Evaluation of the interaction of chlorhexidine and MDP and its effects on the durability of dentin bonding

ObjectiveThis study aimed to evaluate the potential interaction of chlorhexidine (CHX) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and its effects on the durability of dentin bonding.MethodsTwo commercial adhesives were tested: a MDP-free adhesive (Single Bond 2, SB2) and a MDP-containing adhesive (Single Bond Universal, SBU). Teeth were randomly assigned to six groups and tested for micro-tensile bond strength (μTBS): Ctr, direct bonding with SB2; CHX, CHX conditioning and SB2; MDP, MDP conditioning and SB2; CHX + MDP, combined CHX and MDP conditioning and SB2; SBU, direct bonding with SBU; CHX + SBU, CHX conditioning and SBU. The potential interaction of CHX and MDP was assessed by measuring nanoleakage, in situ zymography, and chemoanalytic characterization via Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR). Specimens for μTBS and nanoleakage tests were first subjected to water storage for 24 h or 6 months.ResultsThe initial μTBS values of the Ctr and CHX groups were significantly lower than those of the other four groups (P < 0.05). Water storage for 6 months significantly weakened all groups (P < 0.05), with the Ctr group showing the lowest μTBS. This group also showed more obvious nanoleakage than the other five groups. In situ zymography revealed that the Ctr group showed the strongest fluorescence and that the CHX + MDP group showed greater fluorescence than either CHX or MDP group. FTIR, XPS, and NMR indicated that MDP can interact with hydroxyapatite. NMR detected no Ca²⁺ salt peak for MDP when it was combined with CHX.SignificanceThe application of either CHX or MDP alone can improve dentin bond durability. However, CHX may interfere with the formation of MDP–Ca salts.     

Long-term nanomechanical properties and gelatinolytic activity of titanium tetrafluoride-treated adhesive dentin interface

ObjectiveThis study investigated the effects of dentin pretreatment with 2.5% titanium tetrafluoride (TiF₄) on nanomechanical properties, and the in situ gelatinolytic activity of the dentin–resin interface, for up to 6 months.MethodsTwenty-four human teeth were prepared by exposing occlusal flat dentin surfaces, and were randomly assigned to experimental groups, according to application or non-application of a TiF₄ pretreatment, and to the adhesive systems (Clearfil SE Bond or Scotchbond Universal). Resin composite (Filtek Supreme Ultra) was built up incrementally on the teeth in all the groups. Then, the specimens were sectioned and randomly selected for evaluation at 24 h, 3 months and 6 months of storage time. The reduced modulus of elasticity (E_r) and the nanohardness of the underlying dentin, as well as the hybrid layer and the adhesive layer were measured using a nanoindenter. Gelatinolytic activity at the dentin–resin interfaces was assessed by in situ zymography using quenched fluorescein-conjugated gelatin at 24 h and 6 months. Statistical analyses were performed with ANOVA and Tukey’s tests.ResultsThere were no differences in E_r and nanohardness values between adhesives systems and pretreatment (p = 0.1250). In situ zymography showed significantly higher gelatinolytic activity after 6 months for all the experimental groups (p = 0.0004), but no differences between the adhesive systems (p = 0.7708) and the surface pretreatment (p = 0.4877). Significance: Dentin pretreatment with 2.5% TiF₄ followed by self-etching adhesive systems did not influence nanomechanical properties or gelatinolytic activity of the adhesive–dentin interface layers, over time.     

