Development of an antibacterial root canal filling system containing MDPB

Applications of quaternary ammonium compounds in the prevention and treatment of oral diseases: State-of-the-art and future directions

OBJECTIVES

The aim of this review is to comprehensively summarize the state-of-the-art developments of quaternary ammonium compounds (QACs) in the prevention and treatment of oral diseases. By discussing the structural diversity and the potential killing mechanism, we try to offer some insights for the future research of QACs.

DATA, SOURCES & STUDY SELECTION

A literature search was conducted in electronic databases (Web of Science, PubMed, Medline, and Scopus). Publications that involved the applications of QACs, especially those related to the prevention and treatment of oral diseases, are included.

RESULTS

We have reviewed the relevant research on QACs over the past two decades. The research results indicate that the current applications are mainly focused on dental material modification and direct pharmacological interventions. Concurrently, challenges such as potential risks to normal tissues and impediments in drug resistance and microbial persistence present certain application constraints. The latest studies have encompassed the exploration of smart materials and nanoparticle formulations.

CONCLUSIONS

The killing mechanism may possess a threshold related to charge density. However, the exact process remains enigmatic. The structural diversity and the exploration of intelligent materials and nanoparticle formulations provide directions in development of novel QACs.

CLINICAL SIGNIFICANCE

The intricate oral anatomy, combined with the multifaceted oral microbiome, necessitates specialized materials for the targeted prevention and treatment of oral pathologies. QACs represent a cohort of compounds distinguished by potent anti-infective and anti-tumor attributes. Innovations in intelligent materials and nanoparticle formulations amplify their potential in significantly advancing the prevention and therapeutic interventions for oral diseases.

Evaluation of the long-term antibiofilm effect of a surface coating with dual functionality of antibacterial and protein-repellent effects

The provision of antibacterial properties to resinous restorative/reconstructive materials by incorporating polymerizable bactericides such as 12-methacryloyloxydodecylpyridinium bromide (MDPB) has been attempted. Previously, MDPB was combined with 2-methacryloyloxyethyl phosphorylcholine (MPC) to fabricate a copolymer coating to increase antibacterial effectiveness by protein repelling. In this study, we assessed the longevity of the protein-repelling, antibacterial, and antibiofilm effects of the MDPB-MPC copolymer. After 28 days of water immersion, MPC-containing copolymers exhibited lower adsorption of bovine serum albumin and salivary proteins; after 24 h of incubation, MDPB-containing copolymers demonstrated antibacterial effects against Streptococcus mutans. The copolymer containing both MDPB and MPC showed thinner biofilm formation with a higher percentage of membrane-compromised bacteria than control. The results were consistent with those before aging, indicating the long-lasting antibacterial, protein-repellent, and antibiofilm effects of this copolymer. The durable copolymer developed in this study can be applied to dental resins to control bacteria in the oral environment.

Immobilizing Bactericides on Dental Resins via Electron Beam Irradiation

Polymerizable bactericides, such as quaternary ammonium compound-based monomers, have been intensively studied as candidates for immobilizing antibacterial components on dental resin. However, they predominantly exhibit a bacteriostatic behavior, rather than bactericidal, as the immobilized components are left with insufficient molecular movement to disrupt the bacterial surface structure through contact-mediated action. In this study, we developed a novel strategy to increase the density of the immobilized bactericide and enhance its antibacterial/antibiofilm properties by combining a surface-grafting technique with electron beam irradiation. A solution of the quaternary ammonium compound-based monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), was coated on polymethyl methacrylate (PMMA) resin specimens at the concentrations of 30, 50, and 80 wt%. The coated resins were subsequently exposed to 10 MeV of electron beam irradiation at 50 and 100 kGy, followed by thermal stabilization at 60 °C. The antibacterial effect was evaluated by inoculating a Streptococcus mutans suspension on the coated PMMA resin samples, which exhibited bactericidal effects even after 28 d of aging (P < 0.05, Tukey's honestly significant difference test). Transmission electron microscopy and bacteriolytic activity evaluation revealed that the S. mutans cells had sustained membrane depolarization. Furthermore, the antibiofilm effects against S. mutans and bacteria collected from human saliva were assessed. The thickness and the percentage of membrane-intact cells of the S. mutans and multispecies biofilms formed on the MDPB-immobilized surfaces were significantly lower than the uncoated PMMA specimens, even after 28-d aging (P < 0.05, Tukey's honestly significant difference test). Thus, the immobilization of antibacterial MDPB via electron beam irradiation induced rapid membrane depolarization, increasing membrane permeability and eventually causing cell death. Our strategy substantially enhances the antibacterial properties of the resinous materials and inhibits biofilm formation, therefore demonstrating significant potential for preventing infectious diseases in the oral environment.

