Invasion of dentinal tubules by root canal bacteria

Bacterial invasion of dentinal tubules and the clinical consequences have been recognized for over a century. However, while many components of the infected dentinal tubule microflora have been identified, it is likely that there are etiological agents involved in endodontic infections that have not yet been recognized. Bacterial invasion of coronal dentinal tubules occurs when the dentine is exposed to the oral environment and of radicular dentinal tubules subsequent to infection of the root canal system or as a consequence of periodontal disease. The content and architecture of a dentinal tubule can influence bacterial invasion, with tubule patency being important. This can account for regional variations in bacterial invasion and is particularly seen with dentinal sclerosis, where more advanced sclerotic changes in apical radicular tubules, especially in elderly individuals, limit bacterial invasion in this area. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria are involved in invasion of dentinal tubules. Gram‐positive organisms dominate the tubule microflora in both carious and non‐carious dentine. The relatively high numbers of obligate anaerobes present, such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp., suggests that the environment favors the growth of these bacteria. Gram‐negative obligate anaerobic rods, e.g. Porphyromonas spp., are less frequently recovered; however, with time, fastidious obligately anaerobic bacteria become established as principal components of the microflora and can be found within the deep dentine layers. In the early stages of infection, Gram‐positive bacteria dominate the microflora. The identification of adhesins that mediate these initial interactions of bacteria with dentine is important for understanding the development of tubule infection and in designing adhesion‐blocking compounds. Recent evidence suggests that streptococci and enterococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra‐tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate invasion of dentine by select bacteria. It is important therefore that the mechanisms of invasion and inter‐bacterial adhesion are understood to assist development of novel control strategies.     

Antimicrobial Activity of a Sodium Hypochlorite/Etidronic Acid Irrigant Solution

Introduction

The aim of this study was to evaluate the antimicrobial activity of a 2.5% sodium hypochlorite (NaOCl)/9% etidronic acid (HEBP) irrigant solution on Enterococcus faecalis growing in biofilms and a dentinal tubule infection model.

Methods

The antimicrobial activity of the solutions 2.5% NaOCl and 9% HEBP alone and associated was evaluated on E. faecalis biofilms grown in the Calgary biofilm model (minimum biofilm eradication concentration high-throughput device). For the dentinal tubule infection test, the percentage of dead cells in E. faecalis–infected dentinal tubules treated with the solutions for 10 minutes was measured using confocal laser scanning microscopy and the live/dead technique. Available chlorine and pH of the solutions were also measured. Distilled water was used as the control. Nonparametric tests were used to determine statistical differences.

Results

The highest viability was found in the distilled water group and the lowest in the NaOCl-treated dentin (P < .05). Both NaOCl solutions killed 100% of the E. faecalis biofilms and showed the highest antimicrobial activity inside dentinal tubules, without statistical differences between the 2 (P < .05). The HEBP isolated solution killed bacteria inside dentinal tubules but did not present any significant effect against E. faecalis biofilms. The incorporation of HEBP to NaOCl did not cause any loss of available chlorine within 60 minutes.

Conclusions

HEBP did not interfere with the ability of NaOCl to kill E. faecalis grown in biofilms and inside dentinal tubules.     

Dentin tubule invasion by Enterococcus faecalis under stress conditions ex vivo

Enterococcus faecalis is the species most frequently isolated from failed endodontic treatments because it can survive under stress conditions imposed by root canal treatment. The objective of this study was to determine the ability of E. faecalis to invade dentine tubules under alkaline and energy‐starvation stress and to explore the potential mechanisms. Roots from single‐rooted human teeth were infected with E. faecalis under alkaline and energy‐starvation stress conditions. After 4 wk of culture, samples were processed to establish the tubule‐penetration distance. In addition, the hydrophobicity of E. faecalis cells under these conditions was analysed and the expression of genes involved in adhesion was quantified by real‐time quantitative PCR. Culture of E. faecalis under alkaline and energy‐starvation stress conditions resulted in a marked reduction of tubule‐penetration distance, a significant increase in hydrophobicity of the bacterial surface, and marked down‐regulation of most adhesin genes compared with E. faecalis cultured in tryptic soy broth. The results indicate that the dentine tubule invasion ability of E. faecalis was markedly decreased under alkaline and glucose‐starvation stress conditions, possibly because of the increase of hydrophobicity and down‐regulation of some adhesion genes.     

