Orthodontic resins loaded with niobium silicate particles: Impact of filler concentration on the physicochemical and biological properties.

OBJECTIVES: White spot lesions (WSL) are prevalent in patients using orthodontic appliances. The presence of ion-releasing compounds in the tooth-appliance interface may limit enamel demineralization to control WSL incidence. Thus, this study aims to evaluate the mineral formation on SiNb-containing experimental orthodontic resins and the influence of these fillers on the physicochemical and biological properties of developed materials. MATERIALS AND METHODS: The SiNb particles were synthesized via the sol-gel route and characterized by their molecular structure and morphology. Photopolymerizable orthodontic resins were produced with a 75 wt% Bis-GMA/25 wt% TEGDMA and 10 wt%, 20 wt%, or 30 wt% addition of SiNb. A control group was formulated without SiNb. These resins were tested for their degree of conversion, softening in solvent, cytotoxicity in fibroblasts, flexural strength, shear bond strength (SBS), and mineral deposition. RESULTS: The addition of 10 wt% of SiNb did not impair the conversion of monomers, cytotoxicity, and flexural strength. All groups with SiNb addition presented similar softening in solvent. The presence of these particles did not affect the bond strength between metallic brackets and enamel, with SBS values ranging from 16.41 to 18.66 MPa. The mineral deposition was observed for all groups. CONCLUSION: The use of niobium silicate as filler particles in resins may be a strategy for the adhesion of orthodontic appliances. The 10 wt% SiNb concentration resulted in a material with suitable physicochemical and biological properties while maintaining the bond strength to tooth enamel and promoting mineral deposition.

Iodonium salt incorporation in dental adhesives and its relation with degree of conversion, ultimate tensile strength, cell viability, and oxidative stress.

OBJECTIVE: The aim of this study was to evaluate the degree of conversion, ultimate tensile strength, cell viability, and oxidative stress of two different ternary initiation systems, using two photoinitiation polymerization times. METHODS: The groups investigated were camphorquinone (CQ); CQ and diphenyleneiodonium hexafluorophosphate (DPI); CQ and ethyl 4-dimethylamine benzoate (EDAB); and CQ, EDAB, and DPI, with EDAB in high and low concentration. To assess the degree of conversion (DC) and the ultimate tensile strength (UTS), a real-time Fourier transform infrared spectroscopy and a universal test machine Emic DL-500 were used, respectively. Cell viability and oxidative stress were evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), superoxide dismutase (SOD), total sulfhydryl (SH) content, and thiobarbituric acid reactive species (TBARS) formation assays. RESULTS: Slight lower cell viability was shown when DPI was associated with high concentrations of EDAB; this reduction seemed to be attenuated when lower concentrations of EDAB were used. When EDAB and DPI were associated, no oxidative damage was shown. The degree of conversion was increased in the ternary systems (CQ + EDAB lower concentration + DPI) group, which did not affect the UTS, cytotoxicity, and oxidative stress parameters. The polymerization time did not affect cell viability, total SH, and TBARS; however, a slight increase was shown in SOD levels. CLINICAL RELEVANCE: Our study emphasizes the relevance of incorporating the third element-iodonium salt-in a binary adhesive systems composed exclusively of CQ and EDAB.

Influence of an iodonium salt on the properties of dual-polymerizing self-adhesive resin cements.

