Influence of Access Cavity Preparation and Remaining Tooth Substance on Fracture Strength of Endodontically Treated Teeth

Effect of fiber-reinforced direct restorative materials on the fracture resistance of endodontically treated mandibular molars restored with a conservative endodontic cavity design

OBJECTIVE

This study aimed to evaluate the fracture strength of teeth restored using fiber-reinforced direct restorative materials after endodontic treatment with a conservative mesio-occlusal access cavity design.

MATERIALS AND METHODS

A total of 100 extracted intact mandibular first molars were selected and distributed into a positive control group where teeth left intact and the following four test groups comprised of teeth with conservative mesio-occlusal access cavities that had undergone root canal treatment (n = 20/group): access cavity without restoration (negative control), bulk-fill resin composite with horizontal glass fiber post reinforcement, fiber-reinforced composite with bulk-fill resin and bulk-fill resin composite. Following thermocycling (10,000 cycles), fracture resistance was measured using a universal testing machine. Statistical analyses (one-way analysis of variance and the Tamhane test) were performed, and statistical significance was set at p < 0.05.

RESULTS

Groups with minimally invasive access cavities had lower fracture strength than intact teeth, regardless of the restoration material (p < 0.05). Fiber-reinforced composite groups demonstrated higher fracture strength than bulk-fill resin composite alone (p < 0.05). Fracture types varied among groups, with restorable fractures predominant in the fiber-reinforced composite groups.

CONCLUSION

This study suggests that using fiber-reinforced composite materials, especially in combination with bulk-fill resin composites, can effectively enhance the fracture strength of endodontically treated teeth with conservative access cavities. However, using only bulk-fill resin composite is not recommended based on the fracture strength results.

CLINICAL SIGNIFICANCE

When teeth that undergo endodontic treatment are restored using a conservative access cavity design and fiber-reinforced composite materials, especially in combination with bulk-fill resin composites, the fracture strength of the teeth can be effectively increased.

Influence of Access Cavities on Maxillary Central Incisor Fracture Resistance: Finite Element Study

INTRODUCTION AND AIMS

Altering the position and orientation of the root canal access cavity passway, or modifying the reduction of dentin volume, can influence the strength of dentition. This study aimed to compare the effects of different access cavities on the biomechanical performances of maxillary central incisors with a finite element analysis.

METHODS

Based on the micro-computed tomography (CT) scan of a maxillary central incisor, the finite element models of the intact tooth and teeth with 4 access cavity designs: conservative incisal access cavity, incisal access cavity, conservative access cavity, and traditional access cavity were generated. Simulated occlusal forces were applied at the incisal edge of the incisor in the finite element analysis procedure.

RESULTS

The maximum von Mises stress and maximum principal stress in the cervical area are highest in the traditional access cavity group, followed by the conservative access cavity group, incisal access cavity group, and conservative incisal access cavity group.

CONCLUSION

The conservative access cavities minimise the extent of dentin removal from the cervical region, protecting the mechanical behaviour of the incisor. Moving the access cavity entry point to the incisal edge also improves the fracture resistance of the incisor.

CLINICAL RELEVANCE

This study's findings would help clinicians select the most appropriate endodontics access cavity method when performing the root canal on maxillary central incisors.

Influence of access cavity design on root canal instrumentation efficacy in molars - An in vitro study

Background

Several designs of access cavity have been evolved in the recent past with the concept of minimal tooth tissue removal which would improve the root canal treated teeth fracture resistance.

Aim

To investigate the effect of conservative design access cavity during the instrumentation of maxillary molar root canals.

Materials and Methods

Eighty noncarious maxillary molars were assigned to the traditional and conservative access groups (n = 40 each). After designated access preparations, the teeth were immersed in Lugols's solution for staining the pulp tissue. Root canal instrumentation was performed with TruNatomy file system. Pre- and postinstrumentation nano-computed tomography (CT) images were taken and reconstructed using CT-An software. Root canals volumetric analysis was done with CT-Vol software. The analysis of the data was dealt with Shapiro-Wilk test and independent t-test.

Results

The volume of pulp canal space before and after instrumentation changed significantly between the traditional and conservative access design groups, according to an independent t-test. In comparison, the mean volume of dentin removed was much larger in the TAC group (P = 0.0016). The independent t-test manifests difference significantly between traditional endodontic access cavity (TAC) and conservative access cavity (CAC) with percentage of unprepared canal walls. The mean percentage of unprepared area was significantly lesser in TAC group as compared to CAC group (P = 0.0022).

Conclusion

The volume of dentin removed was greater in TAC than with the CAC design. The amount of untouched canal wall area was significantly higher in conservative access design than with the traditional access design group.

How loss of tooth structure impacts the biomechanical behavior of a single-rooted maxillary premolar: FEA

To evaluate the influence of the loss of coronal and radicular tooth structure on the biomechanical behavior and fatigue life of an endodontically treated maxillary premolar with confluent root canals using finite element analysis (FEA). An extracted maxillary second premolar was scanned to produce intact (IT) 3D model. Models were designed with an occlusal conservative access cavity (CAC) with different coronal defects; mesial defect (MO CAC), occlusal, mesial and distal defect (MOD CAC), and 2 different root canal preparations (30/.04, and 40/.04) producing 6 experimental models. FEA was used to study each model. A simulation of cycling loading of 50N was applied occlusally to stimulate the normal masticatory force. Number of cycles till failure (NCF) was used to compare strength of different models and stress distribution patterns via von Mises (vM) and maximum principal stress (MPS). The IT model survived 1.5 × 1010 cycles before failure, the CAC-30.04 had the longest survival of 1.59 × 109, while the MOD CAC-40.04 had the shortest survival of 8.35 × 107 cycles till failure. vM stress analysis showed that stress magnitudes were impacted by the progressive loss of coronal tooth structure rather than the radicular structure. MPS analysis showed that significant loss of coronal tooth structure translates into more tensile stresses. Given the limited size of maxillary premolars, marginal ridges have a critical role in the biomechanical behavior of the tooth. Access cavity preparation has a much bigger impact than radicular preparation on their strength and life span.

Effect of the progressive taper enlargement of buccal root canals of three-rooted maxillary molars: A stepwise micro-CT study

This study evaluated unprepared canal areas, volume of dentine removal, and dentine thickness after the progressive enlargement of the buccal canals of 22 maxillary molars, with and without the MB2, using instruments with the same tip size (0.25 mm) but 4 different tapers (0.03, 0.05, 0.06 and 0.08 v). Micro-CT scans were performed after each instrument. Data were compared using a general linear mixed model post hoc comparisons with Kenward-Roger for Wald F tests (α = 5%). After each treatment step, it was observed an increase in the percentage volume of removed dentine and a decrease in the unprepared areas and dentine thickness at the pericervical region of all canals (p < 0.05). The percentage reduction of dentine thickness in MB2 canal was higher than in the mesiobuccal and distobuccal canals (p < 0.05). Knowledge of pre-operative dimensions and dentine thickness before enlargement of buccal canals of maxillary molars is an important factor to avoid excessive dentine removal.

The influence of core-build up materials on biaxial flexural strength of monolithic strength-gradient zirconia; an in-vitro study

BACKGROUND

Since their introduction, there has been limited research regarding the mechanical properties of novel strength-gradient monolithic zirconia. In addition to that, studies evaluating the effect of different core-build materials on the strength of indirect restorations are scarce. Therefore, the aim of this study was to investigate the effect of using different core build-up materials on biaxial flexural strength of a new monolithic multilayered zirconia material.

METHODS

Forty zirconia discs were fabricated from IPS e.max ZirCAD Prime (Ivoclar Vivadent AG, Schaan, Liechtenstein) and divided into 2 groups (n = 20). Forty composite discs were prepared from Tetric N-Ceram (Ivoclar Vivadent AG, Schaan, Liechtenstein) and MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein). The zirconia discs were adhesively cemented to the 2 types of composite forming 2 groups (Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow). Biaxial flexural strength was determined using a piston-on-3-ball test. The data were statistically analyzed with an independent t-test for significant differences (p = 0.05).

