Incidence of dentinal defects after root canal filling procedures

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.

Effect of the Modified Methacrylate-Based Root Canal Sealer in Single-Cone Technique

This study aimed to modify EndoREZ with 2.5% dimethylaminododecyl methacrylate (DMADDM) and 1% magnetic nanoparticles (MNP) to study its sealing property, penetration and long-term antibacterial and therapeutic effect in the single-cone technique (SCT) compared with EndoREZ and iRoot SP. Thirty single-root human maxillary premolars were assigned into three groups and obturated with three different root canal sealers by SCT. Every specimen was then scanned using micro-CT to analyze void fraction, and void volumes and confocal laser scanning microscope (CLSM) was used to study the dentin penetration. The long-term antimicrobial effects were tested in vitro before and after aging 1 and 4 weeks by the single-strain Enterococcus faecalis biofilm model. In addition, the beagle canine model of apical periodontitis (AP) was utilized to judge and compare the therapeutic effect of three sealers in SCT. The void fraction and void volumes of the modified root canal sealer were not significantly different from iRoot SP (p > 0.05) but were lower than EndoREZ (p < 0.05). The modified root canal sealant displayed a greater penetration, long-term antibacterial property, and treatment effect than the other groups (p < 0.05). This indicated that after being modified with DMADDM and MNP, it showed better performance in SCT.

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.

The Influence of Root Canal Preparation with ProTaper Next, WaveOne Gold, and Twisted Files on Dentine Crack Formation

(1) Background: Root canal preparation constitutes an important factor for success in endodontics. However, various complications may occur during this stage. The aim of this study was to compare the incidence of cracks within radicular dentin after instrumentation with ProTaper Next (PTN), WaveOne Gold (WOG), and Twisted Files (TF), which utilize different kinematics. (2) Methods: Eighty single-rooted teeth were classified into four groups (n = 20). Three groups were instrumented using PTN (X1, X2), WOG (Primary), and TF (SM1–3). The non-instrumented group constituted the control group. Post-preparation, the roots were sectioned 3, 6, and 9 mm from the apex using a low-speed saw (Southbay Technology Inc., San Clemente, CA, USA). The specimens were viewed through a microscope at x25 magnification (Leica M320, Wetzlar, Germany), and their surface was assessed tactilely to determine the presence of the crack. (3) Results: Partial cracks within radicular dentine were observed in all study groups (PTN: n = 4/20%, WOG: n = 3/15%, TF: n = 4/20%); no cracks were observed in the control group. No significant differences were observed among experimental groups. OR values for the incidence of cracks were: OR = 11.182 for PTN, OR = 8.2 for WOG, and OR = 8.2 for TF. (4) Conclusions: Instrumentation with PTN, WOG, and TF may result in dentinal cracks formation.

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.

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.

Vertical root fracture resistance and dentinal crack formation of root canal-treated teeth instrumented with different nickel-titanium rotary systems: an in-vitro study

To compare the vertical root fracture (VRF) resistance of root canal-treated teeth instrumented with four different nickel-titanium (NiTi) rotary file systems and examine the dentinal crack pattern and direction using a new classification. Eighty mature mandibular premolars were selected and decoronated, leaving 13 mm of the root. The root samples were mounted in acrylic resin and divided randomly into five groups of different NiTi file systems: Group 1-control, Group 2-T-Pro, Group 3-HyFlex CM, Group 4-TG6 and lastly Group 5-ZenFlex. Samples in Group 2 and Group 3 were instrumented up to size 25/0.04, whereas Group 4 and Group 5 were instrumented up to size 25/0.06. Obturation was performed with AH Plus sealer and gutta-percha using single cone technique. Subsequently, all samples were subjected to occlusal compressive force until they were fractured. The force (N) needed to cause root fracture was recorded. The crack patterns and directions were also inspected under magnification and classified using a new and simple classification. The highest (VRF) resistance was noted in the control group (453.15 ± 92.23 N), followed by T-Pro (387.43 ± 76.81 N), HyFlex CM (381.88 ± 52.73 N), ZenFlex (369.15 ± 89.41 N) and finally TG6 (346.05 ± 72.08 N), but there was no significant difference between T-Pro and HyFlex (P = 0.438). A significantly higher prevalence (P = 0.001) of Type 1 crack pattern was observed, especially in samples instrumented with TG6. Majority of the cracks ran buccolingually except in some samples instrumented with ZenFlex (P = 0.898). Smaller file taper increased the VRF resistance of root canal-treated teeth. Majority of the dentinal crack exhibited Type 1 pattern and ran buccolingually.

Fracture Resistance of Titanium, Chrome-Cobalt, and Gold Alloy as Post and Core Materials: A Comparative Evaluation

Aim:

This study aimed to comparatively evaluate the fracture resistance of different metallic post and core materials.

