Enhanced Enzymatic Synthesis of Puerarin Palmitate with Different Acyl Donors for Lipid Solubility Improvement.

Puerarin is a flavonoid known as a natural antioxidant found in the root of Pueraria robata. Its antioxidant, anticancer, and anti-inflammatory effects have attracted attention as a potential functional ingredient in various bioindustries. However, puerarin has limited bioavailability owing to its low lipid solubility and stability. Acylation is proposed as a synthesis method to overcome this limitation. In this study, lipase-catalyzed acylation of puerarin and various acyl donors was performed, and the enzymatic synthetic condition was optimized. Under the condition (20 g/L of Novozym 435, palmitic anhydride, 1:15, 40 °C, tetrahydrofuran (THF)), the synthesis of puerarin ester achieved a significantly high conversion (98.97%) within a short time (3 h). The molecule of the synthesized puerarin palmitate was identified by various analyses such as liquid chromatography-mass spectrometry (LC-MS), Fourier-transform infrared spectroscopy (FT-IR), and carbon-13 nuclear magnetic resonance (13C NMR). The lipid solubility and the radical scavenging activity were also evaluated. Puerarin palmitate showed a slight decrease in antioxidant activity, but lipid solubility was significantly improved, improving bioavailability. The high conversion achieved for puerarin esters in this study will provide the foundation for industrial applications.

Output Performance Enhanced Triboelectric Nanogenerators Induced by Magnetic Ink Trapping Property Act as Wearable Sensors.

The demand for clean-energy collection has gradually increased in recent years, making triboelectric nanogenerators a promising research field, because of their advantages in convenient manufacturing, diversified materials, and diverse synthesis and modification possibilities. However, recent studies indicate that charge decay, a major limiting factor in the triboelectric output, prevents the induced charge from combining with the bottom electrode, leading to charge loss. The use of charge-trapping sites to retain the induced charge generated during the friction process is an important solution in the field of triboelectric nanogenerator research. This study proposes the use of an elastic ink with macroscopic magnetism as trapping sites by coating the ink as dots between the polytetrafluoroethylene (PTFE) dielectric layer and the electrode layer. Nickel particles in the magnetic ink are doped into the system as microcapacitors, which prevent the combination of the friction layer and induced charges on the back electrode. Because the nickel itself can be used as a charge-potential trap to capture the charge introduced by the charge-injection process, the charge can be maintained for a long time and achieve a long-term high-output state. The output voltage was more than 6 times that of the reference group without the magnetic-ink coating after 3 h. The results provide a reference direction for research on preventing charge decay and trapping charges in triboelectric nanogenerators.

Amplified Performance of Charge Accumulation and Trapping Induced by Enhancing the Dielectric Constant via the Cyano Group of 3D-Structured Textile for a Triboelectric Multi-Modal Sensor.

To further improve the output performance of triboelectric devices, reducing charge attenuation and loss has become a hot research topic. Particularly, textiles have emerged as one of the promising research directions for triboelectric devices owing to their special internal structure and large specific surface area. In the present work, polyacrylonitrile fibers are fabricated with two distinct structures to provide a higher dielectric constant due to the strong polar properties brought about by higher dipole moment of the CN group. In addition, the complex and closely connected structure of the textile increases specific internal surface area. As a friction layer, the output voltage is shown to increase to 625% of the initial value (from 8 to 60 V) after the application of friction for a short time due to accumulation property. When acting as a trapping layer, the charge loss after injection is effectively prevented due to excellent charge trapping effect. After 24 h, the triboelectric output performance remains at ≈70% of the initial value (decreasing from 320 to 220 V), which is more than 20 times that of the polytetrafluoroethylene film, which decreases from 125 to 19 V. The device is realized for the advanced application of multi-modal sensors.

A Study on Aqueous Dispersing of Carbon Black Nanoparticles Surface-Coated with Styrene Maleic Acid (SMA) Copolymer.

