Effects of polymerization initiator complexation in methacrylated beta-cyclodextrin formulations.

OBJECTIVES: Methacrylated beta-cyclodextrin (MCD) is a candidate dental monomer that can complex molecules within its hydrophobic cavity. This study determined the effects of complexation of polymerization initiators such as camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (4E) with MCD on the flexural strength (FS) and degree of conversion (DC) of resulting dental composite formulations. METHODS: Complexation of CQ and 4E with MCD was studied by thin layer chromatography. A mass fraction of 44% 2-hydroxyethylmethacrylate or triethyleneglycoldimethacrylate was mixed separately with a mass fraction of 56% MCD to produce a workable formulation. The mixture was activated with varied amounts of CQ and 4E. One part by mass of the activated resin formulation was mixed with three parts by mass of glass filler. Specimens for FS were prepared by filling molds with composites and curing for 2 min. The cured specimens were immersed in 37 degrees C water for 24 h and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. DC in MCD-based resin formulations was measured with a differential photocalorimeter under nitrogen. RESULTS: MCD appears to form inclusion complexes with CQ and 4E. As a result, FS and DC of MCD-based composites vary significantly as a function of the concentration of polymerization initiators used in the formulations. SIGNIFICANCE: Complexation of polymerization initiators with MCD can influence the FS and DC in MCD-based dental formulations and should be taken into consideration when evaluating MCD as a dental monomer.     

The effects of two monofunctional diluent monomers and two photoinitiator systems on the properties of UDMA-based composites

PURPOSE: To compare the effects of two types of monofunctional co-monomers and two types of photoinitiator systems on the properties of urethane dimethacrylate (UDMA) based dental restorative composites. METHODS: The resin blends consisted of UDMA and a diluent co-monomer at a molar ratio of 9:1. The diluent comonomers were neo-decyl vinyl ester (Neo 10) or n-hexyl methacrylate (HMA). The photoinitiator system consisted of a bis-acyl phosphine oxide (BAPO) or camphorquinone plus ethyl 4-(dimethylamino)benzoate (CQ/4E). Each initiator system was utilized at 1% or 2% by mass of the resin blend. These resin blends were mixed by hand with silanized zirconia glass (85.7% by mass) to make the various composites. Flexural strength (FS) specimens, made from these pastes by visible light photopolymerization, were tested to failure after 24 hours water storage. Mercury dilatometry was used to evaluate the shrinkage, and the degree of double bond conversion was evaluated using near infrared spectroscopy (NIR). The first hypothesis tested was that use of Neo 10 in a UDMA composite would not have an effect on properties compared to the methacrylate HMA. The second hypothesis tested was that the BAPO initiator would not have an effect on the properties of a UDMA-based composite compared to the CQ/4E initiator. RESULTS: The hypotheses were tested at alpha = 0.05 and beta = 0.20. The major finding was that the lower level (1% by mass) of BAPO resulted in lower FS, lower conversion and lower shrinkage (rejecting the hypothesis that there was no difference due to initiator used) than composites formulated with the higher level of this initiator or either level of the CQ/4E initiator system, regardless of the comonomer used. The effects of two comonomers used were not differentiated in this study with respect to the properties examined (accepting the hypothesis that there was no difference due to diluent monomer).     

Preparation of a fluorinated dental resin system and its anti-adhesive properties against S. mutans

