The Effect of Isthmus on Vertical Root Fracture in Endodontically Treated Teeth

Incidence of Middle Mesial Canals in Mandibular Molars during Root Canal Treatment and Nonsurgical Retreatment

INTRODUCTION

Large-scale clinical studies on the incidence of middle mesial canals (MMCs) in nonsurgical root canal treatment (RCT) and retreatment of mandibular molars are lacking. The primary aim of this observational study was to determine the incidence of MMCs in mandibular first and second molars that received RCT or nonsurgical retreatment (NSRetx). The secondary aim was to determine factors associated with incidence of MMCs.

METHODS

Included were 3018 mandibular molars that received RCT (n = 1624) or NSRetx (n = 1394) by 3 endodontists in a private practice. Demographic and procedural data were collected. Bivariate and multivariable (Poisson regression model) analyses were performed.

RESULTS

Incidence of MMCs was 8.8% (n = 267). Although the bivariate analysis showed that NSRetx was significantly associated with incidence of MMCs, this association did not reach the threshold for statistical significance after controlling for all covariates (P = .07). Multivariable analysis on the entire cohort showed that incidence of MMCs was significantly associated with younger age (risk ratio [RR] = 1.62; 95% confidence interval [CI], 1.28-2.06), male gender (RR = 1.48; 95% CI, 1.18-1.85), preoperative cone-beam computed tomography (CBCT) (RR = 1.48; 95% CI, 1.17-1.89), and first molar (RR = 2.30; 95% CI:1.74-3.05). Subgroup multivariable analyses revealed that incidence of MMCs was associated with male gender only in the RCT group (RR = 2.26; 95% CI, 1.55-3.30) but not in the NSRetx group (RR = 1.11; 95% CI, 0.82, 1.50); and with preoperative CBCT only in the NSRetx group (RR = 1.78; 95% CI, 1.28, 2.50) but not in the RCT group (RR = 1.10; 95% CI, 0.71, 1.69). Associations with younger age and first molar remained unchanged.

CONCLUSIONS

Overall incidence of MMCs was 8.8%. Incidence of MMCs was significantly higher in younger patients and in mandibular first molars but was not associated with the type of treatment.

Biomechanical impact of different isthmus positions in mandibular first molar root canals: a finite element analysis

OBJECTIVE

This study used image-based finite element analysis (FEA) to assess the biomechanical changes in mandibular first molars resulting from alterations in the position of the root canal isthmus.

METHODS

A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient's mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth's longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading.

RESULTS

In Group A (without an isthmus), the maximum stress was 22.2 MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4 MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8 mm from the root tip, Group B: 13.6 MPa vs. Group A: 11.4 MPa; at 3 mm from the root tip, Group C: 14.2 MPa vs. Group A: 4.5 MPa; at 1 mm from the root tip, Group D: 25.1 MPa vs. Group A: 10.3 MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus.

CONCLUSION

A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.

Impact of Type 2 Diabetes Mellitus on the Occurrence of Vertical Root Fracture: A Case Control Study

INTRODUCTION

The aim of this case-control study was to examine the relationship between type 2 diabetes mellitus (DM) and the occurrence of VRFs. The crack extension, dentin sclerosis, and chemical characteristics of root dentin in teeth with VRF from patients with/without DM were also compared.

METHODS

One hundred and thirty-two patients diagnosed with VRF in crowned root filled posterior teeth were selected. The study was conducted in 2 parts. In Part-1: The cases were matched with control teeth (1:1) for age (±5 years), sex, tooth type, apical extent of root filling, time period after root filling to a diagnosis of VRF, presence or absence of intracanal post and abutment status. The presence or absence of type 2 DM (HbA1c > 6.5) was recorded. In Part-2: The extracted teeth with VRF from the case control study were used to evaluate the extension of VRF, presence of sclerotic dentin and isthmus using a microscopic analysis; while the levels of pentosidine, collagen cross-linking ratio and mineral-collagen ratio were determined by Fourier-transform infrared spectroscopy. The distribution of DM between cases and controls was analyzed using Pearson Chi-Square test and Odds Ratio estimated. Chemical composition data was analyzed using Mann-Whitney test. The extent of sclerotic dentin was analyzed using Pearson Chi-Square test.

