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

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Available online at www.sciencedirect.com

ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/dema

Preparation and evaluation of a BisGMA-free dental composite resin based on a novel trimethacrylate monomer Alma Antonia Pérez-Mondragón a , Carlos E. Cuevas-Suárez b , José Abraham González-López a , Nayely Trejo-Carbajal c , Myriam Meléndez-Rodríguez d , Ana M. Herrera-González c,∗ a

Doctorado en Ciencias de los Materiales, Universidad Autónoma del Estado de Hidalgo, Mineral de la Reforma, Hidalgo, México b Laboratorio de Biomateriales Dentales, Área Académica de Odontología, Instituto de Ciencias de la Salud, Universidad Autónoma del Estado de Hidalgo, San Agustín Tlaxiaca, Hidalgo, México c Laboratorio de Polímeros, Instituto de Ciencias Básicas e Ingeniería, Universidad Autónoma del Estado de Hidalgo, Mineral de la Reforma, Hidalgo, México d Área Académica de Química, Instituto de Ciencias Básicas e Ingeniería, Universidad Autónoma del Estado de Hidalgo, Mineral de la Reforma, Hidalgo, México

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objective. The use of the BisGMA as base monomer in dental composites has been ques-

Received 23 September 2019

tioned because of bisphenol A (BPA) is used as raw material in its synthesis, and BPA

Received in revised form

possess estrogenic potential associated to several health problems. This study describes

10 December 2019

the synthesis of the trimethacrylate tris(4-hydroxyphenyl)methane triglycidyl methacry-

Accepted 4 February 2020

late (TTM) monomer and evaluate its effect when used as base monomer in the formulation

Available online xxx

of experimental photopolymerizable composite resins.

Keywords:

chemical structure was confirmed via

Trimethacrylate monomer

troscopy. Experimental composite resins were formulated by mixing TTM, triethyleneglycol

Methods. The TTM monomer was synthesized by a nucleophilic acyl substitution. Its 1

H and

13

C NMR spectroscopy and FTIR spec-

Dental resins

dimethacrylate (TEGDMA) and inorganic fillers. A BisGMA/TEGDMA based composite resin

BisGMA-free

was prepared and used as control to compare several physicochemical properties. Cell via-

Dental composite

bility assay was used for cytotoxicity evaluation. Results. TTM 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).

∗

Corresponding autor at: Carretera Pachuca-Tulancingo Km. 4.5, Colonia Carboneras, Mineral de la Reforma Hidalgo, C.P. 42184, Mexico. E-mail address: [email protected] (A.M. Herrera-González). https://doi.org/10.1016/j.dental.2020.02.005 0109-5641/© 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

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Significance. TTM monomer could be potentially useful in the formulation of BisGMA free composite resins, which could mean to minimize the human exposure to BPA. © 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

1.

Introduction

Photopolymerizable dental composite resins are generally composed of a methacrylate monomers based organic matrix, a photoinitiation system, and silane coupling agent-treated fillers [1]. The commonly used organic matrix is a mixture of two or more dimethacrylate monomers, which includes the 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl] propane (BisGMA), ethoxylated BisGMA (Bis-EMA), urethane dimethacrylate (UDMA), and triethyleneglycol dimethacrylate (TEGDMA) [2]. Nowadays, BisGMA is the most used as base monomer in commercial dental composites, and this trend is attributed to its low volumetric shrinkage, good reactivity, and mechanical properties, as well as low diffusivity into tissues [3]. However, the use of this monomer 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, including effects on hormonal activity, asthma, diabetes, obesity, behavioral changes, cancer, infertility and genital malformations [4]. Although pure BPA is not a component of dental composite resins, it can be found as a trace material left-over from the manufacturer [5], in addition, BisGMA containing materials can release small quantities of BPA due to hydrolysis promoted by salivary enzymes [6,7]. Actually, it has been previously demonstrated the presence of increased concentrations of BPA in saliva and urine in humans after the placement of sealants and composite materials [8,9]. Although there is a lack of studies analyzing the association between BPA exposure from dental materials and its adverse effects on human health [10], there is a need to develop newer BPA-free resin composites to minimize human exposure to this compound. Accordingly, the objective of this work was to synthesize a novel trimethacrylate BPA-free monomer and to evaluate its performance as a base monomer in the formulation of an experimental photopolymerizable dental composite. The null hypothesis to be tested was that the use of TTM as base monomer in a composite resin would result in a material with similar properties to those of a composite resin formulated with Bis-GMA as base monomer.

2.

Materials and methods

2.1.