Nanoleakage,ultramorphological characteristics,and microtensile bond strengths of a new low-shrinkage composite to dentin after artificial aging

ObjectivesTo study the microtensile bond strengths and nanoleakage of low-shrinkage composite to dentin. The null hypotheses tested were (1) aging does not affect the bonding of low-shrinkage composite; (2) there is no difference in microtensile bond strengths and nanoleakage using different bonding strategies.Methods32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15 s with phosphoric acid + LS System Adhesive (LSpa); Adper Single Bond Plus (SB, 3M ESPE); SB + LS Bond (SBLS). Occlusal dentin was exposed and restored with Filtek LS (3M ESPE). The samples were tested after 24 h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8 ± 0.2 mm² and fractured at a crosshead speed of 1 mm/min. The data were submitted to ANOVA/Duncan's post hoc test, at p < 0.05. Five slabs from each group were selected and immersed in 50 wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal–Wallis at p < 0.05.ResultsNo statistically significant difference was found among the experimental groups for the factor dentin treatment (p = 0.165) and aging (p = 0.091). All experimental groups exhibit some degree of nanoleakage. There was no adhesion of Filtek LS applied directly over dentin surfaces treated with SB.SignificanceThe new low-shrinkage resin composite showed compatibility only with its dedicated adhesive. Pre-etching did not improve the bond strengths to low-shrinkage resin composite. Some degree of nanoleakage was evident in all groups.     

Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations

ObjectivesDental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations.MethodsOne hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max^® ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (n_x = 60) were divided in three groups (control, aged for 5 h, aged for 10 h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P < 0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ₀). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy.ResultsA slight increase of the flexural strength after 5 h, and a decrease after 10 h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P < 0.05). Both ceramics presented a t → m phase transformation, with the m-phase increasing from 4 to 5% at 5 h to around 15% after 10 h.SignificanceThe significant reduction of the flexural strength after 10 h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested.     

An in vitro evaluation of microleakage of resin based composites bonded to chlorhexidine-pretreated dentin by different protocols of a universal adhesive system

PurposeThis study compared microleakage of different resin based composite (RBC) materials bonded to dentin, after chlorhexidine (CHX) application, by different adhesion protocols of a universal adhesive system.MethodsClass V cavities were prepared on the buccal and lingual surfaces of 40 premolar teeth. The “etch-and-rinse” technique of a universal bond adhesive system (Single Bond Universal Adhesive) was used on buccal preparations, while the “self-etch” protocol was used on the lingual surfaces. Two RBCs, one bulk fill (Filtek Bulk Fill [FBF]) and one conventional (Filtek Z350 XT [Z350XT]), were used. Teeth were divided into two groups of 20 teeth each, 10 per each RBC (n = 10): (1) control; and (2) pretreatment with 2% CHX. For FBF groups, teeth were restored with a single increment; however, for Z350XT, a layering technique was used. Teeth were aged by thermo-cycling and prepared for microleakage testing. Dye penetration was evaluated and scored from 0 to 4. Data were analyzed at a significance level of P < 0.05.ResultsThe highest microleakage mean scores were found in the control group of the etched margins for both RBCs (2.80 ± 1.033 FBF and 2.10 ± 1.370 Z350XT). The CHX-pretreated group showed significantly lower microleakage than the control for FBF only (P = 0.008). No significant difference was found between groups for the “self-etch” protocol (χ² = 0.884, P = 0.08). No significant differences were found between FBF and Z350XT in all study groups (P > 0.2).ConclusionsWhen the “self-etch” protocol of the universal adhesive system was used, dentin microleakage was not affected by CHX-pretreatment when teeth were restored with bulk fill or conventional RBCs. In the “etch-and-rinse” protocol, CHX application improved the marginal seal before restoration with bulk fill material. However, in the absence of CHX, the “etch-and-rinse” protocol negatively affected marginal integrity.     

