Effect of monovalent ions in glass ionomer on their uptake and re-release.
OBJECTIVE
The study aims to directly measure uptake of Na and F ions by glass ionomer cement from dilute NaF solution and compare this with the subsequent re-release of these ions into water. In addition, the effect of the presence or absence of Na and/or F as a component of the glass is evaluated.


METHODS
The four glass ionomers used differed only in glass composition; AH2 contained both Na and F, LG26 contained F, MP4 contained Na and LG30 contained neither Na nor F. Discs of cement were set in moulds at 37 degrees C for 1 h and matured in water at 37 degrees C for 3 days. Test discs were immersed in 0.2% NaF solution for 24 h, control discs in water. Discs were subsequently immersed in water which was changed regularly. Ion-selective electrode measurements (F and Na) and atomic absorption spectrometry (Na) were used to determine uptake (change in immersion solution concentration) and re-release into water.


RESULTS
All cements took up large quantities of Na and F ions (range 95-336 mumol g-1). This resulted in internal ion concentrations from 16 to 56 times higher than the immersing solution. All re-release was complete within 97 days. No cement re-released more ion than taken up. Glass ionomers containing fluoride took up more Na and F than fluoride-free ones and then re-released a lower percentage of these ions. The cements all took up Na and F ions in equimolar proportions, but initially re-released more F than Na with F-free cement results tending to unity by 97 days.


CONCLUSIONS
Glass ionomer cements take up Na and F ions from NaF solution in large quantities and in equimolar proportion. This is re-released either wholly or in part in 97 days by which time the release does not differ from the controls. The presence or absence of F in the cement composition markedly influences both uptake and re-release. Fluoride/hydroxyl interchange does not appear to play an important role in uptake.
Hadley
P C
PC
Eastman Dental Institute, London, UK.
Billington
R W
RW
Pearson
G J
GJ
D000180:Acrylic Resins / Q000737:chemistry*; D000838:Anions; D002414:Cations, Monovalent; D005459:Fluorides; D005899:Glass Ionomer Cements / Q000737:chemistry*; D007700:Kinetics; D012822:Silicon Dioxide / Q000737:chemistry*; D012964:Sodium; D012969:Sodium Fluoride / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000180:Acrylic Resins; D000838:Anions; D002414:Cations, Monovalent; D005899:Glass Ionomer Cements; C015897:glass ionomer; D014867:Water; D012822:Silicon Dioxide; D012969:Sodium Fluoride; D012964:Sodium; D005459:Fluorides