Novel pit and fissure sealant containing nano-CaF2 and dimethylaminohexadecyl methacrylate with double benefits of fluoride release and antibacterial function

ObjectivePit and fissure sealants with antibacterial and remineralization properties have broad application prospects in caries prevention. The objectives of this study were to: (1) develop a novel pit and fissure sealant containing CaF₂ nanoparticles (nCaF₂) and dimethylaminohexadecyl methacrylate (DMAHDM); and (2) investigate the effects of nCaF₂ and DMAHDM on biofilm response and fluoride (F) ion release for the first time.MethodsHelioseal F was used as a control. Bioactive sealants were formulated with DMAHDM and nCaF₂. Flow properties, enamel shear bond strength, hardness and F ion releases were measured. Streptococcus mutans (S. mutans) biofilms were grown on sealants. Biofilm metabolic activity, lactic acid production, colony-forming units (CFU), and pH of biofilm culture medium were measured.ResultsAdding 5% DMAHDM and 20% nCaF₂ did not reduce the paste flow and enamel bond strength, compared to control (p < 0.05). Hardness of sealants with 20% nCaF₂ and DMAHDM was higher than control (p < 0.05). The F ion release from 20% nCaF₂ was much higher than that of commercial control (p < 0.05). The sealant with DMAHDM reduced the S. mutans biofilm CFU by 4 logs. The pH in biofilm medium of the new bioactive sealant was much higher (pH 6.8) than that of commercial sealant (pH 4.66) (p < 0.05).SignificanceThe new bioactive pit and fissure sealant with nCaF₂ and DMAHDM achieved high fluoride release and strong antibacterial performance. This novel fluoride-releasing and antibacterial sealant is promising to inhibit caries and promote the remineralizaton of enamel and dentin.     

Protein-repellent nanocomposite with rechargeable calcium and phosphate for long-term ion release

Objective

There has been no report on the effect of incorporating protein repellent 2-methacryloyloxyethyl phosphorylcholine (MPC) into a composite containing nanoparticles of amorphous calcium phosphate (NACP) on calcium (Ca) and phosphate (P) ion rechargeability. The objectives of this study were to develop a Ca and P ion-rechargeable and protein-repellent composite for the first time, and investigate the effects of MPC and NACP on mechanical properties, protein-repellency, anti-biofilm effects, and Ca and P ion recharge and re-release.

Effect of co-precipitation plus spray-drying of nano-CaF2 on mechanical and fluoride properties of nanocomposite

ObjectiveFluoride (F)-releasing restoratives typically are either weak mechanically or release only low levels of F ions. The objectives of this study were to: (1) develop a novel photo-cured nanocomposite with strong mechanical properties and high levels of sustained F ion release via a two-step “co-precipitation + spray-drying” technique to synthesize CaF₂ nanoparticles (nCaF₂); and (2) investigate the effect of spray-drying treatment after co-precipitation of nCaF₂ on mechanical properties and F ion release of composite.MethodsTwo types of CaF₂ particles were synthesized: A co-precipitation method yielded CaF₂cp; “co-precipitation + spray-drying” yielded nCaF₂cpsd. Composites were fabricated with fillers of: (1) 0% CaF₂ + 70% glass; (2) 10% CaF₂cp + 60% glass; (3) 15% CaF₂cp + 55% glass; (4) 20% CaF₂cp + 50% glass; (5) 10% nCaF₂cpsd + 60% glass; (6) 15% nCaF₂cpsd + 55% glass; and (7) 20% nCaF₂cpsd + 50% glass. A commercial F-releasing nanocomposite served as control.ResultsThe nCaF₂cpsd had much smaller particle size (median = 32 nm) and narrower distribution (22–57 nm) than CaF₂cp (median = 5.25 μm, 162 nm–67 μm). The composite containing nCaF₂cpsd had greater flowability, flexural strength, elastic modulus and hardness than CaF₂cp composite and commercial control composite. At 84-day immersion in water, the nanocomposites containing 20% nCaF₂cpsd had 65 times higher cumulative F release, and 77 times greater long-term F-release rate, than commercial control.ConclusionsA novel two-step “co-precipitation + spray-drying” technique of synthesizing nCaF₂ was developed. The photo-cured nanocomposite containing 20% nCaF₂cpsd possessed strong mechanical properties and excellent long-term F-release ability, and hence is promising for dental restoration applications to inhibit secondary caries.     