Adherence of Streptococcus gordonii to smeared and nonsmeared dentine

The purpose of this study was to investigate the adherence of Streptococcus gordonii to smeared and non-smeared dentine and to assess the influence of patent dentinal tubules on bacterial retention. In order to examine bacterial adherence, 10 non-smeared (group 1) and 10 smeared samples (group 2) of outer root dentine were prepared from teeth exhibiting dentine sclerosis. Ten non-smeared samples from inner coronal root dentine that did not exhibit sclerosis were prepared in order to study the influence of patent tubules on bacterial retention (group 3). Cells of the bacterium were radioactively labelled and an adhesion assay was performed. The number of bacteria adhering to the dentine surface was determined by scintillation counting. The results show that the number of bacteria adhering to both smeared and non-smeared outer sclerotic dentine was low (0.3% of inoculum), and there was no significant difference between the groups (P > 0.3). A significantly higher number of bacteria was retained on the inner non-smeared coronal root dentine (P < 0.0001) compared to groups 1 or 2. The results suggest that dentinal smear layers do not enhance or impede bacterial adherence to the dentine matrix. Dentinal surfaces with patent dentinal tubules retain more bacteria than a smeared surface.     

Qualitative comparison of sonic or laser energisation of 4% sodium hypochlorite on an Enterococcus faecalis biofilm grown in vitro

The effectiveness of sonic activation, laser activation and syringe irrigation of 4% sodium hypochlorite in removing an Enterococcus faecalis biofilm was compared. Biofilms were grown in extracted human single rooted teeth using a flow cell apparatus. After 4 weeks' growth, teeth were subjected to each treatment using 4% sodium hypochlorite and radicular dentinal surfaces of the root canals were analysed by scanning electron microscopy. Results showed that sonic activation and syringe irrigation with sodium hypochlorite showed reduced numbers of bacterial cells on the radicular dentine but were not effective in eliminating E. faecalis in the dentinal tubules. Laser activation of sodium hypochlorite resulted in clean dentine walls and undetectable levels of bacteria within dentinal tubules. Qualitatively, sonic or laser activation of 4% NaOCl resulted in greater bacterial reduction compared with syringe irrigation, with laser activation producing the greatest overall reduction.     

Dentin Extends the Antibacterial Effect of Endodontic Sealers against Enterococcus faecalis Biofilms

Introduction

The purpose of this study was to evaluate the antimicrobial effects of root canal sealers on Enterococcus faecalis biofilms in dentinal tubules by using a novel dentin infection model.

Methods

Cells of E. faecalis were introduced into the dentinal tubules by centrifugation and incubated in brain-heart infusion broth for 3 weeks. An equal thickness of AH Plus, Endosequence BC sealer (BC sealer), and pulp canal sealer EWT (PCEWT) was placed on the root canal wall of the dentin specimens for 1, 7, and 30 days in humid conditions at 37°C. Gutta-percha and water were used in a similar manner as the tested sealers. The proportions of dead and live bacteria inside the dentinal tubules after exposure to root canal sealers were assessed by confocal laser scanning microscopy.

Results

Significantly more bacteria were killed in the 3 sealer groups than in the 2 control groups (P < .05). BC sealer and AH Plus resulted in significantly more dead cells than PCEWT did. There was no statistically significant difference between BC sealer and AH Plus at any time point (P > .05). Thirty days of exposure to BC sealer and AH Plus resulted in significantly more dead bacteria in dentin than 7-day and 1-day exposures in the biofilms, whereas no statistically significant increase of the proportion of dead bacteria was detected between 7-day and 30-day PCEWT (P > .05).