STATEMENT OF PROBLEM: Dual-polymerizing self-adhesive resin cements present mechanical properties that may adversely affect the clinical performance of luted fiber-reinforced posts. PURPOSE: The purpose of this in vitro study was to evaluate the properties of dual-polymerizing self-adhesive resin cements after the addition of an onium salt. MATERIAL AND METHODS: The experimental groups were set according to the molar concentration of diphenyliodonium hexafluorphosphate (DPIHFP) (0.5, 1, and 2 mol%). The resin cements were submitted to a push-out bond strength test and assessed for flexural strength (ISO 4049/2009), degree of conversion (Fourier-transformed infrared spectroscopy), depth of polymerization, swelling coefficient, and degradation in solvent. The data were statistically analyzed by ANOVA, Tukey test, Kruskal-Wallis test, Dunn multiple comparison, and paired Student t test (α=.05). RESULTS: All the RelyX U100 groups with onium salt showed the highest degree of conversion after 24 hours and 7 days (P<.001). However, no statistical difference was found among the BisCem groups (P=.054). The addition of 0.5 mol% DPIHFP increased the push-out bond strength and microhardness of RelyX U100 and promoted less degradation after immersion in solvent. The BisCem control group did not present a statistical difference from the experimental groups in terms of bond strength; the control group and the 0.5 mol% group showed no degradation in solvent. For swelling coefficient and flexural strength, no difference was found between the BisCem groups (P=.067 and P=.173), and the RelyX U100 2 mol% group presented the lower value (P<.001 and P=.048). Depth of polymerization was not statistically different in the experimental groups for either resin cement (P=.999). CONCLUSIONS: The addition of 0.5 mol% DPIHFP improved the physical properties of dual-polymerizing self-adhesive resin cements.

Addition of ammonium-based methacrylates to an experimental dental adhesive for bonding metal brackets: Carious lesion development and bond strength after cariogenic challenge.

INTRODUCTION: In this study, we evaluated the caries inhibition and shear bond strength achieved with the addition of the antibacterial monomer [2-(Methacryloyloxy)ethyl] trimethylammonium chloride (MADQUAT) to an adhesive used to bond orthodontic brackets. METHODS: Experimental adhesives were formulated with addition of 0% (control), 5%, or 10% MADQUAT followed by measurement of the degree of conversion. These adhesives were used to lute brackets to the enamel of premolars (n = 30). Biofilm from a microcosm model was cultivated in half of the specimens under cariogenic challenge for 5 days. The brackets were subjected to a shear bond strength test followed by measurement of the internal hardness of the enamel around the brackets to calculate the integrated mineral loss. RESULTS: The addition of MADQUAT slightly increased the degree of conversion. Adhesive containing 10% MADQUAT significantly reduced the integrated mineral loss around the bracket but also resulted in the lowest values of bond strength. No effects on bond strength and integrated mineral loss were observed with the addition of 5% MADQUAT to the adhesive. The cariogenic challenge did not affect the bond strength and the failure mode. CONCLUSIONS: MADQUAT was effective to reduce the integrated mineral loss only when added to the adhesive at a concentration of 10% despite the reduction of bond strength.

Experimental self-etching HEMA-free adhesive systems: cytotoxicity and degree of conversion.

The aim of this study was to evaluate the effect of replacing 2-hydroxyethyl methacrylate (HEMA) by methacrylate surfactant monomers on the cytotoxicity and degree of conversion of two-step self-etching dentin adhesive systems. Five HEMA-free adhesive systems were tested: Bis-EMA 10, Bis-EMA 30, PEG400, PEG400UDMA, PEG1000, and a HEMA group was used as positive control. The cytotoxicity of the experimental primers, with different monomer concentrations (2 or 20 wt%), and bond resins, containing 25 wt% surfactant, was assessed using murine fibroblast cell line 3T3 and the tetrazolium assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)). The degree of conversion of the bond resins was analyzed using Fourier transform infrared spectroscopy. The data were submitted to statistical analysis using level of significance set at P < 0.05. The PEG 1000 group obtained higher cell viability in comparison with HEMA in the 2 % primer. The cell survival rate using 20 % primer showed that PEG1000 and BIS-EMA 10 were less cytotoxic than HEMA. With regard to the eluate from bond resin, the data showed that the groups BIS-EMA 10, BIS-EMA 30 and PEG400UDMA were less cytotoxic than HEMA. No statistically significant difference was found among degrees of conversion of the experimental groups and HEMA. PEG 1000, BIS-EMA 10 and 30 monomers showed the biological potential for use in new adhesive system formulations since they showed lower cytotoxicity and similar degree of conversion when compared with the HEMA-containing group.

