Experimental Resin Research Articles

Anti-demineralizing protective effects on enamel identified in experimental and commercial restorative materials with functional fillers

The aim of this study was to investigate whether experimental and commercial dental restorative materials with functional fillers can exert a protective anti-demineralizing effect on enamel that is not immediately adjacent to the restoration. Four experimental resin composites with bioactive glass and three commercial restorative materials were investigated. Enamel blocks were incubated in a lactic acid solution (pH = 4.0) at a standardized distance (5 mm) from cured specimens of restorative materials. The lactic acid solution was replenished every 4 days up to a total of 32 days. Surfaces of enamel blocks were periodically evaluated by Knoop microhardness measurements and scanning electron microscopy. The protective effect of restorative materials against acid was identified as enamel microhardness remaining unchanged for a certain number of 4-day acid addition cycles. Additionally, the pH of the immersion medium was measured. While enamel microhardness in the control group was maintained for 1 acid addition cycle (4 days), restorative materials postponed enamel softening for 2–5 cycles (8–20 days). The materials capable of exerting a stronger alkalizing effect provided longer-lasting enamel protection. The protective and alkalizing effects of experimental composites improved with higher amounts of bioactive glass and were better for conventional bioactive glass 45S5 compared to a fluoride-containing bioactive glass. Scanning electron micrographs evidenced the protective effect of restorative materials by showing a delayed appearance of an etching pattern on the enamel surface. A remotely-acting anti-demineralizing protective effect on enamel was identified in experimental composites functionalized with two types of bioactive glass, as well as in three commercial ion-releasing restorative materials.

Toughening and polymerization stress control in composites using thiourethane-treated fillers

Filler particle functionalization with thiourethane oligomers has been shown to increase fracture toughness and decrease polymerization stress in dental composites, though the mechanism is poorly understood. The aim of this study was to systematically characterize the effect of the type of filler surface functionalization on the physicochemical properties of experimental resin composites containing fillers of different size and volume fraction. Barium glass fillers (1, 3 and 10 µm) were functionalized with 2 wt% thiourethane-silane (TU-Sil) synthesized de novo and characterized by thermogravimetric analysis. Fillers treated with 3-(Trimethoxysilyl)propyl methacrylate (MA-Sil) and with no surface treatment (No-Sil) served as controls. Fillers (50, 60 and 70 wt%) were incorporated into BisGMA-UDMA-TEGDMA (5:3:2) containing camphorquinone/ethyl-4-dimethylaminobenzoate (0.2/0.8 wt%) and 0.2 wt% di-tert-butyl hydroxytoluene. The functionalized particles were characterized by thermogravimetric analysis and a representative group was tagged with methacrylated rhodamine B and analyzed by confocal laser scanning microscopy. Polymerization kinetics were assessed by near-IR spectroscopy. Polymerization stress was tested in a cantilever system, and fracture toughness was assessed with single edge-notched beams. Fracture surfaces were characterized by SEM. Data were analyzed with ANOVA/Tukey's test (α = 0.05). The grafting of thiourethane oligomer onto the surface of the filler particles led to reductions in polymerization stress ranging between 41 and 54%, without affecting the viscosity of the composite. Fracture toughness increased on average by 35% for composites with the experimental fillers compared with the traditional methacrylate-silanized groups. SEM and confocal analyses demonstrate that the coverage of the filler surface was not homogeneous and varied with the size of the filler. The average silane layer for the 1 µm particle functionalized with the thiourethane was 206 nm, much thicker than reported for traditional silanes. In summary, this study systematically characterized the silane layer and established structure–property relationships for methacrylate and thiourethane silane-containing materials. The results demonstrate that significant stress reductions and fracture toughness increases are obtained by judiciously tailoring the organic–inorganic interface in dental composites.

