| Dentition defect is a common and frequent disease of the oral cavity.At present,removable partial dentures(RPDs)with metal frameworks are the most common prosthetic devices to restore dentition defects.Compared with noble metals and cobalt-chromium alloys,RPDs with titanium frameworks have been increasingly recognized by dentists and patients due to light weight,low modulus of elasticity and good biocompatibility.Previously,titanium frameworks were mainly manufactured by casting,which was likely to form internal porosity and yield a certain failure rate.With the development of computer-aided design(CAD)and computer-aided manufacture(CAM)technologies,RPDs with titanium frameworks can be manufactured by computer numerical controlled(CNC)milling and selective laser melting(SLM).RPDs with titanium frameworks manufactured by casting,milling or SLM require higher surface smoothness,processing accuracy,retention performance and anti-fatiguedeformation ability to be applied in clinical practice.On the basis of previous studies on the scanning accuracy and repeatability of different color gypsum,the surface roughness,processing accuracy,retention force changes and permanent deformation of 0.75-mm undercut titanium clasp were assessed(after nondestructive testing)by constructing a model of clasp and its die data in this study.Three-dimensional profile microscopy,best-fit alignment,insertion and removal in fatigue testing and scanning electron microscopy(SEM)were performed,aiming to provide detailed and sufficient research data for the widespread application of CNC milling and SLM titanium clasps by dentists in clinical settings.This study was divided into the following five sections:Part ?: Construction of RPD clasp-die consortium data and fabrication of the sample productsObjective: To construct the RPD clasp-die consortium data,evaluate the quality of the processed samples,providing testing and reference objects for subsequent experiments.Methods: The simulated data of mandibular molars were constructed and processed.Then,the prototype data of clasp in the dental design software were extracted.The clasp and its die data were fitted into a combination in the Geomagic software.Finally,four groups of clasp samples(n=17 in each group)of casting CPTi,casting Ti,milling CPTi and SLM Ti were processed and X-ray non-destructivetesting was carried out.Results: The data of 0.75-mm undercut clasp-die consortium were successfully constructed,and the data in four groups of clasp samples(casting CPTi,casting Ti,milling CPTi and SLM Ti)with identical shape were obtained.Non-destructive testing demonstrated that casting defects were noted in the CPTi(n=3 samples)and Ti groups(n=2samples)during the casting process,whereas no obvious defects were observed in the milling CPTi and SLM Ti groups.Conclusion: Titanium clasp samples of different processes could be obtained by constructing clasp-die data.However,the overall quality of the clasp samples obtained by milling and SLM was better than that manufactured by casting.Part ?: Study on surface morphology and roughness of clasp samples obtained by different processing technologiesObjective: To analyze or measure the surface morphology and roughness of clasp samples obtained by different processing methods,providing data support for clinical application.Methods: A sample was randomly selected from each group of clasps,and the clasp arm was equally divided into three parts.The middle part was cleaned by ultrasound,and then the characteristics of the internal surface of the clasp arm were observed by SEM.The morphology and roughness of the internal surface of the clasp arm were analyzed by morphological profilometry microscope.Finally,the experimental data were statistically analyzed(?=0.05).Results:Compared with the casting process,the SLM Ti clasp exhibited extensive and less-uniform granular surface,whereas the milling CPTi clasp showed uniform and smooth surface.The roughness in the milling CPTi group significantly differed from those in the SLM Ti,casting CPTi and casting Ti groups(all P<0.05),whereas no statistical significance was documented between the casting CPTi and casting Ti groups(P>0.05).The three roughness indices(Ra,Ry,Rz)did not significantly differ among four groups.Conclusion: In this study,the surface roughness of all clasp groups were greater than 0.3?m.The surface of milling CPTi clasp was the smoothest,followed by the casting CPTi and casting Ti clasps,whereas the surface of SLM Ti clasp was the roughest.Part ?: Study on processing accuracy of clasp samples obtained by different processing technologiesObjective: To analyze the processing accuracy of clasp samples obtained by different processing technologies,offering data support for clinical application.Methods: Twelve clasp samples were randomly assigned into each group.After spraying the imaging powder,the test data(Test1)were obtained by scanning with structured light scanner.Then,the clasp data(REF)were imported into Studio 12 software and divided into the inner and outer surfaces.The RMS values were obtained by "best-fit alignment" with Test1 in Qualify 12 software.Finally,the RMS data werestatistically analyzed(?