Impact of Contracted Endodontic Cavities on Root Canal Disinfection and Shaping

Minimally Invasive Access Cavities: A Benefit/Risk Analysis

Background/Objectives: Contemporary dentistry aims to preserve healthy tissues and perform minimally invasive procedures. The availability of ever-improving equipment allows practitioners to follow this conceptual innovation. This approach is also used in endodontics, as new types of access cavities seem to be gaining popularity, allegedly reducing tissue destruction and loss of mechanical resistance of the treated teeth. Methods: We performed a comprehensive review of the available literature on the subject, focusing on in vitro studies accessible through major search engines and limiting the search to English-language articles published between 2010 and 2024. Results: Our analysis showed that the realization of reduced access cavities seems to preserve the mechanical resistance of the treated teeth, may compromise disinfection, and respects the original root canal path and the quality of obturation. In addition, these procedures appear to increase instrument deformation, fracture susceptibility, and treatment time: Mini-invasive cavities have many limitations and should only be used in situations where there is a high likelihood of success, where there are few difficulties and where sufficient material is available. However, with appropriate case selection, these new approaches can be used and should improve the prognosis of endodontically treated teeth.

Microtomographic Analysis of the Biomechanical Performance of Thermally Treated Instruments in Flattened and Curved Root Canals

INTRODUCTION

This study aimed to evaluate, using microcomputed tomography, the impact of various mechanized systems on the geometry of the root canal system and dentin thickness in mandibular first molars. The hypothesis proposed that different systems would produce significant variations in root canal system preparation.

METHODS

Mesial and distal canals of mandibular molars were selected and divided into 5 groups (n = 10) based on the system used: 2Shape (25.06), Reciproc Blue (25.08), ProTaper Ultimate (25.08), ProTaper Next (25.06), and Univy New (25.06). Biomechanical preparation was performed following each manufacturer's instructions. Microcomputed tomography scans were conducted before and after preparation to assess 3-dimensional parameters (volume, surface area, Structural Model Index, and prepared root canal walls) and 2-dimensional parameters (area, perimeter, diameters, roundness, and transportation).

RESULTS

ProTaper Ultimate exhibited the greatest volume increase in mesial canals (1.73 ± 0.19), while ProTaper Next demonstrated the highest increase in distal canals (1.95 ± 0.25). Furthermore, ProTaper Ultimate resulted in the greatest dentin removal and the largest postpreparation area. Reciproc Blue achieved the best results for roundness and had the lower unprepared walls (15.3 ± 6.97).

CONCLUSIONS

All systems produced comparable outcomes, with ProTaper Ultimate yielding the greatest volume increase and dentin removal, indicating a less conservative preparation. Reciproc Blue provided optimal roundness and minimized unprepared root canal wall surfaces.

Exploring access cavity through non-carious cervical lesions: Impacts on instrumentation, obturation, and fracture resistance in mandibular incisors

AIM

To compare the effects of Cervical Access Cavity (CervAC) and Traditional Access Cavity (TradAC) on root canal preparation, root canal filling, and fracture resistance in mandibular incisors.

METHODOLOGY

Twenty recently extracted and intact mandibular incisors were initially scanned using a micro-CT device. The specimens were anatomically matched to create two groups (n = 10). A wedge-shaped non-carious cervical lesion (NCCL) was created on the buccal aspect of all teeth using a double-faced segmented diamond disc. In group 1, a TradAC was prepared, whilst in group 2, access was created through the simulated NCCL using a round diamond bur 1012. After root canal preparation with Rotate instruments sizes 15/0.04, 20/0.04, and 25/0.04, the teeth were scanned again and evaluated for root canal volume and surface area, static voxels, volume of removed dental tissue, and dentine thickness. After that, the root canals were filled using the single-cone technique, teeth were restored with composite resin, and subsequently rescanned to calculate the volume of filling materials and voids. Then, the restored teeth were subjected to fracture resistance tests using a universal testing machine. Statistical comparisons between groups were performed with the Mann-Whitney test or the Student's t-test, with a statistical significance level of 5%.

RESULTS

Statistical comparisons indicated no significant differences between groups in terms of root canal volume, surface area, static voxels, removed root dentine, root canal filling volume, percentage of voids, or fracture resistance load (p > .05). Conversely, teeth prepared with TradAC showed a significantly higher percentage of dental tissue removed from the crown (p = .001) and a greater volume of filling material remnants in the pulp chamber (p < .001) compared to the CervAC group. A significantly lower percentage reduction in dentine thickness was observed only on the mesial aspect of root at Level 1 in TradAC group (p = .008).

CONCLUSIONS

CervAC can be considered a viable alternative approach in the presence of NCCL in mandibular incisors.

Comparative Micro-CT Analysis of Minimally Invasive Endodontic Systems Using 3D-Printed Replicas and Natural Teeth

(1) Background: This study aimed to compare the shaping abilities of modern minimally invasive endodontic systems using natural teeth and 3D-printed resin replicas. These replicas offer a standardized approach for studying root canal preparation while eliminating the variability and scarcity of natural teeth. (2) Methods: Eleven mandibular molars with Vertucci class IV anatomy and their 3D-printed replicas (n = 132 canals) were scanned using micro-CT before and after preparation with six rotary systems. Shaping abilities were assessed by comparing volume, surface area, and unprepared areas between natural teeth and their 3D replicas, focusing on the apical third. Statistical analysis included the Shapiro-Wilk test to assess data normality and ANOVA and t-tests to compare different endodontic systems. (3) Results: Both qualitative and quantitative analyses revealed high similarity between natural teeth and 3D replicas. No significant differences in volume or surface area were found except in the apical third, where 3D replicas showed slightly larger increases in volume. (4) Conclusions: 3D resin replicas closely mimic natural teeth and provide a practical tool for assessing the shaping abilities of endodontic systems. This study demonstrates that 3D-printed models are suitable for endodontic research, offering a standardized and accessible alternative to natural teeth.

Immediate and delayed shear bond strength evaluation between root canal sealers and restorative materials: an experimental study

BACKGROUND

Several calcium silicate-based sealers have recently emerged in endodontics. This study aimed to compare the immediate and delayed shear bond strength between the bioceramic and calcium hydroxide-based sealers and different resin-based restorative materials.