Materials and instruments

The materials and solvents used in the synthesis of the monomers were purchased from Sigma-Aldrich (St. Louis, MI, USA). The FT-IR spectra were obtained with a Perkin Elmer Frontier spectrophotometer using the reflectance (ATR) technique (Perkin Elmer, Waltham, MA, USA). The solvents used were distilled with the techniques described in the literature

Scheme 1 – Synthesis of monomer TTM.

[11]. The NMR spectra were obtained with a 400-MHz spectrometer Bruker 1400, Inc. Palo Alto, CA, USA) using deuterated chloroform as solvent and tetramethylsilane as an internal reference. The photopolymerization of the materials was carried out using a Bluephase 16i lamp (Ivoclar-Vivadent) with an irradiance of 1000 mW/cm2. The irradiance was periodically monitored using a digital radiometer (Bluephase Meter, Ivoclar-Vivadent). The flexural tests were carried out using a universal Instron 4465 mechanical testing machine (Instron, Norwood, MA). A polymerization Stress Tester (Proto-Tech, Portland, OR, USA) was used for the analysis of the polymerization shrinkage stress. DMA analysis was performed in a Q800 equipment (TA Instruments, Leuven, Belgium).

2.2. Synthesis of monomer tris(4-hydroxyphenyl)methane triglycidyl methacrylate (TTM) The synthesis of the monomer TTM was carried out by an epoxy opening reaction in basic medium. 0.5 g (1.05 mmol) of tris(4-hydroxyphenyl)methane triglycidyl ether were dissolved in 20 mL of ethyl acetate and placed in a two-necked round bottom flask equipped with a magnetic stirring bar and a reflux condenser, under constant agitation. After, 0.3 mL (12.9 mmol) of methacrylic acid, 2 wt.% of triethylamine and 5 ppm of FeCl3 were added (Scheme 1). The reaction was carried out at reflux temperature (78 ◦ C) for 24 h, with constant agitation at 70 rpm, the reaction mixture was protected from light. The progress of the reaction was monitored via thin-layer chromatography and FT-IR. Subsequently, the mixture was allowed to cool to room temperature. At the end of the reaction, the ethyl acetate was evaporated, and 25 mL of dichloromethane were added, then 3 washes were carried out with a saturated solution of sodium carbonate and then, three washes with a 5% HCl solution. The organic phase was dried over anhydrous sodium sulfate. After the solvent was removed using a rotary evaporator. The monomer was obtained as a brown viscous liquid. The final product was maintained at 4 ◦ C until its use. FTIR/ATR (cm−1 ): 1711 (CO), 1162 (CO), 3428 (OH), 1 1610 (CC aromatic) 1629 (CC aliphatic ). NMR H (400 MHz,

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CDCl3 ): 7.02 (12H, m, H2, H3), 6.20 (3H, m, H7), 5.67 (3, m, H8), 4.5 a 3.8 (20H, m, H1, H4, H5, H6, H11), 1.90 (9H, m, H10). NMR 13 C (100 MHz, CDCl3 ): 171.2 (C O), 167.5 (C Caromatic ), 135.9 y 126.2 (Caromatic Caromatic ), 114.3 (C OC H2 ), 156.8 y 130.3 (C CH2 ), CH3 ). 68.5, 65.6 y 60.4 (CH2 CH CH2 ), 21.0 (C), 18.3 (C

2.3.

Viscosity

The viscosity of the TTM, BisGMA and TEGDMA monomers was determined using a rotary rheometer (RS-CPS+, Brookfield, Massachusetts, USA). For the viscosity measurements, the samples were placed directly on the rheometer plate. The measurements were taken at a controlled cutting speed (CSR) from 0 to 31 s−1 . The rheological parameters were calculated using the Rheo3000 program (Brookfield, Massachusetts, USA).

2.4.

modulus (MPa); F1 is the force registered when the deformation stops being directly proportional to the force (N); and d is the deflection corresponding to the load F1 (mm).

2.6.

Dynamic Mechanical Analysis (DMA) was used to know the glass transition temperature (Tg) for the experimental and control materials. The samples (30 × 5 × 1 mm) were made by inserting the unpolymerized material into a plastic mold. The materials were then irradiated 20 s per side by the overlapping method with a photopolymerization unit. The samples (n = 3) were stored in distilled water at 37 ◦ C for 24 h prior their analysis in a DMA equipment using a frequency of 1 Hz, 20 amplitudes and 30 ◦ C.

Preparation of composite resin 2.7.

