title: Accuracy evaluation of intraoral optical impressions: A clinical study using a reference appliance.
abstract: BACKGROUND
  Trueness and precision are used to evaluate the accuracy of intraoral optical impressions. Although the in vivo precision of intraoral optical impressions has been reported, in vivo trueness has not been evaluated because of limitations in the available protocols.
  
  
  OBJECTIVE
  The purpose of this clinical study was to compare the accuracy (trueness and precision) of optical and conventional impressions by using a novel study design.
  
  
  METHODS
  Five study participants consented and were enrolled. For each participant, optical and conventional (vinylsiloxanether) impressions of a custom-made intraoral Co-Cr alloy reference appliance fitted to the mandibular arch were obtained by 1 operator. Three-dimensional (3D) digital models were created for stone casts obtained from the conventional impression group and for the reference appliances by using a validated high-accuracy reference scanner. For the optical impression group, 3D digital models were obtained directly from the intraoral scans. The total mean trueness of each impression system was calculated by averaging the mean absolute deviations of the impression replicates from their 3D reference model for each participant, followed by averaging the obtained values across all participants. The total mean precision for each impression system was calculated by averaging the mean absolute deviations between all the impression replicas for each participant (10 pairs), followed by averaging the obtained values across all participants. Data were analyzed using repeated measures ANOVA (α=.05), first to assess whether a systematic difference in trueness or precision of replicate impressions could be found among participants and second to assess whether the mean trueness and precision values differed between the 2 impression systems.
  
  
  RESULTS
  Statistically significant differences were found between the 2 impression systems for both mean trueness (P=.010) and mean precision (P=.007). Conventional impressions had higher accuracy with a mean trueness of 17.0 ±6.6 μm and mean precision of 16.9 ±5.8 μm than optical impressions with a mean trueness of 46.2 ±11.4 μm and mean precision of 61.1 ±4.9 μm.
  
  
  CONCLUSIONS
  Complete arch (first molar-to-first molar) optical impressions were less accurate than conventional impressions but may be adequate for quadrant impressions.
authors.affiliation: Adjunct Instructor, Department of Operative Dentistry, University of North Carolina School of Dentistry, Chapel Hill, NC. Electronic address: mohammad.attieh@gmail.com.
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Atieh
authors.affiliation: Professor and Chair, Department of Operative Dentistry, University of North Carolina School of Dentistry, Chapel Hill, NC.
authors.forename: André V
authors.initials: AV
authors.lastname: Ritter
authors.affiliation: Professor and Graduate Program Director, Department of Orthodontics, School of Dentistry, University of North Carolina, Chapel Hill, NC.
authors.forename: Ching-Chang
authors.initials: CC
authors.lastname: Ko
authors.affiliation: Associate Professor, Department of Prosthodontics, School of Dentistry, University of North Carolina, Chapel Hill, NC.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Duqum
mesh_terms: D017076:Computer-Aided Design; D003724:Dental Arch; D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation; D006801:Humans; D021621:Imaging, Three-Dimensional; D003765:Models, Dental
chemical_list: D003760:Dental Impression Materials