RESULTS

When compared to patients without DM, patients with DM had 2.67 (95% CI: 1.6-4.45) folds higher odds for occurrence of VRF. Pentosidine (P = .014), collagen cross-linking ratio(P = .047), mineral-collagen ratio (P = .009) and sclerotic dentin extent (P = .0009) were significantly higher in patients with DM and VRF.

CONCLUSIONS

Type 2 DM was more often associated with VRFs in root canal treated teeth with crowns. Root dentin from patients with type 2 DM and VRF had higher levels of pentosidine, collagen cross-linking ratio, mineral to collagen ratio and sclerotic dentin.

Incidence and contributing factors of non-root canal treated teeth with chronic fatigue root fracture: A cross-sectional study

BACKGROUND/PURPOSE

Chronic fatigue root fracture describes a root fracture in a non-root canal treated (non-RCT) tooth. This study aimed to report the incidence and contributing factors of non-RCT teeth with chronic fatigue root fracture in a Taiwanese population.

METHODS

This cross-sectional study included teeth extracted at Taipei Veterans General Hospital in Taiwan between 2018 and 2019. The reasons for extractions were recorded and included vertical and horizontal root fractures (VRF and HRF). Comparisons of clinical factors between teeth with fatigue VRF and teeth with fatigue HRF were performed by chi-square or Fisher exact test, where appropriate.

RESULTS

Of the 4207 extracted teeth examined, 263 (6.25%) had tooth fracture. Thirty-two non-RCT teeth had chronic fatigue root fracture, including 16 with VRF and 16 with HRF. The incidence was 0.76% (32/4207). The occurrence of chronic fatigue root fracture was higher in males (83.9%). The mean age of the 31 patients with chronic fatigue root fracture was 71.7 ± 13.1 years. More than half of these teeth had intact crowns with severe attrition. The fatigue VRF occurred more frequently in molars (P = 0.003), in roots with a long oval cross-section (P = 0.037), and in terminal teeth (P = 0.013) than the fatigue HRF.

CONCLUSION

The incidence of chronic fatigue root fracture is 0.76%. Both VRF and HRF occur mainly in aged males, in posterior teeth with attrition, and in teeth without restoration. Tooth position, cross-section root morphology, and terminal tooth are contributing factors related to chronic fatigue root fracture.

Micro-CT evaluation of frozen and embalmed human cadavers on the effect of root canal preparation on microcrack formation in old dentin

The aim of this study was to evaluate the existence of preoperative dentinal defects among differently preserved dentoalveolar bone-blocks (frozen vs. embalmed) and to investigate the effect of varying apical forces (low: <4 N, high: 4-8 N) during root canal preparation on microcrack formation using micro-computed tomography (micro-CT). Thirteen embalmed and seven frozen bone-blocks containing 1-3 single rooted teeth were collected. The teeth were evenly divided into three groups (n = 10): FLow (frozen, <4 N), ELow (embalmed, <4 N), EHigh (embalmed, 4-8 N). After working length determination all specimens were scanned preoperatively. Root canal preparation was performed using nickel-titanium instruments sizes 25/.06 and 40/.06 (F6 SkyTaper; Komet, Lemgo, Germany). A postoperative scan was performed and image stacks were co-registered. All cross-sectional images were screened to identify the presence of dentinal defects. The results were expressed as the percentage of teeth/slices presenting dentinal defects. The statistical analyses were performed with Kruskal-Wallis-Test and Mann-Whitney-U-Test (α = 5%). Embalmed specimens presented a significantly higher percentage of slices with preoperative microcracks (p<0.05) than frozen specimens. No significant difference between groups was observed regarding the induction of microcracks (p>0.05). Root canal preparation does not induce microcracks in dentoalveolar bone-blocks from donors of old age, irrespective of the preservation method and the apically directed forces.

Evaluation of the band-shaped isthmuses in the mesiobuccal root canal system using micro-computed tomography

OBJECTIVES

This micro-computed tomography (micro-CT) study analyzed band-shaped isthmuses having their floor at the apical third of the mesiobuccal roots of maxillary molars in terms of 2D and 3D morphological parameters.

