IADR Abstract Archives
Hardness of Bioactive Glasses
Objectives: Hardness of bioactive glasses is an important property that will determine their abrasivity towards enamel during tooth brushing and in air abrasion applications. The objective is to determine if there is a correlation between the glass transition temperature and hardness of bioactive glasses in order to predict the hardness of glasses for dental applications.
Methods: Twelve bioactive glasses with varying sodium and fluorine contents were synthesised by a melt quench route and cast to form monolithic blocks which were then mounted in resin and ground and polished. The Vickers hardness of each glass was then determined by using a Vickers hardness tester.(Zwick Universal Hardness Test Machine, Roell AG, Germany using a diamond indenter with an angle of 136° and testing load of 3HV. A Stanton Redcroft DSC1500 (Rheometric Scientific, Epsom, UK) with matched pair platinum crucibles was used to determine the glass transition temperatures of the glasses. Fifty milligrams of fine powder (< 38 μm) was run against an alumina reference at a heating rate of 20° C/min in nitrogen gas at 60 mL/min to 1200° C. Tg was determined by the intercept method.
Results: The glass transition temperarature (Tg) reduced with sodium content as did the Vickers Hardness. The highest sodium content glass had a hardness of about 3.4GPa close to enamel whilst the lowest sodium content glass had a hardness greater than 6.6GPa. The 45S5 glass used in commercial toothpastes and air abrasives had a hardness of about 4.6GPa. There was a good correlation between Hardness and the glass transition temperature with a linear regression giving Hardness=0.0089xTg + 0.031 and the Correlation Coefficient was 0.94.
Conclusions: There is a good correlation between Hardness and Tg that enables the Hardness to be calculated from the Tg. This is important because many bioactive glass compositions can not be cast without crystallisation occurring which would invalidate the hardness measurements. Furthermore various authors have developed models for calculating Tg from the chemical composition of bioactive glasses which can now be used to calculate Hardness.
Methods: Twelve bioactive glasses with varying sodium and fluorine contents were synthesised by a melt quench route and cast to form monolithic blocks which were then mounted in resin and ground and polished. The Vickers hardness of each glass was then determined by using a Vickers hardness tester.(Zwick Universal Hardness Test Machine, Roell AG, Germany using a diamond indenter with an angle of 136° and testing load of 3HV. A Stanton Redcroft DSC1500 (Rheometric Scientific, Epsom, UK) with matched pair platinum crucibles was used to determine the glass transition temperatures of the glasses. Fifty milligrams of fine powder (< 38 μm) was run against an alumina reference at a heating rate of 20° C/min in nitrogen gas at 60 mL/min to 1200° C. Tg was determined by the intercept method.
Results: The glass transition temperarature (Tg) reduced with sodium content as did the Vickers Hardness. The highest sodium content glass had a hardness of about 3.4GPa close to enamel whilst the lowest sodium content glass had a hardness greater than 6.6GPa. The 45S5 glass used in commercial toothpastes and air abrasives had a hardness of about 4.6GPa. There was a good correlation between Hardness and the glass transition temperature with a linear regression giving Hardness=0.0089xTg + 0.031 and the Correlation Coefficient was 0.94.
Conclusions: There is a good correlation between Hardness and Tg that enables the Hardness to be calculated from the Tg. This is important because many bioactive glass compositions can not be cast without crystallisation occurring which would invalidate the hardness measurements. Furthermore various authors have developed models for calculating Tg from the chemical composition of bioactive glasses which can now be used to calculate Hardness.