Materials and Methods:

Twenty-four maxillary–central incisors were selected, standardized, and segregated into three groups (GP I–III) (n = 8) based on the type of alloy used for post and core preparation. GP I (gold alloy [Au]), GP II (chrome–cobalt alloy [Co–Cr]), and GP III (titanium alloy [Ti]) were comparatively evaluated for use as post and core materials. The teeth were endodontically treated and tooth preparation for post core was done.Metal post and cores were fabricated using indirect wax pattern and luted. Teeth were mounted on resin bases, fracture testing was done, and type of fractures were analyzed.

Results:

Mesiodistal type of fracture was the most common among experimental groups with a percentage incidence of 54.20%. The comminuted type of fracture was the next most common with a percentage incidence of 29.2%. The incidence of buccolingual, transverse, and other type of fracture was not common and had a percentage incidence of 29.2%, 4.2%, 8.3% and 4.2% respectively. Group II had the highest fracture resistance with a mean value of 742.89N. Group III and Group I had mean values of 482.33 and 361.1123N. Statistically significant difference between experimental groups (I and II) and (II and III) was observed in load values of root fracture (P < 0.05).

Conclusion:

On the basis of the protocols used and limitations of this study, among metallic post and core materials tested, GP II had the highest fracture resistance values. Further evaluation of these different post and core systems, new alloy formulations designed specifically for use as post and core materials, and assessment in a clinical setting is recommended.

Occurrence of Vertical Root Fractures after Apical Surgery: A Retrospective Analysis

INTRODUCTION

Vertical root fractures (VRFs) are among the most frequent causes of tooth loss, mainly of endodontically treated teeth. However, very few data is available about the occurrence of VRFs following apical surgery.

METHODS

Patient charts from 864 patients with 1058 teeth treated with apical surgery (September 1999 to December 2018) were retrospectively evaluated, if a VRF had occurred after surgery. The following, possibly influencing factors were analyzed: sex and age, type of treated tooth, primary versus resurgery, technique of root-end preparation, and timepoint of VRF diagnosis. Endpoints were either tooth extraction or the last follow-up.

RESULTS

The study cohort (55% women, 45% men) had a mean age of 52.00 ± 13.97 years (range 9-93 years). The overall rate of VRFs after apical surgery was 4% (42 of 1058 teeth). Among these 42 teeth, 33.3% were mandibular first molars and 26.2% were maxillary second premolars. The most frequently affected root was the mesial root of mandibular first molars (28.6%). With regard to the study parameters, significant differences of VRF rates were observed only for the type of tooth treated.

CONCLUSIONS

A low VRF rate of 4% was observed in this study. VRFs commonly occurred in maxillary premolars and mandibular molars, with the mesial root of mandibular first molars affected most frequently. This is in line with previous reports about VRFs in endodontically treated teeth without additional apical surgery.

Diagnosis of root fractures using cone-beam computed tomography: difference of vertical and horizontal root fracture

OBJECTIVES

The aim of this study was to investigate the occurrence of vertical and horizontal root fractures using cone-beam computed tomography (CBCT).

METHODS

We reviewed the CBCT images of 51 patients who were examined by CBCT for the diagnosis of root fracture. The occurrences of vertical and horizontal root fractures were investigated concerning the pulpal vitality and the kind of tooth, and analyzed by cross-tabulation. The fracture direction of vertical root fracture and the fracture angle were also investigated, and analyzed by cross-tabulation and Kruskal-Wallis test, respectively.

RESULTS

The occurrence of vertical and horizontal root fractures was statistically significantly different between vital tooth and non-vital tooth (p = 0.044). The occurrence of vertical and horizontal root fractures was also different among anterior, premolar, and molar teeth (p = 0.004). The kind of tooth on traumatized tooth was only anterior teeth and the number was larger on horizontal root fracture. The occurrence of vertical and horizontal root fractures on non-traumatized tooth was different among the kind of tooth (p = 0.007), and the number of vertical root fracture was larger than that of horizontal root fracture on premolar teeth. Fracture direction was not different, but the fracture angle was different among the kind of tooth on vertical root fracture (p = 0.027).

CONCLUSIONS

The results suggested that the number of vertical root fracture was larger on non-vital tooth and that of horizontal root fracture was larger on vital tooth. The number of vertical root fracture was larger on premolar 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.

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.

Comparison of continuous wave and cold lateral condensation filling techniques in 3D printed simulated C-shape canals instrumented with Reciproc Blue or Hyflex EDM

Aim

To compare the efficiency of continuous wave obturation and cold lateral condensation techniques and filling time in C-shape canals of 3-dimensional (3D)-printed resin teeth shaped with Reciproc Blue (VDW) or Hyflex EDM (Coltene/Whaledent).

