Dental zirconia microwave-sintering followed by rapid cooling protocol.

OBJECTIVES: This study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. MATERIALS AND METHODS: Eighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). RESULTS: All MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. CONCLUSIONS: Microwave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

Effects of Distance-Learning Strategies in Dental Fixed Prosthodontics Amidst the COVID-19 Pandemic: Cross-Sectional Questionnaire Study on Preclinical Dental Students' Perspective.

BACKGROUND: COVID-19's high transmissibility led to gathering restrictions where dental schools experienced disruptions due to restrictions on attending in-person lectures and limitations placed on applied preclinical and clinical activities. Students not only had to rapidly switch to digital technology-based learning (TB-learning) modules but also experienced high levels of social isolation and anxiety around virus transmission. OBJECTIVE: This study aims to evaluate the preclinical students' perception of switching TB-learning modules amidst the COVID-19 pandemic, identifying which module parameters were associated with strong student outcomes. METHODS: A web-based survey of 39 Likert scale questions was delivered to preclinical dental students (Western University) to evaluate students' perceptions concerning TB-learning, fear amidst the COVID-19 pandemic, and the impact on their preclinical training. A Spearman rank correlation coefficient was determined to estimate the relationship between 2 variables in isolation (P=.01). An ordinal regression analysis was performed on variables of interest to determine how module variables (typically within the instructor's control) influenced the student outcomes (P=.05). RESULTS: The response rate was 30% (n=39). TB-learning was considered vital (34/39, 87.2%) as the students' education improved (18/39, 46.2%). However, 53.8% (n=21) of students showed increased difficulties in retaining, visualizing, or understanding the materials using TB-learning, and 64.1% (n=25) found it more difficult to concentrate than in in-person classes. In total, 79.5% (n=31) of students showed different levels of agreement about feeling fatigued from TB-learning. Through Spearman ρ correlation analysis, the quality of questions in quizzes (ρ=0.514; P<.001), relevant handouts (ρ=0.729; P<.001), and high-quality audiovisuals (ρ=0.585; P<.001) were positively correlated with students responding that the modules were useful to preclinical training. Similarly, good organization (ρ=0.512; P<.001), high-quality questions in quizzes (ρ=0.431; P=.01), and relevant handouts (ρ=0.551; P<.001) were positively correlated with web-based classes as an effective way to learn. In total, 91.6% (n=36) of the students agreed that COVID-19 was a dangerous disease, whereas 53.8% (n=21) showed different levels of agreement that they were afraid to be infected personally, and 69.2% (n=27) feared passing COVID-19 along to family and friends. A total of 82.1% (n=32) of the students showed that COVID-19 impacted their overall learning process and had a negative impact on their practical preclinical training (31/39, 79.5%). CONCLUSIONS: The students found a difference between TB-learning and face-to-face learning methods, where the students perceived fatigue toward the web-based method with difficulty concentrating and visualizing the subject. Moreover, there was a consensus that COVID-19 itself affected the students' overall learning process and preclinical training. As dental schools continue implementing TB-learning into their curriculum, this investigation identifies the students' struggles with the paradigm shift. In an effort to improve TB-learning, this work highlights 4 variables (organization, quizzes, quality handouts, and quality audiovisuals) within the control of instructors that can help improve content deliverance, improving the students' experience.