Antibacterial and antibiofilm efficacy of k21-E in root canal disinfection

ObjectivesThe aim of the current project was to study the antimicrobial efficacy of a newly developed irrigant, k21/E against E. faecalis biofilm.MethodsRoot canals were instrumented and randomly divided into the following groups: irrigation with saline, 6% NaOCl (sodium hypochlorite), 6% NaOCl + 2% CHX (Chlorhexidine), 2% CHX, 0.5% k21/E (k21 - quaternary ammonium silane) and 1% k21/E. E. faecalis were grown (3-days) (1 × 10⁷ CFU mL⁻¹), treated, and further cultured for 11-days. Specimens were subjected to SEM, confocal and Raman analysis and macrophage vesicles characterized along with effect of lipopolysaccharide treatment. 3T3 mouse-fibroblasts were cultured for alizarin-red with Sortase-A active sites and Schrödinger docking was performed. TEM analysis of root dentin substrate with matrix metalloproteinases profilometry was also included. A cytotoxic test analysis for cell viability was measured by absorbance of human dental pulp cells after exposure to different irrigant solutions for 24 h. The test percentages have been highlighted in Table 1.ResultsAmong experimental groups, irrigation with 0.5% k21/E showed phase separation revealing significant bacterial reduction and lower phenylalanine 1003 cm⁻¹ and Amide III 1245 cm⁻¹ intensities. Damage was observed on bacterial cell membrane after use of k21/E. No difference in exosomes distribution between control and 0.5%k21/E was observed with less TNFα (*p < 0.05) and preferential binding of SrtA. TEM images demonstrated integrated collagen fibers in control and 0.5%k21/E specimens and inner bacterial membrane damage after k21/E treatment. The k21 groups appeared to be biocompatible to the dental pulpal cells grown for 24 h.SignificanceCurrent investigations highlight potential advantages of 0.5% k21/E as irrigation solution for root canal disinfection.     

Effect of biomimetic mineralization on enamel and dentin: A Raman and EDX analysis

ObjectiveTo investigate the effect of an experimental biomimetic mineralization kit (BIMIN) on the chemical composition and crystallinity of caries-free enamel and dentin samples in vitro.MethodsEnamel and dentin samples from 20 human teeth (10 for enamel; 10 for dentin) were divided into a control group without treatment and test samples with BIMIN treatment. Quantitative analysis of tissue penetration of fluoride, phosphate, and calcium was performed using energy-dispersive X-ray spectroscopy (EDX). Mineralization depth was measured by Raman spectroscopy probing the symmetric valence vibration near 960 cm⁻¹ as a marker for crystallinity. EDX data was statistically analyzed using a paired t-test and Raman data was analyzed using the Student’s t-test.ResultsEDX analysis demonstrated a penetration depth of fluoride of 4.10 ± 3.32 μm in enamel and 4.31 ± 2.67 μm in dentin. Calcium infiltrated into enamel 2.65 ± 0.64 μm and into dentin 5.58 ± 1.63 μm, while the penetration depths for phosphate were 4.83 ± 2.81 μm for enamel and 6.75 ± 3.25 μm for dentin. Further, up to 25 μm of a newly mineralized enamel-like layer was observed on the surface of the samples. Raman concentration curves demonstrated an increased degree of mineralization up to 5–10 μm into the dentin and enamel samples.SignificanceBiomimetic mineralization of enamel and dentin samples resulted in an increase of mineralization and a penetration of fluoride into enamel and dentin.     

Chlorhexidine-modified nanotubes and their effects on the polymerization and bonding performance of a dental adhesive