Carbon black (CB) particles tend to aggregate in aqueous solutions, and finding an optimum dispersing condition (e.g., selection of the type of dispersant) is one of the important tasks in related industries. In the present study, three types of styrene maleic acid (SMA) copolymer dispersants were synthesized, labeled respectively 'SMA-1000', 'SMA-2000', and 'SMA-3000', which have 1, 2, and 3 styrene groups in their repeating units. Then, asymmetrical flow field-flow fractionation (AsFlFFF) was employed to measure the particle size distributions of the aqueous CB dispersions. For the particle size analysis of the CB dispersions, dynamic light scattering (DLS) showed relatively lower reproducibility than AsFlFFF. AsFlFFF showed that the use of SMA-3000 yielded a CB dispersion with the most uniform particle size distribution. When the SMA-3000 dispersant was used, the particle size tended to increase after 1 h of milling as the milling time increased, probably due to the re-agglomeration of the particles by excessive milling. The particle size distributions from AsFlFFF were consistent with the colorimetric observations. With the SMA-3000 dispersant, the lowest L∗ value was observed after 1 h of milling. The AsFlFFF and colorimetric analyses suggest that a stable CB dispersion can be obtained by either 3-h of milling with the SMA-2000 or 1-h of milling with the SMA-3000.

Exosome Release by Glucose Deprivation Is Important for the Viability of TSC-Null Cells.

The control of exosome release is associated with numerous physiological and pathological activities, and that release is often indicative of health, disease, and environmental nutrient stress. Tuberous sclerosis complex (TSC) regulates the cell viability via the negative regulation of the mammalian target of rapamycin complex (mTORC1) during glucose deprivation. However, the mechanism by which viability of TSC-null cells is regulated by mTORC1 inhibition under glucose deprivation remains unclear. Here, we demonstrated that exosome release regulates cell death induced by glucose deprivation in TSC-null cells. The mTORC1 inhibition by rapamycin significantly increased the exosome biogenesis, exosome secretion, and cell viability in TSC-null cells. In addition, the increase in cell viability by mTORC1 inhibition was attenuated by two different types of inhibitors of exosome release under glucose deprivation. Taken together, we suggest that exosome release inhibition might be a novel way for regression of cell growth in TSC-null cells showing lack of cell death by mTORC1 inhibition.

Supplemental or dietary intake of omega-3 fatty acids for the treatment of periodontitis: A meta-analysis.

AIM: To evaluate the intervention effect of omega-3 fatty acids on changes in periodontal parameters. MATERIALS AND METHODS: This meta-analysis included studies published in English language between 2010 and 2020, which were extracted from the Cochrane Library, EMBASE, and PubMed databases. The effects of omega-3 fatty acid intervention were investigated using the amount of omega-3 intake, periodontal pocket depth (PPD), clinical attachment loss (CAL), and bleeding on probing (BOP). The random-effects model was generated for data analysis. To obtain robustness of the model, sensitivity analysis was implemented. Subgroup analyses were performed based on the intervention period for each parameter. RESULTS: All 13 studies included in the meta-analysis were interventional, randomized controlled trials. Two studies implemented omega-3 fatty acid-rich diets, while 11 studies used supplements. Risk of bias was low, and publication bias was not shown. Meta-analysis showed a statistically significant PPD reduction (standardized mean difference [SMD] = -0.81, absolute mean difference [MD] = -0.44 mm), CAL gain (SMD = -0.77, MD = -0.51 mm), and BOP reduction (SMD = -0.65, MD = -9.45%) for the omega-3 fatty acid intervention overall. CONCLUSION: This study suggests that supplemental or dietary intake of omega-3 fatty acids for the treatment of periodontitis may have a positive impact on the disease.

Effect of dietary calcium on the gender-specific association between polymorphisms in the PTPRD locus and osteoporosis.

BACKGROUND & AIMS: Osteoporosis is the most common bone disease and is characterized by low bone mineral density (BMD) and a high risk of fracture. Despite advances in our understanding of the pathogenesis of osteoporosis, complex gene-environment interactions that influence osteoporosis development remain largely unexplored. In this study, we aimed to identify genetic loci associated with low BMD and to evaluate these genetic variants under individual and environmental factors. METHODS: A genome-wide association analysis was conducted using 500,568 single-nucleotide polymorphisms (SNPs) in 8842 individuals aged 40-69 years using clinical, demographic, and dietary data (>260 traits) established by the Korean Genome and Epidemiology Study. The gPLINK program was used to detect SNPs associated with osteoporosis at a genome-wide significance level (P < 1.0 × 10-05) and conduct a haplotype analysis. Statistical differences between the osteoporosis and control groups in categorical variables (sex and dietary profiles) were assessed based on frequency distributions using the chi-squared test. RESULTS: Of the seven SNPs that were associated with osteoporosis, both rs10977574 and rs4390000 lay in the PTPRD locus encoding a protein tyrosine phosphatase-receptor type D, which has been implicated in bone metabolism. Haplotype analysis identified two minor alleles, C and G, at the rs10977574 and rs4390000 loci, respectively, forming a linkage disequilibrium block. The subsequent gender-stratified analysis using dietary calcium intake revealed an increased correlation between the CG haplotype and osteoporosis (OR = 2.069) in the low-calcium-intake-female group but not in the high-calcium-intake-female or any male group. CONCLUSIONS: This study revealed novel evidence of the sex-specific association of the CG haplotype in the PTPRD locus with osteoporosis and indicated that the association can be influenced by dietary calcium intake.