An experimental composite resin was formulated using a mixture of TTM/TEGDMA in a 1:1 weight ratio. A control resin was formulated using a BisGMA/TEGDMA system in the same ratio. For both groups, a binary photopolymerization system of camphorquinone (CQ) and 4-diethylaminobenzoate (E4DMAB) in a concentration of 0.8 and 1.6 wt.% respectively, were used. For the formulation of the composites, 65 wt% of silanized barium borosilicate glass (0.7 ␮m, 1 wt% silane; Esstech Inc., PA, USA) was added to the organic matrix using a high-speed mixer (SpeedMixerTM DAC 150.1 FV, FlackTek Inc., UK). Afterwards, the materials were degassed using an ultrasonic cleaner (CD4860, Gnatus, Brazil) during 15 min.

2.5.

Flexural strength and elastic modulus

The flexural strength and elastic modulus were evaluated according to ISO-4049 International Standard, except for the specimens dimensions [12,13]. Unpolymerized materials were inserted into a rectangular silicone mold (10 × 2 × 2 mm) and irradiated for both sides during 20 s using a photopolymerization unit. After polymerization, the specimens’ dimensions (n = 10) were measured using a digital calibrator with an accuracy of 0.01 mm. Flexural strength was evaluated, after storing the specimens in distilled water for 24 h at 37 ◦ C, using a flexural strength test apparatus coupled to a universal mechanical testing machine (EMIC DL 500, Brazil). The apparatus consists essentially of two rods (2 mm of diameter) mounted parallel with 10 mm between centers, and a third rod (2 mm of diameter) centered between the other two. The mechanical test was performed at a cross-head speed of 1.00 mm/minute until fracture of the specimen. The flexural strength () and elastic modulus (E) were calculated using the following formulas: 3Fl = 2bh2 E=

Dynamic mechanical analysis (DMA)

l3

F1 4bh3 d

Polymerization kinetics

An infrared spectrophotometer was used to measure the polymerization rate and the degree of double bond conversion. The spectrophotometer software package was used in the monitoring scan mode in the range of 1500–1800 cm−1 , a resolution of 4 cm−1 and a mirror speed of 2.8 mm/s. With this configuration, one scan was acquired every 1 s during photoactivation. A small sample (n = 3) of composite resin was placed on the diamond cell of the equipment, then a celluloid sheet and a slide glass were placed to standardize the distance between the photopolymerization unit tip and the diamond of the ATR unit. Before irradiating the sample, an infrared spectrum was taken. Subsequently, the composite resin sample was irradiated for 30 s. After the irradiation, another infrared spectrum was taken. The experiment was performed three times for each of the evaluated groups. In each of the spectra, the height of the absorption band of the aliphatic C C bond was measured at 1638 cm−1 and the height of the absorption band of the aromatic C C bond located at 1609 cm−1 . The degree of conversion (DC) was determined according to the following equation:

DC (%) =



1−

h1638 /h1610 pol h1638 /h1610 mon



× 100%

(3)

where: h1638 is the maximum height of the band at 1638 cm−1 , h1609 is the maximum height of the band at 1609 cm−1 . The term “mon” corresponds to the spectrum of the unpolymerized monomer mixture, and the term “pol” refers to the spectrum of the polymerized material.

2.8.

Polymerization shrinkage

(1)

(2)

where: ␴ is the flexural strength, (MPa); F is the maximum load (N) exerted on the specimen at the point fracture; l is the distance between supports (10 mm); b is the width of specimens (2 mm); h is the height of the specimens (2 mm); E is the elastic

Polymerization shrinkage was calculated based on the specifications provided by ISO-17304 [14]. The measurements were made using an analytical balance coupled to a density determination kit. All measurements were made in a humidity-free room with controlled temperature. Small beads (n = 6) of the unpolymerized material from each group were weighed in air and in a solvent. Also, spheres were prepared and immediately light-cured, and their weight was recorded in air and in

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solvent. For the determination of the density of the spheres the following formula was used: =

mair × 0 mair − msolvent

(4)

where: mair is the weight of the sample in air, in grams; 0 is the density of the buoyancy medium (hexane), in g/cm3 ; and msolvent is the weight of the sample in the buoyancy medium (hexane), in grams. Based on the results, the following equation was applied for the determination of the polymerization shrinkage: S=

 −   c u c

× 100

(5)

where S is the polymerization shrinkage percentage, c is the density of the polymerized sample and u the density of the unpolymerized sample.

2.9.

Polymerization shrinkage stress

The Proto-Tech’s Polymerization Stress Tester was used for this analysis. The equipment is designed to follow in real time the stress produced by the dental restoration material when it is polymerized. A small quantity of the composite (n = 3) was placed in one of the acrylic tubes and subsequently lightcured by the top and bottom of the acrylic tubes for 160 s. The maximum force registered by the load cell was considered as the polymerization stress of the materials. This assay was performed in triplicate.

2.10.