ObjectivesThe purpose of this study was to synthesize chlorhexidine (CHX)-encapsulated aluminosilicate clay nanotubes (Halloysite®, HNTs) and to incorporate them into the primer/adhesive components of an etch-and-rinse adhesive system (SBMP; Scotchbond Multipurpose, 3M ESPE) and to test their effects on degree of conversion, viscosity, immediate and long-term bonding to dentin.MethodsCHX-modified HNTs were synthesized using 10% or 20% CHX solutions. The primer and the adhesive components of SBMP were incorporated with 15 wt.% of the CHX-encapsulated HNTs. Degree of conversion (DC) and viscosity analyses were performed to characterize the modified primers/adhesives. For bond strength testing, acid-etched dentin was treated with one of the following: SBMP (control); 0.2%CHX solution before SBMP; CHX-modified primers + SBMP adhesive; SBMP primer + CHX-modified adhesives; and SBMP primer + CHX-free HNT-modified adhesive. The microtensile bond strength test was performed after immediate (24 h) and long-term (6 months) of water storage. Data were analyzed using ANOVA and Tukey (α = 5%) and the Weibull analysis.ResultsDC was greater for the CHX-free HNT-modified adhesive, whereas the other experimental adhesives showed similar DC as compared with the control. Primers were less viscous than the adhesives, without significant differences within the respective materials. At 24 h, all groups showed similar bonding performance and structural reliability; whereas at the 6-month period, groups treated with the 0.2%CHX solution prior bonding or with the CHX-modified primers resulted in greater bond strength than the control and superior reliability.SignificanceThe modification of a primer or adhesive with CHX-encapsulated HNTs was an advantageous approach that did not impair the polymerization, viscosity and bonding performance of the materials, showing a promising long-term effect on resin-dentin bonds.     

In vivo aging of zirconia dental ceramics – Part I: Biomedical grade 3Y-TZP

ObjectiveIn vivo aging of biomedical grade 3Y-TZP ceramics in the oral environment was assessed and compared to artificially accelerated in vitro hydrothermal aging extrapolations at 37 °C.Methods88 discs were pressed and sintered (1450–1500 °C) from two commercial 3Y-TZP compositions containing 0.25% Al₂O₃ to generate finer- and coarser-grained specimens. As-sintered (AS) and airborne-particle abraded (APA; 50 μm Al₂O₃) surfaces were investigated. In vivo aging was performed by incorporating specimens in lingual flanges of complete dentures of 12 edentulous volunteers who wore them continuously for up to 24 months. For comparison, in vitro hydrothermal aging at 134 °C was also performed and analysed by XRD and (FIB)-SEM. Data was statistically analysed with linear regression models.ResultsFiner and coarser-grained specimens exhibited statistically insignificant differences in aging in vivo. The monoclinic fraction (X_m) on AS surfaces abruptly increased to ～8% after 6 months. The aging process then proceeded with slower linear kinetics (～0.24%/month). After 24 months, X_m reached ～12%. The calculated maximum transformed layer was 0.385 μm representing one layer of transformed grains. APA surfaces were highly aging resistant. The initial X_m of ～4.0% linearly increased by 0.03%/month in vivo. In vitro aging exhibited an initial induction period, followed by linear aging kinetics. Coarser-grained AS surfaces aged significantly faster than fine-grained (2.41%/h compared to 2.16%/h). APA discs aged at a rate of 0.3%/h in vitro. Microcracking within a single grain and pull-out of grain clusters were observed on aged AS surfaces.SignificanceBiomedical grade 3Y-TZP was susceptible to in vivo aging. After 2 years in vivo, the aging kinetics were almost 3-times faster than the generally accepted in vitro-in vivo extrapolation.     

The effect of active components from citrus fruits on dentin MMPs

ObjectivesThis study was aimed to evaluate the anti-matrix metalloproteinases (MMPs) ability of active components from citrus fruits (hesperetin: Hst, hesperidin: Hsd and naringenin: Nge).MethodsInactivation effects of citrus flavonoids (Hst, Hsd, Nge) at different concentrations on soluble collagenase were measured using a fluorometric assay. Matrix-bound endogenous MMPs activity was evaluated via dry mass loss and hydroxyproline (HYP) release of demineralized human dentin. Demineralized dentin beams were pretreated with 500 μg/mL citrus flavonoids for 10 min. Chlorhexidine (CHX) was used as inhibitor control. Beams pretreated with distilled water served as blank control. Dentin slabs were used for in situ zymography and evaluated under confocal microscopy. Ultrastructure of demineralized collagen fibers was exhibited by Transmission Electron Microscopy (TEM).ResultsCitrus flavonoids exhibited inactivation function on soluble MMPs and the extent of inactivation increased in a dose-dependent manner. The inactivation percent of citrus flavonoids reached above 90% at the concentration of 500 μg/mL. Compared with control group, citrus flavonoids pretreated demineralized dentin beams exhibited less dry mass loss, lower hydroxyproline release and more intact collagen architecture after 15 days storage. Dentin samples pretreated with citrus flavonoids showed lower enzymes activities in in situ zymography.ConclusionsHst, Hsd or Nge have anti-MMPs ability and can preserve dentin collagen from degradation.Clinical Significance: Hst, Hsd and Nge may have the potential to be used in dentin bonding systems and improve the resin-dentin bonding durability.     

