Effects of Different Percentages of Microhydroxyapatite on Microhardness of Resin-modified Glass-ionomer and Zirconomer

Abstract

BackgroundHydroxyapatite (HA) is the main mineral component of the tooth structure, which exhibits considerable biological behavior and its incorporation might improve microhardness of dental materials. Microhardness of restorative materials, like glass-ionomer, is critical for the clinical longevity of restorations. The aim of this study was to evaluate the microhardness of two glass-ionomers types by incorporating different percentages of microhydroxyapatite.Material and MethodsIn this study, 80 disc-shaped experimental specimens (6 mm in diameter, 2 mm in height) were prepared in 8 groups, including resin-modified glass-ionomer (RMGI, GC, Gold Label, Japan), zirconia-reinforced glass-ionomer (Zirconomer, Shofu, Kyoto, Japan), and their mixture with 0, 5, 15 and 25 wt% of microhydroxyapatite (Sigma-Aldrich, Germany). All the specimens were stored in deionized water at 37ºC for 24 hours. Then Vickers microhardness test was carried out on the both sides of specimens and data were analyzed using two-way ANOVA and paired t-test (P<0.05).ResultsMicrohardness of Zirconomer and RMGI increased significantly due to adding 5 and 15 wt% of micrhydrox-yapatite (P<0.001). The highest Vickers hardness number (VHN) was recorded in the RMGI group with 5 wt% of microhydroxyapatite. In addition, in all the study groups RMGI exhibited higher microhardness values than Zirconomer (P<0.001). However, microhardness values decreased significantly after adding 25 wt% of microhydroxyapatite to Zirconomer (P<0.001). Similarly, VHN decreased in RMGI groups containing 25 wt% of HA compared to control groups (without HA) (P<0.001).ConclusionsIncorporation of 5 and 15 wt% of microhydroxyapatite to RMGI and Zirconomer improved microhardness, while adding 25 wt% of HA decreased hardness with both experimental materials compared to the control groups (without HA). Key words:Microhardness, Resin-modified glass-ionomer, Zirconia-reinforced glass ionomer, Microhydroxyapatite.

Mechanical Properties of Glass Ionomer Cements after Incorporation of Marine Derived Hydroxyapatite

“…The recorded improved mechanical properties of the Fuji II group after incorporating 10 wt% HA and associated improvements in FS probably resulted from the 'umbrella phenomenon of resin polymer' that protects the calcium polyacrylates from dissociation in the early phase of the setting, before maturation and the formation of more stable aluminum polyacrylates [1]. It was indeed shown that resin-modified GICs are more stable in a wet and acidic environment than are conventional GICs [31,32]. However, unlike conventional GICs, restorative materials containing resin have been shown to have negative effects on dental pulp; they also exhibit cytotoxicity, and they prompt biofilm formation and secondary caries development [33].…”

Evaluation of the effect of micro-hydroxyapatite incorporation on the diametral tensile strength of glass ionomer cements

“…It has been previously demonstrated that the incorporation of 15 wt% of micro-HAP into RMGIC improves microhardness, while the addition of 15 wt% of HAP has a negative effect on the microhardness of RMGIC. [13] Therefore, 15 wt% of micro-HAP was incorporated into a conventional GIC and a RMGIC in the present study. The bioactive hydroxyapatite (HAP)/zirconia-filled GIC demonstrated increased DTS and compressive strength compared to the unmodified GIC in a previous study.…”

“…It seems that HAP incorporation can interfere with the complete reaction of the components of RMGIC which can negatively affect the DTS. [13] However, the probable effects of different concentrations and different particle sizes of the HAP on mechanical and bond strength properties of GICs should be investigated in future studies.…”

“…[10] Considering the high biocompatibility of hydroxyapatite, some researchers have made attempts to evaluate the effects of incorporating hydroxyapatite powder into restorative dental materials such as GICs. [811121314] The interaction between GICs and hydroxyapatite takes place through carboxylate groups in the polyacid structure. It has been reported that hydroxyapatite incorporation into GICs may improve the mechanical properties of GICs.…”

“…An increase in the bond strength of GIC to the tooth structure can also occur due to similarity of hydroxyapatite to the structure of enamel and dentin. [1213]…”