Isobornyl methacrylate as diluent co‐monomer on physical‐mechanical properties of dental resin composites

AbstractThe aim of this study was to evaluate the effects of isobornyl methacrylate (IBOMA) as a diluent co‐monomer on the physical properties of experimental resins. Blends of bisphenol glycidyl methacrylate (Bis‐GMA) were formulated with triethylene glycol dimethacrylate (TEGDMA) and IBOMA in different wt%. The degree of conversion, flexural strength, elastic modulus, and ultimate tensile strength were determined. Immediate and 24 h volumetric shrinkage were calculated. Data were submitted to ANOVA and Tukey's tests (α = 0.05). Blends of Bis‐GMA and IBOMA showed the lowest ultimate tensile strength, flexural strength, elastic modulus, degree of conversion, and immediate and 24 h volumetric shrinkage results. However, when IBOMA was used together with TEGDMA in blends of Bis‐GMA, the resin composites showed best curing performance and high physical‐mechanical properties. Thus, the IBOMA is as diluent co‐monomer that can be used in dental resin composites to reduce the volumetric shrinkage.

The physical properties and anticariogenic effect of experimental resin cement containing ursolic acid.

The aim was to evaluate the physical properties and anti-bacterial activity of resin cement containing ursolic acid (UA) and determine the optimal concentration of UA. Five types of experimental resin cement were prepared according to UA concentration (0, 0.1, 0.5, 1.0, and 2.0 wt%). Flexural strength, film thickness and in vitro cytotoxicity were measured to confirm whether the resin was appropriate under International Organization for Standardization (ISO) criteria. Fifty extracted human molars were prepared, and indirect resin inlays were cemented with experimental resins. Acid-resistant nail varnish was applied, except for the 2-mm area around the restoration. Artificial caries were induced for 6 days through Streptococcus (S.) mutans (ATCC25175). Quantitative light-induced fluorescence (QLF) was used to evaluate the caries progression. One-way analysis of variance (ANOVA) followed by the Dunnett correction were used to statistically analyze the data. In all groups, the physical property of flexural strength, film thickness, and cytotoxicity were satisfied for ISO criteria (p > 0.05). On ∆F (-%) and ∆Q (-%⋅Px) values as QLF parameters, there was a tendency of being lower in groups of resin cement containing higher concentration of UA. Resin cement containing UA of greater than or equal to 0.5% significantly inhibited caries in the area around restoration (p < 0.05). There was no difference between the groups containing UA of greater than or equal to 0.5%. Resin cement containing 0.5% or more UA showed anti-carious effect in the limited range of 2% and satisfied the ISO criteria for flexural strength, film thickness and cytotoxicity.

Physical and Mechanical Properties of Resins Blends Containing a Monomethacrylate with Low-polymerization Shrinkage.

Objectives The aim of this study was to evaluate the Knoop hardness (KH), cross-link density (CLD), water sorption (WS), water solubility (WSB), and volumetric shrinkage (VS) of experimental resins blends containing a monomethacrylate with low-polymerization shrinkage. Materials and Methods A blend of bisphenol glycidyl methacrylate (BisGMA) as base monomer was formulated with (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA), Bis-GMA/isobornyl methacrylate (IBOMA), or Bis-GMA/TEGDMA/IBOMA in different concentrations (40, 50, or 60 wt%). The camphorquinone (CQ)/2-(dimethylamino) ethyl methacrylate (DMAEMA) was used as the photoinitiator system. The KH and CLD were measured at the top surface using an indenter. For WS and WSB, the volume of the samples was calculated in mm 3 . The samples were transferred to desiccators until a constant mass was obtained (m1) and were subsequently immersed in distilled water until no alteration in mass was detected (m2). The samples were reconditioned to constant mass in desiccators (m3). WS and WSB were determined using the equations m2 − m3/V and m1 − m3/V, respectively. VS results were calculated with the density parameters before and after curing. Statistical Analysis Data were submitted to ANOVA and Tukey’s test (α = 0.05). Results The resins containing IBOMA showed lower VS results. TEGDMA 40% and TEGDMA/IBOMA 20/20 wt% showed higher KH values. The IBOMA groups showed lower CLD, while TEGDMA groups had higher values of CLD. The BisGMA/TEGDMA resin presented the highest values of WS, and for WSB, all groups showed no significant differences among themselves. Conclusion The monomethacrylate with low-polymerization shrinkage IBOMA used alone or in combination with TEGDMA may decrease VS, WS, and CLD values.

