The purpose of this study was to prepare radio-opaque E-glass fiber-reinforced composite (EFRC) with synthesized iodine containing methacrylate monomer.
The synthesized iodine containing methacrylate monomer 2-hydroxy-3- methacryloyloxypropyl(2,3,5- triiodobenzoate) (HMTIB) was mixed with Bis-GMA and MMA in different mass ratio to prepare resin impregnating solution (RIS), and RIS without HMTIB was used as control. CQ and DMAEMA were added as photoinitiation system. E-glass fiber was thoroughly wetted by resin impregnating solution to prepare radio-opaque EFRC. Degree of double bond conversion (DC) was investigated by FT-IR analysis. Fiber volume fraction was analyzed by combustion and gravimetric analyzes. The Flexural strength (FS) and modulus (FM) of EFRC were measured using a three-point bending set up. Water sorption (WS) and solubility (SL) were measured until the mass variation of EFRC in distilled water kept stable. Radiographs were taken to determine the radiopacity of EFRC.
The FT-IR and 1 H NMR spectra of HMTIB revealed that it was the same as designed. ANOVA analysis revealed that increasing HMTIB concentration in RIS would decrease DC and increase fiber volume fraction. When compared with control EFRC, all of HMTIB containing EFRCs had higher or comparable FS and FM, no matter before or after water immersion. WS of EFRC decreased with increasing HMTIB concentration, while SL was nearly kept the same. Radiopacity of EFRC increased with increasing HMTIB concentration.
The synthesized monomer HMTIB could be used to prepare EFRC with high radiopacity. Moreover, HMTIB containing EFRC would also have high mechanical properties and low WS.
Fiber-reinforced composites (FRCs) are typical composite materials made of a resin matrix that is reinforced by fine thin fibers . FRCs have extensively been used in fixed prosthodontics, restorative dentistry, periodontology, orthodontics and in repairs of prosthetic devices , since they were first applied into dentistry as denture base materials in 1960s.
Fiber is one kind of high aspect ratio filler that has been utilized for decades in engineering applications to construct devices with high strength and fracture toughness . Glass fibers are preferred in dental application due to their aesthetic appearance and good adhesion to resin matrix via silane coupling agents or plasma-enhanced chemical vapour deposition (PECVD) treatment . Glass fibers that have been used in dentistry can be classified into six categories according to their composition, that is A-glass, C-glass, D-glass, S-glass, AR-glass and E-glass . E-glass fiber, which is made of alumino-borosilicate glass with less than 1 wt.% of alkali oxide, is the most frequently used glass fiber due to its advantages like low cost and high production rates, relative low density, ability to maintain strength properties over a wide range of conditions, relatively insensitive to moisture, chemical-resistant, and heat-resistant . However, E-glass fiber has limited radio-opacity because of the low concentration of radio-opaque elements. This shortcoming of E-glass fiber would limit its application in dentistry for sufficient radio-opacity is highly desirable for dental materials. On the other hand, minor radiopacity is beneficial for the elimination of artifacts in cone-beam computer tomography imaging .
There exist two approaches that can endow E-glass fiber-reinforced composites (EFRCs) with radio-opacity, one is adding radio opaque fillers into composites, and the other is making resin matrix radio opaque. However, the radio opaque fillers require volume which is then taken from the reinforcing fibers of the fiber reinforced composites. Therefore, the optimal fibers volume cannot be reached . Therefore, a resin matrix which could provide radio-opacity would be beneficial in the EFRCs.
As the most commonly used resin matrix for EFRCs, polymerizable methacrylate monomers can be made radio opaque by incorporation high electronic density element like bromine and iodine into the structure. Several polymerizable monomers containing iodine element have been reported in literature , but none of them has been applied into EFRCs.
The aim of this study was synthesizing a iodine containing methacrylate monomer named 2-hydroxy-3-methacryloyloxypropyl(2,3,5-triiodobenzoate) (HMTIB) and applying it as radio-opaque agent of resin matrix for EFRCs. The hypothesis was that HMTIB containing EFRCs would have sufficient radio-opacity. The influence of HMTIB on double bond conversion, fiber volume fraction, flexural strength and modulus, water sorption and solubility were also investigated.
Materials and methods
2,3,5-Triiodobenzoic acid (TIDBA), glycidyl methacrylate (GMA), triethylamine (TEA), hydroquinone, methyl methacrylate (MMA), camphoroquinone (CQ), and N , N ′-dimethyl- aminoethylmethacrylate (DMAEMA) were purchased from Sigma-Aldrich Co., USA. 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)-phenyl]propane (Bis-GMA) was applied from Esstech Inc., USA. All of the components were used without further purification. 2400 tex unidirectional silanated E-glass fiber R338-2400 was applied from Ahlstrom Co., Finland.
