Free Water Loss–induced Heterogeneous Residual Strain and Reduced Fatigue Resistance in Root Dentin: A 3-dimensional Digital Image Correlation Analysis

IntroductionThis study evaluated free water loss–induced residual strain with and without axial compressive loading and assessed the mechanical effect of cyclic loading in fully hydrated and partially dehydrated root dentin.MethodsRoot dentin sections prepared from freshly extracted human premolars were used. Customized 3-dimensional digital image correlation was used to qualitatively and quantitatively analyze the residual strain induced by 2 hours of free water loss in different regions of root dentin. Residual strain in partially dehydrated root dentin during axial compressive loading was also analyzed using 3-dimensional digital image correlation. The effect of cyclic loading on load to fracture in fully hydrated and partially dehydrated dentin and their fractography were analyzed using micro–computed tomographic imaging.ResultsFree water loss resulted in a heterogeneous distribution of residual strain and an overall formation of residual compressive strain with areas of tensile strain localized to the root canal and outer dentin. More residual compressive strain was observed in the apical dentin compared with the cervical dentin (P < .05), and more residual shear strain was observed in outer dentin compared with inner dentin (P < .05). Axial loading resulted in an increase in the load-induced compressive strain in the direction perpendicular to dentinal tubules (P < .05). Fully hydrated roots displayed a higher mean (P < .05) and median (P < .05) number of cycles to fracture with microcracks characteristic of toughness.ConclusionsAfter free water loss, root dentin displayed an increased formation of heterogenous residual strain, which resulted in increased axial compressive load-induced strain and a decreased resistance to fatigue failure. The effect of free water loss in the loss of mechanical integrity of root-filled teeth needs further investigation.     

Impact of Dentin Substrate Modification with Chitosan-Hydroxyapatite Precursor Nanocomplexes on Sealer Penetration and Tensile Strength

IntroductionThe purpose of this study was to evaluate the effect of dentin conditioning with chitosan-hydroxyapatite precursor (C-HA) nanocomplexes on the depth of tricalcium silicate sealer penetration into dentinal tubules and ultimate tensile strength (UTS).Methodssurface charge and size distribution for C-HA nanocomplex formulation was evaluated followed by bioactivity assessment of standardized films of C-HA nanocomplexes (n = 15) incubated in simulated body fluid. Mineralization potential was assessed with X-ray diffraction and Fourier-transform infrared spectroscopy, whereas scanning electron microscopy was used for ultrastructural evaluation. Static water contact angles and UTS were measured on dentin discs (n = 2/group) and dentin beams (n = 10/group) treated with/without sodium hypochlorite/EDTA and C-HA nanocomplex conditioning. In phase 2, the depth of sealer penetration after C-HA nanocomplex conditioning was evaluated using fluorescent imaging (n = 12/group). The percent area penetration and mean/maximum penetration depth were calculated at 4- and 6-mm levels from the root apex. Data from contact angle measurements, mechanical testing, and penetration assessment parameters were subjected to the independent samples t test with a significance level set at P < .05.ResultsA formulation of C-HA nanocomplexes (2 mg/mL) was chosen as a polyanionic, hydrophilic, nonaggregating concentration having bioactivity potential established through the formation of phosphate/carbonate bonds and the crystalline nature of the formed minerals. A significantly lower contact angle and higher UTS were registered for the C-HA nanocomplex–conditioned group (P < .05). Statistically significant (P < .05) greater sealer penetration was recorded at the 4-mm level for all assessment parameters and percent area penetration at 6 mm for the C-HA nanocomplex group.ConclusionsC-HA nanocomplex conditioning enhances dentin surface wettability to facilitate greater tricalcium silicate sealer penetration and UTS of dentin.     

Biomimetic Conditioning of Human Dentin Using Citric Acid

Introduction

In carious teeth, transforming growth factor beta 1 (TGF-β1) is released from the dentin matrix and possibly activated in an acidic environment. Conversely, EDTA solutions with a neutral to slightly alkaline pH are used in clinics to promote cell homing in regenerative endodontic procedures. We hypothesized that citric acid (CA) might be more beneficial.