ObjectivesThe purpose of this study was to characterize physicochemical properties and investigate anti-bacterial adhesion effect of dental resins containing fluorinated monomers.MethodFluorinated dimethacrylate FDMA was mixed with commonly used reactive diluent triethylene- glycol dimethacrylate (TEGDMA) and fluorinated diluent 1 H,1 H-heptafluorobutyl methacrylate (FBMA) separately at a mass ratio of 60 wt./40 wt. to prepare fluorinated resin systems. Double bond conversion (DC), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL), contact angle and surface free energy, surface element concentration, and anti-adhesion effect against Streptococcus mutans (S. mutans) were investigated according to standard or referenced methods. 2,2-bis[4-(2-hydroxy-3-methacryloy-loxypropyl)-phenyl]propane (Bis-GMA)/TEGDMA (60/40, wt./wt.) was used as control.ResultsBoth fluorinated resin systems had higher DC than Bis-GMA based resin (p < 0.05); compared with Bis-GMA based resin (FS, FDMA/TEGDMA resin system had higher FS (p < 0.05) and comparable FM (p > 0.05), while FDMA/FBMA resins system had lower FS and FM (p < 0.05). Both fluorinated resin systems had lower WS and SL than Bis-GMA based resin (p < 0.05), and FDMA/TEGDMA resin system had the lowest WS (p < 0.05) in all experimental resin systems. Only FDMA/FBMA resin system showed lower surface free energy than Bis-GMA based resin (p < 0.05). When the surface was smooth, FDMA/FBMA resin system had lower amount of adherent S. mutans than Bis-GMA based resin (p < 0.05), while after the surface became roughness, FDMA/FBMA resin system had comparable amount of adherent S. mutans as Bis-GMA based resin (p > 0.05).SignificanceResin system prepared exclusively with fluorinated methacrylate monomers reduced the S. mutans adhesion due to their increased hydrophobicity and decreased surface energy., while flexural properties of it should be improved.     

Detection and quantification of monomers in unstimulated whole saliva after treatment with resin-based composite fillings in vivo

Resin-based dental restorative materials contain allergenic methacrylate monomers, which may be released into saliva after restorative treatment. Monomers from resin-based composite materials have been demonstrated in saliva in vitro; however, studies analyzing saliva after restorative therapy are scarce. The aim of this study was to quantify methacrylate monomers in saliva after treatment with a resin-based composite filling material. Saliva was collected from 10 patients at four start points--before treatment, and 10 min, 24 h, and 7 d after treatment--and analysed by combined chromatography/mass spectrometry. The monomers bisphenol-A diglycidyl methacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), and urethane dimethacrylate (UDMA) were detected and quantified in the samples collected shortly (10 min) after treatment. The amounts detected ranged from 0.028 to 9.65 μg ml(-1) for Bis-GMA, from 0.015 to 0.19 μg ml(-1) for HEMA, and from 0.004 to 1.2 μg ml(-1) for UDMA. Triethyleneglycol dimethacrylate (TEGDMA) was detected in four of the samples. Ethoxylated bisphenol-A dimethacrylate (Bis-EMA) was not detected. Monomers were not detected in saliva samples collected before treatment, or 24 h or 7 d after treatment, with the exception of one sample, 24 h after treatment, in which HEMA was detected. In conclusion, monomers from the investigated resin-based composite and adhesive system were present in saliva shortly after treatment. One week after treatment, no monomers could be detected in patients' saliva samples.     

牙科纳米氧化铝复合树脂的制备与性能研究

目的 制备一种新型的光固化纳米氧化铝复合树脂,探讨其用于口腔临床的可行性。方法 以双酚A双甲基丙烯酸缩水甘油酯(Bis-GMA)为树脂基质,甲基丙烯酸羟乙酯(HEMA)为活性稀释剂,添加纳米氧化铝填料对树脂基质进行增强增韧改性,制备一种新型牙科纳米氧化铝复合树脂,并表征其固化程度、弯曲强度、硬度、断面形貌、耐磨性、吸水性与水溶解性。结果 添加纳米氧化铝能提高复合树脂材料的刚性和硬度,当添加量达到3wt%时,复合树脂的力学性能、吸水和溶解性能均为最优。结论 复合树脂中加入一定比例的纳米氧化铝可达到增韧和耐磨的效果,该研究为开发新型牙科复合树脂提供了理论和实验基础。     

The induction of micronuclei in vitro by unpolymerized resin monomers

Components of resin materials may damage DNA, leading to genetic alterations in mammalian cells. Here, monomers were analyzed for the induction of chromosomal aberrations indicated by micronuclei induced in V79 cells. A dose-related increase in the numbers of micronuclei was observed with triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and glycidyl methacrylate (GMA). These effects were reduced, however, by a metabolically active microsomal fraction from rat liver. The very low activity of Bis-GMA and UDMA and the elevated numbers of micronuclei caused by high concentrations of methyl methacrylate and bisphenol A were associated with cytotoxicity. Our findings provide evidence for the induction of micronuclei by TEGDMA, HEMA, and GMA under physiological conditions, indicating clastogenic activity of these chemicals in vitro. Since it has been shown that TEGDMA also caused gene mutations and DNA sequence deletions in mammalian cells, the activity of this substance should be analyzed in vivo.     

