Release and Recharge of Fluoride Ions from Acrylic Resin Modified with Bioactive Glass

Fluoride Release and Rechargeability of Poly(lactic acid) Composites with Glass Ionomer Cement

This study investigates the fluoride release, rechargeability and degradation behaviors of newly developed anticariogenic poly(lactic acid) (PLA) composites. The PLA composite with various concentrations (0%, 5%, 10%, 15% and 20% by weight) of glass ionomer cement (GIC) and sodium fluoride (NaF) were prepared using solvent casting method. The fluoride release, fluoride rechargeability and degradation behavior were evaluated. All experimental groups demonstrated fluoride-releasing ability. The highest level of fluoride ions released was found in PLA composite with sodium fluoride (PLA/NaF). Following the 28-day period, both groups showed a gradual reduction in fluoride ion released, ranging between 0.03 ± 0.01 and 0.53 ± 0.06 ppm, although remaining within the effective range for tooth remineralization. However, the rechargeability was only observed in PLA composite with GIC (PLA/GIC). Following an eight-week in vitro degradation test, all PLA/NaF groups displayed a significantly higher percentage of weight change and water absorption compared to the PLA/GIC and the control group. In SEM analysis, the formation of surface porosities was clearly noticed in all PLA/NaF. All specimens retained their structural integrity throughout the study. In conclusion, the newly developed PLA/GIC displays promising possibilities as an anticariogenic material. Furthermore, the rechargeability of these ions are repeatable, ensuring their long-term utility.

Highlights on Drug and Ion Release and Recharge Capacity of Antimicrobial Removable Prostheses

This article aimed to review the ion and drug release, recharge abilities, and antimicrobial properties of drug/ion-releasing removable prostheses, and to assess their capability in preventing and inhibiting denture stomatitis as well preventing caries and reversing carious lesions. Data was collected from published scientific papers listed in PubMed database from January 1975 to December 2021. English full-text articles, involving clinical or in vitro studies, focusing on removable prostheses and are concerned with drug/ion release and rechargeability as a way to prevent or inhibit denture stomatitis or dental caries were included. The relevant articles reported that ion- or drug-modified polymethylmethacrylate acts as a reservoir for these ions and drugs and is capable of releasing significant amounts with sustained release effect. Recharging of modified resin resulted in greater sustainability of ion and drug release, thus improving the long-term effects of protection against demineralization and reducing the adhesion of Streptococcus mutans and Candida albicans. Modifications of removable prostheses with rechargeable ions and drugs enhance remineralization, hinder demineralization, and reduce microbial adhesion in difficult-to-access areas. Selection of denture base for clinical use will consider its ability to act as an ion/drug reservoir that is capable of release and recharge.

Comparison of Mechanical Properties of Three Tissue Conditioners: An Evaluation In Vitro Study

Introduction: Tissue conditioners have been widely used in various clinical applications in dentistry, such as treating inflamed alveolar ridges, temporarily relining partial and complete dentures, and the acquisition of functional impressions for denture fabrication. This study aimed to investigate the mechanical properties of the most prevalent tissue conditioner materials on the market, including Tissue Conditioners (TC), Visco Gel (VG), and FITT (F). Materials and Methods: The three tissue conditioners, TC, VG, and F, were assessed based on the parameters mentioned above. The following tests were performed based on the ISO 10139-1 and ISO 10139-2 requirements: Shore A hardness, denture plate adhesion, sorption, water solubility, and contraction after 1 and 3 days in water. Additional tests are described in the literature, such as ethanol content and gelling time. The tests were carried out by storing the materials in water at 37 °C for 7 days. Results: The gel times of all tested materials exceeded 5 min (TC = 300 [s], VG = 350 [s]). In vitro, phthalate-free materials exhibited higher dissolution in water after 14 days (VG = -260.78 ± 11.31 µg/mm2) compared to F (-76.12 ± 7.11 µg/mm2) and experienced faster hardening when stored in distilled water (F = 33.4 ± 0.30 Sh. A, VG = 59.2 ± 0.60 Sh. A). They also showed greater contractions. The connection of all materials to the prosthesis plate was consistent at 0.11 MPa. The highest counterbalance after 3 days was observed in TC = 3.53 ± 1.12%. Conclusions: Materials containing plasticizers that are not phthalates have worse mechanical properties than products containing these substances. Since phthalates are not allowed to be used indefinitely in medical devices, additional research is necessary, especially in vivo, to develop safe materials with superior functional properties to newer-generation alternatives. In vitro results often do not agree fully with those of in vivo outcomes.

