the number of cracks when comparing the different systems to each other at any section level. At 3 mm, however, five of the studied systems, namely K3XF (p = 0.004), Protaper Next (p = 0.001), Reciproc Blue (p<0.001), TF adaptive (p = 0.050), and 2Shape (p = 0.009) presented a significantly higher number of cracks than the control group. Within the limitations of this study, instrumented canals presented dentinal cracks, while uninstrumented ones presented no cracks after sectioning. There seems to be no significant difference among the tested systems regarding crack formation in the instrumented root canal wall. Crack formation occurred irrespective of the motion of the rotary system (rotational or reciprocation). Further studies are needed to clarify the factors that contribute to crack formation in the case of each individual rotary system.

Retrograde Instrumentation of Surgically Resected Roots Using Controlled Memory Files: A Human Cadaver Study

INTRODUCTION

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.

METHODS

Thirty maxillary anterior teeth in human cadavers were selected, and nonsurgical root canal treatment was performed on these teeth. A standardized 4-mm osteotomy and a 3-mm root resection with as close to 0° bevel as possible were made on each tooth. A microsurgical diamond tip was used to create a 1- to 2-mm starting point for each retropreparation. A 25/06 and 30/06 VTaper 2H were bent at about 90° angle to mimic the clinical and anatomic restrictions and used to create a retropreparation to a depth of 14 mm. Micro-computed tomography scans were taken and analyzed for volume and percentage of residual obturation material at 5 and 10 mm. In addition, the incidences 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 mm³ (interquartile range, 0.36 mm³) and 1.97 mm³ (interquartile range, 1.99 mm³), respectively. The overall incidence of file separation during retropreparation was 13.33% (4/30). Among the cases analyzed with micro-computed tomography, 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. Although this novel technique is limited in application, it is a safe and effective way to achieve a deep, clean retropreparation.