| The resin monomer, as the most critical component in the dentin adhesive systems, is impossible to achieve complete polymerization under the condition of current technology, which is including bisphenol A diglycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA) and2-hydroxyethyl methacrylate (HEMA) et al. The uncured monomers may elute into the oral environment which bring potential hazards for oral local and systemic system, such as to stimulate oral tissue, to cause allergic reactions, to promote the growth of oral bacteria, leading to secondary caries, and bringing cytotoxic, genotoxic, teratogenic.At present, the main method of qualitative and quantitative residual monomer is chromatography. Therefore, in the experiment, qualitative and quantitative analysis of residual monomer Bis-GMA was accomplished by HPLC, and studying the effect of the types of adhesives and the extractant on resin monomers elution. The experiment provided the theoretical basis and some experimental data to the identification of the mechanism and influence factors on monomers elution in dentin adhesive systems.Objective:To study based on the qualitative and quantitative analysis of the residual monomer Bis-GMA and the influence factors of monomers elution from different clinical dentin adhesive systems. Methods:(1) First, the adhesives, including Solobond Plus, Single Bond2, Clearfil SE Bond and Clearfil3S Bond, were taken about a little onto the surface of spectrometer respectively and recorded infrared spectrum. Then the above four kinds of adhesive coated onto respectively and uniformly the surface of coverslips (8mm×8mm). The infrared spectrums of adhesive were recorded by spectrometer after curing according to manufacturers’instructions. The functional groups of benzene (1608cm-1) was selected as the reference and conducted quantitative analysis the change relative concentrations of C=C double (1637cm-1) before and after light-curing. To compare to the degree of conversion of four adhesives and the data is processed by Origin7.5and calculate the degree of conversion according to the formula.(2) The above four kinds of adhesive coated onto respectively and uniformly the surface of coverslips (8mm×8mm) which were silanated by2.5%MPS. The adhesive discs were immersed in37℃,75%ethanol/water immediately after light-curing according to manufacturers’instructions. To compare to the amounts of Bis-GMA from different adhesives and the quantification of Bis-GMA elution is measured by HPLC at10min,30min,1h,3h,6h,24h,48h,72h,7d and14days respectively.(3) According to the above methods, twenty coverslips (8mm×8mm) were silanated by2.5%MPS and were randomly assigned to four groups according to the selection of extractant, including deionized water group, artificial saliva group, saline group and ethanol group. The adhesive discs were immersed in37℃, above four kinds of extraction agent immediately after light-curing. To discuss the effect of different extractants on resin monomers elution and the quantification of Bis-GMA elution is measured by HPLC at10min,30min,1h,3h,6h,24h,48h,72h and7days respectively.(4) To simulate oral environment, the fresh dentine discs replaced with the coverslips. According to the methods of "(2)", the study was designed to quantify Bis-GMA elution with times from three kinds of adhesive systems, including Single Bond2, Clearfil SE Bond and Clearfil3S Bond. Results:(1) The conversion degree of four dentin adhesives are respectively52.02±0.26%,54.72±0.46%,51.94±0.47%and42.96±0.26%, with the highest conversion degree from Single Bond2and the lowest from Clearfil3S Bond. The difference is statistically significant (p<0.05). The conversion ratio of Solobond Plus and Clearfil SE Bond are closer, the difference is not statistically significant (p>0.05).(2) In a certain time, the amounts of eluted Bis-GMA are not completely the same from four different dentin adhesives in the same immersion time. In the first10minutes, the highest amount of eluted Bis-GMA is Clearfil SE Bond and the lowest is Single Bond2. The difference is statistically significant (p<0.05). The amounts of eluted Bis-GMA from Solobond Plus and Clearfil3S Bond are closer. The difference is not statistically significant (p>0.05). As the soaking time extended, the highest amount of eluted Bis-GMA is Solobond Plus and Clearfil SE Bond is the second at30min,1h,3h and24h. The difference is statistically significant (p<0.05). The amounts of eluted Bis-GMA of Single Bond2and Clearfil3S Bond are closer, the difference is not statistically significant (p>0.05). Up to6h, the amounts of eluted Bis-GMA of Solobond Plus and Clearfil SE Bond are closer, Single Bond2and Clearfil3S Bond are closer. The difference is not statistically significant (p>0.05). There are only a few amounts of eluted Bis-GMA from Solobond Plus when time is between24hours and7days. The amounts of eluted Bis-GMA could not be detected after7d.(3) In a certain time, the amounts of eluted Bis-GMA from Solobond Plus are not completely the same in four different extractants. The artificial saliva group could not detect target Bis-GMA. In the initial stage of immersion, the amounts of eluted Bis-GMA are relatively more from ethanol group at10min,30min and1h. The difference is statistically significant (p<0.05). The amounts of eluted Bis-GMA from deionized water group and saline group are closer. The difference is not statistically significant (p>0.05). As the soaking time extended, the amounts of eluted Bis-GMA of ethanol group and deionized water group or saline group are closer after6h. The difference is not statistically significant (p>0.05). Up to24h, the highest amount of eluted Bis-GMA is ethanol group and the lowest is saline group. The deionized water group is second. The difference is statistically significant (p<0.05). Up to48h, the lowest is also saline group. The difference is statistically significant (p<0.05). The amounts of eluted Bis-GMA from ethanol group and deionized water group are closer. The difference is not statistically significant (p>0.05). After48h, the amounts of eluted Bis-GMA of three groups are closer. The difference is not statistically significant (p>0.05).(4) In the same immersion time, the amounts of eluted Bis-GMA from Single Bond2, Clearfil SE Bond and Clearfil3S Bond showed similar monomer elution kinetics. The whole elution occurred during the24h after the bonding operation, and the highest eluting amount was detected within the first10min. The amounts of eluted Bis-GMA are respectively15.8±3.2ppm/mg,39.2±1.9ppm/mg and20.6±2.5ppm/mg. The difference is statistically significant (p<0.05). Up to30min, the highest amount of eluted Bis-GMA is Clearfil SE Bond and the lowest is Single Bond2. The Clearfil3S Bond group is second. The difference is statistically significant (p<0.05). As the soaking time extended, the highest amount of eluted Bis-GMA is Clearfil SE Bond at1h,3h and6h. The difference is statistically significant (p<0.05). The amounts of eluted Bis-GMA from other two groups are closer. The difference is not statistically significant (p>0.05). Up to24h, the amounts of eluted Bis-GMA of Clearfil SE Bond and Single Bond2or Clearfil3S Bond are closer. The difference is not statistically significant (p>0.05). The amounts of eluted Bis-GMA could not be detected after24h. Conclusion:The instantly conversion degree of four dentin adhesives is low, with the highest conversion degree from Single Bond2and the lowest from Clearfil3S Bond. The conversion ratio of Solobond Plus and Clearfil SE Bond is closer. There is residual monomer Bis-GMA elution in four different dentin adhesives, and the highest eluting amount is detected within the first10min. The effect of different extractants for Bis-GMA elution of Solobond Plus is different. In the initial stage of immersion, the amounts of eluted Bis-GMA are relatively more from ethanol group than, water and water based solution, and even could not be detected. The amounts of eluted Bis-GMA from different dentin adhesives showed similar monomer elution kinetics in the75%ethanol/water. The whole elution occurred during the24h after the bonding operation, and the highest eluting amount was detected within the first10min. |
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