Water sorption and solubility

The water sorption and solubility of the composites were evaluated following the specifications provided by the ISO-4049 International Standard [12]. Cylindrical specimens (n = 6; 5 × 1 mm) were prepared by inserting the unpolymerized material into a silicone mold and irradiated for both sides during 10 s using a photopolymerization unit. Once polymerized, the specimens were placed in a vertical support separated from each other in a desiccator to remove humidity. The specimens were weighed and monitored daily until their mass was constant (±0.01), this mass was registered as m1 . After obtaining m1 , the thickness and diameter of the test pieces were measured to obtain the volume of each of them (V). Subsequently, all the specimens were immersed in distilled water at 37 ◦ C for one week. After that, the specimens were removed from the water, weighed and the mass obtained was recorded as m2 . To finish the process, the specimens were again introduced in a desiccator to achieve the elimination of water and weighed daily until their mass remained constant. This mass was recorded as m3 . The water sorption and solubility were calculated with the following equations: Wsp =

m2 − m3 V

(6)

Wsi =

m1 − m3 V

(7)

where: Wsp is the water sorption value in micrograms, Wsi is the specimen solubility in micrograms per cubic millimeter, m2 is the mass of the specimen in micrograms after immersion in water for 7 days, m3 is the specimen mass reconditioned in micrograms, V is the specimen volume in mm3 .

2.11.

Crosslinking percentage

Crosslinking percentage was indirectly measured through the microhardness determination of the materials before and after softening in ethanol. Vickers microhardness measurements were carried out on cylindrical specimens (n = 3; 5 × 2 mm) with microdurometer (HMV-2, Shimadzu, Tokyo, Japan) under a load of 200 g load for 30 s. Measurements were performed at three locations near the center, and the average value was recorded as the initial Knoop Hardness Number (dry VHN). The same samples were then immersed in pure ethanol for 24 h, before re-measuring the microhardness (wet VHN). The ratio between ethanol VHN and dry VHN (%) was used as an indication of crosslinking percentage.

2.12.

Cell viability assay

Mouse fibroblast cells (L929) were cultured at a density of 2 × 104ˆ cells in 96-well plates containing DMEM medium (Dulbecco’s Modified Eagle Medium culture) supplemented with 10% l-glutamine, 10% serum, fetal bovine (FBS), penicillin 100 U/ml) and streptomycin (100 U/ml). The cells were incubated at 37 ◦ C under 95% air and 5% CO2 for 24 h. The cell viability ratio was evaluated by the WST-1 colorimetric assay. Samples were prepared in the form of a disk (n = 6; 5 × 1 mm). Specimens were placed in 24-well plates with 1 ml of DMEM and stored at 37 ◦ C at pH 7.2. After 24 h, 200 ␮L of each specimen was transferred to the 96-well plate containing the precultured cells. The plate was incubated (37 ◦ C, 5% CO2 ) for 24 h. After this period, the medium was aspirated, and the WST-1 solution was applied. The results were read on a spectrophotometer with a wavelength of 450 nm, where the absorbance values were considered as an indicator of cell viability.

2.13.

Statistical analysis

The statistical analysis was performed using Sigma Plot 12.0 software. The data was analyzed to verify the normal distribution and the homogeneity of the variance. A t-test was made to evaluate each of the dependent variables. The level of significance for all the test was set to ˛ < 0.05.

3.

Results

The TTM monomer structure was confirmed by the 1 H, 13 C NMR and FT-IR absorption spectroscopy techniques. Fig. 1a shows the FTIR spectrum for the TTM monomer, while Fig. 1b shows the 1 H NMR spectrum. 13 C NMR is available as supplementary information. Table 1 shows the viscosity values of the monomers used in the formulation of the composite materials (BisGMA,

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Fig. 1 – (a) FT-IR and (b) NMR 1 H spectrum of TTM monomer.

Table 1 – Molecular weight and viscosity of Bis-GMA, TEGDMA and TTM. Monomer

Molecular weight (g/mol)

Viscosity (pa s)

Bis-GMA TEGDMA TTM

512.60 286.32 718.80

342.77 48.54 345.8

TEGDMA, and TTM). Among the monomers evaluated, the TTM monomer achieved the highest viscosity. The mean values of the flexural strength and elastic modulus for the photopolymerizable composites resins formulated in this study are shown in Table 2. The analysis showed that there were no statistically significant differences between the materials evaluated, for both flexural strength and elastic modulus (p > 0.05).

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Table 2 – Flexural strength values, elastic modulus, water sorption and water solubility of the composite resins formulated. Formulation

Flexural strength (MPa)

Elastic modulus (MPa)

Water sorption (␮g/mm3 )*

Water solubility (␮g/mm3 )

Bis-GMA/TEGDMA TTM/TEGDMA

108.03 (14.45)a 101.92 (17.37)a

4184.89 (900.12)a 3520.68 (602.76)a

3.07 (0.13)a 4.67 (0.64)b

0.54 (0.18)a 0.95 (0.16)b

Same superscript letters in each column indicate that there are no statistically significant differences. Analyzed using U-Mann Whitney test.

