Applied Basic Research On Removable Partial Denture Titanium Alloy Frameworks Fabricated By SLM 3D Printing

Selective laser melting(SLM)is a new metal rapid prototyping technology based on the additive manufacturing technology in recent years.Compared with the traditional lost wax casting technology and subtractive manufacturing technology,SLM technology has the advantages of saving material,can process fine complex structure,high production efficiency,especially suitable for the production of metal removable partial denture(RPD)framework.The suitability of the removable partial denture metal framework is an important index to evaluate the quality and clinical effect of the prosthesis.It can reflect the machining precision of the prosthesis,and has a great influence on the prognosis of patients.However,the processing accuracy of the framework is one of the significant factors that determine its clinical suitability,and its internal quality plays a vital role in the service life of the prosthesis.At present,there are few reports about the processing precision,internal quality and fitness of RPD framework fabricated by SLM technology at home and abroad.In this experiment,the processing accuracy of Ti-6Al-4V titanium alloy RPD framework fabricated by SLM technology was tested by the three-dimensional optical measurement method.The X-ray nondestructive testing technique was used to detect and evaluate the internal quality of the RPD framework.Finally,the “duplicating model method” and the three-dimensional optical measurement method were used to study the suitability of the RPD framework,and to evaluate the feasibility of using SLM technology to produce titanium alloy RPD framework,which provides a theoretical basis for clinical application.Method1.8 Kennedy III Ti-6Al-4V removable partial denture framework were fabricated by selective laser melting technology.Each of them was scanned by the 3D optical scanner to obtain the point cloud data,which were import into the Geomagic Qualify 2013 software with the original CAD data.After that,the data of original CAD and the point cloud of the framework were set as reference parts and test pieces respectively,and the best-fitting algorithm was carried out.Finally,the processing error of RPD framework was analyzed by 3D comparison function,and the machining precision was evaluated.2.The above 8 titanium alloy RPD framework were examined by X-ray nondestructive testing technology,and compared with the conventional casting pure titanium RPD framework.Wilcoxon rank sum test was performed using SPSS 22 software.3.The framework was carefully polished and then completely positioned on the plaster model to observe its suitability.The gypsum model with silicone rubber film obtained by the "impression method" and the original gypsum model without silicone rubber film were scanned by 3D optical scanner,and the data was imported into the Geomagic Qualify 2013 software.The RPD was analyzed by 3D comparison function and the gap between the tissue surface of the major connector and the model was evaluated.The experimental results were subjected to independent sample t test using SPSS 22 software.Result1.The overall average deviation of the titanium alloy RPD framework fabricated by selective laser melting technology is 0.089± 0.076 mm,the RMS error is 0.103 mm.When the deviation is ± 0.100 mm,the coincidence degree is as high as 64.42%.2.There were no obvious defects such as porosity and crack in all the titanium alloy RPD framework,while some of the casting pure titanium framework had 1~6 pores.The number of internal pores of cast framework was 3(1.25,5.50),which was significantly larger than that of SLM framework 0(0,0),the difference was statistically significant(Z =-3.249,P = 0.001).3.In our ocular inspection,we found the fitness of the RPD framework was very well.The framework was completely located in the plaster model,and its tissue surface was fitted with plaster model well.There was no obvious movement.The 3D deviation analysis showed that the average deviation between the tissue surface of the SLM RPD framework and the corresponding surface of the plaster model(0.222 ± 0.070 mm)was no statistically significantly different from that of the casting pure titanium group(0.269±0.068 mm)(P>0.05).ConclusionThe machining accuracy of the titanium alloy RPD framework fabricated by SLM technology is high.Its internal structure is very uniform,without any pores,cracks and other internal defects,and the its tissue surface was fitted with plaster model well,which make it fully meet the clinical requirements.SLM technology is expected to replace the traditional lost wax casting technology,and become an effective method for making removable partial dentures framework.