Synthesis of 2-hydroxy-3-methacryloyloxypropyl(2,3,5-triiodobenzoate) (HMTIB)
52.48 g (0.105 mol) TIDBA and 14.22 g (0.100 mol) GMA were stirred with 50 mL 1,4-dioxane at reflux in the presence of 0.20 g hydroquinone and 2.67 g TEA. The reaction was continued until the infrared absorbance peak of the epoxy group (910 cm −1 ) disappeared in the FT-IR spectra of the samples taken from the reaction medium. After removing the 1,4-dioxane by distillation under vacuum, the raw product was dissolved in dichloromethane and the precipitate was removed by vacuum filtration. The resulting solution was washed successively with 1 mol/L aqueous HCl and 2 mol/L aqueous NaOH solution. The organic layer was then dried overnight with anhydrous magnesium sulfate. After removing the drying agent by filtration, the dichloromethane was removed by distillation under vacuum to obtain a brown viscous liquid. The brown viscous liquid was purified through silica gel chromatography (ethyl acetate:petroleum ether = 6:4, V/V) to obtain HMTIB as yellow viscous liquid (51.36 g) at a yield of 80%. The results of spectroscopic studied for HMTIB were as follows: IR (neat): v (cm −1 ) 3472, 2955, 1720, 1634, 1520, 1451, 1320, 1270,1177, 813, 707. 1H-NMR (CDCl 3 , 400 MHz): δ 8.34, 7.76, 6.17, 5.65, 4.29–4.50, 3.92, 3.30.
Preparation of E-glass fiber-reinforced composites (EFRCs)
40 bundles of 10 cm long unidirectional E-glass fiber were prepared and divided into 5 groups randomly. Each bundle of E-glass fiber was dipped into different resin impregnating solution (components are shown in Table 1 ) until the fiber was thoroughly wetted. The fiber was then pulled out of the resin impregnating solution slowly and hung in an oven under vacuum at room temperature for 30 min to remove most of the MMA. After that, cylinder-shaped EFRCs were light-cured with a LED dental light curing device (Curing Light 2500, λ = 400–520 nm, I ≈ 550 mW cm −2 , 3 M Co., St Paul, MN, USA). Every point of EFRC was irradiated for 60 s until the whole EFRC was irradiated. After irradiation, all EFRCs were cut into small pieces with 25 mm length and 1.3 ± 0.1 mm average diameter. A bundle of unpolymerized EFRC of each group was stored in darkness at 4 °C for the meacurement of double bond conversion.
|Resin impregnating solution of EFRC||Component (g)|
Measurement of double bond conversion (DC)
The DC was determined by using a FTIR spectrometer (Spectrum One, PerkinElmer, Waltham, MA, USA) with an attenuated total reflectance (ATR) accessory. The FTIR spectra were recorded with 16 scans at a resolution of 4 cm −1 . First, the unpolymerized EFRC sample (5 mm long) covered with a Mylar film and a glass plate was pressed tightly onto the crystal of ATR accessory, and scanned to obtain its spectrum. Then, the sample was irradiated for 60 s with a visible light-curing unit the same as mentioned above. After that, the cured sample was ground into powder and the spectrum of powder was obtained as the spectrum of polymerized sample.
In order to determined the percentage of reacted double bonds, the methacrylate C C absorbance peak at 1636 cm −1 , which was decreased after being irradiated, was chosen. The absorption peak of phenyl ring at 1608 cm −1 was used as an internal standard peak. The absorbance intensities of these two peaks were calculated using a baseline method, and DC was then calculated by using the equation
where A C C and A Ph are the absorbance intensity of methacrylate C C at 1636 cm −1 and phenyl ring at 1608 cm −1 , respectively; (A C C /A Ph ) 0 and (A C C /A Ph ) 60 are the normalized absorbances of functional groups before and after radiation.
The measurement was repeated three times for every group of EFRC.
Measurement of E-glass fiber volume fraction
The E-glass fiber volume fraction in the test samples was determined by combustion analysis with a burnout furnace (Radiance Multi-stage msc, Jelrus International, Hicksville, NY, USA). The test samples (n = 5) were dried in a desiccator for 2 days at room temperature and weighed to an accuracy of 0.1 mg prior to combustion. In order to combust the polymer matrix, the temperature was raised 12 °C per min until the temperature reached 700 °C. Test samples were maintained at 700 ± 25 °C for 1 h and reweighed. Usually, the fiber volume fraction (V f , vol.%) was calculated according to the equation reported previously . However, it was difficult to measure the r r in this research, and the volume of EFRC was nearly equal the sum of volume of polymer and E-glass fiber, so V f could be calculated according to the following equation:
where W f is the weight proportion of E-glass fiber, r f (2.45 g/cm3) is the density of E-glass fiber, W c is the weight of EFRC, r c is the density of E-glass fiber that is measured using Archimedes’ principle with a commercial Density Determination Kit of the analytical balance Mettler Toledo X (Mettler Instrument Co., Highstone, NJ, USA).
Measurement of flexural strength (FS) and modulus (FM)
16 samples (25 mm long and 1.3 ± 0.1 mm in average diameter) of each EFRC were chosen and divided into 2 groups: one group (n = 8) for mechanical testing before water immersion, and the other group (n = 8) for mechanical testing after water immersion. The water immersion time was the same as the time for water sorption measurement.
The three-point bending test was used to measure FS and FM of the samples according to ISO 10477:92 standards (span 20.0 mm, crosshead speed 1.0 mm/min). All samples were tested with a material testing machine (model LRX, Lloyd Instruments Ltd., Fareham, England) at room temperature. FS and FM of samples were calculated from the formulas: