Abstract
Objectives
The aim of this study was to examine the effects of 45S5 bioactive glass (BAG) on the acid neutralizing, mechanical and physical properties of pit and fissure sealants.
Methods
45S5BAG (<25 μm) was mixed with the silanized glass (180 ± 30 nm) and added into a resin matrix [Bis-GMA/TEGDMA 50/50 (wt%) containing 1% of DMAEMA/CQ 2:1 (wt%)] with varying filler proportions; 0% 45S5BAG + 50% glass (BAG0); 12.5% 45S5BAG + 37.5% glass (BAG12.5); 25% 45S5BAG + 25% glass (BAG25); 37.5% 45S5BAG + 12.5% glass (BAG37.5); and 50% 45S5BAG + 0% glass (BAG50). To evaluate the acid neutralizing properties, specimens were immersed in lactic acid solution (pH 4.0). Then, the change in pH and the time required to raise the pH from 4.0 to 5.5 were measured. In addition, flexural strength, water sorption and solubility were analyzed.
Results
The acid neutralizing properties of each group exhibited increasing pH values as more 45S5BAG was added, and the time required to raise the pH from 4.0 to 5.5 became shorter as the proportion of 45S5BAG increased ( P < 0.05). Additionally, the flexural strength decreased according to the increasing proportions of 45S5BAG added ( P < 0.05). Water sorption showed an increasing trend with increasing proportions of 45S5 BAG added ( P < 0.05). However, the solubility results were similar among the groups ( P > 0.05), except for BAG50.
Significance
The novel pit and fissure sealants neutralized the acid solution (pH 4.0) and exhibited appropriate mechanical and physical properties. Therefore, these compounds are suitable candidates for caries-inhibiting dental materials.
1
Introduction
Tooth caries or dental caries, a bacterial infection in the mouth, is the most common dental disease. Miller’s chemico-parasitic theory is the most widely accepted mechanism for dental caries, which describes the formation of dental caries in the following steps: 1) various resident bacteria in the mouth metabolize acid from fermentable carbohydrate; 2) the pH decreases as acid is generated by bacteria, causing demineralization of the tooth structure; and 3) demineralization is sustained and caries are formed . For these reasons, cariogenic bacteria play an important role in the formation of dental caries . Therefore, to inhibit this problem, preventive treatment should be considered for high-risk patients.
Occlusal surfaces are the sites most frequently attacked by dental caries because of their structural irregularity and morphological complexity . These sites are considered to be ideal for the retention of bacteria and food remnants .
To inhibit caries on the occlusal surface, pit and fissure sealants have been used as the most effective preventive materials . These materials are placed in the pits and fissures of occlusal surfaces to arrest caries progression by providing a physical barrier that inhibits the accumulation of microorganisms and food remnants . The application of the pit and fissure sealant to patients with a high risk of dental caries has been proven to be cost-effective for public oral health services .
Nevertheless, secondary caries may form around the sealed pits and fissures on the material-tooth interfaces, due to either the partial loss of materials or the microleakage and gaps induced by polymerization shrinkage . Fluoride released from pit and fissure sealants may prevent caries formation by enhancing remineralization and inhibiting microbial metabolism . However, when considering the long term effects, it has been shown that there is no significant difference in results between the pit and fissure sealants that contain fluoride and those that do not contain fluoride, due to the short fluoride releasing period . A previous study used glass-ionomer materials as a pit and fissure sealant, which released high levels of fluoride while chemically bonded to the tooth structure. However, it exhibited high viscosity, which disabled it from penetrating deeply into narrow fissures and showed poor retention rates, which caused secondary caries .
To inhibit secondary caries formation, some dental composite resins have a cariostatic ability to neutralize acidic saliva and prevent decalcification of restorations around the area . This neutralizing effect is due to the release of OH- ions that originated from the alkaline glass filler embedded in the resin .
45S5 Bioglass ® , a bioactive implant material discovered in 1971, has excellent biocompatibility and has been widely used as a bone filling material in the clinic due to its capacity for bone regeneration . 45S5 Bioglass ® is currently used in dentistry for air polishing or caries removal procedures, which simultaneously causes the remineralization of the dental hard tissue, including enamel and dentin . Additionally, this glass particle possesses antibacterial properties that are attributed to the high aqueous pH value, caused by the release of alkali ions .
There have been many studies that have examined either the remineralization effect or the antibacterial ability of the bioactive glass. However, the effects of bioactive glass’ acid neutralizing ability have not been investigated. Therefore, the aim of this study was to investigate the neutralizing ability of 45S5 bioactive glass (BAG) on acid that causes dental caries, for the possible application of these materials as dental pit and fissure sealants. This was accomplished by incorporating varying quantities of 45S5 BAG filler into the resin matrix in order to make novel pit and fissure sealants and examining its effects on the acid neutralizing ability, flexural strength, water sorption and solubility. The null hypothesis of this study was that pit and fissure sealants containing 45S5 BAG filler would not result in significant differences in the acid neutralizing, mechanical and physical properties compared to those of pit and fissure sealants without the 45S5 BAG filler.
2
Materials and methods
2.1
Preparation of 45S5 BAG powder
High purity silicon dioxide (SiO 2 , Junsei Chemical Co., Tokyo, Japan), sodium carbonate (Na 2 CO 3 , Duksan Pure Chemicals Co., Ansan-city, Korea), calcium carbonate (CaCO 3 , Samchun Pure Chemicals Co., Pyeongtaek city, Korea), and phosphorus pentoxide (P 2 O 5 , Sigma–Aldrich, Steinheim, Germany) powders were weighted and mixed to obtain an identical composition to 45S5 Bioglass ® (45.0 SiO 2 , 24.5 CaO, 24.5 Na 2 O, 6.0 P 2 O 5 in wt.%).
The powder mixture was melted in a platinum crucible for 4 h at 1400 °C. The melted product was then conventionally quenched onto a graphite plate at room temperature and ground using a mortar and pestle to make fine powder. The ground powder was filtered through a 500-mesh sieve to obtain fine particles less than 25 μm in size and was not silanized for proper ion release from 45S5 BAG in an aqueous environment.
The amorphous structure of the 45S5 BAG powder was identified by X-ray diffraction analysis (XRD, Ultima IV, Rigaku, Tokyo, Japan). A 2 θ angle range between 10° and 70° was selected with a scanning speed of 1°/min.
2.2
Preparation of novel pit and fissure sealants
To make the pit and fissure sealants, silanized dental glass powder (180 ± 30 nm; NanoFine ® NF180, Schott, Landshut, Germany) was selected, which is used as a conventional glass filler in dental composite resin.
A resin matrix of 49.5% Bisphenol A glycerolate dimethacrylate (Bis-GMA, Sigma–Aldrich, Steinheim, Germany) and 49.5% Triethylene glycol dimethacrylate (TEGDMA, Sigma–Aldrich, Steinheim, Germany) in a 1:1 mass ratio was mixed with 0.3% Camphorquinone (CQ, Sigma–Aldrich, Steinheim, Germany) and 0.6% 2-(Dimethylamino)ethyl methacrylate (Sigma–Aldrich, Steinheim, Germany) for light polymerization. Five groups were fabricated with varying filler proportions ( Table 1 ).
| Group | Resin matrix | Content of 45S5 BAG filler | Content of silanized dental glass filler |
|---|---|---|---|
| BAG0 | 50.0 | 0 | 50.0 |
| BAG12.5 | 50.0 | 12.5 | 37.5 |
| BAG25 | 50.0 | 25.0 | 25.0 |
| BAG37.5 | 50.0 | 37.5 | 12.5 |
| BAG50 | 50.0 | 50.0 | 0 |
2.3
Acid neutralizing property
To make the specimens, a stainless steel mold (25 mm × 2 mm × 2 mm) was placed onto a polyester film on a microscope slide glass (76 mm × 26 mm × 1 mm; Paul Marienfeld GmbH, Bad Mergentheim, Germany). Then, the mold was filled with pit and fissure sealants, avoiding the formation of air bubbles. A polyester film was then placed onto the material and covered with a microscope slide glass. All materials were photocured on one side such that each section had been irradiated for 20 s using a LED light-curing unit (Elipar™ S10, 3 M ESPE Co., Seefeld, Germany) until the entire length of the specimen had been irradiated. The irradiation procedure was repeated on the other side of the material. Then, the specimen was separated from the mold and any flash on the samples was carefully removed with 400 grit abrasive paper.
To investigate the neutralizing ability of each group, lactic acid (Sigma–Aldrich, Steinheim, Germany) solution (pH 4.0) was prepared. Three specimens were immersed in 2.14 mL of lactic acid solution, yielding a specimen/solution ratio of 0.14 cm 3 /1 mL , at a temperature of (25 ± 1) °C. Changes in the acid solution’s pH were determined using a digital pH-meter (Orion 4 Star, Thermo Fisher Scientific Inc., Singapore), which had been calibrated at pH 4.01 and pH 7.00 immediately before use. The pH measurement was performed as soon as the specimens were submerged in lactic acid solution. The pH change of the solution was monitored with a pH electrode for 180 min and data were acquired each minute. Furthermore, the time required for the solution’s pH to rise from 4.0 to 5.5 was recorded for 180 min.
