Olga Polydorou

Long-Term Release of Monomers from Modern Dental-Composite Materials

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

The effect of different bleaching agents on the surface texture of restorative materials.

This blind in vitro study evaluated the effect of a home and an in-office bleaching agent on the surface texture of different tooth-colored restorative materials. Four composites (a hybrid, a flowable, a microhybrid and a nano-hybrid), an ormocer and a ceramic were used, and 2 bleaching agents were tested: 38% hydrogen peroxide and 15% carbamide peroxide. For 38% hydrogen peroxide, the surface morphology of the restorative materials was evaluated after the following time periods: before bleaching, after 15, 30 and 45 minutes of bleaching, 24 hours and 1 month after bleaching. For 15% carbamide peroxide, the time periods were: before bleaching, after 8 and 56 hours of bleaching and 24 hours and 1 month after bleaching. For the 4 composite materials and the ormocer, 2 samples groups were prepared; in 1 group, the specimens were polished and in the other, they stayed unpolished. For the ceramic group, polished samples were prepared. For every material, 3 samples per category and time period were prepared, respectively. Subsequently, the appropriate bleaching procedure was performed on samples of every group. Scanning electron micrographs were produced at 60x, 200x and 2000x magnifications of respective areas of the samples. The results showed that the effect of bleaching on the surface texture was material- and time-dependent. Within the limitations of this study, it was concluded that bleaching with 38% hydrogen peroxide and 15% carbamide peroxide did not cause major surface texture changes on the polished surfaces of the restorative materials.

The efficacy of three different in-office bleaching systems and their effect on enamel microhardness.

This in vitro study evaluated and compared the efficacy of three in-office bleaching systems and investigated their effect on enamel microhardness. Three groups of 12 teeth (third molars) each were bleached as follows: Group A: Opalescence Xtra Boost (38% HP), Group B: Easywhite Ready (30% HP) with plasma unit and Group C: Zoom2 system (25% HP with the Zoom2 unit). The teeth were stained with tea for 24 hours, followed by the appropriate bleaching procedure. Each bleaching cycle was conducted for 15 minutes. The bleaching procedure was repeated until a shade change of six tabs (VITA shade guide) was obtained. The shade of the teeth was evaluated before, immediately after bleaching and one month later, both visually and digitally. Additionally, the change of shade tabs per minute was calculated. For the digital evaluation, the photos were taken under the same circumstances and the L*a*b* values were calculated using Photoshop. Five additional enamel samples for each group were prepared, and Knoop microhardness was evaluated before and after 15 minutes of bleaching. According to the visual shade evaluation, the treatment cycles required to reach the defined level of bleaching were: 1.58 for Group A (23.7 minutes), 1.02 for Group B (16.2 minutes) and 1.25 for Group C (18.7 minutes). Immediately after bleaching, a significant difference was found between Groups A and B (p = 0.0094). However, one month after the bleaching procedure, no significant difference could be observed among the three groups. According to the digital evaluation, no significant differences were found among the three bleaching systems for each of the L*a*b* values and the three times tested (p > 0.05). No significant difference (p = 0.055) was noticed among the three groups regarding microhardness after bleaching.

The antibacterial effect of gas ozone after 2 months of in vitro evaluation

The aim of this study was to evaluate the effect of HealOzone on two microorganisms, 4 and 8xa0weeks after treatment, using a tooth cavity model. Four groups of caries-free third molars (nu2009=u200912) were used (A, B, C and D). Three cavities were prepared into each tooth. After sterilization, groups A and B were inoculated with Streptococcus mutans, and groups C and D, with Lactobacillus casei for 48xa0h. One cavity of each tooth was used to evaluate the infection. After inoculation, groups B and D were treated with ozone (60xa0s), and groups A and C were used as controls. Then, the two cavities of each tooth were filled with composite, and the teeth were stored in sucrose medium. The restorations were removed after 4 and 8xa0weeks, respectively; dentin chips were collected, and the amount of microorganisms was determined. Ozone treatment reduced significantly the amount of S. mutans compared to the control group (pu2009≤u20090.05). This antibacterial effect was able to be seen after 4 (pu2009=u20090.0005) and 8 (pu2009=u20090.0002) weeks. No significant difference was found between the control and treated group as far as L. casei is concerned (pu2009>u20090.05). HealOzone (60xa0s) can provide some antibacterial treatment against S. mutans even after 8xa0weeks. However, an elimination of the microorganisms through HealOzone seems not to be possible. L. casei was more resistant to ozone. Although ozone exerts a significant antibacterial effect against S. mutans, it is probably not enough as the only antibacterial method, during the fillings therapy.

