title: The influence of powder liquid ratio on the flexural strength of fibre reinforced acrylic resin material.
abstract: BACKGROUND
  Often the powder liquid (P/L) ratio of polymethyl methacrylate (PMMA) resins is changed to modify the handling properties of the material. While it is known that this may influence the mechanical properties of unreinforced PMMA resin, little is known about its effect on fibre reinforced resin.
  
  
  OBJECTIVE
  The purpose of this study was to determine how different P/L ratios influence the flexural strength (FS) of a glass fibre reinforced autopolymerizing PMMA resin used for fabricating fixed partial dentures.
  
  
  METHODS
  Two main groups of PMMA resin, 1 unreinforced and 1 reinforced with glass fibre, had 3 subgroups (n=21) each representing a different P/L ratio. The manufacturer's recommended ratio served as control. The specimens were prepared for a 3-point bending test. Using a universal testing machine, maximum force was recorded and the FS was calculated. Median FS values were compared by means of non-parametric analysis of variance (Kruskal-Wallis). A p-value of less than 0.05 was considered significant.
  
  
  RESULTS
  FS values of all reinforced subgroups were significantly higher than the values of the unreinforced subgroups (p<0.05). Among the 3 unreinforced subgroups the difference in FS was insignificant (p>0.05). Within the reinforced group there was a significant difference between the control group, which had a higher median FS value than the two other subgroups (p<0.05).
  
  
  CONCLUSIONS
  When reinforcing PMMA resin with glass fibre, it is important to use the recommended P/L ratio. For unreinforced PMMA resin the P/L ratio can be changed within limits without adverse effects on the FS.
authors: Department of Restorative Dentistry, Faculty of Dentistry, University of the Western Cape (UWC). ggeerts@uwc.ac.za
authors: G A V M
authors: GA
authors: Geerts
authors: M
authors: M
authors: du Rand
mesh_terms: D003188:Composite Resins / Q000737:chemistry; D003764:Dental Materials / Q000138:chemical synthesis / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003819:Denture Bases; D003830:Denture, Partial, Fixed; D005898:Glass / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D011108:Polymers / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000138:chemical synthesis / Q000737:chemistry*; D016062:Porosity; D011208:Powders; D012996:Solutions; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; D011208:Powders; D012996:Solutions; C496140:everStick; C009753:fiberglass; D019904:Polymethyl Methacrylate