title: Effect of immersion time of restorative glass ionomer cements and immersion duration in calcium chloride solution on surface hardness.
abstract: OBJECTIVE
  The objective of this study was to evaluate the effect of immersion time of restorative glass ionomer cements (GICs) and immersion duration in calcium chloride (CaCl2) solution on the surface hardness.
  
  
  METHODS
  Two high-viscosity GICs, Fuji IX GP and GlasIonomer FX-II, were selected. Forty-eight specimens were randomly divided into two groups. Sixty minutes after being mixed, half of them were immersed in a 42.7wt% CaCl2 solution for 10, 30, or 60min (Group 1); the remaining specimens were immersed after an additional 1-week of storage (Group 2). The surface hardness of the specimens was measured and analyzed with two-way ANOVA and the Tukey HSD test (α=0.05). The surface compositions were examined using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.
  
  
  RESULTS
  The surface hardness of Group 1 significantly increased as the immersion duration in CaCl2 increased; that of Group 2 significantly increased only after 60-minute CaCl2 immersion. After CaCl2 immersion, the amounts of Ca increased as the immersion duration increased. The surface hardness after CaCl2 immersion significantly correlated with the amount of Ca in Group 1, but not in Group 2. The binding energy of the Ca2p peak was similar to that of calcium polyalkenoate. These findings indicated that the Ca ions from the CaCl2 solution created chemical bonds with the carboxylic acid groups in the cement matrix.
  
  
  CONCLUSIONS
  Immersion of GICs in CaCl2 solution at the early stage of setting was considered to enhance the formation of the polyacid salt matrix; as a result, the surface hardness increased.
authors.affiliation: Removable Partial Prosthodontics, Department of Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Maho
authors.initials: M
authors.lastname: Shiozawa
authors.affiliation: Oral Biomaterials Engineering, Course of Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan. Electronic address: takahashi.bmoe@tmd.ac.jp.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Takahashi
authors.affiliation: Oral Biomaterials Engineering, Course of Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Naohiko
authors.initials: N
authors.lastname: Iwasaki
authors.affiliation: Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Wada
authors.affiliation: Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Motohiro
authors.initials: M
authors.lastname: Uo
mesh_terms: D002118:Calcium / Q000737:chemistry; D002122:Calcium Chloride / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006244:Hardness; D007101:Immersion; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D056951:Photoelectron Spectroscopy; D011897:Random Allocation; D013052:Spectrometry, X-Ray Emission; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D002264:Carboxylic Acids; C439808:Fuji IX GP Fast; D005899:Glass Ionomer Cements; D014867:Water; D002122:Calcium Chloride; D002118:Calcium
keywords: Calcium chloride; Elemental analysis; Glass ionomer cement; Surface hardness