Glass Ionomer Cement Incorporated Nano- Hydroxyapatite-Silica: The Road towards Improvement

Up till today, no dental material seems to have ideal properties for any dental application. For that, researchers and manufacturers seem to never lose hope in developing the technique, modification and/or formulations that aims to improve the properties of these materials to its possible best. Among the most widely used materials in restorative dentistry is Glass Ionomer Cements (GICs). Their use has been popular due to their unique properties that adhere directly to the tooth structure and base metals [1], exhibit longterm fluoride release [2] and possess good biocompatibility [3]. Despite having those properties, their drawbacks like brittleness, poor abrasion resistance and low flexural and tensile strengths limits their application for use in high stress bearing areas, such as on the posterior teeth. As such, several modifications have been introduced to the conventional GICs. These include the addition of titanium dioxide, hydroxyapatite, glass fibre and bioactive glass, with the aim to improve the mechanical and physical properties of GlCs [4-8].

These days, the application of nano-sized particles for biomaterials is becoming highly popular in dentistry. This nanotechnology involves the use of materials which has the size in the range of 1-100nm. Recent studies have suggested that the incorporation of nano-sized particles or "nanoclusters" can improve the mechanical properties of GIC [6,9,10].

In particular, a few studies have been carried out to incorporate nano-hydroxyapatite-silica (nano-HA-silica) powders into conventional GICs (Fuji IX GP, GC International, Japan) [9,11,12]. It was found that the addition of nano-HA-silica into conventional GIC increased the material hardness by 73% [9]. The increase is believed to be associated with filling of voids between the hexagonal HA particles with nano silica particles. As a subsequent, it enhanced the material packing density thus increase its hardness. Further study supported this belief after carrying out Transmisssion Electron Microscope (TEM) and Scanning Electron Microscope (SEM) investigations. Both type of micrographs revealed good distributions of elongated HA and spherical silica within the specimen, with both of them were in nano-sized particles [11]. On top of that, this material had recently undergone further investigation to assess its cytotoxicity upon being treated with Dental Pulp Stem Cells (DPSCs). It was demonstrated that nano-HA- silica GIC exhibited favourable and comparable cell viability similar to conventional GIC, with the cells placed on each material showed good spindle morphology. In contrast, resin-modified GIC showed significantly lower cell viability compared to nano-HA-silica and conventional GIC [12].

Based on the results of these studies, we can conclude that nano- HA-silica GIC showed favourable findings in terms of mechanical and biological properties and thus can be considered as a future potential restorative material for use in clinical dentistry.

The studies on nano-HA-silica GIC were supported by Ministry of Higher Education of Malaysia under Fundamental Research Grant Scheme (FRGS): 203/PPSG/6171138 and 203/PPSG/6171173.

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