The effects of canal preparation and filling on the incidence of dentinal defects

Unveiling the correlation between in vivo endodontic reciprocate instrumentation and crack formation

INTRODUCTION

Dentinal microcracks have been supposedly associated with unrestorable vertical root fractures and consequently long-term treatment failure. This study aimed to investigate whether in vivo root canal instrumentation in mandibular incisors with vital pulps causes dentinal microcracks using two different irrigating solutions.

METHODS

Five patients with four vital mandibular incisors indicated for extraction were included. In vivo root canal preparation was performed using Reciproc R40 (tip #40 and taper 0.06). From these, two teeth were randomly assigned for root canal instrumentation irrigated with 5.25 % sodium hypochlorite irrigation (n = 10) or 2 % chlorhexidine gel with saline solution irrigation (n = 10). In sequence, all teeth were carefully extracted, stored in saline solution until microtomography (µCT) scan. Images were reconstructed and assessed for the presence or absence of dentinal microcracks where microcracks originating from the root canal lumen would be considered. All reconstructed samples were analysed dynamically and rendered in videos through the entire extension of the teeth, evaluating the axial cuts considering each third separately from the apex to the enamel-dentinal junction. Teeth were analysed using the DataViewer software at 100 % magnification without filters by three examiners blinded to the condition allocation.

RESULTS

No complete dentinal microcracks were observed after root canal instrumentation of mandibular incisors with vital pulps using Reciproc R40 regardless the irrigating solutions, 5.25 % sodium hypochlorite or 2 % chlorhexidine gel.

CONCLUSIONS

In vivo root canal instrumentation of mandibular incisors with vital pulps and bone/periodontal insertion does not cause dentinal microcracks and the irrigating solutions tested did not influence this occurrence. Microcrack evaluation must be performed in vivo conditions of dental tissue moist and periodontal support to avoid dryness dentinal alterations after extraction provoking false positive results.

CLINICAL RELEVANCE

Reciprocating instrumentation performed in vivo is safe and do not induce dentinal microcracks in mandibular incisors.

Topography of root-end surface after freehand and three-dimensional-guided apicoectomy procedure: A scanning electron microscope study

Background

Dentinal microcracks formed during apical resection may lead to increased susceptibility to root fracture and improper sealing of apical preparation that may negatively influence the outcome of endodontic microsurgery.

Aims

This study was performed to analyze the root-end surface for dentinal microcracks using a scanning electron microscope (SEM) after resection with high-speed bur and trephine drill.

Materials and Methods

Thirty extracted single-rooted maxillary premolar teeth were selected and randomly distributed into two groups (n = 15). Working length was established using a #15 K-type file. Canals were prepared with a rotary Ni-Ti system to size 30/0.06 using endomotor, irrigated with 3% sodium hypochlorite, dried with paper points, and obturated with gutta-percha cones using a single-cone technique. All samples were mounted on preformed molds and poured using a mixture of sawdust and gypsum. In Group A; tungsten carbide bur was used to perform a freehand apicoectomy. In Group B; a trephine drill was used with a three-dimensional guide to perform 3 mm of root resection. Apicoectomy was performed in both groups under a dental operating microscope. Resected root ends were inspected for microcracks using SEM. The Shapiro-Wilk and Mann-Whitney U-test were used for statistical analysis.

Results

Microcracks were observed in all samples in both study groups. Trephine drill produced more microcracks on the resected root surface compared to the use of high-speed tungsten carbide bur with a statistically significant difference (P < 0.05).

Conclusions

The trephine drill used during targeted endodontic microsurgery produced more microcracks on the resected root dentine surface compared to the high-speed tungsten carbide bur used during freehand apicoectomy.

Comparative evaluation of hand and rotary file systems on dentinal microcrack formation during pulpectomy procedure in primary teeth: an in vitro study

PURPOSE

Pulpectomy can be used for the management of deep dentinal carious lesions in primary teeth which can be restored. Mechanical preparation of root canals can be performed using hand or NiTi rotary files. However, this may cause dentinal stress and consequently dentinal microcracks. Hence, the aim was comparative evaluation of hand and rotary file systems on dentinal microcrack formation during pulpectomy procedure in primary teeth.

METHODS

60 extracted primary molar teeth were selected comprising of 80 root canals. Simple random sampling was used to divide root canals into four groups (n = 20): Group A-Hedstrom file, Group B-Pro AF Baby Gold rotary, Group C-ProTaper Next rotary, and Group D-unprepared group. Assessment was conducted on presence or absence of microcracks using Chi square test (p < 0.05).

RESULTS

The total number of microcracks in Group A: one (5%), Group B: four (20%), Group C: nine (45%) and Group D: zero (0%) which was statistically significant (p = 0.002). At cervical third, the number of microcracks seen with Group A: one (5%), Group B: zero (0%), Group C: five (25%) and Group D: zero (0%) (p = 0.005). At the middle third, the number of microcracks seen in Group A: zero (0%), Group B: four (20%), Group C: four (20%) and Group D: zero (0%) (p = 0.029).

CONCLUSION

The study concluded that dentinal microcracks are formed with both hand and rotary file systems in primary teeth. ProTaper Next showed significantly higher number of microcracks, followed by ProAF Baby Gold and H files.

The impact of long-term storage conditions on the development of experimental dentinal microcracks

This study evaluated the impact of long-term storage conditions (medium and time) on the development of experimental dentinal microcracks through micro-computed tomography. Sixty freshly extracted premolars were stored in formalin, water, or dry conditions (n = 20) and scanned after 72 h, 30 days, 6 months and 3 years of extraction. The effect of the storage medium and time on the occurrence of dentinal defects was statistically evaluated. A total of 211 000 images were screened revealing the existence of 11 519 slices with dentinal defects. Dry conditions significantly contributed to the development of new defects in all time points. During the 3-year follow-up period, no new defects were detected in the teeth that were stored in water and, in a single tooth, in the formalin group, after 6 months of storage.

Effects of ultrasonics and trephine burs on dentinal microcrack formation during broken instrument removal procedures: A micro-CT analysis

The objective of this study was to compare the effects of ultrasonic and trephine burs on microcrack formation during the removal of broken instruments, utilising micro-computed tomography (Micro-CT). Twenty-five extracted human mandibular molars were used for this study. The hand files were fractured into the mesiobuccal canal, except in the control group. In the ultrasonic group (n = 10), ultrasonic tips were used to retrieve the instrument, while in the trephine group (n = 10), trephine burs (Meitrac, Meisinger) and an extractor device were utilised. For the control group (n = 5), only staging platform was prepared. After the removal procedures, micro-CT images were obtained from the specimens. The chi-squared test was used to analyse the data, and significance was considered to be p < 0.05. Overall, 15 736 cross sections were analysed. No significant differences were found between control and experimental groups. Removal of broken instruments with trephine burs caused significantly more dentinal microcracks compared with ultrasonics (p = 0.016).

Comparative evaluation of incidence of dentinal defects after root canal preparation using three different endodontic retreatment systems - An in vitro study

Context

Safe and efficient removal of all root filling materials from the root canal system without compromising radicular dentin structure is essential for optimal nonsurgical retreatment.

Aims

The aim of this study was to evaluate and compare the incidence of dentinal defects caused during root canal filling removal using conventional, rotary, and reciprocating retreatment file systems.

Settings and Design

A detailed protocol explaining purpose and procedures of the study was submitted to the Institutional Ethics Committee and ethical clearance obtained.