MATERIALS AND METHODS

A total of 199 maxillary first molars were scanned with micro-CT. Twenty-seven specimens, confirmed to have a band-shaped isthmus, were further examined in terms of the isthmus length, volume, structure model index (SMI), and surface area. The distance of apical foramina of mesial canals from the isthmus floor and major-minor diameters, roundness, perimeter, and area of the isthmus roof and floor were compared. Statistical analyses were performed with descriptive statistics and t-test with a 5% significance threshold.

RESULTS

The band-shaped isthmus frequency was 13.5% and its length reached up to 5.5 mm. The distances of the apical foramina of mesiobuccal canals (MB1 and MB2) from the isthmus floor were similar (p > .05). Isthmus roof and floor showed significant differences in terms of their major diameter and area (p < .05), whereas their minor diameter, roundness, and perimeter values were similar (p > .05).

CONCLUSION

The band-shaped isthmuses are not rare and can reach through the half of the root length with oval cross-sections in the floor and roof anatomy. The distance between the isthmus floor and apical foramina did not differ between MB1 and MB2.

CLINICAL RELEVANCE

The band-shaped isthmus morphology contributes to the complexity of the apical anatomy of maxillary first molar teeth with various lengths and diameters.

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.

Vertical root fractures: A time-dependent clinical condition. A case-control study in two colombian populations

Background

This nested case-control study can be viewed as an efficient way to sample subjects from a large cohort study case-control study aimed to analyze the effect of different clinical factors on the appearance of vertical root fractures in endodontically-treated teeth (ETT) over time.

Material and Methods

By matching 90 cases and 270 controls nested in a cohort of 450 patients. Incident “cases” included those ETT in which a confirmed VRF. The “controls” were ETT with clinical and radiographic evidence of normality. When an “incident case” was detected, three random “controls” according to the evaluation time registered in years were selected. Time interval corresponded to the exposure time from the end of the endodontic treatment until the tooth was included in the study. Demographic and clinical parameters included: age, gender, type, and location of the tooth, type of endodontic treatment, number of appointments necessary to complete the endodontic treatment, use of intra-canal medication, the apical extension of the filling, type of coronal restoration, the role of the tooth in the rehabilitation treatment, presence of intra-radicular posts, and presence of an adjacent implant, were analyzed over time. Statistical analysis: univariate descriptive analysis, Pearson’s χ2 test, and a logistic regression model adjusted for the most significant variables with a 95% confidence interval.

Results

The prevalence of vertical root fractures was 16.42%. The multivariate analysis confirmed that re-treatment (OR:12.19; OR:4.28;P<0.05) lasting five to ten years and intra-canal medication (OR:6.16;P=0.004) for more than eleven years significantly more associated with the risk of vertical root fracture. For teeth with intra-canal post or direct coronal restorations, the risk of vertical root fracture was three times lower.

Conclusions

Endodontic re-treatment and the use of intracanal medication such as calcium hydroxide should be considered primary and secondary risk factors, respectively, according to the appearance of VRF over time.

Key words:Apical surgery, endodontic re-treatment, endodontically-treated teeth, risk factors, vertical root fracture.

In vivo detection of vertical root fractures in endodontically treated teeth: Accuracy of cone-beam computed tomography and assessment of potential predictor variables

Background

This study aimed: (a) to determine the diagnostic performance of cone-beam computed tomography (CBCT) for detection of vertical root fractures (VRFs); (b) to evaluate the predictive value of diagnostic criteria regarding the definition of VRFs; and (c) to examine the robustness of the association of patient-, tooth-, and treatment-related variables with VRFs.

Material and Methods

130 root-filled teeth with signs/symptoms of VRFs underwent clinical and CBCT assessments. Definite diagnosis of VRF was confirmed by endodontic microsurgical (EMS) exploration. Determination of diagnostic performance of CBCT was based on standard algorithms derived from two-way contingency table analysis. Predictive value of diagnostic criteria and the association between predictor variables with VRFs were analyzed using logistic regression models.

Results

VRFs were detected during EMS in 50% of the teeth. Based on the finding of fracture lines on CBCT scans, sensitivity, specificity, and accuracy were 86.2%, 13.8%, and 50%, respectively. Teeth having more than three diagnostic criteria present had significant higher odds for VRF diagnosis. After logistic regression analysis, parafunctional habits, one-canal roots, excessive root canal enlargement, and absence of intra-radicular posts remained as robust predictor variables of VRFs.