Monomer permeability of disposable dental gloves

STATEMENT OF PROBLEM: Studies have suggested that monomers may be able to permeate dental gloves. PURPOSE: This study examined the permeability of disposable dental gloves to 6 kinds of dental monomers. MATERIAL AND METHODS: The permeability of 6 kinds of dental monomers (methyl methacrylate [MMA], 2-hydroxyethyl methacrylate [HEMA], triethyleneglycol methacrylate [TEGDMA], ethyleneglycol dimethacrylate [EGDMA], urethane dimethacrylate [UDMA], and Bis-glycidyl methacrylate [Bis-GMA]) through 5 kinds of dental gloves (latex, powder-free latex, coated latex, polychloroprene, and polyvinyl chloride) was examined for up to 180 minutes at 37 degrees C. The fingers of unused gloves without pin holes were cut and used in the experiments. Five specimens per test group were examined. One type of monomer was poured into each finger and dipped in ethanol. The ethanol for extraction was measured by a spectrophotometer at a wavelength of 210 nm, and the results were analyzed by analysis of variance and the Kruskal-Wallis test (P<.05). RESULTS: Four of the monomers tested (MMA, HEMA, TEGDMA, and EGDMA) permeated the gloves tested, whereas 2 (UDMA and Bis-GMA) did not (P>.01). The amount of monomers permeating the latex in 10 minutes was 0.8 +/- 0.6, 0.6 +/- 0.6, 0.07 +/- 0.1, 0.07 +/- 0.1, 0.1 +/- 0.1 and 0.06 +/- 0.1 microL/mL for MMA, HEMA, EGDMA, TEGDMA, UDMA, and Bis-GMA, respectively. The amount of permeated monomer was then increased in relation to the examination time, and in MMA and HEMA, permeation occurred rapidly during the initial 60 minutes at 3 times the 10-minute values, then continued gradually and linearly. The polyvinyl chloride glove showed the greatest monomer permeability. Two-way analysis of variance showed significant correlations between MMA, HEMA, EGDMA or TEGDMA and UDMA or Bis-GMA (P<.01). Statistical significance was shown between polyvinyl chloride and latex, powder-free latex, coated latex or polychloroprene (P<.01). However, there was no significant relation between any kind of dental monomer and any kind of dental glove. CONCLUSION: Within the limitations of this study, 4 of the monomers tested permeated all of the gloves tested.     

Degree of cure and fracture properties of experimental acid-resin modified composites under wet and dry conditions.

OBJECTIVE: Evaluate the effects of core structure and storage conditions on the mechanical properties of acid-resin modified composites and a control material by three point bending and conversion measurements 15min and 24h after curing. METHODS: The monomers pyromellitic dimethacrylate (PMDM), biphenyldicarboxylic-acid dimethacrylate (BPDM), (isopropylidene-diphenoxy)bis(phthalic-acid) dimethacrylate (IPDM), oxydiphthalic-acid dimethacrylate (ODPDM), and Bis-GMA were mixed with triethyleneglycol dimethacrylate (TEGDMA) in a 40/60 molar ratio, and photo-activated. Composite bars (Barium-oxide-glass/resin=3/1 mass ratio, (2mmx2mmx25mm), n=5) were light-cured for 1min per side. Flexural strength (FS), elastic modulus (E), and work-of-fracture (WoF) were determined in three-point bending after 15min (stored dry); and after 24h under dry and wet storage conditions at 37 degrees C. Corresponding degrees of conversion (DC) were evaluated by Fourier transform infrared spectroscopy. Data was statistically analyzed (2-way analysis of variance, ANOVA, Holm-Sidak, p<0.05). RESULTS: Post-curing significantly increased FS, E and DC in nearly all cases. WoF did not change, or even decreased with time. For all properties ANOVA found significant differences and interactions of time and material. Wet storage reduced the moduli and the other properties measured with the exception of FS and WoF of ODPDM; DC only decreased in BPDM and IPDM composites. SIGNIFICANCE: Differences in core structure resulted in significantly different physical properties of the composites studied with two phenyl rings connected by one ether linkage as in ODPDM having superior FS, WoF and DC especially after 24h under wet conditions. As expected, post-curing significantly contributed to the final mechanical properties of the composites, while wet storage generally reduced the mechanical properties.     