Subjects and Methods

Sixty human maxillary permanent central incisors were collected and decoronated to 12-mm standardized length. The canals prepared up to a master apical file size F3 with Protaper hand files, obturated using AH plus sealer, examined under the stereomicroscope (×40 magnification): Group I: Control (n = 15), Group II: Conventional (n = 15), Group III: Protaper Universal Retreatment Files (n = 15), and Group IV: Reciproc Blue (n = 15). After instrumentation, teeth were sectioned at 3, 6, and 9 mm from the apex to evaluate the presence of dentinal defects under the stereomicroscope.

Statistical Analysis Used

Statistics were performed using the SPSS, version, 25 (SPSS Inc., Chicago, IL, USA). Initially, normality test was done using the Shapiro-Wilk test and data were not normally distributed followed by Kruskal-Wallis test. P < 0.05 is considered statistically significant.

Results

Maximum percentage increase in dentinal defects was observed in Protaper Universal Retreatment Files followed by Conventional method and Reciproc Blue.

Conclusions

Significantly Reciproc Blue reduced the incidence of dentinal defects after root canal preparation.

Comparative Evaluation of the Incidence of Dentin Microcracks Following Biomechanical Preparation Using Four Different Nickel-Titanium Rotary File Systems: An In Vitro Study

INTRODUCTION

Biomechanical preparation has gotten easier over time with the development of nickel-titanium (NiTi) rotary instruments. Despite their benefits, research has shown that these files frequently result in microcracks in the root canal dentin, which can fracture the roots. Such mishaps should be prevented, as they compromise the integrity of the root and reduce the long-term survival of endodontically treated teeth.

MATERIALS AND METHODS

This study was conducted at Government Dental College and Hospital, Patiala, Punjab, India. Eighty permanent mandibular premolar teeth were included. All the roots were inspected for any pre-existing cracks or craze lines under a stereomicroscope. The teeth were decoronated and then divided into four groups (n = 20): Group I: TruNatomy, Group II: Neoendo Flex, Group III: ProTaper Gold, and Group IV: 2Shape. The samples were instrumented according to the group to which they belonged. The roots were then sectioned horizontally at 3 mm and 6 mm from the apex and examined under a stereomicroscope at 40x for the presence of microcracks.

RESULTS

The data were analyzed using the IBM SPSS Statistics for Windows, version 26 (released 2019; IBM Corp., Armonk, New York, United States). A chi-square test was applied, and the level of significance was set at p < 0.05. The highest incidence of microcracks was associated with ProTaper Gold (65%), followed by Neoendo Flex (45%), TruNatomy (20%), and 2Shape (20%).

CONCLUSION

 All rotary instruments resulted in dentinal damage. ProTaper Gold exhibited the highest frequency of dentin cracks. TruNatomy and 2Shape exhibited satisfactory results with minimal crack formation.

Assessing the efficacy of jet dispenser versus direct syringe injection for calcium hydroxide paste placement in artificial root canals

This study aimed to evaluate the efficacy of a novel jet dispenser (JD) for filling simulated straight and curved canals with calcium hydroxide (Ca(OH)2) paste by comparing the level of intracanal medicament with traditional direct syringe delivery. The Ca(OH)2 paste was delivered into the canals using either a direct syringe with binding tip and unbinding tip or a JD. The analysis of the ratio of the canal filled area (RCFA) in the coronal, middle, and apical thirds was conducted using the Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). The JD resulted in a significantly higher RCFA of 1.00 in the middle and apical thirds in both the straight and curved canals than the direct syringe method (p < 0.001). Voids were frequently observed in the direct syringe group, whereas JD showed no voids within the filled area. In the direct syringe groups, the apical area was more readily filled in both canal types when the tip was bound (p < 0.001). The JD was found to be more effective in filling the entire canal space than the binding and unbinding conditions of the direct injection method, particularly in the apical area.

Comparison of Dentinal Defects Induced by Rotary, Reciprocating, and Hand Files in Oval Shaped Root Canal - An In-Vitro Study

AIM

To evaluate and compare the formation of dentinal defects using hand Hedstrom files, XP-Shaper, TruNatomy, and Reciproc Blue file systems when used for oval shaped root canals.

MATERIALS AND METHODS

One hundred and five extracted human mandibular premolars with single root and oval canals were selected for the study. Twenty-one teeth were unprepared (control), and the remaining teeth were divided into the prepared groups (n = 21), that is, Group H-Files, Group XP-Shaper, Group TruNatomy, and Group Reciproc Blue. All selected teeth were de-coronated perpendicular to the long axis of the tooth by using a diamond-coated disk with water cooling, leaving root segments approximately 16 mm in length. Each group was prepared according to the above file system. Then all roots were sectioned perpendicular to their long axes at 3, 6, and 9 mm from the apex using a diamond-coated disk under a continuous water stream. Each specimen was then checked for the presence of dentinal defects/microcracks.

RESULT

The XP-Endo shaper group had the lowest number of defects (01/21 roots) 4.7%; TN (04/21) 19%, H-Files (04/21) 19%, and RC Blue (05/21) 23.8% had the highest incidence of defects. However, no significant difference was detected among these groups (P > 0.05).

CONCLUSION

The motor-driven root canal instrumentation with rotary and reciprocating files and hand files may create microcracks in the radicular dentine, whereas the XP-Shaper file system produces minimal or less cracks compared to other tested rotary file systems and H-file instrumentation.

Risk factors for and clinical presentations indicative of vertical root fracture in endodontically treated teeth - a systematic review and meta-analysis

INTRODUCTION

The aim of this study was to identify specific clinical signs or symptoms and potential risk factors which are most likely associated with the presence of a vertical root fracture (VRF) in endodontically treated teeth (ETT).

METHODS

Electronic databases (MEDLINE via PubMed, EMBASE via Ovid, Scopus, and Web of Science) were searched by two reviewers in October 2022 for clinical studies, in which at least either the clinical presentation or potential risk factors associated with a VRF were assessed. Risk of bias was assessed using the Newcastle-Ottawa scale. Meta-analyses of odds ratios (ORs) were performed separately for several signs or symptoms and risk factors.

RESULTS

Fourteen sources reporting on 2,875 teeth (489 with VRF and 2,388 without VRF) were included in the meta-analyses. Regarding the clinical presentation, the presence of sinus tracts (OR=4.87; 95%-CI: 1.58-15.0), increased periodontal probing depths (OR=13.24; 95%-CI: 5.44-32.22), swelling/abscess (OR=2.86; 95%-CI: 1.74-4.70), and tenderness to percussion (OR=1.74; 95% CI: 1.18-2.61) were significantly associated with the presence of a VRF (P_adj. value<.05). None of the assessed risk factors (sex, type of teeth, tooth location, posts, indirect restoration, apical extension of the root canal filling), were found to be significantly associated with the presence of a VRF (P_adj. value>.05).

CONCLUSIONS

Four clinical presentations were identified to be the most significant signs or symptoms for a VRF in ETT: presence of sinus tracts, increased probing depths, swelling/abscess, tenderness to percussion. None of the assessed risk factors pointed out to be significantly associated with a VRF.

REGISTRATION

CRD42022354108 (PROSPERO).