RESULTS

Tetric N-Ceram had significantly higher strength than MultiCore Flow (p < 0.001) but no statistically significant differences were found in strength values between Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow bilayered samples (p = 0.27).

CONCLUSIONS

It was concluded that although the tested composite core materials significantly differ in their biaxial flexural strength values, they had no influence on the biaxial flexural strength of the overlying zirconia.

Comparison of conventional preparation with modified access preparation on fracture resistance of primary molars - A finite element analysis

Objective

To investigate the influence of Conventional Straight (CS) line and Modified Straight (MS) line access preparations with various restorative materials on the fracture resistance of primary molars using Finite Element Analysis (FEA).

Methodology

Three FEA models for each of the primary molars were divided into Group I- Intact tooth model; Group II- Model with CS outline and Group III- Model with MS outline. Based on the restorative material used, Group II and III were further subdivided into subgroup 1- GIC restoration, subgroup 2 - composite resin with GIC base and subgroup 3- Stainless Steel Crown (SSC). Each model was subjected to 5 different force loads directed at the occlusal surface. Maximal von Mises (VM) stresses calculated from stress distribution patterns.

Result

The maximum displacement, in all the models of primary molars were seen in GIC restored models in molars with both CS and MS access whereas the minimal displacement was seen in the SSC restored molars of MS group.

Conclusion

In primary maxillary second molar and mandibular first and second molar with intact marginal ridges, the fracture resistance of tooth with MS outline restored with GIC base followed by Composite resin was comparable with the tooth restored with SSC and CS outline.

Clinical outcome

Based on the results of this FEA analysis, composite restorations with MS outline would be appropriate for endodontically treated primary molars that have intact margins.

Apically extruded debris, canal transportation, and shaping ability of nickel-titanium instruments on contracted endodontic cavities in molar teeth

PURPOSE

Apically extruded debris, canal transportation and shaping ability were compared between contracted endodontic cavities (CECs) and traditional endodontic cavities (TECs) after instrumentation with XP-endo Shaper (XPS), ProTaper Gold (PTG), ProTaper for hand-use (HPT) and Hero Shaper.

METHODS

The CECs or TECs groups were sub-divided into 24 groups according to root canal morphology and nickel-titanium (Ni-Ti) instruments. The weight of apically extruded debris was calculated using the Myers and Montgomery model. Pre- and postoperative images of teeth were scanned using micro-CT and the three-dimensional models were constructed and compared.

RESULTS

Under CECs or TECs, XPS and PTG produced less apical debris and formed less canal transportation than HPT and Hero Shaper (P < 0.05). XPS group under CECs extruded less apical debris than that under TCEs for round canals with curvature of 20°-35° (P < 0.05). The centering ratios of four tested instruments were higher under TECs than those under CECs (P < 0.05). The HPT and Hero Shaper had more transportation under CECs than that under TCEs (P < 0.05). No statistical difference was found regarding shaping ability among all the groups.

CONCLUSION

Under CECs, XPS preserves the original root canal anatomy, meanwhile it produces less apical debris than the other instruments.

Quantifiable design and comparative evaluation of straight-line minimally invasive endodontic cavity based on the anatomical features of the coronal part of root canal

Background/purpose

Minimally invasive endodontics has recently become popular in research. This study aimed to develop a new quantifiable straight-line minimally invasive endodontic cavity (SMIEC) for 3-rooted maxillary first molar based on the anatomical features of the coronal part of root canal.

Materials and methods

Cone-beam computed tomography (CBCT) images of 80 teeth were converted into models in Mimics Research software. Anatomical features of the coronal part of root canal were measured to develop SMIECs with straight-line accesses to root canals in 3-matic Research software. Twenty models were randomly sampled and each was duplicated for 8 simulation groups: non-treated (NT), traditional endodontic cavity (TEC), ninja endodontic cavity (NEC) and 5 SMIECs. Post-simulation models were subjected to finite element analysis to detect von-Mises stresses in ABAQUS software.

Results

Distributions of straight-line accesses to protogenetic root canals had certain manners, hence we developed 5 SMIECs. NEC and SMIECs had less hard tissue loss than TEC and presented different numerical rankings in different structures (P < 0.05). NEC had a less narrow surgery field than SMIECs except SMIEC2/4 (P < 0.05). The peak pericervical stresses of SMIECs were similar, lower than TEC and higher than NEC and NT (P < 0.05). The stress distributions of the 8 groups had certain manners.

Conclusion

Five SMIECs with straight-line accesses to root canals were developed, whose biomechanical properties were worse than NEC but better than TEC. Having appropriate structure preservation and surgery field, SMIEC2/4 was a preferred SMIEC.

Impact of Contracted Endodontic Access Cavities on the Fracture Resistance of Endodontically Treated Teeth After Mechanical Aging by Simulated Chewing Forces

INTRODUCTION

This in vitro study aimed to comparatively evaluate the fracture resistance of contracted endodontic cavities (CECs) versus traditional endodontic cavities (TECs) in mandibular molars after subjecting the samples to a chewing simulator.

METHODS

A total of 24 freshly extracted human mandibular molars were included in the study. Teeth with intact crowns and mature root apices that were devoid of caries, attrition, restorations, and cracks were selected and randomly assigned to 3 groups (n = 8) as follows: Group 1: TECs, Group 2: CECs, and Group 3: intact teeth (control group). After endodontic treatment, the teeth were restored with EverX bulk-fill composite and layered occlusally with nanohybrid composite SolareX and subjected to a chewing simulator where 240,000 masticatory cycles were simulated, which translates to 1 year of clinical function. The teeth were then subjected to static loading in a universal testing machine and the maximum load to fracture and the pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons.

RESULTS

The CEC group had higher fracture resistance when compared with the TEC group; however, the difference was not statistically significant. The fracture resistance of the samples in the control group was statistically higher than those in the experimental groups (P < .005).

CONCLUSIONS

There was no difference observed in the fracture resistance of mandibular molars with TECs and CECs subjected to masticatory loading.

Evaluation of the Fracture Resistance of Conservative and Ultraconservative Access Cavity Designs with Different Treatment Modalities: An In Vitro Study

Introduction

The aim of this study was to evaluate the fracture resistance of endodontically treated mandibular molars using traditional and conservative access cavity preparation.

Materials and Methods

In this in vitro study, 100 extracted healthy human mandibular molars were selected and divided into 10 groups (n = 10). Healthy teeth in one group were considered the control group. In three groups, traditional access cavity preparation was done (groups A) without two marginal ridges (A1), with one marginal ridge (A2), and with two marginal ridges (A3). In three groups (group B), two separate access cavities with a dentinoenamel roof without two marginal ridges (B1), with one marginal ridge (B2), and with two marginal ridges (B3) were prepared. In three other groups (groups C), two separate access cavities were prepared only with a dentinal roof without two marginal ridges (C1), with one marginal ridge (C2), and with two marginal ridges (C3), on which root canal treatment was performed afterward. Then, these teeth were subjected to force until fracture. The fracture force and fracture mode of each tooth were recorded and compared between groups by ANOVA, Tukey's post hoc, and chi-square tests using SPSS ver. 23 (IBM, Somers, NJ, USA).

Results

The control teeth had the highest mean fracture force (2804.5 ± 338.5 N), followed by a conservative access cavity with a dentinoenamel roof and two marginal ridges (2360.4 ± 181.72 N) and a conservative access cavity with a dentinoenamel roof and one marginal ridge (1812.8 ± 263.9 N), respectively. The lowest mean fracture force was found for the conventional access cavity group without two marginal ridges (399.4 ± 95.2 N).

Conclusion

In the condition of this study, with two separate access cavities in mandibular molars and maintenance of the marginal ridges, it is possible to provide teeth with higher fracture resistance against occlusal forces.