Microtissue Engineering Root Dentin with Photodynamically Cross-linked Nanoparticles Improves Fatigue Resistance of Endodontically Treated Teeth

IntroductionMicrotissue engineering root canal dentin with biopolymeric nanoparticles has the potential to improve mechanical properties of iatrogenically compromised root dentin. This study aims to characterize the surface mechanical property, bulk biomechanical response, and fatigue resistance of microtissue-engineered root dentin using photodynamically (photodynamic-activated [PDA]) cross-linked chitosan nanoparticles (CSnps).MethodsExperiments were conducted in 3 parts: part 1, root canal dentin sections were subjected to nanoindentations before/after treatment with CSnps and chemically (1-ethyl-3-[3-dimethylaminopropyl]carbodiimide [EDC] cross-linked CSnps) and photodynamically cross-linked CSnps to determine the properties of treated surfaces (n = 84 points/group); part 2, root canal dentin specimens treated with PDA cross-linked CSnps were subjected to strain analysis using customized moiré interferometry (n = 5/group); and part 3, root canal dentin specimens treated with EDC cross-linked CSnps, PDA cross-linked CSnps, and instrumented controls were tested using an accelerated fatigue loading protocol to evaluate the sustained loads and cycles at failure (n = 15/group). Data were analyzed using the paired sample t test, trend analysis, and Kaplan-Meier with log-rank tests at a significance of .05 in each experiment.ResultsRoot dentin microtissue engineered with PDA cross-linked CSnps showed a 16.8% increase in elastic modulus and a conspicuous decrease in strain distribution in cervical root dentin (P < .01). There was a significant reduction in the tensile strain formed at the apical region of the instrumented root dentin after treatment (P < .05). Survival analysis showed a statistically significant difference (P < .05) among evaluated conditions in fatigue resistance (ie, PDA cross-linked CSnps > EDC cross-linked CSnps > control).ConclusionsThis study highlighted the potential of root canal dentin microtissue engineering with PDA cross-linked CSnps to diminish radicular strain distribution and improve resistance to fatigue loads in endodontically treated teeth.     

Transforming Growth Factor Beta 1 Distribution and Content in the Root Dentin of Young Mature and Immature Human Premolars

IntroductionTransforming growth factor beta 1 (TGF-β1) is a key morphogen in regenerative endodontics; yet, its location within the hard tissue phase of dentin and its availability in mature roots have not been fully elucidated.MethodsYoung mature (n = 8) and immature (n = 11) roots from sound premolars were obtained from 13 orthodontic patients aged 17 ± 1 and 12 ± 1 years, respectively. Roots were cleaned of organic remnants in 5% sodium hypochlorite. The width of the minor foramen was measured using a digital microscope. TGF-β1 distribution was assessed in 3 roots per group by immunostaining combined with confocal laser scanning microscopy. The root dentin of the remaining 13 roots was powdered and decalcified in 17% EDTA to determine the overall levels of hard tissue–embedded TGF-β1 by enzyme-linked immunosorbent assay. Data were compared between groups using the Student t test (α = .05).ResultsThe minor foramen was 168 ± 49 μm versus 557 ± 295 μm in mature compared with immature roots (P < .05). TGF-β1 was highly stainable toward the pulp space in both groups. It was clearly associated with peritubular dentin and apparently absent in nontubular outer dentin. TGF-β1 content was 115 ± 31 pg and 74 ± 35 pg/100 mg mature versus immature root dentin, respectively (P > .05).ConclusionsTGF-β1 is deposited into the peritubular dentin. It should be possible to release this molecule in regenerative endodontic procedures from young mature roots as well as immature roots.     

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

IntroductionThis 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.MethodThirty 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.ResultsCanal 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.ConclusionIncreasing 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 Diabetes on Rotary Instrumentation of Dentin

