Syntheses and antimicrobial activities of a series of new bis-quaternary ammonium compounds

Novel dual-functional implants via oxygen non-thermal plasma and quaternary ammonium to promote osteogenesis and combat infections

OBJECTIVE

Implant-related infections are a primary reason for implant failures that affect millions of patients. It is of paramount importance to develop novel implants that possess the dual functions of osteogenesis-promotion and antibacterial activity. The objectives of this study were to: (1) develop novel dual-functional titanium (Ti) implants by combining oxygen non-thermal plasma and covalent bonding of antibacterial organosilicon quaternary ammonium monomers; (2) investigate the physicochemical properties, bioactivity and antibacterial effects of the modified implants for the first time.

METHODS

Surface characteristics of the modified Ti surfaces were tested. Adherence and viability of rat bone marrow-derived stem cells (rBMSCs) on the surface were evaluated. Metabolic activity of biofilm on the surfaces were measured. The stability of the dual-function after 5000 thermal cycles was also evaluated.

RESULTS

The presence of chemical bonding between Ti and organosilicon monomers demonstrated covalent immobilization of the antibacterial agents. The water contact angle of the treated Ti surfaces decreased from 70.98 ± 3.68° to 59.86 ± 4.91°. The adhesion and proliferation of rBMSCs on the modified Ti were increased by 40%, compared to control group (P < 0.05). The metabolic level of biofilms on modified Ti were reduced by more than half, compared to control (P < 0.05). The modified Ti implants exhibited cell-promotion and antibacterial stability after thermal cycles.

SIGNIFICANCE

The new dual-functional Ti implant is promising to promote osteogenesis while simultaneously preventing infections. Furthermore, the novel surface modification and processing methods have applicability to enhancing a wide range of other implants to improve bioactivity and combat infections.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

The mode of antibacterial action of quaternary N-benzylimidazole salts against emerging opportunistic pathogens

Quaternary ammonium compounds (QACs) are antimicrobial agents displaying a broad spectrum of activity due to their mechanism of action targeting the bacterial membrane. The emergence of bacterial resistance to QACs, especially in times of pandemics, requires the continuous search for new and potent QACs structures. Here we report the synthesis and biological evaluation of QACs based on imidazole derivative, N-benzylimidazole. The antimicrobial activity was tested against a range of pathogenic bacteria and fungi, both ATCC and clinical isolates, showing varying activities ranging in minimal inhibitory concentrations (MICs) from as low as 7 ng/mL. The most promising compound, N-tetradecyl derivative (BnI-14), proved to be very potent against bacterial biofilms, even at sub-MIC doses, suggesting interference with the bacterial growth and/or division process. The BnI-14 treatment induces bacterial membrane disruption, as observed by fluorescence spectroscopy and atomic force microscopy and it also binds to DNA indicating that bacterial membrane might not be the only cellular target of QACs. Most importantly, BnI-14 exhibits low toxicity to healthy human cell lines, suggesting that N-benzylimidazolium-based QACs may be promising new antimicrobial agents.

Investigations into the structure-activity relationship in gemini QACs based on biphenyl and oxydiphenyl linker

Eighteen novel gemini quaternary ammonium compounds were synthesized to examine the effect of linker nature, aliphatic chain length and their relative position on antibacterial and antifungal activity. The synthesized compounds showed strong bacteriostatic activity against a panel of both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and two fungi. Some of these compounds exhibited a wider and more potent antimicrobial spectrum than commonly-used antiseptics, such as benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), chlorhexidine digluconate (CHG) and octenidine dihydrochloride (OCT).

Interaction of Ionenes with Lipid Membrane: Unusual Impact of Charge Density

Synthetic water-soluble polymers are increasingly used for gene delivery, stabilization, and delivery of proteins, and as prospective antimicrobial and antiviral agents. Therefore, study of their interaction with lipid membranes is of special importance. Herein, we studied interaction of aliphatic cationic ionenes (recently tested for gene delivery efficiency) differed in the length of spacer between charged groups (and therefore in charge density) with anionic lipid membrane. A range of approaches such as measurement of particle size and electrophoretic mobility, liposome integrity, ATR-FTIR spectroscopy, isothermal titration calorimetry as well as atomistic molecular modeling was used. Ionene with a spacer of 10 methylene groups has been shown to be incorporated into membrane and interact with its inner hydrophobic part in contrast to ionenes with shorter spacer, which interacted only with outer polar head groups of lipids staying at the water-membrane interface. It affects membrane integrity and results in a different behavior of the polymer-liposome complexes. These findings are relevant for potential biomedical application of ionenes, including creation of composite polymer-liposome systems for drug delivery.