Bioactive Glass-Enhanced Resins: A New Denture Base Material

BACKGROUND

The creation of the denture base material with bioactive properties that releases ions and produces hydroxyapatite.

METHODS

Acrylic resins were modified by the addition of 20% of four types of bioactive glasses by mixing with powders. Samples were subjected to flexural strength (1, 60 days), sorption and solubility (7 days), and ion release at pH 4 and pH 7 for 42 days. Hydroxyapatite layer formation was measured using infrared.

RESULTS

Biomin F glass-containing samples release fluoride ions for a period of 42 days (pH = 4; Ca = 0.62 ± 0.09; P = 30.47 ± 4.35; Si = 22.9 ± 3.44; F = 3.1 ± 0.47 [mg/L]). The Biomin C (contained in the acrylic resin releases (pH = 4; Ca = 41.23 ± 6.19; P = 26.43 ± 3.96; Si = 33.63 ± 5.04 [mg/L]) ions for the same period of time. All samples have a flexural strength greater than 65 MPa after 60 days.

CONCLUSION

The addition of partially silanized bioactive glasses allows for obtaining a material that releases ions over a longer period of time.

CLINICAL SIGNIFICANCE

This type of material could be used as a denture base material, helping to preserve oral health by preventing the demineralization of the residual dentition through the release of appropriate ions that serve as substrates for hydroxyapatite formation.

Effect of Particle Sizes and Contents of Surface Pre-Reacted Glass Ionomer Filler on Mechanical Properties of Auto-Polymerizing Resin

Herein, the mechanical properties of an auto-polymerizing resin incorporated with a surface pre-reacted glass ionomer (S-PRG) filler were evaluated. For this, S-PRG fillers with particle sizes of 1 μm (S-PRG-1) and 3 μm (S-PRG-3) were mixed at 10, 20, 30, and 40 wt% to prepare experimental resin powders. The powders and a liquid (powder/liquid ratio = 1.0 g/0.5 mL) were kneaded and filled into a silicone mold to obtain rectangular specimens. The flexural strength and modulus (n = 12) were recorded via a three-point bending test. The flexural strengths of S-PRG-1 at 10 wt% (62.14 MPa) and S-PRG-3 at 10 and 20 wt% (68.68 and 62.70 MPa, respectively) were adequate (>60 MPa). The flexural modulus of the S-PRG-3-containing specimen was significantly higher than that of the S-PRG-1-containing specimen. Scanning electron microscopy observations of the specimen fracture surfaces after bending revealed that the S-PRG fillers were tightly embedded and scattered in the resin matrix. The Vickers hardness increased with an increasing filler content and size. The Vickers hardness of S-PRG-3 (14.86–15.48 HV) was higher than that of S-PRG-1 (13.48–14.97 HV). Thus, the particle size and content of the S-PRG filler affect the mechanical properties of the experimental auto-polymerizing resin.

Evaluation of the effectiveness of bioactive glass fillers against Candida albicans adhesion to PMMA denture base materials: An in vitro study

Background

Dentures with antimicrobial properties are desirable for preventing Candida albicans adhesion. This study was to assess the effectiveness of bioactive glass (BAG) on C. albicans adhesion, surface roughness, and hardness of denture base materials.

Methods

Heat-polymerized (HP) and autopolymerized (AP) acrylic resins were used to fabricate 240 disk specimens (120/material, 60/C. albicans, 60/surface roughness and hardness). Specimens were divided into five groups (n = 10) based on the BAG concentration: 0.5, 1.5, 3, 5, and 7.5 wt% of the acrylic powder, with a control group comprised of unmodified specimens. Direct culture method was used to assess C. albicans adhesion. A profilometer and Vickers hardness test were used to measure surface roughness and hardness respectively. Analysis of variance (ANOVA) and post hoc Tukey's test were used for data analysis (α = 0.05).

Results

BAG addition significantly decreased the C. albicans count when compared with the control group (P < 0.001) for both HP and AP. Regarding surface roughness, there was no change in the HP acrylic resins (P > 0.05), while the AP acrylic resins exhibited significantly higher surface roughness with BAG addition (P < 0.001). The hardness of the HP and AP acrylic resins were significantly higher with the addition of BAG (P < 0.001).

