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A Long-term Study of the Setting Reaction of Glass Ionomer Cements by IR
C. M. Crowley a , T. Pembroke b , S. Hampshire a ,
a Department of Materials Science and Technology, University of Limerick, Ireland
b Department of Chemical and Environmental Sciences, University of Limerick, Ireland
Clare.Crowley@ul.ie
Abstract
Changes in the positions and intensities of carboxylate
stretching modes during the setting reaction of dental
restorative experimental glass ionomer cements (GICs)
have been monitored by FTIR.
Introduction
Numerous approaches have attempted to characterise
the changes that occur in the cement matrix of GICs
during setting including FTIR [1], Raman [2] and
MAS-NMR ( 13 C NMR [3] and 27 Al MAS-NMR [4, 5]).
This has resulted in alternative hypotheses having been
proposed to account for the long-term changes observed
in the mechanical properties but the mechanism of these
changes is not fully understood [4]. In this study,
changes in the carboxylate stretching modes during the
setting reaction have been monitored by FTIR.
Materials and Methods
Glass compositions
The frits of the glass compositions (Table 1) were
attrition milled to produce powders with a d50 of
approximately 5 µm.
Table 1: Pre-firing constituent molar ratios of the
experimental glasses
Glass
Molar Ratios
SiO2 Al2O3 P2O CaF2 SrO SrF2 LG125 4.5 3 1.5 2 3 -
LG26 Sr 4.5 3 1.5 - 3 2
ART10 4.5 3 0.75 - 3 2
Cement Design
The cements were mixed at powder (glass +
poly(acrylic acid) (PAA200) (Mw = 210,300; Mn =
111,300):water ratio of 3:1. The glass:PAA ratio was
varied so that the charge g -1 of the glass in the cements
was constant. At various times after mixing the
samples were immersed in nitrogen (l), frozen (- 20 °C,
>24 hrs), freeze-dried (-60 °C, > 1 atm, 3 days),
gyromilled and sieved < 45 µm.
FTIR measurements
ATR-FTIR spectra (Perkin Elmer Spectrum 100; zinc
selenide crystal) of the cements (< 45 m) were
collected between 4000 – 600 cm -1 (resolution = 1 cm -1 ,
number of scans = 50). Background spectra were
subtracted from the sample spectra, which were
normalised using 1800 cm -1 as the zero point.
5
174
Deconvolution of the spectra was performed using a
Gaussian model (Peak Fit (Version 4)).
Results
It is suggested that the setting reaction of the LG125
and LG26Sr cements are essentially the same, while the
ART10 cements display an extended secondary
hardening phase (Figure 1). The extended time frame
of the secondary hardening phase in the ART10
cements may be due to the low phosphate content of the
ART10 glass which renders the glass more susceptible
to dissolution and ion release. This view is supported
by the observed changes in the glass peak positions and
intensities in the ART10 cements while no significant
difference in this peak is observed between the 28 day
and 12 month spectra of the LG125 and LG26Sr
cements.
DCL (Area (1453/(1700 +
1453)) and (1405/(1700 + 1405)
1.00
0.75
0.50
0.25
0.00
1703:1407 2 mins - 1 day 1703:1407 1 day - 1 year
1703:1453 2 mins - 1 day 1700:1453 1 day: 1 year
1 1000 1000000
Time (minutes)
Figure 1: Change in the degree of crosslinking (DCL)
of the ART10-PAA200 cements over 12 months. Values of
DCL were determined by the peak areas of the sC-O COO(Al) (1450 cm -1 ),
sC-O COO(Ca,Sr) (1407 cm -1 ) and C=O of the COOH (1700 cm -1 ) from the
ATR:FTIR
References
[1] Young A.M. (2002) FTIR investigation of polymerisation
and polyacid neutralisation kinetics in resin-modified glassionomer
dental cements. Biomaterials 23(15): 3289-95.
[2] Young A.M., Sherpa A., Pearson G., Schottlander B. &
Waters D.N. (2000) Use of Raman spectroscopy in the
characterisation of the acid–base reaction in GICs.
Biomaterials 21(19): 1971-1979.
[3] Prosser H.J., Richards C.P. & Wilson A.D. (1982) NMR
spectroscopy of dental materials. II. The role of tartaric acid
in GICs. J. Biomedical Materials Research 16(4): 431-445.
[4] Zainuddin N., Karpukhina N., Hill R.G. & Law R.V.
(2009) A long-term study on the setting reaction of GICs by
27 Al MAS-NMR spectroscopy. Dent. Mater. 25(3): 290-295.
[5] Munhoz T., Karpukhina N., Hill R.G., Law R.V. & De
Almeida L.H. (2010) Setting of commercial GIC Fuji IX by
27 Al and 19 F MAS-NMR. J. Dentistry 38(4): 325-330.