2.4
Three-point flexural strength
A three-point flexural strength was measured according to the method outlined in ISO 4049 (2009). The specimens were prepared via the same method described above for the acid neutralizing property and stored in distilled water at (37 ± 1) °C until the start of testing.
The specimen was fractured at a crosshead speed of 1 mm/min on a computer-controlled flexural strength test apparatus (Instron 5942, Instron, Massachusetts, USA). The maximum load was recorded and the flexural strength (S) was calculated using the following equation: S = 3 Fl /(2 bh 2 ), where F is the maximum fracture load, l is the distance of support (20 mm), b is the width of specimen, and h is height of specimen.
2.5
Water sorption and solubility
A test was performed to measure the water sorption and solubility of the sealant according to ISO 4049 (2009). Specimens (15 ± 0.1) mm in diameter and (1.0 ± 0.1) mm in thickness were prepared. All the specimens were placed in a desiccator maintained at (37 ± 1) °C. After 22 h, the specimens were removed and stored in a desiccator maintained at (23 ± 1) °C for 2 h, and then they were weighted in an analytical balance (accurate to 0.01 mg) (XS105, Mettler-toledo AG, Greifensee, Switzerland) with a reproducibility of 0.1 mg until a constant mass ( m 1 ) was obtained. The diameter and thickness of the specimens were measured using a digital caliper (accurate to 0.01 mm) (Mitutoyo, Japan). The mean diameter value of the specimen was calculated by measuring two diameters, and the mean thickness value of specimen was calculated by measuring four equally spaced points on the circumference. These values were then used to calculate the volume ( V ) of all samples (in 0.01 mm 3 ). Following these procedures, they were stored for 7 days in distilled water at (37 ± 1) °C, blotted until free from visible moisture, waved in the air for 15 s, and weighed for mass ( m 2 ). Finally, each disk was placed in a desiccator and weighed daily until a constant dry mass ( m 3 ) was obtained. Water sorption and solubility were calculated using the following equations: W sp = ( m 2 − m 3 )/ V , W sl = ( m 1 − m 3 )/ V where W sp is the absorption of the test material (μg/mm 3 ) and W sl is the solubility of the test material (μg/mm 3 ).
2.6
Statistical analysis
The results of each test were analyzed with one-way ANOVA (PASW 18.0, IBM Co., USA) followed by Tukey’s statistical test at a significance level of 0.05.
2
Materials and methods
2.1
Preparation of 45S5 BAG powder
High purity silicon dioxide (SiO 2 , Junsei Chemical Co., Tokyo, Japan), sodium carbonate (Na 2 CO 3 , Duksan Pure Chemicals Co., Ansan-city, Korea), calcium carbonate (CaCO 3 , Samchun Pure Chemicals Co., Pyeongtaek city, Korea), and phosphorus pentoxide (P 2 O 5 , Sigma–Aldrich, Steinheim, Germany) powders were weighted and mixed to obtain an identical composition to 45S5 Bioglass ® (45.0 SiO 2 , 24.5 CaO, 24.5 Na 2 O, 6.0 P 2 O 5 in wt.%).
The powder mixture was melted in a platinum crucible for 4 h at 1400 °C. The melted product was then conventionally quenched onto a graphite plate at room temperature and ground using a mortar and pestle to make fine powder. The ground powder was filtered through a 500-mesh sieve to obtain fine particles less than 25 μm in size and was not silanized for proper ion release from 45S5 BAG in an aqueous environment.
The amorphous structure of the 45S5 BAG powder was identified by X-ray diffraction analysis (XRD, Ultima IV, Rigaku, Tokyo, Japan). A 2 θ angle range between 10° and 70° was selected with a scanning speed of 1°/min.
2.2
Preparation of novel pit and fissure sealants
To make the pit and fissure sealants, silanized dental glass powder (180 ± 30 nm; NanoFine ® NF180, Schott, Landshut, Germany) was selected, which is used as a conventional glass filler in dental composite resin.
