Effect of Semisolid and Heat Treatment Process on Microstructural Refinement of Al-7Si Alloy.

Improving the engineering properties of Al-7Si cast alloys (300 series) provides an attractive alternative to automotive and aircraft engine industries. The solubility limit of silicon (Si) in Al contributes to the precipitation of flake-shaped Si particles with sharp edges, which function as a stress riser and promote crack propagation during the eutectic phase while also weakening the protective layer's durability. In this study, the impact of microstructure refinement of Al-7Si alloys by using cooling slope, thixoforming and the T6 heat treatment process on hardness and corrosion resistance behavior was investigated. Results showed that the microstructures of the as-cast alloy had a very coarse dendritic shape, whereas the dendritic transferred to the globular α-Al phase, and the Si particles were replaced into a lamellar- or acicular-like shape after the cooling slope and thixoforming process, respectively. The as-cast, cooling slope and thixoformed samples were subjected to the T6 heat treatment process, which enhanced the hardness to 79, 99 and 104 HV, respectively, due to Si particle refinement. The potentiodynamic test revealed that the corrosion rate dropped to 0.00790 and 0.00736 mmpy-1 in the heat-treated cooling slope and thixoforming samples. This finding can be attributed to the substantially refined Si particles and reduced eutectic phase area due to the smaller cathodic to anodic area ratio.

Evaluation of the Online Learning Experience of Dalhousie Dentistry and Dental Hygiene Students during COVID-19 Pandemic Outbreak.

PURPOSE/OBJECTIVE: On 11 March 2020, the World Health Organization declared COVID-19 a pandemic, and universities transitioned to online learning. The objective of this study was to evaluate the experience of students with the online education program offered during the initial phase of the pandemic. METHODS: In April 2020, an anonymous online survey was distributed to 248 undergraduate dental and dental hygiene students in Dalhousie University's faculty of dentistry. The survey contained 10 Likert-type and 3 open-ended questions asking students to evaluate their online learning experience and their preferences regarding in-person and online learning. RESULTS: The response rate was 62.5%. Two-thirds (65.8%) of respondents reported that their educational experience in a virtual setting was very or somewhat positive, while only 14.8% said it was negative or somewhat negative. However, 60.6% agreed or strongly agreed that they preferred face-to-face learning over virtual classroom learning. Students were evenly split on whether online teaching should replace classroom teaching where possible (38.1% agreed/strongly agreed, 39.3% disagreed/strongly disagreed). Analysis of the responses to open-ended questions gave rise to 6 themes: online teaching and assessment methods; helpful online instructor behaviours/traits; advantages of online learning; disadvantages of online learning; combining online and in-person learning; online learning during the pandemic. CONCLUSIONS: Although the sudden transition to online learning was generally well received by students, there still appears to be support for maintaining some form of traditional, face-to-face learning methods in dental education. Students felt that ensuring faculty were creative, understanding and flexible was paramount in the transition to teaching in an online format.

Effect of repeated heating and cooling cycles on the degree of conversion and microhardness of four resin composites.

OBJECTIVE: This study evaluated the effect of repeatedly heating and cooling four resin-based composites (RBCs) for up to six cycles. MATERIALS AND METHODS: Four commercial RBCs were heated to 68°C and cooled to room temperature for up to six cycles before photocuring at 30°C. Specimens spent a total of 0, 30, 60, 90, 120, 150 min, or 7 days at 68°C. The degree of conversion (DC) was measured at the bottom of the specimens immediately after photocuring. The Vickers microhardness was measured at the top and bottom of the RBC surfaces 24 h after photocuring. The data were analyzed using one-way analysis of variance, Dunnett's or Bonferroni post-hoc tests, and Spearman correlation analysis (α = 0.05). RESULTS: For two brands of RBC, the DC decreased at various time points; however, these decreases were small, and there was no correlation (negative or positive) between the number of heating cycles and the DC for any of the RBCs. Repeated heated and cooling resulted in small changes in the hardness (compared to the control) in both directions (Dunnett; p < 0.05). Two of the RBCs showed a significant, positive correlation between the number of heating cycles and their hardness at the bottom surface. CONCLUSION: Repeated heating, cooling, and then reheating the RBCs for up to 1 week had little overall effect on their DC and microhardness values. The 2 mm thick specimens of all four RBCs achieved a bottom: top hardness ratio exceeding 0.8 after a 20 s exposure to light from a commercial LED curing light CLINICAL SIGNIFICANCE: Six repeated dry heating and cooling cycles of up to 1 week in duration had little effect on the DC and the microhardness of four commercial resin-based composites.

A Prolonged Time to Diagnosis Due to Misdiagnoses: A Case Report of an Atypical Presentation of Eagle Syndrome.

BACKGROUND Eagle syndrome is an unusual condition in which the styloid process (SP) becomes elongated and causes different clinical symptoms due to pressure on adjacent anatomical structures. The symptoms are non-specific and include severe throat, facial, and ear pain, or headaches. They are usually exacerbated by head rotation, swallowing, yawning, or chewing, but atypical presentations exist. It is a difficult pathology to diagnose and it can take several years before a proper diagnosis is made. CASE REPORT This report describes the case of a dental student presenting with an atypical presentation of Eagle syndrome. His styloid processes were 75 mm long and he was affected with severe pain to his throat, the anterior part of his ears, his submandibular area, and his molar teeth. The pain was exacerbated during maximal mouth opening, yawning, mandibular protrusion, and during downward head tilt, but not during the classically described movements of head rotation, swallowing, yawning, or chewing. Due to the absence of the classic symptoms, even with knowledge of the condition and unusual direct access to several oral and maxillofacial specialists, it took 4 years and multiple misdiagnoses to reach the final diagnosis. Following bilateral styloidectomy, all pain subsided. CONCLUSIONS The clinical presentation of Eagle syndrome varies, and the symptoms are non-specific. This greatly increases the complexity of diagnosing the condition and raises the time to diagnosis and the chances of misdiagnoses. It is, therefore, crucial to recognize the diagnostic tools, applicable imaging, and definitive treatment alternatives to successfully identify and treat patients affected.