Effect of Antibacterial Root Canal Sealer on Persistent Apical Periodontitis

The infection of Enterococcus faecalis and its interacting microorganisms in the root canal could cause persistent apical periodontitis (AP). Antibacterial root canal sealer has favorable prospects to inhibit biofilms. The purpose of this study was to investigated the antibacterial effect of root canal sealer containing dimethylaminododecyl methacrylate (DMADDM) on persistent AP in beagle dogs for the first time. Persistent AP was established by a two-step infection with Enterococcus faecalis and multi-bacteria (Enterococcus faecalis, Lactobacillus acidophilus, Actinomycesnaeslundii, Streptococcus gordonii). Root canal sealer containing DMADDM (0%, 1.25%, 2.5%) was used to complete root canal filling. The volume of lesions and inflammatory grade in the apical area were evaluated by cone beam computer tomography (CBCT) and hematoxylin-eosin staining. Both Enterococcus-faecalis- and multi-bacteria-induced persistent AP caused severe apical destruction, and there were no significant differences in pathogenicity between them. DMADDM-modified sealer significantly reduced the volume of periapical lesion and inflammatory grade compared with the control group, among them, the therapeutic effect of the 2.5% group was better than the 1.25% group. In addition, E.faecalis-induced reinfection was more sensitive to the 2.5% group than multi-bacteria reinfection. This study shows that root canal sealer containing DMADDM had a remarkable therapeutic effect on persistent AP, especially on E. faecalis-induced reinfection.

Synthesis of Novel Dental Nanocomposite Resins by Incorporating Polymerizable, Quaternary Ammonium Silane-Modified Silica Nanoparticles

Diverse approaches dealing with the reinforcement of dental composite resins with quaternary ammonium compounds (QAC) have been previously reported. This work aims to investigate the physicochemical and mechanical performance of dental resins containing silica nanofillers with novel QAC. Different types of quaternary ammonium silane compounds (QASiC) were initially synthesized and characterized with proton nuclear magnetic resonance (¹H-NMR) and Fourier transform infrared (FTIR) spectroscopy. Silica nanoparticles were surface modified with the above QASiC and the structure of silanized products (S.QASiC) was confirmed by means of FTIR and thermogravimetric analysis. The obtained S.QASiC were then incorporated into methacrylate based dental resins. Scanning electron microscopy images revealed a satisfactory dispersion of silica nanoclusters for most of the synthesized nanocomposites. Curing kinetics disclosed a rise in both the autoacceleration effect and degree of conversion mainly induced by shorter QASiC molecules. Polymerization shrinkage was found to be influenced by the particular type of S.QASiC. The flexural modulus and strength of composites were increased by 74% and 19%, while their compressive strength enhancement reached up to 19% by adding 22 wt% S.QASiC nanoparticles. These findings might contribute to the proper design of multifunctional dental materials able to meet the contemporary challenges in clinical practice.

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.