IntroductionDiabetes mellitus (DM) may affect the physical and mechanical properties of dentin, which could potentially have an impact on root canal procedures. This study aimed to compare the amount of dentin removed by an endodontic rotary file, comparing dentin from diabetic patients with dentin from control patients under laboratory conditions.MethodsThe amount of dentin removed was tested using new F3 ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) files applied against the surface of prepared dentin discs for 3 different groups: diabetic type 1 (D1), diabetic type 2 (D2), and nondiabetic (normal). The dentin removed was determined by measuring the depth of penetration of the file using a digital caliper and by measuring the weight loss. Data were analyzed using Kolmogorov-Smirnov, analysis of variance, post hoc Tukey, and Pearson correlation tests (P < .05).ResultsSignificantly more dentin was removed, and the penetration of the F3 instrument was significantly higher (P < .05) in DM specimens. The statistical analysis revealed significant differences between the D1, D2, and normal groups (P < .05) for the weight loss of the specimen as well as the penetration depth at point B (P < .05). Both the weight loss and depth of penetration showed a very high positive correlation (P < .05).ConclusionsThe dentin of patients suffering from both D1 and D2 exhibited an increased amount of dentin removed compared with the nondiabetic dentin specimens. This can be observed by the increased penetration of the rotary instruments into dentin. Under certain circumstances, this may impact instrumentation, increasing procedural accidents and leading to subsequent weakening of root canal–treated teeth in diabetic patients.     

Effect of Ultrasonic Activation of Endodontic Sealers on Intratubular Penetration and Bond Strength to Root Dentin

IntroductionThis study aimed to evaluate the effect of ultrasonic activation (UA) of endodontic sealers on dentin tubule penetration and the bond strength to root dentin.MethodOne hundred single-rooted teeth were prepared with 40.06 nickel-titanium instruments and divided into 2 groups: with or without UA. Three resin-based sealers (MTA Fillapex [Angelus Dental Solutions, Londrina, PR, Brazil], Sealer Plus [MK Life Medical and Dental Products, Porto Alegre, RS, Brazil], and AH Plus [Dentsply, DeTrey GmbH, Konstanz, Germany]; n = 20) and 2 calcium silicate–based sealers (Sealer Plus BC [MK Life Medical and Dental Products] and EndoSequence BC [Brasseler, Savannah, GA], n = 20) were used and subdivided (n = 10) according to the protocols. Fluo-3 (Thermo Fisher Scientific, Waltham, MA) and rhodamine B dyes were added to the calcium silicate- and resin-based sealers, respectively. In the UA groups, the activation was performed for 40 seconds followed by lateral compaction. Samples were transversely sectioned to evaluate the dentin tubule penetration and the bond strength to root dentin. The penetration data were analyzed with the Student t test, 1-factor analysis of variance, and Bonferroni tests. Bond strength was evaluated using the Student t test, Kruskal-Wallis, and Dunn post hoc test.ResultsResin-based sealers showed the highest tubule penetration without UA (P < .05). UA significantly enhanced MTA Fillapex and Endosequence BC dentin tubule penetration (P < .05). AH Plus and Sealer Plus BC improved their bond strength to root dentin after UA (P < .05). AH Plus/UA, Sealer Plus/UA, and Sealer Plus BC/UA presented the highest bond strength values (P < .05). Adhesive failures were predominant in all groups regardless of the use of ultrasound.ConclusionsUA interferes with tubule penetration and the bond strength to root dentin of resin- and calcium silicate–based sealers.     

Influence of Cervical Preflaring on the Incidence of Root Dentin Defects

Introduction

This study evaluated the influence of cervical preflaring on the incidence of root dentin defects after root canal preparation.

Enhancing Effects of Immobilized Chondroitin Sulfate on Odontogenic Differentiation of Dental Pulp Stem Cells and Reparative Dentin Formation

IntroductionChondroitin sulfate (CS) is a major proteoglycan involved in the mineralization of the organic matrix of dentin. In this study, the roles of CS immobilized in cross-linked collagen I (Col I) hydrogels on odontogenic differentiation of dental pulp stem cells (DPSCs) and reparative dentin formation were investigated.MethodsDifferent concentrations of CS were incorporated into the genipin–cross-linked Col I hydrogels (CS-0.05, CS-0.1, and CS-0.2, respectively). The influences of CS on the proliferation and odontogenic differentiation of DPSCs were investigated. Finally, the effect of the functionalized hydrogel on the formation of reparative dentin was analyzed in a rat pulp capping model in vivo.ResultsCS improved the proliferation of DPSCs seeded on the hydrogels (P < .05). CS also enhanced the mineralization activities and increased the expression levels of the odontogenic-related proteins of DPSCs on days 7 and 14 (P < .05). In vivo, CS-0.1 hydrogel induced reparative dentin formation with higher quality compared with mineral trioxide aggregate.ConclusionsCS immobilized in Col I hydrogels could induce odontogenic differentiation of DPSCs in vitro and promote homogeneous mineralized barrier formation in vivo. CS–Col I hydrogel has the potential for reparative dentin formation of high quality in direct pulp capping.     

