A comparative evaluation of properties of zirconia reinforced high impact acrylic resin with that of high impact acrylic resin

AbstractStatement of the problemPoly methyl methacrylate (PMMA) acrylic resin, although being the most popular denture base material, is associated with poor mechanical properties. It has been documented that acrylic resin can be strengthened with an addition of structural component (filler) added in the acrylic matrix, to form a composite structure.ObjectiveTo evaluate and compare the transverse strength, impact strength, surface hardness and water sorption of 10% and 20% zirconia (ZrO2) reinforced high impact acrylic resin with that of high impact acrylic resin (Trevalon HI, Dentsply India).Materials and methodsThere were 30 specimens in each of the four tests, amounting to a total of 120 specimens. Each of the tests had 10 specimens fabricated from high impact acrylic resin (control); 10 specimens fabricated from 10% zirconia (ZrO2) and 10 specimens fabricated from 20% zirconia (ZrO2) reinforced high impact acrylic resin. Specimens were subjected to the test of transverse strength in Universal Testing Machine, impact strength in Izod pendulum impact testing machine and surface hardness by Vickers Microhardness tester according to ISO Specification No. 1567. Water sorption was assessed according to ADA Specification No. 12. Data were analyzed by means of a one-way ANOVA and Bonferroni multiple comparison test.ResultsA significant increase in the transverse strength was observed in the reinforced specimens when compared to the control group. Impact strength and surface hardness were found having lesser values compared to the control group. Water sorption was found to increase on the addition of 10% and 20% zirconia (ZrO2) but the value lied below 0.8mg/cm2 i.e. within the limit of ADA Specification No. 12.ConclusionReinforcement of acrylic resin with zirconia powder affects its physical and mechanical properties significantly

Utilization of Neutral Zone Technique for Rehabilitation of Atrophic Maxillary and Mandibular Ridges: A Clinical Report

The neutral zone technique is an alternative approach for the construction of the complete dentures. It is most effective for dentures where there is a highly atrophic ridge. The techniqueaims to construct a denture that is shaped by muscle function and is in harmony with the surrounding oral structures. This clinical report describes the fabrication of complete denturesfor a patient with poorly formed both maxillary and mandibular ridges

Dietary and nutritional change in India: implications for strategies, policies, and interventions

Despite the global transition to overnutrition, stunting affected approximately 159 million children worldwide in 2014, while an estimated 50 million children were wasted. India is an important front in the fight against malnutrition and is grappling with the coexistence of undernutrition, overnutrition, and micronutrient deficiencies. This report summarizes discussions on trends in malnutrition in India, its evolution in the context of economic growth, intrahousehold aspects, infant and young child feeding practices, women's status, maternal nutrition, and nutrition policymaking. The discussion focuses on a review of trends in malnutrition and dietary intakes in India in the context of economic change over the past four decades, identification of household dynamics affecting food choices and their consequences for family nutritional status in India, and effective malnutrition prevention and treatment interventions and programs in India and associated policy challenges

Effect of denture cleansers on color stability, surface roughness, and hardness of different denture base resins

Aim: The purpose of this study was to evaluate the effect of different denture cleansers on the color stability, surface hardness, and roughness of different denture base resins. Materials and Methods: Three denture base resin materials (conventional heat cure resin, high impact resin, and polyamide denture base resin) were immersed for 180 days in commercially available two denture cleansers (sodium perborate and sodium hypochlorite). Color, surface roughness, and hardness were measured for each sample before and after immersion procedure. Statistical Analysis: One-way analysis of variance and Tukey's post hoc honestly significant difference test were used to evaluate color, surface roughness, and hardness data before and after immersion in denture cleanser (α =0.05). Results: All denture base resins tested exhibited a change in color, surface roughness, and hardness to some degree in both denture cleansers. Polyamides resin immersed in sodium perborate showed a maximum change in color after immersion for 180 days. Conventional heat cure resin immersed in sodium hypochlorite showed a maximum change in surface roughness and conventional heat cure immersed in sodium perborate showed a maximum change in hardness. Conclusion: Color changes of all denture base resins were within the clinically accepted range for color difference. Surface roughness change of conventional heat cure resin was not within the clinically accepted range of surface roughness. The choice of denture cleanser for different denture base resins should be based on the chemistry of resin and cleanser, denture cleanser concentration, and duration of immersion

The effect of incorporating various reinforcement materials on flexural strength and impact strength of polymethylmethacrylate: A meta-analysis