Study on the water and wear resistance of experimental resin composites containing filler treated with polymerizable benzene group silane coupling agent

Study on the water and wear resistance of experimental resin composites containing filler treated with polymerizable benzene group silane coupling agent

Mechanical Properties of Nanohybrid Resin Composites Containing Various Mass Fractions of Modified Zirconia Particles.

PurposeThe aim of this study was to investigate the effect of various mass fractions of 10-methacry-loyloxydecyl dihydrogen phosphate (MDP)-conditioned or unconditioned zirconia nano- or micro-particles with different initiator systems on the mechanical properties of nanohybrid resin composites.MethodsBoth light-cured (L) and dual-cured (D) resin composites were prepared. When the mass fraction of the nano- or micro-zirconia fillers reached 55 wt%, resin composites were equipped with dual-cured initiator systems. We measured the three-point bending-strength, elastic modulus, Weibull modulus and translucency parameter of the nanohybrid resin composites containing various mass fractions of MDP-conditioned or unconditioned zirconia nano- or micro-particles (0%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and 55 wt%). A Cell Counting Kit (CCK)-8 was used to test the cell cytotoxicity of the experimental resin composites. The zirconia nano- or micro-particles with MDP-conditioning or not were characterized by transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS).ResultsResin composites containing 5–20 wt% MDP-conditioned or unconditioned nano-zirconia fillers exhibited better three-point bending-strength than the control group without zirconia fillers. Nano- or micro-zirconia fillers decreased the translucence of the nanohybrid resin composites. According to the cytotoxicity classification, all of the nano- or micro-zirconia fillers containing experimental resin composites were considered to have no significant cell cytotoxicity. The FTIR spectra of the conditioned nano- or micro-fillers showed new absorption bands at 1719 cm−1 and 1637 cm−1, indicating the successful combination of MDP and zirconia particles. The XPS analysis measured Zr–O–P peak area on MDP-conditioned nano- and micro-zirconia fillers at 39.91% and 34.89%, respectively.ConclusionNano-zirconia filler improved the mechanical properties of nanohybrid resin composites, but cannot be the main filler to replace silica filler. The experimental dual-cured composites can be resin cements with better opacity effects and a low viscosity.

Development and properties of endodontic resin sealers with natural oils

ObjectivesTo synthesize and evaluate the physicochemical, antimicrobial, and cytocompatibility properties of experimental resin-based endodontic sealers containing butia or copaiba natural oils. MethodsExperimental groups contained butia (Butia capitata) at 0.5 % (B0.5), 1 % (B1), 2 % (B2), and copaiba (Copaifera spp.) at 0.5 % (C0.5), 1 % (C1), and 2 % (C2). The control group contained no added oils (experimental material, EM) and the commercial group was a methacrylate-based resin material (RealSeal™, SybronEndo Corporation, Orange, CA, USA). Degree of conversion, film thickness, setting time, flow, water sorption and solubility, and radiopacity were measured. Meanwhile, antimicrobial (modified direct contact test) and cytotoxicity assays of the experimental groups and controls were performed. One-way ANOVA was used to determine the effect of the independent variable (material) on the degree of conversion, film thickness, radiopacity, flow, setting time, water sorption and solubility, and cytotoxicity. For antimicrobial assays, data were analyzed using two-way ANOVA and Ŝidák’s test. ResultsThe experimental groups containing natural oils showed higher values of degree of conversion, and lowest water sorption and solubility. EM, B0.5, B1, B2, and RS showed similar film thicknesses. The flow values were statistically similar in all groups. The experimental groups showed adequate cell compatibility. Copaiba oil at 2% increased the antimicrobial effect after 1 and 24 h (p < 0.05). The incorporation of butia or copaiba resulted in a slight modification in some physicochemical properties of the experimental resin sealers. ConclusionNovel resin sealers containing natural oils are a promising alternative for endodontics, because of their good physicochemical properties, antimicrobial effects, and cytocompatibility when compared to a commercially available sealer. Clinical significanceEndodontic sealers containing butia or copaiba had satisfactory cytocompatibility, antimicrobial effects, and adequate physicochemical properties.