Methodology

One tooth with C1-type orifice and root canal morphology and one with C2-type orifice and C2-C3 root canal morphology were selected based on CBCT. Two replicas of selected teeth were manufactured with a 3D-printer and their canals were instrumented with Reciproc Blue or Hyflex EDM. These 4 instrumented replicas were scanned with CBCT. Identical 10 replicas of each group (total of 40) were produced using a 3D-printer and randomly divided into 2 groups (n = 5), root filled with either continuous wave obturation (CW) or cold lateral condensation (LC). Horizontal cross-sections of C1-type were made at 2, 4, 6, 8 mm and C2-type at 2, 4, 6 mm from the apical foramen. Gutta-percha, sealer and void areas were evaluated with image analysis sofware. Data were analysed using nonparametric Kruskal-Wallis and Mann Whitney-U tests and the Factorial ANOVA was used for interaction effects. Time required to fill canals was evaluated using the Mann-Whitney U test.

Results

For C1-type, LC had more gutta-percha and less sealer compared to CW in 2-mm sections (p<0.05). CW had greater percentages of gutta-percha and lower percentages of sealer compared with LC group in 4, 6, 8 mm sections and total area (p<0.05). LC group had higher percentages of voids compared to CW group in 2 and 4 mm sections (p<0.05). For C2-type, CW had more gutta-percha and less sealer versus LC group in all sections and total area (p<0.05). LC had the least gutta-percha and greatest sealer percentages at 6-mm sections (p<0.05). There was no statistically significant difference in the percentages of voids at any level of sections between the filling techniques (p>0.05). In both C-types, there was no significant difference in the percentages of gutta-percha, sealer and voids between Reciproc Blue and Hyflex EDM-shaped groups at any level (p>0.05). Time spent for the LC technique and filling C1-type was significantly longer than when using the CW technique and filling C2-type (p<0.05).

Conclusions

Continuous wave obturation was more effective than lateral condensation in both C1- and C2-type, except for the apical 2 mm section of C1-type, suggesting the need for a modified CW technique.

Effects of Ultrasonic Removal of Fractured Files from the Middle Third of Root Canals on the Resistance to Vertical Root Fracture

INTRODUCTION

This study aimed to analyze the effects of ultrasonic removal of fractured files from the middle third of root canals on the vertical root fracture resistance.

METHODS

This study was an extension of a previous study assessing the effects of fractured file removal on dentinal microcracks. It included 18 bilaterally matched pairs of human mandibular incisors prepared and analyzed in the previous study. Briefly, 1 member of each pair was assigned to an ultrasonic or a control group. In the ultrasonic group, K-files were fractured in the middle third of canals followed by ultrasonic file removal and canal preparation. In the control group, the root canals were simply prepared. Micro-computed tomographic imaging was performed before and after treatment, and the cross-sectional root images were screened for microcracks. For the present study, 3-dimensional reconstruction was performed for volumetric assessments. The fracture resistance was measured using a universal testing machine. All data were statistically analyzed.

RESULTS

Fracture loads were significantly smaller in the ultrasonic group (P < .05). The percentage increase in the canal volume significantly influenced the root fracture resistance (P < .05), whereas microcracks had no significant effect (P > .05).

CONCLUSIONS

Ultrasonic removal of fractured instruments from the middle third of root canals lowers the vertical root fracture resistance, with increased dentin removal being the primary cause.

Relationship between Canal Enlargement and Fracture Load of Root Dentin Sections

OBJECTIVE

To investigate the effect of endodontic instrumentation on fracture susceptibility of root dentin using experiments and stress analysis.

METHODS

Root canals of lower premolars were enlarged with different tapers. After, teeth were cut into 2-mm sections. A metal rod of the same taper was pushed through the center of the sections using a universal test system to fracture them. The fracture load was determined from the peak load on the load-displacement curve. To determine fracture-causing stress, an axisymmetric FE model was created. An analytical solution was developed to understand the relationship between fracture load, geometrical and material parameters.

RESULTS

For the same taper, increased root canal diameter did not lead to reduced fracture load. Both analytical and FE solutions showed positive linear relationship between fracture load and enlarged root canal diameter. The hoop stress was maximum at inner surface of enlarged root canal and reduced with increasing radial distance from the center. Bending of sections introduced further nonuniform stresses along the depth. Predictions for the fracture load based on the maximum hoop stress were closest to experimental values; however, account must be taken of the variation in fracture stress of dentin along the root length. Significance Our results rejected the hypothesis that fracture load of root dentin sections reduced with endodontic instrumentation size. However, the stress distributions in whole endodontically treated teeth are more complicated. Thus, caution is necessary when using thin root sections to investigate the effect of endodontic instruments on vertical root fracture.

Dentinal Microcrack Formation During Root Canal Treatment with Mtwo Instruments and MicroSeal Filling Technique

Objective:

The purpose of this study was to evaluate dentinal microcrack formation during root canal treatment using Mtwo NiTi rotary instruments and MicroSeal filling technique.

