Modification Effect Of Epigallocatechin-3-gallate (EGCG) On Tooth-colored Restorative Materials

Objective:Secondary caries and poor bonding durability are two main reason for the failure of tooth-colored restorations. The objective of this study is to characterize the modification effect of Epigallocatechin-3-gallate (EGCG), the main active ingredient in tea polyphenols, on the tooth-colored materials, dental adhesives and glass ionomer cements. The present study includes three parts:Part one-Observation of the effect of EGCG treatment on demineralized dentine and resin-dentine bonds; Part two:Effect of EGCG incorporation on the therapeutical effect of dental adhesives; and Part three-In vitro and in situ evaluation of the effect of EGCG addition on the antibiofilm and mechanical property of glass ionomer cement.PART ONE-Observation of the effect of EGCG treatment on demineralized dentine and resin-dentine bondsExp.1Effect of EGCG treatment on the mechanical behavior of demineralized dentine and resin-dentine bondsMethods and Methods:Sound human molars were cut into0.5mm thickness×1.7mm width×6.5mm length dentine sticks. The sticks were demineralized and then either treated with EGCG for different time or left untreated. Bacterial collagenase was used to assess resistance to enzymatic degradation of samples. Then the specimens were subjected to ultimate tensile strength (UTS) test. The effect of EGCG precondition on the resin-dentine bond strength was evaluated after1min,5min or15min of exposure time. The microtensile bond strength (?TBS) was assessed either24h or6months later after the bonding procedure.Results:EGCG treatment improved the UTS of the demineralized dentine. After Bacterial collagenase treatment, the UTS of dentine were0for control group while the UTS of dentine pre-treated with EGCG were retaining the same as previous. Resin-dentin bonds significantly increased following treatment with EGCG for5min and15min. The bonding durability was also retained for the EGCG preconditioned groups.PART TWO-Effect of EGCG incorporation on the therapeutic activity of dental adhesivesExp.2Effect of EGCG incorporation on the antibacterial activity of dental adhesiveMethods and Methods:A commercially available dental adhesive Single Bond2was used as control. EGCG was incorporated at a ratio of100,200, and300?g/ml into Single Bond2. The effects of the cured adhesives on the growth of Streptococcus mutans were determined by direct contact test immediately or one month later and by scanning electron microscopy (SEM), respectively.Results:Compared with negative control, the200?g/ml and300?g/ml EGCG-incorporated dental adhesive were found to exhibit inhibitory effect on the growth of S. mutans. The antibacterial activity was still better than control for these two group after one month aging in the distill water. SEM image showed that after24h incubation, bacteria were accumulated on specimens of all4groups. Bacteria were densely packed within extracellular matrix on control and EGCG100group. However, biofilms accumulated on the EGCG200and EGCG300group were not compact.Exp.3Effect of EGCG incorporation on the bonding durability and degree of conversion of dental adhesiveMethods and Methods:Sound human molars were collected and the roots of the teeth were removed by a water-cooled low-speed cutting saw. Then, a flat surface was prepared by removing the occlusal one-third of the tooth crowns to expose midcoronal dentine. The dentine surface was polished with600-grit SiC paper to create a standardized smear layer. The crown segments were randomly allocated to four groups, according to the adhesives tested as Exp.2. Then microtensile bond strength (?TBS) test was used to test the mechanical property of the adhesives immediately or six months later. The degree of conversion (DC) of the adhesives was evaluated by Fourier Transform Infrared Spectroscopy (FTIR).Results:After100?g/ml and200200?g/ml EGCG incorporated, the immediate ?TBS value of the dental adhesive was significantly higher than the control group. After6months of in vitro water storage, the ?TBS of the three EGCG incorporated groups were significantly higher than control. Significant reduction of ?TBS was observed for the control group, while no significant reduction was observed when EGCG was incorporated. After EGCG incorporated, the DC of dental adhesives was decreased slightly. But the difference was not statistically significant.PART THREE-Modification effect of EGCG on the glass ionomer cement. Exp.4Effect of EGCG addition on the antibiofilm activity of glass ionomer cementMethods and Methods:A conventional GIC, Fuji IX was used as control. EGCG was incorporated into GIC at0.1%(w/w) as the experimental group. And chlorhexidine (CHX) powder was added into GIC at1%(w/w) as positive control. The anti-biofilm effect of the materials was assessed by a colorimetric technique (MTT assay) and scanning electron microscopy (SEM). The separate-out antibacterial activity of the materials on Streptococcus mutans was evaluated by agar-diffusion test.Results:The OD values of GIC-EGCG group were significant decreased at4h, but the difference was not significant at24h compared with the GIC group. SEM images showed that after4h incubation, the bacteria was less on the surface of GIC-EGCG and GIC-CHX, but after24h incubation, bacteria accumulated on specimens of all the groups. No obvious inhibition zone was detected for GIC-EGCG and GIC group.Exp.5Effect of EGCG addition on the mechanical property and fluoride release of glass ionomer cement Methods and Methods:Fuji IX was used as control. EGCG and CHX was incorporated into GIC at0.1%or1%(w/w) as the experimental group respectively. The flexural strength of the materials was evaluated using a universal testing machine and the surface microhardness was measured using a microhardness tester. The fluoride-release of the materials was tested by ion chromatography.Results:The incorporation of EGCG into the GIC significantly increased the flexural strength compared with the control group. Data for surface microhardness (VHN) showed a significant increase in the hardness for the experimental GIC-EGCG group, followed by insignificantly reduced flexural strength and surface hardness for GIC-CHX. The fluoride ion release was not influenced by EGCG-incorporation.Exp.6Pilot study of inhibition of early biofilm formation by glass-ionomer incorporated with chlorhexidine in situMethods and Methods:Experimental GIC and RMGIC containing2%CHX were obtained by mixing CHX with the powder of GICs (CHXGIC) and RMGICs (CHXRMGIC). Four groups of specimens were prepared in a standardized size. After polishing and sterilization, they were bonded to the buccal surface of the molars in the1st and2nd quadrant of volunteers and left untouched for4h and24h, respectively. Afterwards, the bacterial vitality of plaque was analyzed by confocal laser scanning microscopy (CLSM). The bacterial morphology and biofilm accumulation were determined by scanning electron microscopy (SEM).Results:CLSM analysis revealed that bacterial vitality of the biofilm on CHXGIC and CHXRMGIC was significantly lower than that on GIC and RMGIC. SEM analysis indicated that the morphology of bacteria on CHXGIC and CHXRMGIC was irregular.Conclusions:1. Increased mechanical properties of dentin matrix can be achieved by the use of EGCG most likely due to the formation of EGCG-collagen complex. The short term bond strength and durability of resin-dentin bonds could be improved after EGCG treatment. 2.200?g/ml EGCG incorporated dental adhesives could accomplish therapeutic goals that play in antimicrobial function while keeping the durability of resin-dentin bond.3. GIC-containing0.1%EGCG is a promising restorative material with improved mechanical properties and tendency of better antibacterial properties.4. Twenty-four hour bacterial vitality on GICs and RMGICs with CHX are lower in microorganisms than on conventional GICs and RMGICs. Antibacterial modification of glass ionomer could be effectively in the complex oral environment.Within the limitation of this study, it could be concluded that EGCG is an effective method for the modification of tooth-colored restorative materials. EGCG can improve the durability of the adhesive restorations and improve the antibacterial properties of materials simultaneously. However, the specific mechanism and clinical effects need to be further explored.