Synthesis of chemically modified BisGMA analog with low viscosity and potential physical and biological properties for dental resin composite

ObjectivesThe currently available commercial dental resin composites have limitations in use owing to the high viscosity and water sorption of Bisphenol A glycidyl methacrylate (BisGMA). The objective of this study was to obtain a BisGMA analog with reduced viscosity and hydrophilicity for potential use as an alternative to BisGMA in dental resin composites.MethodsThe targeted chlorinated BisGMA (Cl-BisGMA) monomer was synthesized via the Appel reaction. The structural modification was confirmed via ¹H- and ¹³C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and mass spectrometry. Five resin mixtures (70:30 wt.%: F1 = BisGMA/TEGDMA; F2 = Cl-BisGMA/TEGDMA; F3 = Cl-BisGMA only; F4 = Cl-BisGMA/BisGMA; F5 contained 15% TEGDMA with equal amounts of BisGMA and Cl-BisGMA) were prepared. The viscosity, degree of double-bond conversion (DC), water sorption (W_SP), and solubility (W_SL) were tested. Cell viability and live/dead assays, as well as cell attachment and morphology assessments, were applied for cytotoxicity evaluation.ResultsCl-BisGMA was successfully synthesized with the viscosity reduced to 7.22 (Pa s) compared to BisGMA (909.93, Pa s). Interestingly, the DC of the F2 resin was the highest (70.6%). By the addition of equivalence concentration of Cl-BisGMA instead of BisGMA, the W_SP was decreased from 2.95% (F1) to 0.41% (F2) with no significant change in W_SL. However, the W_SL increased with high Cl-BisGMA content. Biological tests revealed that all the resins were biocompatible during CL1 incubation.SignificanceThe experimental resins based on Cl-BisGMA exhibited improved properties compared with the control samples, e.g., biocompatibility and lower viscosity, indicating that Cl-BisGMA can be considered as a potential monomer for application in dental resin composites.     

Physicochemical properties of dental resins formulated with amine-free photoinitiation systems

ObjectiveTo assess the mechanical properties of two different dimethacrylate resin blends containing the photosensitizer camphorquinone (CQ) alone or in combination with one or more synergists including an amine and/or an iodonium.MethodsTwo co-monomer resin blends were formulated using Bis-GMA/TEGDMA and UDMA/TEGDMA, both at 1:1 mass ratio. Each resin blend was divided into four groups, comprising the following four photoinitiation systems: (1) CQ + 2-(dimethylamino)ethyl methacrylate (DMAEMA); (2) CQ + DMAEMA + bis(4-methyl phenyl)iodonium hexafluorophosphate (BPI); (3) CQ; and (4) CQ + BPI. Materials were evaluated for polymerisation kinetics, water sorption, solubility, flexural strength and modulus.ResultsBisGMA/TEGDMA with CQ showed minimal and insignificant degree of conversion and was not tested for water sorption/solubility and mechanical properties. The ternary system (i.e., CQ + DMAEMA + BPI), promoted the highest degree of conversion for each monomer blend. The resins containing amine had higher mechanical properties than the amine free. However, the UDMA amine free resins exhibited greater flexural strength and modulus than the corresponding amine free BisGMA resins. BisGMA/TEGDMA containing CQ + DMAEMA or CQ + BPI had significantly higher water sorption and solubility than the other groups.SignificanceResins containing amine presented better properties than the amine-free systems. The addition of iodonium salt (BPI) improved the degree of conversion of the resins, even without an amine co-initiator. The amine-free initiator system (CQ + BPI) was more effective when used with UDMA versus BisGMA based-resins respectively.     