Emerging Contact-Killing Antibacterial Strategies for Developing Anti-Biofilm Dental Polymeric Restorative Materials

Polymeric materials are the first choice for restoring tooth cavities, bonding tooth-colored fillings, sealing root canal systems, and many other dental restorative applications. However, polymeric materials are highly susceptible to bacterial attachment and colonization, leading to dental diseases. Many approaches have been investigated to minimize the formation of biofilms over polymeric restorative materials and at the tooth/material interfaces. Among them, contact-killing compounds have shown promising results to inhibit dental biofilms. Contact-killing compounds can be immobilized within the polymer structure, delivering a long-lasting effect with no leaching or release, thus providing advantages compared to release-based materials. This review discusses cutting-edge research on the development of contact-killing compounds in dental restorative materials to target oral pathogens. Contact-killing compounds in resin composite restorations, dental adhesives, root canal sealers, denture-based materials, and crown cements have all demonstrated promising antibacterial properties. Contact-killing restorative materials have been found to effectively inhibit the growth and activities of several oral pathogens related to dental caries, periodontal diseases, endodontic, and fungal infections. Further laboratory optimization and clinical trials using translational models are needed to confirm the clinical applicability of this new generation of contact-killing dental restorative materials.

Anti-biofilm activity of a novel pit and fissure self-adhesive sealant modified with metallic monomers

Dental plaque is a biofilm composed of a complex oral microbial community. The accumulation of plaque in the pit and fissures of dental elements often leads to the development of tooth decay (dental caries). Here, potent anti-biofilm materials were developed by incorporating zinc methacrylates or di-n-butyl-dimethacrylate-tin into the light-curable sealant and their physical, mechanical, and biological properties were evaluated. The data revealed that 5% di-n-butyl-dimethacrylate-tin (SnM 5%) incorporated sealant showed strong anti-biofilm efficacy against various single-species (Streptococcus mutans or Streptococcus oralis or Candida albicans) and S. mutans-C. albicans cross-kingdom dual-species biofilms without either impairing the mechanical properties of the sealant or causing cytotoxicities against mouse fibroblasts. The findings indicate that the incorporation of SnM 5% in the experimental pit and fissure self-adhesive sealant may have the potential to be part of current chemotherapeutic strategies to prevent the formation of cariogenic oral biofilms that cause dental caries.

Novel Bioactive and Therapeutic Root Canal Sealers with Antibacterial and Remineralization Properties

According to the American Dental Association Survey of Dental Services Rendered (published in 2007), 15 million root canal treatment procedures are performed annually. Endodontic therapy relies mainly on biomechanical preparation, chemical irrigation and intracanal medicaments which play an important role in eliminating bacteria in the root canal. Furthermore, adequate obturation is essential to confine any residual bacteria within the root canal and deprive them of nutrients. However, numerous studies have shown that complete elimination of bacteria is not achieved due to the complex anatomy of the root canal system. There are several conventional antibiotic materials available in the market for endodontic use. However, the majority of these antibiotics and antiseptics provide short-term antibacterial effects, and they impose a risk of developing antibacterial resistance. The root canal is a dynamic environment, and antibacterial and antibiofilm materials with long-term effects and nonspecific mechanisms of action are highly desirable in such environments. In addition, the application of acidic solutions to the root canal wall can alter the dentin structure, resulting in a weaker and more brittle dentin. Root canal sealers with bioactive properties come in direct contact with the dentin wall and can play a positive role in bacterial elimination and strengthening of the root structure. The new generation of nanostructured, bioactive, antibacterial and remineralizing additives into polymeric resin-based root canal sealers are discussed in this review. The effects of these novel bioactive additives on the physical and sealing properties, as well as their biocompatibility, are all important factors that are presented in this article.