METHODS

One hundred and twenty specimens with a 3-mm depth and a 3-mm diameter were prepared. They were evenly divided into two groups, the bioceramic sealer and calcium hydroxide-based sealer groups. Each primary group was subdivided into two subgroups based on the restorative material used; i.e., the flowable resin composite and resin-modified glass ionomer subgroups. Moreover, each subgroup was further divided into the restoration process's timing: either immediately post-sealing or delayed after setting the sealers for seven days. The mode of failure was assessed by stereomicroscopic examination.

RESULTS

The highest shear bond strength was found when the bioceramic sealer was used and restored with the flowable resin composite. The strengths were 8.45 (1.17) and 6.67 (1.60) megapascals (MPa) in the immediate and delayed restoration groups, respectively. In contrast, the lowest strength, 2.91 (1.22) MPa, was recorded when calcium hydroxide-based sealer was employed and restored after allowing the sealer to set completely with resin-modified glass ionomer. Notably, there were no cohesive fractures within the tested restorative materials. All observed fractures occurred within the sealer materials, at the interface of the sealer and restorative material, or in combination. Moreover, the most common failure was a mixed failure.

CONCLUSIONS

When flowable resin composite was used immediately before complete setting, bioceramic sealers showed a higher bond strength than calcium hydroxide-based sealers.

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

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

Principle and antimicrobial efficacy of laser-activated irrigation: A narrative review

In the last two decades, the activation of root canal irrigants with pulsed lasers as an adjunct in root canal treatment has become increasingly popular. This narrative review explains the physical basics and the working mechanism of laser-activated irrigation (LAI), explores the parameters influencing LAI efficacy, considers historical evolutions in the field and summarizes laboratory and clinical evidence with emphasis on the antimicrobial action of LAI. Cavitation is the driving force behind LAI, with growing and imploding vapour bubbles around the laser tip causing various secondary phenomena in the irrigant, leading to intense liquid dynamics throughout the underlying root canal. High-speed imaging research has shown that laser wavelength, pulse energy, pulse length and fibre tip geometry are parameters that influence this cavitation process. Nevertheless, this has not resulted in standardized settings for LAI. Consequently, there is significant variability in studies assessing LAI efficacy, complicating the synthesis of results. Laboratory studies in extracted teeth suggest that, with regard to canal disinfection, LAI is superior to conventional irrigation and there is a trend of higher antimicrobial efficacy of LAI compared to ultrasonic activation. Clinical evidence is limited to trials demonstrating similar postoperative pain levels after LAI versus no activation or ultrasonic activation. Clinical evidence concerning the effect of LAI on healing of apical periodontitis as yet is scarce.

The influence of different root canal open access shapes on the use of rotary root canal enlargement

Background/purpose

The success of root canal treatments is influenced by the shape of the access opening and the outcomes of root canal enlargement. The aim of this study was to evaluate the impact of various rotary instruments on the maintenance of the root canal's central alignment post shaping, considering a range of access cavity designs.

Materials and methods

Using digital tooth simulation, 4 sets of 12 teeth underwent traditional (TradAC) or conservative (ConsAC) access cavity preparations. Root canals were enlarged with TruNatomy or ProTaper Ultimate rotary instruments. Canal transportation and centering ratio were separately measured. Statistical analysis was performed using JMP trial 17 software.

Results

The analysis revealed no significant difference in buccal and lingual canal transportation among different rotary instruments or canal enlargement designs (P > 0.05). TradAC yielded higher centering ratios in MB and ML canals, while ConsAC excelled in the distal canal for the TruNatomy group. Conversely, in the ProTaper Ultimate group, ConsAC demonstrated higher ML canal ratios (P < 0.05).

Conclusion

TruNatomy maintained superior canal centering with ConsAC, while ProTaper performed better with TradAC.

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.

Microcomputed tomographic evaluation of 6 NiTi files on the pericervical dentin and the smallest dentin thickness zones in mesial root canals of mandibular molars: an in vitro study

OBJECTIVE

The aim of this study was to evaluate six files on the pericervical dentin (PCD) and the smallest dentin thickness zones (SDTZ) in mesial root canals of mandibular molars.

MATERIALS AND METHODS

Sixty mandibular molars with two mesial canals and Vertucci configuration were aleatory allocated in 6 experimental groups of 10 molars and 20 root canals. Specimens were scanned before instrumentation using the SkyScan 1275 (Bruker microCT, Kontich, Belgium). Group 1 was treated with WaveOne Gold (WG), group 2 with Reciproc Blue (RB), group 3 with TRUShape (TS), group 4 with XP-endo Shaper (XP), group 5 with iRace (IR), and group 6 with TruNatomy (TN). After instrumentation, the molars were scanned again and the images recorded were reconstructed with the NRecon v.1.7 (Bruker micro-CT) and analyzed with CTAn v.1.20.8 software (Bruker micro-CT) quantifying the changes produced in the surface, volume, structure thickness, SMI, and centroids at the Pericervical Dentin area of the root canals (PCD) located from the root canal orifices at the floor of the pulp chamber to 4 mm in the apical direction, and the changes in the Smallest Dentin Thickness Zones (SDTZ) located (from the furcation to 4 mm and 7 mm in the apical direction. The data obtained were compared using Wilcoxon and ANOVA with a 5% significance level.

RESULTS

XP and TN were similar in all the parameters (P >.05) at the PCD, but TN showed significant differences from WG, RB, TS, and IR (P <.05), while XP showed significant differences from WG (P <.05) in volume, surface, and structure thickness. Regarding the changes in the SDTZ, the amount of dentin removed was similar between the groups in both canals at the middle 1/3, at the cervical 1/3 for MB canals, and in ML canals for RB, TS, XP, IR, and TN (P>.05). The action of WG was significantly different from that of XP and TN in the cervical 1/3 of the ML canal (P <.05).

CONCLUSIONS

XP and TN rotatory files with small taper and volume maintained better with minor changes at the PCD and SDTZ, while WG reciprocation file produced the largest change. All the files were maintained centered at the PCD, and their performances were safe with a minimal thickness higher 0.5 mm at the SDTZ, and without risk of perforation.

