| Background:3D printing technology,which is one of the rapid prototyping technologies(RPT),is able to construct prototype by stacking powder-like,filament like or liquid materials layer by layer based on a digital model.Part with variety shapes could be manufactured directly based on digital data by "addition" method,with which the production cost and time reduced while its productivity and accuracy improved.Due to the complexity and diversity of oral system,the structure requirement of dental prosthesis is highly expected.3D printing technology,which truly realized customized manufacture according to the characteristics and requirements of patients,is particularly suitable for manufacturing of various dental prostheses.In recent years,CAD/CAM and RPT are combined to construct various shapes of prosthesis with improved accuracy,matching the maxillofacial defect precisely.It is considered one of the best methods to manufacture prosthesis for maxillofacial defect now.As one of 3D printing technologies,selective laser melting(SLM),is widely used in constructing dental prostheses.The quality of final product depends on the precision of digital models,as well as suitable printing materials,equipment,and printing processes.However,whether the biocompatibility,accuracy and mechanical properties of the final product would be affected during 3D printing procedure is still under study.Objective:The purpose of this paper is to study the integrated digital design and printing process with CAD-CAM-SLM techniques for prosthetics of maxillofacial defect,and to research into the adaptation and biocompatibility of metal crown produced by SLM technique,as the technique reference for fabricating fixed dental prostheses in clinical practice.Methods:1)A cobalt-chromium alloy prosthesis scaffold for a patient with partial maxilla defect was printed by SLM technique as example.The negative model box was designed and manufactured by SLS after the pontic teeth made by CAD/CAM.With this negative model box,the digital manufacture for maxilla prosthesis was achieved indirectly.2)The minimum pre-set space between crown and abutment tooth was measured,with which the coping of cobalt-chromium alloy crowns were manufactured.The crowns,10 for experimental group and 10 for control group,were fabricated with SLM technique and CAD/CAM casting method respectively.The space in-between and the thickness of coping in cross-sectional were measured by digital "virtual seating" and cement/cutting method.The space in-between the crown and abutment tooth,the thickness deviation of the crowns and the measured value form 2 methods in same point were recorded between the two groups.3)Specimens from Cobalt-chromium alloy and Ti6A14V alloy or titanium were fabricated by SLM and wax loss casting respectively.Then their cytotoxicity was detected by MTT assay from metal leaching solution.After be implanted in subcutaneous tissue of SD rats,the general and local reaction of the specimens around implantation site were observed.The specimens and soft tissues around were harvested and stained for optical microscope examine,with 3 rats killed randomly after 1 week,4 weeks and 12 weeks from the implantation day.Results:1)The digital design and manufacture of prosthesis for maxillary defect were achieved in this study,with good results that meet the clinical application.2)The minimum pre-set die spacer thickness for Cobalt-chromium coping from SLM technique was 50?m.The thickness deviation of the crowns form SLM and CAD/CAM casting were 1.80%and 2.20%respectively,with which no statistically significant differences were found.By digital "virtual seating",the space between crown and abutment tooth on the edge of the crowns form SLM and CAD/CAM casting were 69.97±7.773pm and 71.81±6.661pm respectively.By the cement/cutting method,the spaces were 64.00±5.039?m and 65.50?5.421?m respectively.The space in-between the crown and abutment tooth have no statistically significant difference between the two measuring methods too(P>0.05).3)The cytotoxicity levels were 1 in all specimens(casting cobalt-chromium,pure titanium,SLM cobalt-chromium,Ti6A14V materials).Mild tissue reaction and thicken of the fiber membrane were found in all groups,but without significant difference.Conclusion:The integrated digital design and manufacture of the prosthesis for maxillofacial defect have been realized.The fitting and accuracy of 3D-printed Cobalt-chromium coping satisfied the clinical application.No obvious cytotoxicity was found between the metal specimens from SLM technique and traditional casting method.3D printing technique has no effect on biocompatibility of the materials and could be applied to dental clinical application. |
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