A Study of Fluoride-Containing Bioglass System for Dental Materials Derived from Clam Shell and Soda Lime Silica Glass

Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia Material Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia Department of Prosthodontic, Faculty of Dentistry, Ataturk University, 25030 Erzurum, Turkey


Introduction
Researchers are working hard to improve the formulation of medical products available in market to meet the needs of the public. With the best of knowledge, biomaterials play a main role in the field of biomedical, as they can interact well in biological system [1,2]. Due to their unique features and wide range of applications, researchers work are still working to obtain better properties and performances of biomaterials in biomedical field [3,4]. On the other hand, bioglass with good antimicrobial and mechanical properties has been the potential candidate for biomaterial formulation in orthopedic and dental applications [5,6]. e influence of bioglass in biomedical has proven to solve many problems, especially in dental procedures [7]. Discovered in 1969 by Hench, 45S5 Bioglass ® is an example of biomaterial that provides biological response to the human body through the interaction of their ionic dissolution products with the physiological environment [8,9]. As an early generation of biomaterial, 45S5 Bioglass ® consist of 45SiO 2 -24.5Na 2 O-24.4CaO-6P 2 O 5 (wt.%) glass composition [10].
is composition selection has shown bioactive properties of bioglass and high reactivity behavior at the surface of the material [1,7]. e current clinical use of bioglass shows the formation of hydroxyapatite-like layer during implantation process with the biological system which provides stable adhesion to living tissue [11][12][13]. is proves that bioglass is one of the most successful innovations in the field of biomedical. e alumino-silicate-fluoride (ASF) based bioglass containing fluoride is known to be one of the earliest being produced with SiO 2 -CaO-CaF 2 -P 2 O 5 -Al 2 O 3 composition. e calcium fluoride (CaF 2 ) content has an influence on the physical, chemical, and therapeutic properties of bioactive glass as it is composed of calcium ion (Ca 2+ ) and fluoride ion (F − ) [14]. Additionally, the fluoride ion of CaF 2 is specifically used to characterize glass behavior as it can alter the nature of glass material which contributes to its use in dental and medical field [15][16][17]. Moreover, fluoride ion plays a major role in the composition of glass as it can enhance the remineralization of biological system [18,19]. Besides, fluoride acts as a vital component in which it can reduce the melting point of the bioglass system [20]. From previous studies, various nucleating agents had successfully promoted the crystallization process for glass and improved the formation of fine-grained structure [21,22]. In this work, CaF 2 also acts as a nucleating agent for the ASF bioglass crystallization process. e preparation of ASF bioglass by using pure SiO 2 and CaO is very expensive and requires a high melting point for glass synthesis. To counter the problem, recycled SLS glass and CS will provide SiO 2 and CaO sources where it can reduce the production cost of ASF bioglass [23]. e fabrication of ASF bioglass with composition of silica, aluminium, and fluoride in this study shows soda lime silica (SLS) glass and clam shell (CS) vitreous waste material have been selected to replace certain elements in bioglass composition [14]. Since the major chemical compositions of SLS glass are basically SiO 2 (60-75%) and CaO (5-12%), it can be used as a source of silica in ASF bioglass composition for dental applications [24]. In the field of conventional glasses, SLS is known as a basic commercial glass product containing 95-99% of the glass produced worldwide. Generally, SLS glass is used for utensil, bioactive materials, and building material industries [25,26]. Besides, CS or their scientific name Anadara granosa also become a potential candidate in the preparation of dental application. e CS is widely found in intertidal mudflats area mostly in Southeast Asian countries including Malaysia. It became an alternative biomaterial for biomedical application due to the fact that it richly contains calcium carbonate (CaCO 3 ) [27,28]. Both SLS glass and CS are expected to provide better mechanical and optical properties such as high thermal stability, high transparency, and low melting point.
To the best of our knowledge, the study of the preparation of ASF bioglass from vitreous waste materials is relatively new and very limited in biomedical field. In this work, the preparation of ASF bioglass from vitreous waste material has been reported. e main objective of this work is to synthesis ASF bioglass from vitreous waste material. e effects of CaF 2 in each sample were also studied. e glass has been characterized by studying their physical and structural properties including X-ray fluorescence (XRF), density (ρ), molar volume (V m ), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray (EDX) spectroscopy. e main advantage of the CaO-SLS glass system over the CaO-SiO 2 glass system is that it can reduce the production cost of ASF bioglass. erefore, the idea of this article is to synthesis and characterize the ASF bioglass derived from CaO-SLS glass system.