A novel antibacterial resin-based root canal sealer modified by Dimethylaminododecyl Methacrylate

Persistent apical periodontitis, mainly caused by microorganisms infections, represents a critical challenge for endodontists. Dimethylaminododecyl methacrylate (DMADDM) is a well-studied and potent antibacterial agent used in various studies described in the literature. The aim of this study is to develop a novel antibacterial root canal sealer by incorporating DMADDM into EndoREZ and investigate the properties of the resulting material. Different mass fractions (0, 1.25%, 2.5%, and 5%) of DMADDM were incorporated into EndoREZ and the cytotoxicity, apical sealing ability and solubility of the resulting material were evaluated. Furthermore, a direct contact test, determination of colony-forming units, a crystal violet assay, scanning electronic microscopy and live/dead bacteria staining were performed to evaluate the antibacterial effect of the sealer to multispecies bacteria (Enterococcus faecalis, Streptococcus gordonii, Actinomyces naeslundii, and Lactobacillus acidophilus), in planktonic cells or biofilms. Fluorescence in situ hybridization and quantitative real-time polymerase chain reaction were carried out to assess the composition of the multispecies biofilms. No difference on the cytotoxicity, apical sealing ability and solubility between sealers containing DMADDM (1.25%, 2.5%) and EndoREZ (0%) could be determined. However, when the mass fraction of DMADDM increased to 5%, significantly different properties were found compared to the 0% (p < 0.05) group. Moreover, incorporating DMADDM into the sealer could greatly improve the antibacterial properties of EndoREZ. In addition, the composition ratio of E. faecalis could be decreased in multispecies microecology in sealers containing DMADDM. Therefore, a EndoREZ sealer material containing DMADDM could be considered useful in clinical applications for preventing and treating persistent apical periodontitis.

Novel endodontic sealer with dual strategies of dimethylaminohexadecyl methacrylate and nanoparticles of silver to inhibit root canal biofilms

OBJECTIVE

Endodontic treatment failures and recontamination remain a major challenge. The objectives of this study were to: (1) develop a new root canal sealer with potent and long-lasting antibiofilm effects using dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of silver (NAg); (2) determine the effects of incorporating DMAHDM and NAg each alone versus in combination on biofilm-inhibition efficacy; and (3) determine the effects on sealer paste flow, film thickness and sealing ability, compared to a commercial control sealer.

METHODS

Dual-cure endodontic sealers were formulated using DMAHDM mass fractions of 0%, 2.5% and 5%, and NAg mass fractions of 0.05%, 0.1% and 0.15%. The sealing ability of the sealers was measured using linear dye penetration method. Colony-forming units (CFU), live/dead assay, and polysaccharide production of biofilms grown on sealers were determined.

RESULTS

The sealer with 5% DMAHDM and 0.15% NAg yielded a flow of (22.18 ± 0.58) which was within the range of ISO recommendations and not statistically different from AH Plus control (23.3 ± 0.84) (p > 0.05). Incorporating DMAHDM and NAg did not negatively affect the film thickness and sealing properties (p > 0.05). The sealer with 5% DMAHDM and 0.15% NAg greatly reduced polysaccharide production by the biofilms, and decreased the biofilm CFU by nearly 6 orders of magnitude, compared to AH Plus and experimental controls (p < 0.05).

SIGNIFICANCE

A therapeutic root canal sealer was developed using 5% DMAHDM with biofilm-inhibition through contact-mediated mechanisms, plus 0.15% of NAg to release silver ions into the complex and difficult-to-reach root canal environment. The novel root canal sealer exerted potent antibiofilm effects and reduced biofilm CFU by 6 orders of magnitude without compromising sealer flow, film thickness and sealing ability. This method provided a promising approach to inhibit endodontic biofilms and prevent recurrent endodontic infections.

Novel bioactive root canal sealer with antibiofilm and remineralization properties

OBJECTIVES

(1) To develop a novel bioactive root canal sealer with antibiofilm and remineralization properties using dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); (2) investigate the effects on E. faecalis biofilm inhibition, sealer flow and sealing ability, compared with an epoxy-resin-based sealer AH Plus; and (3) investigate the calcium (Ca) and phosphate (P) ion release from the sealers.

