Difference in formation of a dental multi-species biofilm according to substratum direction.

OBJECTIVES: The aim of this study was to investigate the difference in dental biofilm formation according to substratum direction, using an artificial biofilm model. METHODS: A three-species biofilm, consisting of Streptococcus mutans, Streptococcus oralis, and Actinomyces naeslundii, was formed on saliva-coated hydroxyapatite (sHA) discs oriented in three directions: downward (the discs placed in the direction of gravity), vertical (the discs placed parallel to the direction of gravity), and upward (the discs placed in opposite direction of gravity). The biofilms at 22 h and 46 h of age were analyzed using microbiological and biochemical methods, fluorescence-based assays, and scanning electron microscopy to investigate difference in bacterial adhesion, early and mature biofilm formation. RESULTS: The biofilms formed in the upward direction displayed the most complex structure, with the highest number and biovolume of bacteria, as well as the lowest pH conditions at both time points. The vertical and downward directions, however, had only scattered and small bacterial colonies. In the 22-h-old biofilms, the proportion of S. oralis was similar to, or slightly higher than, that of S. mutans in all directions of substratum surfaces. However, in the 46-h-old biofilms, S. mutans became the dominant bacteria in all directions, especially in the vertical and upward directions. CONCLUSIONS: The direction of the substratum surface could impact the proportion of bacteria and cariogenic properties of the multi-species biofilm. Biofilms in an upward direction may exhibit a higher cariogenic potential, followed by those in the vertical and downward directions, which could be related to gravity.

Chronologic trends of cancer-related lymph node research in PubMed: informetrics analysis.

PURPOSE: Given the long history of investigation into cancer and its relevance to the lymph node (LN), it would be meaningful to plot the trends of research on cancer-related LN. METHODS: Queries such as "cancer," "lymph node," and "cancer and lymph node" were submitted to PubMed to collect articles on cancer and LN published between 1945 and 2017. The collected articles were then extracted by an automatic web crawler and examined through informetrics and linguistic analysis. RESULTS: The number of articles related to cancer was 2,795,476 and 127,897 articles (4.6%) were found to be relevant to LN. With regard to cancer types, breast cancer was the most studied (37%), followed by gastric cancer (17%). With regard to the subjects in which the surgeon is interested, LN metastasis (57%) was found to be the topic most discussed, followed by LN dissection (22%) and sentinel LN (17%). Publications on LN metastasis gradually increased over time from 1988 to 2017 although those on sentinel LN and LN dissection have stagnated since the early 2000s. CONCLUSION: Although research on cancer was abundant, only a small portion was dedicated to investigating its relevance to LN. Western countries had led the research on cancer-related LN, but Asian countries began to participate as major players, expanding their contributions. While LN metastasis, one of the major cancer-related LN topics, showed a steady increase, those involved in oncologic surgery such as LN dissection and sentinel LN did not.

A cross-sectional study on the association between vitamin D levels and caries in the permanent dentition of Korean children.

BACKGROUND: A recent study in Canada reported that vitamin D deficiency is associated with dental caries. Because Koreans have been reported to be deficient in vitamin D, we investigated the relationship between dental caries and reduced serum vitamin D levels in Korean children. The purpose of this study was to analyze the relationships between blood vitamin D [25(OH)D] concentrations and dental caries in the permanent dentition of Korean children. METHODS: Data were collected from the Korea National Health and Nutrition Examination Survey performed in 2008-2013. A total of 1688 children (10-12 years of age) were enrolled. Vitamin D intake was measured through analysis of 25-hydroxy vitamin D [25(OH)D] levels. Caries experience in permanent dentition was assessed using the decay-missing-filled teeth (DMFT) index and decayed-missing-filled (DMF) rate. Statistical analyses included complex samples Chi-square tests, complex samples logistic regression analyses, and Pearson's correlations. RESULTS: The group with 25(OH) D levels lower than 50 nmol/L had a higher proportion of children with caries in the permanent dentition and permanent first molar than the group with 25(OH)D levels of 50 nmol/L or more. When external factors, such as sex, were controlled, 25(OH)D levels were not significantly correlated with caries, but were significantly correlated with first molar caries. Children with 25(OH)D levels lower than 50 nmol/L were 1.295 times more likely to have first molar caries than those with 25(OH)D levels of 50 nmol/L or more. Additionally, 25(OH)D levels and DMFT were negatively correlated; however, the degree of correlation was not strong. CONCLUSIONS: The association between 25(OH)D and dental caries is still not clear. However, our findings suggested that vitamin D insufficiency may be a risk factor for dental caries.

The regulatory mechanism of 4-phenylbutyric acid against ER stress-induced autophagy in human gingival fibroblasts.