Bio-Inspired Hierarchical Carbon Nanotube Yarn with Ester Bond Cross-Linkages towards High Conductivity for Multifunctional Applications.

The cross-linked hierarchical structure in biological systems provides insight into the development of innovative material structures. Specifically, the sarcoplasmic reticulum muscle is able to transmit electrical impulses in skeletal muscle due to its cross-linked hierarchical tubular cell structure. Inspired by the cross-linked tubular cell structure, we designed and built chemical cross-links between the carbon nanotubes within the carbon nanotube yarn (CNT yarn) structure by an esterification reaction. Consequently, compared with the pristine CNT yarn, its electrical conductivity dramatically enhanced 348%, from 557 S/cm to 1950 S/cm. Furthermore, when applied with three voltages, the electro-thermal temperature of esterified CNT yarn reached 261 °C, much higher than that of pristine CNT yarn (175 °C). In addition, the esterified CNT yarn exhibits a linear and stable piezo-resistive response, with a 158% enhanced gauge factor (the ratio of electrical resistance changing to strain change ~1.9). The superconductivity, flexibility, and stable sensitivity of the esterified flexible CNT yarn demonstrate its great potential in the applications of intelligent devices, smart clothing, or other advanced composites.

Leucyl-tRNA synthetase 1 is required for proliferation of TSC-null cells.

Uncontrolled cell proliferation associated with cancer depends on the functional abrogation of at least one of tumor suppressor. In response to nutrient cue, tuberous sclerosis complex (TSC) works as a tumor suppressor which inhibits cell growth via negative regulation of the mammalian target of rapamycin complex (mTORC1). However, the regulation mechanism of nutrient-dependent cell proliferation in TSC-null cells remains unclear. Here, we demonstrate that leucine is required for cell proliferation through the activation of leucyl-tRNA synthetase (LARS1)-mTORC1 pathway in TSC-null cells. Cell proliferation and survival were attenuated by LARS1 knock-down or inhibitors in TSC-null cells. In addition, either rapamycin or LARS1 inhibitors significantly decreased colony formation ability while their combined treatment drastically attenuated it. Taken together, we suggest that LARS1 inhibitors might considered as novel tools for the regression of tumor growth and proliferation in TSC-null tumor cells which regrow upon discontinuation of the mTORC1 inhibition.

Wearable Strain Sensors with Aligned Macro Carbon Cracks Using a Two-Dimensional Triaxial-Braided Fabric Structure for Monitoring Human Health.

Recently, wearable sensors, due to their ability to exhibit characteristics, have been appealing for health monitoring through detection of human motions and vital signals. The development of strain sensors with high sensing performance and wearability has been a great challenge to date. In this study, a textile-based strain sensor with good skin affinity was fabricated through a simple fabrication process of dip-coating 2D triaxial-braided fabrics using carbon ink and then drying. The macro crack aligned on the 2D triaxial-braided fabric with a high-density structure and good recovery force. The sensitivity of textile-based strain sensor can be enhanced due to aligned macro crack formed by prestrained fabricating process and characteristic of the 2D triaxial braided fabric with high dense structure. The optimized sensor exhibits high sensitivity (gauge factor: 128) in a strain range of 0-30%, durability (5000 cycles), washability, low hysteresis, and fast response time (90 ms). Therefore, it can be applied as a wearable sensor that can monitor human motions (large strain) and biosignals (subtle strain).

LUX: Smart Mirror with Sentiment Analysis for Mental Comfort.

As COVID-19 solidifies its presence in everyday life, the interest in mental health is growing, resulting in the necessity of sentiment analysis. A smart mirror is suitable for encouraging mental comfort due to its approachability and scalability as an in-home AI device. From the aspect of natural language processing (NLP), sentiment analysis for Korean lacks an emotion dataset regarding everyday conversation. Its significant differences from English in terms of language structure make implementation challenging. The proposed smart mirror LUX provides Korean text sentiment analysis with the deep learning model, which examines GRU, LSTM, CNN, Bi-LSTM, and Bi-GRU networks. There are four emotional labels: anger, sadness, neutral, and happiness. For each emotion, there are three possible interactive responses: reciting wise sayings, playing music, and sympathizing. The implemented smart mirror also includes more-typical functions, such as a wake-up prompt, a weather reporting function, a calendar, a news reporting function, and a clock.