Comparative Evaluation of Dentinal Defects After Root Canal Preparation Using Various Nickel Titanium Files: An In Vitro Study

AIM

This study set out to compare the damage done to dentin by three distinct titanium file brands - the Hyflex EDM, the ProTaper Next, and the Waveone Gold Nickel - in order to draw conclusions about which one is the most effective.

MATERIALS AND METHODS

Forty-first premolars in the mandible with straight canals and single roots were instrumented using Hyflex EDM, Waveone Gold, and Protaper Next. Dentinal flaws after endodontic treatment were studied by sectioning specimens using a hard tissue microtome and analyzing them under a stereomicroscope.

RESULTS

There was no discernible variation between the groups in the coronal third (p=0.312) or apical third (p=0.076). Hyflex EDM and Protaper Next differed significantly in the middle portion of the tape (p=0.016). The Hyflex EDM sample had the fewest cracks. There was no statistically significant difference between Hyflex EDM and Waveone Gold; however, Hyflex EDM had fewer fractures in the middle third of the sample than Waveone Gold did.

CONCLUSION

Electric discharge machining (EDM) files made from Hyflex proved to be far superior to their Protaper Next and Waveone Gold counterparts as they induced the fewest cracks in the middle third of the root dentin.

The effect of ultrasonic vibration protocols for cast post removal on the incidence of root dentin defects

PURPOSE

To investigate the effects of two ultrasonic vibration protocols for cast post removal (single or double ultrasound units) on the development of defects in root dentin.

METHODS

Sixty bovine incisors were selected. Fifteen roots were left unprepared (control). Forty-five roots were instrumented and filled. A 10-mm post space was prepared using #1-4 Largo drills. Fifteen teeth were prepared for post space and received no further procedure. Thirty roots had cast posts cemented and were submitted to ultrasonic vibration protocols for removal. The time necessary to remove each post was recorded. Roots were sectioned 3, 6, 9, and 12 mm from the coronal portion and viewed through a 25× magnification in a stereomicroscope. The presence of root fractures, partial cracks, and craze lines was registered. Chi-square and Fisher's exact tests were performed to compare the incidence of dentin defects. The Kruskal-Wallis test was performed to explore the difference between the time needed for post removal. The significance level was set at P = 0.05.

RESULTS

Root defects were observed in all experimental groups. There were no statistical differences comparing previous root canal treatment and post removal steps, either with 1 or 2 ultrasonic units, in the formation of defects (P = 0.544) or fractures (P = 0.679).

CONCLUSION

Ultrasonic vibration protocols for removing cast posts did not increase the number of dentin defects compared to root canal preparation and obturation and post space preparation steps.

Comparative Evaluation of Fracture Resistance of Endodontically Treated Teeth Instrumented With K3XF Rotary Files Using Different Tapers

AIM

To compare the effect of different tapers of the K3XF file system on the fracture resistance of endodontically treated mandibular premolars obturated with a three-dimensional (3-D) obturation system.

METHODOLOGY

For the study, 80 freshly extracted human mandibular premolars with single well-developed roots without any curvatures were taken and the tooth roots were wrapped in a single layer of aluminum foil, and they were placed vertically in a plastic mold filled with self-curing acrylic resin. The access was opened, and working lengths were determined. The canals were instrumented keeping an apical size of #30 by different taper rotary files: Group 1: un-instrumented (control group), Group 2: 30/.04, Group 3: 30/.06, Group 4: 30/.08 K3XF file system, and teeth were obturated using a 3-D obturation system, and access cavities were filled using composite. Both experimental and control groups were subjected to fracture load using a conical steel tip (0.5mm) attached to a universal testing machine to record force applied in newton until root fracture.

RESULTS

Root canal instrumented groups showed lower fracture resistance than the uninstrumented group.

CONCLUSION

Hence it could be concluded that endodontic instrumentation with increased taper rotary instruments caused a decrease in fracture resistance of the teeth, and biomechanical preparation of root canal system with rotary or reciprocating instruments caused a significant decrease in fracture resistance of endodontically treated teeth (ETT), thereby decreasing their prognosis and long-term survival.

Influence of moisture content of frozen and embalmed human cadavers for identification of dentinal microcracks using micro-computed tomography

The aim of this study was to investigate the influence of moisture content in frozen and embalmed human cadavers on the detection of dentinal microcracks using micro-computed tomography (micro-CT). The group of embalmed specimens included three mandibular and two maxillary segments each containing one tooth. The group of frozen cadavers consisted of two frozen mandibular bone-blocks with two teeth and one mandibular segment containing one tooth. The final number of teeth for each preservation method was n = 5. All specimens were scanned with eight different moisture conditions: 48 h wet, 2 h dry, 48 h wet, 24 h dry, 48 h wet, 1 wk dry, 48 h wet, 1 wk dry. Micro-CT images were screened for the presence of dentinal microcracks. Statistical analysis was performed by nonparametric analysis of variance (α = 5%). Only few microcracks were observed in wet and in 2 h dried bone-blocks with no significant differences (p = 0.63 and p = 0.23, respectively). There was a significant and steady increase of microcracks within the groups of dried specimens as follows: 2 h dry < 24 h dry < first wk dry < second wk dry (all p < 0.008). Preservation method had no significant influence on the visibility of microcracks (p = 0.98). Identification of dentinal microcracks on micro-CT images is influenced by moisture content of cadaveric bone-blocks irrespective of the preservation method.

Does Low-Taper Root Canal Shaping Decrease the Risk of Root Fracture? A Systematic Review

Minimal root-canal preparation has been suggested to reduce the risk of root fracture, but as a result, satisfactory cleaning and shaping do not take place. Large-scale taper instrumentation can contribute to removing infected tissue; however, it may weaken the tooth structure. The aim of this systematic review is to evaluate whether root-canal shaping with low-taper instruments decreases the risk of root fracture, compared to high-conicity shaping. A search was performed on Ovid MEDLINE, PubMed, and the Web of Science. The inclusion criteria were: studies comparing the root fracture resistance of endodontically treated teeth, shaped with low- and high-conicity taper instruments, in human trials, and via in vitro study. The review includes all types of endodontically treated teeth, with various instrument tapers. The scientific search engines produced 328 results. Only 20 of the results were evaluated after screening. Based on the articles analyzed, it is not clear whether a taper difference can determine differences in root fracture resistance. No randomized controlled trial (RCTs) with long follow-ups have been published to date. It must also be taken into account that the in vitro studies do not consider the numerous differences that there are between in vitro and clinical evaluation. The review was registered on the PROSPERO website, with the protocol number CRD42020151451.

Micro-Computed Tomographic Assessment of Microcrack Formation before and after Instrumentation of Curved Root Canals with Neoniti Rotary Files

The aim of this study was to assess the microcrack formation of moderately and severely curved root canals following instrumentation with Neoniti rotary files using micro-computed tomography. This in vitro study evaluated 18 extracted sound mandibular molars with two separate mesial canals and foramina in two groups (n = 9) with 5−20° (moderate) and 20−40° (severe) root canal curvature. The number of microcracks in the root canal walls was counted at baseline by micro-CT. Subsequently, the root canals were instrumented with 0.20/0.06 v Neoniti files as single files with a torque of 1.5 Ncm and a speed of 400 rpm. The number of microcracks was counted again postoperatively on micro-CT images using Amira software. Statistical analysis was performed using the Shapiro−Wilk test, Levene’s test and repeated-measures ANOVA (α = 0.05). The mean number of microcracks significantly increased postoperatively in both the moderately curved (11.59 ± 9.74 vs. 8.2 ± 7.4; p = 0.001) and the severely curved (13.23 ± 5.64 vs. 7.20 ± 5.94; p < 0.001) groups. However, the differences between the two groups were not significant (p = 0.668). Based on the results obtained, it can be stated that the instrumentation of moderately and severely curved root canals with Neoniti rotary files increases the number of microcracks. However, the higher degree of curvature does not necessarily translate to a higher number of microcracks after root canal instrumentation with this specific rotary system and methodological procedures.

