Effect of hydrogen peroxide on the three-dimensional polymer network in composites

Abstract

Objectives

Less data are available about the effects of hydrogen peroxide on the three-dimensional polymer network of polymerized composites. Therefore the study was performed to test the effects of hydrogen peroxide on the three-dimensional polymer network in composites.

Methods

Polymerized specimens from Tetric Flow ® , Tetric Ceram ® and Filtek™ Supreme XT were bleached with Opalescence ® PF 15% for 5 h or PF 35% for 0.5 h, respectively, and then stored in methanol for 1 d and 7 d. Controls were unbleached specimens. The eluates were analyzed by gas chromatography/mass spectrometry.

Results

More methacrylic acid (MAA), bisphenol-A (BPA), ethoxylated bisphenol-A-dimethacrylate (BisEMA), hydroquinone monomethyl ether (HQME), 1,10-decanediol dimethacrylate (DDDMA) and/or triethylene glycol dimethacrylate (TEGDMA) were eluted from bleached specimens compared with non bleached controls (1 d). The highest DDDMA amount of 419.8 μmol/l was found in the eluates after 7 d in Tetric Flow ® specimens treated with PF 15. The highest HQME amount of 159.6 μmol/l was found in eluates from Tetric Ceram ® specimens treated with PF after 7 d. The highest TEGDMA amount of 178.7 μmol/l was found in eluates from Filtek™ Supreme XT specimens treated with PF 35 after 7 d.

Significance

Bleaching with hydrogen peroxide has an effect on the three-dimensional polymer network in polymerized composites leading to an increase in the release of unpolymerized monomers, additives and unspecific oxidative products.

Introduction

Discoloration of the tooth enamel can result from many reasons such as foods, tobacco smoke, poor oral hygiene, diseases of the enamel or dentin, some medications like tetracycline or doxycycline, aging, and genetic considerations . Normally tooth discolorations are without pathological effect, but there is an increasing number of patients who would like to whiten their teeth for cosmetic reasons . The discoloration can often be removed by applying a bleaching agent to the enamel of the teeth. In these bleaching solutions often peroxide based whitening substances like carbamide peroxide or hydrogen peroxide are used . Various bleaching modalities are offered to patients like in-office bleaching, usually with 25–35% hydrogen peroxide, and home bleaching, usually with 6.5–22% carbamide peroxide (compounded: urea-hydorgen peroxide, which is an oxidizing agent, consisting of hydrogen peroxide compounded with urea, CH 4 N 2 O·H 2 O 2 ) .

The exact mechanism underlying the process of tooth bleaching is not fully understood . However, the bleaching agents carbamide peroxide and hydrogen peroxide produce oxidizers as part of a chemical reaction and these are able to diffuse along a gradient within enamel micropores, gaining direct access to the underlying dentin . Oxidizers can cleave C–C-double bonds within chromophores, which result in their break down and diffusion into the external environment, or a size reduction sufficient to cause them to absorb less light and appear lighter . It is known that bleaching systems can lead to alterations on surface morphology and mineral loss of human enamel as well as to changes in the tooth enamel matrix because of an unspecific oxidation of the organic enamel matrix caused by the hydrogen peroxide in the bleaching system . It is well known that hydrogen peroxide can lead to unspecific oxidation of a variety of substances . It is common currency that hydrogen peroxide can react with C–C-single bonds or C–C-double bonds .

Less data are available in the literature about the reactions of hydrogen peroxide with the three-dimensional polymer network of polymerized dental composites. The polymer network of polymerized dental composites consists of C–C-single bonds which may react with oxidants like hydrogen peroxide. Less data are available about the effects of hydrogen peroxide on the three-dimensional polymer network of polymerized composites.

Methods

All solvents and reagent products were obtained from Merck, Darmstadt, Germany and of highest purity available.