Conclusions

The addition of BAG to HP and AP acrylic resins effectively decreases C. albicans adhesion. The roughness of AP acrylic resins increases with the addition of BAG, while the hardness of both HP and AP acrylic resins increase with the addition of BAG.

Novel protein-repellent and antibacterial polymethyl methacrylate dental resin in water-aging for 6 months

Background

The present study aimed to develop a novel protein-repellent and antibacterial polymethyl methacrylate (PMMA) dental resin with 2-methacryloyloxyethyl phosphorylcholine (MPC) and quaternary ammonium dimethylaminohexadecyl methacrylate (DMAHDM), and to investigate the effects of water-aging for 6 months on the mechanical properties, protein adsorption, and antibacterial activity of the dental resin.

Methods

Four groups were tested: PMMA control; PMMA + 3% MPC; PMMA + 1.5% DMAHDM; and PMMA + 3% MPC + 1.5% DMADDM in acrylic resin powder. Specimens were water-aged for 1 d, 3 months, and 6 months at 37 ℃. Their mechanical properties were then measured using a three-point flexure test. Protein adsorption was measured using a micro bicinchoninic acid (BCA) method. A human saliva microcosm model was used to inoculate bacteria on water-aged specimens and to investigate the live/dead staining, metabolic activity of biofilms, and colony-forming units (CFUs).

Results

The flexural strength and elastic modulus showed a significant loss after 6 months of water-ageing for the PMMA control (mean ± SD; n = 10); in contrast, the new protein repellent and antibacterial PMMA resin showed no strength loss. The PMMA–MPC–DMAHDM-containing resin imparted a strong antibacterial effect by greatly reducing biofilm viability and metabolic activity. The biofilm CFU count was reduced by about two orders of magnitude (p < 0.05) compared with that of the PMMA resin control. The protein adsorption was 20% that of a commercial composite (p < 0.05). Furthermore, the PMMA–MPC–DMAHDM-containing resin exhibited a long-term antibacterial performance, with no significant difference between 1 d, 3 months and 6 months (p > 0.05).

Conclusions

The flexural strength and elastic modulus of the PMMA–MPC–DMAHDM-containing resin were superior to those of the PMMA control after 6 months of water-ageing. The novel PMMA resin incorporating MPC and DMAHDM exhibited potent and lasting protein-repellent and antibacterial properties.

Advances in orthodontic clear aligner materials

Rapid technological improvements in biomaterials, computer-aided design (CAD) and manufacturing (CAM) have endorsed clear aligner therapy (CAT) as a mainstay of orthodontic treatment, and the materials employed for aligner fabrication play an all-important role in determining the clinical performance of clear aligners. This narrative review has attempted to comprehensively encompass the entire gamut of materials currently used for the fabrication of clear aligners and elucidate their characteristics that are crucial in determining their performance in an oral environment. Historical developments and current protocols in aligner fabrication, features of contemporary bioactive materials, and emerging trends related to CAT are discussed. Advances in aligner material chemistry and engineering possess the potential to bring about radical transformations in the therapeutic applications of CAT; in the absence of which, clear aligners would continue to underperform clinically, due to their inherent biomechanical constraints. Finally, while innovations in aligner materials such as shape memory polymers, direct three-dimensional (3D) printed clear aligners and bioactive materials combined with clear aligner materials are essential to further advance the applications of CAT; increased awareness of environmental responsibilities among aligner manufacturers, aligner prescribing clinicians and aligner users is essential for better alignment of our climate change goals towards a sustainable planet.

Effects of hybrid inorganic-organic nanofibers on the properties of enamel resin infiltrants - An in vitro study