The effect of Morinda Citrifolia juice as an endodontic irrigant on smear layer and microhardness of root canal dentin

PurposeThe purpose of this study was to evaluate the effect of Morinda Citrifolia Juice (MCJ) on smear layer removal and microhardness value of root canal dentin in compared with various endodontic irrigants.Material and methodsEighty-four single-rooted human teeth were prepared to apical size of #35. Since decoronation, samples were divided into seven groups of 12 in each (n = 12). Specimens were finally irrigated by either 1: 2.5% NaOCl, 2: 6% MCJ, followed by a final flush of 17% ethylene diaminetetraacetic acid (EDTA), 3: 6% MCJ, 4: 2.5% NaOCl then17% EDTA, 5: MTAD, 6: 2% chlorhexidine (CHX), and 7: saline. After irrigation, all samples were subjected to Vickers microhardness test at 100 and 500-μm depths and then were examined under scanning electron microscopy (SEM) and ImageJ program was used to calculate open dentinal tubules. One way ANOVA and post hoc Tukey tests were used to reveal any significant differences among and between groups respectively.ResultsThe microhardness values at 100 μm and 500 μm for MTAD were significantly lower than for NaOCl + EDTA and MCJ + EDTA groups (p < 0.05). MCJ + EDTA, NaOCl + EDTA, and MTAD protocol significantly removed smear layer in compared with control group (p < 0.05), with no significant differences among these three groups.ConclusionsIt was concluded that 6% MCJ followed by a final flush of 17% EDTA can be regarded as an effective solution on smear layer removal without any adverse influence on microhardness property of root canal dentin.     

Comparison of various 3D printed and milled PAEK materials: Effect of printing direction and artificial aging on Martens parameters

ObjectivesThe aim of this study was to investigate the effect of artificial aging on the Martens parameters of different 3D printed and milled polyaryletherketon (PAEK) materials.MethodsIn total 120 specimens of 4 different polyetheretherketon (PEEK) materials (Essentium PEEK, KetaSpire PEEK MS-NT1, VICTREX PEEK 450 G and VESTAKEEP i4 G) were additively manufactured via fused layer manufacturing (FLM) in either horizontal or vertical directions (n = 15 per group). 75 specimens were milled out of prefabricated PAEK blanks from the materials breCAM.BioHPP, Dentokeep, JUVORA Dental Disc 2 and Ultaire AKP ( = 15 per group). Martens hardness (HM), indentation hardness (H_IT) and indentation modulus (E_IT) were determined initially and longitudinally after thermocycling (5−55 °C, 10,000x) and autoclaving (134 °C, 2 bar). In each case, the surface topography of the specimens was examined for modifications using a light microscope.Data were analysed with Kolmogorov-Smirnov test, univariate ANOVA followed by post-hoc Scheffé test with partial eta squared (η_p²), Kruskal–Wallis-, Mann–Whitney-U-, Friedman- and Wilcoxon-Test. A value of p < 0.05 was considered as significant.ResultsMilled specimens showed higher Martens parameters than printed ones (p < 0.001). Artificial aging had a negative effect on the measured parameters (p < 0.001). Horizontally printed specimens presented higher Martens parameters than vertically printed ones, regardless of material and aging process (p < 0.001). Essentium PEEK and breCAM.BioHPP showed the highest and VICTREX PEEK 450G as well as Ultaire AKP the lowest values of all investigated PAEK materials initially, after thermocycling and after autoclaving (p < 0.001). Microscopic examinations showed that artificial aging did not cause any major modifications of the materials.SignificanceAdditively manufactured PEEK materials showed lower Martens parameters than milled ones, whereas horizontally printed specimens presented higher values than vertically printed ones. Artificial aging had a negative effect on the Martens parameters, but not on the surface topography.     

