title: The effect of placement and quantity of glass fibers on the fracture resistance of interim fixed partial dentures.
abstract: OBJECTIVE
  Polymers used in interim fixed partial dentures (FPD) have recently been reinforced with fibers. The aim of this study was to determine the influence of the position of the fiber reinforcement on the fracture resistance of interim FPDs. In addition, the influence of quantity of fibers and the length of span of the FPD on the fracture resistance was investigated.
  
  
  METHODS
  FPDs were fabricated from a resin mixture of polyethylmethacrylate powder and n-butylmethacrylate liquid. Five FPDs from each group were made, and the FPDs were stored in water for 30 days before testing. The FPDs in the control group were unreinforced, and in the other groups the FPDs were reinforced either with two or three unidirectional continuous glass-fiber reinforcements and one woven glass-fiber reinforcement. Different quantities of fibers were used and the fibers were placed in different locations in the FPD. The load was applied to the FPD by a steel ball placed in the cavity in the middle fossa of the pontic tooth.
  
  
  RESULTS
  The load required to fracture the unreinforced FPDs varied from 372 to 1061 N. Mean fracture load of reinforced FPDs varied from 508 to 1297 N. One-way analysis of variance showed that the length of span and the quantity of fibers significantly affected the fracture load (P < 0.001, n = 5). By lengthening the span of the FPD, the reinforcing effect of glass fibers became more obvious.
  
  
  CONCLUSIONS
  The results of this study suggest that the effectiveness of glass-fiber reinforcement is most evident in interim FPDs with long spans and that the positioning of reinforcement considerably influences the strength of the FPD.
authors.affiliation: Institute of Dentistry and Biomaterials Project, University of Turku, Lemminkäisenkatu 2, FIN-20520 Turku, Finland. tuure.nohrstrom@utu.fi
authors.forename: T J
authors.initials: TJ
authors.lastname: Nohrström
authors.forename: P K
authors.initials: PK
authors.lastname: Vallittu
authors.forename: A
authors.initials: A
authors.lastname: Yli-Urpo
mesh_terms: D000704:Analysis of Variance; D019232:Dental Restoration Failure; D003779:Denture Design; D003830:Denture, Partial, Fixed; D003833:Denture, Partial, Temporary; D005898:Glass / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008768:Methylmethacrylates / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014093:Tooth, Artificial; D014867:Water
chemical_list: D008768:Methylmethacrylates; D011109:Polymethacrylic Acids; C009753:fiberglass; D014867:Water; C009931:poly(ethylmethacrylate); C068872:polybutyl methacrylate