title: Can poly(acrylic) acid molecular weight mixtures improve the compressive fracture strength and elastic modulus of a glass-ionomer restorative?
abstract: OBJECTIVE
  To optimize the compressive fracture strength (σ) and elastic modulus (E) of a glass-ionomer (GI) restorative using poly(acrylic) acid (PAA) weight average molecular weight (M(w)) mixtures.
  
  
  METHODS
  174 PAA solutions were prepared (four control PAA M(w)s at three PAA concentrations (25, 35 and 45%) (n=12) and six M(w) mixtures (Groups A-F at nine blend ratios and three PAA concentrations (n=162))). The viscosity (η) of each PAA solution was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany) and σ and E were determined using cylindrical (6 mm height, 4 mm diameter) specimens (n=20) at 24 h. Data were analyzed using analyses of variance (ANOVA) (three-, two- and one-way) and regression analyses at p<0.05.
  
  
  RESULTS
  The three- and two-way ANOVAs highlighted significant effects of M(w) mixture, blend ratio and PAA concentration (all p<0.0001) on the η, σ and E data. Regression analyses showed significant increases in η, σ and E (p<0.0001) with increasing M(w) from Groups A to F. There was no significant effect of blend ratio on the σ data for Groups A (p=0.178), D (p=0.747) and F (p=0.107) and on the E data (p>0.083).
  
  
  CONCLUSIONS
  The current approach to improving the mechanical properties of GI restoratives using PAA M(w) mixtures is encouraging, however, further manipulation of the GI restorative system by optimizing PAA M(w) mixtures, blend ratios and PAA concentrations is required to elicit further improvements in σ and E without impacting upon the η of the PAA solution.
authors.affiliation: Materials Science Unit, Division of Oral Biosciences, Dublin Dental University Hospital, Trinity College Dublin, Dublin, Ireland. adam.dowling@dental.tcd.ie
authors.forename: Adam H
authors.initials: AH
authors.lastname: Dowling
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000704:Analysis of Variance; D060326:Chemistry Techniques, Synthetic; D019245:Compressive Strength; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D005899:Glass Ionomer Cements / Q000737:chemistry*; D008422:Materials Testing; D008970:Molecular Weight; D012044:Regression Analysis; D014783:Viscosity
chemical_list: D000180:Acrylic Resins; D005899:Glass Ionomer Cements; C541507:ionofil U; C006903:carbopol 940