Effect of methacrylated-based antibacterial monomer on orthodontic adhesive system properties.

INTRODUCTION: Antibacterial adhesives were developed to reduce the incidence of white spot lesions in orthodontic patients. Compounds that contain triazine are known as effective antibacterial agents. The aims of this study were to develop an experimental orthodontic adhesive containing 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAT) and to characterize it. METHODS: TAT was added in 3 concentrations (10%, 15%, and 20%) to the experimental orthodontic adhesive. Antibacterial activity was assayed by brain-heart infusion broth dilution against Streptococcus mutans. The degree of conversion was measured using Fourier transform infrared spectroscopy, and solvent degradation was evaluated by Knoop microhardness before and after immersion in ethanol for 2 hours. The shear bond strength of metal brackets bonded to bovine enamel surface was assessed. RESULTS: All experimental adhesives reduced bacterial growth. The addition of 15% and 20% TAT increased the degree of conversion compared with the control group (0%) and the 10% group. All groups showed a decrease in hardness after ethanol immersion, and there was also a decrease in the percentage of variation of Knoop hardness in the experimental adhesives containing TAT, whereas the shear bond strength increased. CONCLUSIONS: Orthodontic adhesives containing TAT are promising antibacterial materials, especially those with 15% and 20% TAT.

Replacing HEMA with alternative dimethacrylates in dental adhesive systems: evaluation of polymerization kinetics and physicochemical properties.

PURPOSE: To evaluate the mechanical and physical properties of experimental HEMA-containing and HEMA-free resin adhesives. MATERIALS AND METHODS: Experimental HEMA-free adhesives containing alternative dimethacrylates (bis-EMA 10 [B10], bis-EMA 30 [B30], PEG 400 [P400], PEG 1000 [P1000], PEG 400 UDMA [UP400]) were formulated and compared with a HEMA-containing adhesive (control). The adhesives were characterized by rheological analysis, polymerization kinetics (PK), water sorption (WS), and solubility (SL) tests. Flexural strength (FS) and flexural modulus (E) tests were performed under dry or wet conditions (distilled water or 70% ethanol solution). One-way and two-way ANOVA as well as Tukey's test were used to evaluate differences between groups (p < 0.05). RESULTS: The control group showed the lowest viscosity and was the only one with a degree of conversion lower than 50%. The control and the P1000 adhesive showed the statistically significantly highest WS (p < 0.05). The control and the UP400 adhesive showed the highest FS and E, and the dry-stored specimens showed more improved mechanical strength than did the wet-stored specimens (p < 0.05). CONCLUSION: The physicomechanical properties of some of the HEMA-free adhesives were substantially improved when compared with those of the control, indicating that they could be potential monomers for the development of HEMA-free adhesive systems.

Effects of long-term water storage on the microtensile bond strength of five experimental self-etching adhesives based on surfactants rather than HEMA.