Materials and Methods:

Forty-five single-rooted teeth were selected for the present study and divided into 3 different groups ( n = 15): Group 1, in which root canals were instrumented with Mtwo rotary files; Group 2, in which root canals were instrumented with Mtwo rotary files and filled using the MicroSeal technique; and Group 3, that acts as a control group in which no instrumentation nor obturation were performed. Then, roots were sectioned 3 mm, 6 mm, and 9 mm from the apex and the cut surface has been observed under a stereomicroscope to check for the presence or absence of dentinal microcracks. Number of dentinal microcracks was registered for each group at different levels and data were statistically analyzed using the Chi-square test with a level of significance set at P < .05.

Results:

No statistically significant differences were registered among groups ( P < .05). No microcracks were detected in Groups 1 and 3, while two dentinal microcracks were registered in Group 2.

Conclusions:

Mtwo rotary instruments and the MicroSeal root canal filling technique did not significantly induce dentinal microcrack formation.

Effect of root canal preparation, obturation, and retreatment on the induction of dentinal microcracks: A microcomputed tomography study

Introduction:

This study evaluated the effect of root canal preparation, obturation, and different techniques of retreatment on the percentage increase in the number of dentinal microcracks using microcomputed tomography (CT) analysis.

Materials and Methods:

Forty-five mandibular premolars after micro-CT scanning were prepared using Protaper universal files up to F4 and obturated. After the second micro-CT scanning again, the samples were randomly divided into three groups (n = 15) for retreatment procedure. In Group 1, retreatment was done with Protaper universal D1, D2, and D3 retreatment files followed by Protaper universal file till F4. In Group 2, retreatment was performed with R-Endo reciprocating motion, Re, R1, R2, R3, and Rs followed by Hero Shaper size #40. In Group 3, retreatment was performed with H-files and xylene till size #40. After gutta percha removal, the samples were again scanned for micro-CT for the evaluation of percentage increase in dentinal microcracks. Data were analyzed using “Kruskal–Wallis test ANOVA” and “student t-test” at 5% level of significance.

Results:

Few unprepared samples showed preexisting microcracks. There were statistically significant percentage increase dentinal cracks after root canal preparation and obturation as well as after retreatment procedure with statistically significant percentage increase in the number of dentinal microcracks between all three groups.

Conclusion:

Intraradicular procedures such as shaping and cleaning and obturation as well as the use of retreatment file lead to the induction and propagation of dentinal microcracks. In the present study, the maximum microcracks were produced with Protaper universal retreatment file system followed by R-Endo system. H-files produced minimum cracks during retreatment procedures.

Root-originating dentinal defects: methodological aspects and clinical relevance

It was in the 1980s when the association between root-filling procedures and dentinal microcracks was made. Nowadays, root-originating microcracks, also known as dentinal defects, are recognized as a possible precursor that is part of the longitudinal process of root-originating fractures. The presence of dentinal defects has been shown to significantly decrease the outcome through a periapical microsurgery model. Several in vitro articles have been published in the past years in regards to dentinal defects, but most of them have serious methodology concerns that will be discussed in this review.

A total grasp of the development and the role dentinal defects play in endodontics is crucial to the specialty. This review aims to discuss dentinal defects and their causative factors and the research models that have been used and their clinical significance. Through a comprehensive critical review of the literature, this article will express the need for further in vivo clinical research and better ex vivo methods that can replicate the clinical setting to answer several remaining questions about the development of and the role dentinal defects play in endodontics.

Partial Ceramic Crowns Prepared by Dental Students: Clinical Performance Up to Five Years

Partial ceramic crowns (PCCs) are an accepted treatment option for the restoration of posterior teeth with deficient tooth substance. Data on the survival of PCCs fabricated by dental students are scarce. The aim of this retrospective clinical study was to investigate the clinical performance and longevity of PCCs placed by dental students in the last year of their training program at the University of Basel, Switzerland. Eighty-eight patients who had received at least one PCC (n=108) in the program were considered for clinical assessment; their records were analyzed to detect previous complications or failures; and they were contacted by telephone. Criteria regarding aesthetic, functional, and biological aspects were rated with a scoring system from 1=clinically excellent to 5=clinically poor. The response rate was 66.3% (55 of 83 included patients), and 72.2% (n=78) of the PCCs were included in the analysis. Five PCCs had been lost within ten to 78 months after treatment. Six PCCs were recorded as failures (score 5), and ten received clinically unsatisfactory gradings (score 4). The risk of a clinically poor outcome was 14% after five years (86% survival), while the overall success rate was 63.5%. These results suggest that the clinical procedure of PCCs was successfully implemented by these students with satisfactory clinical survival.

Light-emitting diode assessment of dentinal defects: the role of presumed extraction forces

Objectives

The evaluation of iatrogenic dentinal defects in extracted teeth may be influenced by extraction forces and prolonged dry times. The purpose of this study was to compare the presence of dentinal defects in freshly extracted, periodontally compromised teeth with those in a group of teeth with uncontrolled extraction forces and storage time.

