Evaluation Of The Fit Of Multi-units Fixed Dental Prostheses Fabricated By SLM 3D Printing

Selective laser melting(SLM)is an automatic rapid prototyping(RP)production methods.Compared with the traditional casting method,SLM offers several advantages,such as a higher definitive product density,reduced manufacturing time and costs,minimization of human errors,and the prevention of casting defects.Compared to CAD/CAM milling technology,SLM reduce the waste of materials.As a new manufacturing technology in dentistry,insufficient research has been conducted as to their clinical acceptability.Various factors will determine whether these techniques are clinically acceptable.In particular,fit is most important with regard to the satisfactory functioning of FDPs in the oral cavity and to their longevity.This research first compare the marginal fit and internal fit of titanium fixed dental prostheses(FDPs)fabricated by CAD/CAM technology,the lost wax casting method and SLM,to assess the accuracy of SLM technology.Secondly,also compare the marginal fit and internal fit of cobalt–chromium FDPS fabricated by the lost wax casting method and SLM.Meanwhile,the fit of titanium and cobalt–chromium FDPS fabricated by SLM are also compared so that comprehensive evaluation of the fit of different metal FDPS fabricated by SLM can be obtained.So as to provide the theoretical basis for application in the clinical of SLM.Furthermore,in order to get more complete results,the study was designed to fabricate single crowns,three units arch union crowns and six units arch union crowns on the six standard abutments arranged in the bow.So as to analyze the effects to the fit of multi units restorations manufactured by different technologies,also can evaluate whether the fit change when the length of the prostheses increase.MethodTitanium single crowns,three units union crowns and six units union crowns fabricated by CAD/CAM technology(DMG,R+K),the lost wax casting method and SLM for 5 samples in each group.Cobalt–chromium single crowns,three units union crowns and six units union crowns fabricated by SLM(EOSING M270,EOSING M280)and conventional lost wax technique(LW)method for 5 samples in each group.Marginal fit and internal fit was examined using a light-body silicone.After setting the silicon film was cut into two parts and the thickness of silicon layer was measured at 100×magnification using a digital microscope to measure marginal gap(MG)and internal gap(IG).A repeated measure ANOVA for statistical analysis was performed using the SPSS statistical package version 17.0(α=0.05)Results1 The mean gap was the smallest for titanium fixed dental prostheses fabricated by CAD/CAM(26-33μm),followed by selective laser sintering(SLM)(39-43μm),then the lost wax and casting(42-48μm)(P<0.05).There are no statistically significant differences of internal gap are found in the CAD/CAM group,SLM group and the lost wax and casting group.2.In the SLM group,means of marginal gap of titanium single crowns are smaller than six units union crowns,but no statistically significant differences between single crowns and three units union crowns are found.In the CAD/CAM(DMG,R+K)and casting group,means of marginal gap of titanium single crowns are smallest,follow with three units union crowns,the means of marginal gap of six units union crowns are the largest.3.The means of marginal gap of cobalt–chromium prostheses in the SLM group(42-47μm)are smaller than in the casting group(48-57μm)(P<0.05).No statistically significant differences of internal gap between the two groups are found.4.The mean gap was the smallest for cobalt–chromium single crowns,followed by the three units union crowns,then the six units union crowns in both SLM group and the lost wax and casting group.5.The mean gap of titanium and cobalt–chromium fixed dental prostheses fabricated by SLM are obviously smaller than 120μm which is the clinical standard generally accepted.In addition,the mean gap of titanium fixed dental prostheses( 39-43μm) are smaller than cobalt–chromium fixed dental prostheses(42-47μm)both fabricated by SLM.ConclusionThe marginal fit of the SLM group appeared slightly superior compared to that of the conventional LW method and significantly smaller than 120μm clinical generally accepted standard.So the SLM system can satisfy the clinical requirements.