The effect of different endodontic access cavity designs in combination with WaveOne Gold and TruNatomy on the fracture resistance of mandibular first molars: A nonlinear finite element analysis

INTRODUCTION

This study evaluated the effect of traditional and conservative endodontic access cavity designs in combination with WaveOne Gold and TruNatomy instrumentation systems on the fracture resistance of mandibular first molars by means of nonlinear finite element analysis (FEA).

METHODS

Micro-CT images of 4 human mandibular first molars were used to generate representative FEA models. The mandibular first molars samples were scanned before and after endodontic access cavity preparation and instrumentation of all 3 canals. Five nonlinear static loads were applied vertically and horizontally to specific contact points on the occlusal surface of the teeth. Maximum von Mises stress before failure and distribution of von Mises strains were recorded and compared between groups.

RESULTS

Molars with conservative endodontic access cavities required similar levels of loads to reach failure compared with their control samples, whereas molars with traditional endodontic access cavities required significantly reduced loads in order to fail. According to the numerical investigation, the type of instrumentation system was found to have an insignificant effect on the fracture resistance of the teeth under study. Von Mises stress was concentrated around the cervical region and in the larger distal roots for all numerical models.

CONCLUSIONS

The fracture resistance of mandibular first molars is influenced significantly by a reduction in dental hard tissue, which was found to control the level of the ultimate failure load for each tooth.

Effect of Endodontic Irrigating Solutions on Radicular Dentine Structure and Matrix Metalloproteinases-A Comprehensive Review

Irrigating solutions play an important role in the eradication of intracanal microbes and debris dissolution during endodontic treatment. Different combinations of solutions and protocols have been advocated, with sodium hypochlorite (NaOCl), ethylenediamine tetra acetic acid (EDTA), and chlorhexidine (CHX) remaining the most widely used ones by many clinicians. Although these solutions provide efficient inorganic dissolution and antimicrobial capacity, their use has also been reported to cause undesired effects on root dentin composition and mechanical and biomechanical properties, such as microhardness, surface roughness, bond strength, and matrix metalloproteinase (MMP) activity. Several corroborating studies attribute these changes in mechanical properties of dentine to the use of irrigating solutions, and there are limited reports on how the solutions affect the expression of MMPs, which may be a correlating link to understanding the role of these enzymes in dentin collagen and changes in the mechanical properties of dentin. Hence, using the basis of several studies from the literature, the objective is to comprehensively review the influence of individual and combined irrigating solutions on root dentine structure and the activity of the MMPs.

Accuracy of Endodontic Access Cavities Performed Using an Augmented Reality Appliance: An In Vitro Study

INTRODUCTION

The purpose of this study was to compare and contrast the accuracy of endodontic access cavities created using an augmented reality appliance to those performed using the conventional technique.

MATERIALS AND METHODS

60 single-rooted anterior teeth were chosen for study and randomly divided between two study groups: Group A-endodontic access cavities created using an augmented reality appliance as a guide (n = 30) (AR); and Group B-endodontic access cavities performed with the manual (freehand) technique (n = 30) (MN). A 3D implant planning software was used to plan the endodontic access cavities for the AR group, with a cone-beam computed tomography (CBCT) and 3D intraoral surface scan taken preoperatively and subsequently transferred to the augmented reality device. A second CBCT scan was taken after performing the endodontic access cavities to compare the planned and performed endodontic access for accuracy. Therapeutic planning software and Student's t-test were used to analyze the cavities at the apical, coronal, and angular levels. The repeatability and reproducibility of the digital measurement technique were analyzed using Gage R&R statistical analysis.

RESULTS

The paired t-test found statistically significant differences between the study groups at the coronal (p = 0.0029) and apical (p = 0.0063) levels; no statistically significant differences were found between the AR and MN groups at the angular (p = 0.6596) level.

CONCLUSIONS

Augmented reality devices enable the safer and more accurate performance of endodontic access cavities when compared with the conventional freehand technique.

Influence of Access Cavity Design on the Fracture Strength of Endodontically Treated Teeth Restored Using Short Fiber-Reinforced Composite and High Strength Posterior Glass Ionomer Cement

Aim: This in vitro study aimed to determine the influence of access cavity design and residual tooth structure and to compare the fracture resistance of the teeth post endodontically restored with short fiber-reinforced composite (GC everX Posterior; GC, India) and conventional posterior high-strength GIC (Glass Ionomer Cement) (GC Gold Label IX; GC, India).

Methods: Ninety extracted human mandibular molars were classified into five groups, i.e., one control group (n = 10) and four test groups based on the access cavity design (n = 20): Traditional access cavity (TAC), Conservative access cavity (CAC), Ninja access cavity (NAC), and Truss access cavity (TRAC). Then 80 teeth in test groups were endodontically treated and further subdivided (n = 10) based on post-endodontic restorative materials, i.e., short fiber-reinforced composite (SFC) and Type 9 GIC. Samples were then subjected to fracture resistance under a universal testing machine and fracture loads were compared statistically.

Results: The fracture resistance of various access cavity designs (TAC, CAC, NAC, and TRAC) varied significantly (P < .05). Regardless of access cavity design, teeth restored with SFC had higher fracture resistance than teeth restored with high strength posterior GIC (P = .001).

Conclusion: Using newer access cavity designs like (CAC, NAC, and TRAC) and reinforcing the teeth with a post-endodontic restoration such as SFC, fracture resistance of endodontically treated teeth can be improved notably. 

2D radiographs, cone-beam computed tomography and 3D CBCT-based planning software in access cavity preparation: A single blinded randomised controlled in vitro study

This study compared endodontic access cavities prepared by operators of different experience levels (students, general-practitioners and specialists), guided by periapical radiographs, cone-beam computed tomography (CBCT) or 3D CBCT-based planning software, with regards to tooth substance loss and preparation errors. Operators (n = 34) prepared endodontic access cavities in 306 three-dimensionally printed copies of human teeth with standardised anatomies. Access cavities were volumetrically assessed post-operative using digital scans, while preparation errors were evaluated with CBCT. Tooth substance loss was significantly influenced by the operator's experience, being highest with students', followed by general-practitioners and specialists (P < 0.05), with no significant association with the employed imaging/planning modality. Pulp chamber floor, iatrogenic perforations and incomplete pulpal roof removal were insignificant between operator groups or imaging/planning modalities. It can be concluded that irrespective of advancement in imaging/planning modalities the practitioner's experience level remains to be the decisive factor significantly influencing tooth substance loss during endodontic access cavity preparations.

Impact of access cavity cleaning on the seal of postendodontic composite restorations in vitro

AIM

To investigate the influence of cavity cleaning and conditioning on marginal integrity of directly placed postendodontic composite class-I-restorations in vitro.

METHODOLOGY

168 fully intact teeth without caries or fillings received preendodontic composite restorations (class-II) after their extraction. Occlusal endodontic access-cavities were prepared, root-canals were instrumented and filled with guttapercha and an epoxy-resin based sealer. Prior to postendodontic class-I-restoration, access cavities were completely contaminated with sealer, cleaned with alcohol and pretreated as follows: Cleaner only (alcohol), glycine-polishing, Al₂ O₃ -sandblasting, carbide bur (immediate as well as delayed restoration). A positive control (not contaminated with sealer and adhesive used) and negative control (cleaner used but no adhesive) were established. Half of the teeth from each group were subjected to thermocycling and mechanical loading (TCML). Marginal integrity of postendodontic restoration was evaluated in oro-vestibular or mesio-distal sections after AgNO₃ -dye-penetration (DP) by standardized photomacroscopic imaging and expressed in percent of margin length along all segments and separately for enamel, dentine and composite, respectively. Results were analyzed non-parametrically (α=0.05).

RESULTS

No restorations or teeth fractured or debonded completely. Without TCML, the median DP of all segments was significantly higher for the negative control compared to all other groups in oro-vestibular cutting direction (53%; P=0.002) and in mesio-distal cutting direction (51%; P≤0.041). The other groups without TCML revealed 16-24% DP (oro-vestibular) and 12-24% DP (mesio-distal). With TCML, the median DP in oro-vestibular cutting direction for all segments ranged between 48-62% for all groups, a significant difference was only observed between glycine-polishing and carbide bur (P=0.041). In mesio-distal cutting direction, the median DP in negative control was 69% with TCML and significantly higher compared to all other groups (P=0.002). For all other groups, the median DP of all segments ranged between 28% and 40% with TCML without significant differences. Error rates method (k=7) revealed a significant influence of TCML in general on penetration of all segments in both, oro-vestibular and mesio-distal cutting directions.