Materials and Methods

The experimental group consisted of eighteen roots obtained from teeth extracted due to periodontal reasons with class II or III mobility. They were kept in saline and sectioned within 1 hour following extraction. The control group consisted of matched root types obtained from an anonymous tooth collection, consistent with previous dentinal defect studies. The slices were obtained at 3, 6, and 9 mm from the apex. The imaging process exposed all specimens to no more than 60 seconds of dry time. The × 12.8 magnification was used for the 9 mm slices and × 19.2 magnification for the 3 mm and 6 mm slices under light-emitting diode (LED) transillumination. The root canal spaces and periodontal tissues were masked to minimize extraneous factors that might influence the evaluators. Chi-square test was used for statistical analysis.

Results

Dentinal defects were detected in 17% of the experimental group teeth, compared to 61% of control teeth (p = 0.015).

Conclusions

LED transillumination assessment of freshly extracted roots with class II or III mobility showed smaller number of dentinal defects than roots with uncontrolled storage time and extraction forces. The use of freshly extracted roots with mobility should be considered for future dental defect assessment studies.

Evaluation of Dentin Defect Formation during Retreatment with Hand and Rotary Instruments: A Micro-CT Study

The purpose of this study was to compare the incidence and longitudinal propagation of dentin defects after gutta-percha removal with hand and rotary instruments using microcomputed tomography. Twenty mandibular incisors were prepared using the balanced-force technique and scanned in a 19.9 μm resolution. Following filling with the lateral compaction technique, gutta-percha was removed with ProTaper Universal Retreatment (PTUR) or hand instruments. After rescanning, a total of 24,120 cross-sectional images were analyzed. The numbers, types, and longitudinal length changes of defects were recorded. Defects were observed in 36.90% of the cross sections. A total of 73 defects were comprised of 87.67% craze lines, 2.73% partial cracks, and 9.58% fractures. No significant difference in terms of new defect formation was detected between the retreatment groups. The apical and middle portions of the roots had more dentin defects than the coronal portions. Defects in three roots of the PTUR instrument group increased in length. Under the conditions of this in vitro study, gutta-percha removal seemed to not increase the incidence of dentin defect formation, but the longitudinal defect propagation finding suggests possible cumulative dentinal damage due to additional endodontic procedures. Hand and rotary instrumentation techniques caused similar dentin defect formation during root canal retreatment.

Long-term Clinical Outcomes of Endodontically Treated Teeth Restored with or without Fiber Post-retained Single-unit Restorations

INTRODUCTION

The aim of the present study was to evaluate both survival and failure rates of endodontically treated teeth restored with or without fiber post-retained restorations after a mean observation period of at least 5 years.

METHODS

A total of 144 single-rooted and multirooted teeth in 100 subjects were endodontically treated following a predetermined aseptic protocol and restored with either a fiber post and a composite core or a composite filling without intraradicular retention. A fiber post was cemented when the teeth presented with only 1 wall and/or less than one third of the remaining height of the clinical crown. After a comprehensive treatment plan, the teeth were restored with either a direct composite restoration or a single-unit crown. Endodontically treated teeth supporting fixed and removable dental prostheses and telescopic crowns were excluded from the analysis. Success was defined as tooth survival without any treatment of biological and/or technical complications.

RESULTS

The overall tooth survival rate was 89.6% after a mean observation time of 8.8 ± 2.3 years. The survival rate of teeth with a fiber post amounted to 94.3%, and for teeth without a post, it was 76.3% (P < .001). The main reason for tooth loss was root fracture (9.7%). No loss of post retention was observed. Successfully treated teeth without any biological and/or technical complications and requiring no additional treatment during the entire observation period amounted to 79.9%.

CONCLUSIONS

Endodontically treated teeth restored with fiber posts and either a direct composite restoration or a single-unit crown yielded higher survival and success rates compared with teeth restored without fiber posts. Vertical fractures of roots not containing a post represented a frequently encountered and serious problem.

Micro-CT assessment of dentinal micro-cracks after root canal filling procedures

AIM

To evaluate the frequency of dentinal micro-cracks after root canal filling procedures with GuttaCore (GC), cold lateral compaction (CLC) and warm vertical compaction (WVC) techniques in mandibular molars using micro-computed tomographic analysis.

METHODOLOGY

Thirty mesial roots of mandibular molars, with a type II Vertucci's canal configuration, were prepared to working length with a Reciproc R40 instrument and randomly assigned to one of the three experimental groups (n = 10), according to the technique used for root filling: GC, CLC or WVC. The GC group was filled with a size 40 GC obturator, whilst CLC and WVC groups used conventional gutta-percha cones. AH Plus sealer was used in all groups. The specimens were scanned at an isotropic resolution of 14.25 μm before and after root canal preparation and after root filling. Then, all pre- and postoperative cross-sectional images of the roots (n = 41 660) were screened to identify the presence of dentinal defects.