TRIAL REGISTRATION

No clinical trials were indicated in this study.

CLINICAL RELEVANCE

The choice of endodontic files is a relevant factor in the conservative performance of root canal treatments.

Options for Access Cavity Designs of Mandibular Incisors: Mechanical Aspects from Finite Element Study

INTRODUCTION

This study investigated different access cavity designs of mandibular anteriors in terms of their effect on the biomechanical behavior and longevity using finite element analysis (FEA).

METHODS

A 3-dimensional model of a mandibular incisor was created for FEA. After validating the intact tooth (IT) model, 4 experimental models were developed (traditional lingual access cavity [TLA], facial access cavity [FAC], incisal access cavity [ICA], and cervical access cavity [CVA]). Cyclic loading was simulated, and the number of cycles until failure (NCF) was compared to the IT model. Stress distribution patterns, maximum von Mises stresses (vMSs), and maximum principal stresses (MPSs) were analyzed mathematically. The safety factor was also calculated and demonstrated.

RESULTS

The maximum vMS registered on the IT model was 134.16 MPa. The FCA and the CVA provided the highest NCF (193.7% compared with the IT model) followed by ICA (58.2%) and TLA (21.4%). The vM and MPS analysis revealed that the lingual surface is a primary stress channel, and the presence of an access cavity significantly weakens the tooth structure. Although the maximum vMS registered for the IT model was 134.16 MPa, the maximum vMS was 73.97 MPa for both the FCA and the CVA, 152.27 MPa for the ICA, and 173.63 MPa for the TLA.

CONCLUSIONS

The facial and cervical access cavity designs provided considerable reinforcement to the endodontically treated mandibular incisors. With advancements in esthetic restorative materials and endodontic instruments, facial access design could emerge as the new standard for access cavity preparation in mandibular incisors.

The role of systemic statins in the inception and healing of apical periodontitis: a systematic review

OBJECTIVES

Statins are a category of medications widely used to reduce plasma LDL-cholesterol levels, that also possess antibacterial, anti-inflammatory, and immunomodulatory action. The aim of this systematic review was to explore the effects of systemic statins therapy on the development and treatment of apical periodontitis (AP) on humans and animals.

MATERIAL AND METHODS

Three electronic databases (PubMed, Web of Science, and Scopus) and grey literature were searched from their inception until February, 20 2023 (PROSPERO CRD42021246231). For the quality assessment and risk of bias, different guidelines were used according to the typology of the studies considered (Animal Research Reporting of In Vivo Experiments, Newcastle-Ottawa Quality Assessment Form for Cohort Studies, Systematic Review Centre for Laboratory animal Experimentation Risk of Bias tool and Tool to assess risk of bias in cohort studies of CLARITY Group).

RESULTS

Seven hundred eleven records were screened, and six articles were included for this qualitative review. The eligible studies showed a moderate overall quality and risk of bias. Human patients in treatment with statins exhibited a higher healing rate of AP following root canal treatment. In experimental animal models, statins had a beneficial effect on the development of AP.

CONCLUSIONS

Despite the limited number of studies and considering that most of them are on animals, our findings suggest that systemically administered statins make a positive contribution to prevent the development and help healing of AP.

CLINICAL RELEVANCE

There is an increased evidence that a pharmacologic adjunct to endodontic treatment may be considered to enhance healing of AP. Among other medications, statins seem to have a positive impact on the disease.

Influence of access cavity design on calcium hydroxide removal using different cleaning protocols: a confocal laser scanning microscopy study

Objectives

The purpose of this study was to evaluate the influence of endodontic access cavities design on the removal of calcium hydroxide medication of the apical third of mandibular incisor root canal walls and dentinal tubules with different cleaning protocols: EDDY sonic activation, Er,Cr:YSGG laser-activated irrigation, or conventional irrigation with IrriFlex.

Materials and Methods

Seventy-eight extracted human mandibular incisors were assigned to 6 experimental groups (n = 13) according to the endodontic access cavity and cleaning protocol for calcium hydroxide removal: traditional access cavity (TradAC)/EDDY; ultraconservative access cavity performed in the incisal edge (UltraAC.Inc)/EDDY; TradAC/Er,Cr:YSGG; UltraAC.Inc/Er,Cr:YSGG; TradAC/IrriFlex; or UltraAC.Inc/IrriFlex. Confocal laser scanning microscopy images were used to measure the non-penetration percentage, maximum residual calcium hydroxide penetration depth, and penetration area at 2 and 4 mm from the apex. Data were statistically analyzed using Shapiro-Wilk and WRS2 package for 2-way comparison of non-normally distributed parameters (depth of penetration, area of penetration, and percentage of non-penetration) according to cavity and cleaning protocol with the significance level set at 5%.

Results

The effect of cavity and cleaning protocol interactions on penetration depth, penetration area and non-penetration percentage was not found statistically significant at 2 and 4 mm levels (p > 0.05).

Conclusions

The present study demonstrated that TradAC or UltraAC.Inc preparations with different cleaning protocols in extracted mandibular incisors did not influence the remaining calcium hydroxide at 2 and 4 mm from the apex.

Cleaning and Disinfecting Oval-Shaped Root Canals: Ex Vivo Evaluation of Three Rotary Instrumentation Systems with Passive Ultrasonic Irrigation

Background and Objectives: Successful root canal treatment depends on the thorough removal of biofilms through chemomechanical preparation. This study aimed to investigate and compare the cleaning and disinfecting efficiency of oval-shaped root canals using XP-endo Shaper (XPS), ProTaper Next (PTN), and HyFlex CM (HCM) in combination with passive ultrasonic irrigation (PUI). Materials and Methods: Ninety extracted teeth were contaminated and randomly divided into three groups: XPS, PTN, and HCM. Each group was assigned to three subgroups: subgroup A (sterile saline), subgroup B (3% sodium hypochlorite and 17% ethylenediaminetetraacetic acid), and subgroup C (3% sodium hypochlorite, 17% ethylenediaminetetraacetic acid, and PUI). Bacterial sampling was conducted both from baseline samples and samples after chemomechanical preparation. Scanning electron microscopy (SEM) was used to evaluate the residue bacterial biofilms, hard tissue debris, and smear layers on the buccolingual walls of oval-shaped root canals. Results: When combined with sterile saline, XPS demonstrated a higher reduction of bacterial counts and was more effective in eradicating Enterococcus faecalis in the middle third of the canals compared to the other instruments (p < 0.05). Additionally, when used with antimicrobial irrigants, XPS was more effective in disinfecting the coronal third of the canals than the other instruments (p < 0.05). Furthermore, XPS reduced hard tissue debris more effectively in the middle third of canals than in the apical third (p < 0.05). Conclusions: XPS outperforms PTN and HCM in disinfecting oval-shaped root canals. Despite the fact that combining XPS and PUI improves cleaning and disinfecting, removing hard tissue debris from the critical apical area remains challenging.

