Survival of Four Conical Implant Abutment Connections After Removal of the Abutment Screw and Simulated Cyclic Loading: An In Vitro Comparative Study.

This in vitro study evaluated the mechanical behavior of different conical connection implant systems after abutment screw withdrawal. Four conical connection systems were selected based on different conical half-angles: Ankylos (5.7°), Cowell (7.0°), Straumann (7.5°), and Astra (11.0°). In each system, 5 implants and abutments were used (n = 5). According to the recommended value, each abutment screw was torqued to settle the abutment and then withdrawn through a predesigned hole of the cemented crown. The retentiveness of the abutment was evaluated by the following mechanical testing. All specimens were subjected to cyclic loading of 20-200 N, 30°, and 4-mm off-axis to the implant axis, for 106 cycles. The pullout forces and axial displacements of the abutments were measured. The data of the Cowell system was obtained from our previous work. All groups other than Astra group, in which abutment loosened after abutment screw withdrawal, passed the cyclic loading test. Straumann group demonstrated a significantly lower pullout force (27.4 ± 21.1 N) than Ankylos (160.1 ± 41.4 N) and Cowell (183.7 ± 30.5 N) groups. All groups showed abutment rebound after screw withdrawal except Straumann group. In addition, Ankylos, Cowell, and Straumann groups demonstrated axial displacement after cyclic loading. In terms of the retentiveness of the abutment after abutment screw withdrawal examined in this study, Ankylos and Cowell groups had much higher retentiveness than Straumann group, while Astra group had none. Conical angle could be a key design parameter to make abutment screw withdrawal after conical abutment settlement feasible, but more studies must be conducted for clinical application.

Abutment screw withdrawal after conical abutment settlement: A pilot study.

OBJECTIVE: This study investigated the effects of abutment screw withdrawal after conical abutment settlement on the stability of the implant-abutment connection. MATERIALS AND METHODS: Twenty implants of a conical connection system were used. Two two-piece abutment designs were used: cone only (n = 10; NI) and cone plus octagonal index design (n = 10; I); for each design, five samples were used with (S) and without (NS) abutment screw withdrawal before a cyclic test. Finally, four groups, namely Gr S(NI), Gr S(I), Gr NS(NI), and Gr NS(I), were included. The cyclic test included cyclic loading of 20-200 N, 30°, and 4-mm off-axis to implant axis at 10 Hz for 106 cycles, simulating a clinical time interval of 40 months. The fatigue cycles were recorded. The axial displacement of the conical abutments during abutment settlement, screw withdrawal, and cyclic loading were measured. Abutment morphology was examined through scanning electron microscopy (SEM). RESULTS: Only Gr NS(NI) failed the test, indicating that without the index design and abutment screw withdrawal, and connection stability seriously deteriorated. Gr NS(I) exhibited significantly higher axial displacement into the implant after abutment settlement than did Gr NS(NI). It also exhibited continuous axial displacement into the implant after cyclic loading. SEM after cyclic testing in Gr NS(I) revealed marked burnishing on lateral edges of the index, indicating that the index design provides an antitorsional ability. CONCLUSION: Although this study has few limitations, abutment screw withdrawal is feasible in this conical implant-abutment connection system with index design.

Correlation of magnetic resonance imaging grades with cytokine levels of synovial fluid of patients with temporomandibular joint disorders: a cross-sectional study.