RESULTS

Overall, 30.75% (n = 12 810) of the pre- + post-filling images displayed dentinal defects. In the GC, CLC and WVC groups, dentinal micro-cracks were observed in 18.68% (n = 2510), 15.99% (n = 2389) and 11.34% (n = 1506) of the cross-sectional images, respectively. All micro-cracks identified in the post-filling scans were also observed in the corresponding post-preparation images.

CONCLUSION

Root fillings in all techniques did not induce the development of new dentinal micro-cracks.

Synchrotron-based Phase Contrast-enhanced Micro-Computed Tomography Reveals Delaminations and Material Tearing in Water-expandable Root Fillings Ex Vivo

INTRODUCTION

This study evaluated the integrity of calcium silicate sealer-based fillings made with hygro-expandable cones (HEC) that are commercially known as CPoint or Smartpoint.

METHODS

Fourteen human canines were prepared according to a standardized, conventional endodontic treatment protocol and filled with the HEC/calcium silicate sealer. Three-dimensional imaging was performed with laboratory micro-computed tomography (μCT) at its highest resolution and was compared with synchrotron phase contrast-enhanced μCT (PCE-CT) scans of the treatment extending 1-7 mm from the apex. Conventional destructive optical microscopy validated observations by comparison with virtual slices in the tomographic data.

RESULTS

Conventional laboratory μCT at 10-μm resolution did not reveal the existing voids and defects within the root canal fillings. PCE-CT revealed elongated interfacial delamination localized mainly at the HEC-sealer interface forming extended through-and-through gaps along the root canal filling.

CONCLUSIONS

Endodontic studies that use conventional laboratory μCT may underestimate thin defects and delamination within root canal fillings made with HEC because of limited resolution and contrast of laboratory-based broad-spectrum low intensity x-ray sources. These limitations favor use of high-brilliance, monochromatic synchrotron-based PCE-CT to reveal the important micrometer details within large (millimeter sized) samples. PCE-CT revealed the existence of a range of significant structural defects in recently placed HEC fillings, confirmed by optical microscopy after physical sectioning. Substantial delamination spanning 20%-40% of the circumferential interface as well as other structural defects were identified within root canal fillings made of HEC and calcium silicate sealer.

Mechanical or cold lateral compaction: The incidence of dentinal defects

Background:

The incidence of dentinal defects may influence the outcome of root canal treatment. The aims of this study were to evaluate and compare the incidence of dentinal defects following root canal obturation with two different techniques.

Materials and Methods:

A total of 110 mesial roots of human mandibular first molars were selected. Twenty-seven roots were left unprepared as negative controls (NCs). The mesiobuccal canals of 83 roots were prepared using rotary instruments. Twenty-seven roots were left unobturated as positive controls (PCs). Twenty-eight roots were obturated with cold lateral compaction (CLC) technique and the others were obturated with mechanical lateral compaction (MLC) technique. In the CLC and MLC groups, spreader penetration depth was measured by an electromechanical testing machine in canals containing master Gutta-percha cones. After root canal obturation, all the roots were sectioned horizontally at four levels from the apex and evaluated under a stereomicroscope at a magnification of ×40. The presence of dentinal defects was noted. Data were analyzed using the Chi-square and t-tests.

Results:

The number of defects was not significantly different between the CLC, MLC, and PC groups. The CLC, MLC, and PC groups had significantly more defects compared to the NC group.

Conclusion:

According to the results of this study, the MLC and CLC techniques were the same in producing dentinal defects.

Sealing efficacy of a single-cone root filling after post space preparation

Objectives

The aim of the present study was to compare the sealing efficacy of root fillings made by a single-cone technique with three different sealers and a cold lateral compaction technique with an epoxy sealer.

Materials and methods

Eighty extracted single-rooted human teeth were assigned to four experimental groups: group 1, single-cone and epoxy sealer; group 2, single-cone and calcium silicate-based sealer; group 3, single-cone and methacrylate resin-based sealer; and group 4, cold lateral compaction and epoxy sealer. Twenty extra teeth served as negative and positive controls. After preparation of a coronal post space, the sealing efficacy of the root fillings was assessed on a fluid transport setup. The results were analyzed using Kruskal-Wallis and Mann-Whitney U test.

Results

No fluid transport was detected for the negative controls whereas all the positive controls showed rapid fluid transport. No significant difference was detected between groups 1, 3, and 4 whereas group 2 demonstrated significantly more fluid transport than all the other experimental groups.

Conclusions

Root fillings made by a single-cone technique with the epoxy or methacrylate-based sealers were as effective after post space preparation as those made by a cold lateral technique with the epoxy sealer in sealing the root canal.