Endoplasmic reticulum (ER) stress is closely connected to autophagy. When cells are exposed to ER stress, cells exhibit enhanced protein degradation and form autophagosomes. In this study, we demonstrate that the chemical chaperone, 4-phenylbutyric acid (4-PBA), regulates ER stressinduced cell death and autophagy in human gingival fibroblasts. We found that 4-PBA protected cells against thapsigargin-induced apoptotic cell death but did not affect the reduced cell proliferation. ER stress induced by thapsigargin was alleviated by 4-PBA through the regulation of several ER stress-inducible, unfolded protein response related proteins including GRP78, GRP94, C/EBP homologous protein, phospho-eIF-2α, eIF-2α, phospho-JNK1 (p46) and phospho-JNK2/3 (p54), JNK1, IRE-1α, PERK, and sXBP-1. Compared with cells treated with thapsigargin alone, cells treated with both 4-PBA and thapsigargin showed lower levels of Beclin-1, LC-3II and autophagic vacuoles, indicating that 4-PBA also inhibited autophagy induced by ER stress. This study suggests that 4-PBA may be a potential therapeutic agent against ER stress-associated pathologic situations.

Comparison of traditional six-year and new four-year dental curricula in South Korea.

This study aimed to compare the dental curriculum of the traditional six-year system with that of the new four-year (graduate-entry) system in South Korea. There are 11 dental schools in South Korea: six are public and five are private. Eight offer the new four-year program and the other three offer the traditional six-year program. Descriptive analyses were conducted using bibliographic data and local information along with statistical analyses such as chi-square tests. In the six-year programs, clinical dentistry subjects were taught almost equally in practical and didactic courses, while the basic science courses were taught more often as practical courses (P < 0.0001). In the four-year programs, both the basic science and clinical dentistry subjects were taught didactically more often; while more dentistry subjects were taught than basic sciences (P = 0.004). The four-year program model in South Korea is more focused on dentistry than on basic science, while both basic and clinical dentistry subjects were equally taught in the six-year program.

4-phenylbutyric Acid Regulates Collagen Synthesis and Secretion Induced by High Concentrations of Glucose in Human Gingival Fibroblasts.

High glucose leads to physio/pathological alterations in diabetes patients. We investigated collagen production in human gingival cells that were cultured in high concentrations of glucose. Collagen synthesis and secretion were increased when the cells were exposed to high concentrations of glucose. We examined endoplasmic reticulum (ER) stress response because glucose metabolism is related to ER functional status. An ER stress response including the expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), inositol requiring enzyme alpha (IRE-1α) and phosphoreukaryotic initiation factor alpha (p-eIF-2α) was activated in the presence of high glucose. Activating transcription factor 4 (ATF-4), a downstream protein of p-eIF-2α as well as a transcription factor for collagen, was also phosphorylated and translocalized into the nucleus. The chemical chaperone 4-PBA inhibited the ER stress response and ATF-4 phosphorylation as well as nuclear translocation. Our results suggest that high concentrations of glucose-induced collagen are linked to ER stress and the associated phosphorylation and nuclear translocation of ATF-4.

Effect of cytosolic phospholipase A2 on proinflammatory cytokine-induced bone resorptive genes including receptor activator of nuclear factor kappa B ligand in human dental pulp cells.

INTRODUCTION: Although cytokines stimulate prostaglandin E(2) (PGE(2)) production and cyclooxygenase-2 (COX-2) gene expression in human dental pulp cells (HDPCs), the involvement of cytosolic phospholipase A(2) (cPLA(2)) has not been assessed. The purpose of this study was to examine the role of cPLA(2) on the regulation of proinflammatory cytokine-stimulated genes associated with osteoclast differentiation or bone resorption. METHODS: Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1alpha (IL-1alpha)-induced COX-2 and receptor activator of nuclear factor kappa B ligand (RANKL) mRNA and protein expression in the HDPCs was determined by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. PGE(2) release and osteoclast-related gene expression were measured by enzyme-linked immunosorbent assay and RT-PCR. RESULTS: Stimulation with TNF-alpha and IL-1alpha synergistically increased levels of COX-2 as well as RANKL mRNA and protein expression. Osteoclast markers (macrophage colony-stimulating factor [M-CSF], matrix metalloproteinase-9 [MMP-9], and tartrate-resistant acid phosphatase [TRAP]) and osteolysis regulating cytokines or osteoclastogenic cytokines (IL-6, IL-11, and Il-17) were up-regulated in HDPCs after IL-1alpha and TNF-alpha treatment. A cPLA(2) inhibitor attenuated both the cytokine-stimulated PGE(2) release as well as changes in osteoclast differentiation-related genes like RANKL. CONCLUSIONS: These results suggest that cPLA(2) is involved in inflammatory cytokine-induced osteoclastogenic gene expression and consequent damage or destruction.