title: Changes in marginal gap size of provisional resin crowns after occlusal loading and thermal cycling.
abstract: BACKGROUND
  Resin materials used for provisional crowns tend to develop enlarged marginal gaps over time. With the advent of new interim resin materials in dentistry that are used for longer clinical periods, controlled comparative analysis of the structural stability of these materials in the oral environment is required.
  
  
  OBJECTIVE
  This study analyzed marginal gap size changes resulting from occlusal loading and thermal cycling and related these results to material properties.
  
  
  METHODS
  Groups (n = 10) of provisional crowns were made using 4 resin materials (Jet-relined, Snap-relined, Snap-unrelined, Alike-unrelined). Specimens were first fabricated on a metal master die and fitted with and relined on the master die to standardize pretreatment marginal gap size. Custom die stems were fabricated from a low-fusing alloy (Cerroblend) and cemented with Tempbond cement. The samples were treated with occlusal loading (50,000 cycles, 40 N, 4 Hz) and thermocycling (8, 000 cycles, 5 degrees C to 60 degrees C). Measurements of marginal gaps were recorded before and after treatment.
  
  
  RESULTS
  The mean changes in marginal gap sizes were Jet-relined, 152.1 microm +/- 69. 6; Snap-relined, 548.9 microm +/- 168.3; Snap-unrelined, 446.6 microm +/- 91.8; and Alike-unrelined, 43.9 microm +/- 48.7. Two-way ANOVA revealed a significant difference between groups (F=51.758, df 3,1, P</=.0001). Tukey/Kramer (P </=.01 level) indicated a significantly larger gap increase for the Snap-relined and Snap unrelined groups.
  
  
  CONCLUSIONS
  There were significant differences between different brands of resin materials used for provisional crowns. Each must be evaluated individually for stability in the oral environment.
authors.affiliation: University of Medicine and Dentistry of New Jersey, New Jersey Dental School, Newark, NJ 07103-0370, USA. ehrenbda@umdnj.edu
authors.forename: D S
authors.initials: DS
authors.lastname: Ehrenberg
authors.forename: S
authors.initials: S
authors.lastname: Weiner
mesh_terms: D000704:Analysis of Variance; D003442:Crowns; D018772:Dental Marginal Adaptation; D003794:Dental Restoration, Temporary; D003799:Dental Stress Analysis; D008422:Materials Testing; D008768:Methylmethacrylates / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry*; D018709:Statistics, Nonparametric
chemical_list: C414370:Alike dental resin; D008768:Methylmethacrylates; D011109:Polymethacrylic Acids; C069716:Jet, dental resin; C091347:vinyl ethyl methacrylate