Assessment of isthmus filling using two obturation techniques performed by students with different levels of clinical experience.

Background/purpose: Root canal filling is a necessary skill for dental students and an important aspect of endodontic education. This study aimed to evaluate the effect of students' clinical experiences on isthmus filling using different techniques and sealers. Materials and methods: One hundred eight three-dimensional-printed resin replicas of isthmus were divided into six groups and either continuous wave of condensation (CWC) or single-cone obturation (SC) was performed. One of three sealers (AH Plus Jet®, GuttaFlow2, iRoot SP) was used together with a size-fitted gutta-percha master cone. All the obturations were completed by students with three different levels of clinical experience including senior postgraduate students (SPS), junior postgraduate students (JPS), and undergraduate students (US). The percentages of filled areas (PFA) at 2, 4, 6, and 8 mm from the apex were analyzed using a light microscope. Data were analyzed using the Mann-Whitney U test or Kruskal-Wallis 1-way ANOVA with Dunn's tests (α = 0.05). Results: The CWC group exhibited a higher PFA than the SC group (P < 0.05). The PFA was higher in the SPS group than in the JPS group or the US group with CWC (P < 0.05). The three clinical experience groups showed similar PFAs with SC (P > 0.05); however, when using SC with iRoot SP, the PFA was higher than with either of the other two sealers (P < 0.05). Conclusion: CWC was found to be technique-sensitive and required clinical training. With SC, clinical experience did not improve the quality of isthmus filling without additional training. CWC was superior to SC for type IV isthmuses. When using SC, better filling quality was obtained with a bioceramic sealer.

Influence of relative positions of the heat carrier and lateral canal opening on gutta-percha obturation of lateral canals in a three-dimensional-printed model.

Background/purpose: Effective filling of the lateral canals is of great significance in successful root canal treatment, but it is generally being challenging. This study aimed to evaluate the influence of relative positions of the heat carrier and lateral canal opening on gutta-percha obturation of lateral canals in a three-dimensional (3D)-printed model. Materials and methods: Thermal conductivity and real-time temperature transmission of gutta-percha were investigated using laser flash and thermal infrared analyses. 3D-printed root canal models with lateral canals at 1, 3, and 5 mm from the apex were fabricated, and different relative positions of the heat carrier were tested. The obturation process was recorded on video, and the obturation depth of the lateral canals was observed using X-ray micro-computed tomography. Results: Gutta-percha showed low thermal conductivity of 1.07 W/(m·K), and heating increased the temperature of gutta-percha above 60 °C only within 1 mm beyond the heat carrier tip. For lateral canals at 1 and 3 mm from the apex, gutta-percha penetrated further with deeper penetration of the heat carrier (P < 0.05). For 5-mm lateral canals, the heat carrier was always at apical level and the gutta-percha obturation depth was more at 2 mm apically than at 3 or 4 mm (P < 0.05). Conclusion: Gutta-percha is a poor thermal conductor. The position of the heat carrier in relation to the lateral canal opening affects obturation depth. Only when the heat carrier reaches or passes the lateral canal opening can gutta-percha penetrate a lateral canal.

Effect of 3-dimensional Collagen Fibrous Scaffolds with Different Pore Sizes on Pulp Regeneration.

INTRODUCTION: In this study, we generated a 3-dimensional (3D) collagen fibrous scaffold for potential pulp regeneration and investigated the influence of various pore sizes of these scaffolds on proliferation, odontoblastic differentiation of human dental pulp cells (hDPCs), and subsequent tissue formation during pulp regeneration. METHODS: Electrospinning followed by freeze-drying was used to fabricate 3D fibrous collagen scaffolds. hDPCs were cultured on these scaffolds. Cell growth was detected by a Cell Counting Kit-8 assay and observed via scanning electron microscopy. Odontogenic genes and protein expression were analyzed by real-time reverse transcription polymerase chain reaction and immunofluorescence staining. The formation of mineralized nodules was tested by von Kossa staining, scanning electron microscopy, and energy-dispersive X-ray microanalysis. Subcutaneous transplantation of the seeded scaffold/tooth fragments into nude mice was performed to observe tissue formation for pulp regeneration. RESULTS: Collagen 3D fibrous scaffolds with 3 distinct mean pore sizes (approximately 20 µm, 65 µm, and 145 µm) were fabricated, which showed good biocompatibility and bioactivity. Scaffolds with larger mean pore sizes of 65 and 145 µm improved hDPC ingrowth and proliferation, with the 65-µm scaffold group presenting the highest level of odontogenic gene expression (DSPP and DMP-1), protein expression (DMP-1), mineralized area ratio, and vascular pulplike tissue formation after 6 weeks of subcutaneous implantation. CONCLUSIONS: The pore size of collagen 3D fibrous scaffolds significantly affected cell adhesion, proliferation, odontoblastic differentiation, and tissue rehabilitation. Scaffolds with a mean pore size of 65 µm presented superior results and could be an alternative for pulp regeneration.