Materials.
e raw chemical compound for bioglass synthesis, SiO 2 , was replaced with SLS glass waste bottles obtained from local restaurant in Selangor, Malaysia. Meanwhile, CaO was obtained from Cockle Shell (CS) or their scientific name (Anadara granosa sp.) from mangrove forest in Pontian, Johor, in South Coast of Peninsular Malaysia. For other chemical compounds, aluminum oxide 99.5% (Alfa Aesar, a Johnson Matthey Company), phosphorus pentoxide >99.99% (Alfa Aesar, a Johnson Matthey Company), and calcium fluoride >99.95% (R&M Chemicals) were used for ASF bioglass composition.

Preparation of Raw Materials.
For preparing samples, raw materials were categorised into two components which were waste and commercial. Starting with waste materials, SLS glass and CS replaced SiO 2 and CaO, respectively. First, the SLS glass was thoroughly washed with water to remove the impurities and left to dry at room temperature for 24 hours. After drying, the SLS glass bottle was crushed into smaller pieces by using a hammer and followed by a plunge using steel plunger to obtain fine glass powder. Subsequently, the SLS glass was inserted into a milling jar containing 15-25 milling balls for a milling process about 80 r.p.m. for 24 hours. en, it was ground using mortar and pestle continuously followed by sieving below 45 μm grain siever size to obtain SLS glass powder. e purpose of using a 45 μm siever was to achieve the smallest particle size of powder. en, the collected CS wastes were washed with water to remove all impurities and left to dry for 24 hours at room temperature. e CO 2 was released from main composition of CS which is CaCO 3 through calcination process at 900°C for 2 hours in LT098 model SIC4-1600 furnace to obtain the CaO compound. en, the CS was crushed using a plunger followed by sieved process using a 45 μm siever. Next, ASF bioglass was produced from a mixture of all five chemical compounds CaO, SiO 2 , CaF 2 , Al 2 O 3, and P 2 O 5 . Table 1 shows the compositions used in the preparation of Batches 1, 2, 3, and 4 of bioglass samples labeled as B1G, B2G, B3G, and B4G, respectively.

Preparation of ASF Bioglass.
Four batches of ASF bioglass sample were weighed ∼80.0 g for each mixture as shown in Table 1. e samples were weighed by using an electronic digital weighing machine. e electronic digital weighing machine can provide reading up to ±0.0001 g accuracy. After mixing process, the mixture was transferred to a milling jar using a US Stoneware Jar Mill NA model at a speed range of approximately 80 r.p.m. and milled for about 15 minutes to ensure that the powder was homogeneous.
en, homogeneous powder was mixed into the crucible and the mixture was melted in LT Furnace model with a temperature increase rate at 10°C per minute about 4 hours at 1500°C. After 4 hours, the mixture underwent a water quenching process where thermal shock occurs and glass frit was produced. e glass frits underwent a drying process at room temperature for 24 hours to ensure the water was completely removed. Subsequently, the glass frits were crushed and ground to obtain the powder form using plungers and hammers. e powder form was sieved using siever with size of 45 μm to produce a fine powder form. Bioglass samples were characterized to determine the properties of raw CS and SLS glass samples.

Characterization.
Raw CS and SLS glass were characterized by XRF measurement while ASF bioglass samples were characterized by using density, molar volume, XRD, FTIR, FESEM, and EDX. e result for chemical composition of bioglass was determined by analysis technique fundamental parameters (theoretical) through XRF spectroscopy using an Energy Dispersive X-ray Fluorescence model EDX-720 Shimadzu. e density of bioglass was measured using the Archimedes principle in which distilled water acts as an immersion liquid. In order to obtain the density of bioglass sample (ρ sample ), the bioglass sample was weighed in the air (W air ), then the sample was immersed in distilled water (W water ). Meanwhile, the density of distilled water (ρ water ) used in this measurement was 1.00 g/cm 3 : e molar volume of ASF bioglass sample (V m ) is obtainted through the following equation: e total molecular weight of the ASF bioglass sample is represented as (M) while the density of the ASF bioglass is represented as (ρ). e XRD measurement was carried out at 20°to 80°a ngles. X-ray Phillips (model PW 1830) was used to identify the structure of ASF bioglass sample. e results obtained were analyzed using X'Pert Highscore software. FTIR characterization was used to determine the chemical bond of the sample. e sample was analyzed by UATR-FTIR (Universal Attenuated Total Internal Reflection Fourier Transform Infrared) spectra recorded using a ermo Scientific Nicolet 6700 FT-IR spectrometer in the range of 2000-200 cm −1 in 4 cm −1 resolution. en, FESEM analysis was measured on ASF bioglass coated using gold (Au) to detect the morphology of the glass structure by using a high vacuum FEI Nova NanoSEM 230. e gold (Au) coating may disrupt the element at 2.2 keV of energy and phosphorus (P) is a potential element that can overlap to a certain degree at 2.1-2.2 keV of energy [29,30]. As a solution to the overlapping problem, EDX analysis was completed before the sample was coated with gold (Au). e ASF samples were coated with gold (Au) for FESEM to prevent the charging issues. Finally, EDX measurement was performed to analyze the elements present in each sample. Each of the samples also using FEI Nova NanoSEM 230 in high-resolution field emission SEM where it is the main imaging tool for nanoparticles, with a resolution of 1 nm at 15 kV. e identification of weight percentage of C, O, F, Na, Al, Si, P, and Ca was measured by quantitative analysis. e quantitative analysis was conducted by Instruments NanoAnalysis (INCA) microanalysis of system based on standardless analysis. e standardless analysis will detect the element by calculating the area covered by each element below the peak. e Ca/P ratio is calculated to obtain the sensitivity factor by converting the area of peak to weight percentage. e Ca/P ratio is obtained by considering each elemental weight percentage of Ca and P.

