| Objective:To measured micro-tensile bond strength(MTBS)of enamel bonding interface with different degrees of fluorinated teeth after cyclic loading and artificial saliva storage,to evaluate the effect of two artificial aging methods on the enamel bonding interface of dental fluorosis and provide support for further research on enamel bonding aging of dental fluorosis,and to provide data reference for the selection of treatment methods and adhesion improvement of dental fluorosis.Methods:The coal-burning fluorosis patients in Gusu District were selected and 140 freshly extracted mandibular third molars were extracted.The tooth extraction age was 30-40 years old,and the tooth surface was free of sputum,cracks and fillings.Bleaching was not accepted.Thoroughly clean the tooth surface and store it in 10%formalin(Conis)at room temperature.According to the TFI(Thylstrup-Fejerskov Index)score of dental fluorosis,they were divided into four groups A,B,C,and D according to normal,mild,moderate,and severe,and each group was randomly divided into seven groups of a,b,c,d,and e,f,g,and 28 groups in total,5 isolated teeth per each group.Uniformly remove 0.5mm enamel from all molar crowns and expose fresh enamel.Grind non-fluorinated pumice stone and 800 mesh silicon carbide sandpaper under flowing water for 3min.37%phosphoric acid etched the surface of enamel for60 seconds.Clean and dry.The adhesive was bonded and the composite resin was layered and cemented.All the extracted teeth were stored for 24 hours in room temperature.Experiment one:The b,c,and d groups of isolated teeth were fixed in an artificial oral machine,and the crowns were cyclically loaded with 1×10~5,1.2×10~6,and 1.2×10~7 cycles respectively,and the load was 50 N.The loading head used 10 mm diameter round cobalt.The chromium alloy head was vertically loaded with a drop rate of 5 mm/s for the loading head,which mimics the fatigue of the oral material for 2 weeks,6 months and 5 years.After loading,it is soaked in Violet dye for 24 hours with the unloaded group a.Under flowing water,the slow electric grinder was perpendicular to the bonding interface and the bucco-lingual direction was obtained along the long axis of the tooth body.For the distal tooth profile,four observation points were obtained for each tooth and observed with a 25-fold stereoscopic microscope.The staining distances were recorded at each observation point,and the scores were graded.H-tests were performed on the scoring results.The four groups of isolated teeth a,b,c and d were further divided into 8 mm long strips of 1mm×1 mm in cross-section.Four intact specimens were taken as test coupons for each tooth and 20 test specimens in each group.The test piece was fixed on a universal testing machine with a custom fixture for micro-tensile testing.The micro-tensile bond strength of the test piece was recorded.The variation of tensile strength was analyzed by single-factor variance;the fracture mode of the sample was observed by an optical microscope and the card was used.The square test analyzes the fracture of the specimen.Experiment two:The isolated teeth of groups e,f,and g were placed in artificial saliva respectively and soaked for 1 week,4 weeks and 48 weeks respectively.Group a was not soaked into a common control group.The microleakage of enamel adhesion was observed and microstretched.The change in bond strength and the micro-tensile fracture mode are the same as in Experiment one.Result:Experiment one:1.Cyclic loading 1×10~5times,there was no significant difference in microleakage,micro-tensile bond strength and fracture pattern between the enamel enamel and the control group(P>0.05);Cyclic loading was1.2.×10~6 and 1.2×10~7 times.With the increase of loading times,the degree of micro-leakage of the adhesive increases,the micro-tensile bond strength decreases,the interface failure mode increases,and the difference with the control group has statistical significance(P<0.05).2.Cyclic loading 1.2×10~5times,1.2×10~6times and 1.2×10~7 times.With the increase of loading times,the degree of microleakage of the interface between enamel and enamel enamel is increased,and the microstretch bond strength is decreased.The interface disruption pattern was increased,and there was a statistically significant difference from the control group(P<0.05).3.After 1.2×10~7 cycles of loading,1/4 or more moderate fluorogenic plaques and 1/2 or more severe fluorosis teeth,the adhesive micro-leakage exceeds 1/2 of the bonding interface,and the micro-tensile bonding strength Below 5Mpa,it is difficult to meet the enamel bonding requirements.Experiment two:1.There was no significant difference in the degree of microleakage,micro-tensile bond strength,and fracture pattern between the mild enamel enamel and the control group for 1 week after artificial saliva immersion(P>0.05);saliva immersed for 4 weeks At 48 weeks,as the immersion time increased,the degree of microleakage increased,the micro-tensile bond strength decreased,and the interface failure mode increased,and there was a statistically significant difference from the control group(P<0.05).2.Artificial saliva immersed for 1 week,4 weeks and 48 weeks.With the increase of soaking time,the degree of microleakage of the enamel enamel bonding interface between moderate and severe enamel increased,the microstretch bond strength decreased,and the interface failure mode increased.The difference with the control group was statistically significant(P<0.05).3.After 48 weeks of saliva immersion,the micro-leakage of fluorogenic plaques with different degrees of fluoridation did not exceed 1/2 of the bonding interface,and the micro-tensile bond strength was not less than 5 MPa,still satisfying the enamel bonding.Conclusion:1.The durability of the enamel bonding interface with mild fluorosis is good,especially when the cycle loading is low or the artificial saliva immersed for a short time,the bonding performance is very stable.2.In the cyclic loading,the interface durability of the enamel bonding interface of medium-to-severe fluoropolises is poor,and for the adhesive prosthesis that is susceptible to external forces,the repair options need to be more cautious.3.When artificial saliva is immersed,the interface durability of enamel enamel bonding is moderate,and the aging process is relatively slow,which is of positive significance for the repair and bonding of non-forced areas of teeth.4.With the increase of the number of cyclic loading or the prolongation of artificial saliva immersion time,the interface destruction of dental enamel enamel is difficult to avoid,but a reasonable repair design can delay the process of bonding interface destruction. |
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