METHODS

A series of dual-cure endodontic sealers were formulated with DMAHDM and NACP at 5% and 20% by mass, respectively. Flow properties and sealing ability of the sealers were measured. Colony-forming units (CFU), live/dead assay, and polysaccharide production of biofilms on sealers were determined. Ca and P ion releases from the sealers were measured.

RESULTS

The new sealer containing 20% NACP and 5% DMAHDM yielded a paste flow of (28.99 ± 0.69) mm, within the range of ISO recommendations. The sealing properties of the sealer with 5% DMAHDM and 20% NACP were similar to a commercial control (p > 0.05). The sealer with DMAHDM decreased E. faecalis biofilm CFU by more than 4 orders of magnitude, compared to AH plus and experimental controls. The sealer with 20% NACP and 5% DMAHDM had relatively high levels of Ca and P ion release necessary for remineralization.

CONCLUSIONS

A new bioactive endodontic sealer was developed with strong antibiofilm activity against E. faecalis biofilms and high levels of Ca and P ion release for remineralization, without compromising the paste flow and sealing properties.

CLINICAL SIGNIFICANCE

The bioactive antibacterial and remineralizing root canal sealer is promising to inhibit E. faecalis biofilms to prevent endodontic treatment failure and secondary endodontic infections, while releasing high levels of Ca and P ions that could remineralize and strengthen the tooth structures and potentially prevent future root fractures and teeth extractions.

Novel Approaches to the Control of Oral Microbial Biofilms

Effective management of biofilm-related oral infectious diseases is a global challenge. Oral biofilm presents increased resistance to antimicrobial agents and elevated virulence compared with planktonic bacteria. Antimicrobial agents, such as chlorhexidine, have proven effective in the disruption/inhibition of oral biofilm. However, the challenge of precisely and continuously eliminating the specific pathogens without disturbing the microbial ecology still exists, which is a major factor in determining the virulence of a multispecies microbial consortium and the consequent development of oral infectious diseases. Therefore, several novel approaches are being developed to inhibit biofilm virulence without necessarily inducing microbial dysbiosis of the oral cavity. Nanoparticles, such as pH-responsive enzyme-mimic nanoparticles, have been developed to specifically target the acidic niches within the oral biofilm where tooth demineralization readily occurs, in effect controlling dental caries. Quaternary ammonium salts (QAS) such as dimethylaminododecyl methacrylate (DMADDM), when incorporated into dental adhesives or resin composite, have also shown excellent and durable antimicrobial activity and thus could effectively inhibit the occurrence of secondary caries. In addition, custom-designed small molecules, natural products and their derivatives, as well as basic amino acids such as arginine, have demonstrated ecological effects by modulating the virulence of the oral biofilm without universally killing the commensal bacteria, indicating a promising approach to the management of oral infectious diseases such as dental caries and periodontal diseases. This article aims to introduce these novel approaches that have shown potential in the control of oral biofilm. These methods may be utilized in the near future to effectively promote the clinical management of oral infectious diseases and thus benefit oral health.

New adhesive system based in metals cross-linking methacrylate

This study evaluated the anti-antibiofilm potential of silver methacrylate (Ag) or di-n-butyldimethacrylatetin (Sn) in experimental adhesive systems. Ag and Sn methacrylates were incorporated at 0.5mol%, 1mol% and 2mol% in an adhesive resin. The anti-antibiofilm potential, degree of conversion (DC), microtensile bond strength (μTBS), water sorption/solubility (W_SR/SL), bonded interfaces pattern (SEM), cytotoxicity and leaching of Ag and Sn ions were evaluated. Data were statistically analyzed considering α = 0.05. Only Ag at 2% affected DC and μTBS. Ag at 1% and 2% and Sn at 1% and 2% showed anti-biofilm potential against Mutans streptococci. Ag at 1% and 2% and Sn at 2% showed a statistically significant difference to the control in W_SR/SL (p < 0.05). The additions of metal methacrylate did not affect cell viability, being the adhesive resins statistically similar to controls. Leached metals of Ag were more than 100x higher than for Sn. Between the concentration tested, Ag and Sn methacrylate at 1% presented an anti-biofilm effect without altering the mechanical properties evaluated.

Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Innovative root-end filling materials based on calcium-silicates and calcium-phosphates

This in vitro study evaluated the apical sealing ability, bioactivity and biocompatibility of an experimental calcium silicate-based and two light-curing calcium silicate/calcium-phosphate cements as potential root end filling materials. A calcium silicate Portland-based (Control PC), an experimental calcium silicate (Exp. PC) and two light-curing cements (LC-CaP; LC-Si/CaP) were assessed for their alkalinising activity (pH) and biocompatibility. Single-rooted human canines were endodontically treated, filled with gutta-percha and finally submitted to apicoectomy. Root end fillings were performed using all tested cements, and their apical sealing ability was evaluated up to 4 weeks of immersion in simulated body fluid (SBF). The mineral precipitation at the apical region and the cement adaptation to root dentine were also evaluated through non-destructive optical microscopy both at 24 h and after prolonged water storage (four week). LC-CaP and LC-Si/CaP had neutral pH, the greatest sealing ability (24 h) and excellent cytocompatibility. The Exp. PC cement presented sealing ability after two and four weeks, as well as biocompatibility after four and seven days, similar to LC-CaP and LC-Si/CaP. The control PC cement showed the lowest sealing ability and the greatest cytotoxicity. Mineral precipitation was observed in all groups, while some differences were seen in terms of cement adaptation along the root canal dentine walls. The experimental light-curable cements as well as the experimental PC might be suitable root end filling materials with appropriate (in vitro) sealing ability, biocompatibility and aptitude to induce mineral precipitation.

Effect of bioactive dental adhesive on periodontal and endodontic pathogens

The objectives of this study were to: (1) develop a new bioactive dental bonding agent with nanoparticles of amorphous calcium phosphate and dimethylaminohexadecyl methacrylate for tooth root caries restorations and endodontic applications, and (2) investigate biofilm inhibition by the bioactive bonding agent against eight species of periodontal and endodontic pathogens for the first time. Bonding agent was formulated with 5 % of dimethylaminohexadecyl methacrylate. Nanoparticles of amorphous calcium phosphate at 30 wt% was mixed into adhesive. Eight species of biofilms were grown on resins: Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Parvimonas micra, Enterococcus faecalis, Enterococcus faecium. Colony-forming units, live/dead assay, biomass, metabolic activity and polysaccharide of biofilms were determined. The results showed that adding dimethylaminohexadecyl methacrylate and nanoparticles of amorphous calcium phosphate into bonding agent did not decrease dentin bond strength (P > 0.1). Adding dimethylaminohexadecyl methacrylate reduced the colony-forming units of all eight species of biofilms by nearly three orders of magnitude. The killing efficacy of dimethylaminohexadecyl methacrylate resin was: P. gingivalis > A. actinomycetemcomitans > P. intermedia > P. nigrescens > F. nucleatum > P. micra > E. faecalis > E. faecium. Dimethylaminohexadecyl methacrylate resin had much less biomass, metabolic activity and polysaccharide of biofilms than those without dimethylaminohexadecyl methacrylate (P < 0.05). In conclusion, a novel dental adhesive was developed for root caries and endodontic applications, showing potent inhibition of biofilms of eight species of periodontal and endodontic pathogens, and reducing colony-forming units by three orders of magnitude. The bioactive adhesive is promising for tooth root restorations to provide subgingival margins with anti-periodontal pathogen capabilities, and for endodontic sealer applications to combat endodontic biofilms.

