title: Evidence of a complex species controlling the setting reaction of glass ionomer cements.
abstract: OBJECTIVE
  To elucidate the mechanism(s) responsible for the profound impact germanium has on the setting reaction of zinc silicate glass ionomer cements (GICs).
  
  
  METHODS
  Five <45μm glass powder compositions (0.48-xSiO2, xGeO2, 0.36 ZnO, 0.16 CaO; where x=0.12, 0.24, 0.36, 0.48mol. fraction) were synthesized. Glass degradation was assessed under simulated setting conditions using acetic acid from 0.5 to 60min, monitoring the concentrations of ions released using ICP-OES. Subsequently, GICs were prepared by mixing fresh glass powders with polyacrylic acid (PAA, Mw=12,500g/mol, 50wt% aq. solution) at a 1:0.75 ratio. Cement structure and properties were evaluated using ATR-FTIR and rheology (for 60min), as well as 24h biaxial flexural strength.
  
  
  RESULTS
  Reduced Si:Ge ratios yielded faster degrading glasses, yet contrary to expectation, the corresponding ATR-FTIR spectra indicated slower crosslinking within the GIC matrix. Rheology testing found the initial viscosity cement pastes reduced with decreased Si:Ge, and Ge containing cements all set significantly slower than the Si based GIC. Interestingly, biaxial flexural strength remained consistent regardless of setting behavior.
  
  
  CONCLUSIONS
  This counter-intuitive combination of behaviors is attributed to the presence of a chemical complex species specific to Ge-containing glasses that delays, but does not hinder, the formation of the GIC matrix. These findings embody chemical complex species as a mechanism to decouple glass reactivity from cement setting rate, a mechanism with the potential to enhance the utility of GICs in both dental and orthopaedic applications.
authors.affiliation: School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, B3H 1W2, Canada. Electronic address: brett.dickey@dal.ca.
authors.forename: Brett
authors.initials: B
authors.lastname: Dickey
authors.affiliation: Department of Clinical Dental Sciences, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, B3H 1W2, Canada. Electronic address: Richard.Price@dal.ca.
authors.forename: Richard
authors.initials: R
authors.lastname: Price
authors.affiliation: Department of Applied Oral Science, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, B3H 1W2, Canada; School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, B3H 1W2, Canada. Electronic address: d.boyd@dal.ca.
authors.forename: Daniel
authors.initials: D
authors.lastname: Boyd
mesh_terms: D002151:Calorimetry / Q000295:instrumentation; D019245:Compressive Strength; D019232:Dental Restoration Failure; D005857:Germanium / Q000737:chemistry*; D005899:Glass Ionomer Cements / Q000138:chemical synthesis / Q000737:chemistry*; D008422:Materials Testing; D011208:Powders; D017640:Silicates / Q000737:chemistry*; D013054:Spectrophotometry, Atomic; D017550:Spectroscopy, Fourier Transform Infrared; D014783:Viscosity; D014961:X-Ray Diffraction; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D005899:Glass Ionomer Cements; D011208:Powders; D017640:Silicates; D017967:Zinc Compounds; D005857:Germanium; C040516:germanium oxide; C029500:zinc silicate
keywords: Aluminum-free GIC; Glass ionomer cement; Handling characteristics; Polyalkenoate; Setting reaction