Abstract
Intraoral digital impressions have been stated to meet the clinical requirements for some teeth-supported restorations, though fewer evidences were proposed for larger scanning range. The aim of this study was to compare the accuracy (trueness and precision) of intraoral digital impressions for whole upper jaws, including the full dentitions and palatal soft tissues, as well as to determine the effect of different palatal vault height or arch width on accuracy of intraoral digital impressions. Thirty-two volunteers were divided into three groups according to the palatal vault height or arch width. Each volunteer received three scans with TRIOS intraoral scanner and one conventional impression of whole upper jaw. Three-dimensional (3D) images digitized from conventional gypsum casts by a laboratory scanner were chose as the reference models. All datasets were imported to a specific software program for 3D analysis by "best fit alignment" and "3D compare" process. Color-coded deviation maps showed qualitative visualization of the deviations. For the digital impressions for palatal soft tissues, trueness was (130.54±33.95)μm and precision was (55.26±11.21)μm. For the digital impressions for upper full dentitions, trueness was (80.01±17.78)μm and precision was (59.52±11.29)μm. 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 (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). It was feasible to use the intraoral scanner to obtain digital impressions for whole upper jaws. Wider dental arch contributed to lower precision of an intraoral digital impression. It should be confirmed in further studies that whether accuracy of digital impressions for whole upper jaws is clinically acceptable.
Highlights
Digital impressions and scanning systems were introduced in dentistry in the mid 1980s[1]
Some researchers have demonstrated that veneers, single crowns and fixed dental prostheses (FDPs) manufactured from direct intraoral scanning data delivered equivalent or even better marginal and internal fit compared with those fabricated from conventional impressions[1,2,3, 11,12,13,14], which means that accuracy of intraoral digital impressions is able to meet the clinical requirements for teeth-supported restorations of short units
The classifications of arch width and palatal vault height are shown in Tables 1 and 2
Summary
Digital impressions and scanning systems were introduced in dentistry in the mid 1980s[1]. As the initial step of dental CAD/CAM (computer aided designed/computer aided manufactured) techniques, digital impression is increasingly applied in single crowns[2, 3], multi-unit fixed dental prostheses (FDPs), and has expanded in recent years in the field of oral implants[4, 5], complete denture prosthodontics[6] and obturator prostheses[7]. There are two ways to create a digital impression: direct intraoral scanning or indirect extraoral scanning gypsum casts[5]. Some researchers have demonstrated that veneers, single crowns and FDPs manufactured from direct intraoral scanning data delivered equivalent or even better marginal and internal fit compared with those fabricated from conventional impressions[1,2,3, 11,12,13,14], which means that accuracy of intraoral digital impressions is able to meet the clinical requirements for teeth-supported restorations of short units
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