Clinical Relevance

Specific root canal sealers in combination with single-cone technique represent a noteworthy alternative to the use of cold lateral compaction technique when a post space is required. The use of effective endodontic procedures with simplified technical implementation may positively affect endodontic outcome.

A microcomputed tomography-based comparison of root canal filling quality following different instrumentation and obturation techniques

OBJECTIVE

With a microcomputed tomography (microCT) imaging device, we aimed to quantitatively evaluate root canal fillings after commonly used endodontic procedures and also tested the suitability of microCT for this purpose.

MATERIALS AND METHODS

Eighty single roots were instrumented and obturated with gutta-percha and Tubli-Seal. They were divided into 4 groups of 20. The Hand groups were instrumented with hand files and filled with thermoplastic (Th) compaction and cold lateral (CL) condensation, i.e. Hand-Th and Hand-CL, respectively. The Rot groups, i.e. Rot-Th and Rot-CL, were instrumented with a rotary ProFile system and filled as above. The roots were scanned and 3-dimensional (3D) visualization was obtained. The number, size, percentage of volume and distribution of voids at the filling/dentine interface (i-voids) and voids surrounded by filling material (s-voids) were measured.

RESULTS

Canal fillings differed significantly with regard to the size of both types of voids and the average number of i-voids. All canals presented a low volume of voids. The highest percentage (0.69%) was found for i-voids in the Hand-CL group, while the lowest volume (0.11% for s-voids and 0.14% for i-voids) was in the Hand-Th canals. Apically, in the last 3 mm, i-voids were observed mainly in the Th groups, and s-voids occurred mostly in the coronal part of the canal filling in all cases.

CONCLUSION

MicroCT was a useful tool for 3D quantitative evaluations of these root canal fillings. None of the root canal instrumentation and filling methods ensured void-free obturation. CL condensation produced mainly i-voids. With Th compaction, internal s-voids were particularly common, but there were mainly i-voids in the apical part.

Effects of root canal preparation, various filling techniques and retreatment after filling on vertical root fracture and crack formation

AIM

To investigate the incidence of cracks in root dentin after rotary instrumentation and filling with cold lateral condensation (CL), single-cone obturation (SC), and warm vertical compaction (WV) and retreatment of each filling system.

METHODOLOGY

One-hundred sixty mandibular incisors were selected. Twenty teeth were left unprepared and served as a control, and the remaining 140 teeth were instrumented. Twenty teeth were assigned to an only prepared group. The remaining 120 teeth were assigned to three root canal filling groups and three retreatment groups (n = 20), as follows: CL, WV, SC, and retreatment of each filling system. All the roots were sectioned perpendicular to the long axis at 2, 4, 6, and 8 mm from the apex, and the sections were then observed under a stereomicroscope. The absence/presence of cracks and vertical root fractures were recorded, and the data were analyzed with a Pearson's chi-square test (P = 0.05).

RESULTS

No complete vertical root fractures were observed in the unprepared and only prepared groups. However, vertical fractures were observed in the filling and retreatment groups. There were significantly more cracks in the retreatment after WV group than the other groups, with the exception of the retreatment after SC, WV, and CL resulted in significantly more cracks than the only prepared and SC.

CONCLUSIONS

The filling techniques (except SC) caused more cracks than preparation only. The SC caused fewer cracks compared to the other filling techniques. The retreatment following the different filling techniques (except CL) caused more cracks than the original fillings.

The effect of reciprocation versus rotational movement on the incidence of root defects during retreatment procedures

AIM

To compare the incidence of dentinal defects caused by reciprocating and rotary techniques during retreatment procedures.

METHODOLOGY

One hundred and twenty extracted mandibular premolars with single canals were selected. Twenty teeth were left unprepared. The root canals in the remaining 100 teeth were prepared with K-files up to size 35 and filled with Gutta-percha and AH Plus sealer using a passive cold lateral compaction technique. Twenty canals were filled and received no further treatment. Eighty teeth were divided into four groups (n = 20 in each) to undergo the removal of the root filling. In groups 1 and 2, the root filling was removed using ProTaper Retreatment files and Reciproc files, respectively, and the canals were not refilled. In groups 3 and 4, the root filling was removed using ProTaper Retreatment files and Reciproc files, respectively, and the canals were then refilled using a conventional cold lateral compaction technique. The roots were sectioned horizontally at 3, 6 and 9 mm from the root apex and observed under a stereomicroscope at 20× magnification. Defects were categorized as no defect, incomplete defect and fracture. The differences between the groups were analysed using the chi-square exact test (P = 0.05).

RESULTS

No defects were observed in the unprepared and filled groups, in contrast to the experimental groups. In the coronal thirds, groups 2 and 4 had more dentinal defects than groups 1 and 3 (P < 0.05). In the middle thirds, group 4 had more defects than group 1 (P < 0.05). In the apical thirds, group 2 had fewer defects than did group 3 and group 4. Also, group 3 had more defects than group 1 (P < 0.05). When comparing the experimental groups, there were no significant differences with regard to fracture (P > 0.05).