Long-term dentin remineralization by poly(amido amine) and rechargeable calcium phosphate nanocomposite after fluid challenges

Objective

Previous studies investigated short-term dentin remineralization; studies on long-term dentin remineralization after fluid challenges mimicking fluids in oral environment are lacking. The objective of this study was to develop a long-term remineralization method to via poly(amido amine) (PAMAM) and rechargeable composite containing nanoparticles of amorphous calcium phosphate (NACP) after fluid challenges for the first time.

Evaluation of highly reactive mono-methacrylates as reactive diluents for BisGMA-based dental composites

ObjectivesThis study evaluates the performance of highly reactive novel monomethacrylates characterized by various secondary moieties as reactive diluent alternatives to TEGDMA in BisGMA filled dental resins. We hypothesize that these monomers improve material properties and kinetics over TEGDMA because of their unique polymerization behavior.MethodsThe cure rates and final double bond conversion of the resins were measured using real-time FTIR spectroscopy. The glass transition temperature and storage modulus of the formed polymers were measured using dynamic mechanical analysis. Flexural modulus and flexural strength values were obtained using a three-point bending flexural test.ResultsPolymerization kinetics and polymer mechanical properties were evaluated for the novel resin composites. It was observed that upon the use of novel monomethacrylates as reactive diluents, polymerization kinetics increased by up to 3-fold accompanied by increases in the extent of cure from 5% to 13% as compared to the BisGMA/TEGDMA control. Polymer composites formed from resins of BisGMA/novel monomethacrylates exhibited comparable T_g values to the control, along with 27–37% reductions in the glass transition half widths indicating the formation of more homogeneous polymeric networks. The BisGMA/monomethacrylate formulations exhibited equivalent flexural modulus and flexural strength values relative to BisGMA/TEGDMA.SignificanceFormulations containing novel monovinyl methacrylates exhibit dramatically increased curing rates while also exhibiting superior or at least comparable composite polymer mechanical properties. Thus, these types of materials are attractive for use as reactive diluent alternatives to TEGDMA in dental formulations.     

Influence of BisGMA, TEGDMA, and BisEMA contents on viscosity, conversion, and flexural strength of experimental resins and composites

Different monomer structures lead to different physical and mechanical properties for both the monomers and the polymers. The objective of this study was to determine the influence of the bisphenylglycidyl dimethacrylate (BisGMA) concentration (33, 50 or 66 mol%) and the co-monomer content [triethylene glycol dimethacrylate (TEGDMA), ethoxylated bisphenol-A dimethacrylate (BisEMA), or both in equal parts] on viscosity (η), degree of conversion (DC), and flexural strength (FS). η was measured using a viscometer, DC was obtained by Fourier transfer Raman (FT-Raman) spectroscopy, and FS was determined by three-point bending. At 50 and 66% BisGMA, increases in η were observed following the partial and total substitution of TEGDMA by BisEMA. For 33% BisGMA, η increased significantly only when no TEGDMA was present. The DC was influenced by BisGMA content and co-monomer type. Mixtures containing 66% BisGMA showed a lower DC compared with mixtures containing other concentrations of BisGMA. The BisEMA mixtures had a lower DC compared with the TEGDMA mixtures. The FS was influenced by co-monomer content only. BisEMA mixtures presented a statistically lower FS, followed by TEGDMA + BisEMA mixtures, and then by TEGDMA mixtures. Partial or total replacement of TEGDMA by BisEMA increased η, which was associated with the observed decreases in DC and FS. Although the BisGMA content influenced the DC, it did not affect the FS results.     