OBJECTIVES: The purpose of this study is to evaluate the hypothesis that replacing 2-hydroxyethyl methacrylate (HEMA) for surfactant dimethacrylates (SD) does not affect the immediate and long-term microtensile bond strength (µTBS) of experimental two-step self-etch HEMA-free adhesive systems applied on dentin. MATERIALS AND METHODS: Five experimental HEMA-free two-step self-etching systems containing different SD (ethoxylated bisphenol A diglycidyl dimethacrylate (Bis-EMA 10, B10), Bis-EMA 30 (B30), poly-ethyleneglycol (400) dimethacrylate (PEG 400, P400), PEG 1000 (P1000), and PEG 400 urethane dimethacrylate (UDMA) (UP400)) and a HEMA-containing system (control) (HA) were formulated. Specimens were subjected to the µTBS test after 24 h and 6 and 12 months of storage. Data (in megapascals) were analyzed by Kruskal-Wallis and Dunn tests (α = 0.05). RESULTS: Medians of the µTBS data after 24 h of storage are: HA = 57.2(A), B10 = 26.2(BC), B30 = 24.0(C), P400 = 32.6(BC), P1000 = 37.3(B), and UP400 = 57.9(A); after 6 months are: HA = 47.9(A), B10 = 18.5(B), B30 = 7.8(C), P400 = 16.1(B), P1000 = 14.6(BC), and UP400 = 51.6(A); and after 12 months are: HA = 31.2(A), B10 = 15.2(B), B30 = 9.0(B), P400 = 9.1(B), P1000 = 13.3(B), and UP400 = 35.7(A). Between the HEMA-free groups, the adhesive system formulated with PEG 400 UDMA produced similar µTBS to the HEMA-containing group. Also, the storage of specimens decreased the µTBS (p < 0.05). CONCLUSION: Replacing HEMA for PEG 400 UDMA in an adhesive system formulation generated a satisfactory µTBS to dentin. CLINICAL RELEVANCE: Surfactant dimethacrylates have a potential use in the development of HEMA-free self-etching adhesive systems, which are more chemically stable.

Tetrahydrofuran as solvent in dental adhesives: cytotoxicity and dentin bond stability.

OBJECTIVES: The aim of this study was to investigate the cytotoxicity and 1-year dentin bond stability of solvated etch-and-rinse dental adhesives based on tetrahydrofuran (THF), acetone, or ethanol, containing water or not. MATERIALS AND METHODS: Seven primers were prepared using the following solvents: THF, acetone, ethanol, water, THF/water, acetone/water, and ethanol/water. Bovine dentin was used, and specimens for microtensile bond strength (µTBS) test were prepared. Specimens were tested after storage in distilled water for 24 h or 1 year. Cytotoxicity of the solvents was evaluated in 3T3/NIH mouse fibroblasts using a colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay after exposure for 24 h. RESULTS: No significant differences were detected among solvents after storage for 24 h, except for the water-based group, which showed the lowest µTBS values. After storage for 1 year, the THF-based adhesive system resulted in more stable bonds. Yet, THF showed an intermediate cytotoxicity when compared with the other solvents, being less toxic than phosphate monomer and similar to 2-hydroxyethyl methacrylate. CONCLUSION: THF seems to be a suitable solvent for adhesive systems. CLINICAL RELEVANCE: THF is a promising solvent that can be used to improve dentin bond stability.

Addition of zinc methacrylate in dental polymers: MMP-2 inhibition and ultimate tensile strength evaluation.

This study evaluated the effect of zinc methacrylate (ZM) on the inhibition of matrix metalloproteinase 2 (MMP-2) and the ultimate tensile strength (UTS) of an experimental polymer. Enzymes secreted from mouse gingival tissues were analyzed by gelatin zymography in buffers containing 5 mM CaCl(2) (Tris-CaCl(2)) in 50 mM Tris-HCl buffer with various concentrations of ZM (0.5, 1, 2, 4, 8, and 16 mM). The matrix metalloproteinases present in the conditioned media were characterized by immunoprecipitation. The polymer UTS evaluation was performed in eight groups with various concentrations of ZM (0, 0.5, 1, 2.5, 5, 10, 20, and 30 wt.%), in a mechanical testing machine. MMP-2 (62 kDa) was detected in the zymographic assays and inhibited by ZM in all tested concentrations. UTS data were submitted to one-way ANOVA and Tukey's test (α = 0.05), and no significant differences were observed among groups, except in the polymer containing 30% ZM, presenting a significantly lower value when compared with the control group (p < 0.05). The results suggest that ZM inhibits MMP-2 expression in all concentrations tested, while small concentrations did not affect the ultimate tensile strength of the polymer. Zinc methacrylate is a metalloproteinase inhibitor that can be copolymerized with other methacrylate monomers. Yet, the addition of ZM did not affect the resin bond strength. Thus, in vivo tests should be performed to evaluate the performance of this material.

