Finite element analysis of maxillary first molar with mesial-occlusal-distal-palatal defect restored with different post-and-core strategies.

Purpose: To explore which restoration strategy generates the most favorable stress distribution in an endodontically-treated maxillary first molar with mesial-occlusal-distal-palatal defect. Methods: Models with one post in palatal canal (PP), each post in palatal and distobuccal canals (PDP), each post in palatal and mesiobuccal canals (PMP), and each post in all canals (PDMP) were established for an endodontically-treated maxillary first molar with mesial-occlusal-distal-palatal defect either with fiber-reinforced composite (FRC) post or gold alloy cast (GAC) post. A 400-N vertical force and a 225-N lateral force were respectively applied. The Mohr-Coulomb stress ratio (σMC ratio) in the residual tooth structure (RTS), the resin cement, and the crowns, the tensile stress (σt) and compressive stress (σc) in the FRC posts, the von-Mises stress ratio (σvM ratio) in the GAC post-and-cores, and the σt and shear stress (σs) at the adhesive interfaces were calculated using finite element analysis. Results: FRC posts generated lower σMC ratio than GAC posts in the RTS (0.3274-0.3643 vs. 0.3399-0.4118). Among the FRC post groups, the PDMP group got the lowest σs at the dentin-post interface (14.92 MPa) and the abutment-crown interface (8.242 MPa) under vertical loading, as well as the lowest σMC ratio in the RTS (0.3381) and the lowest σs at the dentin-post interface (38.00 MPa) under lateral loading. Conclusions: From the point of stress distribution, placing FRC posts in the palatal, distobuccal, and mesiobuccal canals is the optimal strategy in restoring a severely damaged maxillary first molar, provided that lateral occlusal force is reduced.

Exosomes from Cyclic Stretched Periodontal Ligament Cells Induced Periodontal Inflammation through miR-9-5p/SIRT1/NF-κB Signaling Pathway.

Abundant evidence demonstrates that mechanical stress could induce an inflammatory response in periodontal tissue, but the precise mechanism remains unclear. In the past few years, periodontal ligament cells (PDLCs), as the most force-sensitive cells, have been investigated in depth as local immune cells, associated with activation of inflammasomes and secretion of inflammatory cytokines in response to mechanical stimuli. However, this study innovatively inspected the effect of PDLCs on the other immune cells after stretch loading to reveal the detailed mechanism by which mechanical stimuli initiate immunoreaction in periodontium. In the present study, we found that cyclic stretch could stimulate human PDLCs to secret exosomes and that these exosomes could further induce the increase of phagocytic cells in the periodontium in Sprague-Dawley rats and the M1 polarization of the cultured macrophages (including the mouse macrophage cell line RAW264.7 and the bone marrow-derived macrophages from C57BL/6 mice). Furthermore, the exosomal miR-9-5p was detected to be overexpressed after mechanical stimuli in both in vivo and in vitro experiments and could trigger M1 polarization via the SIRT1/NF-κB signaling pathway in the cultured macrophages. In summary, this study revealed that PDLCs could transmit the mechanobiological signals to immune cells by releasing exosomes and simultaneously enhance periodontal inflammation through the miR-9-5p/SIRT1/NF-κB pathway. We hope that our research can improve understanding of force-related periodontal inflammatory diseases and lead to new targets for treatment.

Finite element analysis of maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule restored with fiber-reinforced composite resin posts and resin core: The number and placement of the posts.

STATEMENT OF PROBLEM: Whether fiber-reinforced composite (FRC) posts should be inserted in root canals to restore teeth with multiple roots remains unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to determine the optimal use of FRC posts in an endodontically treated maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule. MATERIAL AND METHODS: Eight different models of a maxillary first molar were established: no post (NP), post in palatal root (P), post in distobuccal root (DB), post in mesiobuccal root (MB), posts in palatal root and distobuccal root (P+DB), posts in palatal root and mesiobuccal root (P+MB), posts in 2 buccal roots (DB+MB), and posts in all roots (P+DB+MB). Two types of loading were applied: a force of 800 N parallel to the long axis of the tooth to simulate the vertical masticatory force and another force of 225 N at 45 degrees to the long axis of the tooth to simulate the lateral masticatory force. The equivalent stresses on the external surfaces of the tooth tissue, the internal surfaces of the root canals and in the posts, as well as the maximal shear stresses on the post-core interface and the core-dentin interface, were calculated with FEA. RESULTS: All the models showed similar maximal equivalent stress values on the external surfaces of the tooth tissue, and stress concentrations were found at the cervical and furcation area. On the internal surfaces of root canals, an increase of equivalent stress at the middle third of the canals with posts and a decrease at the cervical third were observed. Under vertical loading, the P+DB+MB group showed the largest equivalent stress in the post (76.45 MPa in the palatal post), the DB+MB group showed the largest shear stress on the post-core interface (19.02 MPa), and the MB group showed the largest shear stress on the core-dentin interface (12.07 MPa). Under lateral loading, the P+DB+MB group showed the largest equivalent stress in the post (60.11 MPa in the mesiobuccal post) and the largest shear stress on the post-core interface (13.48 MPa) and the DB group showed the largest shear stress on the core-dentin interface (21.03 MPa). CONCLUSIONS: One post in the palatal canal was found to be appropriate for the FRC post and resin core restoration of a maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule. An additional post in the mesiobuccal canal could help disperse lateral occlusal force and improve retention of the restoration.

The application of individualized abutment-crown integrated provisional restoration in optimizing the peri-implant soft tissue contour in the esthetic zone.