X-Ray Fluorescence (XRF).
e SLS glass and CS known as vitreous waste materials were used in the synthesis of ASF bioglass. Both waste materials become a prime source for SiO 2 and CaO, respectively. e XRF chemical analysis of raw SLS, CS, and CS after calcination can be seen in Table 2. From the table, the main elements present in the SLS glass are Si and Ca. ese elements contain about 79.09 wt.% and 18.10 wt.% of weight percentage from the total composition. Other minor elements such as Al, K, Ti, Cr, Fe, Zn, Sr, and Zr comprise about 2.81% of the total composition. e commercial SLS glass is fundamentally composed of SiO 2 , CaO, Na 2 O, Al 2 O 3 , P 2 O 5 , and other oxide elements [31]. High composition of SiO 2 in SLS glass show the potential in glass production as Si is a dominant element in the glass matrix. As a major element in SLS glass, silica becomes a great source of raw materials for glass production [23,24].
Meanwhile, raw CS shows that Ca is the major element which is around 97.70 wt.% from the total composition. e minor elements present in the composition are Zn, K, Sc, S, Sr, and Cu which is about 2.30 wt.%. From the table, Ca is the major element after calcination which is around 99.55 wt.% while the minor elements present are Sr and Cu around 0.46 wt.%. e CS act as a major source for CaO where it contains high amounts of calcium carbonate (CaCO 3 ). From the calcination process, CaCO 3 will be converted into CaO through the chemical decomposition reaction [27,32]: Minor elements in CS are eliminated during calcination. e Ca 2+ ions have small ionic radius which may generate stronger and shorter Ca−O bond. erefore as a final product of calcination process, CaO act as an oxide modifier which can increase the durability of glass production [33]. Figure 1 shows the graph of the density and molar volume for different ASF bioglass samples. e density of the ASF bioglass for B1G to B4G was 2.37 g/cm 3 , 2.51 g/cm 3 , 2.52 g/cm 3 , and 2.53 g/cm 3 , respectively. e density of the samples increased from B1G to B4G. is is due to the high addition of CaF 2 that leads to the crystalline structure. e higher the amount of CaF 2 added, the higher the density of the sample. is is because CaF 2 acts as a flux that enhances the crystallization process [34,35]. e high crystalline structure will produce strong glass component [14] and thus provide high density of sample. Meanwhile, the molar volume of the ASF bioglass sample is inversely proportional to the density. e density and molar volume show opposite action to each other [33]. From Figure 1, the data show decrement pattern for the molar volume results for B1G to B4G. e molar volumes for 4 batches are 244.86 cm 3 /mol, 230.28 cm 3 /mol, 230.00 cm 3 /mol, and 226.50 cm 3 /mol, respectively. e higher the amount of CaF 2 added, the lower the molar volume of ASF bioglass. is is related to the change in the amorphous structured closedpack lattices to crystalline structured closed-pack lattices due to the presence of fluoride which acts as a nucleation agent in the glass [16]. e crystalline structure of the sample is arranged in highly ordered structure, making the sample more compact thus decreasing the molar volume of the sample. e density and molar volume are related to atomic weight, ionic size, and total amount of different elements in ASF bioglass system.

