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This study aimed to analyze the root anatomy and root canal system morphology of mandibular first premolars in a Chilean population. 186 teeth were scanned using micro-computed tomography and reconstructed three-dimensionally. The root canal system morphology was classified using both Vertucci’s and Ahmed’s criteria. The radicular grooves were categorized using the ASUDAS system, and the presence of Tomes’ anomalous root was associated with Ahmed’s score. A single root canal was identified in 65.05% of teeth, being configuration type I according to Vertucci’s criteria and code 1MP1 according to Ahmed’s criteria. Radicular grooves were observed in 39.25% of teeth. The ASUDAS scores for radicular grooves were 60.75%, 13.98%, 12.36%, 10.22%, 2.15%, and 0.54%, from grade 0 to grade 5, respectively. The presence of Tomes’ anomalous root was identified only in teeth with multiple root canals, and it was more frequently associated with code 1MP1–2 of Ahmed’s criteria. The root canal system morphology of mandibular first premolars showed a wide range of anatomical variations in the Chilean population. Teeth with multiple root canals had a higher incidence of radicular grooves, which were closely related to more complex internal anatomy. Only teeth with multiple root canals presented Tomes’ anomalous root.

Periodontitis is an oral inflammatory disease in which the polymicrobial synergy and dysbiosis of the subgingival microbiota trigger a deregulated host immune response, that leads to the breakdown of tooth-supporting tissues and finally tooth loss. Periodontitis is characterized by the increased pathogenic activity of T helper type 17 (Th17) lymphocytes and defective immunoregulation mediated by phenotypically unstable T regulatory (Treg), lymphocytes, incapable of resolving the bone-resorbing inflammatory milieu. In this context, the complexity of the immune response orchestrated against the microbial challenge during periodontitis has made the study of its pathogenesis and therapy difficult and limited. Indeed, the ethical limitations that accompany human studies can lead to an insufficient etiopathogenic understanding of the disease and consequently, biased treatment decision-making. Alternatively, animal models allow us to manage these difficulties and give us the opportunity to partially emulate the etiopathogenesis of periodontitis by inoculating periodontopathogenic bacteria or by placing bacteria-accumulating ligatures around the teeth; however, these models still have limited translational application in humans. Accordingly, humanized animal models are able to emulate human-like complex networks of immune responses by engrafting human cells or tissues into specific strains of immunodeficient mice. Their characteristics enable a viable time window for the study of the establishment of a specific human immune response pattern in an in vivo setting and could be exploited for a wider study of the etiopathogenesis and/or treatment of periodontitis. For instance, the antigen-specific response of human dendritic cells against the periodontopathogen Porphyromonas gingivalis favoring the Th17/Treg response has already been tested in humanized mice models. Hypothetically, the proper emulation of periodontal dysbiosis in a humanized animal could give insights into the subtle molecular characteristics of a human-like local and systemic immune response during periodontitis and support the design of novel immunotherapeutic strategies. Therefore, the aims of this review are: To elucidate how the microbiota-elicited immunopathogenesis of periodontitis can be potentially emulated in humanized mouse models, to highlight their advantages and limitations in comparison with the already available experimental periodontitis non-humanized animal models, and to discuss the potential translational application of using these models for periodontitis immunotherapeutics.

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Senescent cells express a senescence-associated secretory phenotype (SASP) with a pro-inflammatory bias, which contributes to the chronicity of inflammation. During chronic inflammatory diseases, infiltrating CD4+ T lymphocytes can undergo cellular senescence and arrest the surface expression of CD28, have a response biased towards T-helper type-17 (Th17) of immunity, and show a remarkable ability to induce osteoclastogenesis. As a cellular counterpart, T regulatory lymphocytes (Tregs) can also undergo cellular senescence, and CD28- Tregs are able to express an SASP secretome, thus severely altering their immunosuppressive capacities. During periodontitis, the persistent microbial challenge and chronic inflammation favor the induction of cellular senescence. Therefore, senescence of Th17 and Treg lymphocytes could contribute to Th17/Treg imbalance and favor the tooth-supporting alveolar bone loss characteristic of the disease. In the present review, we describe the concept of cellular senescence; particularly, the one produced during chronic inflammation and persistent microbial antigen challenge. In addition, we detail the different markers used to identify senescent cells, proposing those specific to senescent T lymphocytes that can be used for periodontal research purposes. Finally, we discuss the existing literature that allows us to suggest the potential pathogenic role of senescent CD4+CD28- T lymphocytes in periodontitis.