Conclusions

The 3 endodontic root canal sealers had antibacterial effects against E. faecalis in the dentinal tubules. BC sealer and AH Plus had superior antibacterial effects compared with PCEWT. The antibacterial effects of sealers in dentinal tubules continued after setting.     

In vitro evaluation of the antibacterial effect of four root canal sealers on dental biofilms

Objectives

To dynamically evaluate the effect of four root canal sealers on the killing of biofilms within dentinal tubules.

Materials and methods

Dentin blocks were prepared for infection of the dentinal tubules. Enterococcus faecalis VP3-181 and multi-species bacteria from two donors were cultured. After 3 days of incubation, the infected dentin specimens were rinsed with sterile water for 1 min and subjected to treatment. Additionally, multi-species bacteria from donor 1 were incubated for 3 weeks to allow biofilm maturation and then the specimens were subjected to treatment. Gutta-percha-treated dentin specimens comprised the control group. A root canal sealer (bioceramic sealers: EndoSequence BC Sealer, ProRoot Endo Sealer, or GuttaFlow Bioseal; and a traditional silicone-based sealer: Guttaflow 2) was spread onto the canal walls of the dentin. The specimens were examined with confocal laser scanning microscopy at 7, 30, or 60 days.

Results

In the 3-day-old biofilm group, the proportion of killed bacteria decreased significantly from the first 7 days of treatment to 60 days of treatment for all sealers (p?<?0.05). In the 3-week-old biofilm group, 60 days of exposure to bioceramic sealers resulted in more significant dead bacteria than 7-day exposures of the biofilms (p?<?0.05). Bioceramic sealers were more effective in killing bacteria than the GuttaFlow 2 sealer (p?<?0.05).

Conclusions

Calcium silicate–based sealers showed good antimicrobial effects against biofilms within dentinal tubules, especially in the first week in young biofilms. There is no substantive antibacterial activity observed for the examined root canal sealers against young dentinal tubule biofilms.

Clinical relevance

The bioceramic root canal sealers examined demonstrate minimal additional antibacterial effects after long-term exposure to young biofilms.

     

A new noninvasive model to study the effectiveness of dentin disinfection by using confocal laser scanning microscopy

Introduction

The present study was designed to develop a standardized model for quantification of the effectiveness of dentin disinfection by different antibacterial solutions including a new root canal irrigant, Qmix.

Methods

Dentinal tubules from the root canal side in semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation of the bacterial suspension into the tubules. Scanning electron microscopy (SEM) was used to verify the presence of bacteria in dentin. The outer side of dentin pieces was closed, and the specimens were subjected to 1-minute and 3-minute exposure to sterile water, 1%, 2%, 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and Qmix. Confocal laser scanning microscopy (CLSM) and viability staining were used to quantitatively analyze the proportions of dead and live bacteria inside dentin.

Results

A heavy invasion by E. faecalis was detected by both SEM and CLSM throughout the dentinal tubules. The amount of dead cells in dentin increased with increasing NaOCl concentration and time of exposure (P < .05). Qmix was equally effective in killing bacteria in dentin as 6% NaOCl; more than 40% and 60% of the bacteria were killed by both at 1 minute and 3 minutes, respectively. One percent and 2% NaOCl and 2% CHX killed 20%–30% and 30%–40% bacteria after 1 and 3 minutes of exposure, respectively, with no statistically significant differences among the 3 agents (P > .05). In the control group, which was treated with sterile water, only 4%–6% of the bacteria were dead.

Conclusions

Centrifugation helped to create a heavy, evenly distributed infection deep into the dentinal tubules. The new model made it possible to compare the effectiveness of several disinfecting solutions in killing bacteria inside dentin by a noninvasive CLSM method.     