Surface and mechanical properties of adhesives with calcium phosphates challenged to different storage media

Aim: To evaluate the behavior of experimental dental adhesiveswith hydroxyapatite (HAp), alpha-tricalcium phosphate (α-TCP)or octacalcium phosphate (OCP) after storing them in threedifferent media: dry storage, distilled water, or lactic acid.Methods: An experimental adhesive resin was formulated withbisphenol A glycol dimethacrylate, 2-hydroxyethyl methacrylate,and photoiniciator/co-initiator system. HAp (GHAp), α-TCP(Gα-TCP), or OCP (GOCP) were added to the adhesive resin at 2wt.%, and one group remained without calcium phosphates tobe used as a control (GCtrl). The adhesives were evaluated forsurface roughness, scanning electron microscopy (SEM), andultimate tensile strength (UTS) after storing in distilled water(pH=5.8), lactic acid (pH=4) or dry medium. Results: The initialsurface roughness was not different among groups (p&gt;0.05).GHAp showed increased values after immersion in water(p&lt;0.05) or lactic acid (p&lt;0.05). SEM analysis showed a surfacevariation of the filled adhesives, mainly for Gα-TCP and GHAp. GHApshowed the highest UTS in dry medium (p&lt;0.05), and its valuedecreased after lactic acid storage (p&lt;0.05). Conclusions:The findings of this study showed that HAp, OCP, and α-TCPaffected the physical behavior of the experimental adhesiveresins in different ways. HAp was the calcium phosphatethat most adversely affected the surface roughness and themechanical property of the material, mainly when exposed toan acid medium.

Experimental self-etching resin infiltrants on the treatment of simulated carious white spot lesions

ObjectivesTo evaluate the penetration depth (μm) of experimental resin infiltrants containing different percentages of triethylene glycol dimethacrylate (TEGDMA) and phosphoric acid 2-hydroxyethyl methacrylate ester (PAM) in artificial carious white spot lesions (WSL). Methods: WSL were produced in 65 bovine flat enamel specimens by pH cycling protocol, which were treated with either Icon (control) or experimental acidic infiltrants based on different percentages of TEGDMA and PAM monomers (acidic), and their association or not with previous acid-etching with phosphoric acid. Ten readings using Confocal Laser Scanning Microscopy were conducted on each specimen and the penetration depth was calculated from the surface until the deepest point with the fluorescent dye Rhodamine B (0.02 mg/mL). The pH and the viscosity of the experimental infiltrants were also tested. Data were statistically analyzed with two-way ANOVA and Tukey tests (α < 0.05). Results: The material factor and the interaction material*acid-etching were statistically significant. The lowest penetration depth was observed for the samples treated with the commercial infiltrant after etching with 15% hydrochloric acid. When specimens were pre-treated with PA, highest penetration was seen for specimens treated with 100% TEGDMA, which differed from all other groups. The lowest penetration was seen for those treated with 50:50 TEGDMA:PAM infiltrants. When specimens were not previously etched, highest penetration was seen for Icon, which differed only from those treated with 25% TEGDMA 75% PAM, where the lowest values were seen. The values of viscosity increased and the pH decreased with the addition of PAM in the infiltrant formulations. Conclusion: the association between TEGDMA and PAM seems to allow similar infiltration depth reached by Icon infiltrant without acid etching the enamel surface.