Vertical root fractures in root treated teeth-current status and future trends

Vertical root fracture (VRF) is a common reason for the extraction of root filled teeth. The accurate diagnosis of VRF may be challenging due to the absence of clinical signs, whilst conventional radiographic assessment is often inconclusive. However, an understanding of the aetiology of VRFs, and more importantly, the key predisposing factors, is crucial in identifying teeth that may be susceptible. Thorough clinical examination with magnification and co-axial lighting is essential in identifying VRFs, and although CBCT is unable to reliably detect VRFs per se, the pattern of bone loss typically associated with VRF can be fully appreciated, and therefore, increases the probability of correct diagnosis and management. The prevalence of VRFs in root filled teeth is significantly greater than in teeth with vital pulps, demonstrating that the combination of loss of structural integrity, presence of pre-existing fractures and biochemical effects of loss of vitality, are highly relevant. Careful assessment of the occlusal scheme, presence of deflective contacts and identification of parafunctional habits is imperative in both preventing and managing VRFs. Furthermore, anatomical factors such as root canal morphology, may predispose certain teeth to VRF. The influence of access cavity design and root canal instrumentation protocols should be considered although the impact of these on the fracture resistance of root filled teeth is not clearly validated. The post-endodontic restoration of root filled teeth should be expedient and considerate to the residual tooth structure. Posts should be placed 'passively' and excessive 'post-space' preparation should be avoided. This narrative review aims to present the aetiology, potential predisposing factors, histopathology, diagnosis and management of VRF and present perspectives for future research. Currently, there are limited options other than extraction for the management of VRF, although root resection may be considered in multi-rooted teeth. Innovative techniques to 'repair' VRFs using both orthograde and surgical approaches require further research and validation. The prevention of VRFs is critical; identifying susceptible teeth, utilizing conservative endodontic procedures, together with expedient and appropriate post-endodontic restorative procedures is paramount to reducing the incidence of terminal VRFs.

Nair P, Gowri S, Jayaprakash K. Comparative evaluation of fracture resistance of endodontically treated bicuspids instrumented with hand files, trunatomy, protaper next, protaper gold, and waveone – An In vitro study

Aim:

The study aims to compare and evaluate the fracture resistance of endodontically treated bicuspids instrumented with Hand Files, TruNatomy (TRN), ProTaper Next (PTN), ProTaper Gold (PTG), and WaveOne (WO).

Materials and Methods:

In total, 45 extracted single-rooted human premolar teeth were selected and sectioned at or below the cementoenamel junction to obtain roots 15 mm long. The samples were divided into four experimental groups and one control group (n = 9): instrumentation with nickel–titanium (NiTi) Hand Files (control group), instrumentation with TRN files, instrumentation with PTN files, instrumentation with PTG files, and instrumentation with WO files. The samples were obturated by lateral compaction technique using gutta-percha points and AH Plus sealer. A vertical load was applied to the tooth using the universal testing machine (Tecsol-TSI-BDS-2Kn-Sr No. 170710) for the fracture resistance test. Statistical analysis was performed.

Results:

The study reported that teeth instrumented with NiTi hand files exhibited the highest fracture resistance when compared to all the rotary and reciprocating file systems. Among rotary and reciprocating instruments, root prepared with TRN files showed the most significant resistance to fracture compared with PTN, PTG, and WO files.

Conclusion:

Within the limitations of this study, it can be concluded that minimally invasive instrumentation of the system preserves more pericervical dentin, which may increase the resistance to fracture. Results of this study and other studies support the use of minimally tapered instruments to improve the fracture resistance of endodontically treated teeth.

Influence of optimum torque reverse motion on dentinal cracks after root canal preparation with two nickel-titanium rotary systems

Objectives:

This study was aimed to evaluate the cause-effect relationship between canal preparation with ProTaper Next (PTN) and ProTaper Gold (PTG) using optimum torque reverse (OTR) motion or continuous rotation and dentinal crack formation.

Materials and Methods:

Fifty distobuccal roots of human maxillary first molars were divided into five groups; Group I: PTG Full rotation, Group II: PTG in OTR, Group III: PTN Full rotation, Group IV: PTN in OTR, Group V: unprepared (control group). After mechanical preparation, the distobuccal roots were sectioned horizontally at 3, 6, and 9 mm from the apex. Images were captured using a stereomicroscope at 25X to determine the presence or absence of dentinal cracks. Friedman test was used to compare between root sections followed by Wilcoxon signed-rank test for pairwise comparison. Kruskal–Wallis test was used to compare between tested rotary systems followed by pairwise comparison with Dunn Bonferroni correction (α = 0.05).

Results:

Crack development was significantly higher in PTG using OTR motion 36.7% followed by PTN using OTR 33.3%, while the control group showed no cracks. PTG and PTN with full rotation showed crack development with 23.3% and 13.3%, respectively.

Conclusions:

The type of motion kinematics used during mechanical preparation have an impact on dentinal crack formation. Nickel-titanium instruments with larger taper tend to induce more cracks.

Review of Cracked Tooth Syndrome: Etiology, Diagnosis, Management, and Prevention

Cracked tooth syndrome refers to a series of symptoms caused by cracked teeth. This article reviews the current literature on cracked tooth syndrome from four aspects, etiology, diagnosis, management, and prevention, to provide readers integrated information about this. The article begins with an introduction to the odontiatrogenic factors and then covers the noniatrogenic factors that induce cracked tooth syndrome. While the former discusses inappropriate root canal therapy and improper restorative procedures, the latter covers the topics such as the developmental and functional status of cracked tooth syndrome. This is then followed by the description of common clinical diagnosis methods, the prospects of new technologies, and summaries of current clinical management methods, including immediate management and direct and indirect restoration. In the final section, preventive methods and their importance are proposed, with the aim of educating the common population.

Vertical Root Fracture in Non-Endodontically and Endodontically Treated Teeth: Current Understanding and Future Challenge

A vertical root fracture (VRF) is a complex complication that usually leads to tooth extraction. The aim of this article is to review the prevalence, demography, distribution, diagnostic methods, etiology and predisposing factors, clinical features, radiographic characteristics and treatment strategies of VRFs in non-endodontically treated teeth (VRFNETT) and endodontically treated teeth (VRFETT). Search terms for each subject related to VRFNETT and VRFETT were entered into MEDLINE, PubMed and Google Scholar. Systematic reviews, retrospective cohort studies, demographic research, clinical studies, case reports and case series were reviewed. Most of the VRFs were found in patients older than 40 years old. Older populations were discovered in the non-endodontically treated VRF group when compared to the endodontically treated VRF group. Male patients were found at a greater prevalence than females in the non-endodontically treated VRF group. The initial occurrence of a VRF may accompany radiolucent lines within the root canal, unusual space between the canal wall and intracanal material, a widening of the PDL space along the periradicular surfaces, angular bony destruction, step-like bone defects, V-shaped diffuse bone defects, or root resorptions corresponding to the fracture line before the clear separation of the fractured fragment. The indicative clinical and radiographic signs of VRF included a coronally positioned sinus tract, deep-narrow periodontal defects, the displacement of a fractured fragment, periradicular radiolucent halos and the widening of the root canal space. Interestingly, VRFNETT are more often observed in the Chinese population. Some patients with multiple VRFs were observed, suggesting possible predisposing factors in genetics and tooth development. The management of a VRF usually involves a multidisciplinary approach. The common distribution and features of VRFNETT and VRFETT were elucidated to facilitate recognition and diagnosis. Besides extraction, variable therapeutic schemes, such as the repair of the VRF, root amputation and others reported in earlier literature, are available. A long-term prognosis study of the various therapeutic strategies is needed.