Status of Endodontic Treatment and the Correlations to the Quality of Root Canal Filling and Coronal Restoration

INTRODUCTION

This cross-sectional study evaluated the prevalence and quality of root canal treatment in 1,977 digital radiological files.

MATERIALS AND METHODS

Data were statistically analyzed using descriptive analysis, and the chi-square test was performed with a 5% significance level.

RESULTS

The mean age of the study population was 34.9 years. The endodontic treatment frequency was 6.14%, significantly higher in premolars. Adequate endodontic treatment was observed in 39.7% of analyzed cases. Molars were significantly more frequent with regard to inadequate filling quality. In 47.6% of cases, the filling's apical limit was classified as adequate, and there was a higher incidence of molars that were inadequate. Restorations were classified as adequate in 79.0% of cases, and molars were responsible for the highest frequency of inadequate restorations. The frequency of teeth with endodontic treatment that showed no periapical changes was 47.7%. There was no significant difference in the presence of periapical change according to gender. An increased presence of periapical change was observed with increasing age. The periapical lesions were observed in 45% of cases and related to inadequate filling quality. The apical limit was considered inadequate and related to periapical changes in 42% of cases. Periapical changes were present in 52% of cases, regardless of the quality of the filling and apical limit. Such changes were present in 42% of cases with adequate coronal restoration.

CONCLUSION

It can be concluded that apical periodontitis (AP) is associated with the quality of endodontic treatment. The coronal restoration affects significantly the success rate of endodontic treatment.

CLINICAL SIGNIFICANCE

The quality of the root filling and coronal restoration is closely related to periapical health.

Methacryloxylethyl Cetyl Ammonium Chloride Induces DNA Damage and Apoptosis in Human Dental Pulp Cells via Generation of Oxidative Stress

The polymerizable antibacterial monomer methacryloxylethyl cetyl ammonium chloride (DMAE-CB) has provided an effective strategy to combat dental caries. However, the application of such material raises the question about the biological safety and the question remains open. The mechanism of this toxic action, however, is not yet clearly understood. The present study aims at providing novel insight into the possible causal link between cellular oxidative stress and DNA damage, as well as apoptosis in human dental pulp cells exposed to DMAE-CB. The enhanced formation of reactive oxygen species and depletion of glutathione, as well as differential changes in activities of superoxide dismutase, glutathione peroxidase, and catalase in DMAE-CB-treated cells indicated oxidative stress. By using substances that can alter GSH synthesis, we found that GSH was the key component in the regulation of cell response towards oxidative stress induced by DMAE-CB. The increase in oxidative stress-sensitive 8-Oxo-2'-deoxyguanosine (8-OHdG) content, formation of γ-H2AX and cell cycle G1 phase arrest indicated that DNA damage occurred as a result of the interaction between DNA base and ROS beyond the capacities of antioxidant mechanisms in cells exposed to DMAE-CB. Such oxidative DNA damage thus triggers the activation of ataxia telangiectasia-mutated (ATM) signaling, the intrinsic apoptotic pathway, and destruction of mitochondrial morphology and function.

Evolution of resistance to cationic biocides in Streptococcus mutans and Enterococcus faecalis

OBJECTIVES

The aim of this study was to investigate whether Streptococcus mutans and Enterococcus faecalis develop resistance to the cationic biocides chlorhexidine (CHX), cetylpyridinium chloride (CPC), and 12-methacryloyloxydodecylpyridinium bromide (MDPB).

METHODS

The minimum inhibitory concentrations (MICs) of CHX, CPC, and MDPB were assessed after repeated exposure of S. mutans and E. faecalis to these biocides. Cell-surface hydrophobicity and protein expression profiles of bacterial cells were examined to elucidate possible resistance mechanisms.

