When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Despite significant efforts to improve the clinical performance (e.g. mechanical and remineralizing properties) of glass ionomer cements (GICs), their essential characteristics such as good translucency, adhesion to enamel and dentine, and fluoride-releasing capability cannot yet be fully exploited in load-bearing areas in restorative dentistry. The aim of this study is to introduce a functional approach to improve not only the mechanical properties of GICs, but also to enhance their biomineralizing capacity.
In the first stage of this study, a series of versatile heat treatment profiles are used to tailor the crystallinity of 45S5 Bioglass® within a wide range of 5% to 100% via the formation of solely combeite as a mechanically competent yet bioactive phase. The resulting 45S5 glass-ceramics containing combeite not only are expected to retain beneficial levels of bioactivity, but also show improved mechanical properties compared to those of the amorphous 45S5 Bioglass®. By choosing the proper heat treatment from the proposed profiles in this study, different levels of mechanical properties and bioactivity in Bioglass® can be achieved according to the target application(s).
In the second stage of this study, hybrid GICs with enhanced mechanical and remineralizing properties were developed via incorporation of an optimum amount (5 wt%) of 45S5 bioglass-ceramic particles with a certain degree of crystallinity. The effect of the degree of crystallinity of additives, which is completely overlooked in the current literature, was also addressed in this study. Mechanical properties testing, in vitro studies and microstructural analysis revealed that the bioglass ceramic particles with 74% crystallinity best act as both remineralizing and reinforcing agents. Enhanced remineralizing and mechanical properties may not only broaden the hybrid GICs’ clinical applications but also can potentially enhance their in vivo performance.
In the last stage of this study, a novel aluminum-free, 45S5 Bioglass®-based GIC with standard mechanical properties was developed. For the first time, 45S5 Bioglass® and its bioglass-ceramic were used as the GIC solid component. The bioglass-ceramic particles with 74% crystallinity was used as they favorably act as both remineralizing and reinforcing agents. The early stage progression of setting reaction was monitored. Bimodal particle size distribution was shown to improve the packing density and integrity of the set cement. In such GICs, not only the neurotoxicity of Al is eliminated, but chemical bond formation at cement/hard tissue(s) interface through interfacial biomineralization and adhesion is expected.