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INTRODUCTION: The dentistry industry has seen a number of exciting new advancements in recent years, many of which have been made possible by the introduction of automated technologies such as computer-aided design and computer-aided manufacturing (CAD/CAM). Despite the fact that these new approaches simplify the fabrication process in favor of decreased material consumption and improved time efficiency, it is possible that they may have an effect on the prosthesis's fitness, which in turn may affect how long they will last. PURPOSE: The purpose of this in vitro study was to evaluate the trueness and fitness of cobalt-chromium (Co-Cr) crown copings fabricated by selective laser melting (SLM), milling, and conventional casting methods. MATERIALS AND METHODS: A zirconium die was fabricated and scanned with a laboratory scanner to manufacture the Co-Cr metal copings for three groups (n = 12). In group A, the copings were fabricated by a 3D printing technique called SLM; in group B, the copings were fabricated by the milling technique; and in group C, the copings were fabricated by the conventional lost-wax method. After fabrication, the trueness and the internal fitness of the copings were evaluated using a metrology software program (Geomagic Control X, 3D Systems Inc., Rock Hill, SC). The one-way ANOVA and Tukey's honestly significant difference test were used to statistically analyze the data. RESULTS: The highest root mean square (RMS) value of trueness was for CAD/CAM milling, and the highest mean of horizontal gaps was for the casted (lost-wax technique) group. There were highly significant differences in the mean RMS value of trueness and the mean horizontal gaps between the three groups. CONCLUSION: The fabrication method of Co-Cr crown copings has an effect on the trueness and fitness of the copings.
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BACKGROUND: There are different protocols initiated to maintain the workflow in cardiovascular units around the world. Variable responses were seen in different populations. We adapted certain protocols during coronavirus disease-2019 (COVID-19) pandemic because we want to know the key element that maintains an acceptable standard of cardiovascular care during future pandemics. METHODS: Four hundred and fifty-four cardiac patients were admitted during COVID-19 era. Patients from March to July 2020 were included in this study. Those patients were divided into two periods: strict-COVID-19 from March 19, 2020, to May 18, 2020 (132 patients) and mid-COVID-19 from May 19, 2020, to July 18, 2020 (322 patients). These were compared to admissions at the pre-COVID-19 era from January 19, 2020, to March 18, 2020 (600 patients). All patients' data were collected through the quality department from the electronic medical records. RESULTS: Throughout the COVID-19 pandemic, the admission number and ST-elevation myocardial infarction (STEMI) cases were dramatically reduced during the strict-COVID-19 time yet recovered back in the mid-COVID-19 period. The admission rate was reduced from 600 to 132, while the STEMI cases dropped from 91 in pre-COVID-19 to 41 in strict-COVID-19 and then back to 81 cases in mid-COVID 19 period (P > 0.05/P = 0.02 between pre and mid-COVID-19 periods). CONCLUSION: Our cardiac center continues to serve our population without a complete lockdown period due to multiple key elements adapted during this pandemic. The flexibility in the protocols of managing acute cardiac cases has maintained the mortality rate stable through all COVID-19 periods and return to working efficiently to near-normal levels.
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PURPOSE: The aim of the study was to evaluate and compare the fracture resistance and modes of fracture of monolithic zirconia crowns with two preparation designs.MATERIALS AND METHODS: Forty human maxillary first premolar teeth were extracted for orthodontic purposes and divided into two main groups (n=20): Group A: monolithic traditional zirconia; Group B: monolithic translucent zirconia. The groups were further subdivided into two subgroups (n=10): (A1, B1) shoulder margin design; (A2, B2) feather-edge margin design. Teeth were prepared with either a 1 mm shoulder margin design or a feather-edge margin design. The prepared teeth were scanned using a digital intraoral scanner. The crowns were cemented using self-adhesive resin cement. All cemented teeth were stored in water for 7 days and thermocycling was done before testing. All samples were subjected to compressive axial loading until fracture. The fractographic analysis was done to assess the modes of fracture of the tested samples.RESULTS: The highest mean values of fracture resistance were recorded in kilo-newton and were in the order of subgroup A1 (2.903); subgroup A2 (2.3); subgroup B1 (1.854) and subgroup B2 (1.523). One-way ANOVA showed a statistically significant difference among the 4 subgroups. Concerning modes of fracture, the majority of samples in subgroups A1 and B1 were fracture of restoration and/or tooth, while in subgroups A2 and B2, the majority of samples fractured through the central fossa.CONCLUSION: Even though all the tested crowns fractured at a higher level than the maximum occlusal forces, the shoulder margin design was better than the feather-edge margin design and the monolithic traditional zirconia was better than the monolithic translucent zirconia in terms of fracture strength.