CONCLUSION

Additional access cavity pretreatment after alcohol cleaning did not improve the marginal integrity of postendodontic composite restorations. Thorough cleaning of the access cavity with alcohol seems to assure an acceptable marginal integrity to the tooth and restorative composite.

Influence of minimally invasive access cavities on load capacity of root‐canal‐treated teeth: A systematic review and meta‐analysis

This systematic review (PROSPERO-CRD42020147333) aimed to compare the effects of conservative, ultraconservative and truss access cavities with traditional access cavities on the load capacity of root-canal-treated teeth. Online databases were searched until December 2021, and 25 ex vivo studies in which the effects of different access cavities on load capacity of permanent teeth had been investigated were included. Quality assessment was completed using a modified risk of bias tool for in vitro studies adapted from previous studies. Meta-analysis was performed using the maximum-likelihood-based random-effects model with similar groups. Conservative access cavities significantly improved the load capacity of maxillary premolars (p < 0.01 [-1.32, -0.028]) and molars (p < 0.05 [-0.89, -0.02]) compared to traditional access cavities. Additionally, truss access cavities significantly improved the load capacity of mandibular molars with (p < 0.05, [-1.18, -0.02]) mesio-occluso-distal cavity preparations. Higher levels of evidence are needed to determine the long-term implications of minimal preparations for treatment outcomes.

Success rate of fractured teeth receiving modified crown lengthening surgery and restorations

BACKGROUND

Whether to preserve a structurally compromised tooth or remove it is a dilemma often encountered by clinicians. The aim of this study was to assess the long-term success rate of fractured teeth preserved by modified crown lengthening surgery and restorations.

METHODS

Thirty-nine patients with a total of 45 fractured teeth who had received modified crown lengthening surgery were recruited and examined. Numbers of teeth lost were recorded, and the criteria for successful teeth were defined. Kaplan-Meier estimator was used to determine the success rate. Possible risk factors were compared between successful and unsuccessful groups by a Cox regression analysis to explore the potential predictors of failure with a significant level at α = 0.05.

RESULTS

The mean ± SD of success time without considering variants was 6.2 ± 0.6 years (95% CI 5.1-7.7). The mean survival rates ± SD at 1.0-, 2.0-, 3.0-, 5.0-, 7.0-, and 9.0-year intervals was 97.8 ± 2.2%, 92.2 ± 4.4%, 72.8 ± 7.9%, 68.2 ± 8.6%, 60.7 ± 10.5%, and 40.4 ± 13.6%, respectively. Failure cases in teeth with poor plaque control and step-shaped fracture margin were significantly more than those with good plaque control and knife-shaped fracture margin (HR = 7.237, p = 0.011; HR = 15.399, p = 0.006; respectively).

CONCLUSIONS

Fractured teeth treated with modified crown lengthening surgery are anticipated to have a high clinical success rate for 6.2 ± 0.6 years. Plaque control and fracture morphology appeared to be significantly associated with the success of the multidisciplinary treatment approach.

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.

A critical analysis of research methods and experimental models to study the load capacity and clinical behavior of the root filled teeth

The prognosis of root‐filled teeth depends not only on a successful root canal treatment but also on the restorative prognosis. This critical review discusses the advantages and limitations of various methodologies used to assess the load capacity or clinical survivability of root‐filled teeth and restorations. These methods include static loading, cyclic loading, finite element analysis and randomized clinical trials. In vitro research is valuable for preclinical screening of new dental materials or restorative modalities. It also can assist investigators or industry to decide whether further clinical trials are justified. It is important that these models present high precision and accuracy, be reproducible, and present adequate outcomes. Although in vitro models can reduce confounding by controlling important variables, the lack of clinical validation (accuracy) is a downside that has not been properly addressed. Most importantly, many in vitro studies did not explore the mechanisms of failure and their results are limited to rank different materials or treatment modalities according to the maximum load capacity. An extensive number of randomized clinical trials have also been published in the last years. These trials have provided valuable insight on the survivability of the root‐filled tooth answering numerous clinical questions. However, trials can also be affected by the selected outcome and by intrinsic and extrinsic biases. For example, selection bias, loss to follow‐up and confounding. In the clinical scenario, hypothesis‐based studies are preferred over observational and retrospective studies. It is recommended that hypothesis‐based studies minimize error and bias during the design phase.

Present status and future directions - Minimal endodontic access cavities

In the last decades, the move of Medicine towards minimally invasive treatments is notorious and scientifically grounded. As Dentistry naturally follows its footsteps, minimal access preparation also became a trend topic in the endodontic field. This procedure aims to maximize preservation of dentine tissue, backed up by the idea that this is an effective way to reduce the incidence of post-treatment tooth fracture. However, with the assessment of the body of evidence on this topic, it is possible to observe some key-points (a) the demand for nomenclature standardization, (b) the requirement of specific tools such as ultra-flexible instruments, visual magnification, superior illumination, and three-dimensional imaging technology, (c) minimally invasive treatment does not seem to affect orifice location and mechanical preparation when using adequate armamentarium, but it (d) may impair adequate canal cleaning, disinfection, and filling procedures, and also (e) it displays contradictory results regarding the ability to increase the tooth strengthen compared to the traditional access cavity. In spite of that, it is undeniable that methodological flaws of some benchtop studies using extracted teeth may be responsible for the conflicting data, thus triggering the need for more sophisticated devices/facilities and specifically designed research in an attempt to make it clear the role of the access size/design on long-term teeth survival. Moreover, it is inevitable that a clinical approach like minimal endodontic access cavities that demands complex tools and skilled and experienced operators bring to the fore doubts on its educational impact mainly when confronted with the conflicting scientific output, ultimately provoking a cost-benefit analysis of its implementation as a routine technique. In addition, this review discusses the ongoing scientific and clinical status of minimally invasive access cavities aiming to input an in-depth and unbiased view over the rationale behind them, uncovering not only the related conceptual and scientific flaws, but also outlining future directions for research and clinical practices. The conclusions attempt to skip from passionate disputes highlighting the current body of evidence as weak and incomplete to guide decision making, demanding the development of a close-to-in-situ laboratory model or a large and well-controlled clinical trial to solve this matter.

Three-dimensional analysis of coronal root canal morphology of 136 permanent mandibular first molars by micro-computed tomography

Background/purpose

Minimally invasive endodontic approach become a research hotspot and may prevent the fracture of endodontically-treated teeth. This research aims to measure the coronal root canal morphology of permanent mandibular first molars in 3D and propose a new minimally invasive endodontic approach based on this measurement.

Materials and methods

Data of 136 permanent mandibular first molars were involved and reconstructed in 3D models with canals. Then, the morphology characteristics of the coronal root canal were measured.

Results

Overall, the distribution of root canal orifices was more centralized than other landmarks. The landmarks were located more mesiobuccally to the center of the occlusal plane of molars. Specifically, the measurements of the maximum curvature of coronal root canals in the axial direction were: in 3-canals 2-rooted teeth, the average angles of curvatures were 23°,25°,11° for mesiobuccal (MB), mesiolingual (ML) and distobuccal (DB) canals, respectively; in 4-canals 2-rooted teeth were 23°,25°,12°,16°for MB, ML, DB, and distolingual (DL) canals, respectively; in 4-canals 3-rooted teeth were 25°,27°,17°,39° for MB, ML, DB, and DL canals, respectively. The degrees of coronal root canal curvatures in the horizontal direction were: in 3-canals teeth, the average angles of curvatures were −1°,47°,-2° for MB, ML and DB canals, respectively; in 4-canals 2-rooted teeth were −4°,41°,-25°,48° for MB, ML, DB, and DL canals, respectively; in 4-canals 3-rooted teeth were −3°,33°,-43°,79° for MB, ML, DB, and DL canals, respectively.