Influence of access cavity design, sodium hypochlorite formulation and XP-endo Shaper usage on apical debris extrusion - A laboratory investigation

This study assessed the amount of apically extruded debris during root canal preparation using XP-endo shaper and the supplemental use of XP-endo finisher comparing the use of traditional endodontic access or conservative endodontic access cavities and liquid or gel-based formulations of 5.25% sodium hypochlorite or distilled water as supplemental agents. Maxillary first premolar teeth (N = 148) were randomly divided based on their access cavity design and sub-grouped according to the supplemental agent used. The amount of extruded debris was analysed based on the dry weight of the debris collected using a previously established laboratory methodology. Debris extrusion occurred in all groups. Overall, the traditional endodontic access cavity design was associated with more debris extrusion compared to the conservative type. The use of sodium hypochlorite solution showed higher debris extrusion than the gel, whilst distilled water had intermediate values.

Effects of Conservative Access and Apical Enlargement on Shaping and Dentin Preservation with Traditional and Modern Instruments: A Micro-computed Tomographic Study

INTRODUCTION

This ex vivo study aimed to evaluate the shaping abilities and preservation of dentin with traditional and modern instruments after using sizes 25 and 40 in oval canals of mandibular incisors with conservative access.

METHOD

Thirty mandibular incisors with single straight oval canals were selected and assigned into 2 groups (n = 15) according to the instrument system used during preparation, Slim Shaper (SS) plus Apical Shaper (AS) and Protaper Gold (PG). The samples were subjected to micro-computed tomography before and after preparation with sizes 25 and 40. The shaping parameters evaluated included canal volume and surface area, amount of unprepared root canal walls, and reduction in pericervical dentin.

RESULTS

Canal volume and surface area were significantly increased after enlargement with each instrument size (P < .01). The percentage of unprepared areas showed a significant intragroup decrease after using PG F2 and F4 or SS 3 and AS (P < .05). Intergroup comparison showed no significant differences. Pericervical dentin was reduced in all groups. The intragroup comparison only revealed a significant reduction (P < .01) between PG F2 and F4. In addition, a significant decrease in pericervical dentin (P < .05) was observed between PG F4 40/.06 and AS 40/.03. No significant differences were observed between PG F2 25/.08 and SS 3 25/.04.

CONCLUSION

Increasing the instrumentation size from 25 to 40 significantly reduces the percentage of unprepared areas regardless of the system used. In addition, using a modern system with a regressive taper allows the maintenance of pericervical dentin without compromising shaping efficacy in the apical third of the mandibular incisors with oval canals and conservative access.

Effect of different access cavity designs on fracture toughness of endodontically treated teeth: a systematic review and network meta-analysis

Objective To compare the effect of different endodontic access cavities on fracture toughness of extracted endodontically treated human teeth.Data/sources An electronic literature search was performed in seven databases as well as hand search until September 2020. Risk-of-bias tool was used to evaluate the quality of included studies. Random effects frequentist network meta-analysis was performed, with mean difference (MD) and 95% confidence interval (CI) as the effect measure. Confidence in the documented evidence was assessed through the newly fuelled Confidence in Network Meta-analysis (CINeMA) framework based on the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.Study selection A total of 844 articles were obtained in the electronic and hand search. After the application of the eligibility criteria and duplicate removal, 14 studies were included in this systematic review. All included studies were in vitro that evaluated the influence of conservative endodontic cavities (CECs) on fracture toughness in extracted endodontically treated human teeth and compared to traditional endodontic cavities (TECs). In total, ten studies (n = 456) were included in the network meta-analysis for molars. The overall risk of bias was moderate.Results The results showed that when compared to intact teeth, the greatest reduction in fracture resistance was reported for TEC (MD: -927.52; 95% CI [-1304.80; -550.24]) and CEC showed least reduction in fracture resistance (MD: -365.59; 95% CI [-759.02; 27.83]). The surface under the cumulative ranking curve (SUCRA) value for intact teeth was highest (85.4% probability of being ranked as first), followed by CEC (51.4% probability of being ranked as second), with CEC presenting the highest probabilities to be the most effective access cavity design, according to the RANK (receptor activator of NF-kappaB) table. Level of confidence varied from low to moderate across all formulated comparisons.Conclusion Overall, based on the included in vitro studies in this systematic review, CEC was the most favourable access cavity design when compared to other (truss access cavities, TEC and ninja cavities) and TEC was the least favourable for fracture resistance; however, the level of evidence was moderate.

Shaping outcome of ProTaper NEXT for root canal preparation in mandibular incisors: a micro-CT study

Background

Relatively high incidence of single canals with oval or round shape were observed in human mandibular incisors. In order to investigate the influence of the root canal morphology on root canal preparation, the shaping outcome of ProTaper NEXT in oval and round canals of mandibular incisors were evaluated by using micro-computed tomography (micro-CT) analysis.

Methods

This experiment was approved by the School Medical Ethics Committee. The sample size calculation was conducted using G*Power software. Intact mandibular incisors with a single canal were selected. Oval canals (2 < aspect ratio (AR) ≤ 4) and round canals (AR ≤ 2) were pair-matched according to canal length, and assigned to two experimental groups (13 per group). ProTaper NEXT was used for root canal preparation for both groups. Untouched canal wall (UCW), root canal morphological parameters and three-dimensional (3D) dentin thickness were evaluated in the entire root canal and each canal third after micro-CT scanning. Statistical analysis: Data were collected and analyzed with Mann–Whitney test and Friedman test using SPSS statistics software 25 (P < 0.05). Additionally, correlations of UCW area with canal morphological parameters were also investigated.

