|Year : 2016 | Volume
| Issue : 6 | Page : 517-522
|Dental fluorosis, fluoride in urine, and nutritional status in adolescent students living in the rural areas of Guanajuato, Mexico
Aguilar-Diaz Fatima del Carmen, de la Fuente-Hernández Javier, Cintra-Viveiro Cristina Aline
National Graduate School, Unit León, National Autonomous University of Mexico, Mexico City, Mexico
|Date of Submission||18-May-2016|
|Date of Acceptance||10-Sep-2016|
|Date of Web Publication||12-Dec-2016|
Aguilar-Diaz Fatima del Carmen
National Graduate School, Unit León, National Autonomous University of Mexico
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: The aim of this study was to assess urine fluoride concentration, nutritional status, and dental fluorosis in adolescent students living in the rural areas of Guanajuato, Mexico. Materials and Methods: A cross-sectional study was conducted including participants aged 11–20 years. The presence and severity of dental fluorosis was registered according to the Thylstrup and Fejerskov index (TFI) criteria. Anthropometric measures were also recorded. Urine sample of the first morning spot was recollected to assess urine fluoride concentration by using the potentiometric method with an ion-selective electrode. Water samples were also recollected and analyzed. Bivariate tests were performed to compare urine fluoride concentration according to different variables such as sex, body mass index, and TFI. Nonparametric tests were used. A logistic regression model was performed (SPSS® 21.0). Results: This study included 307 participants with a mean age of 15.6 ± 1.6; 62.5% of the participants showed normal weight. A total of 91.9% of the participants had dental fluorosis, and 61.6% had TFI > 4. Mean fluoride content in urine ranged between 0.5 and 6.65 mg/L, with a mean of 1.27 ± 1.2 mg/L. Underweight children showed greater urine fluoride concentration. The increment of urine fluoride was a related (OR = 1.40) to having severe dental fluorosis. Conclusions: Most of the studied population had moderate or severe dental fluorosis. Urine fluoride concentration was related to fluorosis severity and nutritional status. Underweight children showed greater urine fluoride concentration as well as severe dental fluorosis.
Keywords: Dental fluorosis, nutritional status, urine fluoride
|How to cite this article:|
del Carmen ADF, Javier dH, Aline CVC. Dental fluorosis, fluoride in urine, and nutritional status in adolescent students living in the rural areas of Guanajuato, Mexico. J Int Soc Prevent Communit Dent 2016;6:517-22
|How to cite this URL:|
del Carmen ADF, Javier dH, Aline CVC. Dental fluorosis, fluoride in urine, and nutritional status in adolescent students living in the rural areas of Guanajuato, Mexico. J Int Soc Prevent Communit Dent [serial online] 2016 [cited 2021 Oct 28];6:517-22. Available from: https://www.jispcd.org/text.asp?2016/6/6/517/195510
| Introduction|| |
Fluoride intake in appropriate concentrations prevents the formation of dental caries. However, exposure to high concentrations of fluoride can generate several alterations. Chronic fluoride poisoning is a global health problem that occurs endemically in areas where the fluoride content in water is above the optimal level. World Health Organization's (WHO) international standards of 1958 and 1963 referred to fluoride for drinking water, claiming that consumption of water with fluoride concentrations above 1.0–1.5 mg/L can result in pathological changes in teeth causing dental fluorosis (DF), which is characterized by light yellow to brown–black horizontal lines on the teeth surface and chipped off edges. High concentrations of fluoride can also produce long-term bone damage in children and adults such as skeletal fluorosis. Even intelligence quotient (IQ) has been associated with fluoride exposure.
Traditionally, dental fluorosis has been connected with a higher intake of fluoride coming from drinking water, which may contain high fluoride concentrations, especially in groundwater of areas of volcanic rocks. These high-risk areas are mostly located in arid and semi-arid regions that are characterized by a rapid rate of chemical weathering of geological materials. According to the WHO, permissible fluoride concentration limit in drinking water is 1.0 mg/L, and Mexican normativity stipulates a limit of 1.5 mg/L. Nonetheless, in Mexico, there are some areas that have high amounts of fluoride in water, mainly in the states of the north and center of the country, most notably in Chihuahua, Durango, Aguascalientes, and Guanajuato.