Antibacterial effect of genetically-engineered bacteriophage ϕEf11/ϕFL1C(Δ36)PnisA on dentin infected with antibiotic-resistant Enterococcus faecalis

ObjectiveEnterococcus faecalis is a gram-positive facultative anaerobic bacterium, which is present in 30–89% of teeth with postendodontic treatment failures. E. faecalis is capable of penetrating dentinal tubules and surviving as a monoculture after conventional endodontic therapy, indicating that it is resistant to commonly used endodontic disinfection protocols. Different E. faecalis strains have shown resistance to several antibiotics, and have been associated with both dental pathology and systemic infections. The aim of this study was to evaluate the efficacy of a genetically engineered bacteriophage to disinfect dentin infected with antibiotic resistant strains of E. faecalis.MethodsExtracted human dentin root segments were cemented into sealable two-chamber devices, fabricated from syringe needle caps to form in vitro infected-dentin models. The models were inoculated with an overnight suspension of either E. faecalis V583 (vancomycin resistant strain) or E. faecalis JH2-2 (fusidic acid and rifampin resistant, vancomycin sensitive strain). After 7 days of incubation at 37 °C, a suspension of a genetically engineered phage, ϕEf11/ϕFL1C(Δ36)P^nisA, was added to the root canal of each infected dentin segment, and the incubation was continued for an additional 72-h. Dentin was harvested from the walls of each root canal and assayed for the residual titer of E. faecalis cells.ResultsThe recovered E. faecalis titer was reduced by 18% for the JH2-2 infected models, and by 99% for the V583 infected models.ConclusionTreatment: of E. faecalis-infected dentin with bacteriophage ϕEf11/ϕFL1C(Δ36)P^nisA consistently resulted in a decrease in the residual bacterial population of both vancomycin-sensitive and resistant strains.     

Efficacy of chlorhexidine in disinfecting dentinal tubules in vitro

Abstract Solutions of 0.2% and 2% chlorhexidine, 0.2% and 2% sodium hypochlorite (NaOCl) and normal saline were tested for their efficacy in disinfecting dentinal tubules following root canal irrigation in vitro. Freshly extracted bovine incisor roots were prepared as cylindrical shapes, 4 mm high and 5 mm wide with a lumen 2.1 mm wide. After mechanical removal of the cementum and elimination of the smear layer on the dentine surface with EDTA and NaOCl, the root sections were autoclaved and the dentinal tubules infected with E. faecalis (NCTC 775) by incubating in yeast extract glucose broth for 1 week. The root canals were irrigated with 20 ml of an irrigant solution using a syringe. Each irrigant was used in six specimens. Dentine was removed from the canal wall by sterile burs of increasing diameter to give samples 100, 100–300 and 300–500 μm deep. The dentine samples were then cultured to determine the presence and quantity of remaining micro-organisms. The results indicated that chlorhexidine and NaOCl were equally effective antibacterial agents at similar concentrations against the test microorganism. They significantly reduced the bacterial counts in the first 100 μm of dentinal tubules, however up to 50% of dentine samples remained infected following use of both agents.     

A MODEL SYSTEM TO STUDY ANTIMICROBIAL STRATEGIES IN ENDODONTIC BIOFILMS

The purpose of this work was to develop a model system to study antimicrobial strategies in endodontic biofilms. Enterococcus faecalis suspension was colonized in 10 human root canals. Five milliliters of Brain Heart Infusion (BHI) were mixed with 5 mL of the bacterial inoculums (E. faecalis) and inoculated with sufficient volume to fill the root canal during 60 days. This procedure was repeated every 72 h, always using 24-h pure culture prepared and adjusted to No. 1 MacFarland turbidity standard. Biofilm formation was analyzed by scanning electron microscopy (SEM). E. faecalis consistently adhered to collagen structure, colonized dentin surface, progressed towards the dentinal tubules and formed a biofilm. The proposed biofilm model seems to be viable for studies on antimicrobial strategies, and allows for a satisfactory colonization time of selected bacterial species with virulence and adherence properties.     

Is it really penetration? Locomotion of devitalized Enterococcus faecalis cells within dentinal tubules of bovine teeth

ObjectiveThe aim of the present study was to evaluate the penetration characteristics of devitalized and vital E. faecalis cells into root dentinal tubules.DesignThirteen root canals were incubated with devitalized (4 days, 7 days, 14 days, 28 days) and vital (28 days) E. faecalis strains (streptomycin-resistant strains) after root canal enlargement (size 80, taper 0.02) with 3 % NaOCl solution. The smear layer was intentionally removed with 20 % EDTA before inoculation. Samples were processed for analysis by scanning electron microscopy (SEM) and DAPI (4′,6-diamidino-2-phenylindole) staining. DAPI was conducted for fluorescence microscopic visualization of the bacterial penetration into dentinal tubules. The penetration depth was calculated with the measurement tool of the Axio Vision program (Zeiss, Jena, Germany).ResultsDevitalized E. faecalis strains were able to penetrate into dentinal tubules of the root canal. Apikal penetration depths of the devitalized cells were 100.67 μm ± 26.54 μm after 7 days, 230.67 μm ± 111.5 μm after 14 days and 266.5 μm ± 92.63 μm after 28 days of incubation. The total number and penetration depth of E. faecalis cells was lower compared to a vital suspension of E. faecalis (1002.45 μm) after 28 days. It was noted that bacterial penetration was not common to all of the dentinal tubules in the vital E. faecalis control and especially in the devitalized control.ConclusionsIncreased exposure times of devitalized bacteria into root canals lead to an increased number of penetrated dentinal tubules as well as to a deeper penetration.     

In vitro and in vivo research of atmosphere pressure nonequilibrium plasmas on root canal disinfection: implication for alternative strategy for irrigation

Objective

To investigate an intracanal disinfection methodology of APNPs (atmosphere pressure nonequilibrium plasmas) or modified APNPs in root canal treatment and evaluate the antimicrobial efficiency against in vitro infected dentinal tubules and in vivo experimental apical periodontitis.

Materials and methods

Dentine specimens were centrifugated with Enterococcus faecalis to generate 1-day-old and 3-week-old biofilms, and were treated with 2% chlorhexidine (Chx), APNP or modified APNP for 3 and 10 min (n=4). LIVE/DEAD staining was employed to analyze the ratio of deactivated bacteria. Experimental apical periodontitis in beagles was induced. Root canal therapy with APNPs or modified APNPs was performed and the antimicrobial effect was evaluated by histological and radiographical analyses.

Results

APNP deactivated 1-day-old and 3-week-old E. feacalis in dentinal tubules as much as 2% Chx irrigating. Modified APNP significantly deactivated more E. faecalis biofilms in dentinal tubules for 3-min and 10-min treatments, without thermal damage or dentinal destruction being observed. In beagles’ apical periodontitis, significantly increased BV/TV and decreased lesion volume of apical bone were found in modified APNP group than 2% Chx irrigation group according to μCT. Fewer inflammatory cells and bacterial residual in dentine were observed in modified APNP-treated apical tissue by histology staining compared with those in the 2% Chx irrigation group.

Conclusion

The antimicrobial effect of APNP jet irradiation was comparable to that of 2% Chx irrigation. No structural damage in dentine or tissue necrosis at the periapical region was induced upon treatment. The modified APNP demonstrated an increased antimicrobial efficacy compared with 2% Chx irrigation both in vitro and in vivo.

Clinical relevance

The modified APNPs can be used as an alternative intracanal disinfection strategy.