Surface dissolution and transesterification of thermoset dimethacrylate polymer by dimethacrylate adhesive resin and organic catalyst-alcohol solution

ObjectivesTo evaluate transesterification based dissolution of dimethacrylate and epoxy polymers, the former containing ester groups. Polymer substrates were treated with an adhesive resin (Stick™ Resin) and an organic catalyst-alcohol solution (ethylene glycol and triazabicyclodecene). The surface was chemically and nanomechanically analyzed with Fourier Transform-Infrared (FTIR) spectroscopy, surface profile peak (R_p) and nanohardness and modulus of elasticity.MethodsA total of 100 specimens each of light-cured dimethacrylate polymer and heat-cured diepoxy polymer were prepared. 20 specimens were randomly selected and used as control group (0 s). The remaining specimens were randomly divided into 40 each for treatment with an Stick™ resin and ethylene glycol + triazabicyclodecene. Within each group the 40 specimens were randomly subdivided into 20 each for treatment at 5 min and 24 h, with 10 specimens for FTIR and nanohardness and modulus of elasticity, and the other 10 for SEM and surface R_p analyses.ResultsDimethacrylate polymer showed a reduction in the nanohardness and modulus of elasticity, R_p values and SEM also showed significant topographical changes after being treated with either Stick™ resin or ethylene glycol + triazabicyclodecene, whereas epoxy resin substrate did not. FTIR analyses affirmed changes in the intensity of ester groups.SignificanceEster group containing dimethacrylate polymer showed a reduction in NMP within 5 min of exposure to the treatment agents with softening by solution ethylene glycol + triazabicyclodecene associated to the reduction of ester groups in the polymer structure by transesterification. Epoxy polymer without ester groups was not affected by surface softening with treatment agents. Adhesive resin caused surface swelling.     

Effect of different composite modulation protocols on the conversion and polymerization stress profile of bulk-filled resin restorations

ObjectiveThe aim of this in vitro study was to test the effect of different composite modulation protocols (pre-heating, light-curing time and oligomer addition) for bulk filling techniques on resin polymerization stress, intra-pulpal temperature change and degree of conversion.MethodsClass I cavities (4 mm depth × 5 mm diameter) were prepared in 48 extracted third molars and divided in 6 groups. Restorations were completed with a single increment, according to the following groups: (1) Filtek Z250XT (room temperature – activated for 20 s); (2) Filtek Z250XT (at room temperature – activated for 40 s); (3) Filtek Z250XT (pre-heated at 68 °C – activated for 20 s); (4) Filtek Z250XT (pre-heated at 68 °C – activated for 40 s); (5) Filtek BulkFill (at room temperature – activated for 20 s); (6) Filtek Z250XT (modified by the addition of a thio-urethane oligomer at room temperature – activated for 40 s). Acoustic emission test was used as a real-time polymerization stress (PS) assessment. The intra-pulpal temperature change was recorded with a thermocouple and bottom/top degree of conversion (DC) measured by Raman spectroscopy. Data were analyzed with one-way ANOVA/Tukey's test (α = 5%).ResultsPre-heating the resin composite did not influence the intra-pulpal temperature (p = 0.077). The thio-urethane-containing composite exhibited significantly less PS, due to a lower number of acoustic events. Groups with pre-heated composites did not result in significantly different PS. Filtek BulkFill and the thio-urethane experimental composite presented significantly higher DC.SignificanceResin composite pre-heating was not able to reduce polymerization stress in direct restorations. However, thio-urethane addition to a resin composite could reduce the polymerization stress while improving the DC.     