Synergistic effect of hen egg white lysozyme and lysosomotropic surfactants on cell viability and membrane permeability

The interactions between two types of quaternary ammonium surfactants (N,N,N-trimethyl-2-(dodecanoyloxy)ethaneammonium bromide (DMM-11) and N,N,N-trimethyl-2-(dodecanoyloxy)propaneammonium bromide (DMPM-11)) and hen egg white lysozyme were studied through several techniques, including isothermal titration calorimetry (ITC), circular dichroism (CD) and fluorescence spectroscopy, and surface tension measurement. The average number of surfactants interacting with each molecule of lysozyme was calculated from the biophysical results. Moreover, the CD results showed that the conformation of lysozyme changed in the presence of DMM-11 and DMPM-11. The studies drew a detailed picture on the physicochemical nature of interactions between both surfactants and lysozyme. Both DMM-11 and DMPM-11, with and without lysozyme were studied against three target microorganisms, including Gram-negative (Escherichia coli) and Gram-positive (Enterococcus hirae and Enterococcus faecalis) bacteria. The results revealed a broad spectrum of antibacterial nature of surfactant/lysozyme complexes, as well as their effect on the membrane damage, hence providing the basis to further explore DMM-11 and DMPM-11 combined with lysozyme as possible antibacterial tools.

Aggregation of Plate-like Colloids Induced by Charged Polymer Chains: Organization at the Nanometer Scale Tuned by Polymer Charge Density

We study the aggregation of charged plate-like colloids, Na-montmorillonite clays, in the presence of ionenes, oppositely charged polymer chains. The choice of the charged polymer allows tuning its linear charge density to match/mismatch the average charge separation on the clay surfaces. We assess the nanoscale structure of the aggregates formed by small-angle X-ray and neutron scattering. The nanoscale features of the formed clay aggregates are dominated by the presence of a stacking peak, giving clear evidence for the formation of clay tactoids, that is, a face-to-face aggregation geometry of the clay platelets. The chain charge density of ionenes influences not only the stacking repeat distance within the clay tactoids but also the extent of stacking and abundance of the tactoids. We may distinguish two regimes as a function of clay and ionene polymer charge densities (ρ_c and ρ_p, respectively). The first regime applies to ρ_p > ρ_c and ρ_p ≈ ρ_c, that is, for highly and "matching" charged chains. Under these conditions, the intercalated chains lie in a flat conformation within the tactoids, irrespective of the ionic strength (within the range studied, i.e., up to 0.05 M NaBr). For weakly charged chains, ρ_p < ρ_c, undulation of the ionene chains within the tactoid is seen. The degree of undulation increases with ionic strength due to the decreasing persistence length of the ionene chains. The extent of stacking (5-10 platelets per tactoid) is a general feature of all the systems, and its origin remains unknown. The system corresponding to the closest match in charge separations on the clay surface and on the polymer chain (ρ_p ≈ ρ_c) features the highest abundance of tactoids. This coincides with the highest macroscopic density as deduced from simple visual inspection of sediment volumes. This leads to the open question regarding the link between the density at the nanoscale and the macroscopic density and sedimentation behavior of the aggregate.

Selenium nanoparticles as anti-infective implant coatings for trauma orthopedics against methicillin-resistant Staphylococcus aureus and epidermidis: in vitro and in vivo assessment

Background: Bacterial infection is a common and serious complication in orthopedic implants following traumatic injury, which is often associated with extensive soft tissue damage and contaminated wounds. Multidrug-resistant bacteria have been found in these infected wounds, especially in patients who have multi trauma and prolonged stay in intensive care units.Purpose: The objective of this study was to develop a coating on orthopedic implants that is effective against drug-resistant bacteria.

Methods and results: We applied nanoparticles (30-70nm) of the trace element selenium (Se) as a coating through surface-induced nucleation-deposition on titanium implants and investigated the antimicrobial activity against drug resistant bacteria including Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-resistant Staphylococcus epidermidis (MRSE) in vitro and in an infected femur model in rats.The nanoparticles were shown in vitro to have antimicrobial activity at concentrations as low as 0.5ppm. The nanoparticle coatings strongly inhibited biofilm formation on the implants and reduced the number of viable bacteria in the surrounding tissue following inoculation of implants with biofilm forming doses of bacteria.

Conclusion: This study shows a proof of concept for a selenium nanoparticle coatings as a potential anti-infective barrier for orthopedic medical devices in the setting of contamination with multi-resistant bacteria. It also represents one of the few (if only) in vivo assessment of selenium nanoparticle coatings on reducing antibiotic-resistant orthopedic implant infections.

