title: Frequency of undercuts and favorable path of insertion in abutments prepared for fixed dental prostheses by preclinical dental students.
abstract: BACKGROUND
  Existing publications are lacking regarding guidelines to measure the path of insertion (POI) or placement of multiple abutments for fixed prostheses in terms of angle evaluation other than by the visual judgment of the operator.
  
  
  OBJECTIVE
  The purpose of this preclinical study was to evaluate the incidence of undercuts and favorable path of insertion for prepared typodont abutments for 3-unit fixed dental prostheses by comparing different angles within and between both abutments of 3-dimensional (3D) scanned and digitized preparations and measured with computer-aided design (CAD) software.
  
  
  METHODS
  Sixty-six maxillary first premolar and maxillary first molar prepared typodont abutments were 3D-scanned and digitized using the Prep-Assist optical 3D scanner and exported as stereolithography (STL) files. These files were imported into CAD software, and 18 different angles were measured within and between the 2 abutments to determine the incidence of undercuts and the frequency of obtaining a favorable path of insertion.
  
  
  RESULTS
  Twenty-seven (40.9%) preparations had no clearly visible undercut when viewed virtually. Moreover, a minimum of 12 (44.4%) to a maximum of 26 (96.3%) of the 27 preparations had a favorable POI.
  
  
  CONCLUSIONS
  Fewer than half of the fixed dental prosthesis preparations did not have a clearly visible undercut when viewed virtually. A favorable POI was found in 44.4% to 96.3% of the preparations. Favorable POIs were found to occur more frequently in the faciopalatal dimension than in the mesiodistal dimension.
authors.affiliation: Associate Professor, Oral and Maxillofacial Prosthodontics Department, Fixed Prosthodontics Division, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia. Electronic address: tmarghalani@kau.edu.sa.
authors.forename: Thamer Y
authors.initials: TY
authors.lastname: Marghalani
mesh_terms: D017076:Computer-Aided Design; D000044:Dental Abutments / Q000592:standards; D003761:Dental Impression Technique; D003830:Denture, Partial, Fixed; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D013335:Students, Dental; D019246:Tooth Preparation / Q000379:methods