Effect of Crystallization on Mechanical and Optical Properties of SiO2-Li2O-K2O-P2O5 Glass

  • 陳 聖涵

Student thesis: Master's Thesis


The evolutions of dental restoration begin with metal porcelain fused metal to ceramic or glass-ceramic dental restorative Nowadays glass-ceramic system has been extensively used in esthetic dental restoration due to the advantage of natural tooth-like color of glass-ceramic appearance Lithium disilicate as a glass-ceramic material is superior in esthetic region and sufficient strength than zirconia dioxide and aluminum dioxide based dental restoration Therefore with the changes of compositions heat treatment temperatures and coloring agents may alter the mechanical properties and esthetic of lithium disilicate glass-ceramic system In this study lithium disilicate glass-ceramic based on SiO2-Li2O-K2O-P2O5 system is used to investigate the relationship between the crystallization with the mechanical and optical properties of the glass-ceramic system In the lithium disilicate glass-ceramic the molar ratio of SiO2:Li2O is 2 39:1 which the eutectic composition of SiO2-Li2O-K2O-P2O5 system The lithium disilicate phase and quartz phase tend to form a high strength lamellar eutectic structure The (010) orientation is the preferred growth direction for Li2Si2O5 crystal that result in needle-like grains The interlocking network formed by needle-like grains provides better toughness performance Glass-ceramic has a high transmittance independent color by staining Ce2O3 (yellow) Er2O3 (pink) and V2O5 (blue) coloring agents During the heat treatment process Li2O initially react with SiO2 with a molar ratio of 1:1 to form lithium metasilicate (Li2SiO3) As the heat treatment temperature increased to 600℃ P5+ ions from P2O5 break the Si-Li bonds due to P5+ ions has a higher field strength As the heat treatment increase to 650℃ mainly lithium metasilicate has formed with small amount of lithium disilicate appear due to the heterogeneous nucleation As the two-stage heat treatment of 650℃ followed by 700℃ excess of cristobalite formed however lithium disilicate does not occur due to insufficient in driving force As the two-stage heat treatment of 650℃ followed by 740℃ lithium metasilicate reacted with excess silicon dioxide and precipitate to lithium disilicate As the second-stage heat treatment increased to 800℃ most of the glass phase has completely transform into lithium disilicate With the process of melting cooling and two-stage heat treatment of 650℃ followed by 740℃ lithium disilicate has a biaxial flexural strength of 392MPa Vickers’ hardness of 586HV and fracture toughness of 2 27 K_IC (MPa?√m) Lithium disilicate stained coloring ions Ce2O3 Er2O3 and V2O5 show different level of color changes into yellow pink and blue respectively Their combination can be adjusted into further nature looking color In most case of low concentration of coloring agent addition the mechanical properties of lithium disilicate do not have significant changes Lithium disilicate stained with coloring agents shows only Er2O3 with 1 volume percentage has a decrease in flexural strength The Contrast Ratio shows a decrease in CR value as the specimens thickness increase from 0 5mm to 1mm Glass-ceramic stained with more than 0 8 volume percentage of Ce2O3 and Er2O3 has a significant different in CR value from normal glass-ceramic Adding of 0 4 and 0 6 volume percentage of Ce2O3 has an increase in translucency compare with glass-ceramic without staining color This study concludes the success of fabrication of lithium disilicate with matching mechanical properties with commercial product and color adjustability
Date of Award2015 Jan 27
Original languageEnglish
SupervisorMing-Long Yeh (Supervisor)

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