In order to investigate how to enhance the teeth fracture resistance after the post and core treatment, an in vitro study was conducted to measure the fracture resistance of endodontically treated teeth restored with ...In order to investigate how to enhance the teeth fracture resistance after the post and core treatment, an in vitro study was conducted to measure the fracture resistance of endodontically treated teeth restored with cast post and core with two kinds of surface treatment technology and acid etching preparation on the dentinal surface. Sixty-four recently extracted human single-rooted first premolars were endodontically treated and sectioned approximately 1.5 mm above the cementoenamel junction to remove the coronal portion. Each specimen received a cast post, core build-up and a metal alloy crown restoration. All teeth were randomly divided into the smooth surface post, core repair group, the sand blasting surface post, and core repair group, each group was divided into 10 s, 30 s, 60 s acid corrosion treatment group and control group. In acid test groups, an acid etching solution was applied for 10, 30 and 60 seconds, respectively, to the root canal wall surface. Each specimen was embedded in acrylic resin block and tested in an electronic universal testing machine. Fracture loads results showed that canal acid etching could increase teeth fracture resistance strength both in smooth groups and sandblasting group, and achieved the best effect when acid etching for 30 s. Sand spray treatment on the surface of the cast metal post can improve the flexural strength of the teeth after postcrown restoration. Acid etching on the root canal wall surfaces and sand spray treatment on the surface of the cast metal post can improve the flexural strength of the root after post-crown restoration. Therefore, these two methods could be used to strengthen the tooth fracture resistance, and maintain the long-term therapeutic effect of cast post and core restoration.展开更多
The multi-piece post-crown technique is more effective in restoring residual root than other restoration techniques.Various types of adhesives have different material properties that affect restoration.Therefore,the c...The multi-piece post-crown technique is more effective in restoring residual root than other restoration techniques.Various types of adhesives have different material properties that affect restoration.Therefore,the choice of adhesive is particularly important for patients.However,the effect of different kinds of adhesives was not too precise by experimental methods when concerning about individual differences of teeth.One tooth root can only be restored with one type of adhesive in experiment.After the mechanical test,this tooth root cannot be restored with other adhesives.With the help of medical imaging technology,reverse engineering and finite element analysis,a molar model can be reconstructed precisely and restored using different types of adhesives.The same occlusal and chewing loads were exerted on the same restored residual root models with different types of adhesives separately.Results of von Mises stress analysis showed that the adhesives with low Young’s modulus can protect the root canal effectively.However,a root canal concentration is apparently produced around the root canal orifice when chewing.Adhesives with large Young’s modulus can buffer the stress concentration of the root canal orifice.However,the root canal tissue may be destroyed because the adhesive is too hard to buffer the load.展开更多
Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering.This paper presents the formation mechanism of core discing firstly...Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering.This paper presents the formation mechanism of core discing firstly.Then,the interaction between diamond drill bits and rock was analyzed based on numerical modeling.A novel drill bit with an inner conical crown for the mitigation of core discing was designed and verified by simulation experiments.The mitigation method was applied in the cavern B1 of CJPL-Ⅱand satisfactory results had been achieved.The percentage of core discing had been obviously decreased from 67.8%when drilling with a rectangular crown drill bit,to 26.5%when an inner conical crown drill bit had been adopted.This paper gives full insight into core discing characteristics and provides a new method for core discing mitigation;it will potentially contribute to stress measurement in deep rock engineering.展开更多
A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallicsandwich panels with truss cores under through-thickness gradient temperature field, which is acommon service condit...A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallicsandwich panels with truss cores under through-thickness gradient temperature field, which is acommon service condition for metallic thermal protection system （TPS）. The in-planetemperature distribution is assumed to be uniform, and through-thickness temperature field isdetermined by heat conduction. Two typical conditions are analyzed： nonlinear thermal bendingin fixed inside surface temperature, and thermal post-buckling in fixed temperature differencebetween two surfaces. Temperature-dependent mechanical properties are considered, andgradient shear stiffness and bending stiffness due to non-uniform temperature is included. Resultsindicate that the temperature-dependent material properties obviously affect bending resistance;however, the effect is negligible on post-buckling behavior. Influences of geometric parameters onthe thermo-structural behavior of the sandwich panel according to the present theoretical modelare discussed.展开更多
