27 research outputs found
Genotypic Diversity of Streptococcus mutans in Caries-Free and Caries-Active Preschool Children
Aim.
The aim of the present paper was to evaluate the
genotypic diversity of S.
mutans in caries-free and caries-active
preschool children in Brazil.
Design. Twenty-eight preschool
children were examined regarding caries
experience by the dmft index. DNA from 280
isolates of S. mutans was
extracted. S. mutans evaluated
using to the PCR method, with primers for the
glucosyltransferase gene. The genetic diversity
of S. mutans isolates was
analyzed by arbitrary primed-PCR (AP-PCR)
reactions. The differences between the diversity
genotypic and dmft/caries experience were
evaluated by
χ2
test and Spearman's correlation.
Results. The Spearman
correlation test showed a strong association
between genotypic diversity and caries
experience (r = 0.72;
P < .001).
There were more S. mutans
genotypes in the group of preschool children
with dental caries, compared with the
caries-free group. Among the children with more
than 1 genotype, 13 had dental caries (2 to 5
genotypes) and 4 were caries-free (only 2
genotypes). Conclusion. Our
results support the previous findings of genetic
diversity of S. mutans in
preschool children being associated with dental
caries. The investigation of such populations
may be important for directing the development
of programs for caries prevention
worldwide
Effect of Silicon dioxide coating of acrylic resin surfaces on Candida albicans adhesion.
Acrylic resin has been used in the manufacture of prostheses, however, in the oral cavity, this material starts to retain microorganisms capable of causing gingival inflammation due its porosities. The aim of this study was to evaluate the influence of the use of silicon dioxide as a coating layer applied onto acrylic resin, on the adhesion of Candida albicans (Ca). After the incubation period in Sabouraud Dextrose Broth, a total of 1 ml of the Ca suspension was added to plate wells, each well containing a specimen of acrylic resin. The adhesion ability of Ca on acrylic resin was determined by counting colonies. Three groups (n = 6) of acrylic resin were assessed: with polishing (RP); without polishing (RW); with polishing and coating layer of silicon dioxide (RPC). Ca deposited on the surface of the acrylic resin was also observed using Scanning Electron Microscopy (SEM). Statistical assessment by Kruskal-Wallis and Student-Newman-Keuls Method were done (α = 2%). There was significant difference among the groups. The RPC group showed the lowest growth, with an average of 5.59 Log CFU/cm 2 ; there was a statistically significant difference in relation to group RW, which presented a growth of 6.07 Log CFU/cm 2 and to group RP with 5.91 Log CFU/cm 2 (p < 000.1). SEM images demonstrated that in the RP and RPC group, the surface of the resin had greater regularity, and smaller number of microorganisms. The application of silicon dioxide coating on acrylic resin appears to be a promising alternative, and its use can help in reducing the adhesion of Ca in prostheses
Influence of standard recommendations for the calculation of the column-base connection by socket according to ABNT NBR 9062:2006
Abstract This work studies the column-base connection by external socket in precast structures. A parametric study of the geometric characteristics of the external socket base with smooth interface is presented. In this parametric study, the consumption of concrete and steel are analyzed. The column cross section, the embedded length of the column in the socket base and the thickness of the wall of the socket base were the variables considered in this study. It was observed that with the increase of the embedded length, the minimum cross section of the main horizontal reinforcement reduces. With this modification, the walls of the socket base that are perpendicular to the direction of the applied loads presented a reduction of their stiffness. Besides the parametric study, this paper presents a verification model. This part of the study shows the possibility to generate abacuses that simplifies the project of the socket base foundation. Moreover, a comparative analysis becomes easier to be accomplishe
Discrete element modelling of mechanical behaviour of pervious concrete
This study proposes an alternative numerical strategy that combines different DEM models to simulate the compaction process and predict the mechanical performance of pervious concrete. An experimental program was performed to assess the compressive and tensile behaviours of pervious concrete mixes with 3 aggregate-to-paste content subjected to 3° of compaction. A novel constitutive law was proposed to simulate the particle-particle mechanical interaction at a meso-structural level. Results show that this simulation strategy is capable of predicting the experimental compressive and tensile performances while capturing the fracture pattern observed in the experimental program. This opens up the possibility of performing a numerical parametric design of mix composition and production processes before undertaking experimental verifications, which might reduce the number of tests needed to achieve the composition that better suits the mechanical requirements of each application