Fluoride ingested remains for a long time in the human body, however, approximately 80% of fluoride entering the body is excreted mainly through urine; the rest of it is absorbed into body tissues from where it is released very slowly. Excreted fluoride can be monitored by biomarkers of fluoride, which are values that serve to identify deficient or excessive consumption and bioavailability of fluoride in the body. WHO defines different fluoride biomarkers; current (urine, plasma, and saliva), recent (nails and hair), and historical biomarkers (bones and teeth). Urine fluoride concentration among the biomarkers of fluoride exposure is generally accepted as the best indicator of fluoride exposure  because it can be recollected noninvasively and systematically reflects the burden of fluoride exposure from drinking water. Hence, special attention has been given to it as a biomarker, and is used as an indirect indicator of fluoride intake.
Official Mexican Norms (NOM-013-SSA2-1994) stipulates, periodically monitoring urine fluoride concentration has been stipulated; nonetheless, there is scarce data regarding DF prevalence and urinary fluoride excretion in adolescents living in rural communities with no central water supplies and where concentrations of fluoride may be above optimal. This descriptive study aimed to assess urinary fluoride concentration in a community Where water supplies contain higher amounts of fluoride than recommended.
| Materials and Methods|| |
This cross-sectional study was conducted in an endemic fluorosis area in Guanajuato State where natural high concentrations of fluoride in groundwater and endemic dental fluorosis have been reported. Fluoride concentration in this area ranges from 0 to 16 mg/L, averaging 1.2 mg/L. Areas with the highest concentration of fluoride are located toward the northwest between San Felipe, San Luis de la Paz, and Dolores Hidalgo.
Participants were individuals aged 11–20 years who were born and had resided in the area since their birth. Those with orthodontic appliances were excluded. A questionnaire was administered to all the participants at the time of admission to collect demographic data. Diagnosis of dental fluorosis was performed by clinical examination using the Thylstrup–Fejerskov Index (TFI), which was selected because of its accuracy to identify DF severity. One trained examiner performed clinical evaluations; previously intraexaminer reliability was assessed using the Kappa test (Kappa value = 0.82). Anthropometric measures such as weight and height were registered, and using these data body mass index (BMI) was calculated. Percentage of body fat was also assessed by the bioimpedance method obtained by using a Tanita scale SC240.
Early morning spot urine sample were recollected in polyethylene containers and stored at −20°C until analysis. Urine fluoride (UF) concentrations were determined using an electronic meter (Orion 720A) and a fluoride-specific ion electrode, which was calibrated with fresh, serially diluted standard solutions. During the measurement, ionic strength buffer solution was added to each sample for analysis. Water samples were also recollected and analyzed.
Written informed consent was obtained from all the participants or by their legal guardians in case they were minors. All data were managed to ensure the protection of individual rights and maintaining confidentiality. This study was approved by the Committee of Ethics the National Autonomous University of Mexico, ENES León.
Descriptive analysis of the data (arithmetic mean, standard deviation and percentages) were obtained, bivariate analyses were performed to compare variables, and then a logistic regression model was created. Population was divided into two groups according to the presence or absence of severe fluorosis (TFI < 6 vs TFI > 6). Data was processed using SPSS version 21 for Windows (Statistical Package for the Social Sciences, SPSS Inc. Chicago, Illinois, USA).
| Results|| |
A total of 307 participants were included; 59.9% (n = 184) were females and 40.1% (n = 123) were males. Mean age was 15.6 ± 1.6 years. Fluoride content in urine ranged between 0.5 and 6.65 mg/L, with a mean of 1.27 ± 1.2 mg/L [Table 1]. Fluoride concentration in water was 4.42 ppm.
|Table 1: Descriptive data about age and urine fluoride concentration by sex|
Click here to view
Most of the population (62.5%) showed normal weight; 21.5% were underweight, 11.1% were overweight, and 4.9% were obese. DF was present in 91.9% of the participants, of which 61.6% were (TFI > 4) moderate or severe cases, as observed in [Table 2]. Teeth more frequently affected were premolars and those less affected were central inferior incisors.
Bivariate tests were performed to compare UF concentration according to different variables such as sex, BMI, and TFI. According to the Kolmogorov–Smirnov test, the distribution of data was not normal and hence nonparametric tests were used. No differences in UF concentrations among girls and boys were observed (Mann–Whitney U test = 10589.50, P = 0.335).
