Porous Hydroxyapatite Can Improve Strength and Bioactive Functions of Glass Ionomer Cement

53 Introduction Glass ionomer cement (GIC) was invented by Wilson and Kent in 1971 [1]. GIC is widely used as a dental material, due to its ease of use, low coefficient of thermal expansion, good biocompatibility with bone pulp tissue, and long-term bonding to tooth surfaces and metals [2,3]. In addition, its unique fluoride (F) ion release characteristics have anticaries, antimicrobial and remineralization effects [4,5]. However, its current uses are limited because of its inadequate strength. Several researchers have attempted to overcome these poor mechanical properties by adding reinforcements, but sufficient improvements in mechanical and chemical properties have not yet been achieved [6-8]. As hydroxyapatite (HAp) has great biocompatibility and a composition similar to apatite in the human tooth, Nicholson et al. [9] first attempted to incorporate HAp into GIC prepared from oxide glass and F glass and concluded that the properties of GIC were not affected by the presence of HAp. However, other researchers reported that addition of HAp into commercially prepared GICs improved the mechanical properties [10,11]. In our previous studies, it was demonstrated that the addition of HAp particles was able to enhance both the mechanical and chemical properties of a conventional GIC used for dental restoration, Fuji IX GP (IX-GP; GC Corp., Tokyo, Japan) [12-14]. Moreover, we confirmed that the most suitable HAp for incorporation into GIC was porous HAp with a high specific surface area [14]. However, further investigations are necessary to clarify the mechanisms responsible for the improvement in mechanical and chemical properties by adding HAp to GIC. Porous Hydroxyapatite Can Improve Strength and Bioactive Functions of Glass Ionomer Cement