Longitudinal craze line propagation in human root dentin after instrumentation with NiTi rotary files of different instrument tapers after long-term chewing simulation

Objectives

The aim of this study was to investigate whether file design and taper significantly influence microcrack initiation during machine preparation.

Materials and methods

Sixty extracted teeth with straight single canals were selected. The teeth were randomly assigned to four groups based on their root canal anatomy and the corresponding NiTi rotary file system (I, Mtwo; II, ProTaper Universal; III, F6 SkyTaper; control, no preparation and filling). The root canals of the experimental groups were filled using the single-cone technique. The tested teeth were all subjected to a mechanical chewing simulation with flat lead loading over a period of 3 years (corresponding to 150,000 cycles). The teeth were checked for dentinal defects (accumulative crack growth in length) under the digital microscope (Keyence VHX-5000) at time 0 (baseline prior to chewing simulation) and after 3, 6, 12, 24, and 36 months of loading. The cumulative crack increase was statistically analyzed using the Kruskal–Wallis test, Jonckheere–Terpstra test, and the Wilcoxon rank-sum test. The significance was set at p < 0.05.

Results

In contrast to preparation with greater-tapered instruments, ProTaper Universal (group II) and F6 SkyTaper (group III) instrumentation with the smaller tapered Mtwo files (group I) showed less accumulative propagation of craze lines (p < 0.05) at all time points.

Conclusion

Instruments with greater taper for root canal instrumentation should be used with care to avoid negative long-term effects in the form of propagation of dentinal defects over time. A positive cutting-edge angle and a smaller taper have a positive effect on a lower craze line development.

Clinical relevance

Instruments with a positive cutting-edge angle and a smaller taper are beneficial for the long-term preservation of dentinal tooth structure.

Microscopic Assessment of Dentinal Defects Induced by ProTaper Universal, ProTaper Gold, and Hyflex Electric Discharge Machining Rotary File Systems - An in vitro Study

Background:

Biomechanical preparation of root canal can damage root dentin leading to the formation of dentinal cracks which can eventually lead to fracture and failure of the treatment.

Aim:

The aim was to investigate the incidence of dentinal defects in root canals prepared with ProTaper Universal, ProTaper Gold, and Hyflex electric discharge machining (EDM) rotary file systems using handheld USB digital microscope.

Materials and Methods:

One hundred and fifty extracted mandibular premolar teeth with single canal were randomly divided into five groups (n = 30). Group 1: unprepared (negative control). Group 2: canal preparation done with nickel–titanium hand files (positive control), Group 3: canals prepared with ProTaper Universal rotary system, Group 4: canal preparation done with ProTaper Gold rotary system, and Group 5: canals prepared with Hyflex EDM rotary system. The specimens were sliced at 3 mm, 6 mm, and 9 mm from the apex with a slow-speed saw under water cooling. Digital images of each section were captured at ×40 magnification with the aid of a microscope. Two independent evaluators assessed the images for the presence of dentinal defects. The number of dentinal defects was recorded and Chi-square test was used for statistical analysis (P < 0.05).

Results:

The number of specimens presenting dentinal defects was as follows: Group 3; ProTaper Universal – 9/30 (30.0%), Group 4; ProTaper Gold – 2/30 (6.7%), and Group 5; Hyflex EDM – 1/30 (3.3%). No defects were detected in the negative and positive control groups (Group 1 and Group 2).

Conclusion:

ProTaper Universal showed the highest percentage of defects in comparison to ProTaper Gold and Hyflex EDM.

Dentinal microcracks and cemental tears related to chemo-mechanical root canal instrumentation: a micro-CT Cadaver Study

BACKGROUND

The prevalence of radicular defects after root canal instrumentation is unresolved. This study used micro-CT to assess the relationship between the formation of radicular defects and chemo-mechanical instrumentation in a cadaver model.

METHODS

Maxillary and mandibular molars (n = 24) were sectioned from cadaver specimens as a tissue block containing the teeth, alveolar bone and attached mucogingival tissues. After a baseline micro-CT scan (13.45 μm), the specimens were distributed into 3 groups (n = 8 molars): Reciproc^® , ProTaper Next™ and Mtwo^® . Micro-CT scans of each specimen were obtained after access, glide path and preparation with each instrument. The pre-operative and final post-operative micro-CT cross-sectional images of the roots were screened by two blinded examiners to identify any pre-existing and new radicular defects. Pre-existing and new radicular defects were examined histologically.

RESULTS

Overall, 16 pre-existing radicular defects were identified in 12 of the 24 molars (50%). Most of these were cemental tears (87.5%), and not true dentinal microcracks. New dentinal microcracks were observed in the post-operative micro-CT scans of only 3 canals (3.9%; 3/77). However, only one of these defects was found to be present histologically.

CONCLUSIONS

Within the limitations of the study, chemo-mechanical instrumentation did not routinely promote the formation of radicular defects.

A critical analysis of research methods and experimental models to study dentinal microcracks

The purpose of this narrative review was to discuss the scientific milestones that led to the current understanding of the root dentinal microcrack phenomenon based on the interplay between the usage of micro-computed tomography (micro-CT) as an analytical tool alongside a close-to-mouth experimental model. In 2009, reports on the development of dentinal microcracks in extracted teeth after root canal preparation triggered an awareness of the potential for vertical root fractures (VRFs) of endodontically treated teeth could be developed from defects created by the mechanical stress of nickel-titanium preparation systems on dentine. This assumption was taken for granted, even though no cause-effect relationship had been scientifically demonstrated. Since then, several studies using the sectioning method with extracted teeth have been published and the large discrepancy amongst their outcomes soon become evident. Moreover, the high frequency of reported dentinal microcracks largely contrasted with the clinical incidence of VRFs, raising doubts on their methodological reliability. Using micro-CT technology, it was demonstrated by several studies that, in extracted teeth, dentinal defects already existed before the endodontic procedures, indicating that the initial reports framed a non-existing cause-effect relationship between canal preparation and dentinal microcracks. Although these new findings contributed to a better comprehension of this phenomenon, the misconception that microcracks were the starting point for VRFs was only surpassed with a new in situ approach using fresh cadavers. Surprisingly, microcracks were not identified in sound teeth. As a conclusion, dentinal microcracks in extracted teeth can be considered a non-natural occurrence observed only in a laboratory set-up as a consequence of dehydration and storage conditions. Thus, dentinal microcracks shall not be considered as the starting point for VRFs as they do not manifest in non-extracted teeth. Identifying dentinal microcracks as a laboratory phenomenon highlights the impact of recent scientific developments to disclaim the clinical relevance of laboratory-obtained outcomes.