Correlation between surface roughness and microhardness of experimental composites with varying filler concentration.

AIM: The purpose of this study was to investigate the influence of the surface roughness on the surface microhardness of experimental composites with varying filler concentration. MATERIALS AND METHODS: Experimental resin composites were formulated by mixing Bis-GMA and TEGDMA in a 50/50% weight ratio and CQ/EDAB were added to make the material photosensitive. Silanized glass particles were incorporated in the resin blend in two concentrations: C50 with 50% and C75 with 75% in weight ratio. The surface roughness and the surface microhardness measurements were determined after every three finishing procedures with #280-, #600- and #1200-grit wet sandpapers, respectively. The data were analyzed statistically by Two Way ANOVA and Tukey's test, and comparisons were conducted using the Spearman's correlation test (p > 0.05). RESULTS: The surface roughness and surface microhardness were negatively associated (r = - 0.68) and the finishing procedures of both composites resulted in harder and smoother surfaces than the initial ones. Additionally, in a smooth circumstance, the higher content of fillers has not resulted in a composite with better microhardness and smoothness. CONCLUSION: Finishing procedures decreased the surface roughness and consequently improved the surface microhardness of the composites evaluated. CLINICAL SIGNIFICANCE: Finishing and polishing procedures are effectives in reducing the surface roughness amplitude of composite materials and in improving their surface microhardness. Thus a microhardness test and any hardness evaluation must be conducted only after a properly finished and polished surface is achieved.

Effect of light attenuation through veneers on bond strength of adhesives with photoinitiator combinations.

This study aimed to evaluate the effect of light attenuation through ceramic veneers and resin cement on degree of conversion (DC), cohesive strength (CS), and microshear bond strength (µSBS) of experimental adhesive systems. Experimental etch-and-rinse and self-etch adhesives were combined with different ratios of camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiators: CQ-only; 3CQ:1TPO; 1CQ:1TPO; 1CQ:3TPO and TPO-only. Square-shaped ceramic veneer (IPS Empress Esthetic, Ivoclar Vivadent) (n = 10; 10mm long x 10mm wide x 0.5mm thick) and resin cement specimens (Variolink Esthetic LC, Ivoclar Vivadent) (n = 10; 10 mm long x 10 mm wide and 0.3 mm thick) were prepared. Light transmittance of a multiple-peak LED (Bluephase G2, Ivoclar Vivadent) was measured through restorative materials using a spectrometer (n = 5). Adhesive specimens were analyzed for DC, CS, and µSBS by light-curing the adhesive with or without (control) ceramic veneer, and with resin cement fixed to output region of the light-curing tip (n = 10). Data were submitted to ANOVA and Tukey's test (α = 0.05). Total light transmittance through the restorative materials was attenuated, and this attenuation was more evident for the violet spectrum. The DC for the TPO groups in ratios up to 1CQ:1TPO was similar to the control. 1CQ:3TPO showed lower values for CS. µSBS was reduced for all groups with light attenuation, but lower values were observed for 1CQ:3TPO and TPO-only. In conclusion, light transmission was reduced with interposed restorative materials. Adhesives combined with CQ and TPO up to 1CQ:1TPO showed greater cure efficiency and mechanical properties compared with a higher amount of TPO.

Influence of 2-hydroxyethyl methacrylate concentration on polymer network of adhesive resin.