Long-term release of monomers from modern dental-composite materials

The elution of monomers from composite materials influences the biocompatibility of dental restorations. The purpose of the present study was to investigate the elution of monomers [bisphenol A glycidyl methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A (BPA)] from two light-cured materials (nanohybrid and ormocer) and from a chemically cured composite material, after different curing times (0, 20, 40 and 80 s) and different storage periods (24 h, 7 d, 28 d, and 1 yr after curing). Each specimen was stored in 1 ml of 75% ethanol. This medium was renewed after 24 h, 7 d, 28 d, and 1 yr. The ethanol samples were analyzed using liquid chromatography tandem mass spectrometry (LC–MS/MS). The amount of monomers released from the nanohybrid and the chemically cured composite was significantly higher than released from the ormocer. The curing time exerted a significant effect on the release of monomers. For the nanohybrid, less monomer was released after increasing the curing time. For the ormocer, 80 s of curing resulted in a higher degree of monomer release. The effect of storage differed between the monomers. Although the elution of TEGDMA was significantly decreased after storage for 28 d and 1 yr, a similar amount of BisGMA was released at each storage time-point analyzed, even after 1 yr. The present study showed that ormocer released a very small amount of monomers compared with the other materials.     

Effects of different fluoride recharging protocols on fluoride ion release from various orthodontic adhesives

Objective

The purpose of this study was to find the most effective fluoride recharging protocol for orthodontic adhesives.

Methods

Five orthodontic adhesives were used: a non-fluoride-releasing composite, a fluoride-releasing composite, a polyacid-modified composite (compomer), and two resin-modified glass-ionomer cements (RMGICs). Each specimen was placed into deionized water (DW) and the initial fluoride ion release was measured for 2 months. Each specimen was then subjected to four different treatments to simulate a fluoride recharge: 1000 ppm NaF solution, acidulated phosphate fluoride gel (APF), fluoride-containing dentifrice and DW (control). After topical fluoride treatment, each specimen was submitted to fluoride re-release tests.

Results

Fluoride-containing adhesives initially showed higher rates of fluoride ion release, but significantly declined to lower levels. The overall cumulative fluoride ion release during the initial period was RMGICs > compomer > fluoride-containing composite > non-fluoride-releasing composite. After topical fluoride treatment, the amount of fluoride ion re-released was proportional to the amount of fluoride ion previously released from the adhesives. However, the amount of fluoride ions released only lasted for 2 days and then returned to the levels before fluoride application. The overall cumulative fluoride ion re-release according to the fluoride treatments was APF and NaF solution > dentifrice.

Conclusion

This study suggests that using the combination of RMGICs and a fluoride-containing mouth rinse solution is the most effective protocol for long-term fluoride re-release from orthodontic adhesives, given the difficulty of routine use of APF at home, although all topical fluoride treatments can recharge fluoride ion in adhesives.     

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

Objectives

To study monomer elution from four resin-based composites (RBCs) cured with different light sources.

Methods

Twenty-eight premolars were randomly allocated to four groups. Standardized cavities were prepared and restored with a nanohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1 h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α = 0.05).

Results

The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p < 0.05). LED and halogen light-curing units gave similar results for all RBCs (p > 0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p < 0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p > 0.05).

Significance

: The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical conditions. Light source may affect monomer elution since differences were found for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.     

Preparation and evaluation of a BisGMA-free dental composite resin based on a novel trimethacrylate monomer

ObjectiveThe use of the BisGMA as base monomer in dental composites has been questioned because of bisphenol A (BPA) is used as raw material in its synthesis, and BPA possess estrogenic potential associated to several health problems. This study describes the synthesis of the trimethacrylate tris(4-hydroxyphenyl)methane triglycidyl methacrylate (TTM) monomer and evaluate its effect when used as base monomer in the formulation of experimental photopolymerizable composite resins.MethodsThe TTM monomer was synthesized by a nucleophilic acyl substitution. Its chemical structure was confirmed via ¹H and ¹³C NMR spectroscopy and FTIR spectroscopy. Experimental composite resins were formulated by mixing TTM, triethyleneglycol dimethacrylate (TEGDMA) and inorganic fillers. A BisGMA/TEGDMA based composite resin was prepared and used as control to compare several physicochemical properties. Cell viability assay was used for cytotoxicity evaluation.ResultsTTM was successfully synthesized with quantitative yields. The results showed that the TTM-based composite resin had similar values of flexural strength, elastic modulus, degree of conversion and polymerization shrinkage than the control (p > 0.05). Water sorption and solubility were statistically significantly higher than the control (p < 0.05), however they complied the requirements stablished by the ISO 4049. Finally, this study shows there were no statistically significant differences for the biocompatibility outcomes (p = 0.345).SignificanceTTM monomer could be potentially useful in the formulation of BisGMA free composite resins, which could mean to minimize the human exposure to BPA.     