Regarding BMI and UF, significant differences were found when using the Kruskal–Wallis test (Chi square test = 16.200; P = 0.003). Underweight children showed greater UF concentration, as show in [Table 3]. No difference in the prevalence of DF according to nutritional status was observed (Chi square test = 29.746; P = 0.326). Nonetheless, significant differences (Chi square test = 11.22; P = 0.011) were observed when comparing the prevalence of severe DF (TF ≥ 6) and nutritional status; 42% of the children having TFI ≥ 6 were underweight while of those having TFI < 6 18.6% were underweight, as shown in [Table 3].
|Table 3: Urine fluoride concentration and dental severe fluorosis according to nutritional status|
Click here to view
Positive correlation was observed among urine fluoride concentration
and fluorosis severity (Rho Spearman = 0.224; P< 0.001). To perform bivariate analysis to identify the association between UF concentration and dental fluorosis severity status, this last variable was recoded in order to reduce it into 5 categories; significant differences were noted (Kruskal–Wallis test = 16.200; P = 0.003). Children having dental fluorosis TFI = 7–9 had greater concentration of fluoride in urine [Table 4].
|Table 4: Urine fluoride concentration according to dental fluorosis severity|
Click here to view
A logistic model was constructed to explore the association between severe dental fluorosis (TFI < 6 vs TFI ≥ 6) and fluoride concentration in urine, controlled by age, sex, nutritional status, (BMI) and body fat percentage. It was observed that sex, age, body fat, and UF concentration were variables that were statistically significant in this model. Male gender (OR = 0.127), increment of percentage in body fat (OR = 0.875) and age (OR = 0.640) were protective factors. The increment of UF (OR = 1.40) concentration was a related risk to have severe DF [Table 5].
|Table 5: Logistic model using as dependent variable the presence or absence of severe dental TFI ≥6|
Click here to view
| Discussion|| |
DF was present in 91.9% of the participants in our study. In San Luis Potosí State, in an area where fluoride level was similar (4.54 ppm), DF was present in all participants, of which 95% had severe cases. In a Mexican community where fluoride concentration was lower (1.9 ppm) than that found in our study area, DF prevalence was 98%, being severe in 47%. Rodriguez et al. in Chihuahua, Mexico found DF in 85.5% of the population when fluoride in water was 3.00–5.99 ppm. Ambient temperature, meters above mean sea level, risk practices as direct consumption of boiled water, and preparing food with tap water may explain the differences in DF prevalence, even when concentration of fluoride in water are similar.
Range of fluoride content in urine was similar to that reported in other Mexican children population, aged 6-12, authors reported a range of UF concentration of 11.1 to 5.9 mg/L; with a mean of UF content of (3.14 ± 1.09mg/L., In an Indian group aged 6 to 18, the highest UF concentration recorded was 17 mg/L when fluoride water concentration was of 2.11 mg/l. In other study in Indian population, in individuals aged 11–16 years, fluoride concentration found in urine samples ranged from 0.90 to 3.25 mg/L with an average of 2.35 mg/L. These variations might derived not only from variation on water fluoride content but from different use and consumption practices of water and other sources of fluoride among populations.
We observed a positive correlation among UF concentration and fluorosis severity; these results are congruent with those reported by Jarquín-Yañez et al. who found that urine fluoride concentration was more elevated in those showing greater fluorosis severity. They reported levels of 2.66 (0.89) in children with TFI of 4–5, 3.11 (1.06) in the TFI of 6–7, and 3.75 (1.10) ppm in TFI of 8–9. Nonetheless, Heintze et al. reported no correlation between UF levels and DF, however, that study was conducted in low-fluoride areas, which may be one of the causes of these different results.