Evaluation of the curing depth of two translucent composite materials using a halogen and two LED curing units

This in vitro study evaluated the influence of one halogen and two light-emitting diode (LED) curing units on the curing depth of a conventional hybrid and two translucent resin composites by measuring the Knoop microhardness. In the first part of the study, a conventional hybrid resin composite and three curing units (one halogen: 40xa0s polymerization time, two LEDs: 10 and 20xa0s) were used. Ten cylindrical resin composite samples were prepared for each curing unit and each polymerization time tested. After polymerization, the soft part of the samples was removed. The samples were embedded in a polyacrylic resin and separated in the middle towards the direction, top–bottom. On the section plane, Knoop microhardness measurements were performed every 1xa0mm, starting at 0.5xa0mm under the surface. In the second part of the study, two translucent resin composites and a conventional hybrid composite resin were cured with the three curing units, and the microhardness was measured as mentioned above. The difference between the curing units tested was found statistically significant (pu2009=u20090.0009), as well as the difference between the materials concerning curing depth (pu2009=u20090.0001). Both translucent materials achieved microhardness values equal to the 80% of the surface values, in depths 3.5–5.5xa0mm, depending on the curing units used.

Efficacy of tooth bleaching with and without light activation and its effect on the pulp temperature: an in vitro study

The aim of this in vitro study was to evaluate the colour stability of bleaching after light activation with halogen unit, laser, LED unit or chemical activation up to 3xa0months after treatment. Four groups of teeth (nxa0=xa020) were bleached with Opalescence Xtra Boost (38% hydrogen peroxide) using four different methods: activation with halogen, LED, laser or chemical activation only. All teeth were bleached in one session for four times (4xa0×xa015xa0min) and the colour was evaluated using a spectrophotometer at the following time points: before bleaching, immediately after bleaching, 1xa0day, and 1 and 3xa0months after the end of bleaching. Between the tested time points, the teeth were stored in 0.9% NaCl solution. Additionally, the temperature increase in the pulp chamber was measured using a measuring sensor connected to a computer. Bleaching with the halogen unit showed the highest colour change. Halogen unit, laser and chemical activation resulted in whiter teeth after 1 and 3xa0months compared to the colour after the end of the bleaching procedure (pxa0≤xa00.05). Three months after the end of bleaching, the shade changes observed were—halogen: 7.1xa0>xa0chemical activation: 6.2xa0>xa0LED: 5.4xa0>xa0laser: 5.2. Halogen showed the highest temperature increase (17.39°Cxa0±xa01.96) followed by laser (14.06°Cxa0±xa02.55) and LED (0.41°Cxa0±xa00.66) (pxa0<xa00.0001). Chemical activation did not affect the temperature in the pulp chamber. The use of light activation did not show any advantages compared to chemical bleaching. Although halogen unit showed the higher shade’s change, its use resulted also in the higher pulp temperature. According to the present findings, light activation of the bleaching agent seems not to be beneficial compared to bleaching without light activation, concerning the colour stability up to 3xa0months after bleaching and the pulp temperature caused during the bleaching procedure.

Release of monomers from different core build-up materials

OBJECTIVEnThe aim of the present study was to evaluate and compare the elution of monomers from three different core build-up composite materials and correlate it with the degree of conversion.nnnMETHODSnThree different core build-up composite materials (a chemically cured, a photo-cured, and a dual-cured) were tested. Ten samples (diameter: 4.5 mm and thickness: 2 mm) of each material were fabricated to evaluate the release of monomers. The photo-cured samples were polymerized for 40s and the dual-cured samples for 20 s. The samples remained undisturbed for 10 min and then were stored in 1 ml of 75% ethanol at room temperature, and the storage medium was renewed after 24 h, 7 and 28 days. From the storage medium that was removed, samples were prepared and analyzed by LC-MS/MS. Additionally, four samples of each material were tested for the degree of conversion by using a FT-IR spectrometer.nnnRESULTSnThe three composite materials differed significantly concerning the elution of monomers (BisGMA: p<0.0001; TEGDMA: p<0.0001; and Bisphenol A: p<0.0001). A significantly higher amount of BisGMA and TEGDMA was released from the chemically cured composite compared to the other two materials. Between the photo-cured and the dual-cured material the latter eluted significantly higher amounts of BisGMA and TEGDMA. During the storage of the samples, the amounts of the eluted substances decreased. The degree of conversion of the chemically cured composite was significantly lower compared to the other two materials.nnnSIGNIFICANCEnUsing the present parameters, the photo-cured material released less monomer and therefore they might be less dangerous with respect to toxicological effects.