Conclusion

The results of this study are similar to those previously obtained using CBCT and can help us design endodontic approaches.

A comparison of volume of tissue removed and biomechanical analysis of different access cavity designs in two-rooted mandibular first molars: a multi-sample three-dimensional finite element analysis

INTRODUCTION

The aim of this study was to compare the biomechanical properties and the amount of coronal tissue removed among the different access cavities with a multi-sample three-dimensional finite element analysis in mandibular first molar. The correlation between the amount of tissue removed and the fracture resistance of the teeth was also analysed.

METHODS

Micro-CT data from 20 two-rooted mandibular first molars were included in this study as three-dimensional modelling prototypes. The models of untreated molars and molars treated with the Traditional Access Cavity (TradAC), the Conservative Access Cavity (ConsAC) and the straight-line minimally invasive endodontic access cavities (SMIAC) were created. Each model was loaded in 3 ways to simulate the functional conditions of occlusion. The amount of tissue removed and the maximum stress in the cervical region were recorded and analysed, and the correlation between them was also analysed.

RESULTS

The amount of coronal tissue and peri-cervical dentin (PCD) removed in SMIAC and ConsAC was less than that of TradAC. The mean maximum stress in the cervical region was significantly smaller in SMIAC and ConsAC than in TradAC. The amount of hard tissue and PCD loss was positively correlated with the maximum stress in the cervical region of the tooth.

CONCLUSIONS

In mandibular first molars, it could be beneficial to improve the fracture resistance of the tooth after endodontic treatment by the minimally invasive access cavity to reduce the loss of coronal tooth tissue and PCD. The SMIAC may be an option balancing biomechanical properties and clinical convenience.

Fracture Resistance of Upper Central Incisors with Different Endodontic Accesses Restored with Lithium Disilicate Partial Laminate Veneers

Purpose

Materials and Methods

Results

Conclusion

Current strategies for conservative endodontic access cavity preparation techniques-systematic review, meta-analysis, and decision-making protocol

OBJECTIVES

To assess related studies and discuss the clinical implications of endodontic access cavity (AC) designs.

MATERIALS AND METHODS

A systematic review of studies comparing the fracture resistance and/or endodontic outcomes between different AC designs was conducted in two electronic search databases (PubMed and Web of Science) following the PRISMA guidelines. Study selection, data extraction, and quality assessment were performed. Meta-analyses were undertaken for fracture resistance and root canal detection, with the level of significance set at 0.05 (P = 0.05).

RESULTS

A total of 33 articles were included in this systematic review. The global evaluation of the risk of bias in the included studies was assessed as moderate, and the level of evidence was rated as low. Four types of AC designs were categorized: traditional (TradAC), conservative (ConsAC), ultraconservative (UltraAC), and truss (TrussAC). Their impact on fracture resistance, cleaning/disinfection, procedural errors, root canal detection, treatment time, apical debris extrusion, and root canal filling was discussed. Meta-analysis showed that compared to TradAC, (i) there is a significant higher fracture resistance of teeth with ConsAC, TrussAC, or ConsAC/TrussAC when all marginal ridges are preserved (P < 0.05), (ii) there is no significant effect of the type of AC on the fracture resistance of teeth when one or two marginal ridges are lost (P > 0.05), and (iii) there is a significantly higher risk of undetected canals with ConsAC if not assisted by dental operating microscope and ultrasonic troughing (P < 0.05).

CONCLUSIONS

Decreasing the AC extent does not necessarily present mechanical and biological advantages especially when one or more surfaces of the tooth structure are lost. To date, the evidence available does not support the application of TrussAC. UltraAC might be applied in limited occasions.

CLINICAL RELEVANCE

Maintaining the extent of AC design as small as practical without jeopardizing the root canal treatment quality remains a pragmatic recommendation. Different criteria can guide the practitioner for the optimal extent of AC outline form which varies from case to case.

Ten years of minimally invasive access cavities in Endodontics: a bibliometric analysis of the 25 most-cited studies

Objectives

This study aimed to analyze the main features of the 25 most-cited articles in minimally invasive access cavities.

Materials and Methods

An electronic search was conducted on the Clarivate Analytics' Web of Science ‘All Databases’ to identify the most-cited articles related to this topic. Citation counts were cross-matched with data from Elsevier's Scopus and Google Scholar. Information about authors, contributing institutions and countries, year and journal of publication, study design and topic, access cavity, and keywords were analyzed.

Results

The top 25 most-cited articles received a total of 572 (Web of Science), 1,160 (Google Scholar) and 631 (Scopus) citations. It was observed a positive significant association between the number of citations and age of publication (r = 0.6907, p < 0.0001); however, there was no significant association regarding citation density and age of publication (r = −0.2631, p = 0.2038). The Journal of Endodontics made the highest contribution (n = 15, 60%). The United States had the largest number of publications (n = 7) followed by Brazil (n = 4), with the most contributions from the University of Tennessee and Grande Rio University (n = 3), respectively. The highest number of most-cited articles were ex vivo studies (n = 16), and ‘fracture resistance’ was the major topic studied (n = 10).

Conclusions

This study revealed a growing interest for researchers in the field of minimally invasive access cavities. Future trends are focused on the expansion of collaborative networks and the conduction of laboratory studies on under-investigated parameters.

The effects of endodontic access cavity design on dentine removal and effectiveness of canal instrumentation in maxillary molars

AIM

To evaluate in a laboratory setting, the impact of three designs of endodontic access cavities on dentine removal and effectiveness of canal instrumentation in extracted maxillary first molars using micro-computed tomography (micro-CT).

METHODOLOGY

A total of 30 extracted intact maxillary first molars were selected and scanned by micro-CT with a voxel size of 24 µm and randomly distributed into three groups: the traditional endodontic cavity (TEC) group, the conservative endodontic cavity (CEC) group and the guided endodontic cavity (GEC) group. The pulp chambers of teeth in the groups were accessed accordingly. After root canal preparation, the teeth were rescanned. The volume of dentine removed after canal preparation, the noninstrumented canal areas, canal transportation and centring ratio were analysed. Data were analysed statistically using one-way analysis of variance. Tukey's post hoc test was used for multiple comparisons. The significance level was set at p < .05.

RESULTS

The total volume of dentine removed was significantly greater in the TEC group after root canal preparation (p < .05). No significant differences in the volume of dentine removed occurred between the CEC and GEC groups (p > .05). The volume of dentine removed in the crown, pericervical dentine and coronal third of the canal was significantly lower in CEC and GEC groups when compared to that in the TEC group (p < .05), no difference was observed in the middle third of the canal and apical third of the canal amongst the three groups (p > .05). There was no significant difference in noninstrumented canal area, canal transportation and centring ratio amongst the TEC, CEC and GEC groups (p > .05).

CONCLUSIONS

In extracted maxillary molars tested in a laboratory setting, CEC and GEC preserved more tooth tissue in the crown, pericervical dentine and coronal third of the canal compared with TEC after root canal preparation. The design of the endodontic access cavity did not impact on the effectiveness of canal instrumentation in terms of noninstrumented canal area, canal transportation and centring ratio.

Influence of Minimally Invasive Access Cavity Designs on the Fracture Resistance of Endodontically Treated Mandibular Molars Subjected to Thermocycling and Dynamic Loading

INTRODUCTION

The aim of this study was to investigate the fracture resistance of endodontically treated and restored permanent mandibular molars with minimally invasive access cavities subjected to thermocycling and dynamic loading.

METHODS

Forty first and second mandibular molars were randomly assigned to 4 groups (n = 10/group) as follows: group 1, control (intact teeth); group 2, traditional access cavity (TradAC); group 3, conservative access cavity (ConsAC); and group 4, truss access cavity (TrecAC). After endodontic treatment, teeth were restored with SDR core (Dentsply Caulk, Milford, DE) and subjected to thermocycling followed by dynamic and static loading with a multiaxial fatigue testing machine (Instron, Canton, MA). The maximum load to fracture and pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons.

