Morphology and classification of the second mesiobuccal canal in maxillary first molars: a cone-beam computed tomography analysis in a Chinese population.

BACKGROUND: Understanding the tooth anatomy is crucial for ensuring effective endodontic treatment. This study investigated the root canal morphology of the second mesiobuccal (MB2) canal in maxillary first molars (MFMs) in a Chinese population using cone-beam computed tomography (CBCT). METHODS: This study evaluated 486 MFMs with MB2 canals from 285 participants undergoing CBCT examination and determined the Vertucci's classification and position of the MB2 canal orifice. The prevalence of the MB2 canal was correlated with the sex, age, and tooth side. The correlations between the prevalence of the MB2 canal and sex and tooth side were assessed using the Fisher's exact test. The chi-square test was used for evaluating the correlation between the prevalence of the MB2 canal and age. RESULTS: The number of type II, III, IV, V, VI, VII, and other root canals in the MFMs was 30.9%, 0.6%, 65.0%, 1.2%, 1.2%, 0.4%, and 0.6%, respectively. Among the 201 cases with bilateral inclusion, 87.6% showed consistent canal configuration. Results of the first clear apparent position (FCAP) of the MB2 canals showed that 434, 44, and 3 teeth had FCAP at the upper, middle, and bottom one-third of the root, respectively. The FCAPs of the MB2 canal in the MFMs with types II, IV, and VI, as well as types III and V canals showed significant differences (p<0.05). The horizontal distance between the MB1 and MB2 canal orifices in the type II canals of MFMs was significantly lesser than those in the type IV canals of MFMs (p < 0.01). The longitudinal distance between the pulp chamber floor plane and MB2 canal orifice significantly correlated with age (p < 0.05). CONCLUSIONS: The morphology of the mesiobuccal root canal in the MFMs is complex. Complete understanding of the anatomical morphology of the root canal combined with the CBCT and dental operating microscope is necessary for the accurate detection of the MB2 canal and consequently improved success rate of root canal treatment. Our study findings can help endodontists improve endodontic treatment outcomes.

Contribution of stochastic processes to the microbial community assembly on field-collected microplastics.

A growing body of evidence suggests that microplastics may be colonized with a unique microbiome, termed 'plastisphere', in aquatic environments. However, the deep mechanisms (deterministic and/or stochastic processes) underlying the community assembly on microplastics are still poorly understood. Here, we took the estuary of Hangzhou Bay (Zhejiang, China) as an example and examined the assembly mechanisms of bacterial communities in water and microplastic samples. Results from high-throughput sequencing showed that Proteobacteria, Firmicutes, and Actinobacteria were the dominant phyla across all samples. Additionally, microorganisms from plastisphere and planktonic communities exhibited contrasting taxonomic compositions, with greater within-group variation for microplastic samples. The null model analysis indicated the plastisphere bacterial communities were dominantly driven by the stochastic process of drift (58.34%) and dispersal limitation (23.41%). The normalized stochasticity ratio (NST) also showed that the community assembly on microplastics was more stochastic (NST > 50%). Based on the Sloan neutral community model, the migration rate for plastisphere communities (0.015) was significantly lower than that for planktonic communities (0.936), potentially suggesting that it is the stochastic balance between loss and gain of bacteria (e.g., stochastic births and deaths) critically shaping the community assembly on microplastics and generating the specific niches. This study greatly enhanced our understanding of the ecological patterns of microplastic-associated microbial communities in aquatic environments.

Multiple root canals in the maxillary molar: an unusual case report.

BACKGROUND: The objective of this report was to highlight the importance of using a dental operating microscope (DOM) to locate supernumerary canals and diagnose variations in root canals using cone-beam computed tomographic (CBCT) images. CASE PRESENTATION: A 35-year-old Chinese female had repeated swelling in the upper right posterior maxilla for 3 months and was referred to evaluate symptomatic apical periodontitis and mesotaurodonts for upper right first permanent molar and upper right second permanent molar. Root canal therapy was proposed and conducted with the use of DOM and CBCT. CONCLUSIONS: Proper diagnosis and careful clinicoradiological examination are necessary, and it is essential to reinforce the knowledge of the rare morphology of root canals for clinicians.

Biodegradable microplastics enhance soil microbial network complexity and ecological stochasticity.

