Research On Micro-leakage And Mechanical Properties Of Several Bulk-fill Resin Restorations

Objectives: The purpose is to provide a scientific basis in selection a good repair products in the clinical work on the solid position,mechanical properties and convenient operation by the comparison of several bulk-fill dental resin materials and traditional composite resin on the differences of the micro-leakage situation,compressive strength,flexural strength and elastic modulus.Methods:1 Experiment one: Microleakage-testDuring three months before the experiment,complete extracted molar due to periodontitis were collected.A total of 50 teeth without caries and cracked conditions were randomly divided into five groups of 10 samples each.Class Ⅰcavities(4mm*4mm*4mm)were prepared on the occlusal surface of 50 freshly extracted molar teeth with high-speed diamond burs.A,B,C,D groups were filled 4mm deep once respectively with Surfill Smart Dentin replacement,Sonicfill,TetricN-Ceram Bulk Fill and X-tra Fil after using the self-etching with Adper ? Easy One and then they were light cured once in 20 second.E group was the control group filled with Spectrum TPH3-2mm-2mm layering and light cured in 20 second.All specimens were placed in artificial saliva for two months.Then the teeth were putted into 5℃(±0.5℃)and 55℃(±0.5℃)water alternately 30 seconds in each bath.A total of 1000 cycles were used for all specimens in the thermal cycler.The apical foramen of all teeth were closed with wax,and then the entire tooth was coated with nail varnish except for the restoration and 1 mm of the tooth surface adjacent to the restoration.The teeth were placed in a 50% ammoniacal silver nitrate aqueous solution for 24 hours in the dark after natural drying.They were exposed to a fluorescent light for 8 hours.After removal from the developing solution,the teeth were rinsed thoroughly in running water for 5 min.The specimens were sectioned longitudinally through the center of the restorations after taken out and dried.The depth of penetration was measured under root canal microscope.Micro-leakage values were statistically analyzed by Kruskal-Wallis test and Student-Newman-Keuls at the 5% confidence level with spss 13.0 software.The bonding interface was observed by scanning electron microscope.2 Experiment two: Physical and mechanical properties experimentUsing electronic universal testing machine we tested the compressive strength,the flexural strength,and the modulus of elasticity of the following maximum depth of cure 4 mm bulk-fill resin Surfill Smart Dentin replacement,Sonicfill,TetricN-Ceram Bulk Fill,X-tra Fil and Spectrum TPH3 which is layering filled traditionally.One-way variance analysis and StudentNewman-Keuls were used to determine the statistical differences among groups(P< 0.05)with spss 13.0 software.Results:1 Experiment one: Bulk-fill resin in the four groups showed the least microleakage.Kruskal-Wallis test showed statistical difference in the extent of microleakage among the five groups(P<0.05).Microleakage depth of five groups are not identical completely.There were no statistical significance in terms of remarkable difference between group A,group B,group C and group D in the multiple comparisons of the sample means by SNK(StudentNewman-Keuls)test.Microleakage in group E was different from that in group A,group B,group C and group D,indicating that group A,group B,group C and group D had better marginal seal.From specimen noumenal pictures,silver leakage could hardly be seen in group A and group B.There was silver staining in the individual sectional dentin in group C.Group D showed slightly more than group C in the interface and sectional dentin.Group E was the most serious.Some reached the adhesive interface of dentin and resin 2/3 or more,and there was more silver staining in the sectional dentin,indicating that group E had bad marginal seal.From scanning electronic micrographs,the combination between resin and dentin was tight in group A and B.Silver leakage could hardly be seen in the interface of dentin and resin.A little silver stained dentinal tubulesin group A.There was gaps between material and dentin in group C,and a little silver distributed in gaps.Group D showed wider gaps where a long strip of microleakage was seen at the dentin-material interface,and there was a small amount of silver leakage in the dentinal tubules and material pores.While the gaps in group E were the widest relatively,and the gaps and dentinal tubules were distributed a large amount of silver.The particles inside the material contacted closely while silver leaked like thick raindrops.2 Experiment two: While five sets of data compression strength of materials,flexural strength and modulus of elasticity meet data normality,homogeneity of variance,one-way variance analysis showed statistical difference among the five groups in the extent(P<0.05).Compression strength,flexural strength and modulus of elasticity of five groups of materials were not identical completely,and they were multiple compared by SNK(Student-Newman-Keuls)test.There were no statistical significance between group B,group C,group D and group E of compressive strength.Poor compressive strength of material suggests that it can not be directly subjected to occlusion pressure in group A.There were no statistical significance between group B,group C,group D and group E of flexural strength except group A.Modulus of elasticity was no significant difference between groups B,Group C and Group E.As well as relatively low modulus of elasticity of group A,high modulus of elasticity of the group D was statistical difference from group B,group C and group E.Group A and group D were significantly different,suggesting group D material has better rigidity.Conclusions:1 In the comparison of traditional layered composite resin,four bulk-fill dental resin materials(Surfill Smart Dentin replacement,Sonicfill,TetricNCeram Bulk Fill,X-tra Fil)have good marginal seal performance,easy operation and saving time.2 Surfill Smart Dentin replacement,Sonicfill,TetricN-Ceram Bulk Fill and X-tra Fil have good mechanical properties,and all of them can meet the requirements of dental materials.Surfill Smart Dentin replacement has low compressive strength,and can be used as an intermediate layer of dentin resin.