RESULTS

Fracture resistance of the samples in the control group were higher than those in the experimental groups (P < .005). TradAC exhibited the least resistance to fracture (P < .005). There was no statistically significant difference in the fracture resistance of ConsAC and TrecAC (P = .361) Unrestorable fractures were more frequent in the TradAC group compared with all other groups.

CONCLUSIONS

Mandibular molars with ConsAC and TrecAC exhibited superior fracture resistance compared with TradAC. TradAC had the highest number of unrestorable fractures.

Retrospective study of fracture survival in endodontically treated molars: the effect of single-unit crowns versus direct-resin composite restorations

Objectives

This study was conducted to compare the post-fracture survival rate of endodontically treated molar endodontically treated teeth (molar ETT) restored with resin composites or crowns and to identify potential risk factors, using a retrospective cohort design.

Materials and Methods

Dental records of molar ETT with crowns or composite restorations (recall period, 2015–2019) were collected based on inclusion and exclusion criteria. The incidence of unrestorable fractures was identified, and molar ETT were classified according to survival. Information on potential risk factors was collected. Survival rates and potential risk factors were analyzed using the Kaplan-Meier log-rank test and Cox regression model.

Results

The overall survival rate of molar ETT was 87% (mean recall period, 31.73 ± 17.56 months). The survival rates of molar ETT restored with composites and crowns were 81.6% and 92.7%, reflecting a significant difference (p < 0.05). However, ETT restored with composites showed a 100% survival rate if only 1 surface was lost, which was comparable to the survival rate of ETT with crowns. The survival rates of ETT with composites and crowns were significantly different (97.6% vs. 83.7%) in the short-term (12–24 months), but not in the long-term (> 24 months) (87.8% vs. 79.5%).

Conclusions

The survival rate from fracture was higher for molar ETT restored with crowns was higher than for ETT restored with composites, especially in the first 2 years after restoration. Molar ETT with limited tooth structure loss only on the occlusal surface could be successfully restored with composite restorations.

Impact of Canal Taper and Access Cavity Design on the Life Span of an Endodontically Treated Mandibular Molar: A Finite Element Analysis

INTRODUCTION

This study investigated the impact of different canal tapers and access cavity designs on the life span of endodontically treated mandibular first molars using the finite element method.

METHODS

Finite element analysis was performed on simulated models with 3 access cavity designs (traditional, conservative, and truss). The mesial canals were prepared to either constant tapers of 25/.04 and 25/.06 or a variable taper corresponding to the cumulative canal preparation shapes of TruNatomy Prime (Dentsply Sirona, Charlotte, NC) and ProTaper Gold F2 (Dentsply Sirona). The distal canals in all models had a 40/.04 preparation. Using occlusal fingerprint analysis, all models were subjected to cyclic occlusal loading until model failure. The number of cycles until failure, the location of failure, stress distribution patterns, and the maximum von Mises stresses were assessed.

RESULTS

The traditional access models showed a lower life span than the conservative and truss models regardless of the canal taper, whereas there was not a notable difference in the conservative and truss models. The stresses migrated apically along the root surface and remarkably on the mesial aspect of the mesial root and the furcation area's outer surface. After root canal preparation with different tapers, there were no evident changes in the pattern and magnitude of the stresses distributed along the root surface.

CONCLUSIONS

The life span of the tooth is affected more significantly by the access cavity design than the root canal preparation taper. Because stress patterns migrate apically rather than concentrate in the pericervical area, crack initiation and propagation might occur anywhere on the root surface.

Computer-Controlled CO2 Laser Ablation System for Cone-beam Computed Tomography and Digital Image Guided Endodontic Access: A Pilot Study

Introduction:

Ideal endodontic access provides unobstructed entry to the pulp chamber and visualization of the canal orifices while preserving the maximum amount of tooth structure. The aim of this study was to implement the use of lasers to accurately and predictably access teeth to follow the principles of minimally invasive endodontics.

Methods:

Traditional, conservative, ultraconservative, bridge, truss, and orifice-directed accesses were performed. A computer-controlled 9.3-μm CO₂ laser ablation system was assembled and coupled with custom software capable of combining cone-beam computed tomographic (CBCT) volumetric data with spatially calibrated digital images of teeth to provide an augmented reality environment for designing and preparing endodontic accesses. Twenty (N = 20) sound posterior teeth with fully developed root canal systems were imaged with CBCT scans and accessed via laser ablation in vitro.

Results:

All 20 (20/20) teeth were successfully accessed without iatrogenic errors. Volumetric renderings from post-access CBCT scans were used to verify the access and determine accuracy qualitatively. The volumetric measurements of hard tissue removed were as follows: traditional = 39.41 mm³, conservative = 9.76 mm³, ultraconservative = 7.1 mm³, bridge = 11.53 mm³, truss = 19.21 mm³, and orifice directed = 16.86 mm³.

Conclusions:

Digital image guidance based on feature recognition and registration with CBCT data is a viable method to address the challenge of dynamic navigation for accessing the pulp chamber. Modern lasers with high pulse repetition rates integrated with computer-controlled scanning systems are suitable for the efficient cutting of dental hard tissues.

Conservative shaping combined with three-dimensional cleaning can be a powerful tool: Case series

Conservative endodontics has been introduced about a decade ago. Since then, it has been demonstrated that less canal preparations lead to more dentin preservation resulted in decreased stress on tooth structure, mainly in the coronal third of the root, and potentially a higher resistance to fracture. In addition, smaller and larger canal preparations were comparable with regard to the cleanliness of the root canal. The purpose of this case series was to report on the outcome of root canal treatments following a conservative canal preparation, followed by three-dimensional cleaning technique (intracanal heating and ultrasonic activation of NaOCl).

Effect of MTA versus CEM apical plugs on fracture resistance of endodontically treated simulated immature teeth restored with cast metal posts: an in-vitro study

BACKGROUND

Endodontically treated immature teeth which are restored with cast metal posts are of the most susceptible teeth to fracture. An apical plug is usually used as root end filling in order to seal the wide apical foramen. The current study was performed to evaluate the effect of different apical plug materials (MTA and Calcium enriched mixture cement) at varied thicknesses on fracture resistance of teeth restored with cast metal posts.

METHODS

A total of 40 extracted intact single-rooted human mandibular premolars (removed for orthodontic reasons) were used in the study. The coronal part of each tooth was removed and root canal preparation was performed. A size 4 Gates Glidden drill was used to enlarge the canal and was passed through the apical foramen in order to simulate an immature apex. Samples were randomly divided into 5 groups (n = 8) according to apical plug (control group: No plug, group MTA5: 5 mm MTA plug, group CEM5: 5 mm CEM plug, group MTA3: 3 mm MTA plug, group CEM3: 3 mm CEM plug). Post-space preparations were performed and cast metal post-and-cores were fabricated and cemented. Fracture resistance was assessed using a universal testing machine. Fracture thresholds were recorded and data were analyzed using One-way ANOVA and Dunnett's T3 tests with significance level at P value < 0.05.

RESULTS

The analysis showed a significant difference of fracture resistance between groups (P value < 0.05). The mean fracture resistance of samples in control group was significantly lower than MTA5 (P value = 0.003). There was no significant difference between other groups (P value > 0.05).

CONCLUSIONS

Within the limits of this study, the evidence indicated that placement of a 5 mm MTA apical plug increased the fracture resistance in simulated immature teeth which are restored with cast metal posts, compared to control group (gutta-percha and sealer). While the results were not as promising for a 3 mm MTA apical plug or either 3 or 5 mm CEM apical plug.

Laboratory simulation of longitudinally cracked teeth using the step-stress cyclic loading method

AIM

To simulate in a laboratory setting longitudinal cracking in root filled premolar teeth, using cyclic mechanical fatigue.