Preparation of samples

From the light-curable tooth restorative materials Tetric Flow ® (LOT M61775; Ivoclar Vivadent, Ellwangen, Germany), Tetric Ceram ® (LOT N01397; Ivoclar Vivadent) and Filtek™ Supreme XT (LOT 7KU; 3M ESPE, Seefeld, Germany) specimens of approximately 100 mg (thickness of 1.8 mm, diameter of 6 mm; color A2, with a resulting surface of the cylinder of 90.4 mm 3 ) were prepared under exclusion of day light. The specimens were covered with plastic matrix strips US-120KN (Frasaco, Tettnang, Germany) and polymerized according to the instructions of the manufacturer by using an Astralis 10 ® light source (Ivoclar Vivadent).

After preparation of the specimens, they were bleached with Opalescence ® PF 15% Tooth Whitening System (PF 15; LOT Z022; Ultradent, South Jordan, Utah, USA) or Opalescence ® PF 35% Tooth Whitening System (PF 35; LOT U032; Ultradent,), respectively. From each composite 4 specimens were bleached with PF 15 or PF 35, respectively. According to the instructions of the manufacturer the bleaching times were: 0.5 h (PF 35) and 5 h (PF 15). After bleaching of the specimens the paste was removed from the surface of the specimens with a Heidemann spatula and then carefully swabbed with a cotton stick without the use of water not to wash out monomers or additives from the specimen. Then the bleached specimens were incubated in methanol (100 mg/mL) at 37 °C for 1 d and 7 d. The control specimens ( n = 4 from each composite) were not bleached and only incubated in methanol (100 mg/mL) at 37 °C for 1 d and 7 d. Caffeine (CF; 0.1 mg/mL) was added to the eluates and each aliquot was analyzed by GC/MS.

GC/MS analysis

The analysis of the eluates was performed on a Finnigan Trace GC ultra gas chromatograph connected to DSQ mass spectrometer (Thermo Electron, Dreieich, Germany). A FactorFour ® capillary column (length 25 m, inner diameter 0.25 mm, coating 0.25 μm; Varian, Darmstadt, Germany) was used as capillary column for GC. The GC oven was heated from 50 °C (2 min isotherm) to 300 °C (5 min isotherm) with a rate of 10 °C/min and 1 μl of the solution was injected with a split of 1:30. Helium was used as carrier gas at a constant flow rate of 1 mL/min. The temperature of the split-splitless injector as well as of the direct coupling to the mass spectrometer was 250 °C. MS was operated in electron ionization mode (EI, 70 eV), ion source was operated at 200 °C; only positive ions were scanned. Scan ran over the range m / z 50–500 at a scan rate of 1 scan/s for scans operated in full scan mode to identify and qualify analytes. The results were referred to an internal CF standard (0.1 mg/mL CF = 100%), which allows to determine the relative quantities of substances released from various resin-based materials. All eluates were analyzed five times. The integration of the chromatograms was carried out over the base peak or other characteristic mass peaks of the compounds, and the results were normalized by means of the internal CF standard. Identification of the various substances was achieved by comparison of their mass spectra with those of reference compounds, the NIST/EPA library, literature data and/or by chemical analysis of their fragmentation patterns .

Calculations and statistics

The results are presented as means ± standard error of mean (SEM). The statistical significance ( p < 0.05) of the differences between the experimental groups was tested using the t -test, corrected according to Bonferroni–Holm .

Methods

All solvents and reagent products were obtained from Merck, Darmstadt, Germany and of highest purity available.

Preparation of samples

From the light-curable tooth restorative materials Tetric Flow ® (LOT M61775; Ivoclar Vivadent, Ellwangen, Germany), Tetric Ceram ® (LOT N01397; Ivoclar Vivadent) and Filtek™ Supreme XT (LOT 7KU; 3M ESPE, Seefeld, Germany) specimens of approximately 100 mg (thickness of 1.8 mm, diameter of 6 mm; color A2, with a resulting surface of the cylinder of 90.4 mm 3 ) were prepared under exclusion of day light. The specimens were covered with plastic matrix strips US-120KN (Frasaco, Tettnang, Germany) and polymerized according to the instructions of the manufacturer by using an Astralis 10 ® light source (Ivoclar Vivadent).

