Dissertation
Dissertation > Medicine, health > Oral Sciences > Oral orthotics

Improvement of Mechanical Strength and Toughness of Dental Machinable Fluorosilicic MICA Glass-ceramics

Author ZhangYaLi
Tutor ZhangShaoFeng
School Fourth Military Medical University
Course Clinical Stomatology
Keywords Fluorosilicate mica glass-ceramics Nano-material SPS Sintering Flexural strength Mechanical strength
CLC R783
Type Master's thesis
Year 2012
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The development of dentistry is relying on the development of dentalmaterials and corresponding manufacture technology. Dental CAD/CAM chairside manufacturing system is widely used in clinic now. While in application,the widespread of the system is limited by high cost and insufficient strength ofnative materials. We have cooperated with Tsinghua university and developed adental machinable glass ceramic, which is good in color and transparency. Butthis material is also with comparatively low strength (100-150MPa) and needsfurther improvement. If the strength of this novel fluorosilicic MICAglass-ceramics can be improved, it will be very beneficial for its clinicalapplication. In current study, nanophase raw particles were used and differentsintering method was attempted to obtain a ceramic with high mechanicalstrength to satisfy the need of clinical application. This study was divided intothree parts: Experiment1Influence of nano-SiO2on the strength of fluorosilicate micaglass-ceramicsFirstly, nanophase raw particles were used and fluorosilicic micaglass-ceramics were prepared by traditional sintering technique. The nanophaseSiO2was with a particle size of7nm. SEM and XRD was separately used toobserve the microstructure and testify the phase composition. The flexiblestrength and toughness was also tested and compared with the contrast. Flexuralstrength and fracture toughness of specimens fabricated with nano-SiO2powderwere respectively34%and23%higher compared to normal glass-ceramic.Thecrystalline phases of two groups were similar. The density and contraction ratioof nano-group was higher than normal group. SEM showed that nano-groupconsisted of more even and interlayer crystals and less glass matrix phase. Theapplication of nano-SiO2powder in fluorosilicate mica glass-ceramic canachieve much higher flexural strength and fracture toughness.Experiment2Influence of sintering parameters on the strength offluorosilicate mica glass-ceramicsIn this experiment the sintering parameter was revised to preparefluorosilicate mica glass-ceramic to improve the mechanical strength andtoughness. The nanophase raw material was still used. After the preparation ofbasic glass powder, the shaped bulks was sinterd at different temperaturesincluding1000℃,1050℃and1100℃. SEM and XRD was separately used toobserve the microstructure and testify the phase composition. The flexiblestrength and toughness was also tested and compared. The result indicated thatthere were no increase observed in mechanical strength and toughness.Furthermore, the microstructure of samples were similar. So the variation of sintering termperature within observation cannot improve the strengtheffectively.Experiment3Primary research of spark plasma sintering technology inmanufacture of fluorosilicic MICA glass-ceramicsSpark plasma sintering technology was used to prepare fluorosilicic MICAglass-ceramics. Microstructure was observed with scanning electron microscope,x-ray diffraction to determine crystal phases, flexural strength and fracturetoughness of samples were also determined. The results indicated that flexuralstrength((209.84±7.78Mpa) and fracture toughness (2.250±0.11Mpa.m1/2) ofSPS group increased69.7%and90.6%respectively compared to traditionalsintering method. XRD showed two groups of crystalline structure are different.SEM shows that crystal of SPS group was with less size and compact and evenstructure. The increase of bending strength and fracture toughness are bothsignificant. SPS technology can be adopted for sintering fluorosilicic MICAglass-ceramic.

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