∗

statistically significant differences between the experimental and control composite (p = 0.052). The viability of L929 cells that were cultured with the extraction medium of different composite resin systems formulated with BisGMA/TEGDMA and TTM/TEGDMA was 92.57 (0.12) and 92.94 (0.13), respectively. The differences among the means were not statistically significant (p = 0.345).

Fig. 2 – Glass transitions temperature for the composite materials.

Fig. 2 shows the Tg value for the composites formulated with the BisGMA or TTM monomers. The glass transition temperatures observed were 133.04 ◦ C for control and 131.2 ◦ C for TTM. Table 3 shows the degree of double bond conversion of the materials evaluated. The composite resin formulated with the TTM monomer has a degree of double bond conversion similar to the control resin (p = 0.089). Fig. 3a and b shows the polymerization rate of the resin-based materials evaluated. The experimental composite formulated with the TTM monomer has a lower polymerization rate than the control material. Table 3 shows the polymerization shrinkage values observed for the materials evaluated in this study. The analysis performed revealed that there were no statistically significant differences between the materials (p = 0.470). The polymerization stress observed for the materials evaluated in this study is summarized in Table 3. The statistical analysis performed revealed that composites formulated with TTM monomer achieved higher values of polymerization stress (p < 0.001). Table 2 shows the mean values of water sorption and solubility for the materials evaluated. According to the analysis, composites formulated with TTM as base monomer presented statistically higher values for both properties (p < 0.05). The values obtained for crosslinking percentage are shown in Table 3. According to the statistical analysis, there were no

4.

Discussion

4.1.

FT-IR and NMR characterization

The data of FT-IR and 1 H NMR confirmed that TTM monomer had the same structure as designed. The analysis of FT-IR spectra showed the main evidence of its obtention is the absorption band located at 1711 cm−1 , which corresponds to the elongation vibration mode of the carbonyl group C O; also, the absorption band located at 1629 cm−1 , which was assigned to the elongation vibration of the C C bond of the methacrylic groups. Another evidence can be found in the appearance of the elongation vibration of the hydroxyl group at 3428 cm−1 , which can confirm the opening of epoxy rings of the raw material. With regards to NMR1 H spectroscopy, the main evidence of the formation of TTM monomer can be found in the multiple signal located at 6.20 and 5.67 ppm, which corresponds to the protons in trans (H7) and cis (H8) position with respect to the methyl of the methacrylic group, respectively. A multiple and wide signal is also observed in a range of 4.5–3.8 ppm that integrate for twenty protons (H1, H4, H5, H6, H11) corresponding to the methylene, methines and hydroxyl protons (OH) of the TTM monomer aliphatic chain. Finally, the multiple signal observed at 1.90 ppm integrates for nine protons (H9) and corresponds to the methyl of the methacrylic groups (Fig. 1b).

4.2.

Viscosity

The viscosity values of the TTM monomer are higher than those of BisGMA and TEGDMA monomers. Several reasons can explain this result, first, TTM monomer has a higher molecular weight than BisGMA; also, as TTM contains three hydroxyl groups within its structure, a greater amount of intra and intermolecular hydrogen bonds are formed when compared to the BisGMA monomer, who presents only two hydroxyl groups [15,16].

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Table 3 – Degree of double bond conversion, polymerization shrinkage and polymerization stress of the materials. Formulation

Crosslinking density (%)

Polymerization shrinkage (%)

Polymerization stress (N)

Bis-GMA/TEGDMA TTM/TEGDMA

88.61 (2.83)a 85.20 (3.96)a

6.13 (3.23)a 4.98 (1.00)a

26.80 (0.84)b 35.60 (1.14)a

Same a-b letters indicate that there are no statistically significant differences between the groups.

Fig. 3 – Degree of conversion (A) and polymerization kinetics (B–C) of the experimental and control materials. In A, the square and circle points represent the experimental data. Polymerization kinetics parameters were calculated considering the fitted data (dotted and straight line). Differences in the degree of conversion values among the groups were not statistically significant (p = 0.089).

4.3.

Flexural strength and elastic modulus

Statistical analysis performed demonstrated the absence of statistically significant differences in both flexural properties of the materials evaluated. This behavior could be attributed to the fact that the TTM monomer has within its structure three aromatic rings that confer rigidity to the material [17]. As flexural strength has a strong relationship with some important clinical features [18], it could be expected that the substitution of BisGMA for TTM monomer could lead to composite resin-based materials with optimal clinical performance. On the other hand, similar values for elastic modulus were observed between the materials, which guarantees that restorations with composites formulated with TTM monomer would have adequate marginal quality [19].