METHODOLOGY

Mesial-occlusal-distal (MOD) cavities were prepared in twenty root filled, single-rooted, mandibular premolars restored with fibre posts and resin composites. The samples were randomly divided into two groups based on the loading approaches: static loading with a crosshead speed of 0.5 mm/min and step-stress cyclic loading (1 Hz) with increasing amplitude. The loads and numbers of cycles to failure were recorded. Micro-CT was also used to identify the fracture modes. Statistical analysis was performed using Student's t-test. The level of significance was set at 0.05.

RESULTS

The mean fracture loads for the static loading and cyclic loading groups were 769 ± 171 N and 720 ± 92 N, respectively. There was no significant difference between the two groups (P > 0.05). The proportions of longitudinal, cuspal and mixed-mode fractures under cyclic loading were 50%, 20% and 30%, respectively. Longitudinal fractures occurred with larger numbers of cycles and higher average loads per cycle compared with the other fractures. Static loading produced only cuspal fractures.

CONCLUSIONS

Longitudinally cracked premolar teeth with root fillings were successfully produced using the step-stress cyclic loading method. This provides a more clinically representative methodology for studying cracked teeth in a laboratory setting.

Impact of Conservative Endodontic Cavities on Root Canal Preparation and Biomechanical Behavior of Upper Premolars Restored with Different Materials

INTRODUCTION

The purpose of this study was to evaluate the impact of conservative endodontic cavities (CECs) on root canal preparation, restoration, and biomechanical behavior of teeth prepared using different shaping systems and restorative materials.

METHODS

Ninety upper premolars with a bifurcated root were matched based on morphology and randomly assigned to a control group (n = 10) or 1 of the following experimental groups (n = 40): traditional endodontic cavity and CEC. Teeth were subdivided according to instrumentation (n = 10) as follows: ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland), Reciproc (VDW GmbH, Munich, Germany), Reciproc Blue (VDW GmbH), and Hyflex EDM (Coltene/Whaledent, Altstätten, Switzerland). After canal obturation, teeth were restored using temporary material, conventional composite, regular bulk fill composite, or bulk fill flow combined with conventional composite. Before and after preparation and after obturation, the teeth were scanned using micro-computed tomographic imaging. Canal transportation (CT), the percentage of untouched canal surfaces (UCSs), voids in restoration (VRs), and residual filling material in the pulp chamber were evaluated. Finite element analysis, fracture resistance, and the failure pattern were recorded. The data were analyzed using analysis of variance and the Tukey and chi-square tests.

RESULTS

CECs had greater CT, percentage of filling material, and VRs compared with traditional endodontic cavities (P < .0001). The highest CT and UCSs were observed in CEC with ProTaper Universal. Bulk fill flow combined with conventional composite showed a lower percentage of VRs compared with other restorative materials (P < .05). Finite element analysis, fracture resistance, and failure pattern revealed similar behaviors in all groups (P > .05) .

CONCLUSIONS

CECs had a negative impact on root canal centralization, UCSs, cleaning of the pulp chamber, and percentage of VRs. Controlled memory instruments were the most adequate for the root canal preparation of CECs. The endodontic cavity did not influence the biomechanical behavior of restored teeth.

Preserving dentine in minimally invasive access cavities does not strength fracture resistance of restored mandibular molars

AIM

To evaluate the correlation between the volume of dental hard tissues removed and the fracture resistance of mandibular molar teeth with ultraconservative (UltraAC) or traditional (TradAC) access cavity preparations.

METHODOLOGY

Sixty recently extracted and intact mandibular first molars were scanned in a microcomputed tomographic (micro-CT) device, anatomically matched and assigned at random to 2 groups (n = 30), according to the access cavity type: UltraAC or TradAC. After access preparation, mesial and distal canals were prepared using Reciproc instruments and a new scan was taken. The volumes of pulp chamber and dental hard tissues in each specimen were measured before and after the experimental procedures, and the percentage volume reduction of hard tissues calculated for the entire tooth and for the crown separately. Teeth were then root filled, restored and subjected to fracture resistance tests in an universal testing machine. The force required to fracture was recorded in Newtons (N). The adherence of the variables to a Gaussian curve was verified using a Shapiro-Wilk test. Skewed data were analysed with nonparametric Wilcoxon signed rank or Spearman correlation tests, whilst the normally distributed data were analysed with a dependent samples Student t-test. Level of significance was set at 5%.

RESULTS

Pre-operatively, no difference was observed between groups regarding the volume of pulp canal space or dental hard tissues (P > 0.05). After access preparation, volumes of the removed hard tissues from the entire tooth and from the crown were significantly greater in teeth prepared with TradAC than with UltraAC (P < 0.05). No significant difference was observed in the fracture resistance values between TradAC (902.9 ± 347.8 N) and UltraAC (948.7 ± 405.7 N) groups (P = 0.975). The Spearman test was unable to identify a correlation between fracture resistance and percentage volume of removed dental hard tissues in the entire root (P = 0.525, r = -0.084) or only in the crown (P = 0.152, r = -0.187).

CONCLUSION

The volume of hard dental tissues removed, although greater in teeth with TradAC compared to UltraAC, did not correlate with the fracture resistance results, indicating that a minimally invasive access cavity did not increase the resistance of restored mandibular first molars to fracture.

A comparative evaluation of the effect of different access cavity designs on root canal instrumentation efficacy and resistance to fracture assessed on maxillary central incisors: An in vitro study

Aim:

The purpose of this study is to evaluate and compare the effect of different access cavity designs on root canal instrumentation efficacy using micro-computed tomography (CT) scan and resistance to fracture evaluated using the universal testing machine on maxillary central incisor.

Materials and Methodology:

Forty extracted human permanent maxillary central incisors were divided into four groups for each access cavity. The access cavities were prepared according to predefined criteria and were further assessed under Micro-CT to evaluate pre and postoperative instrumentation efficacy. After biomechanical preparation and obturation, the teeth were wrapped with tin foil to maintain a thickness of 0.2–0.3 mm as periodontal ligament. Then, the silicon impression material was applied in the acrylic alveolus, to maintain and simulate the thickness of periodontal ligament and fracture resistance was checked using the universal testing machine.

Statistical Analysis:

Data were analyzed using one-way analysis of variance test. Pair-wise comparison was made using post hoc multiple comparison (Tukey) test.

Results:

Fracture resistance was highest (1272 N) for the control group followed by the Lingual Conventional Access Group (1153.90 N). Fracture resistance for Lingual Cingulum Access Group was 1130.70 N and least for the Lingual Incisal Straight-Line Access Group (1022.80 N). This difference in fracture resistance among all the groups was significant (P = 0.001). Overall comparison showed that dentin volume reduction (DVR) for Group II was 22.45 mm3, for Group III was 17.37 mm³ and for Group IV was 28. 41 mm³. This difference in DVR among the three groups was significant (P = 0.001).

Conclusion:

The most effective instrumentation efficacy was obtained in lingual incisal straight-line access group, followed by lingual cingulum access group, followed by lingual conventional access group. The most effective fracture resistance was obtained in the lingual conventional access group, followed by the lingual cingulum access group, followed by the lingual incisal straight-line access group.

Impact of Access Cavity Design on Fracture Resistance of Endodontically Treated Molars: A Systematic Review

Objective

The main aim of this present systematic review is to ascertain whether a conservative endodontic cavity (ConsAC) has a better fracture resistance than a traditional access cavity (TradAC) in endodontically treated molars.

Materials and Methods

Three independent reviewers researched without limits in multiple engines: PubMed, ScienceDirect, Scopus, ResearchGate, EBSCOhost, Wiley Online Library, and Google Scholar, in addition to reference and hand search. Articles were chosen according to a certain inclusion and exclusion criteria, which, in brief, are in vitro studies assessing the fracture resistance difference between ConsAC and TradAC performed on extracted sound human molar teeth. A quality assessment criteria was produced to evaluate the chosen articles and categorized them according to their risk of bias into low, moderate and high.

Results

Out of a total of 105 studies, which were obtained from seven different search engines, only eight in vitro studies were included after eliminating the duplicates followed by the application of the eligibility criteria. Five of the articles showed low risk of bias while the others revealed a moderate risk of bias.