Analysis of eluate extracted from dental filling resin by high performance liquid chromatography (author's transl)]

Since the residual monomer of cured filling resin has been implicated in toxicological effects, a high performance liquid chromatography (HPLC) was used to analyze the eluate of bisphenol A diglycidylmethacrylate (Bis-GMA) and methyl methacrylate (MMA) type resins presently used. The main chemicals of the eluate from resin into three kinds of solution, water, 85% methanol water solution and 100% methanol were the residual monomers which formely were Bis-GMA, triethylenglycol dimethacrylate and latterly MMA. Residual initiators, benzoyl peroxide and hydroquinone were also determined. This investigation has shown that HPLC is rapid, reliable and an acurate method to analyze the residual monomers of cured dental filling resins.     

The effect of adding a new monomer “Phene” on the polymerization shrinkage reduction of a dental resin composite

Objective

A new photocurable monomer, “Phene” (N-methyl-bis(ethyl-carbamate-isoproply-α-methylstyryl)amine) was synthesized and incorporated into Bis-GMA/TEGDMA with the aim of reducing polymerization shrinkage swithout detriment to the physical properties and wearing of the resin composites.

Evaluation of two Bis-GMA analogues as potential monomer diluents to improve the mechanical properties of light-cured composite resins.

OBJECTIVES: The aim of this study was to investigate the influence of new diluent agents, diluent ratio and filler content, on relevant mechanical properties of several novel composite resins containing Bis-GMA as resin matrices, and to compare these with the properties of composites based on TEGDMA, a conventionally used diluent. METHODS: Two Bis-GMA analogues were synthesized and 20 experimental composite resins were prepared combining three monomer mixtures (Bis-GMA/TEGDMA, Bis-GMA/CH3 Bis-GMA and Bis-GMA/CF3 Bis-GMA), at three dilution rates (85/15, 10/90, 0/100) and three levels of hybrid filler content (barium aluminosilicate glass): 0, 10 and 35%. Flexural strength (FS), modulus of elasticity (ME) and microhardness (VHN) of the composites were evaluated. Five specimens of each material were prepared for each mechanical test, light-cured over 120 s and stored in water at 37 degrees C for 1 week. Three-point bending test was used for FS measurement and VHN was quantified by using a Vickers microindentor. Data were analyzed by ANOVA and Student-Newman-Keuls tests (P<0.05). RESULTS: Materials with CH3 Bis-GMA showed an enhanced VHN. Mean FS was higher for matrices containing TEGDMA. Overall, dilution favored FS and VHN but not ME. Filler loading specially improved ME and VHN. SIGNIFICANCE: Results correlate with an increase in the extent of polymerization due to the higher flexibility of the less viscous comonomer starting system and the hydrophobic character of the Bis-GMA analogues.     

Fabrication and evaluation of Bis-GMA/TEGDMA dental resins/composites containing nano fibrillar silicate.