Biodegradable plastics have emerged as an ecological alternative to conventional petroleum-based plastics. Despite the recent advances in the effects of conventional microplastic on soil ecosystems, the ecological impact of biodegradable microplastics in soil environments remains poorly understood. Here, we performed soil microcosms with conventional (polyethylene and polystyrene) and biodegradable (polybutylene succinate and polylactic acid) microplastics to estimate their effects on the success patterns, co-occurrence networks, and the assembly mechanisms of soil bacterial communities. Biodegradable microplastics significantly altered the soil bacterial community composition with steeper temporal turnovers (rate: 0.317 - 0.514) compared to the conventional microplastic treatments (rate: 0.211 - 0.220). Network under biodegradable microplastics showed greater network complexity, including network size, connectivity, average clustering coefficient, and the number of keystone species, as compared with the conventional microplastic treatments. Additionally, the biodegradable microplastic network had higher robustness, which may be potentially due to the enhanced dissolved organic carbon contents in the soil treated with biodegradable microplastics. The bacterial community assembly was initially governed by deterministic homogeneous selection (93 - 100 %) under the stress of microplastics, but was progressively structured by increasing stochastic homogeneous dispersal (17.8 - 73.3 %) over time. The normalized stochasticity ratio also revealed that the application of microplastics increased the importance of stochastic processes following incubation. These findings greatly enhanced our understanding of the ecological mechanisms and interactions of soil bacterial communities in response to microplastic stress.

Biodegradable and conventional microplastics exhibit distinct microbiome, functionality, and metabolome changes in soil.

Environmental concerns with liberal petroleum-based plastic use have led to demand for sustainable biodegradable alternatives. However, the inadequate end-of-life treatment of plastics may emit microplastics, either conventional or biodegradable, to the terrestrial environment. It is essential to evaluate the possible effects of conventional and biodegradable microplastics on the composition and function of soil microbial communities. Therefore, we conducted a soil microcosm experiment with polyethylene (PE), polystyrene (PS), polylactide (PLA), or polybutylene succinate (PBS) microplastics. The soil microbiome and metabolome were evaluated via 16S rRNA gene sequencing, metagenomics, and untargeted metabolomics. We reported that the presence of conventional or biodegradable microplastics can significantly alter soil microbial community composition. Compared to the control soils, the microbiome in PBS and PLA amended soils exhibited higher potential for uptake of exogenous carbohydrates and amino acids, but a reduced capacity for related metabolic function, potentially due to catabolite repression. No differences in soil metabolome can be observed between conventional microplastic treatments and the control. The potential reason may be that the functional diversity was unaffected by PE and PS microplastics, while the biodegradable particles promoted the soil microbial multifunctionality. Our findings systematically shed light on the influence of conventional and biodegradable microplastics on soil microorganisms, facilitating microplastic regulation.

Effects of microplastics on soil microbiome: The impacts of polymer type, shape, and concentration.

Increasing research has recognized that the ubiquitous presence of microplastics in terrestrial environments is undeniable, which potentially alters the soil ecosystem properties and processes. The fact that microplastics with diverse characteristics enter into the soil may induce distinct effects on soil ecosystems. Our knowledge of the impacts of microplastics with different polymers, shapes, and concentrations on soil bacterial communities is still limited. To address this, we examined the effects of spherical microplastics (150 µm) with different polymers (i.e., polyethylene (PE), polystyrene (PS), and polypropylene (PP)) and four shapes of PP microplastics (i.e., fiber, film, foam, and particle) at a constant concentration (1%, w/w) on the soil bacterial community in an agricultural soil over 60 days. Treatments with different concentrations (0.01-20%, w/w) of PP microplastic particles (150 µm) were also included. The bacterial communities in PE and PP treatments showed a similar pattern but separated from those in PS-treated soils, indicating the polymer backbone structure is an important factor modulating the soil bacterial responses. Fiber, foam, and film microplastics significantly affected the soil bacterial composition as compared to the particle. The community dissimilarity of soil bacteria was significantly (R2 = 0.592, p < 0.001) correlated with the changes of microplastic concentration. The random forest model identified that certain bacteria belonging to Patescibacteria were closely linked to microplastic contamination. Additionally, analysis of the predicted function further showed that microplastics with different characteristics caused distinct effects on microbial community function. Our findings suggested that the idiosyncrasies of microplastics should not be neglected when studying their effects on terrestrial ecosystems.

Selection of antibiotic resistance genes on biodegradable and non-biodegradable microplastics.

Growing evidence have demonstrated that microplastics in the marine ecosystem can provide novel substrates for biofilm formation, potentially facilitating the spread of antibiotic resistance. However, the occurrence of antibiotic resistance genes (ARGs) in the biofilm on microplastics has not been fully explored. This study used the metagenomic data of biodegradable and non-biodegradable microplastics staged at a coastal lagoon in the northern Gulf of Mexico to profile the ARGs and their bacterial hosts. The abundance and Shannon diversity of ARGs on biodegradable poly hydroxy alkanoate (PHA) and non-biodegradable polyethylene terephthalate (PET) have no significant differences. Nevertheless, the abundance of multidrug resistance genes on PET (3.05 copies per 16S rRNA) was statistically higher than that on PHA (2.05). Beta diversity showed that the overall pattern of resistome on PHA was significantly distinct with that on PET. Procrustes analysis suggested a good-fit correlation between ARG profiles and bacterial community composition. The host-tracking analysis identified that Pseudomonas was always the major host for glycopeptide and multidrug resistance genes in PET and PHA biofilms, whereas the primary host for macrolide-lincosamide-streptogramin (MLS) changed to Desulfovibrio on PET. This study provided the first metagenomic insights into the ARGs and their hosts on biodegradable and non-biodegradable microplastics, suggesting that both two types of plastics harbor ARGs with preferences.