Evaluation of a photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition polymer network with improved water stability and high mechanical performance as an ester-free dental restorative

ObjectiveThe objective is to develop and characterize an ester-free ether-based photo-CuAAC resin with high mechanical performance, low polymerization-induced stress compared with common BisGMA/TEGDMA (70/30) resins, and improved water stability in comparison to previously developed urethane-based photo-CuAAC resins.MethodsTriphenyl-ethane-centered ether-linked tri-azide monomers were synthesized and co-photopolymerized with ether-linked tri-alkyne monomers under visible light irradiation using a copper(II) pre-catalyst and CQ/EDAB as the initiator. The ether-based CuAAC formulation was investigated for thermo-mechanical properties, polymerization kinetics and shrinkage stress, and flexural properties with respect to a conventional BisGMA/TEGDMA (70/30) dental resin. In addition, both the ether-based CuAAC resin and the urethane-based CuAAC resin were examined for their water stability using the BisGMA/TEGDMA (70/30) resin as a control.ResultsThe ether-based CuAAC network (AK/AZ-1) exhibited a slightly lower glass-transition temperature compared with the BisGMA/TEGDMA network (108 °C vs 128 °C), but because of its much sharper glass transition, the AK/AZ-1 CuAAC-network maintained storage modulus higher than 1 GPa up to 100 °C. In addition, the ether-based AK/AZ-1 network exhibited reduced shrinkage stress (0.56 MPa vs 1.0 MPa) and much higher flexural toughness (7.6 MJ/m³ vs 1.6 MJ/m³) while showing slightly lower flexural modulus and slightly higher flexural strength compared with the BisGMA/TEGDMA network. Moreover, the ether-based AK/AZ-1 CuAAC network displayed comparable water stability in comparison to the BisGMA/TEGDMA network with slightly higher water sorption (46 μg/mm³ vs 38 μg/mm³) and much lower water solubility (2.3 μg/mm³ vs 4.4 μg/mm³).SignificanceEmploying the ether-based hydrophobic CuAAC formulation significantly improved the water stability of the CuAAC network compared with previously developed urethane-based CuAAC networks. Furthermore, compared with the conventionally used BisGMA/TEGDMA formulation, the reduced shrinkage stress, comparable flexural strength/flexural modulus, and the superior flexural toughness of the ether-based CuAAC network make it a promising ester-free alternative to the currently widely-used methacrylate-based dental restoratives.     

The effects of light intensity, temperature, and comonomer composition on the polymerization behavior of dimethacrylate dental resins.

One of the most common combinations for the organic phase of dental restorative materials is BisGMA (2,2bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]propane) and TEGDMA (triethylene glycol dimethacrylate). However, this copolymer has some drawbacks, such as volume shrinkage during cure and lack of complete double-bond conversion. If the properties of this system are to be improved, an attempt must be made to understand the underlying kinetics of the reaction. This work examines the effects of light intensity, temperature, and composition on the polymerization behavior of BisGMA/TEGDMA copolymerizations. Using differential scanning calorimetry, we monitored the rates of photopolymerization for various experimental conditions. The BisGMA/TEGDMA copolymerization behaved similarly to other dimethacrylate systems and exhibited diffusion-controlled kinetics. It was found that the maximum rate of polymerization was significantly affected by the intensity of the light, and the temperature of the polymerization affected the conversion at which the maximum rate occurred. When the composition of the mixture was varied, it was discovered that the viscosity of the system played a significant role in the polymerization rate and the onset of reaction-diffusion-controlled termination. Mixtures which contained from 50 wt% to 75 wt% BisGMA displayed the highest maximum rate. This feature suggests that TEGDMA is an excellent diluent, since it increases the mobility of the reacting medium; however, the high reactivity is due to the presence of BisGMA. Therefore, based on compositional dependence, we conclude that the BisGMA portion of the mixture largely controls the polymerization mechanisms and kinetics.     