Age was significantly associated with DF, suggesting that age is a protective factor; nonetheless, this does not imply that DF decreases as age. Increases, but it is not possible because DF is irreversible. Rather, these results might suggest that the problem is exacerbating, probably reflecting an increase in the consumption of fluoride in new generations that could come from higher concentration of fluoride in the water of the zone, as suggested by some authors who reported that as the depth of water extraction increases the concentration of this element also increases, raising the risk of developing DF. Pontigo-Loyola et al. also reported similar results showing that children aged 12 years had greater chance to have fluorosis compared to those aged 15 years. The epidemiology system for oral diseases (SIVEPAB) in 2010 also proposed an increase in DF prevalence, especially in the younger age groups (under 25 years). Similarly, this has been observed in other countries, for instance, in a study performed in rural areas of Brazil was observed that children between 10 and 12 years and those between 13 and 15 years of age had greater chance of having severe dental fluorosis in comparison with the younger children and individuals aged between 16 and 22 years. These results contrast to the study by Rwenyonyi et al. who found significant increase in the severity of fluorosis with increasing age in a community with high concentration of fluoride in water. On the other hand, it was found that underweight children showed greater urine fluoride concentration. Not many studies exist reporting this association; one study by Das and Mandal. reported that overall fluoride exposure dose has negative correlation with BMI (r = −0.083), which would be similar to that found in our population.
We found no difference in the prevalence of DF according to nutritional status, nonetheless significant differences were observed when comparing the prevalence of severe DF, with 42% of the children having TFI ≥ 6 being underweight. Some epidemiological studies have indicated that manifestations of fluorosis are more marked among communities exposed to chronic malnutrition. Choubisa et al. showed that, among participants with poor nutrition, the prevalence of DF increased to 61.6% And skeletal fluorosis increased to 23.9%. Furthermore in a study by Irigoyen et al. in Mexico, association between malnutrition and defects in the enamel were observed in an area where the water contained 2.7 mg/L of fluoride. Similarly Pérez-Pérez et al. observed statistically significant differences in height for age, and reported a OR = 2.66 for children with short stature to present fluorosis TF ≥ 4. In addition, it was observed that males have less risk to present severe DF than girls, these results are congruent to those reported by Ramezani et al. who observed greater prevalence of severe fluorosis in girls (65%) than in boys (34.2%). Nonetheless, in Pakistan, boys were more affected.
Fluoride concentration in the water of this population exceeds the permissible limits for human consumption (0.7–1.5mg/L); owing to the potential of adverse health effects of this situation, immediate actions are needed to reduce the exposure, thus diminishing adverse health effects in this population as DF, which is an irreversible alteration. Hence, actions Taken would not only reduce dental fluorosis in future generations but also would prevent the prevalence or severity of other alterations that excessive consumption of fluoride can cause.
| Conclusions|| |
Most of the studied population had DF and most of the cases were moderate or severe. Positive correlation between fluorosis severity and UF concentration was observed, also nutritional. Nutritional status was associated with severe DF. Water fluoride concentration of this population exceeds the limits stipulated by national and international norms. Given the potential of adverse health effects that this may produce, immediate actions are needed to reduce the exposure to this element.
Authors would like to acknowledge the support received by the UNAM, DGAPA through PAPIIT IN116010-2 project.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Qin X, Wang S, Yu M, Zhang L, Li X, Zuo Z, et al
. Child Skeletal Fluorosis from Indoor Burning of Coal in Southwestern China. J Environ Public Health 2009;2009:969764.
Das K, Mondal NK. Dental fluorosis and urinary fluoride concentration as a reflection of fluoride exposure and its impact on IQ level and BMI of children of Laxmisagar, Simlapal Block of Bankura District, W.B., India. Environ Monit Assess 2016;188:218.
Rango T, Kravchenko J, Atlaw B, McCornick PG, Jeuland M, Merola B, et al
. Groundwater quality and its health impact: An assessment of dental fluorosis in rural inhabitants of the Main Ethiopian Rift. Environ Int 2012;43:37-47.
Guidelines for drinking-water quality. 3rd
ed. Geneva, Switzerland: World Health Organization; 2004.
González-Horta C, Ballinas-Casarrubias L, Sánchez-Ramírez B, Ishida MC, Barrera-Hernández A5, Gutiérrez-Torres D, et al
. A Concurrent Exposure to Arsenic and Fluoride from Drinking Water in Chihuahua, Mexico. Int J Environ Res Public Health 2015;12:4587-601.
Molina Frechero N, Sánchez Pérez L, Castañeda Castaneira E, Oropeza Oropeza A, Gaona E, Salas Pacheco J, et al
. Drinking water fluoride levels for a city in northern Mexico (Durango) determined using a direct electrochemical method and their potential effects on oral health. ScientificWorldJournal 2013;2013:186392.