4.4.

Dynamical mechanical analysis

According to the glass transition temperatures observed (133.04 ◦ C for control and 131.2 ◦ C for TTM), the evaluated composite resins are not flexible at room temperature, neither at body temperature. This result is relevant because if Tg values are exceeded by intraoral temperatures, softening and consequently, failure of the clinical restoration is expected [20].

that the physical and mechanical properties of resin-based composites are influenced by the level of monomer to polymer conversion achieved during the polymerization process [22]. On the other hand, it could be noticed that TTM composite achieved lower polymerization rate than the control composite. This behavior was surprising since TTM monomer has three methacrylate groups, and therefore more functionalities created by the initiation reaction are expected, which in turns would result in a higher rate of polymerization [23]. In order to better understand this result, Rp was plotted against DC (Fig. 3a), and in the resulting graph it could be observed that the polymerization rate progressively increases until a certain degree of double bond conversion. After this point, the vitrification of each polymer occurs, the polymerization rate of the materials decreases markedly. This deacceleration observed occurs because the polymer vitrification immobilizes the diffusion of growing radicals. The graph of the composite formulated with TTM monomer revealed that vitrification occurs at lower double bond conversion percentage, which can be explained by the restricted mobility of radical and the increase steric hindrance of TTM monomer, which reduces the radicals diffusion, and consequently, the propagation of the polymerization reaction is limited [24].

4.6. 4.5.

Polymerization shrinkage

Polymerization kinetics

The composite resin formulated with the TTM monomer showed a degree of double bond conversion similar to the control resin. This behavior could occur due to the similarity in the viscosity observed among the base monomers used [21]. The obtaining of the same values of degree of conversion can also explain the results obtained for flexural strength and elastic modulus, this is because it has been already demonstrated

When comparing the polymerization shrinkage values, a slight reduction was observed for the experimental composite. This reduction observed could be attributed to the fact that the TTM monomer has a higher molecular weight compared to BisGMA [25]. Also, the TTM polymer network has more free volume than BisGMA, the presence of a considerable amount of free volume prevented a reduction in the polymerization shrinkage.

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4.7.

Polymerization stress

According to the results, the experimental material had the highest polymerization stress values. This behavior could be related to the fact that TTM composites vitrificated in earlies stages of during the polymerization reaction the polymer conversion. As previously stated, stress development occurs only after the polymer reached a stage where mobility is limited [26].

4.8.

Water sorption and solubility

The comparison of the materials showed that control composites achieved statistically lower values for both water sorption and solubility. This increase in the water sorption observed for the experimental TTM composite could be explained by the presence of three pendant hydroxyl within the structure of this monomer, which ones can form hydrogen bonds with water molecules [27]. With regards to the solubility, it could be hypothesized that the higher solubility observed for the experimental material is related to the increase in water sorption and to the slight reduction in the crosslinking density observed in the experimental material. The study of the hydric behaviour is important in the development of new materials for restoration purposes. ISO 4049 includes the water sorption and solubility tests in order to assess the hydrophobic behaviour of composite resins. This international standard also stablishes a maximum of 40 ␮g/mm3 for water sorption and 7.5 ␮g/mm3 of solubility allowed, and in this case, our experimental material formulated with the TTM monomer complies with this requirement.

4.9.

5.

Conclusion

In this study, a new trimethacrylate monomer was synthesized in a single step reaction with quantitative yields. The resulted monomer is liquid at room temperature and capable of photopolymerize with visible light. This monomer was used to formulate experimental free BisGMA composites. Considering that TTM-based composite resin has comparable mechanical and biological properties than a BisGMA composite used as control, it could be concluded that TTM monomer has the potential to be used as alternative for Bis-GMA in the formulation of composite dental resins. Despite this promising results, further research is needed to investigate whether TTM-based composite materials have stability over time.

Acknowledgements Author Carlos Enrique Cuevas-Suárez would like to thank PRODEP, México [DSA/103.5/15/6615].

Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j. dental.2020.02.005.

references

Crosslinking percentage

Crosslinking percentage is an important feature related to the long-lasting mechanical behavior of composites [28]. The statistical analysis revealed that the experimental composite has a similar performance than the control. Considering this, it should be theorized that restorations performed with TTM monomer could have optimal mechanical properties after aging, and that the substitution of BisGMA by the TTM monomer in composite resins is viable.

4.10.

of the majority of the leachable components occurs within this period of time [33].