Effect of Root Dentin Conditioning on the Pushout Bond Strength of Biodentine

Introduction

Sodium hypochlorite (NaOCl) is the main irrigant to clean root canals. Decalcifying agents are advocated as additional means to condition the root dentin. The aim of this study was to evaluate the effect of alternating (EDTA) or continuous 1-hydroxyethane 1,1-diphosphonic (HEDP) chelation in conjunction with NaOCl irrigation on the pushout bond strength of Biodentine (Septodont, Saint Maur des Fosses, France).

Effect of Diabetes on Tubular Density and Push-out Bond Strength of Mineral Trioxide Aggregate to Dentin

IntroductionThis study compared the tubular density and push-out bond strength of mineral trioxide aggregate (MTA) to dentin in diabetic and nondiabetic patients.MethodsTen extracted single-rooted human teeth from diabetic and nondiabetic patients (n = 5 in each group) were decoronated, prepared up to a #5 Gates-Glidden drill, and sectioned horizontally at the midroot area to prepare 3 dentin slices, each measuring 2 mm in thickness (1 slice for the push-out test and 2 slices for the tubular density test). MTA was prepared and packed into the root canal space followed by incubation for 3 days. The push-out bond strength values were determined using a universal testing machine. Specimens were viewed under a stereomicroscope and a scanning electron microscope to determine the failure types at the cement-dentin interface. Ten slice specimens in each group were evaluated under SEM at 3 different sites to determine the tubular density. Comparisons were performed using the Mann-Whitney U test (P < .05).ResultsDiabetic patients exhibited significantly lower push-out bond strength of MTA to root canal dentin (P < .05). The pattern of failure at the MTA-dentin interface was different between the 2 groups. The tubular density was significantly higher in diabetic patients (P < .05).ConclusionsThe dentin in diabetic patients exhibited different physicochemical properties. The failure patterns and modes in diabetic patients might be explained by the changes in the push-out bond strength, the calcification mechanism of the dentin-pulp complex, a higher dentinal tubule density, and less peritubular dentin. These differences could explain the higher failure rate of root canal treatment in these patients.     

Assessment of Root Canal Sealers Loaded with Drug-Silica Coassembled Particles Using an In Vitro Tooth Model

IntroductionThe purpose of this study was to assess the antimicrobial activity of root canal sealers modified with novel highly loaded antimicrobial drug-silica coassembled particles (DSPs) on Enterococcus faecalis–infected root canal dentin.MethodsDSPs were synthesized through coassembly of silica and octenidine dihydrochloride (OCT) surfactant drug (35% w/w OCT). DSPs (1% wt of the total mass of the sealer) were mixed homogenously with either epoxy resin sealer (AH Plus [AH]; Dentsply Sirona, Tulsa, OK) or calcium silicate–based sealer (EndoSequence BC Sealer [BC]; Brasseler, Savannah, GA). To assess the antimicrobial activity of DSP-loaded sealers, the apical third of single-rooted teeth was obtained and infected with E. faecalis for 3 weeks followed by the application of experimental (DSP-loaded) sealers or corresponding controls for up to 28 days. Microbiological analysis and laser scanning confocal and scanning electron microscopy were used to determine the colony-forming unit (CFU)/mL, the percentage of live bacteria, and the intratubular bacterial and sealer penetrations. Factorial analysis of variance and Tukey post hoc tests were used to assess the antimicrobial effect of DSPs on different sealers.ResultsAll experimental groups showed significant reductions in CFUs at all-time points compared with positive controls (P < .05). The addition of DSPs to BC significantly reduced the CFUs (2.11 ± 0.13, 2.22 ± 0.19, and 2.25 ± 0.17 at 1, 7, and 28 days, respectively) compared with the unmodified sealer (3.21 ± 0.11, 4.3 ± 0.15, and 4.2 ± 0.2 at 0, 7, and 28 days). DSPs enhanced the antimicrobial performance of AH only at 1 day (4.21 ± 0.17 vs 5.19 ± 0.12, P < .05). AH and AH + DSPs showed higher bacterial viability compared with BC and BC + DSPs at all incubation periods (P < .05).ConclusionsLoading endodontic sealers with DSPs had a material-dependent effect on the antimicrobial properties and could reduce the incidence of secondary infections.     