Physicochemical Properties of Experimental Resin-Based Materials Containing Fluoridated Calcium Phosphates

The aim of this study was to evaluate the physicochemical properties of experimental adhesives containing tailored fluoridated calcium phosphate fillers. Five experimental resins were formulated, one contained no calcium phosphate filler (Control) and the other four resins contained 40wt% of calcium phosphate fillers doped with increasing concentration of fluoride: adhesives CaP (no fluoride), CaP-2F (2wt% F), CaP-4F (4wt% F) and CaP-8F (8wt% F). Resin specimens were prepared for three-point bending test to evaluate the elastic modulus (E) and flexural strength (FS) at 24h and after 2 months of water storage. Disk-shaped specimens were prepared to analyze the water sorption (Ws) according to ISO 4049. The degree of conversion (DC) of the tested resins was also assessed through FTIR. Statistical analysis was performed with ANOVA and Tukey’s test (p 0.05) compared to the filler-free resin. However, these same experimental resins showed the highest E after water storage. All resins had a significant reduction of the FS after water storage (p<0.001), but at lower percentage rate for those experimental resins containing fluoride-free CaP or fluoride-doped CaP-2F.. These latter experimental resins achieved similar Ws to control filler-free resin. Conversely, those resins containing 4wt% or and 8wt% fluoride-doped CaP promoted had a significant Ws increase (p<0.05). In conclusion, the incorporation of calcium phosphate particles without fluoride and or with 2wt% fluoride may represent be a promising strategy to generate adhesive resins with specific physicochemical properties. Fluoride incorporation in CaP fillers for dental resin adhesive should be performed at low concentrations in order to avoid excessive water sorption and decrease of polymerization.

FGF-2 release and bonding/physical properties of 4-META/MMA-based adhesive resins incorporating small FGF-2-loaded polymer particles

ObjectivesNon-biodegradable particles comprising hydroxyethyl methacrylate (HEMA) and trimethylolpropane trimethacrylate (TMPT) have been reported as useful carriers for fibroblast growth factor-2 (FGF-2). They have also been successfully incorporated into the 4-[2-(methacryloyloxy)ethoxycarbonyl]phthalic anhydride/methyl methacrylate-tri-n-butyl borane (4-META/MMA-TBB) resin to promote tissue regeneration. However, smaller particles are required to obtain restorative materials acceptable for clinical use. The aim of this study was to investigate the ability of the 4-META/MMA-TBB resin that comprises small FGF-2-loaded particles to release FGF-2 and promote cell proliferation. In addition, the bonding and physical properties of the experimental resin were evaluated. MethodsThe small particles loaded with FGF-2 were newly fabricated and incorporated into the commercial 4-META/MMA-TBB resin. Release profiles of FGF-2 from the experimental resins were assessed, and the cell proliferation cultured with the eluate was evaluated. The bonding and physical properties of the resins were evaluated using shear bond strength and three-point bending tests, and by measuring the curing time, water absorption, and water dissolution. ResultsSustained release of FGF-2 from the experimental resins for two weeks was observed, and the released FGF-2 was demonstrated to promote cell proliferation. All bonding and physical properties of the 4-META/MMA-TBB resins were found acceptable for clinical use. SignificanceThe small FGF-2-loaded particles incorporated into the 4-META/MMA-TBB resin had the same abilities to release FGF-2 and proliferate cells, as those exhibited by the conventionally sized particles. In addition, there were no adverse influences on bonding and physical properties, suggesting that the bioactive adhesive resin was acceptable for clinical use.

Effect of the addition of functionalized TiO2 nanotubes and nanoparticles on properties of experimental resin composites