CONCLUSIONS

Both nickel-titanium systems were associated with dentinal defects during retreatment procedures in extracted premolar teeth.

Synchrotron light-based μCT to analyse the presence of dentinal microcracks post-rotary and reciprocating NiTi instrumentation

OBJECTIVES

The purpose of this study was to determine in vitro using a synchrotron radiation-based μCT (SRCT) whether rotary and reciprocating nickel titanium (NiTi) instrumentations lead to the formation of dentine microcracks.

MATERIAL AND METHODS

Fourteen extracted human molars were obtained with ethical approval. Seven distobuccal roots of the maxillary molars and seven mesial roots of the mandibular molars were assigned to two experimental groups: (A) prepared with rotary Pro Taper instrumentation (n = 6) and (B) reciprocating WaveOne (n = 6). Irrigation with 1 % NaOCl and 17 % EDTA solutions was carried out. The remaining roots served as positive control with induced fractures (group C). SRCT was used to scan all samples pre and post-operatively. An imaging software was used to determine the number and length of microcracks. Statistical analyses weighed differences between pre and post-instrumentation and between shaping methods.

RESULTS

A significant increase in the number and length of microcracks was detected post-shaping. No significant difference between rotary and reciprocating instrumentation was observed.

CONCLUSIONS

Within the limitations of this in vitro study, an increased number and length of microcracks was induced by mechanical instrumentation. Reciprocating and rotary instrumentation are similar in terms of effect.

CLINICAL SIGNIFICANCE

Dentinal damage may occur following rotary and reciprocating instrumentation.

Dentinal defects before and after rotary root canal instrumentation with three different obturation techniques and two obturating materials

Aim:

To evaluate the role of rotary root canal instrumentation followed by obturation with three different techniques and two different materials on the incidence of dentinal defects.

Materials and Methods:

One hundred and sixty mandibular premolars were divided into eight groups (n = 20). Group I was left untreated and served as control. The other seven groups were prepared with profile rotary instruments till #40.06 taper. After preparation, group II was left unfilled, groups III, IV, and V were obturated with Gutta-percha and AH Plus sealer using passive technique, lateral compaction and warm vertical compaction, respectively. Groups VI, VII, and VIII were obturated with Resilon and Realseal sealer using passive technique, lateral compaction, and warm vertical compaction, respectively. Roots were then sectioned at 3, 6, and 9 mm from the apex and inspected under a stereomicroscope (50×) for dentinal defects. Chi-square test was performed to compare the incidence of dentinal defects between the groups (P < 0.05).

Results:

The unprepared control group had no dentinal defects. The instrumentation group (group II) and the obturation group (groups III-VIII) showed significantly more defects than the uninstrumented control group (group I) (P < 0.001). There was no significant difference between the root canal obturating techniques (group III-VIII) when compared with the instrumentation group (group II). On inter group comparison among the obturation groups the number of defects after lateral compaction with Gutta-percha (group IV) was significantly larger than passive Gutta-percha obturation (group III) (P < 0.05).

Conclusions:

The results suggest that root canal instrumentation significantly influenced the incidence of dentinal defects or fracture. Dentinal defects were more significantly attributed to the role of root canal instrumentation rather than the type of obturation technique or material. Lateral compaction with Gutta-percha significantly produces more defects than passive Gutta-percha obturation.

Device and materials for in vitro evaluation of forces developed to teeth and periodontal structures during dental practices

This study aimed at providing a gauge device (Ekontak et al Gauge K-Device) in order to analyze the forces applied to teeth and periodontal tissues during dental practices in vitro. This force gauge device can be used in the investigation of the possible defect generation to tooth structures when overloaded forces are applied during dental procedures in vitro. Ekontak et al Gauge K-Device consists of three units: the specimen's holder, a high-performance digital force gauge, and the support frame. The holder was fabricated by an Al alloy providing a steady detachable attachment between the specimens and the force gauge's pin connector. The clinical simulation was achieved with the use of a proper silicone material, selected to provide similar elastic behavior with the human periodontal ligament and to join the teeth inside a solid matrix of an acrylic resin. The digital force gauge is a high-speed collection and recording (1000 Hz) product coupled with data recording software. The forces developed to 15 specimens' root canals during lateral condensation and vertical compaction of cold gutta-percha obturation procedures were monitored, saved as graphs, CSV, and excel files and presented over time. The forces developed during vertical compaction (mean maximum force per obturation circle = 13.22 N) were more excessive than those during lateral condensation (mean maximum force per obturation circle = 10.14 N). In conclusion, Ekontak et al Gauge K-Device is provided as a modern gauge device, capable of performing clinical simulation in vitro, under the terms of its protocol.