OBJECTIVES: Magnetic resonance imaging (MRI) is a standardized method for assisting joint diagnosis. To validate the reliability of different imaging-based grading systems, this study examined (1) the associations between grading systems for osseous change, joint effusion, and the Wilkes classification of temporomandibular joint (TMJ) disorders and (2) the correlation between cytokines in synovial fluid and imaging-based joint scores. MATERIALS AND METHODS: Twenty-seven patients, who routinely received numeric rating scale (NRS) and MRI assessment before TMJ arthrocentesis, were enrolled. Each joint was evaluated through the grading criteria for severity of osseous change and joint effusion by blinded observers using MRI. ImageJ was employed for classifying joint effusion. Joint synovial fluid, collected through arthrocentesis, was examined for cytokine expression by using a Luminex multiplex assay. All data were analyzed using the Pearson correlation analysis. RESULTS: The Wilkes classification was strongly correlated with osseous change scores, but not with joint effusion scores. Joint effusion scores significantly correlated with NRS scores, but not with the Wilkes classification and osseous change scores. Compared with osseous change scores, joint effusion scores had a higher correlation with the levels of inflammatory cytokines (interleukin (IL)-8 and soluble IL-6 receptor (sIL-6R)) and with anti-inflammatory cytokines (soluble tumor necrosis factor receptors I and II (sTNF-RI/II)). CONCLUSIONS: In patients with TMJ disorders, MRI grades are strongly correlated with NRS scores and levels of cytokines (IL-8, sIL-6R, and sTNF-RI/II) in the synovial fluid. CLINICAL RELEVANCE: Joint effusion scoring can be a reliable and valid indicator for pathological assessment of TMJ disorders.

Effect of online learning for dental education in asia during the pandemic of COVID-19.

BACKGROUND/PURPOSE: Online learning has been utilized in the world to continue educational activities in dentistry, which was severely affected by the pandemic of coronavirus disease 2019 (COVID-19). The purpose of this study was aimed to evaluate the effect of online learning during the pandemic of COVID-19 in different dental schools of different countries in Asia by the questionnaire survey. MATERIALS AND METHODS: Mantel-Haenszel chi-square tests were used to analyze the difference between dental schools with and without shutdown. A questionnaire-based online survey was used to evaluate the online learning effect on undergraduate students in 13 dental schools of 7 Asia countries and regions. RESULTS: For the question that blended learning class has better learning efficiency, the agreement rate was significantly higher in the students (80.3%) from the dental schools that did not suspend face-to-face education activities than in the students (50.3%) from the dental school that was shut down. CONCLUSION: Within the limitation of this study, it is concluded that a combination of physical and online classes in terms of blended learning courses will be the future trend for dental education.

Innovation of dental education during COVID-19 pandemic.

BACKGROUND/PURPOSE: The impact of the pandemic of COVID-19 has a certain influence on various walks of life around the world. Because of the pandemic of this novel coronavirus in terms of COVID-19, the social life global wide has been changed a lot. To keep the social distance between human being to prevent from being infected is the most important strategy for all the countries. Many dental schools have been locked down to minimize the spread out of this coronavirus infection. Close contact between human being are required for all those learning process in traditional dental education. Learning methods should be innovated to keep on the learning process but away from being infected for dental education during pandemic. The purpose of this manuscript is to exchange the information and experience of those dental educators from different countries to prepare for the future demand for dental education during pandemic. MATERIALS AND METHODS: By means of three online symposiums, dental educators from different countries were invited to give presentation and discussion regarding to the information and experience in the innovation of dental education during the pandemic. RESULTS: The results showed that the impact of the pandemic of COVID-19 affects the dental education a lot. Intelligent technology has certain benefit for the learning process of dental education during the pandemic. CONCLUSION: The impact of the pandemic of COVID-19 affects dental education a lot. The model of dental education should be innovated to suit different situations and novelty intelligent technology should be applied for future dental education.

Guidelines for innovation in dental education during the coronavirus disease 2019 pandemic.

During the current coronavirus disease 2019 (COVID-19) pandemic, dental education and training requiring face-to-face interaction must prioritize infection prevention and the safety of students, staff, and patients. In July 2020, the Association for Dental Education, Asia Pacific (ADEAP) published safety guidelines for safe dental education during the COVID-19 pandemic. These guidelines summarize ADEAP recommendations for classroom-based courses, reopening of simulated training courses and dental clinics, and provision of clinical skills training courses in dentistry during the COIVID-19 pandemic. They have been formulated to ensure the safety of students and teaching staff, dental auxiliary staff, and patients. However, the present guidelines are considered appropriate only when the number of COVID-19 epidemic cases has been significantly reduced, i.e. when the epidemiological curve has flattened in the area concerned. The criteria for lifting restrictions on activities should be consistent with relevant jurisdictional guidelines.