Gender disparities in childhood obesity and household food insecurity.

OBJECTIVES: Childhood obesity is a critical health issue. The etiology of childhood obesity is multifactorial, with age, gender, race/ethnicity, and socioeconomic status interacting to affect risk. Food insecurity is known to be associated with risk of childhood obesity, but the body of evidence regarding Koreans is lacking. This study investigated the association between childhood obesity and household food insecurity in Koreans. Other lifestyle and nutritional factors associated with obesity were also examined. METHODS: Using data from the Korean National Health and Nutrition Examination Survey, a cross-sectional study was conducted with 1527 boys and 1366 girls. A comparison of general characteristics and nutritional intake between the groups was made using Student's t tests, χ2 tests, and general linear models. The association between childhood obesity and food insecurity was estimated with logistic regression models, and presented with odds ratios and 95% confidence intervals either with or without covariates. RESULTS: Boys who were obese dined out less frequently and engaged less in regular exercise, but no differences in nutrition intake were observed between children who were and were not obese. Girls who were obese were less likely to have a caregiver and consumed a higher percentage of energy from protein. Boys experiencing household food insecurity were less likely to be obese (adjusted odds ratio, 0.25; 95% confidence interval, 0.06-0.99), but girls with food insecurity were at three times higher risk of obesity (adjusted odds ratio, 3.00; 95% confidence interval, 1.23-7.31). CONCLUSIONS: Differential lifestyle factors are associated with obesity phenotypes in boys and girls. Food insecurity also showed a contrasting association with obesity risk by gender in young Koreans.

A Knitted Sensing Glove for Human Hand Postures Pattern Recognition.

In recent years, flexible sensors for data gloves have been developed that aim to achieve excellent wearability, but they are associated with difficulties due to the complicated manufacturing and embedding into the glove. This study proposes a knitted glove integrated with strain sensors for pattern recognition of hand postures. The proposed sensing glove is fabricated at all once by a knitting technique without sewing and bonding, which is composed of strain sensors knitted with conductive yarn and a glove body with non-conductive yarn. To verify the performance of the developed glove, electrical resistance variations were measured according to the flexed angle and speed. These data showed different values depending on the speed or angle of movements. We carried out experiments on hand postures pattern recognition for the practicability verification of the knitted sensing glove. For this purpose, 10 able-bodied subjects participated in the recognition experiments on 10 target hand postures. The average classification accuracy of 10 subjects reached 94.17% when their own data were used. The accuracy of up to 97.1% was achieved in the case of grasp posture among 10 target postures. When all mixed data from 10 subjects were utilized for pattern recognition, the average classification expressed by the confusion matrix arrived at 89.5%. Therefore, the comprehensive experimental results demonstrated the effectiveness of the knitted sensing gloves. In addition, it is expected to reduce the cost through a simple manufacturing process of the knitted sensing glove.

The effect of diet, exercise, and lifestyle intervention on childhood obesity: A network meta-analysis.

BACKGROUND & AIMS: Trials investigating the efficacy of different interventions for overweight children are limited and controversial. Therefore, the aim of this study is to perform a network meta-analysis on the efficacy of various interventions for children with obesity (an average age of 6-12 years old). METHODS: We obtained the data of trials reporting pre-post obesity relevant outcomes (e.g. BMI, BMI z-score, percent body fat, or percent overweight) from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid), PubMed, and Web of Science databases (completed before February 25, 2019) and included at least one pair of direct comparison groups. The mean difference of outcomes and their associated 95% CI were used to determine the efficacy. The P-score was calculated to illustrate the rank probability of various treatments for different outcomes using a network meta-analysis. Our meta-analysis included 24 studies that evaluated the interventions for childhood obesity. RESULTS: All 24 trials had no high risk of bias. Interventions such as exercise without parents (E w/o P); diet with parents (D w/P); and diet, exercise, and lifestyle with parents (D+E+L w/P) were significantly effective for children with obesity when compared with no intervention. CONCLUSIONS: E w/o P exhibited the highest P-score, with the D w/P and D+E+L w/P ranks having P-scores of 0.7486 and 0.5464, respectively. Moreover, the results indicate that E w/o P, D w/P, and D+E+L w/P were significantly effective treatments for children with obesity when compared with no intervention.

