The influence of bioactive glass (BGS-7) on enamel remineralization: an in vitro study
Article information
Abstract
Objectives
The aim of this study was to compare the remineralizing capacity of bioactive glass (BGS-7, CGBIO) with other agents.
Methods
Twenty caries-free third molars were sectioned and demineralized. Specimens were divided into four groups: (1) control, (2) Clinpro XT varnish (Solventum), (3) 1.23% acidulated phosphate fluoride gel, and (4) a new type of CaO-SiO2-P2O5-B2O3 system of bioactive glass ceramics (BGS-7). Agents were applied and stored in simulated body fluid at 37℃ for 2 weeks. Microhardness was measured using the Vickers hardness testing method. Five specimens per group were analyzed using quantitative light-induced fluorescence (QLF) to assess mineral loss. Field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to examine the surface morphology and elemental composition. Data were analyzed using paired t-test and one-way analysis of variance (p < 0.05).
Results
BGS-7 showed the highest microhardness values and the greatest recovery in QLF analysis (p < 0.05). FE-SEM revealed granular precipitates on demineralized enamel in the BGS-7 group. EDS confirmed the presence of newly formed silicon and fluoride layers.
Conclusions
BGS-7 demonstrated superior remineralization capacity compared to other agents, suggesting its potential as an effective remineralizing material.
INTRODUCTION
When enamel is exposed for a prolonged period to an acidic environment, such as that found in caries, an imbalance between the demineralization and remineralization processes occurs, causing the cycle to shift toward demineralization. Meanwhile, remineralization is a natural repair process that primarily relies on the deposition of calcium phosphate, mainly sourced from saliva, to form a new layer on the damaged surface [1]. Modern strategies for managing caries focus on halting its progression [2]. This remineralization process of enamel can be promoted by using several topical remineralizing agents [3].
Fluoride has been a cornerstone in enamel remineralization for many years, primarily working to prevent caries by inhibiting demineralization and promoting the formation of fluorapatite on the enamel surface. Fluorapatite is less soluble, therefore increasing the resistance of enamel to dissolution relative to hydroxyapatite during acid attack [4]. But its long-term viability and sustainable effects are still controversial.
Clinpro XT varnish (Solventum, St. Paul, MN, USA) is a professional fluoride varnish that is formulated to release fluoride more efficiently and maintain its release over a longer period compared to fluoride gels. While fluoride gels typically require multiple applications to provide significant fluoride absorption, Clinpro XT varnish’s unique delivery system allows for more effective and sustained fluoride uptake. This ensures prolonged protection against tooth decay, especially in patients at high risk for caries [5].
Nevertheless, the maximum effectiveness of fluoride-based products in the treatment and prevention of dental caries remains limited, as their remineralizing effects are predominantly confined to the enamel surface and are insufficient to fully restore deeper or advanced carious lesions [6]. As a result, it is necessary to incorporate other agents into remineralization therapy, such as bioactive materials, which can boost remineralization when combined with fluoride and serve as a complement to it [7,8].
Bioactive glass has been developed in various forms and has been widely studied for its favorable properties as a restorative material, particularly its ability to promote enamel and dentin remineralization [6,9–11]. Numerous studies and reviews have reported that bioactive glass can enhance the remineralization of carious lesions by forming an apatite-like layer on tooth surfaces [6]. BGS-7 (CaO-SiO₂-P₂O₅-B₂O₃; CGBIO, Seoul, Korea) is a novel bioactive glass-ceramic with a composition distinct from existing bioactive glasses, but research on its application for enamel remineralization is still limited. Therefore, this study aimed to evaluate the remineralizing effect of BGS-7 on demineralized enamel. The null hypothesis was that BGS-7 would not show superior remineralization capacity compared to other remineralizing agents.
METHODS
The products used in this study are listed in Table 1, and the overall experimental procedures are illustrated in Figure 1. The specific materials and methods are described below.
Composition of the materials
Schematic diagram of the study design and methodology. CEJ, cementoenamel junction; QLF, quantitative light-induced fluorescence; FE-SEM, field-emission scanning electron microscopy; EDS, energy-dispersive X-ray spectroscopy; SBF, simulated body fluid.
Specimen preparation and demineralization treatment
The study protocol was approved by the Institutional Review Board of Wonkwang Dental Hospital, Iksan, Korea (WKDIRB202409-02). Twenty caries-free extracted human third molars were selected. The roots of the teeth were removed at the cementoenamel junction, and the crown was sectioned mesiodistally into two parts. The sections were embedded in acrylic resin (Ortho-Jet; Lang Dental Manufacturing Co., Wheeling, IL, USA) with the exposed enamel surface, and then the enamel surface was ground flat and polished with water-cooled 400, 600, 1,200 grit silicon carbide discs (DEERFOS Co., Seoul, Korea). Phosphoric acid (37%) was applied on the enamel surfaces for 20 minutes to form a demineralized lesion [12].