Vertical and horizontal polymerization shrinkage in composite restorations

ObjectivePolymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold.MethodsVertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured.ResultsThere was a significant correlation between vertical and horizontal polymerization shrinkage (r = 0.647, p = 0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r = −0.697, p = 0.025) and dentin (r = −0.752, p = 0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r = 0.829, p = 0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p > 0.05).SignificanceDuring the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.     

Effect of Proanthocyanidin-enriched extracts on the inhibition of wear and degradation of dentin demineralized organic matrix

ObjectivesThe aim of this study was to evaluate the effect of Cranberry and Grape seed-enriched extract gels in inhibiting wear and degradation of demineralized organic matrix (DOM).Design225 dentin specimens obtained from bovine incisors were randomly allocated into 5 groups (n = 45): 10% Grape seed extract gel (GSE), 10% Cranberry extract gel (CE), 0.012% Chlorhexidine gel (CX), 1.23% NaF gel (F), and no active compound gel (P, placebo). Before the treatments, samples were demineralized by immersion in 0.87 M citric acid, pH 2.3 (36 h). Then, the studied gels were applied once over dentin for 1 min. Next, the samples were immersed in artificial saliva containing collagenase obtained from Clostridium histolyticum for 5 days. The response variable for dentin wear was depth of dentin loss measured by profilometry and for collagen degradation was hydroxyproline determination. Data were analyzed by ANOVA followed by Tukey's test and Pearson Correlation Test (p < 0.05).ResultsGrape seed extract significantly reduced dentin wear compared to the other groups (p < 0.05). Cranberry extract and Chlorhexidine did not differ statistically and were able to reduce wear when compared to NaF and placebo treatments. The hydroxyproline analysis showed that there was no significant difference among groups for all treatments (p < 0.05). Correlation analysis showed a significant correlation between the amount of degraded DOM evaluated by profilometry and the determination of hydroxyproline.ConclusionCranberry extract was able to reduce the dentin wear and collagen degradation, likely due to the proanthocyanidin content and its action. Therefore, Cranberry could be suggested as an interesting natural-based agent to prevent dentin erosion.     

Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic

ObjectiveThe objective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth.MethodsRectangular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N = 30/group) with polished (15 μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2 Hz (N = 44) and 10 Hz (N = 36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37 °C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software.ResultsSCG parameters determined were n = 21.7 and A = 4.99 × 10⁻⁵ for 2 Hz, and n = 19.1 and A = 7.39 × 10⁻⁶ for 10 Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α₁), the stress term (α₂), and the interaction term (α₃) had estimates and 95% confidence intervals of α₁ = −3.16 (−15.1, 6.30), α₂ = −21.2 (−34.9, −9.73), and α₃ = 0.820 (−1.59, 4.02). Only α₂ was significantly different from zero.Significance(1) Cyclic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material.     

Hydrogen peroxide induces cell proliferation and apoptosis in pulp of rats after dental bleaching in vivo: Effects of the dental bleaching in pulp

