The increase in bacterial resistance to one or several antibiotics has become a global health problem. Recently, nanomaterials have become a tool against multidrug-resistant bacteria. The metal and metal oxide nanoparticles are one of the most studied nanomaterials against multidrug-resistant bacteria. Several in vitro studies report that metal nanoparticles have antimicrobial properties against a broad spectrum of bacterial species. However, until recently, the bacterial resistance mechanisms to the bactericidal action of the nanoparticles had not been investigated. Some of the recently reported resistance mechanisms include electrostatic repulsion, ion efflux pumps, expression of extracellular matrices, and the adaptation of biofilms and mutations. The objective of this review is to summarize the recent findings regarding the mechanisms used by bacteria to counteract the antimicrobial effects of nanoparticles.

In recent years, the use and research in nanomaterials have increased considerably. In dentistry, nanomaterials have been investigated in all their specialties like dental prosthesis, implantology, dental operative, periodontics, and endodontics. The nanomaterials are investigated in the areas of dentistry due to their application in the improvement of the physical and chemical properties of conventional materials, as well as the use of the antimicrobial activity of nanomaterials such as silver nanoparticles. Recently, silver nanoparticles (AgNPs) have been studied for their use as an endodontic irrigator due to their high antimicrobial activity. But little is known about the possible mechanisms of the adaptation to AgNPs by endodontic bacteria. These mechanisms may be intrinsic (such as efflux pumps, downregulation of porins, and chromosomal resistance genes) or extrinsic (such as point and adaptive mutations and plasmids with resistance genes) adaptation systems. In addition to this, it has been reported that coselection or coregulation of metal resistance mechanisms, as in the case of nanoparticles, is accompanied by increased resistance to various antibiotics. For these reasons, the objective of this article is to do a review of the literature on the possible mechanisms used by endodontic bacteria to generate resistance to silver nanoparticles and the possible side effects of these mechanisms.

Background: on 7 January 2020, a new type of coronavirus was isolated, the Severe Acute Respiratory Syndrome Coronavirus2 (SARS-CoV-2), the organism causing the outbreak that has affected the lives of all humans and has modified the rules of coexistence around the world. In Mexico, from 3 January 2020 to 9 January 2021, there have been 1439, 569 confirmed cases of COVID-19 with 131,031 deaths. The World Health Organization reported that Mexico was ranked twelfth, in terms of confirmed cases of COVID-19 by country. Aim: the objective of this study was to determine what modifications dentists from the Mexican Republic have made to their dental practice during theCOVID-19 pandemic. Methods: the study was conducted based on a questionnaire to evaluate the dentists’ response and knowledge on the modifications in their dental practice to combat the new coronavirus’s cross-transmission. The questionnaire was piloted before it was distributed. The questionnaire was disseminated through the social network Facebook. The questionnaire was distributed to groups of dentists on Facebook, in each of the Mexican Republic states. The survey was carried out during June 2020. Results and Conclusions: from the 32 states of the Mexican Republic, 29 participated with at least one respondent. The results of the applied survey suggest that dentists, at least the population of surveyed ones, have proper knowledge of detection methods of patients suspected of COVID-19, preventive measures that must be applied in the dental office to decrease the risk of infection, and the appropriate procedures and solutions for dental office disinfection.

Background and Objectives: The aim of this systematic review is to summarize the current data about the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its entry factors in oral tissues and cells. Materials and Methods: This systematic review was carried out based on the Preferred Reporting Items for a Systematic Review and Meta-Analysis (PRISMA). Three databases were analyzed (Pubmed, Web of science and Scopus) by three independent researchers. From the 18 identified studies, 10 of them met the inclusion criteria. The presence of SARS-CoV-2 or its entry factors (angiotensin-converting enzyme II (ACE2), transmembrane serine proteases (TMPRSS), and furin) was analyzed in these 10 studies during the pandemic. Results: ACE2 expression was analyzed in 9 of the 10 studies. ACE2 is expressed mainly in the tongue, oral mucosa, salivary glands and epithelial cells. The expression of the TMPRSS2 gene or protein was analyzed in 6 studies. These studies reported that the expression of TMPRSS2 was mainly in the salivary glands, tongue, sulcular epithelium and oral mucosa; as well as in cells of the salivary glands (ductal, acinar and myoepithelial cells) and the tongue (the spinous-based cell layer, horny layer and the epithelial surface). Other TMPRSS were also reported. The expression of TMPRSS3, TMPRSS4, TMPRSS5, TMPRSS7 and TMPRSS11D was reported mainly in salivary glands and in epithelial-type cells. Furan expression was analyzed in three studies. The expression of furin was detected mainly in epithelial cells of the tongue. A variety of methods were used to carry out the detection of SARS-CoV-2 or its input molecules. Conclusions: These results show that SARS-CoV-2 can infect a wide variety of oral tissues and cells, and that together with the theories dedicated to explaining the oral symptoms present in SARS-CoV-2 positive patients, it provides us with a good scientific basis for understanding the virus infection in the oral cavity and its consequences.