PURPOSE: To evaluate the effect of variations in 2-hydroxyethyl methacrylate (HEMA) concentrations in an experimental comonomer blend on degree of conversion, water sorption, solubility, and ultimate tensile strength of adhesive resin. MATERIALS AND METHODS: The effect of HEMA content (0, 15, 30, and 50%wt - control, G15, G30, and G50 groups, respectively) was tested in an experimental comonomer blend of bis-GMA, bis-EMA, TEG-DMA, and HEMA. The degree of conversion, polymerization rate, ultimate tensile strength, water sorption, and solubility of the adhesive resin blends were determined. RESULTS: At 40 s of light activation time, groups G30 and G50 showed a decrease of 30% and 61%, respectively, in degree of conversion compared to control. Water sorption and solubility differed for all groups, and was statistically higher in G50. For ultimate tensile strength, the control and G15 groups showed statistically higher values than the other groups (p < 0.05). CONCLUSION: Higher HEMA content increases dental adhesive resin degradation.

Inhibition of the activity of matrix metalloproteinase 2 by triethylene glycol dimethacrylate.

The aim of this study was to evaluate the effect of different concentrations of triethylene glycol dimethacrylate (TEGDMA) on the inhibition of matrix metalloproteinase 2 (MMP-2). Mouse gingival explants were cultured overnight in DMEM and the expression of secreted enzymes was analyzed by gelatin zymography in buffers containing 5 mM CaCl(2) (Tris-CaCl(2)) in 50 mM Tris-HCl buffer with the addition of TEGDMA at different concentrations (0.62%, 1.25%, 2.5%, or 5.0% (v/v)). The gelatinolytic proteinase present in the conditioned media was characterized as matrix metalloproteinase by means of specific chemical inhibition. The matrix metalloproteinases present in the conditioned media were characterized as MMP-2 by immunoprecipitation. The eletrophoretic bands were scanned and the transmittance values were analyzed. Data was plotted and submitted to linear regression to investigate MMP-2 inhibition as a function of TEGDMA concentration. Three major bands were detected in the zymographic assays. These bands were characterized as MMP-2. Zymogene (72 kDa), intermediate (66 kDa) and active forms of MMP-2 (62 kDa) were inhibited by TEGDMA in a dose-dependent way. These findings suggest that TEGDMA could inhibit MMP-2 expression even at small concentrations.

Niobium silicate particles as bioactive fillers for composite resins.

OBJECTIVES: This study aimed to evaluate the influence of niobium silicate (SiNb) particles in the physicomechanical and biological properties of an experimental composite resin. METHODS: The SiNb particles were incorporated (50 wt%) into a polymeric matrix formulated with 70 wt% Bisphenol A-Glycidyl Methacrylate and 30 wt% Triethylene Glycol Dimethacrylate to formulate an experimental composite resin. A control group was formulated with barium silicate glass (SiBa) as filler for the same polymeric matrix. The composite resins were tested for their refractive index, polymerization kinetics, flexural strength, radiopacity, softening in solvent, pH, cytotoxicity and mineral deposition. RESULTS: The SiBa group presented refractive index results between 1.50 and 1.52 and the SiNb between 1.43-1.45. No statistically significant difference in the degree of conversion, flexural strength, and softening in solvent was observed between different groups. Radiopacity was lower for SiNb, while the addition of these particles increased cell viability. The pH was increased for all groups after immersion. The mineral deposition analysis resulted in increased deposition above specimens after the immersion in SBF. SIGNIFICANCE: Niobium silicate particles may be used as an alternative inorganic filler to achieve an adequate balance between physical-chemical and biological properties for the development of bioactive composite resins.

Incorporation of amoxicillin-loaded microspheres in mineral trioxide aggregate cement: an in vitro study.