Aim To describe the radicular dentine thickness in mandibular first premolars presenting C‐shaped root canals, to identify the canal walls with less thickness as potential danger zones. In addition, to describe the internal and external anatomical characteristics of these teeth and associate them with the dentine thickness. Methodology A total of 70 mandibular first premolars presenting C‐shaped root canals were examined. Their internal morphology was analysed using Vertucci’s and Fan’s criteria, and their external morphology was analysed using the ASUDAS score. Besides, the dentine thickness around the root canals was two/three‐dimensionally determined at five root planes and quantified in the distal and the mesial aspects. Results According to Fan’s, ASUDAS, and Vertucci’s classifications, the most common canal configurations were category C3, grade 3, and type V, respectively. In Vertucci's type III anatomy, the mesial root wall of the lingual canal showed significantly less dentine thickness than the distal wall in the middle plane (p = .031). Similarly, in Vertucci's type V anatomy, significantly less dentine thickness was observed in the mesial root wall of the buccal and lingual canals in the middle plane (p < .001) and the buccal canal in the middle‐apical plane (p = .014) than the distal root wall of these canals. In teeth with ASUDAS grade 3 and 4 scores, significantly less dentine thickness was observed in the mesial in comparison with the distal root wall of these canals. These differences were demonstrated in the middle and middle‐apical planes (p < .001) of grade 3 teeth and the middle‐apical plane (p < .001) of grade 4 teeth. In these root planes, the Ver1‐AS3 and VerV‐AS3 combinations presented a 4‐times greater risk of presenting walls with a critical dentine thickness of 0.6 mm (odds ratio [OR] = 4, p = .025) than the combinations Ver1‐AS2, VerV‐AS2, VerV‐AS4, and VerIII‐AS3. Conclusions The root canal system configuration of mandibular first premolars with C‐shaped canals showed a wide range of anatomical variations. The lowest dentine thickness was located in the mesial wall of the canals in the middle and apical root thirds of Vertucci’s type III and V anatomies and in teeth with deep radicular grooves scored as ASUDAS grades 3 and 4. In the middle and middle‐apical planes, the presence of the combinations Ver1‐AS3 and VerV‐AS3 showed a high risk of presenting a critical dentine thickness of 0.6 mm. Therefore, these root canal walls with less dentine thickness represent potential instrumentation danger zones in mandibular first premolars with C‐shaped canals.

Natural killer T (NKT) cells constitute a unique subset of T lymphocytes characterized by specifically interacting with antigenic glycolipids conjugated to the CD1d receptor on antigen-presenting cells. Functionally, NKT cells are capable of performing either effector or suppressor immune responses, depending on their production of proinflammatory or anti-inflammatory cytokines, respectively. Effector NKT cells are subdivided into three subsets, termed NKT1, NKT2, and NKT17, based on the cytokines they produce and their similarity to the cytokine profile produced by Th1, Th2, and Th17 lymphocytes, respectively. Recently, a new subgroup of NKT cells termed NKT10 has been described, which cooperates and interacts with other immune cells to promote immunoregulatory responses. Although the tissue-specific functions of NKT cells have not been fully elucidated, their activity has been associated with the pathogenesis of different inflammatory diseases with immunopathogenic similarities to periodontitis, including osteolytic pathologies such as rheumatoid arthritis and osteoporosis. In the present review, we revise and discuss the pathogenic characteristics of NKT cells in these diseases and their role in the pathogenesis of periodontitis; particularly, we analyze the potential regulatory role of the IL-10-producing NKT10 cells.

Introduction Root-scaling procedures on the root surface show to increase root surface roughness during instrumentation. The use of a prophylactic paste reduces the roughness. Objetive This study evaluated the influence of prophylaxis paste on the surface roughness of root dentin after hand instruments (HI), ultrasonic scalers (US) and rotational instruments (RI) were applied to root surfaces. Material and method Fifty bovine roots were prepared and randomly divided into 10 groups (n=5) in which instrumentation with HI, US, or RI was carried out with or without prophylaxis using either conventional or 3% hydroxyapatite paste; additionally, a control group without treatment was included. The Ra and Rz roughness values were measured using a perfilometer. The morphological aspects of the root surfaces were analysed qualitatively by scanning electron microscopy (SEM). Data were analysed using two-way ANOVA followed by Tukey’s test (α = 0.05). Result The scaling method and the prophylaxis procedure significantly influenced (p < 0.05) root surface roughness. Treatment with US and prophylaxis with 3% hydroxyapatite paste resulted in lower values of Ra (0.14 μm ± 0.02 μm) and Rz (0.89 μm ± 0.18 μm) compared to the other groups. SEM analysis showed smoother and more homogeneous surfaces in the groups with prophylaxis compared to the groups without prophylaxis. There were no substantial differences between the results of applying different pastes. Conclusion The prophylaxis procedure performed with the experimental paste containing 3% hydroxyapatite reduced the roughness of root surfaces treated with HI, US and RI at the same level as the conventional prophylactic paste.