Novel Synthesis of Substituted 2-Trifluoromethyl and 2-Perfluoroalkyl N-Arylpyridinium Compounds-Mechanistic Insights

We report a new one-pot synthesis of 2-trifluoromethylated/2-perfluoroalkylated N-aryl-substituted pyridiniums, 5,6,7,8-tetrahydroquinoliniums and 6,7,8,9-tetrahydro-5H-cyclohepta[b]-pyridinium compounds starting from an activated β-dicarbonyl analogue (here a perfluoro-alkylated gem-iodoacetoxy derivative), an aromatic amine and a (cyclic or acyclic) ketone. The key step of this multicomponent reaction, involves the formation of a 3-perfluoroalkyl-N,N’-diaryl-1,5-diazapentadiene intermediate, various examples of which were isolated and characterized for the first time, together with investigation of their reactivity. We propose a mechanism involving a concurrent inverse electron demand Diels-Alder or Aza-Robinson cascade cyclisation, followed by a bis-de-anilino-elimination. Noteworthy, a meta-methoxy substituent on the aniline directs the reaction towards a 2-perfluoroalkyl-7-methoxyquinoline, resulting from the direct cyclization of the diazapentadiene intermediate, instead of pyridinium formation. This is the first evidence of synthesis of pyridinium derivatives from activated β-dicarbonyls, ketones, and an aromatic amine, the structures of which (both reactants and products) being analogous to species involved in biological systems, especially upon neurodegenerative diseases such as Parkinson’s. Beyond suggesting chemical/biochemical analogies, we thus hope to outline new research directions for understanding the mechanism of in vivo formation of pyridiniums, hence possible pharmaceutical strategies to better monitor, control or prevent it.

Quaternary Ammonium Compounds: Simple in Structure, Complex in Application

Quaternary ammonium compounds, referred to as QACs, are cationic substances with a structure on the edge of organic and inorganic chemistry and unique physicochemical properties. The purpose of the present work is to introduce QACs and their wide application potential. Fundamental properties, methods of preparation, and utilization in organic synthesis are reviewed. Modern applications and the use of QACs as reactive substrates, reagents, phase-transfer catalysts, ionic liquids, electrolytes, frameworks, surfactants, herbicides, and antimicrobials are further covered. A brief discussion of the health and environmental impact of QACs is also provided. The emphasis is largely on tetraalkylammonium compounds bearing linear alkyl chains.

Modifying Adhesive Materials to Improve the Longevity of Resinous Restorations

Dental caries is a common disease on a global scale. Resin composites are the most popular materials to restore caries by bonding to tooth tissues via adhesives. However, multiple factors, such as microleakage and recurrent caries, impair the durability of resinous restorations. Various innovative methods have been applied to develop adhesives with particular functions to tackle these problems, such as incorporating matrix metalloproteinase inhibitors, antibacterial or remineralizing agents into bonding systems, as well as improving the mechanical/chemical properties of adhesives, even combining these methods. This review will sum up the latest achievements in this field.

DNA-Polyelectrolyte Complexation Study: The Effect of Polyion Charge Density and Chemical Nature of the Counterions

Complexes of polycations and DNA, also known as polyplexes, have been extensively studied in the past decade, as potential gene delivery systems. Their stability depends strongly on the characteristics of the polycations, as well as the nature of the added salt. We present here a study of the DNA ionene complexation in which we used fluorescence, UV, and CD spectroscopy, combined with molecular dynamics computer simuations, to systematically examine the influence of the polycation charge density, as well as the influence of the nature of the counterion, on the stability of these systems. Ionenes as polycations, depending on their structural characteristics, have previously been found to possess low cytotoxicity, and are therefore particularly interesting as potential gene delivery agents. The results show that the DNA solutions in the presence of the polycation are more stable in the case of very large or very small ionene charge density, suggesting different mechanism of complexation. The computer simulations show that the ionenes with high charge density bind to the minor groove of the DNA molecules, while the ionenes with lower charge density bind to the major groove of the DNA. The nature of the counterions play only a minor role: precipitation of the DNA molecules occurs at slightly lower ionene concentration when fluoride counterion are present, compared to the bromide counterions.