Polymethylmethacrylate (PMMA) is a widely used denture base material with a major drawback of inferior mechanical properties. In the existing published reports, most studies indicate the superiority of the incorporation of various reinforcement materials in PMMA in terms of the flexural strength (FS) and impact strength (IS), whereas none shows the compilation and comparison of all. The present meta-analysis aims at synthesizing all the available data. The purpose of this study was to systematically review the existing reports to compare and evaluate the effect of various reinforcement materials on FS and IS of heat-cured acrylic resin (PMMA) by combining the available evidence in a meta-analysis. A search strategy was adopted using PubMed, ScienceDirect, Ebscohost, Google Scholar, and Cochrane Central Register of Controlled Trials in February 2018 to screen research studies. These studies were screened against predetermined criteria for eligibility for meta-analysis. In the present meta-analysis, twenty articles were included. Out of 15 data available on reinforcement, 14 showed better results for IS of reinforced PMMA resin as compared to their respective control group. Out of the 25 available data, 11 showed better results for FS of reinforced PMMA resin when compared to their respective control group. The homogeneity test of meta-analysis confirmed acceptable heterogeneity among 15 reinforcement techniques of IS (i2 = 95.8%) and 25 reinforcement techniques of FS (i2 = 96.2%). A random-effects model and fixed-effects model were used for analysis. The present meta-analysis showed that reinforcement of PMMA can significantly increase FS and IS. Hence, it can be incorporated in clinical practice

A novel digitisation method for pulse switchable memristive chemical sensors

Memristors, typically considered for their non-volatile resistive memory for high-density memory designs, have shown very good sensitivity to various chemicals. As such, these devices can also be fabricated as chemical sensors with intrinsic memory. When fabricated for sensing chemicals, the switching state of the devices, depending on the amount of the applied bias voltage/current, also changes in the presence of the chemicals, compared to when the chemicals are not present. We have observed that this property can be combined with the device’s intrinsic memory to directly digitise sensed information. To this end, in this paper, we propose an innovative technique to directly digitise the sensor readings, e.g. gas concentrations, simply by pulsing the devices to exploit the memory behaviour in the presence of a chemical to change the state of the device. Essentially, we are relying on the sensors to tell us when a certain property of a chemical is sensed by switching its state while this information is digitised. This method obviates the need to use separate Analogue-to-Digital converters (ADC), thereby significantly simplifying the sensor architecture in terms of power consumption and circuit complexity. Additionally, owing to the observed high non-linearity of the fabricated devices, this digitisation method is also highly nonlinear, which can provide an added layer of security in the sensed information

Spontaneous transmesenteric hernia: a rare cause of small bowel obstruction in an adult

The authors report a case of spontaneous transmesenteric hernia with strangulation in an adult. Transmesenteric hernia (TMH) is a rare cause of small bowel obstruction and is seldom diagnosed preoperatively, and most TMHs in adults are related to predisposing factors, such as previous surgery, abdominal trauma, and peritonitis. TMH are more likely to develop volvulus and strangulation or ischemia. A brief review of etiology, clinical features, diagnosis, and treatment is discussed

Cloning, expression, and characterization of recombinant nitric oxide synthase-like protein from Bacillus anthracis

Nitric oxide synthase (NOS) is amongst a family of evolutionarily conserved enzymes, involved in a multi-turnover process that results in NO as a product. The significant role of NO in various pathological and physiological processes has created an interest in this enzyme from several perspectives. This study describes for the first time, cloning and expression of a NOS-like protein, baNOS, from Bacillus anthracis, a pathogenic bacterium responsible for causing anthrax. baNOS was expressed in Escherichia coli as a soluble and catalytically active enzyme. Homology models generated for baNOS indicated that the key structural features that are involved in the substrate and active site interaction have been highly conserved. Further, the behavior of baNOS in terms of heme-substrate interactions and heme-transitions was studied in detail. The optical perturbation spectra of the heme domain demonstrated that the ligands perturb the heme site in a ligand specific manner. baNOS forms a five-coordinate, high-spin complex with l-arginine analogs and a six-coordinate low-spin complex with inhibitor imidazole. Studies indicated that the binding of l-arginine, N<SUP>ω</SUP>-hydroxy-l-arginine, and imidazole produces various spectroscopic species that closely correspond to the equivalent complexes of mammalian NOS. The values of spectral binding constants further corroborated these results. The overall conservation of the key structural features and the correlation of heme-substrate interactions in baNOS and mammalian NOS, thus, point towards an interesting phenomenon of convergent evolution. Importantly, the NO generated by NOS of mammalian macrophages plays a potent role in antimicrobicidal activity. Because of the existence of high structural and behavioral similarity between mammalian NOS and baNOS, we propose that NO produced by B. anthracis may also have a pivotal pathophysiological role in anthrax infection. Therefore, this first report of characterization of a NOS-like protein from a pathogenic bacterium opens up avenues for further studies in understanding the importance of this protein in pathogenicity