ObjectiveTo evaluate the influence of the addition of functionalized and non-functionalized TiO2 nanostructures on properties of a resin composite. MethodsTiO2 nanostructures were synthesized and functionalized, using 3-(aminopropyl)triethoxysilane (APTMS) and 3-(trimethoxysilyl)propyl methacrylate (TSMPM). Characterizations were performed with XRD, EDS, TEM, and TGA. Resin composites containing Bis-GMA/TEGDMA, CQ, DABE, and barium-aluminum silicate glass were produced according to TiO2 nanostructure (nanotube or nanoparticle), concentration (0.3 or 0.9 wt%), and functionalization (APTMS or TSMPM). The resin composite without nanostructures was used as control. The amount of fillers was kept constant at 78.3 wt% for all materials. The degree of conversion (DC - at 0 h and 24 h), maximum polymerization rate (Rpmax), and Knoop microhardness (KHN before and after ethanol softening) were evaluated. Data were analyzed with two-way ANOVA with repeated measures and Tukey's HSD (α = 0.05). ResultsTGA results demonstrated that functionalizations were effective for both nanostructures. For DC, resin composites, time and interaction effect were significant (p < 0.001). Higher DC was found for 0.3-wt%-functionalized-nanotubes at 24 h. For nanoparticles, only 0.9-wt%-non-functionalized and 0.3-wt%-APTMS-functionalized showed DC similar to the control and all other groups showed higher DC (p < 0.05). Rpmax was higher for 0.3-wt%-APTMS-nanotubes, which corresponded to higher DC after 24 h. The lowest Rpmax occurred for 0.9-wt%-TSMPM-nanotubes, which showed smaller DC at 0 h. For KHN, resin composites, ethanol softening and interaction effect were significant (p < 0.001). KHN decreased after ethanol softening all groups, except for 0.3-wt%-TSMPM-nanotubes, 0.9-wt%-TSMPM-nanotubes, and 0.3-wt%-non-functionalized-nanoparticles. ConclusionThe resin with 0.3-wt%-TSMPM-nanotubes showed higher DC after 24 h, while being the most stable material after the ethanol softening. SignificanceThe addition of functionalized TiO2 nanostructures in resin-based materials may improve the properties of the material.

Effect of Filler Content and Waiting time Before Light-Curing on Mechanical Properties of Dual-Cured Cement

Objective:: To investigate the effect of filler content and the time spent before light-curing on mechanical properties of dual-cured cement. Methods:: Experimental dual-cured resin cements were formulated with 60, 65 or 68wt% of filler. The viscosity of experimental cement was measured using a digital viscometer. Bar-shaped specimens (25 x 2 x 2 mm) were fabricated, while the light-curing was started immediately or 5 minutes after the insertion of cement into the mold (n = 7). A three-point bending test was performed and the values of flexural strength and elastic modulus were measured. The Vickers hardness of fractured specimens was measured on the surface of the cement. Data from viscosity were submitted to oneway ANOVA, while the data from mechanical properties were analyzed by two-way ANOVA. All pair-wise comparisons were performed using Tukey’s test (α = 0.05). Results:: The experimental cement with 68wt% of filler showed the highest viscosity and those with 60wt% showed the the lowest viscosity. Irrespective of the time spent before light-curing, the cement with 65wt% of filler presented the highest values of flexural strength and elastic modulus. The addition of 60wt% of filler resulted in the lowest elastic modulus, while 68wt% of filler resulted in lowest flexural strength. Regarding the hardness, the cement with 68wt% of filler showed the highest values, while there was no difference between 60 and 65wt% of filler. Conclusion:: Filler content affected the mechanical properties of the experimental cement and this effect did not depend on the waiting time before the light-curing procedure.

Polymerization and shrinkage stress formation of experimental resin composites doped with nano- vs. micron-sized bioactive glasses.

This study investigated the effect of adding bioactive glass 45S5 (BG) of different particle sizes to dental composite on resin polymerization and shrinkage stress formation. Commercial flowable composite was mixed with either 15 wt% BG fillers (nanometric, micrometric, or hybrid BG) or inert barium glass. Real-time linear polymerization shrinkage and shrinkage stress were recorded, and the degree of conversion was measured using FTIR spectroscopy. The commercial (unmodified) composite developed significantly higher linear shrinkage and shrinkage stress than the groups with 15 wt% added inert or BG fillers. After adding inert barium glass, the composite showed significantly higher linear shrinkage than when micrometric BG was added. The addition of bioactive or inert glass fillers did not affect the degree of conversion. Shrinkage stress can be reduced by adding inert or bioactive fillers (nano- and/or microparticulate BG) without affecting monomer conversion.