The antibacterial efficacy of photon-initiated photoacoustic streaming in root canals with different diameters or tapers

BACKGROUND

In recent years, the concept of minimally invasive endodontics has been proposed, which could be described as preventing or treating diseases by preserving more dental tissue and creating minimal damage. In the process of root canal preparation, it was recommended to use instruments with a smaller taper to preserve more tooth tissue and improve the preservation rate of the affected teeth. Photon-induced photoacoustic streaming (PIPS) was a new type of laser-activated irrigation technology, which was now widely used in endodontic treatment. The purpose of this article was to evaluate the bactericidal effect of PIPS with NaOCl in root canals with different widths or tapers.

METHODS

Twenty-three maxillary first molars with three independent root canals were included in this study. The mesiobuccal (MB), distobuccal (DB), and palatal (P) root canals were prepared at sizes of #10/.02, #25/.02, and #25/.06, respectively. After being incubated with a bacterial suspension for 4 weeks, the specimen were irrigated with 2% NaOCl activated by conventional needle irrigation (CNI) (n = 10) or PIPS (n = 10). Three specimen were not treated (control group). Before and after irrigation, the presence of bacteria was assessed with an adenosine 5'-triphosphate (ATP) assay kit and biofilms were assessed using confocal laser scanning microscopy and scanning electron microscopy.

RESULTS

In specimen prepared using PIPS irrigation, the ATP was reduced by more than 98%. When the root canal taper was 0.02, the size #25 root canals had a higher percentage of dead bacteria than the size #10 root canals in all regions (P < 0.05) in the PIPS group. When the root canal width was #25, the 0.02 taper group had a higher percentage of dead bacteria than the 0.06 taper group in the apical region (P < 0.05), except coronal and middle regions (P > 0.05). PIPS irrigation results in a greater percentage of dead bacteria and reduction of ATP in size #10/.02 root canals than CNI in size #25/.06 root canals in three regions (P < 0.05).

CONCLUSION

Increasing the width from #10 to #25 improves the bactericidal effect of PIPS in the root canal. Increasing the taper of the root canal from 0.02 to 0.06 at size #25 did not affect the bactericidal effects of PIPS. PIPS resulted in more dead bacteria in specimen with smaller tapers and root canal widths than CNI. PIPS can be used to clean the smear layer in the coronal region and open the dentin tubules.

CLINICAL SIGNIFICANCE

Activation of irrigants with PIPS brought about significant bacterial reduction smaller tapers and width root canals compared to CNI, which was beneficial to prevent excessive loss of tooth tissue and conserve the structural integrity of teeth.

Stereomicroscopic Evaluation of Microcrack Formation in Dentin by ProTaper Next, Revo S, and WaveOne Gold File System

Background

During the biomechanical preparation of the root canal by rotary file systems, stress is generated within the canal, which leads to dentinal microcrack formation. Such defects are evaluated only under the microscope.

Aim

The present study aimed to evaluate dentinal microcrack formation after instrumentation with ProTaper Next (M-wire), Revo S (conventional NiTi), and WaveOne Gold (Gold-wire) file systems under the stereomicroscope.

Materials and Methods

Forty single-rooted teeth free from any defect were selected and divided into four groups (Control, PTN, RS, and WOG). Experimental groups were instrumented with file system used in the study, and the control group were left unprepared. Samples were further decoronated and sectioned at 3 mm, 6 mm, and 9 mm from the apex perpendicular to the long axis and examined under a stereomicroscope at ×25 for different types of microcracks (no fracture, complete fracture, partial fracture, and other fracture).

Statistical Analysis Used

Data analysis was done by the Chi-square test using the SPSS version 17.0 software. A two-sided (α = 2) P < 0.05 (P < 0.05) was considered statistically significant.

Results

The null hypothesis was rejected. There was a statistically significant difference between the groups. All file systems created microcracks in the root dentin. WOG group showed an incidence of 66.7% for no fracture, PTN group had 40% for other fracture, and RS group had 60% for complete fracture.

Conclusion

Single file system WOG with gold wire technology proves to be the best choice for canal preparation among the tested groups in terms of least dentinal crack formation.

A laboratory study to assess the physical, mechanical, and 3-D structural properties of nano-apatite grafted glass fibre-based endodontic posts

AIM

To fabricate and characterize nano-hydroxyapatite (nHA) grafted and non-grafted glass fibre-based endodontic posts.

METHODOLOGY

Experimental glass fibre posts were fabricated using silanized nHA grafted (ex-HA) and non-grafted glass fibre (ex-P) reinforced resins. The structural analysis and morphological patterns were analysed with Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. EverStick^® glass fibre posts (eS) were used as a control group. The degree of conversion, flexural strength, and flexural modulus was investigated and the fractured structure was evaluated with a scanning electron microscope. Root canals were prepared in human extracted teeth restored with experimental and control posts. The push-out bond strength was evaluated with radicular dentine at days 7, 30, and 90, and the presence of voids at the interface were measured at day 1, 7, 30, and 90 with micro-computed tomography. The Shapiro-Wilk test and one-way ANOVA post-hoc Tukey's test were performed. The level of significance was set at 0.05.

RESULTS

The SEM and FTIR confirmed the presence of a silane-coupling agent on the glass fibres. The ex-HA post had a significantly lower degree of conversion compared to the ex-P post (p = .0008), but a significantly higher conversion than the eS post (p = .0014). The maximum flexural strength value was obtained with the ex-HA post with an insignificant difference (p = .366) compared to ex-P post and a significant difference (p = .029) compared to the eS post. The flexural modulus of ex-HA, ex-P, and eS posts were significantly different (p = .037). Similarly, the ex-HA post had a significantly higher push-out bond strength at days 7 and 30 (p = .037) compared to the ex-P and eS posts. The volume of voids had a nonlinear behaviour amongst the groups with no significant difference between the posts.

CONCLUSION

The fabrication of the experimental posts was successful and the ex-HA post had greater flexural strength and push-out bond strength compared to the ex-P post. The degree of conversion of the ex-HA post was lower than the ex-P and eS posts. The volume of voids of ex-HA and ex-P posts was lower than that of eS posts.

Influence of obturating techniques on root dentin crack propagation: A micro-computed tomography assessment

Aim:

The aim is to assess and compare the microcrack formation in radicular dentin after obturating the root canals with cold lateral condensation (CLC), warm vertical condensation (WVC), and injectable gutta-percha (IGP) techniques using micro-computed tomography (CT).

Materials and Methods:

Human extracted mandibular premolar teeth (n = 60) were haphazardly assigned based on the obturation technique into three experimental groups (n = 20 each). Root canals are cleaned and shaped with M Two rotary files and 3% sodium hypochlorite irrigant. Cross-sectional images were taken with Micro-CT to record the baseline defects present on root samples. After root canal obturation either with CLC or WVC or injectable obturation techniques, micro-CT images were captured again to analyze the increase in the number and type of dentinal defects. Statistical analysis of data was performed using the Mann–Whitney U test and the Mcnemar test at 5% significance level.

Results:

An increase in the number of radicular micro-cracks was identified in samples obturated with lateral condensation technique (1.66%). No change in the percentage of micro-cracks was recorded after obturation with warm vertical or injectable guttapercha (IGP) techniques (P > 0.05). The three obturation techniques were not statistically different in the occurrence of micro-cracks after obturation.