After preparation of the specimens, they were bleached with Opalescence ® PF 15% Tooth Whitening System (PF 15; LOT Z022; Ultradent, South Jordan, Utah, USA) or Opalescence ® PF 35% Tooth Whitening System (PF 35; LOT U032; Ultradent,), respectively. From each composite 4 specimens were bleached with PF 15 or PF 35, respectively. According to the instructions of the manufacturer the bleaching times were: 0.5 h (PF 35) and 5 h (PF 15). After bleaching of the specimens the paste was removed from the surface of the specimens with a Heidemann spatula and then carefully swabbed with a cotton stick without the use of water not to wash out monomers or additives from the specimen. Then the bleached specimens were incubated in methanol (100 mg/mL) at 37 °C for 1 d and 7 d. The control specimens ( n = 4 from each composite) were not bleached and only incubated in methanol (100 mg/mL) at 37 °C for 1 d and 7 d. Caffeine (CF; 0.1 mg/mL) was added to the eluates and each aliquot was analyzed by GC/MS.

GC/MS analysis

The analysis of the eluates was performed on a Finnigan Trace GC ultra gas chromatograph connected to DSQ mass spectrometer (Thermo Electron, Dreieich, Germany). A FactorFour ® capillary column (length 25 m, inner diameter 0.25 mm, coating 0.25 μm; Varian, Darmstadt, Germany) was used as capillary column for GC. The GC oven was heated from 50 °C (2 min isotherm) to 300 °C (5 min isotherm) with a rate of 10 °C/min and 1 μl of the solution was injected with a split of 1:30. Helium was used as carrier gas at a constant flow rate of 1 mL/min. The temperature of the split-splitless injector as well as of the direct coupling to the mass spectrometer was 250 °C. MS was operated in electron ionization mode (EI, 70 eV), ion source was operated at 200 °C; only positive ions were scanned. Scan ran over the range m / z 50–500 at a scan rate of 1 scan/s for scans operated in full scan mode to identify and qualify analytes. The results were referred to an internal CF standard (0.1 mg/mL CF = 100%), which allows to determine the relative quantities of substances released from various resin-based materials. All eluates were analyzed five times. The integration of the chromatograms was carried out over the base peak or other characteristic mass peaks of the compounds, and the results were normalized by means of the internal CF standard. Identification of the various substances was achieved by comparison of their mass spectra with those of reference compounds, the NIST/EPA library, literature data and/or by chemical analysis of their fragmentation patterns .

Calculations and statistics

The results are presented as means ± standard error of mean (SEM). The statistical significance ( p < 0.05) of the differences between the experimental groups was tested using the t -test, corrected according to Bonferroni–Holm .

Results

Tetric Flow ® specimens

Twenty-four hours after the beginning of experiment significant ( p < 0.05) higher amounts of substances were found eluted from Tetric Flow ® specimens treated with PF 15, compared with non bleached Tetric Flow ® specimens ( Table 1 ): methacrylic acid (MAA; 65.9 vs. 0.6 μmol/l), bisphenol-A (BPA; 14.5 vs. 2.1 μmol/l), ethoxylated bisphenol-A-dimethacrylate (BisEMA; 7.9 vs. 1.5 μmol/l), hydroquinone monomethyl ether (HQME; 70.1 vs. 33.9 μmol/l) and 1,10-decanediol dimethacrylate (DDDMA; 419.8 vs. 233.3 μmol/l). Twenty-four hours after the beginning of the experiment a significant ( p < 0.05) higher amount of eluted DDDMA was found from Tetric Flow ® specimens treated with PF 15, compared with Tetric Flow ® specimens treated with PF 35 (419.8 vs. 290.4 μmol/l). 7 d after the beginning of the experiments in methanolic eluates from Tetric Flow ® specimens treated with PF 35 triphenyl stibane (TPSB) was found in amount of 0.22 μmol/l.