Antibacterial Effect and Bioactivity of Innovative and Currently Used Intracanal Medicaments in Regenerative Endodontics

IntroductionThe purpose of this study was to determine the antibacterial effect and bioactivity of triple antibiotic paste (TAP), calcium hydroxide (Ca[OH]₂), and calcium hypochlorite (Ca[OCl]₂).MethodsRoot canals were infected with 3-week-old Enterococcus faecalis biofilm and then medicated for 7 days with TAP, Ca(OH)₂, or Ca(OCl)₂ (n = 10/group). Untreated and uninfected canals were used as positive and negative controls. The antibacterial effect was determined using colony-forming units and a Live/Dead bacterial viability kit. Dental pulp stem cells were seeded on medicated dentin surfaces for 7 days. Sodium thiosulfate and various concentrations of ascorbic acid (1%, 5%, and 10%) were also used to neutralize the samples treated with Ca(OCl)₂ before cell seeding (n = 3 in triplicate). Cell viability and morphology were evaluated using a viability assay and Live/Dead cell analysis. Alkaline phosphatase (ALP) activity was also measured to determine the cells’ mineralization activity.ResultsAll medicaments decreased the initial bacterial load (P < .05). The highest bacterial reduction in the main canal and dentinal tubules was observed in the Ca(OCl)₂ group (P < .05). TAP- or Ca(OH)₂-treated dentin surface improved cell viability and ALP activity compared with the untreated dentin surface (P < .05), whereas Ca(OCl)₂ decreased cell viability and ALP activity (P < .05). Ten percent ascorbic acid neutralized the effect of Ca(OCl)₂ on the treated dentin surface, showing higher cell viability (P < .05) and similar ALP activity with the untreated dentin surface and the other groups (P > .05).ConclusionsCa(OCl)₂ medication improved root canal disinfection against E. faecalis biofilm compared with TAP and Ca(OH)₂. The adverse effects caused by Ca(OCl)₂ on cell viability and mineralization activity can be neutralized with 10% ascorbic acid.     

Potential of Treated Dentin Matrix Xenograft for Dentin-Pulp Tissue Engineering

IntroductionThis study aims to develop and characterize the regenerative potential of an atelopeptidized treated dentin matrix xenograft using in vitro and in vivo models.MethodsFreshly extracted bovine dentin was pulverized into 250- to 500-μm particles and demineralized with 17% EDTA for 1, 7, and 13 days. The samples were atelopeptidized with pepsin. The degree of demineralization and the effect of atelopeptidization were assessed using field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy, respectively. The expression of dentin matrix acidic phosphoprotein 1, dentin sialophosphoprotein, and osteopontin was evaluated in dental pulp stem cells using quantitative real-time polymerase chain reaction. The samples were then implanted intramuscularly in rats for 30 days, and the inflammatory cells were quantified histologically.ResultsField emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed an exposed tubular structure of dentin after 1 and 7 days of demineralization. Fourier transform infrared spectroscopy confirmed the absence of amide peaks at 1260 to 1640/cm after atelopeptidization. The dental pulp stem cell expression of dentin matrix acidic phosphoprotein 1 and dentin sialophosphoprotein increased in all compared with the untreated control group (P < .05). The maximum expression rates were observed for the 1-day demineralized and atelopeptidized group. The 1-day demineralized group elicited the highest inflammatory response compared with the 7- or 13-day demineralized groups (P < .001). Atelopeptidization significantly decreased the inflammatory response only in the 1-day demineralized dentin group (P < .05).ConclusionsAtelopeptidization of 1-day demineralized dentin xenograft preserved the collagen structure, minimized the immune reaction, and provided sufficient regenerative potential.     