Conclusion:

The three obturating techniques tested showed no significant increase in radicular dentin defects' occurrence or propagation.

Micro-computed tomographic assessment of dentinal microcrack formation in straight and curved root canals in extracted teeth prepared with hand, rotary and reciprocating instruments

AIM

To compare microcrack formation in roots of extracted teeth after the shaping of straight and curved root canals with hand, rotary and reciprocating files using micro-computed tomographic (micro-CT) analysis.

METHODOLOGY

Thirty straight mandibular incisors and 30 severely curved mesial roots of mandibular molars were randomly divided into 6 experimental groups (n = 10) according to the systems used for the root canal preparation and the root canal curvature: ProTaper Universal for Hand Use (Dentsply Sirona, Ballaigues, Switzerland), HyFlex EDM (Coltene-Whaledent, Altstätten, Switzerland) and Reciproc Blue (VDW, Munich, Germany) files used in mandibular incisors (straight canals) and mesial roots of mandibular molars (curved canals). The roots were imaged with micro-CT scanning at an isotropic resolution of 14 μm before and after root canal preparation, and the cross-sectional images generated were assessed to detect microcracks.

RESULTS

All dentinal defects identified after root canal preparation were already present before instrumentation, and no new microcracks were detected. Dentinal microcracks were present in 19% (ProTaper Universal for Hand Use), 11% (Hyflex EDM) and 23% (Reciproc Blue) of the cross-sections when the instrumentation was performed in mandibular incisors. Instrumentation of mandibular molars revealed microcracks in 15% (ProTaper Universal for Hand Use), 16% (Hyflex EDM) and 17% (Reciproc Blue) of the cross-sections.

CONCLUSIONS

Preparation of straight and curved root canals with ProTaper Universal for Hand Use, HyFlex EDM and Reciproc Blue systems did not produce microcracks in extracted teeth when evaluated with micro-CT.

Light emitting diode assessment of dentinal microcracks after root canal preparation with 4 different heat-treated file systems

AIM

The purpose of this research was to evaluate the dentinal microcracks formation after root canal preparation with Hyflex EDM (Electrical Discharge Machining), Neolix Neoniti A1 EDM, Wave One Gold and Edge File X1 under illumination and magnification.

MATERIALS AND METHODS

150 mandibular molars with 2 different mesial canals extracted for periodontal reasons were included in the study. The samples were decoronated at 15mm from the apex using a carborundum disc under copious water cooling. Access opening was done using a round bur. Sectioning of the distal root was done. Patency of mesial canals were checked using a 10K file. The samples were randomly divided into 5 groups using simple randomization technique. Group 1: Uninstrumented group. Group 2: Hyflex EDM(HEDM). Group 3: Neolix Neoniti A1(NA1). Group 4: Wave One Gold (WOG). Group 5: Edge File X1(EFX). Biomechanical preparation in all groups was done following the manufacturer's instructions. Sectioning was done at 3mm, 6mm, and 9mm from the apex using a 0.13mm circular saw under copious water cooling. Sections were observed at 16x magnification under the dental operating microscope and illumination using a Light Emitting Diode (LED) curing light. The chi-square test was used to determine the statistically significant differences at P < .05. Intergroup comparison was done by the Post hoc Tukey test.

RESULTS

Total of 1800 images were analyzed. The highest number of cracks was seen in Neoniti A1 group (43.33%) while the least number of cracks were seen with Wave One Gold group (13.33%). There was statistically difference between reciprocating groups and the rotary group.

CONCLUSIONS

Within the limitations of this study, it can be concluded that all the heat-treated file systems produced dentinal microcracks. Rotary group(NA1 and HEDM) produced significantly more cracks than Reciprocation group (WOG and EFX).

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.

A Digital Microscopic Inspection of Dentinal Defects after Using Endodontic Retreatment Files

Aim

The study aimed at evaluating the incidence of dentinal defects after root canal retreatment with ProTaper Universal retreatment (PTUR) and XP-endo Shaper and Finisher R (XP).

Materials and Methods

Sixty extracted single-rooted human premolars were selected and divided into 4 groups of 15 teeth each. In the negative control group, the teeth were left unprepared. In the positive control group, the teeth were prepared with ProTaper Next and obturated with no further retreatment. In the PTUR and XP groups, the teeth were prepared and obturated followed by removal of the filling material at body temperature using PTUR and XP instruments, respectively. The roots were then sectioned at 3, 6, and 9 mm from the apex and observed under a digital microscope to detect defects.

Results

PTUR group showed significantly higher (p value <0.05) incidence of defects than the other groups. Comparison of no defects versus defects between groups in different areas of root canals demonstrated significant difference among the groups in the apical and cervical regions.

Conclusion

Within the limitations of the present study, PTUR files created significantly more dentinal defects than XP files, with most of those defects at the cervical and apical areas of the root canals.

Accuracy of Microcomputed Tomography in Detecting Dentinal Cracks: A Correlative Study with Scanning Electron and Operative Microscopy

The aim of the study was to evaluate the accuracy of microcomputed tomography (mCT) to detect dentinal cracks when compared with scanning electron microscopy (SEM) and operating microscopy (OM). Different conditions of pixel size (10 or 17 μm), sample moisture (dry/moist), and transillumination (with/without) were evaluated. Additionally, the influence of the dentinal defect width on its detection was analyzed. The root canals of human mandibular incisors were prepared with the Reciproc R40 instrument (VDW, Munich, Germany). The roots were sectioned 5 and 10 mm from the apex, and mCT scans of middle and apical segments were performed at two pixel sizes: 10 μm and 17 μm, under dry and moist conditions (groups: 10dry, 10moist, 17dry, and 17moist). The operating microscope was used with and without transillumination (groups: OMTrans and OM). Findings showed that accuracy was moderate for the 10dry, 10moist, and OMTrans groups, poor for OM and very poor for 17dry and 17moist. The thickness of the dentin crack significantly influenced its detection by mCT using the resolution of 10 μm in both dry and wet conditions (P = .002), 17 μm in the dry condition (P = .002), and by the operating microscope using transillumination (P = .009). Some cracks visualized in SEM were not detected by mCT and an operating microscope. Not only the mCT resolution but also the sample moisture condition and the dentinal crack width can significantly influence its detection.

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.

Fracture Resistance of Roots Filled With Bio-Ceramic and Epoxy Resin-Based Sealers: In Vitro Study

Objective

This study aimed to assess the resistance of roots to fracture after being root canal filled with two types of endodontic sealers; bio-ceramic based sealer (TotalFill) and epoxy-resin based sealer (AH Plus).

Methods

Fifty-nine single canal mandibular premolars were instrumented. Group I (n=14, negative control): root canals were left without instrumentation and unfilled, group II (n=15, positive control): root canals were instrumented only and left unfilled, group III and IV (n=15 each): root canals were instrumented and filled with either gutta-percha/TotalFill or gutta-percha/AH Plus, respectively. The resistance of the roots to fracture was measured with a universal testing machine "Instron Corp" through recording the maximum force in Newton (N) needed to fracture each root. To analyze the data Kruskal-Wallis test was utilized, followed by Dunn's Bonferroni post hoc test for multiple comparisons. The level of significance was set at 0.05 (P≤0.05).

Results

TotalFill group showed slightly better fracture resistance (734.62 N) than AH Plus group (728.29 N). However, no statistical significant difference was found between the two groups (P>0.05). The greatest mean fracture force was shown in the negative control group (913.915 N) with statistical significant difference between the other three groups (P<0.05).