Long-acting and broad-spectrum antimicrobial electrospun poly (ε-caprolactone)/gelatin micro/nanofibers for wound dressing

Trimethoxysilylpropyl octadecyldimethyl ammonium chloride (QAS), which forms facile bonds with hydroxyl groups, acts asa cationic antibacterial agent. In this work, QAS was introduced into a polycaprolactone (PCL)/gelatin hybrid in increasing concentrations to fabricate a long-acting and broad-spectrum antimicrobial micro/nanofiber membrane as a novel wound dressing. The physical interactions and chemical bonding between QAS/PCL and QAS/gelatin were demonstrated by infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS. Measured water contact angle between the PCL-gelatin/QAS (PG-Q) nanofiber membranes suggested a hydrophobic surface, which has been shown to aid in removal of wound dressings. The mechanical strength of the membranes was sufficient to meet the clinical requirements. Furthermore, the 15% QAS (PG-Q15) and 20% QAS (PG-Q20) formulated nanofiber membranes showed a considerable increase in their bacteriostatic activity towards Staphylococcus aureus (gram-positive) and Pseudomonas aeruginosa (gram-negative) bacteria, suggesting a broad-spectrum bactericidal effect by the PG-Q membranes. The PG-Q membranes with various QAS formulations demonstrated little cytotoxicity. Therefore, the long-acting and broad-spectrum antimicrobial electrospun PG-Q micro/nanofibers membrane demonstrate potential efficacy asan antibacterial wound dressing.

Aromatic ionene topology and counterion-tuned gelation of acidic aqueous solutions

Unusual gelation of acidic solutions was achieved using polycations bearing quaternary ammonium moieties. These ionene polymers are based on a disubstituted phenylene dibenzamide core, which allows the construction of different topomers (i.e. ortho-1, meta-2 and para-3). The topology of the polymers was found to play a key role on their aggregation behaviour both in pure water and in a variety of aqueous acidic solutions leading to the formation of stable acidic gels. Specifically, ortho-1 showed superior gelation ability than the analogues meta-2 and para-3 in numerous solutions of different pH and ionic strengths. Lower critical gelation concentrations, higher gel-to-sol transition temperatures and faster gelation were usually observed for ortho-1 regardless the solvent system. Detailed computational molecular dynamic simulations revealed a major role of the counterion (Cl^-) and specific polymerpolymer interactions. In particular, hydrogen bonds, N-Hπ interactions and intramolecular π-π stacking networks are distinctive in ortho-1. In addition, counterions located at internal hydration regions also affect to such polymerpolymer interactions, acting as binders and, therefore, providing additional stability.

Evaluation of the effectiveness of the potent bis-quaternary ammonium compound, 4,4'-(α,ω-hexametylenedithio) bis (1-octylpyridinium bromide) (4DTBP-6,8) on Pseudomonas aeruginosa

AIMS

Quaternary ammonium compounds (QACs), including benzalkonium chloride (BAC) and cetylpyridinium chloride (CPC) are cationic surfactants and have been used widely as general disinfectants in the medical field due to their strong antibacterial effects and low cytotoxicity to human cells. 4,4'-(α,ω-hexametylenedithio) bis (1-octylpyridinium bromide) (4DTBP-6,8) is one of the potent bis-QACs synthesized to improve the antimicrobial activities of mono-QACs such as BAC. This study aimed to assess the effectiveness of 4DTBP-6,8 against Pseudomonas aeruginosa, a prevalent hospital pathogen.

METHODS AND RESULTS

The minimum inhibitory concentrations of 4DTBP-6,8, CPC and BAC against P. aeruginosa were measured. 4DTBP-6,8 exhibited strong antibacterial activity. We assessed the bactericidal effects of QACs against P. aeruginosa under certain conditions and their cytotoxicities in human epithelial cells using lactate dehydrogenase (LDH) release. 4DTBP-6,8 exerted excellent bactericidal effects against high concentrations of bacteria, biofilm cells and even in the presence of contaminated proteins. Cellular LDH was not released by the treatment with 4DTBP-6,8.

CONCLUSIONS

4DTBP-6,8 exhibited the strongest bactericidal activity against P. aeruginosa among the three QACs tested without any cytotoxicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potent bis-QAC, 4DTBP-6,8 has the potential to be an effective disinfectant in preventing hospital infections caused by P. aeruginosa.

In Vitro Evaluation of the Biocompatibility of Newly Synthesized Bis-Quaternary Ammonium Compounds with Spacer Structures Derived from Pentaerythritol or Hydroquinone

