title: Telescopic crowns: extra-oral and intra-oral retention force measurement--in vitro/in vivo correlation.
abstract: OBJECTIVE
  This study deals with the determination of the retentive forces of telescopic crowns measured extra- and intra-orally and the correlation of these values.
  
  
  BACKGROUND
  The telescopic denture is a well-documented solution for prosthetic rehabilitation for a partially edentulous jaw. Acceptable retention forces are needed to avoid inadvertent removal of the denture during movement of the jaws. Recent literature suggests 3-7 N per attachment to be acceptable. These values are only supported by in vitro studies. In vivo data are scarce, and a correlation of the in vitro and in vivo values is lacking.
  
  
  METHODS
  Twenty-five combined fixed-removable prostheses with a total of 72 double crowns were used for extra-oral retention force measurement prior to cementation (in vitro). The intra-oral measurement was performed at 72 defined measuring points of the dentures 4-6 weeks after prosthetic rehabilitation (in vivo). A specifically designed measuring device was used.
  
  
  RESULTS
  The rank correlation showed that the in vitro and in vivo values correlate with each other (Spearman's ρ = 0.5052). Additionally, it was found that the median values measured before (1.97N) insertion of the dentures were significantly lower than after (4.70N) insertion (Mann-Whitney test, p ≤ 0.0001).
  
  
  CONCLUSIONS
  The retention forces measured before and after insertion of the denture correlate with each other although their dimension is significantly higher after insertion. The reason for this behaviour might be some tilting during removal. Nevertheless, the correlation allows a prediction of the clinically relevant forces by a measurement of the extra-orally measured retentive values.
authors: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany. sbayer@uni-bonn.de
authors: Stefan
authors: S
authors: Bayer
authors: Helmut
authors: H
authors: Stark
authors: Lina
authors: L
authors: Gölz
authors: Ludger
authors: L
authors: Keilig
authors: Dominik
authors: D
authors: Kraus
authors: Anja
authors: A
authors: Hansen
authors: Norbert
authors: N
authors: Enkling
mesh_terms: D000328:Adult; D000368:Aged; D000537:Aluminum Oxide / Q000737:chemistry; D001641:Bicuspid; D001696:Biomechanical Phenomena; D003442:Crowns; D003481:Cuspid; D045662:Dental Etching / Q000379:methods; D003779:Denture Design; D003781:Denture Retention; D003828:Denture, Overlay; D003830:Denture, Partial, Fixed; D003832:Denture, Partial, Removable; D005898:Glass / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007180:Incisor; D007576:Jaw, Edentulous, Partially / Q000534:rehabilitation; D008153:Lubrication; D008422:Materials Testing; D008875:Middle Aged; D012464:Saliva, Artificial / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D006047:Gold Alloys; D012464:Saliva, Artificial; D012965:Sodium Chloride; D000537:Aluminum Oxide