Remineralization treatment
Four experimental groups were assigned according to treatment modalities. All specimens were divided randomly into four groups (n = 10): (1) control, no application of remineralizing agent, (2) Clinpro XT varnish (group XT), (3) 1.23% APF gel (Natural-F Gel, Denbio, Gwangju, Korea; group FG), and (4) BGS-7 (group B7). After the demineralization procedure, the specimens received the following remineralizing treatments:
• Control group: No remineralizing agent was applied after demineralization.
• Group XT: Clinpro XT varnish was applied according to the manufacturer’s instructions. It was applied to the enamel surface once, light-cured for 20 seconds, and then rinsed with deionized water for 30 seconds.
• Group FG: Fluoride gel was applied daily for 14 days, with each application lasting 4 minutes. Thirty minutes after each application, the specimens were carefully rinsed with deionized water for 30 seconds, according to the manufacturer’s instructions.
• Group B7: A 1:1 mixture of BGS-7 and distilled water was applied to the enamel surface once for 2 hours, followed by rinsing with deionized water for 30 seconds.
Subsequently, all specimens from the four groups were stored in simulated body fluid (SBF) (Biochemazone, Edmonton, AB, Canada) at 37°C for 2 weeks.
Surface microhardness test
All specimens were air-dried at room temperature and used for the microhardness test. The surface microhardness of the specimens was measured with a Vickers microhardness (VHN) tester (HM-122, Mitutoyo Corp, Kawasaki, Japan) at two stages: after demineralization and after remineralization. A load of 100 g was applied to the surface for 10 seconds. The average value was determined. Each group was measured at 10 different points, with each point spaced at a constant distance from the others. The difference between VHNremin and VHNdemin (ΔVHN) was calculated to evaluate the remineralization effect of materials [12].
Quantitative light-induced fluorescence measurement
Quantitative light-induced fluorescence (QLF) was performed to quantitatively assess the degree of enamel demineralization and remineralization by measuring changes in fluorescence [13]. Five specimens of each group were used for QLF. All specimens were assessed by using the Qraypen C device based on QLF technology (AIOBIO, Seoul, Korea). Before imaging, specimens were washed with distilled water and dried sufficiently with compressed air for 5 seconds, and then imaging was performed. The amount for fluorescence loss of the specimen was measured using Qray software (AIOBIO) by measuring ΔF (%), which indicates the amount of fluorescence loss, and ΔF max, which indicates the amount of the most severe fluorescence loss compared to the sound surface in the fluorescence image. Recovery amount and recovery rate were calculated as follows:
Recovery amount (Δ(Δ(F))) = ΔFremin – ΔFdemin
Recovery rate (ΔF(rate)) = (ΔFremin-ΔFdemin)/ΔFdemin × 100
Field-emission scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis
To complete the preparation process, the specimens were dehydrated using ethanol solutions (25%, 50%, 75%, 95%, and 100%) for various durations (20, 20, 20, 30, and 60 minutes). After dehydration, the specimens were examined under a field-emission scanning electron microscope (FE-SEM; S-4800, Hitachi, Tokyo, Japan) equipped with a secondary electron detector for energy-dispersive X-ray analysis (EDS) using an accelerating voltage of 6.0 kV. Images were obtained from the center of each specimen with a magnification of ×5,000 and ×25,000. The same specimens were characterized using the EDS for calcium, phosphorus, fluoride, and silicon.
Statistical analysis
All data are expressed as the mean ± standard deviation. Paired t-test was utilized to compare the ΔVHN and ΔF of the specimens between values before and after remineralization within the group. One-way analysis of variance was used for comparison of enamel microhardness and amount of fluorescence loss of four groups (p < 0.05). All statistical analyses were performed using IBM SPSS version 25.0 (IBM Corp, Armonk, NY, USA). Differences were considered statistically significant at p < 0.05.
RESULTS
Surface microhardness test
Microhardness values of all groups are shown in Table 2. Among all groups, group B7 exhibited the highest ΔVHN value (58.57 ± 3.79), followed by group XT (49.22 ± 4.68), group FG (36.46 ± 2.66), and control group (0.45 ± 0.35). Statistically significant differences were observed among all groups (p < 0.05).
Vickers microhardness values (VHN) of the experimental groups
Quantitative light-induced fluorescence measurement
The results of QLF measurement of all groups are shown in Table 3. The recovery amount and rate were calculated by comparing ΔF values, which reflect fluorescence changes due to enamel demineralization, before and after remineralizing treatment. The recovery amount and rate of group B7 were significantly higher than those of the other groups (p < 0.05). Group B7 exhibited the highest recovery amount and rate (1.66 ± 0.11 and 25.58 ± 2.28, respectively), followed by group XT (1.04 ± 0.12 and 15.63 ± 2.43), group FG (0.46 ± 0.11 and 7.27 ± 1.90), and the control group (0.14 ± 0.05 and 2.17 ± 0.85). Statistically significant differences were observed among all groups (p < 0.05).