Conclusions

Although the sensitivity of CBCT for VRFs detection is high, the risk of false-positive results related to its low specificity makes that all suspected cases must be confirmed by surgical exploration. VRFs cannot be reliably diagnosed by isolated clinical signs/symptoms; instead those teeth possessing more than three diagnostic criteria might be considered practically pathognomonic. The parafunctional habits, one-canal roots, excessive root canal enlargement, and the absence of intra-radicular posts may act strongly/independently for the occurrence of VRFs in endodontically treated teeth.

Key words:Cone-beam computed tomography, diagnostic accuracy, diagnostic surgery, predictor variables, root canal treatment, vertical root fracture.

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.

Topographic Analysis of the Isthmus in Mesiobuccal and Mesial Roots of First Molars in a South Korean Population

The purpose of this study was to evaluate the incidence and microscopic anatomy of the isthmus to provide more precise anatomical information about the mesiobuccal (MB) roots of the maxillary first molars and the mesial (M) roots of the mandibular first molars. Twenty-eight maxillary and 31 mandibular first molars were embedded, sectioned, stained, and observed at 30× magnification to evaluate the incidence and microscopic anatomy of the isthmus. The incidence of an isthmus 3 mm from the apex was 89.3% and 100% in the MB roots of the maxillary first molars and in the M roots of the mandibular first molars, respectively. The mean dentin thickness between the isthmus and the distal root surface was <1 mm at a distance of 3 mm from the apex in both types of roots. In this study, whenever two main canals were located in the MB roots of the maxillary first molars and in the M roots of the mandibular first molars, the likelihood of the presence of an isthmus increased. Therefore, clinicians should be aware of the thinnest dimensions in the distal surface of the MB roots of the maxillary first molars and the M roots of the mandibular first molars during nonsurgical and surgical root canal treatment.

Assessment of extracting molars and premolars after root canal treatment: A retrospective study

Background

The loss of dentition after root canal treatment is a multifactorial entity which might differ between different teeth. The extraction can be more critical, as well as the rehabilitation options.

Aim

To analyze if the etiology of extracting root canal treated teeth is different between premolars and molars.

Materials and methods

The study included a total of 403 cases with non-surgical root canal therapy (NSRCT) and crown coverage that was referred to the oral surgery clinic for extraction. Tooth type, patient’s age, gender, time since treatment completion, and the reason for extractions were recorded and analyzed.

Results

The most frequently extracted teeth were molars (55.6%), followed by premolars (30.3%) and anterior teeth (14.1%). The reasons for extraction were subgingival decay (SGD) (62.5%), vertical root fractures (VRF) (25.3%), and patient demands after uncomfortableabscess discharge (12.2%). Most of the teeth survived between 13 and 36 months after NSRCT. The statistical power of 0.92 was demonstrated, and a P-value of less than 0.05 presented significant correlations.

Conclusion

Molars were extractedafter NSRCT due to SGD followed by premolars, which were extracted due to VRF. Special care should be taken while planning NSRCT treatment for molars, in particular, with emphasis on the importance of oral hygiene and follow-up visits.

Stress Analyses of Retrograde Cavity Preparation Designs for Surgical Endodontics in the Mesial Root of the Mandibular Molar: A Finite Element Analysis-Part I

INTRODUCTION

The aim of this study was to investigate the influence of various apical preparation designs for surgical endodontics on stress concentrations in the mesial root of the mandibular molar under different experimental conditions using finite element analysis.

METHODS

We designed 2 apical preparation groups according to whether an isthmus was present or not. Each group contained 4 subgroups according to the size of the apical preparation. We constrained the displacement of all nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for the groups and subgroups.

RESULTS

In the subgroups, the von Mises and maximum principal stresses reduced gradually according to the enlargement of the prepared cavity. However, when the preparation extended excessively in the isthmus preparation groups, the situation reversed (ie, both von Mises and maximum principal stresses increased).

CONCLUSIONS

Within the limitations of this study, the apical preparation design influenced the distribution of stress concentration. Unlike the overall pattern in which stress decreased as the amount of apical preparation increased, stress increased when the amount of residual dentin was extremely thin.

