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Additional analysis revealed the P272L mutation recurred frequently and independently in other variants. Dolton et al. report that P272L ranked in the top 15 Spike mutations observed globally. In 2022, P272L spontaneously arose in variants of concern including B.1.1.7/Alpha, B.1.351/Beta, B.1.617.2/Delta, P.1/Gamma, and BA.1/Omicron. The mutation also transmitted locally. Examples include Campania, Italy and Nebraska, USA. Variants carrying the mutation comprised 32% and 29% (respectively) of reported sequences between February 2021 to June 2021.
For this study, the researchers wanted to determine if vaccinated individuals over the age of 80 had reduced immune responses compared to younger individuals. To do this, they compared the serum of older patients to younger patients when performing neutralization assays. They found that older individuals had lower titers of neutralization antibodies overall but had an increase in serum neutralization after two vaccine doses. This study justifies the use of booster vaccine shots that can increase the immune response to SARS-CoV-2. Utilizing neutralization studies is a useful first step to understanding how vaccines can protect people from severe COVID-19.
The B.1.1.7 variant, which is believed to increase transmission by up to 50 percent, has quickly become the dominant strain in the United Kingdom, leading to a runaway surge in cases and hospitalizations, pushing already strained hospitals to the brink. As of mid-January, one in fifty people in England had Covid-19, and nearly one in thirty in London.
As of January 22, 144 cases of the B.1.1.7 variant had been confirmed across 20 U.S. states, accounting for less than 0.5 percent of new cases. (The B.1.351 and P.1. strains have not yet been detected in the United States.) But the true number of B.1.1.7 cases is likely much higher, and the CDC has warned that it expects the B.1.1.7 strain to become the dominant strain in the United States by March.
While the B.1.1.7 variant is not more fatal, it may be up to 50 percent more transmissible than strains currently circulating. Because the baseline in the United States is already astronomically high, a more transmissible variant could drive cases and hospitalizations up rapidly, further overwhelming hospitals that are already at capacity, potentially leading to many more deaths.
Gawande, on a conference call with reporters Tuesday, cited a study released over the weekend by researchers from the University of California, Scripps Research Institute, and the University of Arizona that performed a genetic analysis of viral samples across the country in search of a fast-spreading strain that has become dominant in the U.K. They found that the strain, referred to as B.1.1.7, appeared in U.S. samples as early as late November and has spread to 30 states. They also found that the variant increases transmission rates by between 35 percent and 45 percent, causing cases to double every week and a half. The researchers projected that it will become the dominant strain here in March.
Experimental research has shown that the addition of cross-linking agent or methacrylic acid or both did not improve the fatigue characteristics of the dental PMMA as well as that the fatigue resistance of the denture specimens decreased dramatically (P = 0.002) when there was a notch at the anterior margin of the palatal plate in the denture specimen. It has also been shown that the fatigue resistance of acrylic resin removable partial dentures reinforced with glass fibers is superior to those removable partial dentures reinforced with conventional metal wire. Additionally, the fatigue life of the maxillary partial dentures test specimens varied greatly and the correlation between the number of loading cycles and the midline section was poor (r = 0.455) [19 - 23]. Other researchers used experimental apparatuses to study the phenomenon of the CUD fracture. Among other things, the phenomenon of the onset and propagation of the crack was measured, as well as the propagation velocity, which was estimated at 250 m/s .
The two electromagnetic switches S1 and S2 were connected to the two copper sensors (very thin sheets of Cu measuring 20 × 2 × 0.2 mm) cemented on the anterior and posterior area of the palate, while the third switch was connected to the two copper sensors cemented on the most anterior and posterior boundaries of the CUD. The electromagnetic switches, the sensors, and the digital electric pulse meters were installed in such a way as to detect the location of the crack initiation (anterior or posterior area) as well as the direction of its propagation.
When a crack appears in the sensor area, this crack runs through not only the acrylic base but also through the corresponding sensor. Subsequently the electromagnetic switch, which is connected to the sensor opens, the corresponding pulse meter is interrupted, and its operation stops. In this way, it is ascertained in how many loadings cycles a crack is created in the corresponding sensor area (anterior or posterior palatal area).
