Highlights• 2:1 CaAl and MgAl LDH dental composites were developed with varying LDH loading.• Fluoride absorption/release was studied (five recharge cycles) in DW and AS.• Water uptake, solubility, cation release, and mechanical properties were studied.• LDH-composites repeatedly absorbed/released fluoride maintaining a sustained release.• Physico-mechanical properties of composites were maintained with LDH-composites.
This systematic review appraises studies conducted with layered double hydroxides (LDHs) for fluoride release in dentistry. LDH has been used as antacids, water purification in removing excess fluoride in drinking water and drug delivery. It has great potential for controlled fluoride release in dentistry, e.g., varnishes, fissure sealants and muco-adhesive strips, etc. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement was followed with two reviewers performing a literature search using four databases: PubMed, Web of Science, Science Direct and Ovid Medline with no date restrictions. Studies including any LDH for ion/drug release in dentistry were included, while assessing the application of LDH and the value of the methodology, e.g., ion release protocol and the LDH production process. Results: A total of 258 articles were identified and four met the inclusion criteria. Based on two in vitro studies and one clinical study, LDH was previously studied in dental materials, such as dental composites and buccal muco-adhesive strips for fluoride release, with the latter studied in a clinical environment. The fourth study analysed LDH powder alone (without being incorporated into dental materials). It demonstrated fluoride release and the uptake of volatile sulphur compounds (VSC), which may reduce halitosis (malodour). Conclusion: LDHs incorporated in dental materials have been previously evaluated for fluoride release and proven to be clinically safe. LDHs have the potential to sustain a controlled release of fluoride (or other cariostatic ions) in the oral environment to prevent caries. However, further analyses of LDH compositions, and clinical research investigating any other cariostatic effects, are required.
Objective. Tetrahydrofurfuryl-methacrylate (THFM) and hydroxypropyl-methacrylate (HPM) were used to partially or fully replace HEMA in experimental RMGICs. The experimental materials were compared with home and commercial products in terms of degree of conversion, polymerization shrinkage and exotherm. Methods. Two commercial RMGICs used were Fuji-Plus (GC, Japan) and RelyX-Luting (RX, 3M-ESPE, USA). Two additional in-house liquids were prepared based on the commercial materials liquids. Eight experimental liquid compositions (F1, F2, F3 and F4 based on Fuji-Plus; R1, R2, R3 and R4 based on RelyX-Luting) were prepared replacing 100% HEMA with HPM in F1 and R1 or HPM/THFM in F2 and R2. 50% HEMA was replaced with THFM in F3 and R3 compared to 30% in F4 and R4. All liquids were mixed with the corresponding commercial powder. Degree of conversion was determined using Fourier-transform infrared spectroscopy (FT-IR). Polymerization shrinkage and exotherm were measured using the bonded-disk method. Results. Compositions containing HPM (FP and RX) showed lower degree of conversion compared to experimental compositions containing THFM, home and commercial materials (p<0.0001). FP-commercial showed significantly higher polymerization shrinkage and exotherm compared to all other materials in both groups (p<0.0001). FP-commercial showed higher degree of polymerization shrinkage and exotherm at 5 minutes compared to all materials due to the incorporation of an additional cross-linker (glycerol-dimethacrylate). In general, compositions containing THFM, presented polymerization shrinkage and degree of conversion values similar to their corresponding commercial products. Significance. THFM monomer showed promising results and could be potentially useful in the development of new RMGICs with improved properties.
All new experimental compositions demonstrated working and setting times that are clinically acceptable. The new experimental FP compositions containing THFM (especially F3 and F4) demonstrated improved mechanical properties compared to their corresponding home material.
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