OBJECTIVE: To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and composites (with conventional glass filler) with various mass fractions of nano fibrillar silicate (FS). METHODS: Three dispersion methods were studied to separate the silanized FS as nano-scaled single crystals and uniformly distribute them into dental matrices. The photo-curing behaviors of the Bis-GMA/TEGDMA/FS resins were monitored in situ by RT-NIR to study the photopolymerization rate and the vinyl double bond conversion. Mechanical properties (flexural strength, elastic modulus and work-of-fracture) of the nano FS reinforced resins/composites were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of nano FS and the representative fracture surfaces of its reinforced resins/composites were examined by SEM/TEM. RESULTS: Impregnation of small mass fractions (1% and 2.5%) of nano FS into Bis-GMA/TEGDMA (50/50 mass ratio) dental resins/composites improved the mechanical properties substantially. Larger mass fraction of impregnation (7.5%), however, did not further improve the mechanical properties (one way ANOVA, P>0.05) and may even reduce the mechanical properties. The high degree of separation and uniform distribution of nano FS into dental resins/composites was a challenge. Impregnation of nano FS into dental resins/composites could result in two opposite effects: a reinforcing effect due to the highly separated and uniformly distributed nano FS single crystals, or a weakening effect due to the formation of FS agglomerates/particles. SIGNIFICANCE: Uniform distribution of highly separated nano FS single crystals into dental resins/composites could significantly improve the mechanical properties of the resins/composites.     

Evaluation of dental restorative composites containing polyhedral oligomeric silsesquioxane methacrylate.

OBJECTIVES: The aim of this study was to explore novel polymeric dental restorative composites, in which polyhedral oligomeric silsesquioxane methacrylate monomer (POSS-MA) was used to partially (or completely) replace the commonly used base monomer 2,2'-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA). METHODS: The composites were cured (hardened) by photo-initiated free radical polymerization. Mechanical properties (i.e. flexural strength, Young's modulus and diametral tensile strength) of the composites were tested by a universal mechanical testing machine; photopolymerization induced volumetric shrinkage was measured using a mercury dilatometer; and near infrared (NIR) technique was used to study the degree of methacrylate double bond conversion and photopolymerization rate. RESULTS: Small percentage POSS-MA substitution of Bis-GMA (i.e. mass fraction of 10% or less) in the resin system improved the mechanical properties of the composites; while large amount substitution led to less desirable mechanical properties, lower methacrylate double bond conversion, and slower photopolymerization rate. Statistical examinations showed the maximum flexural strength of the composites occurred when 10% (mass fraction) of Bis-GMA was replaced by POSS-MA, while the highest modulus occurred when the mass fraction of POSS-MA was 2%. SIGNIFICANCE: Polymeric dental restorative composites with improved mechanical properties may be designed by judicious choice of monomer (POSS-MA, Bis-GMA and TEGDMA) compositions.     

Water sorption and solubility of dental composites and identification of monomers released in an aqueous environment

Water sorption and solubility of six proprietary composite resin materials were assessed, and monomers eluted from the organic matrix during water storage identified. Water sorption and solubility tests were carried out with the following storage times: 4 h, 24 h and 7, 60 and 180 days. After storage, water sorption and solubility were determined. Eluted monomers were analysed by high performance liquid chromatography (HPLC). Correlation between the retention time of the registered peak and the reference peak was observed, and UV-spectra confirmed the identity. The results showed an increase in water sorption until equilibrium for all materials with one exception. The solubility behaviour of the composite resin materials tested revealed variations, with both mass decrease and increase. The resin composition influences the water sorption and solubility behaviour of composite resin materials. The HPLC analysis of eluted components revealed that triethyleneglycol dimethacrylate (TEGDMA) was the main monomer released. Maximal monomer concentration in the eluate was observed after 7 days. During the test period, quantifiable quantities of urethanedimethacrylate (UEDMA) monomer were observed, whereas 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (Bis-GMA) was only found in detectable quantities. No detectable quantities of bisphenol-A were observed during the test period.     

Evaluation of methylene lactone monomers in dental resins.