Evaluation of new coinitiators of camphorquinone useful in the radical photopolymerization of dental monomers

This work reports the design and synthesis of two new monomers with tertiary amines and four methacrylic (MBTTM) or acrylic (MBTTA) terminal unsaturations, and their evaluation as coinitiators in the photopolymerization of monomers useful in dentistry. Both monomers were characterized by FT-IR, 1H NMR, and UV–vis spectroscopies. Experimental Bis-GMA/TEGDMA or UDMA/TEGDMA resins were formulated using camphorquinone as the photoinitiator and the MBTTM or MBTTA compounds as coinitiators. As control, resins using EDAB as coinitiator were formulated. The photopolymerizable resins formulated using the new coinitiators achieved double bond conversion values close to 40% in 30 s. Regarding polymerization rate, experimental resins formulated with MBTTM or MBTTA had lower values. The flexural strength of the experimental BisGMA/TEGDMA resins did not have statistically significant differences with the control group (p > 0.05). On the other hand, the experimental resins formulated with UDMA/TEGDMA presented higher flexural strength and elastic modulus. Finally, the cell viability test showed that none of the resins formulated with MBTTM or MBTTA as coinitiators were cytotoxic. Due to their characteristics, MBTTM and MBTTA monomers are potentially useful as coinitiators in the formulation of photopolymerizable materials for dental use.

Does Pigment Incorporation into Regular Composite Resins for Posterior Buildups Alter Their Bond Strength?

Posterior build-ups are auxiliary devices to orthodontic treatment which are made with resin-based or glass ionomer composites. Their removal requires care to protect the tooth surface, therefore, pigmented materials are preferred for a better visualization. This study proposed a pigmentation experimental technique of a regular composite resin, evaluating the microshear bond strength test (µ-SBT) of this experimental pigmented resin and comparing with a blue-colored polyacid-modified composite resin, used for posterior buildups. Forty-eight buccal and lingual surfaces of human teeth were used and randomly divided into 4 groups (n=12). The groups were divided into: C (control), regular composite resin; P, regular composite resin pigmented; UBL, Ultra Band Lok™; OB, Ortho Bite™. The composites were bonded using a matrix to obtain microcylinders and prepared for each experimental groups. The samples were then stored in distilled water for 24h at 37°C followed by a µ-SBT. The types of bond failures were evaluated using a stereoscopic magnifying glass (10×). The data were analyzed by ANOVA with Fisher post hoc and Dunnett´s test. Means of µ-SBT± standard deviation (MPa) were: C (39.98a±13.0), P (40.09a± 14.3); UBL (33.26ab±8.6); OB (28.70b±5.5). The most prevalent type of failure was adhesive (80.4%). Further, was not observed a statistically significant correlation between the bond strength values and failure patterns. The pigmentation of a commercially available resin did not alter the µ-SBT and exhibited similar adhesiveness as a polyacid-modified composite resin.

Bis(4-methyl phenyl)iodonium as an alternative component to diphenyliodonium in camphorquinone-based ternary initiating systems