Active Bacteria in Carious Dentin of Mandibular Molars with Different Pulp Conditions: An In Vivo Study

IntroductionThis study evaluated the relative abundance and ribosomal activity of selected bacteria in carious dentin of teeth with different pulp conditions.MethodsThirty healthy patients with class I occlusal caries in molars were categorized into 3 groups based on the pulp diagnosis: normal pulp (NP, n = 10) with caries extending less than half the thickness of dentin (as assessed radiographically), reversible pulpitis (n = 10), and symptomatic irreversible pulpitis (n = 10) with caries extending more than two thirds of the thickness of dentin. Carious dentin samples were collected from the deepest part of the cavity and stored in RNAlater solution (Ambion Inc, Austin, TX). Eight bacterial taxa were evaluated from the samples: Streptococcus mutans, Lactobacillus fermentum, Veillonella, Actinomyces, Rothia dentocariosa, Olsenella profusa, Prevotella intermedia, and Bifidobacterium dentium. The 16S ribosomal RNA (rRNA) gene and 16S rRNA were quantified by real-time polymerase chain reaction and used to calculate the relative genome abundance and relative ribosomal abundance. The Fisher exact test was used to compare proportions between groups. The mean rank difference between the various groups was assessed using the Kruskal-Wallis test with the Bonferroni-Holm correction.ResultsThe reversible pulpitis group had significantly higher 16S rRNA gene and rRNA counts of Actinomyces (P < .001 and P = .002) and B. dentium (P = .005 and P = .007) relative to the NP group. The symptomatic irreversible pulpitis group had significantly higher 16S rRNA gene and rRNA counts of L. fermentum (P < .001 and P < .001), Actinomyces (P < .001 and P < .001), O. profusa (P < .001 and P < .001), P. intermedia (P = .001 and P = .002), and Bifidobacterium (P < .001 and P < .001) relative to the NP group.ConclusionsSpecific bacterial activity varies in carious dentin of teeth with different pulp conditions.     

Effect of a Residual Biofilm on Release of Transforming Growth Factor β1 from Dentin

IntroductionSeveral studies have reported regeneration of the pulp-dentin complex when treating noninfected root canal systems. However, current protocols applied to infected root canal systems are much less predictable for the formation of dentin. Converging lines of evidence implicate residual biofilm as an important factor for these variable histologic outcomes. Here we studied the effect of a residual polymicrobial biofilm on the release of transforming growth factor beta 1 (TGF-β1) from dentin. We hypothesized that the presence of bacterial biofilm attenuates the release of bioactive molecules from dentin.MethodsUsing bacteria commonly found in infected immature teeth, we developed a multispecies biofilm in an organotypic root canal model. Root segments were then subjected to various irrigation or intracanal medicament protocols. Subsequently, the release of TGF-β1 from dentin was measured using the enzyme-linked immunosorbent assay.ResultsOur data show that sterile root segments released greater amounts of TGF-β1 when conditioned with 17% EDTA alone (P < .001) or with the combination of 1.5% sodium hypochlorite and 17% EDTA (P < .05) compared with root segments infected with the multispecies biofilm. Similar results were also observed with the intracanal medicament protocol. Sterile root segments medicated with various concentrations of triple antibiotic paste and full-strength calcium hydroxide released greater amounts of TGF-β1 when compared with their infected counterparts.ConclusionsThis is the first study to report the detrimental effects of a residual biofilm on dentin conditioning and, therefore, the release of growth factors critical for regenerative procedures.     

Push-out Bond Strength of Resilon/Epiphany and Resilon/Epiphany Self-Etch to Root Dentin

IntroductionThe present study was designed to investigate the bond strength produced by Epiphany and Epiphany SE to root canal dentin.MethodsA sample of 36 human upper canines was prepared and assigned to experimental groups (n = 12), designated as group 1, Resilon/Epiphany; group 2, Resilon/Epiphany SE; and group 3, AH Plus/gutta-percha. After the filling procedures, each tooth was prepared for push-out assessment by using root slices of 1-mm thickness. Loading was performed on a universal testing machine at a speed of 0.5 mm/min. One-way analysis of variance and Tukey test for multiple comparisons were used to compare the results among the experimental groups.ResultsAH Plus/gutta-percha root fillings showed significantly higher push-out bond strength than both Resilon/Epiphany and Resilon/Epiphany SE (P < .05). There was no significant difference between Epiphany/Resilon and Epiphany SE/Resilon (P > .05).ConclusionsUnder the present in vitro conditions, the adhesiveness quality to root dentin promoted by both Epiphany sealers is compromised even when teeth with simple anatomic features were obturated under well-monitored laboratory conditions.     

