Effects of SiO2 Incorporation on the Flexural Properties of a Denture Base Resin: An In Vitro Study.

OBJECTIVE: The aim of this study was to evaluate the effects of the addition of low-silicon dioxide nanoparticles (nano-SiO2) on the flexural strength and elastic modulus of polymethyl methacrylate (PMMA) denture base material. MATERIALS AND METHODS: A total of 50 rectangular acrylic specimens (65 × 10 × 2.5 mm3) were fabricated from heat-polymerized acrylic resin. In accordance with the amount of nano-SiO2, specimens were divided into the following five groups (n = 10 per group): a control group with no added SiO2, and four test groups modified with 0.05, 0.25, 0.5, and 1.0 wt% nano-SiO2 of acrylic powder. Flexural strength and elastic modulus were measured by using a 3-point bending test with a universal testing machine. A scanning electron microscope was used for fracture surface analyses. Data analyses were conducted through analysis of variance and Tukey's post hoc test (α = 0.05). RESULTS: Compared with the control group, flexural strength and modulus of elasticity tended to significantly increase (p ˂ 0.001) with the incorporation of nano-SiO2. In between the reinforced groups, the flexural strength significantly decreased (p ˂ 0.001) as the concentrations increased from 0.25 to 1.0%, with the 1.0% group showing the lowest value. Furthermore, the elastic modulus significantly increased (p ˂ 0.001) at 0.05% followed by 1.0%, 0.25%, 0.5%, and least in control group. CONCLUSION: A low nano-SiO2 addition increased the flexural strength and elastic modulus of a PMMA denture base resin.

Reinfection, recurrence, or delayed presentation of COVID-19? Case series and review of the literature.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-cov-2), first described in December 2019, has now infected more than 28 million cases with almost one million deaths. Reinfection is not definitely established however disease recurrence is increasingly reported. CASES PRESENTATION: Four patients presented with a second episode of coronavirus disease 2019 (COVID-19) occurring 27-85 following their first illness. The initial episode was mild or asymptomatic while the second attack was severe requiring hospital admission. All four patients had a SARS-CoV-2 PCR test positive in the second episode. The chest-X-ray and/or computerized tomography (CT) scan showed bilateral alveolar shadows. Furthermore, the inflammatory markers were raised in the four patients. Three patients recovered following treatment with favipravir in addition tocilizumab and/or dexamethasone. CONCLUSION: Covid19 reinfection Recurrent COVID-19 is increasingly reported. However; other etiologies including superadded infection or pulmonary embolism should be ruled out, particularly if recurrence occurs less than 3 weeks.

Antifungal Efficacy and Physical Properties of Poly(methylmethacrylate) Denture Base Material Reinforced with SiO2 Nanoparticles.

PURPOSE: To evaluate the effect of the addition of low concentration of silicon-dioxide nanoparticles (nano-SiO2 ) to poly(methylmethacrylate) (PMMA) denture base material on Candida albicans adhesion, surface roughness, contact angle, hardness, and translucency. MATERIALS AND METHODS: A total of 150 acrylic disks were fabricated from heat-polymerized acrylic resin and specimens were divided into 3 groups of 50 per test. They were further subdivided into 5 subgroups (n = 10) according to the concentration of nano-SiO2 : control (no addition) and four tested groups modified with 0.05, 0.25, 0.5, and 1.0 wt% nano-SiO2 of acrylic powder. Slide count and direct culture methods were used to measure C. albicans count (CFU/mL). The surface roughness values (Ra ; µm) were determined using a profilometer. The contact angle (o ) measurement was performed by a goniometer using the sessile drop method. Vickers hardness was used to analyze surface hardness. Translucency was measured using a spectrophotometer. Data analysis was conducted through analysis of variance and Tukey's post hoc tests (α = 0.05). RESULTS: Compared to the control group, direct culture and slide count methods illustrated a significant decrease in C. albicans count (p ˂ 0.001) with the addition of nano-SiO2 , and this decrease was correlated with the concentration of nano-SiO2 . The addition of nano-SiO2 significantly decreased the contact angle (p ˂ 0.001), whereas hardness and surface roughness significantly increased (p ˂ 0.001). The addition of nano-SiO2 significantly decreased translucency (p ˂ 0.001), and this decrease was concentration dependent. CONCLUSION: Addition of low concentration of nano-SiO2 decreased C. albicans adhesion to PMMA denture base resin. Also, low additions of nano-SiO2 have positive effects on contact angle and hardness, whereas surface roughness and translucency were adversely affected at high concentrations.