Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Medical Biophysics

Supervisor

Dr. Amin Rizkalla

Abstract

Metallic dental implants are an important treatment for the replacement of missing teeth. However, for esthetic and environmental issues, there is a need to develop non-metallic dental implant materials. In this thesis, two novel glass-ceramics (GCs), miserite and wollastonite, were synthesized for one-piece dental implant applications. Glasses were synthesized by wet chemical methods, followed by calcination, melting and quenching. The crystallization kinetics of these glasses were determined by differential thermal analysis (DTA). GC specimens were produced by cold pressing of the glass powder and sintering using schedules determined by DTA. The crystalline phases and microstructure of the GC samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Miserite GC displayed an interlocking lath-like crystalline morphology. Mechanical testing results showed Dynamic Young’s modulus (E), 96±3 GPa, true hardness (Ho), 5.27±0.26 GPa, fracture toughness (KIC), 4.77±0.27 MPa∙m0.5, and brittleness index (BI), 1.11±0.05 µm-0.5, indicating suitable mechanical properties and machinability. Miserite GC showed excellent bioactivity, with formation of a hydroxyapatite surface layer when soaked in simulated body fluid (SBF). Osteoblast-like cells exhibited attachment, spreading and proliferation on miserite GC surfaces, demonstrating biocompatibility. However, preliminary studies revealed that the chemical stability of miserite GC was not optimal, prompting us to modify the GC composition. Accordingly, wollastonite GC was synthesized; it consisted of dense acicular interlocking crystals and demonstrated excellent machinability. E, Ho and KIC were 90±3 GPa, 5.15±0.47 GPa and 4.91±0.26 MPa∙m0.5, respectively. Importantly, chemical durability of wollastonite GC satisfied ISO 6872 specification for dental ceramics. Furthermore, when evaluated according to ISO 10993-14, there was little chemical degradation. In addition, the chemical stability tests had no significant effect on KIC (p>0.05). Bioactivity tests revealed that wollastonite GC induced the formation of bone-like carbonated hydroxyapatite when soaked in SBF. Moreover, wollastonite GC supported osteoblast attachment and proliferation. Osteoblast spreading, focal adhesion formation and alkaline phosphatase activity on this GC were comparable to those on a control zirconium-oxide-based ceramic, indicating excellent biocompatibility. In conclusion, wollastonite GC is a promising material for non-metallic dental implant applications based on five tested qualities: mechanical properties, chemical stability, machinability, excellent bioactivity and biocompatibility.


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