Novel Upgrading of Conventional Glass Ionomer Cement Using Nanohydroxyapatite, Silica and Zirconia

Glass ionomer cement (GIC) or term by the International Organization for Standardization, (ISO), is “glass polyalkenoate cement” [1]. was one of the mostly used material in dentistry since its invention in 1972 by Wilson and Kent. Conventional GIC was an acid-base cements produced from the reaction of weak polymeric acids with powdered glasses [2], composed of water soluble, polyacrylic acid and a fluoroaluminosilicate glass [3,4]. Later, the resin modified GIC (RMGIC) was produced by an incorporation of hydrophilic resin monomer into GIC and set by light curing [5]. Conventional GIC was well liked due to its easy to use [6], moisture less sensitive and the main attractions of GIC are the adhesive properties to enamel and dentin where it bond chemically to hard dental tissues by the formation of ionic bonds between carboxylate gropes and calcium [7], It is anti-cariogenic due to the ability to release fluoride and also act as fluoride reservoir if recharge [8], one of the magnificent inhibitor for caries process [9], inadequacy of exothermic polymerization and close thermal expansion to tooth [10,11]. It was highly used for treatment of deciduous teeth, as a liner or base, temporary restoration for permanent teeth and very suitable for atraumatic restorative treatment (ART) [12].

However, there are few weaknesses regarding to this material where its lack in strength and low resistance to abrasion and wears [13]. It has low hardness which cannot withstand occlusal stress for a long period of time [10]. Even it is tooth-coloured material but has poor aesthetic due to too opaque, not easily polished and has very poor resistance to acidic exposure in a situation of mouth with highly acidic environment [14]. Higher compressive strength of RM-GIC is may be due to the presence of resinous polymer that are absent in conventional GIC [15]. Compare to other material such as amalgam that highly controversial with its hazardous effect and metallic colour which is not aestrhetic especially for anterior restoration, GIC has better features. Also comparing to composite resins which become more popular. there are concerns that resin composites may be toxic based on the fact that they may release components which is harmful to pulp tissue if carelessly applied [16], GIC is more safe.

Due to its important usage many studies for improvement has been done by researchers since many years ago. The filler has been modified by incorporating elements such as silver-cermet, stainless steel powder [17], titanium dioxide, silver tin alloy, carbon and alumina-silicate fibres [3,7,10,18]. Hydroxyapatite, silica and recently zirconia have been used to modify the nano powder of the conventional GIC. HA participates in the setting reaction of GIC which increased the flexural strength [19]. The resemblance between chemical formula of HA (Ca10(PO4)6(OH)2) and natural bone and teeth due to the continuous formation of aluminum salt bridges, improved the final strength of the cements [3,20,21,22]. In other circumstances, the incorporation of HA alone into GIC did not improve the mechanical properties of GIC as HA did not involve in the cross-linking matrix and also disrupts the stetting reaction of GIC [23].

On the other hand, limited literatures can be found on the incorporation of silica into GIC. Rahman, et al. [2014] described on one pot synthesis of nanosilica-hydroxyapatite (nanoSiO₂-HA) via sol-gel method has successfully produced elongated nanoHA with size of~103nm and spherical nanoSiO₂ with size of~30nm. This incorporation of nanoSiO₂-HA resulted in the hardness enhancement of~73 % when compared to conventional GIC [22]. Studies have found that the incorporation of a HA-SiO2 phase in a conventional GIC enhanced its mechanical properties with favorable cytotoxic response [24,25]. A comprehensive review of the available literature has revealed that not all modifications in glass powder have resulted in the desirable strengthening of GICs.

Lately, zirconia has been used to modify the powder of GIC. Zirconia was popularized into dentistry in the early 1990s, as an endodontic posts and hard framework cores for crowns and fixed partial dentures [26]. Earlier, Gu and colleague reported on the improvements on mechanical strength with the addition of hydroxyapatite/zirconia (HA/ZrO₂) into the GIC. but the presence of voids on the fractured surface and cracks at the interface showed the failure of HA/ZrO₂ in improving the brittle manner of GIC [23]. Study using HA/yittra-stabilized ZrO₂ nanocomposite has successfully improved the characteristic of GIC owing to the high strength, fracture toughness and biocompatibility of ZrO₂ [11]. Recently, a new prototype named GiZiDent which is a GICnanozirconia- silica-HA hubrid has been produced by Wan Bakar, et al. 2017 [27]. They have found a specific tec technique of synhesizing and specific ratio of addition the new nano powder to the conventional GIC to produce new hybrid material with many mprovedvements following ISO standard [28].