This in vitro study aimed to evaluate the overall mechanical properties of resin infiltrants doped with bioactive nanofibers and their ability in inhibiting enamel demineralization or achieving remineralization of the adjacent enamel to white spots. A commercial resin infiltrant (ICON, DMG) was doped with hybrid inorganic-organic nanofibers and analyzed for degree of conversion (DC, n = 3) and surface hardness (SH, n = 6). Subsequently, enamel specimens (6 × 4 × 2 mm³) were prepared and submitted to a demineralizing/remineralizing process to produce a subsurface caries-like lesion. The specimens were treated with one of the following materials: ICON infiltrant, DMG (control); ICON + nanofibers of poly-lactic acid (PLA)-filled with silica (PLA-SiO₂); ICON + nanofibers of (PLA)-filled with calcium incorporated into a silica network (SiO₂-CaP). Then, the specimens were subjected to a pH-cycling demineralizing/remineralizing model for 7 days at 37 °C. The %ΔSH change (after treatment), %SH loss and %SH recovery (after pH-cycling regimen) were calculated after SH evaluation (n = 9/group). The Ca/P weight ratio before and after pH-cycling regimen was evaluated through SEM/EDX. The results of DC were analyzed through the T-test (p < 0.05). ANOVA followed by Tukey's test (p < 0.05) was performed for hardness and EDX. A significant SH increase was observed in the ICON/SiO₂CaP group (p < 0.05). The ICON/PLA-SiO₂ presented higher DC values than the control group (p = 0.043). All groups presented significant difference in %ΔSH (p < 0.05), although the specimens treated with ICON/SiO₂CaP presented greater values. Regarding the %SHL and %SHR, the ICON/SiO₂CaP and ICON/PLA-SiO₂ were significantly different compared to the control group (p < 0.001). However, no difference was observed between the ICON/SiO₂CaP and ICON/PLA-SiO_2. The Ca/P ratio showed that the ICON/SiO₂CaP and ICON/PLA-SiO₂ after the pH-cycling regimen differed from sound enamel and modified infiltrants before pH-cycling. In conclusion, tailored hybrid nanofibers may be incorporated into enamel resin infiltrants without compromise the mechanical properties of such experimental materials. These latter can inhibit the demineralization of enamel and increase its hardness during pH-clycling challange.

Mechanical Properties, Cytotoxicity, and Fluoride Ion Release Capacity of Bioactive Glass-Modified Methacrylate Resin Used in Three-Dimensional Printing Technology

Background: Clinically, three-dimensional (3D) printing technology is becoming a popular and efficient dental processing technology. Recently, there has been an increasing demand for dental materials that exhibit bioactive properties. The present study aimed to evaluate the mechanical properties, cytotoxicity, and fluoride ion release capacity of 3D-printed dental resins modified with bioactive glass. Materials and methods: The resin FotoDent splint used in the production of removable orthodontic splints, was modified by the addition of two types of bioactive glasses that are capable of releasing fluoride ions. The novel materials used for the production of dental splints were examined for their mechanical, physical, and biological properties (fracture resistance, sorption, solubility, elution of nonpolymeric substances, and release of fluoride ions over time) and cytotoxic effects on cell cultures. Results: Initially, the fracture toughness of the 3D-printed resin was found to be 55 MPa, but after modification with glass, the resistance was reduced to about 50 MPa. Sorption and solubility values of the materials (19.01 ÷ 21.23 µg/mm³ and 0.42 ÷ 1.12 µg/mm³, respectively) complied with the safety limits imposed by ISO standard. Modified resins were capable of releasing fluoride ions, and the maximum releasing effect was observed after 14 days of incubation. Both the modified resins, after four days of contact with human gingival fibroblasts, exhibited moderate cytotoxic properties. Conclusions: The experimental results showed that modification of methacrylate resin, used in 3D printing technology, with bioactive glasses produces novel dental materials that possess desirable bioactive properties. The findings of this study indicate the potential ability of modified polymethacrylate resins to release fluoride ions in the oral cavity environment. The modified materials are characterized with a moderate decrease in physical properties and mild cytotoxicity on direct contact with human fibroblasts.

Assessment of Microstructure and Release of Fluoride Ions from Selected Fissure Sealants: An In Vitro Study

The aim of this study was to compare fluoride release from four selected fissure sealants: fissure sealant manufactured by Arkona, Helioseal F, Helioseal F Plus, and Conseal. Tested parameters included emission of fluoride ions into saline (0.9% NaCl) and deionized water over a period of 2 weeks. Values were recorded after 1, 3, 24, 48, 72, and 96 h, and then after 1 and 2 weeks. All sealants were characterized by a constant fluoride release level. The highest fluoride release level was noted for Conseal (0.0169 ppm/mg), while the lowest was noted for fissure sealant manufactured by Arkona (0.063 ppm/mg). Fissure sealants, which contain fluoride, release it not only during polymerization, but also for several days after application. The use of fissure sealants whose composition includes fluoride is an effective method of preventing tooth decay.