Inorganic Compounds as Remineralizing Fillers in Dental Restorative Materials: Narrative Review

Secondary caries is one of the leading causes of resin-based dental restoration failure. It is initiated at the interface of an existing restoration and the restored tooth surface. It is mainly caused by an imbalance between two processes of mineral loss (demineralization) and mineral gain (remineralization). A plethora of evidence has explored incorporating several bioactive compounds into resin-based materials to prevent bacterial biofilm attachment and the onset of the disease. In this review, the most recent advances in the design of remineralizing compounds and their functionalization to different resin-based materials' formulations were overviewed. Inorganic compounds, such as nano-sized amorphous calcium phosphate (NACP), calcium fluoride (CaF₂), bioactive glass (BAG), hydroxyapatite (HA), fluorapatite (FA), and boron nitride (BN), displayed promising results concerning remineralization, and direct and indirect impact on biofilm growth. The effects of these compounds varied based on these compounds' structure, the incorporated amount or percentage, and the intended clinical application. The remineralizing effects were presented as direct effects, such as an increase in the mineral content of the dental tissue, or indirect effects, such as an increase in the pH around the material. In some of the reported investigations, inorganic remineralizing compounds were combined with other bioactive agents, such as quaternary ammonium compounds (QACs), to maximize the remineralization outcomes and the antibacterial action against the cariogenic biofilms. The reviewed literature was mainly based on laboratory studies, highlighting the need to shift more toward testing the performance of these remineralizing compounds in clinical settings.

Bibliometric Analysis of Literature Published on Antibacterial Dental Adhesive from 1996-2020

This study aimed to investigate the current state of research on antibacterial dental adhesives. The interest in this field can be drawn from an increasing number of scholarly works in this area. However, there is still a lack of quantitative measurement of this topic. The main aim of this study was to consolidate the research published on the antibacterial adhesive from 1996 to 2020 in Web of Science indexed journals. The bibliometric method, a quantitative study of investigating publishing trends and patterns, was used for this study. The result has shown that a gradual increase in research was found, whereby a substantial increase was observed from 2013. A total of 248 documents were published in 84 journals with total citations of 5107. The highly cited articles were published mainly in Q1 category journals. Most of the published articles were from the USA, China, and other developed countries; however, some developing countries contributed as well. The authorship pattern showed an interdisciplinary and collaborative approach among researchers. The thematic evaluation of keywords along with a three-factor analysis showed that 'antibacterial adhesives' and 'quaternary ammonium' have been used commonly. This bibliometric analysis can provide direction not only to researchers but also to funding organizations and policymakers.

Use of Protein Repellents to Enhance the Antimicrobial Functionality of Quaternary Ammonium Containing Dental Materials

An advancement in preventing secondary caries has been the incorporation of quaternary ammonium containing (QAC) compounds into a composite resin mixture. The permanent positive charge on the monomers allows for electrostatic-based killing of bacteria. Spontaneous adsorption of salivary proteins onto restorations dampens the antimicrobial capabilities of QAC compounds. Protein-repellent monomers can work with QAC restorations to achieve the technology's full potential. We discuss the theory behind macromolecular adsorption, direct and indirect characterization methods, and advances of protein repellent dental materials. The translation of protein adsorption to microbial colonization is covered, and the concerns and fallbacks of the state-of-the-art protein-resistant monomers are addressed. Last, we present new and exciting avenues for protein repellent monomer design that have yet to be explored in dental materials.