Effects of monomer ratios and highly radiopaque fillers on degree of conversion and shrinkage-strain of dental resin composites

ObjectivesThe degree of conversion (DC) and polymerization shrinkage of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as an increase in monomer conversion leads to a high polymerization shrinkage. This paper aims to determine the effect of opaque mineral fillers and monomer ratios on the DC and the shrinkage-strain of experimental composites based on (BisGMA/TEGDMA) monomers (traditionally used monomers). A relationship between the shrinkage-strain and the degree of conversion values was also investigated. The radiopacity of these experimental composites has been investigated in a previous paper.MethodsExperimental resin composites were prepared by mixing different monomer ratios of (BisGMA/TEGDMA) with Camphoroquinone and dimethyl aminoethyl methacrylate (DMAEMA) as photo-initiator system. Five different radiopacifying filler agents: La₂O₃, BaO, BaSO₄, SrO and ZrO₂ at various volume fractions ranging from 0 to 80 wt.% were added to the mixture. The degree of conversion of experimental composites containing different opaque fillers contents was measured using FTIR/ATR spectroscopy. The shrinkage-strain of specimens, photopolymerized at circa 500 mW/cm², was measured using the bonded-disk technique at room temperature with respect to time.ResultsThe result revealed that the DC and the shrinkage-strain decrease slightly with the increasing of opaque fillers loadings, but this decrease is not significant. However, these two properties are closely related to the monomer concentration of the organic matrix. The results have also showed a linear correlation between the shrinkage-strain and DC of experimental composites investigated.SignificanceThe nature and the volume effects of the opaque fillers on the DC and shrinkage of the experimental composites investigated were not significant. However, this study has confirmed the importance of viscosity in the system and shrinkage behavior of dimethacrylate monomers studied. Then we confirmed that direct relationships linked the shrinkage and the DC of filled dental resin composites.     

Fluoride release and re-uptake in direct tooth colored restorative materials.

OBJECTIVES: Glass ionomers may be "recharged" through topical fluoride (F-) treatments; however, this reported "recharging," may be attributed to surface changes after F- treatment. This study examined differences in F- release and re-uptake among dual-cured and chemically-cured glass ionomers, and a photo-cured F- releasing composite. A secondary goal was to determine if tensile strength or surface roughness changed due to F- release, or F- re-uptake and re-release. METHODS: In Phase 1, initial surface roughness and diametral tensile strength were measured. F- release was measured for 30 days. Strength and roughness were then remeasured. In Phase 2, surface roughness was measured, then materials were treated with a 5000 ppm neutral F- gel, the same gel without F-, or phosphoric acid. F- release was measured for 30 days, then final surface roughness and strength were determined. RESULTS: Significant differences were found in amount and rate of F- release, and F- re-uptake and re-release among study materials and enamel controls (p < 0.001). The amount and rate of F- re-release after NaF treatment differed significantly from F- release after acid treatment in glass ionomers, although both groups showed increased F- release after surface treatment (p < 0.001). There were no significant changes in tensile strength or surface roughness after F- release or F- re-uptake and re-release as determined by ANOVA. SIGNIFICANCE: The results of this in vitro study indicate that applications of neutral 5000 ppm F- gel to aged glass ionomer restorations results in a significant fluoride uptake and subsequent release. The data suggest that the application of neutral fluoride gel to glass ionomer restorations in situ may result in increases in oral fluoride concentrations, without affecting the restoration's surface roughness or tensile strength.     