A resin matrix of 49.5% Bisphenol A glycerolate dimethacrylate (Bis-GMA, Sigma–Aldrich, Steinheim, Germany) and 49.5% Triethylene glycol dimethacrylate (TEGDMA, Sigma–Aldrich, Steinheim, Germany) in a 1:1 mass ratio was mixed with 0.3% Camphorquinone (CQ, Sigma–Aldrich, Steinheim, Germany) and 0.6% 2-(Dimethylamino)ethyl methacrylate (Sigma–Aldrich, Steinheim, Germany) for light polymerization. Five groups were fabricated with varying filler proportions ( Table 1 ).
| Group | Resin matrix | Content of 45S5 BAG filler | Content of silanized dental glass filler |
|---|---|---|---|
| BAG0 | 50.0 | 0 | 50.0 |
| BAG12.5 | 50.0 | 12.5 | 37.5 |
| BAG25 | 50.0 | 25.0 | 25.0 |
| BAG37.5 | 50.0 | 37.5 | 12.5 |
| BAG50 | 50.0 | 50.0 | 0 |
2.3
Acid neutralizing property
To make the specimens, a stainless steel mold (25 mm × 2 mm × 2 mm) was placed onto a polyester film on a microscope slide glass (76 mm × 26 mm × 1 mm; Paul Marienfeld GmbH, Bad Mergentheim, Germany). Then, the mold was filled with pit and fissure sealants, avoiding the formation of air bubbles. A polyester film was then placed onto the material and covered with a microscope slide glass. All materials were photocured on one side such that each section had been irradiated for 20 s using a LED light-curing unit (Elipar™ S10, 3 M ESPE Co., Seefeld, Germany) until the entire length of the specimen had been irradiated. The irradiation procedure was repeated on the other side of the material. Then, the specimen was separated from the mold and any flash on the samples was carefully removed with 400 grit abrasive paper.
To investigate the neutralizing ability of each group, lactic acid (Sigma–Aldrich, Steinheim, Germany) solution (pH 4.0) was prepared. Three specimens were immersed in 2.14 mL of lactic acid solution, yielding a specimen/solution ratio of 0.14 cm 3 /1 mL , at a temperature of (25 ± 1) °C. Changes in the acid solution’s pH were determined using a digital pH-meter (Orion 4 Star, Thermo Fisher Scientific Inc., Singapore), which had been calibrated at pH 4.01 and pH 7.00 immediately before use. The pH measurement was performed as soon as the specimens were submerged in lactic acid solution. The pH change of the solution was monitored with a pH electrode for 180 min and data were acquired each minute. Furthermore, the time required for the solution’s pH to rise from 4.0 to 5.5 was recorded for 180 min.
2.4
Three-point flexural strength
A three-point flexural strength was measured according to the method outlined in ISO 4049 (2009). The specimens were prepared via the same method described above for the acid neutralizing property and stored in distilled water at (37 ± 1) °C until the start of testing.
The specimen was fractured at a crosshead speed of 1 mm/min on a computer-controlled flexural strength test apparatus (Instron 5942, Instron, Massachusetts, USA). The maximum load was recorded and the flexural strength (S) was calculated using the following equation: S = 3 Fl /(2 bh 2 ), where F is the maximum fracture load, l is the distance of support (20 mm), b is the width of specimen, and h is height of specimen.
2.5
Water sorption and solubility
A test was performed to measure the water sorption and solubility of the sealant according to ISO 4049 (2009). Specimens (15 ± 0.1) mm in diameter and (1.0 ± 0.1) mm in thickness were prepared. All the specimens were placed in a desiccator maintained at (37 ± 1) °C. After 22 h, the specimens were removed and stored in a desiccator maintained at (23 ± 1) °C for 2 h, and then they were weighted in an analytical balance (accurate to 0.01 mg) (XS105, Mettler-toledo AG, Greifensee, Switzerland) with a reproducibility of 0.1 mg until a constant mass ( m 1 ) was obtained. The diameter and thickness of the specimens were measured using a digital caliper (accurate to 0.01 mm) (Mitutoyo, Japan). The mean diameter value of the specimen was calculated by measuring two diameters, and the mean thickness value of specimen was calculated by measuring four equally spaced points on the circumference. These values were then used to calculate the volume ( V ) of all samples (in 0.01 mm 3 ). Following these procedures, they were stored for 7 days in distilled water at (37 ± 1) °C, blotted until free from visible moisture, waved in the air for 15 s, and weighed for mass ( m 2 ). Finally, each disk was placed in a desiccator and weighed daily until a constant dry mass ( m 3 ) was obtained. Water sorption and solubility were calculated using the following equations: W sp = ( m 2 − m 3 )/ V , W sl = ( m 1 − m 3 )/ V where W sp is the absorption of the test material (μg/mm 3 ) and W sl is the solubility of the test material (μg/mm 3 ).
2.6
Statistical analysis
The results of each test were analyzed with one-way ANOVA (PASW 18.0, IBM Co., USA) followed by Tukey’s statistical test at a significance level of 0.05.
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