Results

After root canal preparation, no significant difference was observed in all analyzed parameters in the apical third between oval and round canal groups (P > 0.05). In the coronal two thirds of the canal, the post-operative structure model index (SMI), form factor and roundness were significantly increased, while the AR was significantly decreased in both groups (P < 0.05). In addition, in the coronal two thirds, significantly more UCW and higher UCWΔ% was observed in oval canal group (P < 0.05). Furthermore, UCW correlated very strongly to canal major diameter (0.924) and initial volume (0.938), and strongly to canal form factor (− 0.724), minor diameter (0.799) and canal area (0.882). Proximal dentin wall was associated with significantly thinner pre-operative dentin thickness and higher amount of dentin removal after root canal preparation in both oval and round canal groups.

Conclusions

(1) Both types of canals were more conical after root canal preparation, but oval root canals tend to leave more UCW area than round canals in the coronal two thirds of mandibular incisors, which contributes to the challenge for endodontic infection control. (2) Root canal preparation usually results in excessive dentin removal in the proximal dentin wall comparing with buccal and lingual walls in both types of canals of mandibular incisors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02335-7.

Fracture resistance and biomechanical behavior of different access cavities of maxillary central incisors restored with different composite resins

OBJECTIVES

The aim of this study was to compare the effect of three different access cavities on the tissue removal, deflection, fracture resistance, and stress distribution of extracted maxillary central incisors.

MATERIALS AND METHODS

Forty human maxillary central incisors were randomly assigned in four experimental group (n = 10) including conservative access cavity "CAC," traditional access cavity "TAC," invasive access cavity "IAC," and without access cavity (control group). Cone-beam computed tomography "CBCT" scans were used to evaluate the tissue removal during the different access cavities. All specimens were restored with composite resin (Admira Fusion, Voco, Cuxhaven, Germany) and embedded in acrylic resin blocks after simulating the periodontal ligament using red wax, then the specimens were submitted to the deflection test applying a load of 250 N and to the load-to-fracture test after artificial aging in a mechanical cycling machine (150 N, 5 × 106 cycles, 10 Hz). Lastly, stress distribution was assessed by three-dimensional finite element analysis (3D-FEA), simulating the specimens restoration by two types of composite resins of low and high elastic modulus (8 and 18 GPa respectively) after the access cavities. The data were submitted to Shapiro-Wilk and KS normality tests. Then, they were analyzed by one-way ANOVA and Tukey tests with a significance level (α ≤ 0.05).

RESULTS

CBCT scans showed a significant difference of worn tissues in CAC and TAC when compared to the IAC (P < 0.0001). In deflection test, CAC showed lower deformation values than the TAC and IAC. Load-to-fracture test presented no significant difference among the three experimental groups (P = 0.6901). 3D-FEA showed that the more conservative the access cavity, the higher the stress magnitude.

CONCLUSIONS

CAC promote less worn tissue; however, this does not improve the stress distribution or fracture resistance of endodontically treated maxillary incisors.

CLINICAL RELEVANCE

Clinicians should reconsider the pros and cons of the conservative access cavity.

An Appraisal on Newer Endodontic File Systems: A Narrative Review

AIM

This narrative review aims to explore and elicit the newer endodontic file systems used for root canal treatments.

BACKGROUND

The primary goals of endodontic therapy continue to be the mechanical enlargement and shaping of the intricate endodontic root canal systems to aid in disinfection. Nowadays endodontists have access to a wide range of endodontic file systems for root canal preparations with various design characteristics and benefits.

REVIEW RESULTS

ProTaper Ultimate (PTU) files' tip have a triangular convex cross-section, an offset mass of rotating design, a maximum flute diameter of 1.0 mm, and are constructed of gold wire, hence, commonly applied in conditions with restricted accessibility or an extremely curved canal. TruNatomyhas advantages over other cutting-edge file systems like maximum flute diameter of the corona, reduced distance between active cutting flutes, and shorter handles in comparison to SX instruments. In comparison to PTU files, ProTaper Gold (PTG) files are noticeably more elastic and fatigue-resistant. Compared to files in the F1-F3 range, size S1 and S2 files have a significantly longer fatigue life. MicroMega One RECI is more resistant to cyclic fatigue because of its heat treatment and reciprocating action and the C-wire heat treatment of the former gives it flexibility and controlled memory, enabling the prebending of the file. The RECIPROC blue demonstrated enhanced flexibility, increased fatigue resistance, and lower microhardness while maintaining the same surface qualities.

CONCLUSION

As per the necessity and requirement on case to case basis, every endodontic file system has advantages and disadvantages as mentioned in this narrative review. According to the need, an endodontist can select the file system which is required specifically. Although several studies are comparing these various systems in the literature, this narrative review aims to give the clinician a summary of some recently launched endodontic rotary file systems available in the market and their clinical uses.

CLINICAL SIGNIFICANCE

As per the priority and need of the case, whether removal and extrusion of debris, reduction of micro-organisms, keeping canal anatomy, and cutting efficiency, a specific required file system can be utilized.

Impact of contracted endodontic cavities on instrumentation efficacy-A systematic review

The aim of the present systematic review was to summarise and evaluate the studies comparing the role of contracted endodontic cavities (CECs) and traditional endodontic cavities (TECs) in terms of instrumentation efficacy. The present systematic review comprised of a search of the online databases of Cochrane, PubMed, Google Scholar and grey literature. The articles which were pertaining to instrumentation efficacy in contracted and traditional endodontic cavities were selected based on the PRISMA checklist. Out of the 660 articles which were obtained, irrelevant articles were excluded and a total of 17 articles were selected for this systematic review which assessed the instrumentation efficacy. Eleven studies compared the volume of dentin removed and canal transportation ability. Four studies compared the pulp debridement, and two studies compared the anti-bacterial efficacy between the two groups. The extrusion of debris between the groups was compared by one study. Out of the 17 studies included, 11 studies proved that contracted endodontic cavities negatively impacted the instrumentation efficacy. Hence, the data suggest that the traditional endodontic access cavities have better results when comparing the instrumentation efficacy.