Doxorubicin conjugated to D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS): conjugation chemistry, characterization, in vitro and in vivo evaluation.

To develop a polymer-anticancer drug conjugate, D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) was employed as a carrier of doxorubicin (DOX) to enhance its therapeutic effects and reduce its side effects. Doxorubicin was chemically conjugated to TPGS. The molecular structure, drug loading efficiency, drug release kinetics and stability of the conjugate were characterized. The cellular uptake, intracellular distribution, and cytotoxicity were accessed by using MCF-7 breast cancer cells and C6 glioma cells as in vitro cell model. The conjugate showed higher cellular uptake efficiency and broader distribution within the cells. Judged by IC(50), the conjugate was found 31.8, 69.6, 84.1% more effective with MCF-7 cells and 43.9, 87.7, 42.2% more effective with C6 cells than the parent drug after 24, 48, 72 h culture, respectively. The in vivo pharmacokinetics and biodistribution were investigated after an i.v. administration at 5 mg DOX/kg body weight in rats. Promisingly, 4.5-fold increase in the half-life and 24-fold increase in the area-under-the-curve (AUC) of DOX were achieved for the TPGS-DOX conjugate compared with the free DOX. The drug level in heart, gastric and intestine was significantly reduced, which is an indication of reduced side effects. Our TPGS-DOX conjugate showed great potential to be a prodrug of higher therapeutic effects and fewer side effects than DOX itself.

Fabrication of SnO2/porous silica/polyethyleneimine nanoparticles for pH-responsive drug delivery.

To create novel nanocarriers for achieving excellent drug delivery performance, pH-responsive fluorescent porous silica (PS) nanocarriers were developed by encapsulating SnO2 nanoparticles and coating polyethyleneimine (PEI) layer. SnO2/porous silica (SnO2/PS) nanoparticles have an average diameter of 80nm and center-radial large pore channels. The large channels endow them high surface area with a Brunauer-Emmett-Teller (BET) area of 939m(2)g(-1). Aspirin was used as test drug to evaluate the releasing behavior of SnO2/porous silica/polyethyleneimine (SnO2/PS/PEI) nanoparticles. Results indicated that aspirin can be successfully incorporated into the SnO2/PS/PEI nanoparticles and the SnO2/PS/PEI nanoparticles displayed excellent pH-responsive release. The release rate in pH7.4 buffer is higher than that in pH5.5 buffer, which attributed to the PEI structure change in varied pH buffer. In addition, the SnO2/PS/PEI nanoparticles presented novel drug-dependent fluorescence, which could be used to trace the drug release.

Doxorubicin conjugated to D-alpha-tocopheryl polyethylene glycol succinate and folic acid as a prodrug for targeted chemotherapy.

This research developed a prodrug strategy to conjugate doxorubicin (DOX) to D-alpha-tocopheryl polyethylene glycol succinate (TPGS) and folic acid (FOL) for targeted chemotherapy to enhance the therapeutic effects and reduce the side effects of the drug. We synthesized two conjugates, TPGS-DOX and TPGS-DOX-FOL, to quantitatively evaluate the advantages of TPGS conjugation and FOL conjugation through passive and active targeting effects. The successful conjugation was confirmed by (1)H nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. The in vitro drug release was found pH dependent, which is in favor of cancer treatment. The in vitro cellular uptake and cytotoxicity were evaluated with MCF-7 breast cancer cells. It was found that the cellular uptake of DOX increased 15.2% by TPGS conjugation and further 6.3% by FOL conjugation after 0.5-h cell culture. The IC(50) after 24-h cell culture with MCF-7 cancer cells showed that TPGS-DOX conjugate could be 1.19-fold effective versus DOX and that TPGS-DOX-FOL could be 38.6-fold effective than TPGS-DOX and thus 45.0-fold more effective versus DOX. In vivo experiment showed that the half-life of TPGS-DOX and TPGS-DOX-FOL were increased 3.79- and 3.9-fold than the free DOX, and the area under the curve were increased 19.2- and 14.5-fold than the DOX, respectively. The biodistribution data showed that TPGS-DOX and TPGS-DOX-FOL significantly lowered drug accumulation in the heart, thereby reducing the cardiotoxicity, which is the main side effect of the DOX. Furthermore, TPGS-DOX can limit, and TPGS-DOX-FOL can further deduce, the gastrointestinal side effect of the drug.