title: Effect of filler fraction on strength, viscosity and porosity of experimental compomer materials.
abstract: OBJECTIVE
  The primary goal is to develop a self-cured polyacid-modified resin composite with good mechanical and rheological properties. To achieve such a goal, the aim of this study is to determine how volume filler fraction (VFF) affects mechanical properties and viscosities of such materials containing different filler volumes.
  
  
  METHODS
  A series of self-cured polyacid-modified composites made from polyacid modified resins and TEGDMA, mixed with filler particles, were evaluated regarding compressive strength (CS), diametral compressive strength (DCS) and viscosity. The maximum filler content, which could be incorporated into the materials, was calculated from CS tests as well as from viscosity measurements using Mooney's equation. Porosity contents were also determined in an attempt to explain different failure behaviours.
  
  
  RESULTS
  The CS values peaked at 18.9 vol.% filler particles and declined afterwards for self-cured polyacid-modified resin composites cured in air. Using photopolymerisation and barium filler in the polyacid-modified resin composites resulted in the highest CS and DCS values. The viscosity increased continuously with increased VFF. VFF results determined experimentally and with Mooney's equation at shear rates of 0.01, 0.1, 1.0, and 10.0 s(-1) revealed that the maximal filler fraction values were 54.9+/-1.8, 55.9+/-1.3, 56.3+/-0.9, and 56.8+/-0.8 vol.%, respectively. The largest porosity content occurred at a VFF value of 53 vol.%
  
  
  CONCLUSIONS
  We conclude that an increase in filler fraction of the investigated experimental polyacid-modified resin composite materials above a certain value (20-30 vol.%) does not result in improved mechanical properties.
authors.affiliation: Department of Dental Biomaterials, School of Dentistry, College of Dentistry, University of Florida, Gainesville PO Box 100446, Gainesville, FL 32610-0446, USA. karen_schulze@yahoo.com
authors.forename: Karen A
authors.initials: KA
authors.lastname: Schulze
authors.forename: Abbas A
authors.initials: AA
authors.lastname: Zaman
authors.forename: Karl-Johan M
authors.initials: KJ
authors.lastname: Söderholm
mesh_terms: D000704:Analysis of Variance; D020770:Compomers / Q000737:chemistry*; D019245:Compressive Strength; D003799:Dental Stress Analysis; D004548:Elasticity; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D016062:Porosity; D012044:Regression Analysis; D012212:Rheology; D033081:Shear Strength; D014783:Viscosity
chemical_list: D020770:Compomers; D011108:Polymers