الفهرس 
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Abstract
A phantom model was used to simulate patient’s mouth. Polyether secondary impression was taken for the phantom model and poured to fabricated stone casts. Stone casts were scanned by two intraoral scanners 3shape, Dental Wings) and two extraoral scanners (Zirkonzahn, Ceramill+ Amann girrbach) to obtain an accurate digital models. Reference teeth (canines, 2nd premolars, 2nd molars) were measured on the intraoral and extraoral digital models by Geomagic software and compared to measurements of stone cast done by stereomicroscope. The measurements were done on three aspects (mesiodistally, buccolingually and occlusocervically) for each examined tooth. Intra operator consistency was assessed using intra class correlation coefficient (ICC) and Dahleberg formula. General linear model was used to compare scanners regarding the discrepancy of measurement relative to reference cast.
While regarding the second aim of the study, the reference model was scanned using two intraoral scanners (Trios 3shape (3S) and Dental wings (DW)) producing two digital impressions. Then, stereolithography 3D printing (SLA) technique was used to print dental models from the digital impressions, and polyether impressions were poured up in dental stone to produce conventional models. Measurements of the 4 types of model (3S digital, DW digital, and 3S printed and DW printed models) were compared with the conventional stone models. Teeth measurements (maxillary and mandibular canines, 2nd premolars and 2nd molars) included mesiodistal (crown width) and incisal/occlusalgingival (crown height). Arch measurements included intercanine and intermolar widths. All printed and conventional stone models were measured using digital caliper. Geomagic Qualify software (3D Systems, Rock Hill, SC) analysis software was used to make measurements on digital models. One-way ANOVA analysis was used to assess differences between groups.
Results. There were no significant differences among the 4 scanners in the discrepancies (p= 0.97) which were <0.5 mm. Discrepancies differed by tooth (p< 0.0001) with the least discrepancy observed in canines and direction of measurement (p= 0.008) with the greatest discrepancy observed in molars.
In case of 3D printed models and conventional stone casts, they showed less errors than digital models. These digital models had the greatest errors in intercanine (ICW) and intermolar width (IMW). Digital DW model had significantly greater errors than all others for all measurements. All errors were within the clinically acceptable level (< 0.5 mm).