Mean amount of fluorescence loss (ΔF) of the experimental groups
Field-emission scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis
1. FE-SEM observation
FE-SEM images revealed distinct differences among the groups after remineralization treatment and 2 weeks of storage in SBF. In the control group, as shown in Figure 2A and B, typical features of demineralized enamel were observed, such as surface porosity with loss of enamel prism cores while retaining the periphery. In contrast, groups XT (Figure 2C, D) and FG (Figure 2E, F) showed the deposition of granular precipitates on the enamel surface. Notably, in group B7, dense granular precipitates were observed on the enamel surface (Figure 2G), and at higher magnification, characteristic needle-like crystallites were prominently observed (Figure 2H), suggesting advanced remineralization and the formation of an apatite-like layer.
Representative field-emission scanning electron microscopy (SEM) images of all the experimental groups in this study (A, C, E, G: ×5,000; B, D, F, H: ×25,000). SEM images of enamel specimens stored in simulated body fluid for 2 weeks. (A, B) Control group: The smear layer was removed, and eroded enamel rods were observed. (C, D) Group XT and (E, F) group FG: granular precipitates were observed around the enamel rods. (G, H) Group B7: dense granular precipitate formation (G), and at higher magnification, characteristic needle-like crystallites (white arrows) were prominently observed (H). Group definitions are provided in Table 1.
2. Energy-dispersive X-ray spectroscopy analysis
The results of EDS analysis of all groups of enamel specimens stored in SBF for 2 weeks are shown in Figure 3. Control group (Figure 3A) showed elemental composition consistent with demineralized enamel (Ca: 67.72%, P: 32.28%; Ca/P ratio: 2.1). Group XT (Figure 3B) showed composition primarily of calcium (66.10%) and phosphorus (33.90%) without detectable fluoride or silicon. Group FG (Figure 3C) revealed fluoride incorporation (3.75 weight percent [wt%]) along with calcium (64.35%) and phosphorus (31.89%). Group B7, in Figure 3D, showed silicon presence (5.53 wt%) from bioactive glass and fluoride content (3.01 wt%), along with calcium (65.95%) and phosphorus (25.51%).
Energy-dispersive X-ray spectroscopy analysis of enamel specimens stored in simulated body fluid for 2 weeks. (A) Control group showed elemental composition consistent with demineralized enamel (Ca, 67.72%; P, 32.28%; Ca/P ratio, 2.1). (B) Group XT showed a composition primarily of calcium and phosphorus, without detectable fluoride or silicon. (C) Group FG revealed fluoride incorporation along with calcium and phosphorus. (D) Group B7 showed the presence of both silicon (from bioactive glass) and fluoride, along with calcium and phosphorus. Group definitions are provided in Table 1.
DISCUSSION
Based on the results of this study, the null hypothesis was rejected. In both surface microhardness and QLF measurements, BGS-7 demonstrated the highest values, followed by the XT, FG, and control groups, respectively, with statistically significant differences observed among all groups (p < 0.05) (Tables 2 and 3). These findings are consistent with previous studies, which have demonstrated that enamel surfaces treated with bioactive glass exhibit significantly greater surface microhardness recovery compared to other remineralizing agents such as fluoride or casein phosphopeptide (CPP)- amorphous calcium phosphate (ACP) [11,14]. Meanwhile, the higher microhardness recovery and fluorescence recovery rates observed for the XT varnish compared to the fluoride group are presumed to be due to the prolonged and stable fluoride release provided by its resin-modified glass ionomer (RMGI) formulation.
QLF is widely utilized as a clinical diagnostic tool for the detection and monitoring of dental caries due to its ability to detect the loss of fluorescence that occurs as a result of enamel demineralization [15]. Its capacity to objectively measure the extent of mineral loss has facilitated its application in a variety of research studies, such as pH-cycling models [13], and it has also been employed in studies monitoring the remineralization of white spot lesions in vivo [16]. Moreover, it offers a valuable clinical advantage by enabling objective pre- and posttreatment comparisons in clinical trials, such as those employing split-mouth designs [17]. In the present study, QLF analysis shows that BGS-7 exhibits the highest recovery amount and recovery rate, suggesting it has superior remineralization potential (Table 3).
Bioactive glass, an innovative bioactive material, has been developed and is now widely used in various clinical applications across both medicine and dentistry [9]. One of the most extensively studied forms of bioactive glass is 45S5, which has demonstrated the ability to bond with bone and has been used as a bone replacement material [10]. More recently, it has also been utilized to treat dentin hypersensitivity by blocking the dentinal tubules, as its dissolution products precipitate and adhere to the dentine surface, thereby alleviating pain [10,11]. In addition, 52S4 bioactive glass has shown greater efficacy in enamel remineralization than sodium fluoride and CPP-ACP formulations [3].
