Accuracy Of Intraoral Digital Impression For Whole Upper Jaws And Adaptation Of CAD/CAM Major Connectors

PURPOSE:The aim of this study was to compare the accuracy of intraoral digital impressions for palatal soft tissues and full dentitions,as well as to determine the effect of different palatal vault height or arch width on the accuracy of intraoral digital impressions;and compare the adaptation between the major connectors of removable partial dentures derived from intraoral digital impressions and conventional impressions.METHODS: 1.Thirty-two volunteers were divided into three groups according to the arch width or palatal vault height.Each volunteer received digital impressions of whole upper jaw with an intraoral scanner(TRIOS,3Shape,Denmark)and one conventional impression with a vinyl polysiloxane impression material.Gypsum models manufactured from the conventional impressions were digitized with a laboratory three-dimensional scanner(D500 3D Scanner,3Shape,Denmark)as the reference datasets.The datasets of the digital impressions and conventional models were imported to Geomagic Qualify 12(Raindrop Geomagic,Inc,Morrisville,NC)for three-dimensional analysis by "best-fit alignment" and "3D Compare" process.Deviations between datasets were measured and expressed as average deviations accounting for trueness and standard deviations for precision.Color-coded deviation map displays allowed qualitative visualization of the deviations.2.Each of the twenty-four volunteers received an intraoral digital impression of full upper jaw with TRIOS intraoral scanner and one conventional impression with a vinyl polysiloxane impression material.The conventional impressions were poured with type IV dental stone and then digitized with D500 three-dimensional scanner.A specific design software was used to create the major connectors of the removable partial dentures on both the digital and the conventional impression datasets.After all the virtual major connectors designed from Group digital impression(Group DI)and Group conventional impression(Group CI)were directly fabricated with a clear bio-compatible material using three-dimension print technique,the adaptation of the final major connectors in volunteers' mouths were measured.RESULTS: 1.For the digital impressions for palatal soft tissues,trueness was(130.54±33.95)?m and precision was(55.26±11.21)?m.For the digital impressions for upper full dentitions,trueness was(80.01±17.78)?m and precision was(59.52±11.29)?m.Trueness of digital impressions for palatal soft tissues was worse than that for full dentitions(p<0.001).Precision of digital impressions for palatal soft tissues was slightly better than that for full dentitions(p=0.049).There was no significant effect of palatal vault height on accuracy of digital impressions for palatal soft tissues(p>0.05),but arch width was found to have a significant effect on precision of intraoral digital impressions for full dentitions(p=0.016).A linear correlation was found between arch width and precision of digital impressions for whole upper jaws(r=0.326,p=0.034 for palatal soft tissues and r=0.485,p=0.002 for full dentitions).2.The adaptation of the major connectors ranged from 159.87 to 577.99?m in the mouth in Group DI while the adaptation was from 120.83 to 536.17?m in Group CI.Statistically significant differences in adaptation were found between the major connectors in Group DI and Group CI(p<0.05),except at Location R1.At Location M2 and M3,major connectors in Group DI revealed better adaptation than those in Group CI(p<0.05).At other locations(M1,L1,R2,L2,R3 and L3),major connectors in Group CI revealed better adaptation than those in Group DI(p<0.05).The adaptation of major connectors in Group DI were found better at the midline palatine suture than at the two sides of the palatal vault(p<0.001),while the adaptation of major connectors in Group CI were found better at the two sides of the palatal vault than at the midline palatine suture(p<0.001).In both groups,the highest accuracies in adaptation were revealed at the anterior margin of the major connectors(p<0.001)and there were no significant differences in adaptation between the middle sections and the posterior margin of the major connectors(p>0.05).CONCLUSIONS: 1.It is feasible to use the intraoral scanner to obtain digital impressions for whole upper jaws.Larger deviations were found between intraoral digital impressions and conventional impressions in the areas of palatal soft tissues than that in the areas of full dentitions.Arch width could influence the precision of intraoral digital impressions,while palatal vault height might have no effect.It should be confirmed in further studies that whether the accuracy of digital impressions for whole jaws is clinically acceptable.2.It is feasible to manufacture the major connectors of removable partial dentures by intraoral digital impression and 3D print technique.Though the adaptation of major connectors derived from intraoral digital impressions were worse than that from conventional impressions,both the adaptation of the two kinds of impressions were clinically acceptable.Moreover,CAD/CAM technique for removable partial denture needs to be further improved.