OBJECTIVES: In this study, we investigated the potential of amoxicillin-loaded polymeric microspheres to be delivered to tooth root infection sites via a bioactive reparative cement. MATERIALS AND METHODS: Amoxicillin-loaded microspheres were synthesized by a spray-dray method and incorporated at 2.5% and 5% into a mineral trioxide aggregate cement clinically used to induce a mineralized barrier at the root tip of young permanent teeth with incomplete root development and necrotic pulp. The formulations were modified in liquid:powder ratios and in composition by the microspheres. The optimized formulations were evaluated in vitro for physical and mechanical eligibility. The morphology of microspheres was observed under scanning electron microscopy. RESULTS: The optimized cement formulation containing microspheres at 5% exhibited a delayed-release response and maintained its fundamental functional properties. When mixed with amoxicillin-loaded microspheres, the setting times of both test materials significantly increased. The diametral tensile strength of cement containing microspheres at 5% was similar to control. However, phytic acid had no effect on this outcome (p > 0.05). When mixed with modified liquid:powder ratio, the setting time was significantly longer than that original liquid:powder ratio (p < 0.05). CONCLUSIONS: Lack of optimal concentrations of antibiotics at anatomical sites of the dental tissues is a hallmark of recurrent endodontic infections. Therefore, targeting the controlled release of broad-spectrum antibiotics may improve the therapeutic outcomes of current treatments. Overall, these results indicate that the carry of amoxicillin by microspheres could provide an alternative strategy for the local delivery of antibiotics for the management of tooth infections.

Addition of phosphates and chlorhexidine to resin-modified MTA materials.

To evaluate the properties of experimental mineral trioxide aggregate (MTA) resin-modified materials for root-end filling procedures, varying their compositions regarding the addition of hydroxiapatite (HA) or dicalcium phosphate dihydrate, with or without chlorhexidine digluconate. White MTA (Angelus, Londrina, Brazil) was used as a reference material. Degree of conversion (DC) was evaluated by Fourier transformed infrared (FTIr) spectroscopy (n = 5). Flowability (n = 3) and radiopacity (n = 3) were evaluated following ISO 6876:2001 methods. For splitting tensile strength analysis, cylindrical samples (n = 10) were subjected to compressive load using a universal testing machine (Instron Corporation, Norwood, MA). Water sorption and solubility tests were performed according to ISO 4049:2009 methods. Calcium ion release and pH analysis (n = 10) were evaluated using a pH meter (Orion, Watsonville, CA). Cytotoxicity (n = 8) of materials extracts was evaluated as cell viability percentage. Statistical analysis was performed using Kolmogorov-Smirnov for normal distribution and data was subjected to one-way ANOVA and Tukey test (α = 0.05). Addition of chlorhexidine digluconate reduced DC mean values for experimental materials (<50%). White MTA demonstrated lower flowability (5.3 mm) and higher radiopacity (9.8 mm Al), splitting tensile strength (9.1 MPa), solubility (8.2 µg/mm3 ), calcium ion release (~26.5 ppm), cytotoxicity (55.2%), and pH mean values (10.8), when compared to experimental materials. All groups demonstrated a decrease in calcium release (<85%) and pH (<13%). Formulation containing HA demonstrated similar pH values after 28 days when compared to white MTA. Evaluated experimental resin-modified MTA based materials without chlorhexidine digluconate showed satisfactory results for all physico-chemical properties tested and cytotoxicity. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2195-2201, 2019.

Synthesis of phosphate monomers and bonding to dentin: esterification methods and use of phosphorus pentoxide.

OBJECTIVES: The aim of this study was to synthesize an acidic monomer using an alternative synthetic pathway and to evaluate the influence of the acidic monomer concentration on the microtensile bond strength to dentin. METHODS: The intermediary 5-hydroxypentyl methacrylate (HPMA) was synthesized through methacrylic acid esterification with 1,5-pentanediol, catalyzed by p-toluenesulfonic acid. To displace the reaction balance, the water generated by esterification was removed by three different methods: anhydrous sodium sulfate; molecular sieves or azeotropic distillation. In the next step, a phosphorus pentoxide (4.82 mmol) slurry was formed in cold acetone and 29 mmol of HPMA was slowly added by funnel addition. After the reaction ended, solvent was evaporated and the product was characterized by 1HNMR and FTIR. The phosphate monomer was introduced in a self-etch primer at concentrations of 0, 15, 30, 50, 70 and 100 wt%. Clearfil SE Bond was used as commercial reference. Microtensile bond strength to dentin was evaluated 24h after the bonding procedures, followed by fracture analysis (n=20). Data was submitted to ANOVA and Tukey's post hoc test. RESULTS: The highest yield was obtained (62%) when azeotropic distillation was used, while the reaction with molecular sieves was not feasible. The phosphoric moiety attachment to the monomer was successfully performed with a quantitative yield that reached around 100%. The acidic monomer concentration significantly affected the bond strength and the highest mean (55.1+/-12.8 MPa) was obtained when 50% of acidic monomer was used. CONCLUSION: The synthesis pathways described in the present study appear to be a viable alternative for developing phosphate monomers.

