The Effect Of Carbodiimide On The Micro-tensile Bonding Strength Of Dentin

In the process of dentin etching and bonding,the depth of demineralization is inconsistent with the penetration depth of the adhesive,resulting in the exposure of collagen fibers at the bottom of the mixed layer.In addition,because the hydrophilic monomer in the adhesive absorbs moisture and solvent volatilization cannot completely take away the water and the dentin tubule fluid flows out,resulting in moisture residue to affect adhesive polymerization,and the incompletely polymerized adhesive is prone to hydrolysis.The collagen fibers are further exposed.The local weakly acidic environment activates matrix metalloproteinases in the form of zymogen when dentin is bonded.They degrade the exposed collagen fibers,destroy the integrity of the mixed layer and ultimately lead to failure of the bonding repair.In order to improve the bonding strength and durability of dentin,scholars at home and abroad have proposed a variety of methods and strategies,such as applying hydrophobic coatings,using collagen cross-linking agents and using MMPs inhibitors.The use of collagen cross-linking agent as a common method has the advantages of significant effect and simple operation.Because 1-ethyl-3-（3-dimethylaminopropyl）carbodiimide acts as a collagen cross-linking agent,which can promote collagen cross-linking and inhibit the activity of MMPs,so EDC is often used as a pretreatment agent for dentin bonding.This experiment directly added EDC to the eighth-generation adhesive Single Bond Universal to reduce the operation steps and tested its related properties.Objective:The effect of 1-ethyl-3-（3-dimethylaminopropyl）carbodiimide on the double bond conversion rate,cytotoxicity and bonding performance of the eighth-generation adhesive Single Bond Universal was explored to provide reference basis for clinical application.Methods:EDC was added to the eighth-generation adhesive Single Bond Universal to configure the experimental adhesives containing different concentrations(0.1,0.2 and0.3 mol.L^-1)of EDC.Fourier transform infrared spectrometer was used to detect the double bond conversion rate of 0mol.L^-1group（without EDC）,0.1mol.L^-1group,0.2mol.L^-1group and 0.3 mol.L^-1group.The adhesive film was prepared,obtaining the extract.The extract was co-cultured with L929 mouse fibroblasts for 24,48and72h,seting up a negative control group and a blank control group.The cell relative growth rate was measured by the CCK-8 method,and the cytotoxicity was graded.28freshly extracted third molars without caries were selected.They were randomly divided into 4 immediate groups（n=4）:0mol.L^-1group,0.1mol.L^-1group,0.2mol.L^-1group and 0.3mol.L^-1group;3 aging groups（n=4）:0mol.L^-1group,0.1mol.L^-1group and 0.2mol.L^-1group.The enamel of tooth surface was removed and polished under running water with 600 mesh silicon carbide sandpaper for 60 seconds to prepare micro-tensile bonding specimens.The electronic universal testing machine was used to test the immediate and aging micro-tensile bonding strength of the specimens in various groups,and the fracture mode of the specimens was observed with a stereo microscope.Results:1.In the test of double bond conversion rate,the double bond conversion rates of0mol.L^-1group,0.1mol.L^-1group,0.2mol.L^-1group and 0.3mol.L^-1group were（61.15±5.25%）,（59.46±5.44%）,（58.26±6.35%）and（56.34±2.87%）.2.The CCK-8 test results showed that the RGR was above 75%and the cytotoxicity was level 1 after the adhesive extract was co-cultured with the cells for24,48and 72h.3.In the immediate test,the bonding strengths of 0mol.L^-1group,0.1mol.L^-1group,0.2mol.L^-1group and 0.3 mol.L^-1group respectively were（30.35±4.31）,（38.10±6.24）,（26.39±8.24）and（18.63±5.29）MPa.Compared with 0mol.L^-1group,the bonding strength of the 0.1mol.L^-1group was obviously improved（p<0.05）,the bonding strength of the 0.3mol.L^-1group was obviously reduced（p<0.05）.The interface failure was the main performance in 0mol.L^-1group,0.2 mol.L^-1group and0.3mol.L^-1group,and the mixed failure was the main performance in 0.1mol.L^-1group.4.In the aging test,the bonding strengths of 0mol.L^-1group,0.1mol.L^-1group and0.2mol.L^-1group respectively were（21.29±3.19）,（34.70±4.16）and（17.22±3.76）MPa.Compared with 0mol.L^-1group,the bonding strength of the 0.1mol.L^-1group was obviously improved（p<0.05）,and the bonding strength of the 0.2mol.L^-1group was obviously reduced（p<0.05）).The interface failure was the main performance in0mol.L^-1group and 0.2mol.L^-1group,and the mixed failure was the main performance in 0.1mol.L^-1group.Conclusions:1.When EDC is added to the eighth-generation adhesive Single Bond Universal,within the concentration range of 0.1-0.3mol.L^-1,EDC has no significant effect on its double bond conversion rate and cytotoxicity.2.The eighth-generation adhesive Single Bond Universal containing 0.1mol.L^-1EDC has significantly improved immediate and aging bonding strength,and significantly improved bonding performance.