alpha-Methylene-gamma-butyrolactone (MBL), which can be described as the cyclic analog of methyl methacrylate, exhibits greater reactivity in free radical polymerizations than conventional methacrylate monomers. Unfilled resin formulations composed of Bis-GMA/MBL or Bis-GMA/TEGDMA/MBL were light-cured. The effect of the more reactive methylene lactone monomer on mechanical properties and the degree of conversion of the polymers was examined. The infrared absorption bands for the carbon-carbon double bonds of MBL and the methacrylate monomers are well resolved and allow the conversion of each component to be calculated individually. The incorporation of a small amount of MBL (5 w/o) to Bis-GMA significantly increased the conversion; however, additional MBL (10 to 30 w/o) did not further increase the Bis-GMA conversion level. This appears to indicate an incompatibility between MBL and the bulky Bis-GMA monomer. Addition of 10 w/o MBL to Bis-GMA/TEGDMA (7:3) resulted in a cured resin with 71% methacrylate and 75% overall conversion efficiencies compared with the 57% conversion of the control formulation. The diametral tensile and the transverse strengths were approximately 10% greater for the MBL resin compared with the Bis-GMA/TEGDMA control; however, these differences were not statistically significant. The synthesis and polymerization of several substituted methylene lactones was also studied.     

Influence of polymerization initiator for base monomer on microwave curing of composite resin inlays

Microwave polymerization was used to make composite resin inlays and the effect examined of the concentration of polymerization initiator for the base monomer. The monomers used were 2,2-bis [4-(3-methacriloxy-2-hydroxypropoxy) phenyl] propane (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA). Bis-GMA and TEGDMA were mixed in a ratio of 6:4 by weight and were separated into five groups. To each group was added benzoyl peroxide (BPO) in the ratios of 0.1, 0.3, 0.5, 0.7 and 0.9 wt% as the polymerization initiator. These were used as the base monomers. The results showed that the degree of conversion of the cured sample increased with increasing concentration of BPO from 0.1 to 0.5 wt%, however there was no significant difference at 0.5, 0.7 and 0.9 wt% (P> 0.01). Compression strength, diametral tensile strength and the Knoop hardness showed a similar tendency as the degree of conversion. No significant difference was recorded in the Knoop hardness between the top and the bottom surfaces (P> 0.01), which suggested a uniform polymerization in the cured sample. Thus, microwave polymerization would be an efficacious method for making resin inlays with the addition of BPO to the base monomer (Bis-GMA:TEGDMA, 6:4). The maximum conversion was found at a concentration of 0.5 wt%.     

Network structure of Bis-GMA- and UDMA-based resin systems

OBJECTIVES: The commonly used dental base monomers 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenylene]propane (Bis-GMA) and 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) require the use of a diluent monomer, such as triethylene glycol dimethacrylate (TEGDMA). The aim of this study was to measure double bond conversion of UDMA/TEGDMA and Bis-GMA/TEGDMA polymeric systems, determine the leachable portion, and analyze network formation by evaluating crosslinking and pendant double bonds. METHODS: UDMA or Bis-GMA was combined with TEGDMA in systematic increments and irradiated to form light cured polymers. Fourier transform infrared spectroscopy in the near-infrared region was used to measure double bond conversion. The leachable sol fraction was analyzed by 1H NMR. Resin composites were formulated. Flexural strength was measured by three-point bending and volumetric shrinkage was determined with a mercury dilatometer. RESULTS: The amount of base monomer greatly influenced double bond conversion, sol fraction, and crosslinking. Increasing base monomer concentration decreased double bond conversion, increased the leachable fraction, and decreased crosslinking and network formation. At mole fractions higher than 0.125, the UDMA polymers had significantly higher conversion than the Bis-GMA polymers. Bis-GMA polymers had higher leachable amounts of unreacted monomer, while UDMA mixtures had more crosslinking than the Bis-GMA mixtures. In regards to the physical properties of resin composites, increasing the base monomer improved flexural strength and decreased volumetric shrinkage. SIGNIFICANCE: This systematic study for the evaluation of conversion, leachability, crosslinking, and network structure along with physical properties, like volumetric shrinkage and flexural strength, are required for the optimization of competing desirable properties for the development of durable materials.     