Ortega-Guerrero MA. Occurrence, distribution, hydrochemistry and origin of arsenic, fluoride and other trace elements dissolved in groundwater at basin scale in central Mexico. Rev Mex Cienc Geol 2009:26:143-61.
World Health Organization. Trace elements in human nutrition and health. Geneva: World Health Organization; 1996.
World Health Organization. Fluorides and oral health: Report of a WHO Expert Committee on oral health status and fluoride use. WHO Technical report series 846. Geneva; 1994.
Watanable M, Kono K, Orita Y, Dote T, Usuda K, Takahashi Y. Influence of dietary fluoride intake on urinary fluoride concentration and evaluation of corrected levels in spot urine. In: Proceedings of the 20th
Conference of the International Society for Fluoride Research, Beijing, China, September 5-9, 1994.
Betancourt A, Irigoyen ME, Mejía A, Zepeda M, Sánchez. Prevalencia de fluorosis dental en localidades mexicanas ubicadas en 27 estados y el D.F. a seis años de la publicación de la Norma Oficial Mexicana para la fluoruración de la sal. Rev Invest Clínica 2013;65:237-47.
Thylstrup A, Fejerskov O. Clinical appearance of dental fluorosis in permanent teeth in relation to histologic changes. Community Dent Oral Epidemiol 1978;6:315-28.
Jarquín-Yañez L, Mejia-Saavedra JJ, Molina-Frechero N, Gaona E, Rocha-Amador DO, López-Guzmán OD, et al
. Association between urine fluoride and dental fluorosis as a toxicity factor in a rural community in the State of San Luis Potosí. ScientificWorldJournal 2015;2015:647184.
Juárez-López ML, Huízar-Álvarez R, Molina-Frechero N, Murrieta-Pruneda F, Cortés-Aguilera Y. Fluoride in Water and Dental Fluorosis in a Community of Queretaro State Mexico. J Environ Prot 2011;2:744-9.
Rodríguez Dozal S, Alarcón Herrera MT, Cifuentes E, Barraza A, Loyola Rodríguez JP, LH Sanin. Dental Fluorosis in Rural communities of Chihuahua, México. Fluoride 2005;38:143-50.
Medina-Solis CE, Pontigo-Loyola AP, Maupome G, Lamadrid-Figueroa H, Loyola-Rodríguez JP, Hernández-Romano J, et al
. Dental fluorosis prevalence and severity using Dean's index based on six teeth and on 28 teeth. Clin Oral Invest 2008;12:197-202.
Ramesh M, Narasimhan M, Krishnan R, Chalakkal P, Aruna RM, Kuruvilah S. The prevalence of dental fluorosis and its associated factors in Salem district. Contemp Clin Dent 2016;7:203-8.
Singh B, Gaur S, Garg VK. Fluoride in drinking water and human urine in Southern Haryana India. J Hazardous Materials 2007;144:147-51.
Heintze SD, Bastos JR, Bastos R. Urinary fluoride levels and prevalence of dental fluorosis in three Brazilian cities with different fluoride concentrations in the drinking water. Community Dent Oral Epidemiol 1998;26:316-23.
Pontigo-Loyola AP, Medina-Solís CE, Lara-Carrillo E, Patiño-Marín N, Escoffié-Ramirez M, Mendoza-Rodríguez M, et al
. Impact of socio-demographic, socioeconomic, and water variables on dental fluorosis in adolescents growing up during the implementation of a fluoridated domestic salt program. Odontology 2014;102:105-15.
Epidemiological profile of oral health in Mexico 2010. SINAVE / DGE / HEALTH / epidemiological Oral health profile in Mexico 2010.
Ferreira EF, Vargas AM, Castilho LS, Velásquez LN, Fantinel LM, Abreu MH. Factors Associated to Endemic Dental Fluorosis in Brazilian Rural Communities. Int J Environ Res Public Health 2010;7:3115-28.
Rwenyonyi CM, Birkeland JM, Haugejorden O, Bjorvatn K. Age as a determinant of severity of dental fluorosis in children residing in areas with 0.5 and 2.5 mg fluoride per liter in drinking water. Clin Oral Investig 2000;4:157-61.
Siddiqui AH. Fluorosis in Nalgonda district, Hyderabad Deccan. Br Med J 1955;2:1408-13.
