Preliminary Study On Properties Of A Domestic Transparent Zirconia By Different Sintering Methods

Objective:The purpose of this paper was to explore the effects of different sintering methods:conventional sintering(CS)and speed sintering(SS),on the immediate and long-term properties of domestic translucent zirconia,to provide a reference for clinical work.Methods:Taking transparent zirconia as the object,this experiment was divided into two parts:Part one:To investigate the effects of different sintering methods on the immediate and long-term properties of fully anatomical single crowns.The maxillary first molar of standard dental model was selected as an abutment.To prepare teeth according to the standard,the scanning model printed the same single crown resin substitute(n=20),The crowns sintered by different sintering methods were divided into immediate groups(A)and aging groups(B)according to whether aged or not.Groups A was used to observe the immediate properties of the crown under different sintering methods,and Groups B was used to observe the effects of different sintering methods on the properties of the crown after 5000 cycles of aging.Part two:To investigate the effects of different sintering methods on the immediate and long-term performance of fully anatomical three-unit fixed bridges.Simulating the situation of the second premolar missing,the first premolar and the first molar were used as abutment teeth,printed the exact resin replacement(n=20).The preparation process was consistent with the crowns.The related tests of the two-part prosthesis were as follows:1.Using silicone rubber impression replication method for suitability test,measuring site:Marginal Gap、Axial Gap,Occlusal Gap,and Axial-occlusal transition area,repeated three times in each sites,and the average value was taken.to measurement results were tested by SPSS 16.0.2.The fracture strength of the prosthesis were measured by universal tester,and the loading head with a diameter of 6mm was used to slowly increase the load until the prosthesis cracked,and the loading force at this time was taken as the breaking load value of the specimen.3.XRD was used to detect the crystal phase composition of each group of restorations.4.The surface morphology and fracture surface of the two groups of restorations were characterized by scanning electron microscope.5.The above experiments were repeated after cold and hot cycling aging treatment to observe the influence of different sintering methods on the long-term performance of the prosthesis.Results:1.Fit test results:(1)Crowns:The adaptability of CSA groups were less than SSA groups.There were statistical differences in the areas of MG and AOT between the two groups(P<0.05).OG had significant statistical difference(P<0.01).The OG value of SSB was significantly higher than that of CSB(P<0.001).By comparing group A and group B,it was found that the MG value in CSB groups were higher than that in CSA groups(P<0.01),but there were no significant difference in the remaining sites(P>0.05).(2)FPD:The adaptability of CSA groups was smaller than SSA groups.CSA and SSA had significant statistical differences in MG with premolar and molar area(P<0.001).OG,AOT,AG in premolar area,AG and OG in molar area were significantly different(P<0.01).no statistical difference in AOT of molar area(P>0.05).The fitness value changes after aging treatment.The fitness of CSB groups in premolar area was lower than that of SSB in OG,AG and AOT,and there was significant statistical difference between them(P<0.01).There was statistical difference in AG(P<0.05).The fitness of CSB groups was higher than that of CSA group,and there was a significant statistical difference in MG(P<0.001).Different abutments in SSB groups had distinct changing trends,and MG and AOT in SSB groups were lower than those in SSA in premolar area.In molar area,the fitness value of MG in SSB groups was lower than that in SSA groups,while OG and AOT were higher than SSA groups.2.Strength test results:There was no significant difference in fracture load between crowns and fixed bridges under different sintering methods(P>0.05).Although the fracture load was slightly lower than that before aging,there was no significant statistical difference(P>0.05).3.XRD:The crystal phase structure of zirconia crown and fixed bridges were composed of stable tetragonal phase,and there was no obvious crystal phase change after aging.4.SEM:(1)Crowns:The surface morphology show that the grain size of the samples prepared by the rapid groups was small,but compared with the conventional groups,the grain arrangement was not uniform enough and pores could be seen.the grains of the two groups did not increase significantly after aging.The fracture modes of full crowns were both trans granular fracture and intergranular fracture.(2)FPDs:The surface morphology show that the grains in the conventional group were dense and uniform,and a large number of pores and unevenly grown grains could be seen in the speed groups.the crystal size of the fixed bridge surface had increased to varying degrees after aging treatment.The fracture mode of fixed bridge under different sintering methods were trans granular fracture and inter granular fracture.Conclusion:1.The marginal and internal fit of CAD/CAM crowns and fixed bridges both are within the range of clinical requirements.The influence of aging treatment on fixed bridge is greater than crown.2.There is no obvious difference in strength of restorations under different sintering methods,Although it decrease after aging treatment,it is greater than the maximum physiological bite force in the mouth.3.Zirconia is a stable tetragonal phase structure under different sintering methods.Although the grain size increase after aging treatment,it is not reach the phase transformation level,and the crystal phase structure composition meets the dental zirconia standard.The fracture modes of restorations after different sintering methods and aging treatment are trans granular fracture and inter granular fracture.