ObjectiveThis study provides an in vivo evaluation of the inflammatory response, levels of cell proliferation and apoptosis, and the presence of necrosis after dental bleaching with two concentrations of hydrogen peroxide (H₂O₂).DesignWistar rats were divided into Control (placebo gel), BLUE (20% H₂O₂, 1 × 50 min), and MAXX (35% H₂O₂, 3 × 15 min) groups. At 2 and 30 days, the rats were killed (n = 10). The jaws were processed for histology analysis and PCNA and Caspase-3-cleaved immunohistochemistry, and data were submitted to the Mann-Whitney or ANOVA test (P < 0.05).ResultsAt 2 days, the MAXX group showed necrosis and the BLUE group revealed moderate inflammation on the occlusal third of the crown (P < 0.05). At 30 days, tertiary dentin had formed and there was an absence of inflammation. The level of cell proliferation was higher in the middle third of the BLUE group (P < 0.05), and cervical of MAXX at 2 days (P < 0.05), decreasing at 30 days. The apoptosis was present at 2 days, particularly in the cervical third of the crown in the bleached groups (P < 0.05), with a decrease only at 30 days in the BLUE group (P < 0.05).ConclusionsThe concentration of H₂O₂ influences effects on the pulp tissue, where a higher concentration of H₂O₂ can cause necrosis in the pulp and a prolonged effect within the apoptotic process; lower concentrations of H₂O₂ provide moderate inflammation, cell proliferation and apoptosis with a reduction of these processes over time.     

Wettability and surface morphology of eroded dentin treated with chitosan

ObjectiveTo assess the effect of chitosan, at concentrations of 2.5% and 5.0%, on the wettability of the eroded dentin, followed by analysis of surface morphology by SEM.Methods104 bovine dentin slabs were ground, polished and then immersed in 20 mL of citric acid (pH = 3.2) under continuous stirring for 2 h. Specimens were randomly divided according to the dentin substrate: sound and eroded, and then, subdivided into 4 groups (n = 10): without rewetting (control), 1% acetic acid, 2.5% chitosan and 5.0% chitosan. Then, a drop of the adhesive system Single Bond 2 (3M) was deposited onto surface of each specimen. The contact angle between dentin surface and the adhesive system was measured by using a goniometer. The other 24 specimens were subjected to analysis under SEM. Statistical analysis was performed using the normality test (Kolmogorov-Smirnov) and Analysis of Variance (ANOVA) (p > 0.05).ResultsNo differences were found between the angles produced on the eroded dentin rewetting with chitosan at the concentrations of 2.5% and 5%.ConclusionThe chitosan, regardless of the concentration used, did not influence the eroded dentin wettability. Through SEM analysis, it was found particles of chitosan deposited on the surface and within the dentinal tubules.     

Influence of TiO2 nanoparticles on the optical properties of resin composites

ObjectivesTo determine the influence of titanium dioxide (TiO₂) nanoparticle addition on the opalescence, color, translucency and fluorescence of experimental resin composites.MethodsA light curing resin matrix was made by mixing 60 wt.% Bis-GMA and 40 wt.% TEGDMA. Silane coated glass filler (mean particle size: 1.55 μm) was added in the ratio of 50 wt.% of the resin composites. A fluorescent whitening agent was also added (0.05 wt.%). TiO₂ nanoparticles (<40 nm) were added with the concentrations of 0, 0.1, 0.25 and 0.5 wt.%. Reflected and transmitted colors of 1 and 2 mm thick specimens were measured relative to the illuminant D65 with reflection spectrophotometers. Opalescence parameter (OP), color difference (ΔE*_ab), translucency parameter (TP), fluorescence parameter (FL), and fluorescence and opalescence spectra were calculated.ResultsFor the 1 mm thick specimens measured with 3 mm × 8 mm rectangular aperture, when the concentration of TiO₂ increased from 0% to 0.5%, OP increased from 2.4 to 18.0, TP decreased from 35.4 to 13.1, and fluorescence spectra remained unchanged. Color difference between these specimens was in the range of 3.4–6.6 ΔE*_ab units. OP values were significantly influenced by the thickness of the specimens and the configuration of the spectrophotometers (p < 0.05).SignificanceAddition of TiO₂ nanoparticles significantly increased the opalescence of resin composites while leaving the fluorescence spectra unchanged; however, it significantly decreased the translucency and also changed the color (p < 0.05). Resin composites with 0.1–0.25% TiO₂ nanoparticle would simulate the opalescence of human enamel.