title: Preliminary study on chitosan modified glass ionomer restoratives.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of chitosan (CH), a biocompatible polysaccharide, on the flexural strength of glass ionomer restoratives (GIR) and on the release of fluoride ions from GIR.
  
  
  METHODS
  Commercial GIR (Vidrion, SS White) has been modified by adding chitosan (CH, Fluka). Samples containing 0.0044, 0.012, 0.025 and 0.045wt% CH were prepared, molded and weighed. For flexural strength, sets of 10 specimens 10mmx2mmx2mm of commercial and CH modified GIR were prepared. Differences were analyzed by the one-way analysis of variances (ANOVA) test, at significance level 0.05. The data were also analyzed by post hoc Tukey's HSD for unequal n (Spjotvoll/Stoline) test. Scanning electron microscopy analyses were performed on the composites cryo-fracture surfaces. For the fluoride release tests and medium pH determination, discs with 10mm diameter and 2mm height were prepared in a PTFE mold placed between two glass slides. Samples were weighed in order to normalize each material test group. At least 10 samples of each material were prepared. Approximately 5min after preparation the discs were transferred into individual glass flasks containing 50mL of distilled water. The concentration of released fluoride was determined as a function of time by means of a fluoride ion selective electrode Orion 94-09 SC connected to an Ionanalyser (Orion Research Inc., USA). The medium pH was monitored as a function of time at (25+/-1 degrees C), using a Digimed DM20 potentiometer (Digicrom Instrumentos, Brazil) equipped with a combined glass electrode. Ellipsometric measurements were performed to quantify the thickness of adsorbed polymer (poly(acrylic acid) or the mixture of poly(acrylic acid) with CH).
  
  
  RESULTS
  The addition of 0.0044wt% of CH led to a significant increase in the flexural resistance. CH contents higher than 0.022wt% led to poor performance. For the same period of time the amount of fluoride ions released from CH modified GIR was much larger than that released from commercial GIR. CH catalyzed the fluoride release from GIR to the medium, especially from those with 0.0044wt% of CH. As a consequence, the medium pH increased from 5.0 to 6.3. A model based on the formation of a polymeric network around the inorganic particles was proposed to explain the experimental findings. The adsorption of CH and poly(acrylic acid) onto planar Si/SiO(2) substrates was quantified and supported the proposed model.
  
  
  CONCLUSIONS
  The results presented here showed that the flexural strength of a commercial GIR can be considerably improved by the addition of a tiny amount of CH. Moreover, in the presence of CH, the release of fluoride ions from GIR is catalyzed.
authors.affiliation: Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil. dfsp@usp.br
authors.forename: Denise F S
authors.initials: DF
authors.lastname: Petri
authors.forename: Juliana
authors.initials: J
authors.lastname: Donegá
authors.forename: André M
authors.initials: AM
authors.lastname: Benassi
authors.forename: Jorge A J S
authors.initials: JA
authors.lastname: Bocangel
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D001672:Biocompatible Materials; D048271:Chitosan; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D005459:Fluorides / Q000032:analysis; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D015394:Molecular Structure; D018583:Pliability; D018709:Statistics, Nonparametric
chemical_list: D000180:Acrylic Resins; D001672:Biocompatible Materials; D005899:Glass Ionomer Cements; C100647:Vidrion-R; C006903:carbopol 940; D048271:Chitosan; D005459:Fluorides