Isthmus Incidence in Human Permanent Mandibular First Molars of a South Indian Population: A Cone-Beam Computerized Tomographic Study

Aim:

This study aimed to analyze incidence of isthmus in human permanent mandibular first molar teeth using cone-beam computed tomographic imaging techniques in a South Indian population.

Materials and Methods:

Three hundred permanent mandibular first molar teeth were collected, cleaned, and stored in normal saline. They were divided into groups (GPs) I and II based on number of roots, and were further subdivided (right and left [RL] subgroups A and B for GP I; and RL subgroups C and D for GP-II). Samples were processed and isthmus incidence was evaluated by cone-beam tomography, compared, and statistically analyzed.

Results:

Overall in mandibular first molars, the isthmus incidence in mesial root was 97.2%, distal root was 39%, and distolingual root was 0%. There was no statistically significant difference between the right and left mandibular first molar teeth with regard to incidence of isthmus (P > 0.05). There was an incidence of type I (38.67%), type II (56.33%), type III (3%), and type IV (2%) isthmuses in mesial root and type I (12.33%), type II (16%), and type III (10.67%) in distal root.

Conclusion:

Incidence of isthmus was very high in the mesial root of the mandibular first molar and should be factored during nonsurgical and surgical endodontic treatment procedures to achieve successful treatment outcomes.

Influence of voxel size on cone-beam computed tomography-based detection of vertical root fractures in the presence of intracanal metallic posts

Purpose

This study was performed to evaluate the influence of voxel size and the accuracy of 2 cone-beam computed tomography (CBCT) systems in the detection of vertical root fracture (VRF) in the presence of intracanal metallic posts.

Materials and Methods

Thirty uniradicular extracted human teeth were selected and randomly divided into 2 groups (VRF group, n=15; and control group, n=15). The VRFs were induced by an Instron machine, and metallic posts were placed in both groups. The scans were acquired by CBCT with 4 different voxel sizes: 0.1 mm and 0.16 mm (for the Eagle 3D V-Beam system) and 0.125 mm and 0.2 mm (for the i-CAT system) (protocols 1, 2, 3, and 4, respectively). Interobserver and intraobserver agreement was assessed using the Cohen kappa test. Sensitivity and specificity were evaluated and receiver operating characteristic analysis was performed.

Results

The intraobserver coefficients indicated good (0.71) to very good (0.83) agreement, and the interobserver coefficients indicated moderate (0.57) to very good (0.80) agreement. In respect to the relationship between sensitivity and specificity, a statistically significant difference was found between protocols 1 (positive predictive value: 0.710, negative predictive value: 0.724) and 3 (positive predictive value: 0.727, negative predictive value: 0.632) (P<.05). The least interference due to artifact formation was observed using protocol 2.

Conclusion

Protocols with a smaller voxel size and field of view seemed to favor the detection of VRF in teeth with intracanal metallic posts.

Endoscopic Evaluation of Cut Root Faces and Histologic Analysis of Removed Apices Following Root Resection: A Clinical Study

Objective:

To evaluate the resection plane after root-end resection during apical surgery using endoscopy.

Methods:

Following apicectomy of 69 roots, the cut root faces were inspected with a rigid endoscope for the presence of unfilled areas of the root canal space, gaps between the obturated root canal and dentinal wall, isthmi, ‘opaque’ dentine and cracks. Endoscopic pictures were captured and assessed using a 12-sectorn transparent grid for determination of location of the studied elements. Furthermore, the removed apices were examined histologically (n=47). The surfaces of the removed apices opposite the cut root faces were histologically analysed for the same outcome measures.

Results:

Endoscopy revealed the following findings: opaque dentine in 84.1%, unfilled parts of the root canal system in 59.4%, gaps between the existing root canal filling and dentinal walls in 49.3%, and cracks in 10.1% of cases. With regard to isthmi, histology of the removed apices demonstrated an isthmus in two-thirds of those seen with endoscopy at the root end. Ramifications were histologically observed only in 6 root apices.

Conclusion:

The studied elements may cause failure of the root canal treatment, and conventional root canal retreatment or apical surgery may be indicated. The clinical significance of opaque dentine with regard to tooth prognosis after apical surgery remains unclear and warrants further research.