     

A quantitative and diametral analysis of human dentinal tubules at pulp chamber ceiling and floor under scanning electron microscopy

The purposes of this study are (i) to evaluate and compare the dentinal tubule density, tubule diameter and percentage area of dentin occupied by tubules at the pulp chamber ceiling and floor; and (ii) to evaluate the effects of age on the number and dimensions of tubule openings. Twelve intact, human mandibular third molars were recruited. Six teeth belonged to patients up to 30 years of age and six teeth belonged to patients over 50 years. Scanning electron microscopic evaluations were made at two different locations: the pulp chamber ceiling and floor. The pulp chamber ceiling presented higher tubule density (P < 0.0001) and greater percentage area of dentin occupied by tubule openings (P < 0.0001) compared to the pulp chamber floor. Also, younger age group had greater tubule diameter (P < 0.0001), higher tubule density (P < 0.0001) and greater percentage area of dentin occupied by tubule openings (P < 0.0001) compared to older age group. Pulp chamber ceiling presents higher tubule density and greater area of exposed tubules. In younger people, the pulp chamber floor presents considerably high tubule diameter. The number and dimensions of dentinal tubule openings significantly decrease with age.     

Influence of Enterococcus faecalis proteases and the collagen‐binding protein,Ace, on adhesion to dentin

Enterococcus faecalis is a pathogen that persists in medicated root canals. Here, we tested the hypothesis that the E. faecalis proteases, serine protease and gelatinase, and the collagen‐binding protein (Ace) contribute to adhesion to the root canal. Scanning electron microscopy was used to examine dentin binding by four E. faecalis strains: OG1RF, the wild type, and three mutant derivatives of OG1RF, TX5128, TX5243 and TX5256 deficient in serine protease and gelatinase, serine protease, and Ace, respectively. For each strain, 20 root halves were exposed to 3 × 10⁹ to 5 × 10⁹ cells/ml for 6 h, and 50 fields per root half were examined for adherent bacteria. Statistical analysis revealed that adherence of OG1RF was significantly greater than the mutant strains (P < 0.001), while significant differences were not detected between the protease mutants. The data indicate that serine protease and Ace aid E. faecalis binding to dentin, while the role of gelatinase is uncertain.     

Influence of Endodontic Procedure on the Adherence of Enterococcus faecalis

IntroductionThe purpose of this study was to investigate the effects of instrumentation and irrigation on the initial adherence of Enterococcus faecalis to root canal dentin and to explore initial microbial adhesion to root filling materials.MethodsThe following specimens were prepared: instrumented and uninstrumented dentin, dentin treated with different irrigation protocols, and root filling materials. The number of E. faecalis cells adhered on dentin was measured. The adhesion force of E. faecalis cells on different materials and the roughness of different surfaces were measured. The contact angle of the surfaces was recorded. The results were analyzed using the t test.ResultsInstrumented dentin specimens had a significantly higher amount of E. faecalis adherence than uninstrumented dentin. There were higher numbers of adhering bacteria on the dentin when EDTA was used alone (P < .05) compared with other irrigants alone. The use of chlorhexidine (CHX) as the last irrigant for a certain time resulted in a reduced number of adhering bacteria when the specimens were first exposed to sodium hypochlorite (NaOCl) followed by EDTA. EDTA used alone had the highest adhesion force followed by NaOCl alone and CHX alone (P < .05). Dentin treated with EDTA alone had the highest roughness and contact angle followed by NaOCl alone and CHX alone (P < .05). CHX added as the final irrigant after NaOCl with EDTA irrigation reduced the contact angle (P < .05). Larger amounts of adhering bacteria and higher adhesion force were detected on the surface of gutta-percha and sealer than on the dentin surface (P < .05).ConclusionsInstrumentation and irrigation alter the initial adherence of E. faecalis to root canal dentin and the surface properties of the dentin as well.     

iRoot SP牙本质小管渗透性的研究

目的:通过扫描电镜评价iRoot SP牙本质小管渗透性。方法:单根管下颌前磨牙28颗截冠保留牙根14 mm,机扩备根管至F2,随机数字表法将标本分为实验组(A、B组,n=12)和对照组(n=4)。A组:iRoot SP+热牙胶充填;B组:AH Plus+热牙胶充填。实验组样本取冠、中、尖横截面,对照组样本取根管纵切面,SEM观察,实验组测量根管封闭剂在牙本质小管的渗透深度,对照组观察牙本质小管玷污层的去除程度。结果:实验组中,在根尖部AH Plus较iRoot SP牙本质小管渗透深度长,两者有显著差异(P＜0.05),在根管冠部、中部两者渗透深度相当,无统计学意义。对照组中,根管中上段牙本质小管口明显开放,玷污层基本去除,根尖段,有玷污层未完全去除。结论:iRoot SP与AH Plus相比,后者牙本质小管渗透性更强;两者在根管中上段渗透性高于根尖部;玷污层在一定程度上影响了根管封闭剂的渗透性。     