OBJECTIVE: This article introduced a modified method to fabricate an individualized abutment-crown integrated provisional restoration for single-tooth implant restoration in the esthetic zone, which created a satisfactory peri-implant soft tissue architecture. CLINICAL CONSIDERATIONS: Three months after the implant placement, the individualized abutment-crown integrated provisional restoration was designed and fabricated in the laboratory, by referring to the profile of natural contra-lateral tooth digitally, and seated on the implant afterwards. The peri-implant soft tissue architecture was evaluated and the Pink Esthetic Score (PES) was recorded. The provisional restoration stayed on the implant for 3 months until the individualized definitive ceramic abutment and crown were fixed on the implant. CONCLUSIONS: This protocol provided an alternative solution for shaping the peri-implant soft tissue morphology in the esthetic zone by using an individualized abutment-crown integrated provisional restoration and showed promising effect on the esthetics of anterior single-tooth implant restoration. CLINICAL SIGNIFICANCE: The individualized abutment-crown integrated provisional restoration whose emergence profile mirroring that of the natural contra-lateral tooth, was designed with the help of computer-aided design-manufacture (CAD/CAM). It may help shaping the peri-implant soft tissue in the esthetic zone with merits of saving amount of hand labor of technicians as well as clinicians, and reducing the visits of patients.

The protective role of Ephrin-B2/EphB4 signaling in osteogenic differentiation under inflammatory environment.

Inflammation and alveolar bone destruction constitute the main pathological process of periodontitis. However, the molecular mechanisms of bone destruction under the inflammation environment remain unclear. This study aims to explore the role of Ephrin-B2/EphB4 signaling in osteogenic differentiation under the inflammation environment. Mouse pre-osteoblasts MC3T3-E1 were pretreated with lipopolysaccharide of Porphyromonas gingivalis (Pg-LPS). The Ephrin-B2/EphB4 signaling was activated, and the osteogenic differentiation of cells was examined. The results showed that activation of Ephrin-B2/EphB4 signaling promoted the expression levels of osteogenic differentiation-related genes, and also relieved the inhibitory effect of Pg-LPS on osteogenesis. Noticeably, the effect of Ephrin-B2/EphB4 signaling might be related to the mitogen-activated protein kinase (MAPK) pathway. While applying Ephrin-B2-Fc and EphB4-Fc to periodontitis mice, we observed the reduction of alveolar crest destruction. The current study revealed the possible role of Ephrin-B2/EphB4 signaling in reducing bone destruction in periodontitis and suggested its potential values for further research.

Evaluation of influence factors on the width, length, and width to length ratio of the maxillary central incisor: A systematic review and meta-analysis.

OBJECTIVES: The aim of this study was to analyze whether symmetry of left and right sides, gender, measuring method, and ethnicity have influences on width (W), length (L), and width to length ratio (W/L) of the maxillary central incisor (MCI) and provide a reference for dental treatment planning in the esthetic zone. MATERIALS AND METHODS: An electronic search was conduct of the dental literature. Studies reporting data about measurements were included. Data were extracted and analyzed for the differences between left and right, male and female, different measuring methods, and ethnicities by Review Manager and Stata statistical software. RESULTS: Seventeen studies were included. There were no differences between measurement of the left and right groups, perceived and actual measuring groups. However, differences were found between genders in MCI's W and L but no difference in W/L. Differences were also found between Asians and Caucasian subjects in MCI's W, L, and W/L. CONCLUSIONS: The results of this meta-analysis suggest that symmetry of left and right sides and measuring method do not influence MCI dimension. Gender and ethnicity are found as influence factors for MCI dimension. We believe these findings can be helpful for dentists to decide and design the dimensions of the restorations for maxillary anterior teeth in clinical practices. CLINICAL SIGNIFICANCE: In the process of designing maxillary anterior teeth for implantation, the contralateral MCI can be helpful to create a symmetrical esthetic restoration. For patients with maxillary anterior tooth loss or diastemas, dentists should divide the left and right space equally and keep the MCI contact area aligned with the midline. Dentists should take face size and gender into consideration when making treatment plans for the MCI. Facial parameters as well as the size ratios of the previous teeth can be evaluated and may influence the size and shape of the teeth. When measuring anterior teeth or facial dimensions for esthetic evaluation, the recommended method is to measure the perceived sizes of a facial view image created by a digital camera. Slight discrepancies may exist between the actual and measured values due to the curvature of the arch and the angle in which the photograph was taken.

Suppressing ROS generation by apocynin inhibited cyclic stretch-induced inflammatory reaction in HPDLCs via a caspase-1 dependent pathway.

It has been reported that cyclic stretch could induce inflammatory reaction in human periodontal ligament cells (HPDLCs). Though reactive oxygen species (ROS) has been reported to be involved in pathogen-induced periodontal inflammatory reaction, its role in the force-related periodontal diseases has not been well clarified. This study inspected the role of ROS in the cyclic stretch-induced inflammatory reaction in HPDLCs and studied the inhibitory effect of antioxidant apocynin on this inflammatory reaction. Results confirmed that cyclic stretch induced inflammatory reaction and production of ROS in HPDLCs. This inflammatory reaction was inhibited by apocynin through blocking the production of ROS. The cyclic stretch also induced the expression of caspase-1 and NLRP3 inflammasome, which could also be inhibited by apocynin. Moreover, the cyclic stretch-induced inflammatory reaction was inhibited by caspase-1 inhibitor. Collectively, it is the first time that increased intracellular ROS was proved to play as an intermediate signal in the cyclic stretch-induced inflammatory reaction in HPDLCs, via a caspase-1-dependent pathway. The inhibitory effect of apocynin on the cyclic stretch-induced inflammatory reaction in HPDLCs shows the potential of antioxidants in the treatment of force-related periodontal inflammatory diseases.