Effect Of Selective Laser Melting On The Manufacturing Accuracy Of Single Crown And Multi-units Crowns

ObjectivesAt present,there are many researches on selective laser cladding(SLM)technology,but most of them focus on the basic research of standard specimen.In the field of practical application,especially in prosthodontics,there are few reports.In our study,the single crown was used as a test specimen,and the laser parameters were taken as variables to study the parameters affecting the adaptability of the single crown and the factors affecting its surface roughness.The multi-unit crowns was used as a test specimen,and the support structures were used as a variable to study the influence on the dimensional accuracy of the multi-unit crown,and whether the SLM technology meets the accuracy requirements for the manufacturing of complex denture.Methods1.The standard single crowns of CoCrMo alloy were made by using the 52-91J/mm~3gradient laser energy density as a variable.The traditional casting specmens were taken as a control.The internal gap and marginal gap were measured by silicone replicate method,and the internal surface of the crowns was observed by stereomicroscope and the obstacles affecting the seating were analyzed.2.By cutting and detecting the inner surface roughness of the single crown made by different energy densities,the correlation analysis between the surface roughness of the inner crown and the crown fitting was conducted,and the relationship between the roughness and the crown fitting degree was assessed.3.6,8,10,12,14 units crowns are manufactured using cross support and cylindrical support design as variables,and the casting was taken as control.Geomagic Qualify software is used to detect the inner surface forming accuracy and horizontal deformation by reverse engineering,and the edge gap is measured by silicone replicate method to assess the vertical deformation.Results1.In the experiment of single crown adaptability,the gap distribution between each parameter group of SLM and CAST group was as follows:the middle-axial gap was the lowest,followed by the marginal gap,and the middle-occlusal gap was the highest.In the energy density of 52-91J/mm~3,the marginal gap and the middle-occlusal gap of the crown first decreased and then increased with the increase of the energy density,and the gap value was the lowest when it was73J/mm~3.The middle-axial gap value does not change regularly with the increase of energy density.The adaptability of SLM crown is better than that of casting crown.2.With the increase of energy density,the variation of inner surface roughness of the single crown was significantly correlated with the variation of marginal and occlusal gap of the single crown(p<0.05).At 73J/mm~3,the surface roughness of the axial(12.12μm),shoulder(10.54μm)and the occlusal(9.94μm)reached the lowest.The crown inner surface roughness distribution of each parameter group of SLM was as follows:the surface roughness of the axial surface was the highest(16.94μm),the shoulder surface(14.57μm)and the surface roughness of the shoulder surface(14.45μm)were similar(p<0.05).3.In the 6-14 units crown restoration,no significant surface accuracy,vertical and horizontal deformation occurred in the SLM group with the increase of units.Compared with the casting specimens of the same unit,the horizontal and vertical dimensional accuracy and surface accuracy of the SLM specimens were better than that of the casting specimens.In the SLM experimental group,the horizontal and vertical dimensional accuracy of the cylindrical support specimen is better than that of the cross support specimen.ConclusionThe energy density has a great influence on the surface roughness,which affects the adaptability of the single crown.When the energy density is 73.47 J/mm3,the surface roughness is the lowest,and the marginal and occlusal gap are the smallest.For the multi-unit crown,the cylindrical support design is more conducive to the control of deformation.Compared with casting specimens,SLM multi-unit crowns do not increase in surface accuracy and deformation degree with the number of units.SLM technology is superior to traditional casting technology in the manufacturing accuracy of single crown and multi-unit crown.