Preparation and evaluation of novel bio-based Bis-GMA-free dental composites with low estrogenic activity

ObjectiveAlthough bisphenol Aglycidyl methacrylate (Bis-GMA) are widely used in the dental composite, its raw materials include the petroleum-based product bisphenol A (BPA) with high estrogenic activity (EA). In this study, two new BPA-free dimethacrylate monomers from bio-based material creosol were synthesized and evaluated.MethodsThe renewable bisphenol monomer 5, 5'-methylenedicreosol (BCF) was prepared from bio-based material creosol. By the human breast cancer cells (MCF-7 cells) proliferation assay, a risk assessment of BCF was performed to determine if BCF possessed reduced EA in comparison to BPA. Then, the novel monomers 5, 5'-methylenedicreosol diglycidyl ether diacrylate (BCF-EA) and 5, 5'-methylenedicreosol diglycidyl ether dimethacrylate (BCF-GMA) were synthesized from BCF with epichlorohydrin and (meth)acrylate. All products were investigated by ¹H NMR and FT-IR spectra. The control resin was a mixture based on Bis-GMA and tri(ethyleneglycol) dimethacrylate (TEGDMA) with a weight ratio of 5:5 (5B5T). Similarly, experimental resin matrix was a mixture based on BCF-EA/TEGDMA (5E5T) and BCF-GMA/TEGDMA (5G5T). And their corresponding composites were then prepared with corresponding resin matrices and hybrid SiO₂ (5E5TC, 5G5TC and 5B5TC). The properties of these composites were investigated according to the standard or referenced methods. Each sample was evaluated for double bond conversion (DC), shrinkage stress (SS) and volumetric polymerization shrinkage (VS). Water sorption (WS), water solubility (SL), mechanical properties and cytotoxicity were also measured.Results¹H NMR and FT-IR spectra confirmed the chemical structure of each monomer. EA test revealed that bio-based bisphenol monomer BCF as the precursor of BCF-EA and BCF-GMA showed lower EA than BPA. Cured resin matrix: Both 5E5T and 5G5T had nearly the same DC (p < 0.05), which was higher than 5B5T (p < 0.05); 5E5T and 5G5T had lower VS, SL and cytotoxicity than 5B5T (p < 0.05); mechanical properties of 5E5T and 5G5T were all better than those of 5B5T (p < 0.05). Cured composite: There was no significant difference in conversion (p < 0.05); 5E5TC and 5G5TC had significantly lower VS (p < 0.05); WS of 5E5TC and 5G5TC were similar (p < 0.05), but higher compared to 5B5TC (p < 0.05); 5E5TC and 5G5TC had the deeper depth of cure (p > 0.05); before water immersion, there was no significant difference in flexural strength between 5E5TC and 5G5TC (p > 0.05), and higher than 5B5TC (p < 0.05); 5E5TC and 5G5TC showed less cytotoxicity than 5B5TC (p < 0.05).SignificanceThe new BPA-free di(meth)acrylates are promising photocurable dental monomers owning to bio-based raw material, high degree of conversion coupled with low curing shrinkage and good mechanical properties. Therefore, BCF-EA and BCF-GMA has a potential to be used as the substitution for Bis-GMA to prepare Bis-GMA-free dental composite.     

Synthesis and evaluation of new oxaspiro monomers for double ring-opening polymerization.

Polymerization with expansion in volume can be achieved with spiro orthocarbonate monomers through a double ring-opening process wherein two bonds are cleaved for each new bond formed. The resulting expansion can be applied to counter the polymerization shrinkage associated with the conventional methacrylate monomers used in dental composites and thereby provide formulations with drastically reduced degrees of shrinkage. New monomers have been prepared that exhibit enhanced reactivities and ring-opening efficiencies compared with earlier free-radical-polymerizable oxaspiro compounds. In dental composite formulations, the monofunctional oxaspiro monomers provided DTS values equivalent to those of the controls under certain curing conditions; however, only modest reductions in polymerization shrinkage were observed. 2,3-Bis(methylene) spiro orthocarbonate monomers with a conjugated diene structure were also synthesized and evaluated. These novel monomers appear to offer significant potential for future development of free-radical ring-opening polymerization. While visible-light-cured formulations of the bis(methylene) compounds with methacrylate comonomers did not yield acceptable composite materials in this initial attempt, the high reactivity and the ability to form rigid, cross-linked polymers make this type of monomer worthy of continued investigation. These properties may allow the bis(methylene) oxaspiro monomers to be used alone or in concert with other ring-opening monomers for special applications.     

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

OBJECTIVES: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS: These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE: Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.