Middle Mesial Canal Preparation Enhances the Risk of Fracture in Mesial Root of Mandibular Molars

IntroductionThe aim of this investigation was to evaluate the effect of the presence and preparation of middle mesial (MM) canals on the fracture resistance of the mesial root of mandibular molars.MethodsForty intact mesial roots of mandibular first molars having 2 (n = 20) or 3 (n = 20) independent canals from the furcation level for up to at least 5 mm apically were selected based on preoperative micro–computed tomographic scanning. The selected roots were then distributed into 2 experimental (n = 10) and 2 control groups (n = 10) according to the root length, canal configuration (2 or 3 independent canals), and root thickness at the furcation level. In the experimental groups 1 (2 independent canals) and 3 (3 independent canals), root canals were enlarged up to the ProTaper Next X3 rotary instrument (Dentsply Sirona, Ballaigues, Switzerland), whereas in groups 2 (2 independent canals) and 4 (3 independent canals) root canals were not prepared. The specimens were embedded in acrylic resin after their surfaces were coated with a thin layer of silicone and subjected to a fracture strength using a universal testing machine. The types of fracture extension and course were recorded and statistically compared with the chi-square test, whereas fracture strength was analyzed using 1-way analysis of variance and post hoc Tukey tests (α = 5%).ResultsNo statistical difference in fracture strength was observed between nonprepared roots with 2 (group 2, 696.1 ± 186.3 N) or 3 (group 4, 558.4 ± 154.6 N) independent canals (P > .05), whereas the lowest values were obtained in the prepared roots with an MM canal (groups 3, 377.1 ± 77.2 N) (P < .05). The mean fracture strength observed in the prepared roots with 2 canals (group 1, 528.4 ± 134.3 N) showed no statistically significant difference compared with nonprepared roots with 3 canals (group 4, 558.4 ± 154.6 N) (P > .05). The chi-square test revealed no significant differences in fracture extent, types, and courses among groups (P > .05). Fracture extensions in all groups were mostly central and buccal-central types, whereas the highest frequency of fracture course was the curved and zigzag types.ConclusionsThe fracture resistance of the mesial roots of the mandibular molars decreased after the preparation of mesial canals with large-tapered instruments. Preparation of the MM canal further diminished the fracture resistance of the mesial roots. The resultant fracture displayed a distinct pattern in the buccolingual plane.     

Similar Influence of Stabilized Alkaline and Neutral Sodium Hypochlorite Solutions on the Fracture Resistance of Root Canal–treated Bovine Teeth

Introduction

Stabilizing sodium hypochlorite (NaOCl) at an alkaline pH is proposed to increase solution stability and tissue dissolution ability; however, a reduction on the flexural strength of dentin discs has been found to be a side effect. This study sought to determine whether a stabilized alkaline NaOCl reduces the fracture resistance of root canal–treated bovine teeth after root canal preparation compared with a neutral solution counterpart.

Methods

The 4 anterior incisors were removed from 20 mandibular bovine jaws, and each 1 was randomly assigned to 1 of 4 groups (20 teeth each). Teeth were prepared with a sequence of 6 K-type files. The following experimental groups received a different irrigation regimen: G1: distilled water (negative control), G2: 5% NaOCl at a pH of 7.2, and G3: 5% NaOCl at a pH of 12.8; in the positive control group (G4), teeth remained untreated. The time of contact and volume of solution were carefully standardized. After bone and periodontal ligament simulation, teeth were subjected to a fracture resistance test.

Results

A significant difference was observed among the 4 groups tested (analysis of variance, P < .05). The 5% NaOCl groups (G2 and G3) presented significantly lower resistance to fracture than the control (G1 and G4) (Tukey test, P < .05). Both NaOCl solutions similarly reduced the fracture resistance at approximately 30% (Tukey test, P > .05). No differences were observed between positive and negative control groups (Tukey test, P > .05).

Conclusions

Stabilized alkaline and neutral NaOCl solutions similarly reduced the fracture resistance of root canal–treated bovine teeth by about 30%.