Biomaterials 25 (2004) 4029–4035
Spheroidization of glass powders for glass ionomer cements
*, A.U.J. Yap
, P. Cheang
, R. Kumar
School of Materials Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore
Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075, Singapore
Department of Restorative Dentistry, Faculty of Dentistry, National University of Singapore, 5 Lower Kent Ridge Road,
Singapore 119074, Singapore
Received 20 August 2003; accepted 24 October 2003
Commercial angular glass powders were spheroidized using both the ﬂame spraying and inductively coupled radio frequency
plasma spraying techniques. Spherical powders with different particle size distributions were obtained after spheroidization. The
effects of spherical glass powders on the mechanical properties of glass ionomer cements (GICs) were investigated. Results showed
that the particle size distribution of the glass powders had a signiﬁcant inﬂuence on the mechanical properties of GICs. Powders with
a bimodal particle size distribution ensured a high packing density of glass ionomer cements, giving relatively high mechanical
properties of GICs. GICs prepared by ﬂame-spheroidized powders showed low strength values due to the loss of ﬁne particles during
ﬂame spraying, leading to a low packing density and few metal ions reacting with polyacrylic acid to form cross-linking. GICs
prepared by the nano-sized powders showed low strength because of the low bulk density of the nano-sized powders and hence low
powder/liquid ratio of GICs.
r 2003 Elsevier Ltd. All rights reserved.
Keywords: Glass ionomer cements; Spheroidization; RF plasma spraying; Flame spraying; Mechanical property
Glass ionomer cements (GICs) were ﬁrst developed by
Wilson and Kent in the late 1960s . Their favorable
adhesive-and ﬂuoride- releasing properties have led to
their widespread use in clinical dentistry [2–4]. Outside
dentistry, GICs have begun to ﬁnd use that exploits their
good biocompatibility . These include artiﬁcial ear
ossicles and bone substitute plates for craniofacial
reconstruction . GICs have been suggested as cement
materials in orthopedics surgery  for ﬁxation of
cochlear implants and sealing defects in the skull .
They are anticipated to become more important in a
variety of surgical applications in the years ahead.
GICs consist of an aqueous solution of poly(acrylic
acid) and an acid-decomposable ﬂuoro-aluminosilicate
glass powder. GICs have been classiﬁed as acid–base
reaction cements . They set by the reaction of liquid
polyacid ionomer with the metal ions released from the
glass to form an insoluble polysalt. The diffusionally
controlled cross-linking of the polymer matrix enhances
the strength, stiffness and insolubility of the cements.
GICs have a number of advantages over polymethyl-
methacrylate (PMMA) bone cements. These include
their good adhesion to bone, their stability in an
aqueous environment and their lack of exothermic
polymerization [10,11]. Despite the many attractive
features, GICs do suffer from disadvantages, including
brittleness and poor wear characteristics. A number of
attempts have been made to overcome these problems.
These include the application of metal or ﬁber reinforce-
ment [12–14], dual-setting resin-modiﬁed GICs  and
highly viscous GICs , etc.
It has been reported that the angular-shaped glass
powders made from milled glass technology currently
employed in all commercial GICs are detrimental to the
mechanical properties of GICs, as the sharp edges are
stress concentration regions [17,18]. Spherical particles
could theoretically increase the powder liquid ratios and
improve the mixing characteristics and ﬂowability of
powders. The mechanical properties of GICs thus could
be improved. The spheroidization of the angular glass
powders for GICs has not been studied thus far .In
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