Influence of water concentration in an experimental self-etching primer on the bond strength to dentin.

PURPOSE: To investigate the influence of different water concentrations in the solvents of self-etching primers on microtensile bond strength (LTBS) of an experimental adhesive system. MATERIALS AND METHODS: Five experimental self-etching primers with 0, 5, 10, 20 and 40 (wt%) water as solvent were formulated. An experimental adhesive resin (AD-50) was also synthesized to create one experimental self-etching adhesive system. Clearfil SE Bond (CSEB) was used as the commercial reference. Sixty bovine incisors were randomly separated into 6 groups. Buccal enamel was removed to expose the superficial coronal dentin; this surface was polished wet to create a standardized smear layer. After rinsing, water was removed, leaving the surface visibly dried. The dentin surfaces were etched with primer and air dried, adhesive resin was applied and photoactivated, then the composite resin restoration was placed. After storage for 24 h, the specimens were sectioned with a cooled diamond saw at low speed. Microtensile bond strength was measured and data were analyzed with one-way ANOVA/Tukey's test (alpha = 0.05). RESULTS: ANOVA showed that primer composition was a significant factor for bond strength. There was no significant difference in bond strengths between the primers with a water concentration of 40% (53.9 +/- 12.7 MPa), 20% (51.1 +/- 11.5 MPa, and 10% (47.5 +/- 11.4 MPa), and CSEB (50.7 +/- 9.8 MPa). The groups with 5% (38.6 +/- 12.9 MPa) and 0% (31.5 +/- 7.5 MPa) water presented similar bond strengths amongst themselves but were statistically significantly lower than that of the other groups. CONCLUSION: The water concentration in the primer solvent exercises a significant influence on the bond strength of this experimental self-etching adhesive system.

Bond Strength of Experimental Root Canal Sealers Based on MTA and Butyl Ethylene Glycol Disalicylate.

This study investigated the bond strength of two experimental root canal sealers based on MTA and butyl ethylene glycol disalicylate: MTAe and MTAe-HA. The reference materials used for comparison were AH Plus and MTA Fillapex. Twenty human upper incisors were selected and one 1 mm slice was obtained from the cervical third of each root. On the coronal surface of each slice, four 0.9 mm wide holes were drilled through the dentine. Standardized irrigation was performed and holes were filled with one of the four tested sealers: AH Plus, MTA Fillapex, MTAe, and MTAe-HA. The filled slices were stored in a PBS solution (pH 7.2) for 7 days at 37 °C. A push-out assessment was performed with a 0.7 mm plunger tip. Load was applied at a crosshead speed of 0.5 mm/min until sealer displacement. The results were expressed in MPa. The Kruskal-Wallis test was applied to assess the effect of each sealer on the push-out bond strength. Mann-Whitney with Bonferroni correction was used to isolate the differences. The alpha-type error was set at 0.05. Significant differences among medians values obtained by materials were observed (p<0.001). AH Plus displayed the highest value of bond strength (p<0.001). In contrast, MTA Fillapex presented the lowest bond strength among all tested sealers (p<0.001). Experimental sealers showed intermediary bond strength values, with no statistical differences between them (p>0.05). In conclusion, experimental root canal sealers presented suitable bond strength outcomes when compared to MTA Fillapex.