ObjectiveTo evaluate the influence of different co-initiators (diphenyliodonium hexafluorophosphate - DPI - and bis(4-methyl phenyl)iodonium hexafluorophosphate – BPI) on chemical and mechanical properties of resins. MethodsNine experimental resins (50% Bis-GMA and 50% TEGDMA, w/w) with 60 wt% filler particles were formulated. The initiating system used was camphorquinone (CQ-1 mol%) and ethyl dimethylaminobenzoate (EDAB-2 mol%). Experimental groups were established according to DPI and BPI quantities (0.25, 0.5, 0.75, and 1 mol%). The control group was a resin containing only CQ-EDAB. Light transmission through the resin during polymerisation was analysed with a UV–vis spectrophotometer. Real-time polymerisation of the systems was evaluated using an FTIR spectrometer. Real-time polymerisation shrinkage strain was evaluated, and the flexural strength and modulus of materials were obtained by 3-point bending. Experimental groups were statistically analysed by Analysis of Variance and Tukey’s test (α = 0.05). Dunnett’s test was applied to compare experimental groups with control. ResultsLight transmission rapidly increased initially for resins containing DPI or BPI. After 30 s cure, the irradiance on the lower surface of resin specimens was similar for all groups. After 10 s of light irradiation, groups containing DPI and BPI had higher conversion than the control. However, conversion after 120 s post-irradiation was similar for all groups. The rate of polymerisation, shrinkage strain, and the maximum strain rate were higher for groups containing DPI/BPI. The use of iodonium salts increased the flexural strength and flexural moduli of resins. SignificanceDPI and BPI increased resin reactivity similarly. Increased rate of polymerization influenced light transmission through the resin in the first seconds of polymerisation and increased resin shrinkage and rate of shrinkage, as well as flexural strength and moduli.

Dental composite resins with low polymerization stress based on a new allyl carbonate monomer

The objective of this study was to synthesize a diallyl carbonate monomer, allyl(2-(2-(((allyloxy)carbonyl)oxy)benzoyl)-5-methoxyphenyl) carbonate (BZ-AL), and to evaluate its effect as Bis-GMA diluent in the formulation of photopolymerizable dental composite resins. The chemical structure of BZ-AL monomer was determined by means of H1 NMR, C13 NMR and FTIR spectroscopies. An experimental composite comprising a mixture of Bis-GMA and BZ-AL monomers and silanized inorganic filler was formulated. Experimental material was compared with a control composite formulated with Bis-GMA/TEGDMA. Double bond conversion, polymerization kinetics, volumetric shrinkage, polymerization stress, and flexural properties were investigated. The data were analyzed through a Student t-test (α = 0.05). Flexural strength of the experimental materials with BZ-AL monomer showed a statistically significant increase (p < 0.001). The experimental composite has a lower polymerization rate than the control composite, on the other hand, the experimental composite resin has the highest degree of double bond conversion. There are no differences in the polymerization shrinkage of the composites, however, the polymerization stress of the experimental materials was 50% lower than the control resin. Finally, the cell viability test showed that the experimental resins formulated with the BZ-AL monomer was not cytotoxic. Due to its characteristics, BZ-AL monomer is potentially useful for the formulation of composite materials with applications in dentistry.

Development of Chlorhexidine Loaded Halloysite Nanotube Based Experimental Resin Composite with Enhanced Physico-Mechanical and Biological Properties for Dental Applications

Objective: The objective of this study was to explore the effect of Chlorhexidine-loaded Halloysite nanotubes (HNT/CHX) fillers (diverse mass fractions from 1 to 10 wt.%) on physicochemical, morphological and biological properties of newly developed experimental dental resin composite, in order to compare with the properties of composites composed of conventional glass fillers. Methods: The dental resin composites were prepared by incorporating various proportions of HNT/CHX. Six different groups of specimens: control group and five groups composed of varied mass fractions of HNT/CHX (e.g., 1.0, 2.5, 5.0, 7.5 and 10 wt.%) as fillers in each group were fabricated. Mechanical properties of the composites were monitored, using UTM. The degree of conversion of dental resin composites and their depth of cure were also evaluated. Antimicrobial properties of dental composites were studied in vitro by applying agar diffusion test on strain Streptococcus mutans and cytotoxicity were studied using NIH-3T3 cell line. Results: The incorporation of varied mass fractions (1.0 to 5.0 wt.%) of HNT/CHX in dental resins composites enhanced mechanical properties considerably with significant antibacterial activity. The slight decrease in curing depth and degree of conversion values of composites indicates its durability. No cytotoxicity was noticed on NIH-3T3 cell lines. Significance: Consistent distribution of HNT/CHX as a filler into dental composites could substantially improve not only mechanical properties but also biological properties of dental composites.