Cell viability assay

Determining the viability of eukaryotic cells is an important component in the evaluation of new materials for use in dentistry. Evaluating the biocompatibility of a material using an in vitro cell culture assay represents an attempt to predict in vivo oral tissue responses [29]. Mouse fibroblast cell line (L929) was chosen for this study because of their high sensitivity to toxic products [30,31]. According to the results, experimental system formulated with TTM monomer showed values of cell viability above 70%, which according to ISO 10993-5, it is considered non-cytotoxic. The lack of toxic leachables from the TTM based composite could be related to its relatively high crosslinking density [32]. Additionally, it should be noted that the present study only considered the effects of leachables from the first 24 h, since it’s well known that elution

[1] Ferracane JL. Resin composite—state of the art. Dent Mater 2011;27:29–38, http://dx.doi.org/10.1016/j.dental.2010.10.020. [2] Moszner N, Salz U. Recent developments of new components for dental adhesives and composites. Macromol Mater Eng 2007;292:245–71, http://dx.doi.org/10.1002/mame.200600414. [3] Gajewski VES, Pfeifer CS, Fróes-Salgado NRG, Boaro LCC, Braga RR. Monomers used in resin composites: degree of conversion, mechanical properties and water sorption/solubility. Braz Dent J 2012;23:508–14. [4] Söderholm KJ, Mariotti A. BIS-GMA-based resins in dentistry: are they safe? J Am Dent Assoc 1999;130:201–9, http://dx.doi.org/10.14219/jada.archive.1999.0169. [5] Joskow R, Barr DB, Barr JR, Calafat AM, Needham LL, Rubin C. Exposure to bisphenol A from bis-glycidyl dimethacrylate-based dental sealants. J Am Dent Assoc 2006;137:353–62, http://dx.doi.org/10.14219/jada.archive.2006.0185. [6] Kingman A, Hyman J, Masten SA, Jayaram B, Smith C, Eichmiller F, et al. Bisphenol A and other compounds in human saliva and urine associated with the placement of composite restorations. J Am Dent Assoc 2012;143:1292–302, http://dx.doi.org/10.14219/jada.archive.2012.0090. [7] Akeroyd JM, Maserejian NN. Composite restorations may lead to increased concentrations of salivary and urinary BPA. J Evid Based Dent Pract 2013;13:64–6, http://dx.doi.org/10.1016/j.jebdp.2013.04.006. [8] McKinney C, Rue T, Sathyanarayana S, Martin M, Seminario AL, Derouen T. Dental sealants and restorations and urinary bisphenol a concentrations in children in the 2003-2004 national health and nutrition examination survey. J Am

Please cite this article in press as: Pérez-Mondragón AA, et al. Preparation and evaluation of a BisGMA-free dental composite resin based on a novel trimethacrylate monomer. Dent Mater (2020), https://doi.org/10.1016/j.dental.2020.02.005

DENTAL-3504; No. of Pages 9

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 2 0 ) xxx–xxx

[9]

[10]

[11] [12] [13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

Dent Assoc 2014;145:745–50, http://dx.doi.org/10.14219/jada.2014.34. Maserejian NN, Trachtenberg FL, Wheaton OB, Calafat AM, Ranganathan G, Kim HY, et al. Changes in urinary bisphenol A concentrations associated with placement of dental composite restorations in children and adolescents. J Am Dent Assoc 2016;147:620–30, http://dx.doi.org/10.1016/j.adaj.2016.02.020. Löfroth M, Ghasemimehr M, Falk A, Vult von Steyern P. Bisphenol A in dental materials—existence, leakage and biological effects. Heliyon 2019;5:e01711, http://dx.doi.org/10.1016/j.heliyon.2019.e01711. Coetzee JF. Recommended methods for purification of solvents and tests for impurities. Pergamon Press; 1982. International Organization for Standarization. ISO 4049:2009 Dentistry polymer based restorative materials; 2009. Yap AU, Teoh SH. Comparison of flexural properties of composite restoratives using the iso and mini-flexural tests. J Oral Rehabil 2003;30:171–7, http://dx.doi.org/10.1046/j.1365-2842.2003.01004.x. International Organization for Standarization. ISO 17304:2013 Dentistry—polymerization shrinkage: method for determination of polymerization shrinkage of polymer-based restorative materials; 2013. Atai M, Watts D, Atai Z. Shrinkage strain-rates of dental resin-monomer and composite systems. Biomateriales 2005;26:5015–20. Taylor DF, Kalachandra S, Sankarapandian M, McGrath JE. Relationship between filler and matrix resin characteristics and the properties of uncured composite pastes. Biomaterials 1998;19:197–204, http://dx.doi.org/10.1016/S0142-9612(98)80001-X. Sokolov AP, Kunal K, Robertson CG, Pawlus S, Hahn SF. Role of chemical structure in fragility of polymers: a qualitative picture. Macromolecules 2008;41:7232–8, http://dx.doi.org/10.1021/ma801155c. Heintze SD, Ilie N, Hickel R, Reis A, Loguercio A, Rousson V. Laboratory mechanical parameters of composite resins and their relation to fractures and wear in clinical trials—a systematic review. Dent Mater 2017;33:101–14, http://dx.doi.org/10.1016/j.dental.2016.11.013. Benetti AR, Peutzfeldt A, Lussi A, Flury S. Resin composites: modulus of elasticity and marginal quality. J Dent 2014;42:1185–92, http://dx.doi.org/10.1016/j.jdent.2014.07.004. Rueggeberg FA, Maher FT, Kelly MT. Thermal properties of a methyl methacrylate-based orthodontic bonding adhesive. Am J Orthod Dentofacial Orthop 1992;101:342–9, http://dx.doi.org/10.1016/S0889-5406(05)80327-0. Sideridou I, Tserki V, Papanastasiou G. Effect of chemical structure on degree of conversion in light-cured dimethacrylate-based dental resins. Biomaterials