This new noivel material has improved tmechano-physicochemico and biological properties of the conventional GIC [28,29]. The incorporation of nanoceramics (HA, SiO₂, ZrO2) has resulted in improved mechanical properties of GICs due to their ability to release F-, high surface area, and better particle size distribution [3,24,30]. GIC nano ZrOO₂-SiO₂-HA demonstrated, a statistically significant difference in cell viability at both 100 and 200mg/ml concentrations for the 24h and 72h. incubation periods [31]. Study result showed an overall higher F- ion elusion from the GIC-nano- ZrO2-SiO₂-HA when compared to conventional GIC throughout the duration of the study (p≤0.05) [32]. Nanozirconia which is translucent may also improve the aesthetic property of GIC as shown in a study by Rahman, et al. [30].

The new novel nano GIC-ZrOO₂-SiO₂-HA can be a promising dental restorative material in future for a wider scope of used including high stress bearing area.

None.

The authors declare no conflict of interest.

1. (2007) Dental Water Based Cements. International Organization for Standardization; Geneva, Switzerland, ISO 9917-1.
2. Sidhu SK, Nicholson JW (2016) A review of glass-ionomer cements for clinical dentistry. J Funct Biomater 7(3): 16.
3. Moshaverinia A, Roohpour N, Chee WWL, Schricker SR (2011) A review of powder modifications in conventional glass-ionomer dental cements. J Mater Chem 21: 1319-1328.
4. Croll T P, Nicholson J W (2002) Glass ionomer cements in pediatric dentistry: review of the literature. Pediatr Dent 24(5): 423-429.
5. Davidson CL, Mjor IA (1999) Advances in glass-ionomer cements. Chicago: Quintessence Int Co, USA, p: 51-57.
6. Khoroushi, M, Keshani, F (2013) A review of glass-ionomers: From conventional glass-ionomer to bioactive glass-ionomer. Dent Res J (Isfahan) 10(4): 411-420.
7. Lin A, McIntyre NS, Davidson RD (1992) Studies on the adhesion of glass‐ionomer cements to dentin. J Dent Res 71: 1836-1841.
8. Jingarwar MM, Pathak A, Bajwa NK, Sidhu HS (2014) Quantitative assessment of fluoride release and recharge ability of different restorative materials in different media: an in vitro study. J Clin Diagn Res 8: 31-34.
9. Mount GJ (2003) An Atlas of Glass-Ionomer Cements: A Clinician's Guide, CRC Press, USA.
10. Lohbauer U (2010) Dental glass ionomer cements as permanent filling materials?-properties, limitations and future trends. Materials (Basel) 3(1): 76-96.
11. Rajabzadeh G, Salehi S, Nemati A, Tavakoli R, Solati Hashjin M (2014) Enhancing glass ionomer cement features by using the HA/YSZ nanocomposite: a feed forward neural network modelling. J Mech Behav Biomed Mater 29: 317-327.
12. Kumar PD, Chowdhury SA, Lynch E, Chowdhury CR (2019) Factors influencing fluoride release in atraumatic restorative treatment (ART) materials: A review. Journal of Oral Biology and Craniofacial Research 9(4): 315-320.
13. Cho SY, Cheng AC (1999) A review of glass ionomer restorations in the primary dentition. J Can Dent Assoc 65(9): 491-495.
14. Wan Bakar WZ, McIntyre J (2008) Susceptibility of selected tooth‐coloured dental materials to damage by common erosive acids. Aust Dent J 53 (3): 226-234.
15. Mallmann A, Ataíde JCO, Amoedo R, Rocha PV, Jacques LB (2007) Compressive strength of glass ionomer cements using different specimen dimensions. Braz Oral Res 21(3): 204-208.