Improvement in the Microbial Resistance of Resin-Based Dental Sealant by Sulfobetaine Methacrylate Incorporation

Prevention of dental caries is a key research area, and improvement of the pit and fissure sealants used for caries prevention has been of particular interest. This report describes results of incorporating a zwitterion, sulfobetaine methacrylate (SB), into photo-polymerized resin-based sealants to enhance resistance to cariogenic bacteria and protein adhesion. Varying amounts (1.5–5 wt%) of SB were incorporated into a resin-based sealant, and the flexural strength, wettability, depth of cure, protein adhesion, bacterial viability, and cell cytotoxicity of the resultant sealants were evaluated. The flexural strength decreased with the increasing SB content, but this decrease was statistically significant only for sealants containing ≥3 wt% SB. Incorporating a zwitterion led to a significant reduction in the water contact angle and protein adhesion. The colony-forming unit count showed a significant reduction in the bacterial viability of S. mutans, which was confirmed with microscopic imaging. Moreover, cell cytotoxicity analysis of SB-modified sealants using an L929 fibroblast showed a cytotoxicity comparable to that of an unmodified control, suggesting no adverse effects on the cellular metabolism upon SB introduction. Hence, we conclude that the addition of 1.5–3 wt% SB can significantly enhance the inherent ability of sealants to resist S. mutans adhesion and prevent dental caries.

Functional Coatings for Orthodontic Archwires-A Review

In this literature review, the current state-of-art of coatings for orthodontic archwires’ increasing antimicrobial and relevant mechanical properties, such as surface topography, friction or corrosion resistance, has been presented. There is a growing request for orthodontic appliances, therefore, most researchers focus on innovative functional coatings to cover orthodontic archwires and brackets. Orthodontic appliances are exposed to the unfavorable oral cavity environment, consisting of saliva flow, food, temperature and appliance force. As a consequence, friction or biocorrosion processes may occur. This can affect the functionality of the orthodontic elements, causing changes in their microstructure, surface topography and mechanical properties. Furthermore, the material which the orthodontic archwire is made from is of particular importance in terms of the possible corrosion resistance. This is especially important for patients who are hypersensitive to metals, for example, nickel, which causes allergic reactions. In the literature, there are some studies, carried out in vitro and in vivo, mostly examining the antibacterial, antiadherent, mechanical and roughness properties of functional coatings. They are clinically acceptable but still some properties have to be studied and be developed for better results. In this paper the influence of additives such as nanoparticles of silver and nitrogen-doped TiO₂ applied on orthodontic brackets by different methods on the antimicrobial properties was analyzed. Future improvement of coating techniques as well as modification of the archwire composition can reduce the release of nickel ions and eliminate friction and bacterial adhesion problems, thus accelerating treatment time.

Synergetic Effect of 2-Methacryloyloxyethyl Phosphorylcholine and Mesoporous Bioactive Glass Nanoparticles on Antibacterial and Anti-Demineralisation Properties in Orthodontic Bonding Agents

2-methacryloyloxyethyl phosphorylcholine (MPC) is known to have antibacterial and protein-repellent effects, whereas mesoporous bioactive glass nanoparticles (MBN) are known to have remineralisation effects. We evaluated the antibacterial and remineralisation effects of mixing MPC and MBN at various ratios with orthodontic bonding agents. MPC and MBN were mixed in the following weight percentages in CharmFil-Flow (CF): CF, 3% MPC, 5% MPC, 3% MPC + 3% MBN, and 3% MPC + 5% MBN. As the content of MPC and MBN increased, the mechanical properties of the resin decreased. At 5% MPC, the mechanical properties decreased significantly with respect to CF (shear bond strength), gelation of MPC occurred, and no significant difference was observed in terms of protein adsorption compared to the control group. Composition 3% MPC + 5% MBN exhibited the lowest protein adsorption because the proportion of hydrophobic resin composite decreased; CF (91.8 ± 4.8 μg/mL), 3% MPC (73.9 ± 2.6 μg/mL), 3% MPC + 3% MBN (69.4 ± 3.6 μg/mL), and 3% MPC + 5% MBN (55.9 ± 1.6 μg/mL). In experiments against S. mutans and E. coli, addition of MPC and MBN resulted in significant antibacterial effects. In another experiment, the anti-demineralisation effect was improved when MPC was added, and when MBN was additionally added, it resulted in a synergetic effect. When MPC and MBN were added at an appropriate ratio to the orthodontic bonding agents, the protein-repellent, antibacterial, and anti-demineralisation effects were improved. This combination could thus be an alternative way of treating white spot lesions.