A more recently developed type of bioactive glass, BGS-7, has garnered considerable attention in biomedical research and has been actively investigated for various clinical applications [18–22]. Unlike conventional bioactive glasses (eg, 45S5 and 52S4), which are primarily composed of SiO₂, Na₂O, CaO, and P₂O₅, BGS-7 replaces sodium oxide (Na₂O) with boron trioxide (B₂O₃), thereby enhancing its structural and bioactive properties. The incorporation of boron is known to improve ion release kinetics through controlled dissolution, thus sustaining remineralization capacity by promoting hydroxyapatite formation [23]. Furthermore, BGS-7 contains a higher concentration of CaO than other bioactive glasses, which contributes to its superior mechanical strength, even compared to hydroxyapatite, a widely used bioactive ceramic [18].
In addition to its compositional advantages, BGS-7 has demonstrated biocompatibility, osteogenic potential, and controlled ion release properties, which are critical for bone regeneration and soft tissue integration. In orthopedics, its ability to enhance osteoblastic differentiation and osseointegration has been extensively documented [20,21], while in plastic surgery, BGS-7-polymer composites (polycaprolactone/BGS-7) have exhibited favorable bone-binding properties and clinical safety with minimal complications in clinical applications in vivo [22]. However, despite these promising properties, studies on the dental applications of BGS-7, particularly regarding its potential efficacy in enamel remineralization, remain limited. Thus, the present study aimed to investigate the remineralizing effect of BGS-7 on demineralized enamel.
The superior remineralization capacity of BGS-7 compared to fluoride-based agents (Clinpro XT varnish and 1.23% APF gel) may be attributed to its unique apatite-like layer formation, as evidenced by FE-SEM images showing dense needle-like crystallites on demineralized enamel surfaces (Figure 2H). EDS data revealed the simultaneous presence of silicon (5.53 wt%) and fluoride (3.01 wt%) in the newly formed layers (Figure 3D), suggesting a synergistic mechanism where silica gel matrix formation facilitates sustained Ca²⁺/PO₄³⁻ deposition through silicon dissolution [24]. This prolonged ion release from BGS-7, mediated by its boron-substituted composition, contrasts with the rapid fluoride depletion observed in APF gel. Clinpro XT’s intermediate performance may stem from its RMGI properties, though its efficacy remains limited by surface-level fluorapatite formation [25].
Supporting the current findings, several reviews have established that bioactive glass facilitates the formation of an apatite-like layer on enamel and dentin surfaces, enhancing remineralization of carious lesions [6]. In line with these studies, our results demonstrate that BGS-7 exhibits superior remineralization efficacy on demineralized enamel surfaces compared to the fluoride-based agents used in this study. For a more comprehensive understanding of the remineralization capacity of BGS-7, it will be necessary to conduct comparative studies with other established types of bioactive glass.
Nonetheless, this study has several limitations. VHN and QLF values for sound enamel were not obtained, which would have provided a more comprehensive baseline for comparison. Additionally, the relatively small sample size may limit the generalizability of the findings. To minimize inter-specimen variability and enhance consistency, the same specimens were used for QLF and FE-SEM analyses after microhardness measurement. However, to obtain more reliable results and to minimize interference between analyses on the specimens, it would be preferable to use separate specimens for each analysis with an increased sample size. Moreover, employing advanced analytical methods such as micro-computed tomography, X-ray diffraction, Fourier-transform infrared spectroscopy, or Raman spectroscopy would enable a more comprehensive analysis of the remineralized layer’s structural and compositional characteristics [26,27]. Furthermore, future studies are needed to establish standardized clinical application protocols, including determination of the optimal concentration and duration, as well as the development of clinically convenient and effective formulations.
CONCLUSIONS
Within the limitations of this study, we can infer that the application of BGS-7 varnish promoted the remineralization of demineralized enamel, as demonstrated by the evaluations conducted. Among the experimental groups, BGS-7 exhibited superior remineralization capacity. These results suggest the potential use of BGS-7 as a remineralizing material.
Notes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING/SUPPORT
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (NRF-2022R1G1A1010061).
AUTHOR CONTRIBUTIONS
Conceptualization, Funding acquisition, Investigation, Supervision: Choi Y. Data curation, Formal analysis, Resources, Visualization: Lee C. Methodology: Jeong E. Project administration, Validation: Park SJ. Software: Sung KH. Writing - original draft: Lee C. Writing - review & editing: Choi Y.
DATA SHARING STATEMENT
The datasets are not publicly available but are available from the corresponding author upon reasonable request.