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M. tuberculosis, an etiological agent of tuberculosis, requires a long treatment regimen due to its ability to respond to stress and persist inside the host. The second messenger (p)ppGpp-mediated stress response plays a critical role in such long-term survival, persistence, and antibiotic tolerance which may also lead to the emergence of multiple drug resistance. In mycobacteria, (pp)pGpp molecules are synthesized predominantly by two bifunctional enzymes-long RSH-Rel and short SAS-RelZ. The long RSH-Rel is a major (p)ppGpp synthetase and hydrolase. How it switches its activity from synthesis to hydrolysis remains unclear. RelMtb mutant has been reported to be defective in biofilm formation, cell wall function, and persister cell formation. The survival of such mutants has also been observed to be compromised in infection models. In M. smegmatis, short SAS-RelZ has RNase HII activity in addition to (pp)Gpp synthesis activity. The RNase HII function of RelZ has been implicated in resolving replication-transcription conflicts by degrading R-loops. However, the mechanism and regulatory aspects of such a regulation remain elusive. In this article, we have discussed (p)ppGpp metabolism and its role in managing the stress response network of mycobacteria, which is responsible for long-term survival inside the host, making it an important therapeutic target.
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CONTEXT: The displacement of the gingiva around the tooth allows proper access during preparation, precise impression taking, and cementation procedures that has a direct bearing on the health of the periodontium. Several methods and agents are used for this purpose. AIMS: The primary aim of the study was to clinically evaluate the efficacy of naphazoline as a gingival retraction agent. The secondary aim was to compare it with tetrahydrozoline and aluminum chloride. SETTINGS AND DESIGN: Fifteen patients participated in a randomized crossover clinical trial at the Army College of Dental Sciences, Secunderabad, Telangana, India. SUBJECTS AND METHODS: Preliminary maxillary impressions were made with irreversible hydrocolloid for all patients to fabricate custom trays. After that, baseline impressions and cast for control group measurements were prepared. Gingival displacement was carried out in the right maxillary central incisor for all, with retraction cord soaked in three agents, either, aluminum chloride, tetrahydrozoline, or naphazoline. These agents were used in all patients with a washout period of 14 days. Elastomeric monophase impressions and die stone casts were recorded for each group. The central incisors were sectioned, and gingival retraction was measured using a measuring stereomicroscope. STATISTICAL ANALYSIS USED: The gingival displacement was statistically analyzed using one-way ANOVA and post hoc Bonferroni. RESULTS: Naphazoline had the highest retraction (138.160 µm) followed by tetrahydrozoline (136.039 µm) and aluminum chloride (130.759 µm). CONCLUSIONS: Naphazoline, tetrahydrozoline, and aluminum chloride show a clinically and statistically significant amount of displacement when compared to control. Among the three agents, naphazoline showed maximum displacement and maybe a good alternative with fewer side effects.
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Background. The present study was undertaken to evaluate the incidence of dentinal cracks during root canal preparation with different periodontal ligament simulating materials in vitro. Methods. Seventy freshly extracted human mandibular first premolars were selected and divided into 7 groups in terms of simulating material: group 1: polyether impression material; group 2: polyvinyl acetate adhesive; group 3: polyvinyl siloxane impression material; group 4: cyanoacrylate adhesive; group 5: epoxy resin adhesive; group 6: positive control, without any periodontal ligament simulation; and group 7: negative control, where neither a periodontal ligament simulating material was used nor canal preparation was carried out. Root canal preparation was carried out in all the groups followed by sectioning of roots at 3 mm, 6 mm and 9 mm. The sections were evaluated under a stereomicroscope at ×2.5 for the presence or absence of cracks. Chi-squared test was used to compare the appearance of defective roots between the different experimental groups. Results. The least number of cracks were found in the negative control group, followed by group 1 where polyether impression material was used for periodontal ligament simulation. The difference was significant with a P-value of 0.002 for coronal sections. Conclusion. Under the limitation of the present study, polyether and polyvinyl siloxane (light body) can both be used for simulation of periodontal ligament.
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CONTEXT: Noncarious cervical lesions may penetrate the pulp and require root canal treatment followed by crown placement. Such teeth may be susceptible to fracture, especially at the cervical area. AIMS: To estimate which combination of restorative material and crown resulted in homogenous stress-strain distribution of endodontically treated abfracted mandibular premolar using three-dimensional finite element model (FEM). SETTINGS AND DESIGN: A three-dimensional model of mandibular single-rooted premolar along with alveolar bone was created in finite element analysis (FEA) software preprocessor ANSYS rel 14.5 FEM software (ANSYS Inc., Houston, USA, 1994). Cervical lesion was created in the model with specific dimensions, 3 mm mesiodistally and 2 mm gingivoocclusally with enamel occlusal margin and dentin gingival margin. MATERIALS AND METHODS: Tooth was simulated to be root canal treated and restored with different types of cements and crowns followed by placing a static load of 300 N at an angle of 135°. Analysis was run and stress distribution pattern was studied. RESULTS: Cervical region of an endodontically treated tooth is subjected to stresses, irrespective of restorative material used. Porcelain fused to metal (PFM) crowns showed least strain values with different postendodontic, restorative materials. CONCLUSIONS: FEA is a predictable and reproducible model to predict stress-strain behavior. PFM crowns with different postendodontic restorative materials showed least strain values in the cervical area of abfracted, endodontically treated premolars.
