title: Effects of impression levels and trays on the accuracy of impressions taken from angulated implants.
abstract: OBJECTIVE
  It is crucial to keep the misfit of the abutment-fixture unit at the lowest possible rate. There are a few controversial studies on the accuracy of impression making of angulated implants, and much fewer (and controversial) studies on the abutment-level impression technique, which is a convenient and clinically favorable method. Besides, there are no studies on comparison of sectional vs. full-arch trays. We aimed to assess these.
  
  
  METHODS
  A trapezoidal model with four angulated implants installed at 20° and 30° buccal tilts was fabricated. Forty impressions were taken from this model, with two groups of full-arch and sectional custom trays (n = 2 × 20), each divided into two subgroups of implant-level and abutment-level techniques (n = 2 × 2 × 10 in four subgroups). Absolute and non-absolute linear and angular impression errors were estimated by comparing the fabricated casts with the model, using a coordinate measuring machine. The effects of sectional/full-arch trays and abutment-level and fixture-level techniques on impression accuracies were analyzed using one- and two-way analyses of variance (ANOVA), Tukey, Mann-Whitney, and one-sample t-tests (α = 0.05, Mann-Whitney's α using the Bonferroni Bonferroni method).
  
  
  RESULTS
  No significant differences between the absolute linear errors of the two trays (P = 0.100 [ANOVA]) and the two levels (P = 0.400 [ANOVA]) were observed. The assessment of absolute angular errors showed no significant differences (all P values ≥ 0.4 [ANOVA]). The difference between the linear errors in the full-arch vs. sectional trays was not significant in the fixture-level group (P = 0.290). However, in the abutment-level group, the linear error was significantly greater in the sectional tray compared to full-arch tray (P = 0.013, α = 0.025 [Mann-Whitney]).
  
  
  CONCLUSIONS
  Using sectional trays might not be advantageous over full-arch trays. Sectional trays are not recommended for taking abutment-level impressions. The abutment-level impression technique is as accurate as the studied fixture-level technique. Increasing the angle of implants' divergence from 40° to 60° might not usually lead to a significant increase in the errors, particularly when using abutment-level impressions.
authors.affiliation: Department of Prosthodontics, Dental School, Tehran University of Medical Sciences, Tehran, Iran.|Implant Research Center, Dental School, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Farideh
authors.initials: F
authors.lastname: Geramipanah
authors.affiliation: Department of Prosthodontics, Dental School, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Majid
authors.initials: M
authors.lastname: Sahebi
authors.affiliation: Prosthodontist in Private Practice, Tehran, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Davari
authors.affiliation: Department of Prosthodontics, Dental School, Tehran University of Medical Sciences, Tehran, Iran.|Dental Research Center, Dental School, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammadreza
authors.initials: M
authors.lastname: Hajimahmoudi
authors.affiliation: Iranian Tissue Bank and Research Center, Tehran University of Medical Sciences, Tehran, Iran.|Department of Dental Anatomy and Morphology, Dental Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Vahid
authors.initials: V
authors.lastname: Rakhshan
mesh_terms: D000704:Analysis of Variance; D000044:Dental Abutments; D015921:Dental Implants; D003761:Dental Impression Technique; D003765:Models, Dental
chemical_list: D015921:Dental Implants
keywords: angulated dental implants; impression accuracy; impression levels (implant-level abutment-level); impression trays