Glass - Back to the Future!

Presenting Author:
Tomas Duminis

article posted 16 May 2016

Tomas Duminis is currently a PhD student at Queen Mary University of London. He graduated with a bachelor’s degree in Biomedical Science from London Metropolitan University in March 2014. He was then inclined towards research in tissue regeneration. In June 2014 he joined QMUL as a research assistant on a collaborative R&D project with Cera Dynamics Limited, a UK-based glass manufacturer specialising in the manufacture of biomedical glasses containing volatile elements. After a year of RA experience, Tomas is now undertaking doctorate studies under the supervision of Professor Hill and Dr Shahid. Tomas’ PhD project is on the development of a novel class of bio-remineralising dental cements made from reactive fluoro-alumino-silicate glasses containing nano-scale phases of apatite.

Strontium-substituted nano-scale fluorapatite glass-ceramics for remineralising glass ionomer cements

Tomas Duminis*, Saroash Shahid & Robert Hill
Unit of Dental Physical Sciences, Centre for Oral Growth and Development,
Institute of Dentistry, Barts and the London School of Medicine and Dentistry, Queen Mary University of London

Fluorapatite (FAp) additives in glass ionomer cements (GIC) are used as nuclei for apatite formation and remineralisation, however they cause opacity. Upon controlled heat-treatment of GIC glasses, they can nano-crystallise to produce glass-ceramics (GC) with FAp within the glass matrix. Crystals smaller than the wavelength of light in the GC result in optical transparency; therefore cements formed from GC containing nano-scale crystals will remain highly translucent and aesthetic. The aim of this study is to develop novel strontium-substituted GCs for use in GICs. A series of glasses of varying strontium substitution for calcium, based on the SiO2-Al2O3-P2O5-CaO/SrO-CaF2 system were produced by the melt-quench route. For heat-induced apatite crystallisation all glasses were subjected to a heat-treatment regime at the following temperatures Tg, Tg+50°C, Tg+100°C and Tg+150°C for 1 hour. Glasses were then analysed by HT-DSC, multinuclear MAS-NMR, XRD, ATR-FTIR, SEM and TEM before and after heat-treatment to assess apatite crystallisation. HT-DSC data indicates that increasing strontium content results in reduced volume crystallisation and a linear reduction in Tg, which is supported by a previous study. 31P MAS-NMR analyses of the glasses showed presence of apatite after heat treatment. 19F MAS-NMR analysis confirmed this be in the form of fluorapatite. Increasing heat-treatment temperature resulted in increased apatite crystallisation. SEM and TEM of heat-treated glasses showed needle-like fluorapatite crystals within the amorphous glass matrix. Fluorapatite containing glasses have been successfully developed for use in GICs. Increasing strontium content in the above systems was found to have a profound effect on the crystallisation behaviour of the glasses. The crystalline phase in the developed apatite containing glasses was identified to be a mixed strontium/calcium fluorapatite phase.

Figure 1: Differential scanning calorimetry (DSC) traces of glasses of varying stontium substitution showing reducing Tg and crystallisation exotherms with increasing stontium content.

Figure 2: 31P MAS-NMR of heat-treated glasses showing apatite crystallisation as a function of temperature.

Figure 3: Transmission electron micrograph (left) and scanning electron micrograph (right) of a glass particle showing needle-like nano (left) and macro (right) fluorapatite crystals.