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

9

2002;23:1819–29, http://dx.doi.org/10.1016/S0142-9612(01)00308-8. Ferracane JL, Greener EH. The effect of resin formulation on the degree of conversion and mechanical properties of dental restorative resins. J Biomed Mater Res 1986;20:121–31, http://dx.doi.org/10.1002/jbm.820200111. Leprince JG, Palin WM, Hadis MA, Devaux J, Leloup G. Progress in dimethacrylate-based dental composite technology and curing efficiency. Dent Mater 2013;29:139–56, http://dx.doi.org/10.1016/j.dental.2012.11.005. Srivastava R, Wolska J, Walkowiak-Kulikowska V. Fluorinated bis-GMA as potential monomers for dental restorative composite materials. Eur Polym J 2017;90:334–43, http://dx.doi.org/10.1016/j.eurpolymj.2017.03.027. Yin M, Liu F, He J. Preparation and characterization of Bis-GMA free dental resin system with synthesized dimethacrylate monomer TDDMMA derived from tricyclo[5.2.1.0(2,6)]-decanedimethanol. J Mech Behav Biomed Mater 2016;57:157–63, http://dx.doi.org/10.1016/j.jmbbm.2015.11.020. Stansbury JW. Dimethacrylate network formation and polymer property evolution as determined by the selection of monomers and curing conditions. Dent Mater 2012;28:13–22, http://dx.doi.org/10.1016/j.dental.2011.09.005. Prakki A, Cilli R, Vieira IM, Dudumas K, Pereira JC. Water sorption of CH3- and CF3-Bis-GMA based resins with additives. J Appl Oral Sci 2012;20:472–7, http://dx.doi.org/10.1590/s1678-77572012000400014. De Paula FC, Valentin RDS, Borges BCD, Medeiros MCDS, De Oliveira RF, Da Silva AO. Effect of instrument lubricants on the surface degree of conversion and crosslinking density of nanocomposites. J Esthet Restor Dent 2016;28:85–91, http://dx.doi.org/10.1111/jerd.12182. Murray PE, García Godoy C, García Godoy F. How is the biocompatibilty of dental biomaterials evaluated? Med Oral Patol Oral Cir Bucal 2007;12:258–66. Pissiotis E, Spanberg LSW. Toxicity of Pulpispad using four different cell types. Int Endod J 1991;24:249–57, http://dx.doi.org/10.1111/j.1365-2591.1991.tb01150.x. Donadio M, Jiang J, He J, Wang YH, Safavi KE, Zhu Q. Cytotoxicity evaluation of Activ GP and Resilon sealers in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endodontol 2009;107:74–8, http://dx.doi.org/10.1016/j.tripleo.2009.01.041. Lee MJ, Kim MJ, Kwon JS, Lee SB, Kim KM. Cytotoxicity of light-cured dental materials according to different sample preparation methods. Materials (Basel) 2017;14:3, http://dx.doi.org/10.3390/ma10030288. Mazzaoui SA, Burrow MF, Tyas MJ, Rooney FR, Capon RJ. Long-term quantification of the release of monomers from dental resin composites and a resin-modified glass ionomer cement. J Biomed Mater Res 2002;63:299–305, http://dx.doi.org/10.1002/jbm.10184.

Please cite this article in press as: Pérez-Mondragón AA, et al. Preparation and evaluation of a BisGMA-free dental composite resin based on a novel trimethacrylate monomer. Dent Mater (2020), https://doi.org/10.1016/j.dental.2020.02.005