RESULTS

The MIC of CHX against E. faecalis showed constant increases up to 10 passages. No changes in the MICs of CPC and MDPB against E. faecalis were observed. The MICs of CHX, CPC, and MDPB against S. mutans did not increase. The surface hydrophobicity of E. faecalis significantly increased with increasing exposure to CHX and CPC. However, changes in protein expression profiles were only found in CHX-adapted E. faecalis, as evidenced by the emergence of a novel, approximately 19-kDa band following sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

CONCLUSIONS

While E. faecalis and S. mutans did not exhibit increased resistance to CPC or MDPB, repeated exposure of E. faecalis to CHX led to resistance. It is likely that the acquisition of resistance is related to an altered protein composition.

CLINICAL SIGNIFICANCE

Alkyl pyridinium compounds, such as CPC and MDPB, could have a lower risk to cause adaptation of E. faecalis, which is advantageous compared with CHX.

N-Acetyl Cysteine (NAC)-Directed Detoxification of Methacryloxylethyl Cetyl Ammonium Chloride (DMAE-CB)

Methacryloxylethyl cetyl ammonium chloride (DMAE-CB) is a polymerizable antibacterial monomer and has been proved as an effective strategy to achieve bioactive bonding with reliable bacterial inhibitory effects. However, the toxicity of DMAE-CB may hamper its wide application in clinical situations. Thus, this study was designed to investigate the toxicity of DMAE-CB and explore the possible protective effects of N-acetyl cysteine (NAC). High performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) analysis showed that chemical binding of NAC and DMAE-CB occurred in a time dependent manner. Pre-incubation of fourty-eight hours is required for adequate reaction between DMAE-CB and NAC. DMAE-CB reduced human dental pulp cells (hDPCs) viability in a dose-dependent manner. The toxic effects of DMAE-CB were accompanied by increased reactive oxygen species (ROS) level and reduced glutathione (GSH) content. NAC alleviated DMAE-CB-induced oxidative stress. Annexin V/ Propidium Iodide (PI) staining and Hoechst 33342 staining indicated that DMAE-CB induced apoptosis. Collapsed mitochondrial membrane potential (MMP) and activation of caspase-3 were also observed after DMAE-CB treatment. NAC rescued hDPCs from DMAE-CB-induced apoptosis, accompanied by lower level of MMP loss and caspase-3 activity. This study assists to elucidate the mechanism underlying the cytotoxic effects of DMAE-CB and provides theoretical supports for the searching of effective strategies to reduce toxicity of quaternary ammonium dental monomers.

A new improved protocol for in vitro intratubular dentinal bacterial contamination for antimicrobial endodontic tests: standardization and validation by confocal laser scanning microscopy

Objectives

To compare three methods of intratubular contamination that simulate endodontic infections using confocal laser scanning microscopy (CLSM).

Material and Methods

Two pre-existing models of dentinal contamination were used to induce intratubular infection (groups A and B). These methods were modified in an attempt to improve the model (group C). Among the modifications it may be included: specimen contamination for five days, ultrasonic bath with BHI broth after specimen sterilization, use of E. faecalis during the exponential growth phase, greater concentration of inoculum, and two cycles of centrifugation on alternate days with changes of culture media. All specimens were longitudinally sectioned and stained with of LIVE/DEAD^® for 20 min. Specimens were assessed using CLSM, which provided images of the depth of viable bacterial proliferation inside the dentinal tubules. Additionally, three examiners used scores to classify the CLSM images according to the following parameters: homogeneity, density, and depth of the bacterial contamination inside the dentinal tubules. Kruskal-Wallis and Dunn’s tests were used to evaluate the live and dead cells rates, and the scores obtained.

Results

The contamination scores revealed higher contamination levels in group C when compared with groups A and B (p<0.05). No differences were observed between group A and B (p>0.05). The volume of live cells in group C was higher than in groups A and B (p<0.05).

Conclusion

The new protocol for intratubular infection resulted in high and uniform patterns of bacterial contamination and higher cell viability in all specimens when compared with the current methods.