Optimized Dyeing Process for Enhancing the Functionalities of Spent Coffee Dyed Wool Fabrics Using a Facile Extraction Process.

Spent coffee grounds are the byproduct of coffee brewing and are generally discarded as waste. However, spent coffee has high levels of organic compounds that have multiple biological effects, including antibacterial and antioxidant activities. In this light, spent coffee grounds were tested for fabric dyeing to both functionalize as well as color the fabrics. The dyeing solution was prepared by extracting spent coffee grounds collected from a local coffee house by using a manual espresso machine. The spent coffee extract was applied to wool fabrics using a laboratory infrared dyeing machine. After the dyeing process was completed, the fabrics were mordanted with a tannic acid aqueous solution. To optimize the dyeing conditions, the times and temperatures during the process were varied, and the functionalities and other properties including color and strength of the wool fabrics dyed with the spent coffee extract were investigated. The wool fabrics dyed with the spent coffee extract were significantly colored, and the color withstands the effect of washing and light exposure. Moreover, the dyeing process with the spent coffee extract and the mordanting process with tannic acid gave the wool fabrics antibacterial and antioxidant properties.

Acoustic radiation force impulse imaging of biopsy-proven Kikuchi disease: initial experiences for evaluating feasibility in pediatric patients.

PURPOSE: This study evaluated the feasibility of acoustic radiation force impulse (ARFI) elastography and characterized the sonographic features of lymph nodes (LNs) with Kikuchi disease in pediatric patients. METHODS: Seventy-six cervical LN biopsies were performed for the diagnosis of cervical lymphadenopathy. ARFI imaging was performed, and the characteristic ultrasound features of the biopsied LNs and the contralateral LNs were analyzed. We also reviewed clinical and conventional ultrasonographic findings. RESULTS: On histology, 56 patients were diagnosed with Kikuchi disease. These LNs were large and elongated, with increased perinodal echogenicity and capsular thickening. In 38 of them, ARFI elastography was performed, and the median shear wave velocity (SWV) of the biopsied LNs with Kikuchi disease (2.19 m/sec; range, 1.45 to 4.57 m/sec) was higher than of the contralateral LNs (1.72 m/sec; range, 0.95 to 2.65 m/sec; P<0.001). In patients with reactive hyperplasia, the mean SWV of the biopsied LNs (2.00 m/sec; range, 1.49 to 2.26 m/sec) was higher than that of the contralateral LNs (1.55 m/sec; range, 1.21 to 2.32 m/sec; P=0.031). CONCLUSION: The SWV of LNs with Kikuchi disease was significantly higher than that of the contralateral LNs. Morphologically, LNs with Kikuchi disease showed an enlarged, elongated, and oval shape, increased perinodal echogenicity, and capsular thickening. In addition to the conventional ultrasonographic findings, the application of ARFI is feasible even in pediatric patients for the evaluation of cervical lymphadenopathy.

Treatment of non-odontogenic orofacial pain using botulinum toxin-A: a retrospective case series study.

BACKGROUND: The purpose of this study was to evaluate the clinical outcomes of treatment of non-odontogenic atypical orofacial pain using botulinum toxin-A. METHODS: This study involved seven patients (seven females, mean age 65.1 years) who had non-odontogenic orofacial pain (neuropathic pain and atypical orofacial pain) and visited the Seoul National University Bundang Hospital between 2015 and 2017. All medication therapies were preceded by botulinum toxin-A injections, followed by injections in the insignificant effects of medication therapies. Five of the seven patients received intraoral injections in the gingival vestibule or mucosa, while the remaining two received extraoral injections in the masseter and temporal muscle areas. RESULTS: In five of the seven patients, pain after botulinum toxin-A injection was significantly reduced. Most of the patients who underwent surgery for dental implantation or facial nerve reconstruction recovered after injections. However, the pain did not disappear in two patients who reported experiencing persistent pain without any cause. CONCLUSIONS: The use of botulinum toxin-A for the treatment of non-odontogenic neuropathic orofacial pain is clinically useful. It is more effective to administer botulinum toxin-A in combination with other medications and physical therapy to improve pain.

Zinc transporter SLC39A11 polymorphisms are associated with chronic gastritis in the Korean population: the possible effect on spicy food intake.