基金Funded by the Construction Engineering Special Fund of Taishan Scholars(No.201511106)the Youth Scientific Research Funds of School of Stomatology,Shandong University(No.2018QNJJ01)+1 种基金Shandong Medical and Health Science and Technology Development Plan(No.2017WS112)National Key Research and Development Program of China(No.2016YFC1102705)
文摘In order to investigate how to enhance the teeth fracture resistance after the post and core treatment, an in vitro study was conducted to measure the fracture resistance of endodontically treated teeth restored with cast post and core with two kinds of surface treatment technology and acid etching preparation on the dentinal surface. Sixty-four recently extracted human single-rooted first premolars were endodontically treated and sectioned approximately 1.5 mm above the cementoenamel junction to remove the coronal portion. Each specimen received a cast post, core build-up and a metal alloy crown restoration. All teeth were randomly divided into the smooth surface post, core repair group, the sand blasting surface post, and core repair group, each group was divided into 10 s, 30 s, 60 s acid corrosion treatment group and control group. In acid test groups, an acid etching solution was applied for 10, 30 and 60 seconds, respectively, to the root canal wall surface. Each specimen was embedded in acrylic resin block and tested in an electronic universal testing machine. Fracture loads results showed that canal acid etching could increase teeth fracture resistance strength both in smooth groups and sandblasting group, and achieved the best effect when acid etching for 30 s. Sand spray treatment on the surface of the cast metal post can improve the flexural strength of the teeth after postcrown restoration. Acid etching on the root canal wall surfaces and sand spray treatment on the surface of the cast metal post can improve the flexural strength of the root after post-crown restoration. Therefore, these two methods could be used to strengthen the tooth fracture resistance, and maintain the long-term therapeutic effect of cast post and core restoration.
文摘The multi-piece post-crown technique is more effective in restoring residual root than other restoration techniques.Various types of adhesives have different material properties that affect restoration.Therefore,the choice of adhesive is particularly important for patients.However,the effect of different kinds of adhesives was not too precise by experimental methods when concerning about individual differences of teeth.One tooth root can only be restored with one type of adhesive in experiment.After the mechanical test,this tooth root cannot be restored with other adhesives.With the help of medical imaging technology,reverse engineering and finite element analysis,a molar model can be reconstructed precisely and restored using different types of adhesives.The same occlusal and chewing loads were exerted on the same restored residual root models with different types of adhesives separately.Results of von Mises stress analysis showed that the adhesives with low Young’s modulus can protect the root canal effectively.However,a root canal concentration is apparently produced around the root canal orifice when chewing.Adhesives with large Young’s modulus can buffer the stress concentration of the root canal orifice.However,the root canal tissue may be destroyed because the adhesive is too hard to buffer the load.
基金Projects(U1765206,51979268,51621006)supported by the National Natural Science Foundation of China。
文摘Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering.This paper presents the formation mechanism of core discing firstly.Then,the interaction between diamond drill bits and rock was analyzed based on numerical modeling.A novel drill bit with an inner conical crown for the mitigation of core discing was designed and verified by simulation experiments.The mitigation method was applied in the cavern B1 of CJPL-Ⅱand satisfactory results had been achieved.The percentage of core discing had been obviously decreased from 67.8%when drilling with a rectangular crown drill bit,to 26.5%when an inner conical crown drill bit had been adopted.This paper gives full insight into core discing characteristics and provides a new method for core discing mitigation;it will potentially contribute to stress measurement in deep rock engineering.
基金The financial support from the National Natural Science Foundation of China (91016025, 11472276, 11602271, and 11332011)the Defense Industrial Technology Development Program of China (JCKY2016130B009)
文摘A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallicsandwich panels with truss cores under through-thickness gradient temperature field, which is acommon service condition for metallic thermal protection system （TPS）. The in-planetemperature distribution is assumed to be uniform, and through-thickness temperature field isdetermined by heat conduction. Two typical conditions are analyzed： nonlinear thermal bendingin fixed inside surface temperature, and thermal post-buckling in fixed temperature differencebetween two surfaces. Temperature-dependent mechanical properties are considered, andgradient shear stiffness and bending stiffness due to non-uniform temperature is included. Resultsindicate that the temperature-dependent material properties obviously affect bending resistance;however, the effect is negligible on post-buckling behavior. Influences of geometric parameters onthe thermo-structural behavior of the sandwich panel according to the present theoretical modelare discussed.