Table 1
Substances identified and quantified in methanolic eluates from Tetric Flow ® after 1 d and 7 d of elution of polymerized specimens treated with the bleaching gels PF 15 (15% carbamide peroxide) or PF 35 (35% hydrogen peroxide). Control specimens were not treated with a bleaching gel. Data are presented as mean (MW) ± standard error of mean (SEM).
24 h 7 d
Controls 15% 35% Controls 15% 35%
MW ± SEM MW ± SEM MW ± SEM MW ± SEM MW ± SEM MW ± SEM
MAA 0.61 ± 0.12 65.91 ± 9.28 41.76 ± 3.79 30.46 ± 1.22 37.25 ± 9.02 18.40 ± 6.77
HQME 33.90 ± 2.89 70.10 ± 6.75 56.24 ± 6.47 103.46 ± 6.28 56.22 ± 13.55 127.00 ± 11.12
EGDMA 5.43 ± 0.45 26.20 ± 2.61 31.46 ± 4.62 15.00 ± 0.65 19.97 ± 4.54 9.32 ± 3.12
CQ 37.34 ± 4.05 0.49 ± 0.21 0.00 63.41 ± 7.18 0.64 ± 0.30 1.11 ± 0.83
CSA 1.67 ± 0.23 5.34 ± 0.64 16.65 ± 8.10 6.18 ± 0.50 1.55 ± 0.67 21.23 ± 10.21
BHT 1.22 ± 0.21 2.02 ± 0.30 1.82 ± 0.19 2.47 ± 0.33 1.72 ± 0.40 2.48 ± 0.11
BL 26.99 ± 0.70 30.23 ± 3.65 31.46 ± 3.34 59.68 ± 3.96 66.88 ± 30.73 18.01 ± 18.01
DMABEE 118.40 ± 10.59 169.39 ± 21.70 137.63 ± 4.56 246.46 ± 19.57 105.40 ± 44.52 315.27 ± 6.93
TEGDMA 0.53 ± 0.08 2.44 ± 0.08 3.77 ± 0.37 1.33 ± 0.17 1.04 ± 0.16 2.09 ± 0.76
DEDHTP 2.46 ± 0.08 2.31 ± 0.30 1.89 ± 0.64 4.50 ± 0.30 0.40 ± 0.40 3.79 ± 0.87
TINP 29.51 ± 1.31 74.00 ± 7.98 49.66 ± 5.55 85.35 ± 3.69 40.15 ± 11.40 113.26 ± 10.92
DDDMA 233.32 ± 42.52 419.78 ± 73.52 290.37 ± 16.24 376.38 ± 70.89 2.47 ± 0.66 411.32 ± 22.24
BPA 2.09 ± 0.10 14.49 ± 1.01 7.05 ± 1.67 4.78 ± 0.23 5.07 ± 0.27 5.56 ± 1.61
TPSB 0.00 0.07 ± 0.02 0.18 ± 0.06 0.00 0.08 ± 0.02 0.22 ± 0.07
DCHP 3.19 ± 0.40 5.33 ± 0.76 4.78 ± 0.38 8.05 ± 0.17 18.05 ± 6.63 9.40 ± 0.39
BisEMA 1.49 ± 0.09 7.92 ± 0.93 7.05 ± 0.40 11.29 ± 1.07 55.86 ± 41.32 4.60 ± 0.78
Abbreviations : MAA, methacrylic acid; HQME, hydroquinone methyl ether; EGDMA, ethylene glycol dimethacrylate; CQ, camphorquinone; CSA, campheracid anhydride; BHT, butylated hydroxytoluene; BL, benzil; DMABEE, 4-N,N-dimethylaminobenzoic acid ethyl ester; TEGDMA, triethylene glycol dimethacrylate; DEDHTP, diethyl 2,5-dihydroxyterephthalate; TINP, Tinuvin P (2(2′-hydroxy-5′-methylphenyl) benzotriazol); DDDMA, 1,10-decanediol dimethacrylate; BPA, bisphenol A; TPSB, triphenylstibane; DCHP, dicyclohexyl phthalate; BisEMA, ethoxylated bisphenol-A-dimethacrylate.
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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Effect of hydrogen peroxide on the three-dimensional polymer network in composites
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