Comparison of Er:YAG laser and ultrasonic in root canal disinfection under minimally invasive access cavity

The disinfection of root canal through minimally invasive access cavity remains questionable. This in vitro study compared the effectiveness of three disinfection measures including conventional irrigation, ultrasonic assisted irrigation, and erbium:yttrium-aluminum-garnet (Er:YAG) laser assisted irrigation through conventionally or minimally invasive access. Sixty-six extracted maxillary first molars were randomly divided into group 1 conventionally invasive access group (CIA) and group 2 computer-guided minimally invasive access group (MIA). Each group was further randomly divided into three subgroups, (A) conventional irrigation (CI), (B) passive ultrasonic agitation (PUI), and (C) Er:YAG laser activated irrigation (LAI). Enterococcus faecalis (E. faecalis) infection model was established inside all root canals after instrumentation was performed up to ProTaper Universal F2. After various disinfection methods, microbial samples were collected from root canals by paper tip method and cultured, and colony forming units (CFU) values of each sample were calculated. Then the root canals were enlarged to the size of F3, after which dentin debris was collected from the F3 file. After dilution and culturing, the CFU value was calculated for each group. Two-way analysis of variance (ANOVA) was performed to test the interaction. The results revealed a significant antagonism (F = 3.394, P = 0.043). The bacterial CFU counts of group B and group C were significantly less than that of group A (P < 0.05), and there was no significant difference between group B and C (P > 0.05). Additionally, group 2A was better than group 1A (P < 0.05); there was no significant difference between group 1B and group 2B, group 1C and group 2C (P > 0.05). Comparison of the bacterial CFU counts in dentin debris after disinfection, the results revealed a significant antagonism (F = 7.224, P = 0.002), and group C had the least. The disinfection effect of Er:YAG laser or ultrasonic assisted computer-guided minimally invasive access is similar to conventionally invasive access, and Er:YAG laser is better than ultrasonic in removing bacteria from dentinal tubules and is easy to operate, which is more suitable for minimally invasive root canal treatment.

Impact of Different Access Cavity Designs and Ni–Ti Files on the Elimination of Enterococcus faecalis from the Root Canal System: An In Vitro Study

The present research aimed to reveal the in vitro effects of different endodontic file systems utilizing different endodontic access cavity designs on the elimination of Enterococcus faecalis from root canal systems. One hundred and fifty mandibular molar teeth were separated into three groups with respect to the access cavity design: traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), and truss access cavity (TAC) (n = 50). After access cavity preparation, inolulation of teeth with E. faecalis was undertaken for 21 days. Following the first sampling (S1), further division of the groups into five subgroups (n = 10) was performed: ProTaper Gold, 2Shape, TruNatomy, Reciproc Blue, and WaveOne Gold. After instrumentation, bacterial sampling (S2) was performed. Bacterial reduction was evaluated in colony-forming units/mL, and statistical analysis was carried out. The E. faecalis count decreased significantly in all groups (p < 0.05). The range of mean values for a decrease in E. faecalis in log numbers was lowest in the TAC and Reciproc Blue groups, while the highest values of bacterial reduction were detected in the TEC and ProTaper Gold groups. The highest level of antibacterial action was obtained with the use of ProTaper Gold compared to the other file systems tested.

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.

Effect of guided conservative endodontic access and different file kinematics on debris extrusion in mesial root of the mandibular molars: An in vitro study

Background

Guided conservative endodontic access is a novel technique and the influence of such access cavities on apical debris extrusion (ADE) can have a significant effect on postoperative pain.

Objective

This study compared ADE and preparation time (PT) in the mesial canals of the mandibular first permanent molars in different access cavity designs and the amount of sodium hypochlorite in the extruded debris using attenuated total reflection-Fourier transform infrared spectrometer (ATR-FTIR).

Materials and Methods

Human mandibular first permanent molars (N = 72) were selected and randomly divided into six groups (n = 12) based on type of cavity design and files used: Group 1, Conservative Access Cavity [ConsAC])-WaveOne Gold; Group 2, ConsAC-Mtwo; Group 3, ConsAC-XP-endo shaper; Group 4, Traditional Access Cavity [TradAC])-WaveOne; Group 5, TradAC-Mtwo; and Group 6, TradAC-XP-endo shaper. All the ConsAC were prepared with a customized template fabricated using cone beam computed tomography. ADE evaluation was done using the Myers and Montgomery set up. All the instruments were used according to the manufacturers' instructions, followed by a final irrigation using Endoactivator. The time taken for preparation was calculated using a digital watch. Five samples in each group was taken and subjected to ATR-FTIR analysis.

Results

There was no significant difference between the groups with respect to ADE (P > 0.05). Whereas, a statistically significant difference was seen in PT between the TradAC and ConsAC (P < 0.05). Using ATR-FTIR, it was found that all the samples of extruded debris had the presence of sodium hypochlorite.

Conclusions

All instrumentation systems produced ADE irrespective of access cavity design. The time taken for preparation of canals in ConsAC was significantly longer compared to TradAC.

Clinical Relevance

ADE can translate clinically as postoperative pain. Assessing the ADE in ConsAC could shed light on the type of file systems that can be used in such cavities in order to minimize postoperative pain clinically.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

CLINICAL SIGNIFICANCE

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

Qualitative Assessment of the Surface Topographic Changes of XP-endo Shaper and TruNatomy files after exposure to Sodium Hypochlorite and Ethylenediaminetetraacetic Acid

OBJECTIVE

TruNatomy and XP-endo Shaper are recently introduced file systems showing increased fatigue resistance rate. The present study aims to evaluate the surface topographic changes and nickel (Ni) and titanium (Ti) elemental loss of XP-endo Shaper (XPS) and TruNatomy (TN) files on exposure to conventionally used root canal irrigants; [5.25% sodium hypochlorite (NaOCl) and 17% ethylenediaminetetraacetic acid (EDTA)] at a 10 minute time frame using atomic force microscopy (AFM) and energy dispersion X-ray spectroscopy (EDX) analytical techniques.