The objective of this article is to conduct a systematic review of the literature to contrast the existing evidence regarding the use of hydrogels during and after experimental orthodontic treatment in animals. An extensive search was performed through the electronic databases, Medline, Web of Science and Scopus, from December 2020 to April 2021 for in vivo animal studies. A total of 282 studies were reviewed. Eight studies were included for final revision; four studies were conducted in rats, two in rabbits, one study in mice and one study in guinea pigs. The quality assessment of the eight included studies was performed according to the ARRIVE guidelines and the risk of bias was assessed using the Center for Systematic Review of Laboratory Animal Experimentation tool; in four of the eight articles evaluated, a high risk-of-bias rating was obtained in 40% of the criteria evaluated. In the studies reviewed, the hydrogel acted as a carrier, and inhibition (post-treatment retention) or acceleration of orthodontic tooth movement was assessed according to the active substance used in each of the articles. The uses of hydrogels for transporting active substances to regulate the rate of orthodontic tooth movement remains debatable. Future studies are suggested to evaluate the feasibility of hydrogel as a transport method in humans.

Introduction. Silver nanoparticles are used in endodontics due to their antimicrobial activity, although it is considered that bacteria are unable to develop resistance to silver nanoparticles. Silver resistance genes have been related to resistance to nanoparticles and antibiotics. The presence of these resistance genes has not been studied in endodontic bacteria. The objective of this study is to report the prevalence of silver resistance genes in endodontic bacteria. Methods. The selected teeth were isolated using a rubber dam and any restoration, post, or caries was eliminated. The operative field was disinfected, and the root-filling material was removed. The samples were obtained using three sterile paper points to absorb the fluid of the root canal. The DNA from the samples and the control organism was extracted, and the detection of the silCBA resistance genes was carried out by PCR. Results. The results of this study show a high prevalence (73.3%) of silCBA silver resistance genes. The Spearman rank correlation coefficient was utilized to identify correlations between the presence of genes and clinical variables. Conclusions. This study reports a high frequency of silver resistance genes related to nanoparticle resistant from bacteria.

The objective of this article was to conduct a systematic review of the literature to contrast the existing evidence regarding the relationship between periodontal disease (PD) and diabetes mellitus (DM) with the possibly increased risk of SARS-CoV-2 infection, as well as to establish a hypothesis that explains the ways in which this interaction could take place. A literature search up from 1 January 2020 to 21 March 2021 was conducted in three electronic databases, namely, PubMed, Web of Science, and Scopus, in order to identify studies on periodontal disease alone or in conjunction with diabetes mellitus, reporting any relation with SARS-CoV-2 infection as a primary outcome. Only articles published in the English language were included. Due to the lack of studies, we decided to collect all the theoretical and clinical evidence suggesting a possible biological pathway evidencing the relationship among PD, DM, and SARS-CoV-2 infection. From a total of 29 articles, 12 were included for final review studies (five reviews, two hypotheses, one Special Issue, one perspective, one commentary, one case–control study, and one case report). In addition, this systematic review article hypothesizes the correlation between PD and type 2 diabetes mellitus (T2DM) by expression of angiotensin-converting enzyme 2 (ACE2) in periodontal tissue and the risk of SARS-CoV-2 infection. T2DM is a metabolic disorder characterized by high blood glucose levels resulting from altered insulin secretion or action. Likewise, periodontitis and T2DM are inflammatory disorders with a bidirectional association, and both diseases have a similar immunomodulatory cascade and cytokine profile. ACE2 is a crucial component of the renin–angiotensin system (RAS) and the key factor of entry in the cells by the new SARS-CoV-2. ACE2 is widely distributed in the lung and kidneys, and interestingly has a great distribution in the oral cavity, principally in the tongue and periodontal tissue. ACE2 in periodontal tissue plays a crucial role between health and disease. Moreover, the ACE2/Ang-(1-7)/MasR axis is downregulated in the dysbiotic and inflammatory periodontal environment. Nevertheless, the balance of ACE2 activity is modified in the context of concurrent diabetes, increasing the expression of ACE2 by the uncontrolled glycemia chronic in T2DM. Therefore, the uncontrolled hyperglycemia possibly increases the risk of developing periodontitis and triggering overexpression of ACE2 in periodontal tissue of T2DM patients, with these events potentially being essential to SARS-CoV-2 infection and the development of mild-to-severe form of COVID-19. In this sense, we would like to point out that the need for randomized controlled trials is imperative to support this association.

Alterations in saliva, temporomandibular joint disorders, dysphagia, Sjogren's syndrome, dental caries, periodontal disease, and tooth loss have been identified in patients with Rheumatoid Arthritis. The aims of this research were 1) to study the association between newly diagnosed rheumatoid arthritis and dental caries and 2) to identify most frequent teeth with caries in study groups. A descriptive pilot study was performed. A total of 620 participants were evaluated, 29 met the selection criteria. The subjects were divided into 2 groups: 13 subjects with newly diagnosed rheumatoid arthritis and 16 subjects without rheumatoid arthritis. Salivary parameters, DMFT index, care index, FS-T index and Treatment Needs Index were evaluated in all participants. The Fisher’s Exact test and Mann-Whitney U test we used to establish the differences between groups. Low mean in all salivary parameters and a high caries frequency were observed in subjects with newly diagnosed rheumatoid arthritis compared to a control group (p<0.01). The right maxillary second premolar (n=6, 46%, p=0.0100); right mandibular second premolar (n=7,54%, p=0.0462) and left mandibular second molar (n=10,77%, p=0.0001) were the most frequent teeth with caries. Early diagnosis and early treatment of rheumatoid arthritis can improve the prognosis in most of patients. The development of new public health policies and care based on the prevention are necessary to improve the quality of patient's lives.