Primum non nocere - The effects of sodium hypochlorite on dentin as used in endodontics

The medical literature is replete with the maxim 'primum non nocere', cautioning health care providers to avoid doing any harm to human subjects in their delivery of medical care. Sodium hypochlorite (NaOCl) is a well-established irrigant for root canal treatment because of its antimicrobial and organic tissue remnant dissolution capability. However, little is known about the deleterious effect of this strong oxidizing agent on the integrity of human mineralized dentin. Iatrogenically-induced loss of dentin integrity may precipitate post-treatment root fracture and has potential medico-legal complications. In the present work, transmission electron microscopy provided evidence for collagen destruction in the surface/subsurface of dentin treated with high NaOCl concentrations and long contact times. Size exclusion chromatography showed that the hypochlorite anion, because of its small size, penetrated the water compartments of apatite-encapsulated collagen fibrils, degraded the collagen molecules and produced a 25-35µm thick, non-uniform "ghost mineral layer" with enlarged, coalesced dentinal tubules and their lateral branches. Fourier transform-infrared spectroscopy identified increases in apatite/collagen ratio in NaOCl-treated dentin. The apatite-rich, collagen-sparse dentin matrix that remained after NaOCl treatment is more brittle, as shown by the reductions in flexural strength. Understanding the deleterious effects of NaOCl on mineralized dentin enables one to balance the risks and benefits in using high NaOCl concentrations for lengthy periods in root canal debridement. Delineating the mechanism responsible for such a phenomenon enables high molecular weight, polymeric antimicrobial and tissue dissolution irrigants to be designed that abides by the maxim of 'primum non nocere' in contemporary medical practices.

STATEMENT OF SIGNIFICANCE

The antimicrobial and tissue-dissolution capacities of NaOCl render it a well-accepted agent for root canal debridement. These highly desirable properties, however, appear to be intertwined with the untoward effect of collagen matrix degradation within mineralized dentin. Because of its small size, the hypochlorite anion is capable of infiltrating mineralized collagen and destroying the collagen fibrils, producing a mineral-rich, collagen sparse ghost mineral matrix with reduced flexural strength. Findings from the present work challenge the biosafety of NaOCl when it is used in high concentrations and for lengthy time periods during root canal treatment, and laid the background work for future biomaterials design in debridement of the canal space.

Effect of root morphology on the susceptibility of endodontically treated teeth to vertical root fracture: An ex-vivo model

Vertical root fracture (VRF) of endodontically treated teeth is relatively common, and the involved teeth have a poor prognosis. Previous destructive methodologies applied force to the root in an uneven manner; thus, the associated experiments could not truly assess the mechanical behavior of VRF. This problem was resolved in the current study via the novel application of a bursting pressure methodology to endodontically treated maxillary central incisors and premolars. Hydrostatic pressure was applied inside the root canal through a cannula bonded to the coronal access cavity, and the apical foramen was sealed. VRFs were observed as water burst from the fractured root surface. Morphometric parameters were measured by staining and serially sectioning the roots. The bursting pressure was significantly lower in the premolars compared with that in the incisors (19.1±3.3MPa and 25.5. ±4.5MPa, respectively, p=0.001). Cracks in the roots appeared from the apex to the cement enamel junction (CEJ) (61%), apex to mid-root (26%) and mid-root to CEJ (13%), and they involved either two root surfaces (52%) or one root surface (48%) and closely resembled clinical VRF cases. Positive correlations were found between the bursting pressure and the proximal root wall thickness, whereas correlations were not observed between the bursting pressure and the buccal or lingual wall thicknesses. Statistical Analyses of Covariance (ANCOVA) models showed that the proximal wall thickness and an elliptically shaped root cross section were the variables that indicated the differences in strength between premolars, which are more prone to VRF, and maxillary central incisors, which are less prone to VRF.

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.