Novel Endodontic Disinfection Approach Using Catalytic Nanoparticles

Introduction

The aim of this study was to test a new disinfection technology using biomimetic iron oxide nanoparticles (IO-NPs) with peroxidaselike activity to enhance antibacterial activity on root canal surfaces and in dentinal tubules.

Effect of dentinal tubules and resin-based endodontic sealers on fracture properties of root dentin

ObjectiveTo investigate the role of dentinal tubules in the fracture properties of human root dentin and whether resin-filled dentinal tubules can enhance fracture resistance.Materials and methodsCrack propagation in human root dentin was investigated in 200 μm thick longitudinal samples and examined by light and scanning electron microscopy. 30 maxillary premolar teeth were prepared for work of fracture (Wf) test at different tubule orientations, one perpendicular and two parallel to dentinal tubules. Another 40 single canal premolars were randomly divided into four groups of 10 each: intact dentin, prepared but unobturated canal, canal obturated with epoxy rein (AH Plus?/gutta percha), or with UDMA resin sealer (Resilon^®/RealSeal^®). The samples were prepared for Wf test parallel to dentinal tubules. Wf was compared under ANOVA with statistical significance set at p < 0.05.ResultsDentinal tubules influenced the path of cracks through dentin, with micro-cracks initiated in peritubular dentin of individual tubules ahead of the main crack tip. A significant difference (p < 0.001) was found between Wf perpendicular to tubule direction (254.9 J/m²) vs. parallel to tubule direction from inner to outer dentin (479.4 J/m²). Neither canal preparation nor obturation using epoxy- or UDMA-based resins as sealer cements substantially influenced fracture properties of root dentin, despite extensive infiltration of dentinal tubules by both sealer cements.     

Final Endodontic Irrigation with 70% Ethanol Enhanced Calcium Hydroxide Removal from the Apical Third

IntroductionThe purpose of this study was to evaluate the cleanliness of root canal walls and dentinal tubules after attempting to remove the calcium hydroxide dressing with different irrigant solutions and the use of nonactivated irrigation or passive ultrasonic irrigation (PUI).MethodsAfter root canal instrumentation, 80 single-rooted teeth were filled with calcium hydroxide mixed with propylene glycol and 0.1% rhodamine B dye and inserted into canals with a Lentulo spiral. The calcium hydroxide dressing was initially removed with 10 mL saline solution and reinstrumentation with the master apical file. Then, the samples were randomly assigned into 8 experimental groups (n = 10) according to the irrigant solution with or without PUI: 2.5% sodium hypochlorite, 17% ethylenediaminetetraacetic acid + 1.25% sodium lauryl ether sulfate (EDTA-T), 37% phosphoric acid, or 70% ethanol. A final flush with 5 mL saline solution was performed. The percentage of clean root canal walls and the depth of clean dentinal tubules were measured with images of confocal laser scanning microscopy. The groups were compared using the 2-way analysis of variance test with the Bonferroni post hoc test for depth analysis and the Kruskal-Wallis with Dunn post hoc test for the perimeter analysis.ResultsIrrigation with 70% ethanol presented a significantly higher percentage of clean root canal walls and a higher depth of clean dentinal tubules when compared with irrigation with 2.5% sodium hypochlorite and 17% EDTA-T for both irrigation methods (P < .05). No differences were observed between nonactivated irrigation or PUI protocols (P > .05).ConclusionsSeventy percent ethanol enhanced calcium hydroxide removal from the apical root third compared with 2.5% sodium hypochlorite or 17% EDTA-T.