Conclusion

Gutta-percha/TotalFill and gutta-percha/AH Plus did not reinforce the root canal treated teeth.

Evaluation of different root canal filling techniques in severely curved canals by micro-computed tomography

AIM

To fill the severely curved root canals with different filling techniques and to compare these techniques using micro-computed tomography (micro-CT).

MATERIALS AND METHODS

Sixty extracted mandibular first molars (degree of root canal curvature >25°) were selected. All samples were divided into four groups and filled with one of the following techniques: lateral condensation, single-cone, continuous-wave obturation, and core carrier. After they were scanned by micro-CT, the total area, filled area and void area of the root canal were calculated. The Mann-Whitney U and Kruskal-Wallis tests were used for statistical analysis (p < 0.05).

RESULTS

It was shown that significantly more filling material was used in the lateral condensation and core carrier technique groups at 2 and 5 mm than in the single-cone and continuous-wave obturation technique groups (p < 0.05). It was observed no statistically significant difference at 8 mm (p > 0.05).

CONCLUSION

No technique could completely fill in root canal. Regarding the coronal part, all techniques can be used for more effective filling as long as a good condensation is achieved. The use of a plugger with an optimal size according to the localisation of root canal curvature and the choice of a heat-resistant root canal sealer affects the success of the treatment in the thermoplastic techniques.

Fracture necrosis: A risk indicator for tooth loss

BACKGROUND AND OVERVIEW

The term "fracture necrosis" has been used to describe the condition found in a minimally restored tooth without a history of trauma when the suspected etiology for the loss of pulpal vitality is a crown-originating fracture. Teeth with fracture necrosis have a poor prognosis, and, when accompanied by characteristic radiographic findings, extraction may be considered the primary treatment option.

CASE DESCRIPTIONS

Two adult men with crown-originating fractures and suspected fracture necrosis had localized periodontal bone and attachment loss associated with severe pain on mastication from mandibular second molars. In case 1, the patient desired to retain the tooth despite an unfavorable prognosis. Nonsurgical root canal therapy and a crown prolonged tooth survival for only 30 months. The patient in case 2 requested extraction after a thorough review of his dental condition and tooth prognosis.

CONCLUSIONS

A tooth with fracture necrosis may continue to harbor virulent microorganisms after root canal therapy. When these microorganisms have access to the periodontal attachment, progressive loss of supporting tissues can be expected.

PRACTICAL IMPLICATIONS

When weighing treatment options for teeth with fracture necrosis associated with characteristic radiographic findings, preference toward extraction and tooth replacement, rather than treatment aimed at tooth retention, may represent a sound clinical approach.

Effect of post space preparation drills on the incidence of root dentin defects

Objectives

This study investigated the incidence of root dentin defects after the use of different post space preparation (PSP) drills.

Materials and Methods

Seventy-two bovine incisors were selected and obtained 14-mm-long root sections. Twelve roots served as controls with no intervention (G1). The 60 root canals remaining were instrumented using the crown-down technique with the ProTaper Next system and obturated using the lateral condensation technique. Specimens were randomly distributed into 5 groups (n = 12) according to the operative steps performed: G2, root canal instrumentation and filling (I+F); G3, I+F and PSP with Gates-Glidden drills; G4, I+F and PSP with Largo-Peeso reamers; G5, I+F and PSP with Exacto drill; and G6, I+F and PSP with WhitePost drill. Roots were sectioned at 3, 6, 9, and 12 mm from the apex, and digital images were captured. The presence of root dentin defects was recorded. Data were analyzed by the χ² test, with p < 0.05 considered to indicate statistical significance.

Results

Root dentin defects were observed in 39.6% of the root sections. No defects were observed in G1. G5 had significantly more cracks and craze lines than G1, G2, and G3 (p < 0.05), and more fractures than G1, G2, G3, and G4 (p < 0.05). When all root sections were analyzed together, significantly more defects were observed at the 12-mm level than at the 3-mm level (p < 0.05).

Conclusions

PSP drills caused defects in the root dentin. Gates-Glidden drills caused fewer root defects than Largo-Peeso reamers and Exacto drills.

Periapical Microsurgery: Assessment of Different Types of Light-emitting Diode Transilluminators in Detection of Dentinal Defects

INTRODUCTION

This study evaluated 4 different light-emitting diode (LED) transilluminators and the impact of operator experience in the detection of dentinal defects through an ex vivo TRUEJAW surgical model (Dental Engineering Laboratories, Santa Barbara, CA).

METHODS

Forty-four extracted and endodontically treated mandibular premolar teeth were evaluated. Teeth were mounted in the models followed by surgical flaps and osteotomies to expose the apical third of the roots. After apical resection, the root-end surfaces were randomly inspected for the presence or absence of dentinal defects using a dental operating microscope (DOM) at ×19.4 magnification by experienced and novice LED evaluators. The assessment was made with the DOM light and 4 masked LED transilluminators of different diameters and luminous flux. The teeth were examined outside the models to establish the ground truth. The sensitivity, specificity, and kappa and McNemar test values of each light source by examiner were calculated.

RESULTS

The use of LED transilluminators improved the diagnostic sensitivity of dentinal defects when compared with the DOM light alone for both examiners. For the LED-experienced evaluator, the medium-low transilluminator had statistically significant higher sensitivity than the DOM light and the small-low and small-high transilluminators (P < .05). For the novice LED evaluator, the medium-high transilluminator had the highest sensitivity. There was a statistically significant difference between the sensitivities of the medium-low transilluminator between the examiners (P < .05).

CONCLUSIONS

Within the limitations of this ex vivo surgical study, dentinal defects were more often detected with the LED transilluminators with a larger diameter and increased lumens. The operator's LED transilluminator experience was found to have a positive effect on the detection of dentinal defects using transillumination.

Effect of ultrasonic root-end cavity preparation on dentinal microcrack formation: A micro-computed tomography study

Background:

Root-end preparation during surgical endodontics may produce dentinal microcrack formation and/or propagation, leading to vertical root fractures.

Aim:

This study aimed to evaluate and compare the microcrack formation and propagation during ultrasonic root-end cavity preparation, with diamond- and zirconium nitride-coated tips using micro-computed tomography (CT).

Methodology:

Twenty-eight extracted, mature, free-of-defect, mandibular premolars were decoronated and micro-CT scanned for the presence of preexisting microcracks. Samples were prepared till F4, were obturated, and were re-scanned to determine an increase in the number of microcracks. After 3 mm of root-end resection, the samples were randomly divided for ultrasonic root-end preparation into Group 1 (n = 12): preparation was done with ProUltra Surg tip, Group 2 (n = 12): preparation was done with KiS tip, and Group 3 (n = 4): no preparation was done. The samples were rescanned, and data collected were analyzed using ANOVA and Student's t-test. The level of significance was set at 5%.

Results:

Preexisting microcracks were observed in few samples. The mean percentage number increase of microcracks after root-end preparation in ProUltra Surg group was 1.25 and in KiS group, it was 0.5. The difference in mean percentage increase for the number of microcracks after root-end cavity preparation using ProUltra Surg tip and KiS tip was 0.75. However, this difference was not statistically significant (P = 0.34).

Conclusion:

Both diamond- and zirconium nitride-coated ultrasonic tips resulted in more number of dentinal crack formation and propagation when preexisting cracks were present.