16. Reichl FX, Seiss M, Kleinsasser N, Kehe K, Kunzelmann KH, et al. (2000) Distribution and excretion of BisGMA in guinea pigs. J Dent Res 87: 378-380.
17. Elsaka SE, Hamouda IM, Swain MV (2011) Titanium dioxide nanoparticles ddition to a conventional glass-ionomer restorative: influence on physical and antibacterial properties. J Dent 39(9): 589-598.
18. Oldfield CWB, Ellis B (1991) Fibrous reinforcement of glass-ionomer cements. Clinical Materials 7(4): 313-323.
19. Arita K, Lucas ME, Nishino M (2003) The effect of adding hydroxyapatite on the flexural strength of glass ionomer cement. Dent Mater J 22(2): 126-136.
20. Barandehfard F, Kianpour Rad M, Hosseinnia A, Khoshroo K, Tahriri M, et al. (2016) The addition of synthesized hydroxyapatite and fluorapatite nanoparticles to a glass-ionomer cement for dental restoration and its effects on mechanical properties. Ceramics International 42(15): 17866-17875.
21. Chiu SY, Shinonaga Y, Abe Y, Harada K, Arita K (2017) Influence of porous spherical-shaped hydroxyapatite on mechanical strength and bioactive function of conventional glass ionomer cement. Mater 10(1):1-13.
22. Rahman I A, Masudi SAM, Luddin N, Shiekh RA (2014) One-pot synthesis of hydroxyapatite–silica nanopowder composite for hardness enhancement of glass ionomer cement (GIC). Bull Mater Sci 37(2): 213-219.
23. Gu YW, Yap AU, Cheang P, Khor KA (2005) Effects of incorporation of HA/ZrO(2) into glass ionomer cement (GIC). Biomaterials 26(7): 713-720.
24. Ahmad Shiekh, Rahman IA, Masudi SM, Luddin N (2014) Modification of glass ionomer cement by incorporating hydroxyapatite-silica nano-powder composite: Sol–gel synthesis and characterization. Ceramics International 40(2): 3165-3170.
25. Noorani TY, Luddin N, Rahman IA, Masudi SM (2017) In vitro cytotoxicity evaluation of novel nano-hydroxyapatite-silica incorporated glass ionomer cement. J Clin Diagn Res 11(4): ZC105-ZC109.
26. Elie ED, Maha AG (2014) The zirconia restoration properties: a versatile restorative material. Dentistry 4(4):
27. Wan Bakar WZ, Rahman IA, Ghazali NAM, Sajjad A, Mohamad D, et al. (2019) Glass ionomer nano zirconia- silica- hydroxyapatite hybrid material-GiZiDent, Poster for Conference: Malaysia Technology Expo 2019, Kuala Lumpur.
28. Ghazali AM, Wan Bakar WZ, Rahman IA, Masudi SM (2017) Fabrication of modified GIC: GIC-nanoSiO2-HA-ZrO2 using two different mixing methods. AIP Conference Proceedings 1901(1): 020007.
29. Sajjad A, Wan Bakar WZ, Rahman IA, Mohamad D, Kannan TP (2018) osc26: characterization and physico-chemical evaluation of a novel glass ionomer nanozirconia-silica-hydroxyapatite hybrid material. J Indian Prosthodont Soc 201818(Suppl 1): S18-S19.
30. Rahman IA, Ghazali AM, WanBakar WZ, Masudi SM (2017) Modification of glass ionomer cement by incorporating nanozirconia-hydroxyapatitesilica nano-powder composite by the one-pot technique for hardness and aesthetics improvement. Ceramics International 43(16): 13247-1325.
31. Sajjad A, Wan Bakar WZ, Mohamad D, Kannan TP (2019) Cytotoxic effect of a novel glass ionomer nano zirconia-silica-hydroxyapatite hybrid material on human gingival fibroblasts. Malaysian Journal of Microscopy 15: 92-102.
32. Sajjad A, Wan Bakar WZ, Mohamad D, Kannan TP (2019) Characterization and efficacy of fluoride elusion of a novel glass ionomer nano zirconia silica hydroxyapatite hybrid material. Fluoride 52(4): 507-516.