Analytical Perspectives on Cement Sheath Integrity: A Comprehensive Review of Theoretical Research.

The cement sheath, serving as the primary element of well barriers, plays a crucial role in maintaining zonal isolation, protecting the casing from corrosion, and providing mechanical support. As the petroleum industry shifts from conventional to deep unconventional resources, the service environment for cement sheaths has become increasingly complex. High temperatures, high pressures, cyclic loading, and thermal stresses in downhole conditions have significantly increased the risk of cement sheath failure. A growing trend toward theoretical analysis of stress distribution, failure modes, and control mechanisms within the casing-cement sheath-formation system is evident. This paper comprehensively reviews theoretical research on cement sheath integrity from four key perspectives: (1) the concept of cement sheath integrity failure, (2) cement sheath constitutive models, (3) analytical models of the cement sheath-casing-formation system, and (4) numerical simulations of the cement sheath-casing-formation system. Through these discussions, this review provides profound insights into cement sheath integrity failure and offers valuable guidance for future research and practices.

Identification of ssDNA aptamers specific to clinical isolates of Streptococcus mutans strains with different cariogenicity.

Streptococcus mutans, a Gram-positive facultative anaerobic bacterium, is considered to be a major etiological factor for dental caries. In this study, plaques from dental enamel surfaces of caries-active and caries-free individuals were obtained and cultivated for S. mutans isolation. Morphology examination, biochemical characterization, and polymerase chain reaction were performed to identify S. mutans The cariogenicity of S. mutans strains isolated from clinical specimens was evaluated by testing the acidogenicity, aciduricity, extracellular polysaccharide production, and adhesion ability of the bacteria. Finally, subtractive SELEX (systematic evolution of ligands by exponential enrichment) technology targeting whole intact cells was used to screen for ssDNA aptamers specific to the strains with high cariogenicity. After nine rounds of subtractive SELEX, sufficient pool enrichment was achieved as shown by radioactive isotope analysis. The enriched pool was cloned and sequenced randomly, followed by MEME online and RNA structure software analysis of the sequences. Results from the flow cytometry indicated that aptamers H1, H16, H4, L1, L10, and H19 could discriminate highly cariogenic S. mutans strains from poorly cariogenic strains. Among these, Aptamer H19 had the strongest binding capacity with cariogenic S. mutans strains with a dissociation constant of 69.45 ± 38.53 nM. In conclusion, ssDNA aptamers specific to highly cariogenic clinical S. mutans strains were successfully obtained. These ssDNA aptamers might be used for the early diagnosis and treatment of dental caries.

[Preliminary screen of high cariogenicity Streptococcus mutans strains isolated from clinical specimens].

OBJECTIVE: To screen of high cariogenicity Streptococcus mutans (S. mutans) strains isolated from clinical specimens preliminary. METHODS: Acidogenicity, aciduricity, extracellular polysaccharide production and adhesion of 41 strains of S. mutans isolated from clinical specimens were investigated to screen high cariogenicity S. mutans strains. RESULTS: There were different cariogenicity among 41 strains of S. mutans, in which 3 strains of S. mutans had all high ability to produce extracellular polysaccharide, adhere to the saliva-coated hydroxyapatite, produce acid and tolerate acid, indicated there were 3 strains with high cariogenicity S. mutans strains isolated from clinical specimens. Another 3 strains of S. mutans with all low ability to produce extracellular polysaccharide, adhere to the saliva-coated hydroxyapatite, produce acid and tolerate acid indicated they were low cariogenicity S. mutans strains isolated from clinical specimens. CONCLUSION: We may have obtained high cariogenicity S. mutans strains isolated from clinical specimens.

[Selection and identification of ssDNA aptamers specific to clinical isolates of Streptococcus mutans strains with different cariogenicity].

OBJECTIVE: To select and identify ssDNA aptamers specific to Streptococcus mutans strains with different cariogenicity isolated from clinical specimens. METHODS: Subtractive SELEX technology targeting the whole intact cells was used to screen for ssDNA aptamers specific to the clinical isolates Streptococcus mutans strains with different cariogenicity. Radioactive isotope, flow cytometry, gene cloning and sequencing, MEME online software and RNA structure analysis software were employed to analyze the first and secondary structures of the aptamers and identify the screened aptamers. RESULTS: Detection by radioactive isotope showed sufficient pool enrichment after 9 rounds of subtractive SELEX. Flow cytometry showed that the selected aptamers H1, H16, H4, L1, L10 and H19 were capable of binding specifically with highly cariogenic Streptococcus mutans strains but not with strains with a low cariogenicity. The aptamer H19 had the strongest binding capacity to highly cariogenic Streptococcus mutans strains, with a dissociation constant of 69.45∓38.53 nmol/L. CONCLUSION: We have obtained the ssDNA aptamers specific to the clinical isolates of highly cariogenic Streptococcus mutans strains.

[Isolation and identification of Streptococcus mutans strains with different genotype from clinical samples].

OBJECTIVE: To identify Streptococcus mutans (S. mutans) strains from clinical samples. METHODS: Plaque samples from caries-active and caries-free sites on enamel surfaces were obtained and cultivated for S. mutans isolation. Morphology, biochemistry, automatic microorganism analysis system and polymerase chain reaction using primers homologous to surface protein antigen I/II (spaP), glucosyltransferase B (gtfB) and dextranase (dexA) were used to identify S. mutans. Genotype of isolated S. mutans was determined by arbitrarily primed polymerase chain reaction. RESULTS: Forty-six strains of S. mutans were obtained from the 32 subjects and were identified as S. mutans by biochemistry, automatic microorganism analysis system and polymerase chain reaction. Five identical genotypes were found by arbitrarily primed polymerase chain reaction. CONCLUSION: Forty-one strains of S. mutans with different genotype were obtained from clinical samples.

Dissection of the functional structure of aptamer17, which specifically recognizes differentiated PC12 cells.

A specific single-stranded DNA (ssDNA) aptamer (aptamer17) that specifically recognizes differentiated PC12 cells had been previously obtained after 6 rounds of whole cell-based subtractive systematic evolution of ligands by exponential enrichment selection from a random ssDNA library. To further investigate the relationship between the structure and function of this aptamer, 3 truncated ssDNA aptamers were designed according to the predicted secondary structure of aptamer17. Our results show that the stem-loop is the core structure of the aptamers required for specific binding to differentiated PC12 cells, specifically loops I and II. Aptamer17 and the truncated aptamers with this basic structure could bind specifically to differentiated PC12 cells and identify these cells from a mixture of differentiated and undifferentiated PC12 cells. Therefore, truncated forms of aptamer17 may be useful in the clinic to identify undifferentiated and differentiated PC12 cells from a mixture of cells.