Choubisa SL, Choubisa L, Choubisa D. Osteo-Dental Fluorosis In Relation To Nutritional Status, Living Habits, And Occupation In Rural Tribal Areas Of Rajasthan, India. Fluoride 2009;42:210-5.
Irigoyen-Camacho ME, García Pérez A, Mejía González A, Huizar Alvarez R. Nutritional status and dental fluorosis among schoolchildren in communities with different drinking water fluoride concentrations in a central region in Mexico. Sci Total Environ 2016;541:512-9.
Perez-Perez GN, 2015. Fluorosis and dental caries prevalence in communities with different degrees of marginalization in the State of Oaxaca, Mexico (Unpublished doctoral dissertation). National Autonomous University of Mexico.
Ramezani GH, Valaei N, Eikani H. Prevalence of DMFT and fluorosis in the students of Dayer city (Iran). J Indian Soc Pedod Prev Dent 2004;22:49-53.
Sami E, Vichayanrat T, Satitvipawee P. Dental fluorosis and its relation to socioeconomic status, parnts knowledge and awareness among 12-year-old-school children in Quetta, Pakistan. Southeast Asian J Trop Med Public Health 2015;46:360-8.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
|This article has been cited by|
||Urinary fluoride and micronutrients intake in children from San Luis Potosi, Mexico
| ||Lizet Jarquin-Yañez,Jaqueline Calderon Hernandez,Laura Gonzalez,Nelly Molina-Frechero,Jose de Jesus Mejia-Saavedra |
| ||International Journal of Environmental Health Research. 2021; : 1 |
|[Pubmed] | [DOI]|
||Health implications among school children due to fluoride in underground aquifers of Haryana state, India
| ||Jabrinder Singh,Pooja Bhardwaj,Abhishek Awasthi |
| ||Environmental Quality Management. 2021; |
|[Pubmed] | [DOI]|
||Pharmacokinetics of fluoride in human adults: The effect of exercise
| ||Maria Mahmood,Liane B. Azevedo,Anne Maguire,M. Buzalaf,Fatemeh Vida Zohoori |
| ||Chemosphere. 2021; 262: 127796 |
|[Pubmed] | [DOI]|
||Health risk assessment of co-occurrence of toxic fluoride and arsenic in groundwater of Dharmanagar region, North Tripura (India)
| ||Piyal Bhattacharya,Suman Adhikari,Alok Chandra Samal,Ramen Das,Dhiraj Dey,Avijit Deb,Suleman Ahmed,Jakir Hussein,Ayan De,Antara Das,Madhurima Joardar,Ashis Kumar Panigrahi,Tarit Roychowdhury,Subhas Chandra Santra |
| ||Groundwater for Sustainable Development. 2020; : 100430 |
|[Pubmed] | [DOI]|
||Maternal and fetal exposures to fluoride during mid-gestation among pregnant women in northern California
| ||Dawud Abduweli Uyghurturk,Dana E. Goin,Esperanza Angeles Martinez-Mier,Tracey J. Woodruff,Pamela K. DenBesten |
| ||Environmental Health. 2020; 19(1) |
|[Pubmed] | [DOI]|
||Low-to-moderate fluoride exposure, relative mitochondrial DNA levels, and dental fluorosis in Chinese children
| ||Guoyu Zhou,Lu Yang,Chen Luo,Hongliang Liu,Pei Li,Yushan Cui,Li Liu,Xingchen Yu,Qiang Zeng,Jingwen Chen,Qian Zhao,Lixin Dong,Qiang Niu,Shun Zhang,Aiguo Wang |
| ||Environment International. 2019; 127: 70 |
|[Pubmed] | [DOI]|
||Assessment of fluoride in groundwater and urine, and prevalence of fluorosis among school children in Haryana, India
| ||A. K. Haritash,Ankur Aggarwal,Jigyasa Soni,Khyati Sharma,Mohnish Sapra,Bhupinder Singh |
| ||Applied Water Science. 2018; 8(2) |
|[Pubmed] | [DOI]|
| Article Access Statistics|
| Viewed||2428 |
| Printed||46 |
| Emailed||0 |
| PDF Downloaded||252 |
| Comments ||[Add] |
| Cited by others ||7 |