X-Ray Diffraction (XRD).
e XRD patterns for various ASF bioglass samples are shown in Figure 2; B1G and B2G indicate that the ASF bioglass system is in an amorphous phase and no sharp peaks exist due to the optimum CaF 2 concentration, which acts as a stabilizer for the bioglass system [36]. However, the presence of peaks in B3G and B4G is due to the presence of initial crystalline peaks in ASF bioglass samples. e observed small and sharp peaks are known as fluorapatite (Ca 5 (PO 4 ) 3 F) with reference code JCPDS no. 98-001-7206. is may be due to the high fluoride content from CaF 2 in both samples [37]. Higher percentages of CaF 2 lead to crystalline structured while lower fluoride content gives amorphous structured [38]. is is because CaF 2 acts as a flux which increases the crystallization [34,35]. In addition, fluoride enhances the nucleation and growth of crystalline phase through the incorporation of F − ions into the ASF bioglass network where it replaces       Journal of Spectroscopy nonbridge oxygen ions and lowers the aggregation extent of the glass network [39][40][41][42]. Table 3 and Figure 3 present the FTIR spectra of ASF bioglass with different weight percentages of CaF 2 . Based on the figures, the major bands exist in all batches represented by the infrared (IR) spectra belong to glass modes such as Si−O−Si, P−O, and C−O mode band. However, the presence of hydroxide group existing at the range of ∼1600 cm −1 is known as O−H stretching mode [43,44]. e IR spectrum of all ASF bioglass samples at the range of ∼400 cm −1 due to Si−O−Si bending [45][46][47]. e presence of Si−O−Si tetrahedral in the range ∼800 to 1000 cm −1 is due to the formation of the silica-rich layers. e P−O bending mode exists at the range ∼500 cm −1 showing the formation of calcium phosphate layers in glass sample [48,49]. Another band spectrum exists at the range of 1300 cm −1 known as C−O stretching.

Fourier Transform Infrared (FTIR).
is C−O bond exists in all batches indicating the presence of carbonate groups in CaO. e carbonate presents in the powder may be due to the dissolution of carbon dioxide (CO 2 ) from the atmosphere [23,44]. e same intensity level across all bands indicates a consistent ASF Bioglass formation in all samples. Figure 4 shows FESEM micrographs of 4 batches of glass samples. e microstructure observations show nonuniform particle distribution based on the formation of irregular shapes and sharp particle edges in all glass samples [50]. e amount of CaF 2 content added does not affect the glass structure of ASF bioglass. e use of ASF bioglass in dental applications is due to the good adhesive properties and biocompatibility that make glass a potential candidate in medical procedures [7].

Energy Dispersive X-Ray Analysis (EDX).
e EDX spectra for Batches 1 to 4 are shown in Figure 5 for the identification of weight percentage of C, O, F, Na, Al, Si, P, and Ca by quantitative analysis. e Ca/P ratio calculations are shown in Figure 5 for each sample. e Ca/P ratio for calcium phosphate bioglass around 1.5 and 1.67 belongs to apatite groups such as fluorapatite or hydroxyapatite [51].
e Ca/P ratio calculation for each sample increased from 1.17 to 1.77 due to an increase in the amount of CaF 2 in the ASF bioglass. e release of calcium and phosphorus ions helps in the formation of apatite layers in glass structure [37]. e high amounts of ion release will form apatite layer as the ionic activity increases during apatite nucleation process [52]. e formation of Ca and P ions is important in dental applications as it can increase the apatite saturation by enhancing the remineralization [53]. e ASF bioglass materials are chemically identical to the dental structure components. erefore, it can help repair damaged tissues in the biological system. From the previous study of bioglass, the Ca/P values higher than 1 were suitable for the body implantations while Ca/P values lower than 1 were not appropriate for biological implants due to high solubility [30,54]. From the figure, the Ca/P ratio of the ASF bioglass is acceptable because its ratio is within the required range.

Conclusions
ASF based bioglass was synthesised from SLS glass and CS waste material as a SiO 2 and CaO source using conventional melt-quenching methods. e XRF results showed that the major elements in the SLS glass and CS were Si and Ca, respectively. e density of ASF bioglass was observed to increase with increasing CaF 2 content in the composition. However, molar volume showed the opposite trend. e different physical behaviors of ASF bioglass were closely related to CaF 2 content in each composition.
e XRD results revealed that B1G and B2G are in an amorphous phase and no sharp peaks exist due to the optimum CaF 2 concentration , which is a stabilizer for the bioglass system. However, presence of peaks in B3G and B4G was due to the presence of initial crystalline peaks in ASF bioglass samples. e small and sharp peaks observed were known as fluorapatite (Ca 5 (PO 4 ) 3 F). Meanwhile, FTIR measurements revealed the presence of various chemical bonds such as Si−O−Si, P−O, C−O, and O−H in samples showing ASF bioglass formation. e FESEM microstructure showed the nonuniform particle distribution based on the formation of irregular shapes and sharp particle edges in all glass samples. Finally, EDX analysis showed that Ca/P values obtained from 1.17 to 1.77 were appropriate for biological implantation. e ASF bioglass system provided 4 batches of samples where B1G and B2G produce clear glass structures with amorphous phases. From the observations, this was the optimum weight percentage of CaF 2 to produce ASF based bioglass. Meanwhile, B3G and B4G with high CaF 2 composition showed weak crystalline phase. In conclusion, ASF bioglass has been successfully synthesised from SLS glass and CS vitreous waste material. It is known as a high potential application in material science, medicine, and biomedical field.

Data Availability
All data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors have no conflicts of interest relevant to this manuscript.