Conclusion

To sum up, there is insufficient evidence to give a final decision whether ConsAC is more advantageous than TradAC in terms of fracture resistance and further studies regarding this topic are needed.

Comparative Analysis of Fracture Strength of Remaining Tooth Structure after Endodontic Treatment with Various Access Cavity Preparation Techniques

Background:

A perfect balance needs to be maintained between various types of endodontic access cavity preparation designs like - Traditional and conservative designed preparation to have access to the root canal system for proper cleaning and shaping of root canals without compromising the fracture resistance of the tooth structure.

Aims and Objectives:

We aimed to assess as well as draw comparisons of resistance against fracture of remaining tooth structure post the endodontic treatment after preparing access cavity through a variety of techniques so that we can estimate which type of cavity design technique will help endodontically treated teeth to withstand excessive load without fracture.

Methods:

Forty-two intact teeth (mandibular molars) were randomly selected and then were assigned to 07 different groups, inclusive of control and test groups. Various designs of access cavity preparation were done on sample teeth. The groups were divided based on different access cavity preparation designs as well as residual walls. The samples were then mounted on a composite cylinder, which was loaded under a mechanical testing machine at 0.5mm/min speed till the tooth structure fractured. This measurement of force was denoted in newton. The later analysis was carried out with the help of two-way Analysis of Variance (ANOVA) as well as Tukey’s post-hoc statistical tests.

Results:

There was negligible statistically relevant variance in strength towards fracture between traditional and conservative designs in teeth having three remaining walls. However, teeth with only two remaining walls fractured easily.

Conclusion:

Fracture resistance of teeth with remaining 03 residual walls did not show any significant difference among Traditional (TEC) and Conservative Cavity (CEC) design groups, but increased fracture strength was reported in CEC with 02 residual walls.

Evaluating the Effect of Oblique Ridge Conservation on Stress Distribution in an Endodontically Treated Maxillary First Molar: A Finite Element Study

INTRODUCTION

Although the maxillary first molar (MFM) has been frequently subjected to stress analysis in endodontic investigations, the available data about the effect of its oblique ridge are quite sparse. The aim of this study includes evaluating the effect of the residual oblique ridge on the stress distribution after preparing conservative access cavities.

METHODS

Based on the cone-beam computed tomographic data, the model of an intact MFM and 5 cavity designs were prepared for endodontic treatment, which were consequently filled with gutta-percha and dental resin composite (6 total models). All models were subjected to 4 types of occlusal loading; finite element analysis via ABAQUS CAE software (Dassault Systemes, Vélizy-Villacoublay, France) was accomplished, whereas other software programs such as (Mimics Research Materialise, Leuven, Belgium) and 3-Matic Research (Materialise) were also incorporated in different stages for detecting stress distribution.

RESULTS

The stress distribution on the MFM is not only dependent on the remaining width of the oblique ridge but also on the type of loading. The most stress on the cervical region was concentrated on the palatal root in some type of loading, whereas the least stress on the occlusal surface was recorded when the whole oblique ridge was replaced by the composite resin.

CONCLUSIONS

When the occlusal contacts are occurring only on the palatal cusp, the stress distribution on the oblique ridge is noticeably affected by the cavity design.

Minimization of Tooth Substance Removal in Normally Calcified Teeth Using Guided Endodontics: An In Vitro Pilot Study

INTRODUCTION

This study evaluated the success rate of and tooth substance removal required for computer-guided preparation of endodontic access cavities.

METHODS

Thirty acrylic typodont teeth with root canals (10 each of tooth numbers 11, 14, and 17) were randomly allocated to a study or control group (15 teeth per group). In the study group, teeth were fixed in acrylic resin and subsequently digitized using a laboratory scanner. A cone-beam computed tomographic scan was then taken. Access cavity preparations were planned virtually, and a template was 3-dimensionally printed. In the control group, access cavities were prepared using the conventional access technique. Tooth substance removal was assessed by weighing teeth before and after preparation. Volume loss was analyzed statistically by use of the Wilcoxon-Mann-Whitney test at a significance level of P < .05.

RESULTS

Using guided endodontics, 93.3% of root canals were located successfully compared with 100% of root canals using the conventional technique. In the control group, the mean tooth substance removal was 16.1 ± 3.7 mm³ for incisors, 44.2 ± 8.9 mm³ for premolars, and 99.3 ± 3.1 mm³ for molars. In the study group, significantly less tooth substance was removed; substance loss was 10.3 ± 1.1 mm³ for incisors, 29.3 ± 4.2 mm³ for premolars, and 51.8 ± 5.3 mm³ for molars.

CONCLUSIONS

The use of guided endodontics in normally calcified teeth enables the preservation of a significant amount of tooth substance. However, this advantage must be carefully balanced against a greater radiation burden and risk of perforation, higher costs, and more difficult debridement and visualization of the pulp chamber and root canals.

Chamberless Endodontic Access for Treatment of Calcified Anterior Central Incisors

INTRODUCTION

Modern techniques for treating maxillary anterior central incisors with calcified canals emphasize maintaining coronal dentin with small crown access. Alternatively, traditional retrograde surgical procedures are focused on creating an apical seal predominately limited to the remaining resected apical one third of the root canal space. A treatment option for calcified anterior teeth, with avoidance of traditional orthograde access, is presented. Chamberless endodontic access (CEA) to the canal is chosen in this case, leveraging a previous surgical treatment and osseous defect to create straight line canal access.

METHODS

A tooth presenting with a chronic apical abscess and an apparent previous apical surgery was instrumented and obturated using a CEA avoiding the traditional orthograde approach to the root canal system. Straight line approach was achieved retrograde and canal instrumentation was performed using ultrasonic activated U-files. Canal obturation was accomplished with warm vertical condensation technique followed by placement of an apical retroseal.

RESULTS

A successful 52-month outcome demonstrated the viability of CEA facilitating retrograde instrumentation and obturation.

CONCLUSIONS

Use of CEA simultaneously protected the clinical crown and provided a successful clinical outcome. A viable option for treatment of an anterior calcified canal and abscess due to dental trauma, CEA mitigates many of the risks associated with the treatment of calcified root anatomy.

A survey of current trends in root canal treatment: access cavity design and cleaning and shaping practices

The purpose of this study was to evaluate current trends in access cavity design and cleaning and shaping among endodontists. A survey was e-mailed to active members of the American Association of Endodontists. Data showed that most respondents used traditional (57%) or conservative (43%) access cavities; less than 1% reported using ultraconservative access cavities. A glide path was created by 93% of respondents; NaOCl was used as lubricant by 51% of respondents, while 28% used RC Prep, 9% used liquid EDTA, 7% used Glyde, and 2% did not use any lubricant. Most respondents used NaOCl at 5.25% or higher concentration. Smear layer was removed by 92% of endodontists. Apical gauging was mostly accomplished with hand files. Clinical preferences varied among surveyed endodontists and among different age groups. Currently, very few endodontists use ultraconservative access preparations. There was large variation among the respondents suggesting a possible need for quality guidelines.

Controversies in endodontic access cavity design: A literature review

The purpose of this article is to compare and contrast the different types of endodontic access cavity designs based on the current available evidence. Four types of access cavity designs, namely, traditional endodontic access cavity design (TEC), contracted/conservative endodontic access cavity design (CEC), ultra-conservative or ninja endodontic access cavity design (NEC) and truss endodontic access cavity design (TREC) have been suggested, and the latter three are currently in the limelight. Studies in vitro have been performed comparing the TECs, CECs, TRECs and NECs; except for the TECs, the other three types have not undergone clinical trials on patients. The choice of endodontic access cavity design affects fracture strength of the tooth, but remnants of pulpal tissue, due to ineffective instrumentation, can cause root canal treatment failure.

CPD/Clinical Relevance: Root canal treatment with new access cavity designs has been proposed. However, there is lack of evidence to support such practices. It is important to consider the potential deleterious effects of such access cavity designs rather than emphasizing the preservation of tooth structure alone.