METHODS

Twelve samples for each of XPS (30/.04 taper) and TN (26/.04 taper; prime) instruments were dynamically exposed to 5.25% NaOCl, 17% EDTA separately for 10 minutes and in combination of 5.25% NaOCl (8 minutes)+17% EDTA (2 minutes) for a total of 10 minutes. Post exposure, the files were subjugated to AFM and EDX analysis. Independent t test and one-way ANOVA were used for statistical analysis, and the level of significance was set at 0.05.

RESULTS

XPS and TN showed a significant increase of surface roughness (Ra) and roughness mean square (RMS) on exposure to various irrigants (P<0.05) using AFM analysis. Increased overall roughness was observed with TN in comparison to XPS (P<0.05). Elements Ni and Ti loss was found in both XPS and TN files using EDX analysis. Both files exhibited Ni and Ti loss with the loss of Ni content higher for TN after exposure to 17% EDTA. Loss of Ti was seen for both files on exposure to a combination of 5.25% NaOCl+17% EDTA.

CONCLUSION

After exposure to root canal irrigants, the surface roughness was lesser in XPS compared to TN files. 17% EDTA caused significantly higher surface roughness in both file systems when compared to 5.25% NaOCl. TN exhibited overall higher elemental (Ni and Ti) loss on exposure to 17% EDTA and 5.25% NaOCl+17% EDTA in comparison to XPS files.

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.

Influence of access cavity preparation on the dentine thickness of mesial canals of mandibular molars prepared with reciprocating instruments

AIM

To evaluate the influence of traditional and conservative access cavity preparations on the remaining dentine thickness in the coronal third of mesial canals of extracted mandibular molars prepared with reciprocating instruments using micro-computed tomography as the analytical tool.

METHODOLOGY

Seventy extracted mandibular molars were scanned at a pixel size of 19 μm. From this initial sample, 20 teeth were selected, pair-matched and distributed into two groups (n = 10) according to the access cavity preparation: traditional (TradAC) or conservative (ConsAC). The root canals were sequentially enlarged with Reciproc Blue R25 (size 25, 0.08v taper) and R40 (size 40, 0.06v taper) instruments. A new scan was performed and the postoperative stacks were coregistered with their respective preoperative datasets. A colour-coded cross sections of the roots were created and used to identify and measure the smallest dentine thickness related to both MB and ML canals at 1.0-mm intervals from the furcation level of up to 5 mm in the apical direction, in both mesial and distal aspects of the roots, before and after preparation. The statistical analyses were performed with paired-samples t-test, independent-samples Student T-test and Chi-Square test with a significance level of 5%.

RESULTS

At all levels of both groups, dentine thickness before preparation was greater than after preparation (p < .05). No difference in the percentage of dentine reduction was observed between TradAC and ConsAC groups (p > .05), but a significantly greater reduction was observed to the distal aspect of the roots (p < .05). After root canal preparation, dentine thinner than 0.5 mm was observed mostly along the distal aspect of the root (10% to 15%) of the MB and ML canals, with no influence of the access cavity type on its incidence to either mesial (X²  = 1.66; p = .2) or distal (X²  = 0.40; p = .5) directions. In the TradAC group, dentine thickness in most slices was greater than 1.0 mm after preparation (n = 124) whilst, in the ConsAC, it ranged from 0.5 to 1.0 mm (n = 136).

CONCLUSION

Traditional or conservative access cavity preparation in extracted mandibular molars did not influence the remaining dentine thickness in the coronal third of mesial canals enlarged with thermomechanically treated nickel-titanium reciprocating instruments.

Influence of conservative endodontic access cavities on instrumentation of oval-shaped straight root canals

AIM

To evaluate the influence of the design of endodontic access cavities on the percentage of unprepared areas of canal walls and flexural fatigue of instruments activated by reciprocating movement in oval-shaped straight root canals of extracted teeth.

METHODOLOGY

Forty-two mandibular incisors with oval canals were scanned by a microcomputed tomography (micro-CT) device for homogeneous selection and distribution of the samples. Then, the teeth were divided into two groups (n = 21) according to the design of access cavity being tested: ultraconservative endodontic access cavity (UltraAC) and traditional access cavity. The canals were accessed with the aid of a surgical microscope, instrumented with the WaveOne Gold Medium system and irrigated with 2.5% NaOCl and 17% EDTA. The unprepared areas of the canal wall were analysed by overlaying images before and after instrumentation and expressed as percentages. micro-CT data were analysed using t-test, Mann-Whitney and Wilcoxon tests. The endodontic instruments used during instrumentation were subjected to static flexural fatigue testing using an artificial stainless steel canal with a 60° angle of curvature and a radius of 5 mm, located 5 mm from the tip of the instrument. The instruments were activated until fracture occurred, and the time in seconds for the fracture was recorded using a digital timer. The number of cycles to fracture was calculated and analysed statistically. For flexural fatigue data, an anova test complemented by a Tukey range test was used. The significance level of 5% was used for all analyses.

RESULTS

There was no significant difference between the groups related to unprepared areas by the instrument during canal preparation (p > .05). The difference in flexural fatigue resistance between the groups was not significant.

CONCLUSION

The use of UltraAC did not interfere with the canal instrumentation of extracted mandibular incisors with straight and oval canals. There was no difference in the flexural fatigue resistance of the instruments in relation to access cavity design.

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.

Unprepared surface areas, accumulated hard tissue debris, and dentinal crack formation after preparation using reciprocating or rotary instruments: a study in human cadavers

OBJECTIVES

This study using contralateral teeth from human cadavers assessed the amount of unprepared wall surface areas (USA), accumulated hard tissue debris (AHTD), and dentinal crack formation after root canal preparation using either reciprocating or rotary instruments.

MATERIALS AND METHODS

Incisors with a single root canal from 11 human mandibles had their root canals prepared with Reciproc or Mtwo. Each contralateral tooth was treated with one of the test instruments in order to create matched pairs. Micro-CT scans were taken before and after preparation to instrument sizes 40 and 50 in both groups. USA and AHTD were evaluated in the full canal length or the apical portion only. Crack formation was also evaluated in the full root length.