Vertical root fracture: Biological effects and accuracy of diagnostic imaging methods

This review assessed the most up-to-date literature on the accuracy of detecting vertical root fractures (VRFs] using the currently available diagnostic imaging methods. In addition, an overview of the biological and clinical aspects of VRFs will also be discussed. A systematic review of the literature was initiated in December of 2015 and then updated in May of 2016. The electronic databases searched included PubMed, Emabse, Ovid, and Google Scholar. An assessment of the methodological quality was performed using a modified version of the quality assessment of diagnostic accuracy studies tool. Twenty-two studies were included in this systematic review after applying specific inclusion and exclusion criteria. Of those, 12 favored using cone beam computed tomography (CBCT) for detecting VRF as compared to periapical radiographs, whereas 5 reported no differences between the two methods. The remaining 5 studies confirmed the advantages associated with using CBCT when diagnosing VRF and described the parameters and limitations associated with this method, but they were not comparative studies. In conclusion, overwhelming evidence suggests that the use of CBCT is a preferred method for detecting VRFs. Nevertheless, additional well controlled and high quality studies are needed to produce solid evidence and guidelines to support the routine use of CBCT in the diagnosis of VRFs as a standard of care.

Diagnosis of Vertical Root Fractures in Restored Endodontically Treated Teeth: A Time-dependent Retrospective Cohort Study

INTRODUCTION

The purpose of this study was to examine different patient- and treatment-related factors associated with the time of presentation of vertical root fractures (VRFs) in endodontically treated teeth restored with crowns.

METHODS

One hundred ninety-seven root-filled, crowned teeth with no post and suspected of VRFs were included in the study. Patient details with relevance to endodontic treatment and clinical signs/symptoms were documented, and radiographs were taken. A diagnosis of a VRF was confirmed after surgical flap elevation. Frequency distributions were determined, and statistical analyses were performed using Pearson chi-square analysis, Fisher exact test, cross tabulation, Pearson correlation, and multiple logistic regression.

RESULTS

Mandibular molars (34%) and maxillary premolars (22.8%) were the most frequently affected teeth. The postoperative time to the diagnosis of a VRF was 4.35 (±1.96) years. Female patients, posterior teeth, overfilled canals, and patients older than 40 years were associated with the presentation of VRFs within 5 years of the postoperative period. Clinical findings most frequently observed were pain on percussion (60%), pain on palpation (62%), presence of a deep narrow pocket (81%), and sinus tract/swelling (67%). "Halo"-type radiolucency (48.7%) was the most common radiographic feature related to VRFs.

CONCLUSIONS

Pain on palpation/percussion, deep narrow pocket, sinus tract, and halo-type radiolucency are characteristic features of VRFs. Posterior teeth, overfilled canals, female patients, and older patients (>40 years) presenting with the previously described clinical features in endodontically treated teeth restored with crowns are more likely to present with VRFs within 5 years postoperatively.

Strain Distribution in Root Surface Dentin of Maxillary Central Incisors during Lateral Compaction

AIM

To precisely quantify the circumferential strains created along the radicular dentin of maxillary incisors during a simulated clinical procedure of lateral compaction.

METHODS

Six miniature strain gauges were bonded on the roots of fourteen recently extracted maxillary central incisors that were subjected to root canal instrumentation. The strain gauges were bonded at three levels (apical, middle, and coronal) and four aspects (buccal, lingual, mesial, and distal) of the roots. Each tooth was embedded in a PVC cylinder containing polyvinyl-siloxane impression material. Root filling was then performed by simulating the clinical procedure of lateral compaction using nickel-titanium finger spreaders. The force applied to the spreader and the strains developing in the surface root dentin were continuously recorded at a frequency of 10 Hz.

RESULTS

The highest strains that developed during lateral compaction were in the mesial and distal aspects at the apical level of the root. The magnitudes of the maximal mesial/distal strains at the apical as well as the mid-root levels were approximately 2.5-3 times higher than those at the buccal/lingual aspects (p = 0.041). The strains decreased significantly (p<0.04) from the apical through the mid-root levels to the coronal level, yielding gradients of 2.5- and 6-fold, respectively. The mesial and distal strains were consistently tensile and did not differ significantly; however, the buccal strains were generally 35-65% higher than the lingual strains (p = 0.078). Lateral compaction resulted in the gradual build-up of residual strains, resulting in generation of a 'stair-step' curve. These strains declined gradually and almost completely disappeared after 1000 sec.

CONCLUSIONS

With proper mounting of several miniature strain gauges at various levels and aspects of the root, significant circumferential strains can be monitored under clinically relevant compaction forces. The residual strains at the end of lateral compaction are not stored in the dentin but decrease gradually to negligible levels.