Thermochemical Mechanism of Optimized Lanthanum Chromite Heaters for High-Pressure and High-Temperature Experiments.

High-pressure heaters in large volume presses must reconcile potentially contradictory properties, and the whole high-pressure and high-temperature (HPHT) community has been engaged for years to seek a better heater. LaCrO3 (LCO)-based ceramic heaters have been widely applied in multianvil apparatus; however, their performance is far from satisfactory, motivating further research on the chemical optimization strategy and corresponding thermochemical mechanism. Here, we adopted a chemical-screening strategy and manufactured tubular heaters using the electrically, chemically, and mechanically optimized Sr-Cu codoped La0.9Sr0.1Cr0.8Cu0.2O3-δ (LSCCuO-9182). HPHT examinations of cylindrical LSCCuO-9182 heaters on Walker-type multianvil apparatuses demonstrated a small temperature gradient, robust thermochemical stability, and excellent compatibility with high-pressure assemblies below 2273 K and 10 GPa. Thermochemical mechanism analysis revealed that the temperature limitation of the LSCCuO-9182 heater was related to the autoredox process of the Cu dopant and Cr and the exchanging ionic migration of Cu and Mg between the LSCCuO-9182 heater and the MgO sleeve. Our combinatorial strategy coupled with thermochemical mechanism analysis makes the prioritization of contradictory objectives more rational, yields reliable LCO heaters, and sheds light on further improvement of the temperature limitation and thermochemical stability.

Solid-State Electrolytes for Rechargeable Magnesium-Ion Batteries: From Structure to Mechanism.

Rechargeable magnesium (Mg)-ion batteries have received growing attention as a next-generation battery system owing to their advantages of sufficient reserves, lower cost, better safety, and higher volumetric energy density than lithium-ion batteries. However, Mg as an anode can be easily passivated during charging/discharging by most common solvents, which are inconducive for magnesium deposition/stripping. Based on this, the development of Mg-ion solid-state electrolytes in the last decades led to the formulization of several concepts beyond previously reported designs. These exciting studies have once again sparked an interest in all-solid-state magnesium-ion batteries. In this review, Mg solid-state electrolytes, including inorganic (oxides, hydrides, and chalcogenides) and organic (metal-organic frameworks and polymers) materials are classified and summarized in detail. Moreover, the structural characteristics and the migration mechanism of Mg2+ ions are also discussed with a focus on pending questions and future prospects.

Streptococcus mutans cell division protein FtsZ has higher GTPase and polymerization activities in acidic environment.

The acid tolerance of Streptococcus mutans plays an important role in its cariogenic process. Streptococcus mutans initiates a powerful transcriptional and physiological adaptation mechanism, eventually shielding the cellular machinery from acid damage and contributing to bacterial survival under acidic stress conditions. Although S. mutans contains complex regulatory systems, existing studies have shown that S. mutans, unlike Escherichia coli, cannot maintain a neutral intracellular environment. As the pH of the extracellular environment decreases, the intracellular pH decreases in parallel. There is insufficient knowledge regarding the acid resistance of the intracellular proteins of S. mutans, particularly when it comes to the key cytoskeletal division protein FtsZ. In this study, the data showed that S. mutans had similar cell division progress in acidic and neutral environments. The splitting position was in the middle of cells, and the cytoplasm was divided evenly in the acidic environment. Additionally, the tread milling velocity of S. mutans FtsZ in the middle of cells was not affected by the acidic environment. Streptococcus mutans FtsZ had higher GTPase activity in pH 6.0 buffer than in the neutral environment. Furthermore, the polymerization of S. mutans FtsZ in the acidic environment was more robust than that in the neutral environment. After two particular amino acids of S. mutans, FtsZ amino acids were mutated (E88K, L269K), the polymerization of S. mutans FtsZ in the acidic environment was significantly reduced. Overall, S. mutans FtsZ exhibited higher functional activity in pH 6.0 buffer in vitro. The acid resistance of S. mutans FtsZ is affected by its particular amino acids.

Effects of surface properties of polymer-based restorative materials on early adhesion of Streptococcus mutans in vitro.