RESULTS

After size 40, no significant differences in USA and AHTD were observed in the full canal length (P > .05). Separate analysis of the apical 4-mm canal revealed no difference in AHTD, but significantly more USA with Mtwo than Reciproc (P < .05). After size 50, the amount of USA was similar between groups both in the full canal and in the apical canal (P > .05). More AHTD were observed in the full canal after using Mtwo size 50 (P < .05), but no difference occurred in the apical canal only (P > .05). Intragroup analyses showed a significant decrease of USA and a significant increase of AHTD when preparation size increased from 40 to 50 (P < .05). In teeth without any pre-existing detectable dentinal defect (n = 38), crack formation occurred in 4 teeth, 2 from each preparation system.

CLINICAL RELEVANCE

Reciproc instrument size 40 resulted in more prepared areas in the apical canal than Mtwo instrument of the same size. However, the amount of AHTD did not differ between them at this file size. Canal enlargement to size 50 prepared more walls but created more debris. Dentinal defects were produced after preparation with both systems.

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.

Ex vivo ability of a noninstrumentation technique to disinfect oval-shaped canals

Context:

Oval-shaped canals represent a challenge in endodontics. Infected tissue may remain in their recesses. This concern may be more critical with minimally instrumentation techniques.

Aims:

The present study evaluated the disinfection ability in oval-shaped canals of a noninstrumentation technique using ultrasonic agitation and intracanal heating of sodium hypochlorite (NaOCl) compared to rotary canal preparation and ultrasonic agitation with and without heating of NaOCl.

Settings and Designs:

Sixty extracted mandibular incisors were included. The teeth had pulp necrosis and apical periodontitis and oval-shaped canals. They were divided into three groups depending on the treatment protocol: (1) IHAN: intracanal heating and ultrasonic agitation of NaOCl only, (2) R-IHAN: Rotary preparation followed by IHAN, and (3) R-passive ultrasonic agitation (PUA): Rotary preparation and ultrasonic agitation of NaOCl.

Methods:

Root canal samples were taken before (S1) and after (S2) the endodontic procedures were completed and cultured anaerobically.

Statistical Analysis Used:

Wilcoxon tests were performed to compare colony-forming units (CFUs) before and after the endodontic procedures for the three groups. The percentage of variation of CFUs was compared among the three groups using Kruskal–Wallis tests, followed by Mann–Whitney U-tests.

Results:

All S1 samples were positive. All S2 samples showed bacterial growth in R-PUA compared to 17 in R-IHAN. None of the S2 samples in IHAN were positive. Bacteria reduction was significant in each group (P < 0.001). The percentage of bacteria reduction was highest for IHAN and lowest for R-PUA (P < 0.001).

Conclusions:

Intracanal heating and ultrasonic agitation of NaOCl without instrumentation completely eliminated bacteria from infected oval-shaped canals.

Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature

In the last decade, several access cavity designs involveing minimal removal of tooth tissue have been described for gaining entry to pulp chambers during root canal treatment. The premise behind this concept assumes that maximum preservation of as much of the pulp chamber roof as possible during access preparation would maintain the fracture resistance of teeth following root canal treatment. However, the smaller the access cavity, the more difficult it may be to visualize and debride the pulp chamber as well as locate, shape, clean and fill the canals. At the same time, a small access cavity may increase the risk of iatrogenic complications as a result of poor visibility, which may have an impact on treatment outcome. This study aimed to critically analyse the literature on minimal access cavity preparations, propose new nomenclature based on self-explanatory abbreviations and highlight the areas in which more research is required. The search was conducted without restrictions using specifics terms and descriptors in four databases. A complementary screening of the references within the selected studies, as well as a manual search in the highest impact journals in endodontics, namely International Endodontic Journal and Journal of Endodontics, was also performed. The initial search retrieved 1831 publications. The titles and abstracts of these papers were reviewed, and the full text of 94 studies was assessed. Finally, a total of 28 studies were identified as evaluating the influence of minimally invasive access cavity designs on the fracture resistance of teeth and on the different stages of root canal treatment (orifice location, canal shaping, canal cleaning, canal filling and retreatment). Overall, the studies had major methodological drawbacks and reported inadequate and/or inconclusive results on the utility of minimally invasive access preparations. Furthermore, they offered limited scientific evidence to support the use of minimally invasive access cavities to improve the outcome of root canal treatment and retreatment; they also provided little evidence that they preserved the fracture resistance of root filled teeth to a greater extent than traditional access cavity preparations. It was concluded that at present, there is a lack of supporting evidence for the introduction of minimally invasive access cavity preparation into routine clinical practice and/or training of undergraduate and postgraduate students.

Effect of Sonic Agitation of a Binary Mixture of Solvents on Filling Remnants Removal as an Alternative to Apical Enlargement-A Micro-CT Study

BACKGROUND

This work aimed to evaluate the efficacy of sonic agitation of a binary mixture of solvents (methyl ethyl ketone/tetrachloroethylene) on filling remnants removal and compare the effects of solvent agitation with the enlargement to the next instrument size.

METHODS

Twenty-four mandibular incisors were prepared with ProTaper Next (X1, X2) and obturated with the single-cone technique and AH Plus sealer. The teeth were retreated with ProTaper Universal Retreatment and ProTaper Next and divided into two groups (n = 12) according to the final instrument (X3 or X4). All canals were submitted to a supplementary procedure consisting of a mixture of solvents-methyl ethyl ketone/tetrachloroethylene, agitated with EndoActivator. The volume of filling remnants was assessed through micro-computed tomography in the apical 5 mm. Statistical analysis was performed with a significance level of 5%.

RESULTS

The supplementary procedure of agitation of the solvent mixture was beneficial in both groups (p < 0.05). There were no statistically significant differences between canals re-prepared until X4 and canals re-prepared until X3 plus solvent (p > 0.05).

CONCLUSIONS

An additional step with a two-solvent solution potentiated by EndoActivator showed to be very effective for the removal of gutta-percha and resinous sealer remnants from apical root canals of mandibular incisors, avoiding further enlargement.