The effect of storage medium on the elution of monomers from composite materials

The aim of this study was to evaluate the effect of four different storage media on the elution of monomers from two composite materials. Samples (n = 10, diameter: 4.5 mm, thickness: 2 mm) of two different composite materials (Ceram X™ & Filtek™ Supreme XT) were stored after polymerization in four different media (NaCl, saliva, ethanol 75% & acetone) for 24 h, 7 days, and 28 days. From the storage medium of each tested time period, samples were prepared and analyzed by LC-MS/MS, for the elution of BisGMA, TEGDMA, HEMA, Bisphenol A, and two types of UDMA. No monomers were detected in the samples of Ceram X™, independently of the storage medium used. In the samples of Filtek™ Supreme XT, no Bisphenol A, HEMA, and UDMA 1 were found. BisGMA was detected only in the ethanol and acetone samples. The amount of BisGMA eluted in acetone was significant higher compared with ethanol 75% (p < 0.0001). TEGDMA was the only monomer that could be detected in all tested storage media. Storage in acetone resulted in higher release of TEGDMA when compared with other media. The amount of TEGDMA released in saliva was similar to the one released in ethanol 75%. It can be concluded that acetone is not a suitable medium for elution experiments and although ethanol 75% can simulate saliva concerning the elution of TEGDMA, it does not represent a laboratory substitute of saliva with respect to the elution of monomers like BisGMA.

Effect of bleaching on the elution of monomers from modern dental composite materials

OBJECTIVEnThe aim of this study was to evaluate the effect of bleaching on the elution of monomers from two modern composite materials.nnnMETHODSnTwo different resin composites (a nanohybrid the Filtek Supreme XT and an ormocer the Ceram X) were bleached with two products (hydrogen peroxide 38% for 45 min and carbamide peroxide 15% for 56 h). Four groups (n=10, diameter: 4.5 mm, thickness: 2 mm) of each material were fabricated, two for each bleaching product. One group was used as unbleached control and the other one was bleached. Then the samples were stored in 1 ml of 75 vol% ethanol at room temperature, and the storage medium was renewed after 24 h, 7 days, and 28 days. From the storage medium that was removed samples were prepared and analysed with LC-MS/MS.nnnRESULTSnNone of the bleaching products had an effect on the amount of Bis-GMA and TEGDMA released from Ceram X. The amount of Bisphenol A released from the bleached samples of Ceram X was significantly lower compared to the control samples. Bleaching reduced significantly the amount of Bis-GMA released from Filtek Supreme XT. The amount of TEGDMA released from Filtek Supreme XT was not affected by bleaching.nnnSIGNIFICANCEnThe bleaching agents tested in the present study reduced the amount of some of the monomers released from the two composite materials. Bleaching of modern composite materials does not increase the release of monomers.

Uthethane dimethacrylate: A molecule that may cause confusion in dental research

In recent years, the elution of monomers from dental materials has been a cause for public concern. Urethane dimethacrylate, commonly abbreviated to UDMA, is one of the monomers that are most often tested with regard to elution from and cytotoxicity of resin-based materials. Although each chemical name represents the chemical type, chemical structure, and molecular weight of a molecule, it does not seem to be the same with UDMA. In the present paper, the different forms of UDMA are presented. These include those used by dental manufacturers to produce composite materials and the different types of urethane dimethacrylate used in studies concerning the elution of monomers from composite materials. High-performance liquid chromatography (HPLC) is usually used to detect the eluted monomers, but it does not appear to be adequate in determining the different forms of UDMA. The combination of HPLC with mass spectrometry is shown to be able to specifically identify the compounds eluted in addition to those compounds used as standards in the various studies. The fact that the same name is given to different molecules causes confusion about the results of studies testing the elusion of monomers from composite materials and their possible toxicity.