　With the object of developing new biocides milder for human use than the current antiseptics, we synthesized a series of bis-quaternary ammonium compounds (bis-QACs). The antimicrobial activity of the newly synthesized bis-QACs and common biocides used as antiseptics was compared by examining minimum inhibitory concentrations and minimum bactericidal concentrations (MBCs). Moreover, the cytotoxicity of these compounds against human cells was determined to calculate the biocompatibility index (BI) of these compounds. BI was the ratio of the concentration of a biocide giving a 50% lethal effect on normal human epidermal keratinocytes to its MBC against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The commonly used antiseptics tested were benzalkonium chloride (BAC), octenidine dihydrochloride (OCT), chlorhexidine digluconate (CHG) and polyhexamethylene biguanide (PHMB). In comparison with these antiseptics, it was shown that some of new bis-QACs exhibited a wider and more potent antimicrobial spectrum than OCT. The cytotoxicity of these bis-QACs was equal or lower compared to that of the quaternary ammonium compounds (BAC and OCT), although these bis-QACs showed higher toxicity than the biguanide-based compounds (CHG and PHMB). Finally, the comparison of BIs revealed that new bis-QACs such as N-dodecyl ｛4,4'-(2,4,8,10-tetraoxaspiro［5.5］undecan-3,9-diyl) ｝dipyridinium dibromide (4TOSU-12), 3,3'-［1,4-Phenylenebis (oxy)］bis (1-dodecylpyridinium) dibromide (3PHBO-12) and 3-(3-Hydroxy-2-(hydroxymethyl)-2-｛［(1-dodecylpyridinium-3-yl) oxy］methyl｝propoxy)-1-dodecylpyridinium dibromide (3HHDMP-12) had equal or greater biocompatibility than the commonly used biocides tested. Thus, these results strongly suggested that 4TOSU-12, 3PHBO-12 and 3HHDMP-12 could be useful as antiseptics for topical application to the skin.

Preparation, characterization and antibiotic properties of silver–silicon nanocomposites

Ag nanoparticles supported on porous silicon showing excellent antibiotic properties against both E. coli and S. aureus were presented.

Gemini quaternary ammonium salt waterborne biodegradable polyurethanes with antibacterial and biocompatible properties

Novel antibacterial waterborne polyurethanes based on gemini quaternary ammonium salt with good biodegradable and biocompatible properties.

A Novel Surface Structure Consisting of Contact-active Antibacterial Upper-layer and Antifouling Sub-layer Derived from Gemini Quaternary Ammonium Salt Polyurethanes

Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them.

Synthesis, characterization, antimicrobial and biofilm inhibitory studies of new esterquats

Novel esterquats (monoesterquats and diesterquats) were synthesized from 11-bromo undecanoic acid (11-BUA) and different alkyl amines. The prepared compounds were characterized by FT-IR, (1)H NMR, (13)C NMR and mass spectral analysis. 11-BUA was converted into methyl 11-bromo undecanoate which was further converted into amine ester (amine monoester and diester) by reacting with different aliphatic amines (hexyl, dodecyl, octadecyl, dioctyl and dicyclohexyl amine). Finally, the obtained amine esters were converted into esterquats (monoesterquat and diesterquat) by reacting with methyl iodide followed by ion exchange to afford chloride counter ion esterquats (5a-h). The synthesized esterquat products were studied for their antimicrobial and biofilm inhibitory activities. Among all the compounds, amine ester 3a and esterquat 5d showed potent antimicrobial activity towards pathogenic Gram-positive bacterial strains with minimum inhibitory concentration (MIC) values in the range of 3.9-15.6 μg mL(-1) and 1.9-7.8 μg mL(-1), respectively. The esterquat 5d also showed promising antifungal activity against Candida albicans MTCC 3017, Candida albicans MTCC 4748 and Candida aaseri MTCC 1962 strains with MIC value of 7.8 μg mL(-1) which was identical to standard Miconazole. The compounds which exhibited antimicrobial activity were also effective in anti-biofilm activity and it was found that compound 5d exhibited excellent biofilm inhibitory activity with IC50 value of 0.9 μg mL(-1) against Staphylococcus aureus MLS16 MTCC 2940.

Synthesis, physiochemical property and antibacterial activity of gemini quaternary ammonium salts with a rigid spacer

Aggregate morphologies of GQASs change from vesicles and micelles to network aggregates and then to globular vesicles with increase of concentration.

The Use of Quaternary Ammonium to Combat Dental Caries

Resin composites and adhesives are increasingly popular in dental restorations, but secondary caries is one of the main reasons for restoration failure. Quaternary ammonium monomers (QAMs) have an anti-microbial effect and are widely used in many fields. Since the concept of the immobilized antibacterial effect was put forward, dental restorations containing QAMs have been studied to reduce secondary caries. Previous studies have been struggling to develop novel anti-caries materials which might have triple benefits: good mechanical properties, antibacterial effects and remineralization potentials. Different kinds of QAMs have been proven to be effective in inhibiting the growth and metabolism of biofilms. Combination of QAMs and other nanoparticles in resin composites and adhesives could enhance their anti-caries capability. Therefore, QAMs are promising to show significant impact on the future of restorative and preventive dentistry.