OBJECTIVE: We investigated the effects of the surface properties of polymer-based restorative materials on early adhesion of Streptococcus mutans (UA159) in vitro. METHODS: Four direct polymer-based restorative materials, including a nanoparticle restorative (Filtek™ Z350, 3M ESPE, USA), a nano hybrid universal restorative (Filtek™ Z250 XT, 3M ESPE, USA), a low shrink posterior restorative (Filtek™ P90, 3M ESPE, USA) and a polymer-based pre-reacted glass ionomer (Beautifil II, Shofu, Japan), were selected. After polishing under different conditions, surface morphology was examined using scanning electron microscopy. Surface roughness (SR), water contact angle (CAW) and surface free energy (SFE) were determined by profilometry and the sessile drop method. Early adhesion of S. mutans was investigated using confocal laser scanning microscopy. The area occupied by adherent bacteria (A%) was calculated with COMSTAT2 software. The correlations between A% and SR, CAW, and SFE were analyzed by linear regression using SPSS 20.0 software at a significance level of 0.05. RESULTS: The value of A% was strongly correlated with SR (r=0.893, P<0.01) for surface roughness (Ra) of 0.02-0.80µm, whereas a weaker correlation was obtained between A% and SR when Ra≤0.20µm (r=0.643, P < 0.01). On super smooth surfaces (0.02µm≤Ra≤0.06µm), SR did not influence early bacterial adhesion (r=0.001, P>0.05), a medium positive correlation between A% and SFE was obtained (r=0.426, P<0.01), and no correlation between A% and CAW was found (r=-0.028, P>0.05) CONCLUSIONS: Early adhesion of S. mutans on direct polymer-based restorative materials was mainly affected by SR. SFE influenced early adhesion of S. mutans on super smooth surfaces, while hydrophobicity did not.

[Antibacterial effect of self-etching adhesive systems on Streptococcus mutans].

OBJECTIVE: To investigate the antibacterial effect of different self-etching adhesive systems against Streptococcus mutans (S. mutans). METHODS: Six reagents Clearfil(TM) SE Bond primer (SP), Clearfil(TM) SE Bond adhesive (SA),Clearfil(TM) Protect Bond primer (PP), which contained antibacterial monomer methacryloyloxydodecylpyridinium bromide (MDPB), ClearfilTM Protect Bond adhesive (PA), positive control chlorhexidine acetate [CHX, 1% (mass fraction)], and negative control phosphate buffer solution (PBS) were selected. They were mixed with S. mutans for 30 s respectively, then colony-forming units (CFU) were counted after incubated for 48 h on brain heart infusion (BHI) agar medium. The 6 reagents were applied to the sterile paper discs, and distributed onto the BHI agar medium with S. mutans and incubated for 24 h, then the inhibition zones were observed. CHX, PBS, PP, and SP were added on the dentin with artificial caries induced by S. mutans and kept for 30 s, then confocal laser scanning microscope (CLSM) was used to observe the live and dead bacteria after staining. The ratio of live to dead bacteria was calculated. PP+PA and SP+SA were applied on the dentin according to the manual and light cured. S. mutans were incubated on the samples for 2 h, ultrasonically treated and incubated on BHI agar medium for 48 h, then CFU was counted. The data were analyzed by non-parametric analysis and one-way ANOVA. RESULTS: Compared with PBS, the PP, SP, PA, SA and CHX showed the antibacterial effect on free S. mutans (P<0.05); SP and PP showed stronger antibacterial effect than PA, SA and CHX (P<0.05). CHX, SP and PP presented inhibition zones, while PBS, SA and PA did not. Compared with PBS, the CHX, SP and PP could lower the ratio of the live to dead bacteria significantly (P<0.05). Cured self-etching adhesive systems did not show any antibacterial effect on the free S. mutans. CONCLUSION: The primer of self-etching adhesives Clearfil(TM) SE Bond and Clearfil(TM) Protect Bond showed significant antibacterial effect on free and attached S. mutans. The adhesive only showed antibacterial effect on free S. mutans before light-cured polymerization. After being cured, the self-etching adhesive systems did not show antibacterial effect anymore.

[Identification of Streptococcus mutans in carious patients' saliva samples by MALDI-TOF mass spectrometry].

OBJECTIVE: To identify Streptococcus mutans (S. mutans) in carious patients' saliva using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and to establish a faster and more accurate method to identify S. mutans. METHODS: In this study, a total of 90 carious patients from Department of Endodontics of Peking University School of Stomatology were recruited. All these patients' saliva was collected. After extracting the protein of the samples, they were identified by MALDI-TOF MS. The composite profile was analyzed using BioExplorer 1.0 software. The scores ≥ 25 were considered as S. mutans, whereas the scores <25 were as considered as non S. mutans. Finally, these results were compared with 16S rDNA sequencing to figure out the sensitivity and concordance rate, respectively. RESULTS: The sensitivity of MALDI-TOF MS was 96.0%, and the concordance rate compared with 16S rDNA sequencing was as high as 98.7%. CONCLUSION: MALDI-TOF MS is high throughput, rapid and easy to perform in comparison to other conventional methods. It has a high sensivity and concordance rate. Thus, MALDI-TOF MS can serve as an effective tool for identification of S. mutans.