Herein, we hypothesized that ZIP11 variants would be important risk factors for chronic gastritis and that there would be an interaction effect of the relationship between their variants and spicy food intake on the development of chronic gastritis. Participants in this cross-sectional study (n = 3882 + 252) were recruited from a cohort of the Korean Genome and Epidemiology Study in 2001. Age, sex, education, smoking and drinking status, exercise, stress, and income level of all participants were determined by a questionnaire. Demographic and anthropometric data were collected. Fasting blood samples were collected to determine the serum levels of glucose, insulin, total bilirubin, total cholesterol, high-density lipoprotein cholesterol, and triglycerides. The presence of chronic gastritis was defined as a confirmed diagnosis by a physician. Food consumption was determined using a semiquantitative food frequency questionnaire. We found 8 different single nucleotide polymorphisms (SNPs) that are significantly different between subjects without gastritis and those with gastritis. Of these 8 SNPs, 3 SNP (rs17183225 [C/T], rs17780814 [A/C], and rs17780820 [A/G]) are closely located in the intronic region of zinc transporter SLC39A11, commonly known as ZIP11, and show linkage disequilibrium (D' = 1.0). We also found that participants with (TCA + TCG) haplotype of ZIP11 at high levels of dietary intake of spicy foods show a significantly increasing tendency in the odds of having chronic gastritis when compared with those with CAA haplotype (odds ratio, 2.620; 95% confidence interval, 1.207-5.689). The data indicate positive associations between higher meal frequency and lower spicy food preference and gastritis. In conclusion, we found that zinc transporter gene ZIP11 is associated with chronic gastritis in the Korean population and it may interact with spicy food, which suggests ZIP11 as a therapeutic target for precision nutrition.

Presence of Dental Caries Is Associated with Food Insecurity and Frequency of Breakfast Consumption in Korean Children and Adolescents.

Dental caries remains one of the most common chronic diseases affecting children worldwide with a multi-factorial etiology. The objective of the study was to evaluate the association between socioeconomic status (SES), dietary intake, food insecurity (FI), and dental caries in Korean children and adolescents. The study utilized data from the 2-year Korean National Health and Nutrition Examination Survey (KNHANES) conducted with 1,559 Korean boys and 1,391 girls aged 2 to 18 years from 2012 to 2013. Fathers' education (P=0.017), mothers' education (P<0.001), and household income (P=0.049) were all significantly associated with dental caries among Korean boys. As for dietary practices, both eating breakfast (P<0.001) and frequency of eating out (P<0.001) were strongly associated with dental caries (P<0.001). Three models of FI were used and no differences were found regarding genders. In model 3, both food insecure male [odds ratio (OR)=1.682, 95% confidence interval (CI): 0.999~2.832] and female (OR=1.900, 95% CI: 1.094~3.299) subjects had higher odds of developing dental caries than food secure subjects after adjusting the confounding factors. The present study showed a strong association between FI mediated by SES and dental caries. Nutrition education programs targeting low-socioeconomic families are necessary as a tool to prevent dental caries in Korea.

Anatomical analysis of the resected roots of mandibular first molars after failed non-surgical retreatment.

OBJECTIVES: Understanding the reason for an unsuccessful non-surgical endodontic treatment outcome, as well as the complex anatomy of the root canal system, is very important. This study examined the cross-sectional root canal structure of mandibular first molars confirmed to have failed non-surgical root canal treatment using digital images obtained during intentional replantation surgery, as well as the causative factors of the failed conventional endodontic treatments. MATERIALS AND METHODS: This study evaluated 115 mandibular first molars. Digital photographic images of the resected surface were taken at the apical 3 mm level and examined. The discolored dentin area around the root canal was investigated by measuring the total surface area, the treated areas as determined by the endodontic filling material, and the discolored dentin area. RESULTS: Forty 2-rooted teeth showed discolored root dentin in both the mesial and distal roots. Compared to the original filled area, significant expansion of root dentin discoloration was observed. Moreover, the mesial roots were significantly more discolored than the distal roots. Of the 115 molars, 92 had 2 roots. Among the mesial roots of the 2-rooted teeth, 95.7% of the roots had 2 canals and 79.4% had partial/complete isthmuses and/or accessory canals. CONCLUSIONS: Dentin discoloration that was not visible on periapical radiographs and cone-beam computed tomography was frequently found in mandibular first molars that failed endodontic treatment. The complex anatomy of the mesial roots of the mandibular first molars is another reason for the failure of conventional endodontic treatment.