Alternative monomer for BisGMA-free resin composites formulations

ObjectiveWater sorption, high volumetric shrinkage, polymerization stress, and potential estrogenic effects triggered by leached compounds are some of the major concerns related to BisGMA-TEGDMA co-monomer systems used in dental composites. These deficiencies call for the development of alternative organic matrices in order to maximize the clinical lifespan of resin composite dental restorations. This study proposes BisGMA-free systems based on the combination of UDMA and a newly synthesized diurethane dimethacrylate, and evaluates key mechanical and physical properties of the resulting materials.Methods2EMATE-BDI (2-hydroxy-1-ethyl methacrylate) was synthesized by the reaction between 2-hydroxy-1-ethyl methacrylate with a difunctional isocyanate (1.3-bis (1- isocyanato-1-methylethylbenzene) – BDI). The compound was copolymerized with UDMA (urethane dimethacrylate) at 40 and 60 wt%. UDMA copolymerizations with 40 and 60 wt% TEGDMA (triethylene glycol dimethacrylate) were tested as controls, as well as a formulation based in BisGMA (bisphenol A-glycidyl methacrylate)-TEGDMA 60:40% (BT). The organic matrices were made polymerizable by the addition of DMPA (2.2-dimethoxyphenoxy acetophenone) and DPI-PF6 (diphenyliodonium hexafluorophosphate) at 0.2 and 0.4 wt%, respectively. Formulations were tested as composite with the addition of 70 wt% inorganic content consisting of barium borosilicate glass (0.7 μm) and fumed silica mixed in 95 and 5 wt%, respectively. All photocuring procedures were carried out by a mercury arc lamp filtered to 320–500 nm at 800 mW/cm². The experimental resin composites were tested for kinetics of polymerization and polymerization stress in real time. Flexural strength, elastic modulus, water sorption, and solubility were assessed according to ISO 4049. Biofilm formation was analyzed after 24 h by luciferase assay. Data were statistically analyzed by one-way ANOVA and Tukey's test (α ≤ 0.05).ResultsIn general, the addition of 2EMATE-BDI into the formulations decreased the maximum rate of polymerization (RP_MAX), the degree of conversion at RP_MAX (DC at RP_MAX), and the final degree of conversion (final DC). However, these reductions did not compromise mechanical properties, which were comparable to the BT controls, especially after 7-day water incubation. The incorporation of 60 wt% 2EMATE-BDI reduced water sorption of the composite. 2EMATE-BDI containing formulations showed reduction in polymerization stress of 30% and 50% in comparison to BT control and TEGDMA copolymerizations, respectively. Biofilm formation was similar among the tested groups.SignificanceThe use of the newly synthesized diurethane dimethacrylate as co-monomer in dental resin composite formulations seems to be a promising option to develop polymers with low-shrinkage and potentially decreased water degradation.     

Ion-releasing dental restorative composites containing functionalized brushite nanoparticles for improved mechanical strength

Objectives

This study describes the synthesis of brushite nanoparticles (CaHPO₄·2H₂O) functionalized with triethylene glycol dimethacrylate (TEGDMA) and their application in dental restorative composites with remineralizing capabilities.

Contraction stress determinants in dimethacrylate composites

The influence of composite organic content on polymerization stress development remains unclear. It was hypothesized that stress was directly related to differences in degree of conversion, volumetric shrinkage, elastic modulus, and maximum rate of polymerization encountered in composites containing different BisGMA (bisphenylglycidyl dimethacrylate) concentrations and TEGDMA (triethylene glycol dimethacrylate) and/or BisEMA (ethoxylated bisphenol-A dimethacrylate) as co-monomers. Stress was determined in a tensilometer. Volumetric shrinkage was measured with a mercury dilatometer. Elastic modulus was obtained by flexural test. We used fragments of flexural specimens to determine degree of conversion by FT-Raman spectroscopy. Reaction rate was determined by differential scanning calorimetry. Composites with lower BisGMA content and those containing TEGDMA showed higher stress, conversion, shrinkage, and elastic modulus. Polymerization rate did not vary significantly, except for the lower value of the 66% TEGDMA composite. We used linear regressions to evaluate the association between polymerization stress and conversion (R(2)=0.905), shrinkage (R(2)=0.825), and modulus (R(2)=0.623).