When a crack appears (according to the literature it is expected in the anterior palatal area) the operation of the corresponding pulse meter stops (due to crack, sensor opening and shutdown of the pulse meter) but the operation of the machine does not stop. When the crack propagates to the posterior palatal area, the operation of the second (rear) pulse meter is interrupted, with the same mechanism described for the anterior sensor. With the propagation of the crack along the entire length of the midline, the operation of the third electromagnetic switch is interrupted at which point the operation of the machine ceases. In this way, it is possible to detect the starting point of the crack, since at the end of the experiment if the two pulse meters have different indications, this means that the crack appeared at one point and extended to the other.
As shown by the data in Table 1, in the unreinforced specimens, the crack first appeared in the anterior palatal area (incisive papilla) in 33,537 loading cycles on average. After a number of loading cycles (approximately 33,775 cycles on average), the crack propagated to the posterior palate and caused the complete rupture (catastrophic failure) of the denture-specimen.
In the reinforced specimens of the present research, the crack appeared in the anterior palatal area after, on average, 149,191 loading cycles. In four of these specimens, the crack extended to the posterior palate area after an average of 48,014 loading cycles, causing the test pieces to fracture catastrophically. In the other two reinforced specimens, the crack did not extend to the posterior surface, so after an average of 462,546 loading cycles, the experiment was stopped. This phenomenon of preventing the propagation of cracks should be studied and analysed in future research.
In some studies, using machines of own design and construction, the samples of the acrylic denture bases were kept with the non-tissue side, that is the acrylic teeth, on the platform of the testing machine and a round plunger was placed in midline on the most prominent point of the tissue surface of the palate, between premolar and molar region, for loading in compression. In addition, shorter experiments applied a frequency of 3.3 Hz (i.e., approximately three loadings per second) [20 - 22]. This frequency is much higher than the frequency of masticatory loads in the oral cavity, which is 1.5 Hz (i.e., one and a half loadings per second). The frequency of 1 Hz, which is close to 1.5 Hz, was chosen to conduct the experiments of the present study in combination with the deployment of a high load (80 kg) in cyclic loading . The use of the higher load favours the strong scatter of data, in contrast to the use of the higher frequency, which weakens the scatter of the data. Furthermore, a high load does not replicate the partial relaxation of the stresses during mastication, where the load is exerted with lower frequency [13 , 23 , 31 , 32].
Another important innovation of this machine, compared to previous ones, is the ability to detect the moment of the appearance of the crack and how it propagates, using special switches and sensors mounted on the surface of the denture-specimen, interconnected with a special circuit. With this method, it was found that in all tests of identical dentures, the crack initially appeared in the anterior palatal area (the area of the incisive papilla) and, after a number of loading cycles, it propagated backwards and led to the complete separation of the denture into two pieces. The results of this study confirm previous research into the deformation of the CUD that showed that during loading, the maximum tensile stress tends to develop in the anterior palatal region, approximately in the area of the incisive papilla [23 , 25 , 27]. It has also been demonstrated that the area of the notch for the labial frenum is not the starting point of the crack, since this specific stress field is characterised by two compressive principal stresses. These stresses are more beneficial than detrimental in the process of starting a crack in this area . For all these reasons, it seems that reinforcing the anterior residual ridge and the anterior palate area of the denture, as applied in this study, is sufficient and significantly improves its resistance to fatigue.
The factors to be considered in the practical application of this machine are on the one hand the fact that the fatigue is dry (without the presence of artificial saliva) and on the other hand that the machine will not stop operating until the generated crack propagates to the most posterior or anterior area of the denture leading to complete fracture. The dry conditions of the experiment are not a problem in comparative studies as all the specimens are loaded under the same conditions. As for the automatic cessation of the machine, this is not possible if the crack formed does not extend along the entire length of the specimen. In these cases, the experiment is interrupted. 2b1af7f3a8