=0.05).Results: The processing accuracy of the inner surface did not significantly differ among the four clasp groups(all P>0.05).However,the processing accuracy of the outer surface and the whole area in the milling CPTi group was significantly higher than those in the casting CPTi and casting Ti groups(both P<0.05),whereas the processing accuracy of the outer surface and the whole area in the SLM Ti group was significantly lower compared with those in the casting CPTi,casting Ti and milling CPTi groups(all P<0.05).No statistical significance was noted between the casting CPTi and casting Ti groups(P>0.05).Conclusion: All the inner surfaces of the clasp arms yielded equivalent processing accuracy and the stability of the clasp arms in each group is good(standard deviation of accuracy is less than 6 microns).Nevertheless,the highest processing accuracy of the outer surface and the whole area of the clasp was achieved in the milling CPTi group,followed by the casting CPTi and casting Ti groups,and the processing accuracy in the SLM Ti group was the lowest.Part ?: Study on retention force of clasps obtained by different processing technologies before and after insertion / removal cyclesObjective: To evaluate the initial retention force and fatigue retention performance of different clasp samples after insertion / removal cycles,providing experimental data for clinical application.Methods: Five of the12 samples of clasps that had been scanned were randomly selected for the retention testing.Firstly,the Co-Cr die was fixed in the fatigue testing device.Fifteen cycles were run at a speed of 50 mm/min according to the set procedure to obtain the initial retention force.Then,10000 insertion /removal cycles were run at a speed of 950 mm/min.Fifteen retention forces were obtained from 500 cycles,and then 15 retention forces were recorded every 1000 cycles until the end of the cycle.Finally,12 groups of retention data were obtained and statistically analyzed(?=0.05).Results: The initial retention in the SLM Ti group was significantly larger than those in the other groups(all P=0.000).The retention force in the milling CPTi,SLM Ti,casting Ti and casting CP Ti groups began to decrease after 500,1000,2000 and 3000 insertion / removal cycles,respectively.The retention force in the SLM Ti group significantly declined after 2000 cycles,and all the samples in the SLM Ti group were broken after 4000 insertion /removal cycles.The clasps in the remaining three groups were not broken after 10000 insertion / removal cycles.Compared with the casting CPTi and casting Ti,milling CPTi yielded lower retention reduction rate(9.5%).Conclusion: Compared with the casting process,the retention force of milling CPTi clasp was less decreased after 10000 insertion / removal cycles.However,all SLM Ti clasps were broken,and the fatigue retention performance remained to be improved.Part?: Study on the permanent deformation of clasps obtained by different processing technologies before and after insertion /removal cyclesObjective: To observe and compare the permanent deformation of different clasp samples before and after the insertion / removal cycles,offering theoretical basis for clinical application.Methods: The clasp samples that had completed the insertion / removal cycles were removed from the fatigue testing device,the imaging powder was sprayed after ultrasonic cleaning,and the complete test data(Test2)were obtained by using structural optical scanner.Then,all Test 2 data were imported into Geomagic Quality 12 software for best-fit alignment with Test1(the scanning data of clasp samples before insertion / removal cycle).The RMS data were statistically analyzed(?=0.05).Results: SEM revealed that no deviation was observed in the connecting body and the starting part of the clasps in three groups,whereas the deviation of the clasp arm was gradually increased from the middle part to the end.Statistical analysis showed no statistical significance in the permanent deformation after 10000 insertion / removal cycles between the casting CPTi(153.6±35.6 ?m)and the milling CPTi(199.6±79.2 ?m)/the casting Ti groups(94.9 ±39.1 ?m)(both P>0.05).However,statistical significance was noted between the milling CPTi(199.6±79.2 ?m)and the casting Ti groups(94.9±39.1 ?m)(P<0.05).Conclusion: After 10000 insertion / removal cycles,the permanent deformation of the milling CPTi clasp was larger than that of the casting Ti clasp,which might increase the life expectancy of the clasp to certain extent. |
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