Elution Of Resin Monomers Under A Simulated Root Barrier

Objective:The purpose of this study was to explore the possible correlation between the thickness of root canal wall and the permeability of root barrier after post preparation.Study model using a simulated root barrier was established to detect the elution of resin monomers?Bis-GMA,UDMA,TEGDMA,HEMA?from 3 different composite resins?RelyX Unicem,Clearfil DC core one,ParaCore?,which provided a reference for the clinical application.Methods:?1?Sixty single-rooted human premolar teeth were decoronated 4 mm above the CEJ and were treated with root canal therapy and post preparation in vitro,and the apical sealing area of 5 mm was retained.X-ray were taken for all samples to measure the thickness of the root canal wall at 5 mm and 10 mm away from the apex.A fluid filtration device was then designed to measure the permeability of the root barrier at100 cmH₂O pressure,and the precision of the device was verified.The correlation analysis was performed between the thickness of root canal wall and the permeability of after post preparation.?2?42 teeth with suitable root canal wall thickness and permeability were obtained and randomly divided into 7 groups?n=6?:for groups A,B and C,the fiber posts were bonded with RelyX Unicem,Clearfil DC core one and ParaCore,respectively.Then groups A,B,and C were divided into two subgroups.For groups A1,B1 and C1,the specimens were fixed in the centrifugal tube through silicone materials?with the root barrier?.The specimens in the groups A2,B2 and C2 were fractured and placed directly in centrifugal tube as the positive control group?without the root barrier?.Group D is the negative control group.The specimens in group D were without fiber post bonding and directly fixed the specimen in the centrifugal tube.Macro-lock Illusion Post?3^#,RTD?were placed into the post space,bonded with the respective resin materials,and light cured for 40 s.The centrifugal tube is equipped with 1 ml solution composed of 75%ethanol and 25%deionized water.The tube was wrapped in tin foil to avoid any lights.All specimens were then stored at 37?.The immersion solution was changed at 1 d,8 d and 15 d.?3?Eluates of the specimens were analyzed by High-Performance Liquid Chromatography?HPLC?.Calibration curves were drawn for each standard material?HEMA,TEGDMA,UDMA,Bis-GMA?at different concentrations.Identification and quantitative analysis of components were performed by comparison of the elution time and the integration of absorption peak area of the eluates with those of the authentic sample.Results:?1?After post preparation,the thickness of the root canal wall at 5 mm away from the apex were as follows:buccal wall?1.65±0.21?mm,tongue or palatine wall?1.97±0.30?mm,mesial wall?1.09±0.18?mm,distal wall?1.09±0.18?mm.The thickness of the root canal wall at 10 mm away from the apex were as follows:buccal wall?2.05±0.21?mm,tongue or palatine wall?2.36±0.25?mm,mesial wall?1.48±0.20?mm,distal wall?1.49±0.18?mm.The permeability of root barrier was?1.49±0.76?X10^-3?l min^-1 cmH₂O^-1 at 100 cmH₂O pressure.The relative standard deviation?0-12.8%?measured by the precision test of the fluid filter device are all less than 15%,indicating that the repeatability of the device is good.The results showed that there was a significant correlation between root canal wall thickness and root barrier permeability at 5 mm away from the apex?P<0.05?,R2=0.380,and between root canal wall thickness and root barrier permeability at 10 mm short of the apex?P<0.05?,R2=0.208.There was a negative correlation between them?r<0?,but the correlation was low.?2?Compared with the chromatogram of the reference standards,the high performance liquid chromatogram of A1,B1,C1 and D groups revealed no detectable monomer.However,monomers were detected in A2,B2 and C2 groups.Only the monomer TEGDMA was detected in A2 group.The amount of monomers released was as follows:1 day?691.16±41.49?g/ml?,8 days?265.27±39.12?g/ml?and 15 days?26.66±6.94?g/ml?,respectively.The monomers HEMA,TEGDMA and Bis-GMA were detected in B2 group.The amount of monomers released was as follows:HEMA 1 day?525.59±34.22?g/ml?,8 days?151.59±21.72?g/ml?and 15 days?37.57±10.64?g/ml?,respectively.TEGDMA 1 day?115.61±14.66?g/ml?,8 days?21.84±5.51?g/ml?,15days?0?g/ml?.Bis-GMA 1 day?236.30±25.18?g/ml?,8 days?58.72±9.91?g/ml?,15days?12.15±4.83?g/ml?.The monomers HEMA,TEGDMA,UDMA and Bis-GMA were detected in C2 group.The amount of monomers released was as follows:HEMA1 d?522.55±47.56?g/ml?,8 days?224.77±37.78?g/ml?,15 days?66.99±18.43?g/ml?.TEGDMA 1 day?148.25±50.50?g/ml?,8 days?23.76±13.55?g/ml?,15 days?0.71±0.50?g/ml?.UDMA 1 day?338.20±157.35?g/ml?,8 days?100.70±36.38?g/ml?,15 days?33.91±11.12?g/ml?.Bis-GMA 1 day?113.33±56.56?g/ml?,8 days?38.52±17.59?g/ml?,15 days?5.97±4.85?g/ml?.The results of statistical analysis showed that the amount and rate of monomer elution were different among different groups.The amount of HEMA eluted in group C2 was the most,followed by group B2,and no elution was found in group A2.At the first day,the amount of monomers released in group C2 was similar to that in group B2,and there was significant difference between the two groups at 8 days?P<0.05?.The amount of TEGDMA monomers released was the highest in A2 group,but less in B2 and C2 groups?P<0.05?,and there was significant difference between A2 and B2?C2 groups?P<0.05?.However,there was no significant difference between B2 and C2 groups?P>0.05?.The amount of Bis-GMA eluted in group B2 was the most,followed by group C2,and no elution was found in group A2.In the first day,there was significant difference between B2group and C2 group?P<0.05?.In different immersion time,the elution amount and rate of monomers are also different.The amount of monomers released from TEGDMA in A2 group,Bis-GMA in B2 group and HEMA in C2 group was significantly different at1 day,8 days and 15 days?P<0.05?.There was significant difference in the amount of monomers released from HEMA in B2 group,TEGDMA and UDMA in C2 group between 1 day and 8 days,1 days and 15 days?P<0.05?.No matter what kind of material and type of monomer,the amount of monomer eluted was the most in the first 1 day.With the prolongation of immersion time,the elution of monomers decreased significantly even to zero at 8 days and 15 days.Compared with the first day,the difference was statistically significant?P<0.05?.Conclusions:?1?The root barrier model was successfully constructed.The permeability of the model was?1.49±0.76?X10^-3?l min^-1 cmH₂O^-1 at 100 cmH₂O pressure.?2?With the root barrier,the resin monomers could not be eluted.