Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 12 de 12
Filtrar
1.
Arch Public Health ; 82(1): 6, 2024 Jan 12.
Artículo en Inglés | MEDLINE | ID: mdl-38216978

RESUMEN

PURPOSE: To describe the changes that occurred in the SARS-CoV-2 and influenza Prevalence, epidemiology, clinical picture, and prevalent genotypes among the Egyptian pilgrims returning from Hajj and Umrah 2022 seasons. METHODS: Pilgrims were contacted at the airport and invited to participate in the survey. Pilgrims who consented were interviewed using a standardized line list that included participant demographics, respiratory symptoms if any, previous COVID-19 infection, influenza vaccination whereas COVID-19 vaccination information were collected from vaccination cards. Participants were asked to provide throat and nasopharyngeal swabs for SARS-CoV-2 and influenza testing using RT-PCR and a subset of isolates were sequenced. Descriptive data analysis was performed to describe the epidemiology and clinical symptoms of SARS-CoV-2 and influenza. Prevalence rates of SARS-CoV-2 and influenza during Hajj were calculated and compared to Umrah surveys using chi2 and t-test with a significance level < 0.05. RESULTS: Overall, 3,862 Egyptian pilgrims enrolled, their mean age was 50.5 ± 47 years, half of them were > 50 years of age and 58.2% were males. Of them, 384 (9.9%) tested positive for SARS-CoV-2 and 51 (1.3%) for influenza viruses. Prevalence of SARS-CoV-2 infections (vaccine breakthrough) increased significantly between the Umrah and Hajj surveys (6.7% vs. 9.9%, p < 0.001), and variants of the virus varied considerably. Whereas no significant difference was found in influenza prevalence, vaccine coverage and vaccine breakthrough infection rates (11.7 vs. 9.2%, 26.9 vs. 26.8%, and 1.4 vs. 1.1% respectively). CONCLUSIONS: SARS-CoV-2 prevalence among Egyptian pilgrims returning from Hajj in July increased with reduced vaccine effectiveness compared to Umrah in March 2022 suggesting a possible wave of SARS-CoV-2 in the upcoming winter.

2.
BMC Oral Health ; 23(1): 631, 2023 09 04.
Artículo en Inglés | MEDLINE | ID: mdl-37667213

RESUMEN

BACKGROUND: The innovation of leukocyte platelet-rich fibrin (L-PRF) has added enormous impact on wound healing dynamics especially the field of periodontal regeneration. The release of growth factors (GF) is thought to improve the clinical outcomes in infrabony defects. The aim of this study was to evaluate the clinical effect of covering L-PRF contained infrabony defects with collagen membranes (CM), and to compare their GF release profile to uncovered L-PRF defects and open flap debridement (OFD). METHODS: Thirty non- smoking patients with infrabony pockets participated to be randomly assigned to OFD group (n = 10), L-PRF group (n = 10), or L-PRF protected CM group (n = 10). Plaque index (PI), gingival index (GI), probing depth (PD), clinical attachment level (CAL) and the radiographic defect base fill (DBF) were measured at baseline and at 6 month following surgical intervention. Gingival crevicular fluid samples were obtained on days 1, 3, 5, 7, 14, 21 and 30 days following surgery for the Platelet Derived Growth Factor-BB (PDGF-BB) and Vascular Endothelial Growth Factors (VEGF) release profile evaluation. RESULTS: For all patients, a statistically significant (P ≤ 0.05) reduction in PI, GI, PD and CAL were reported throughout the study period. Differences between the three treatment modalities were not statistically significant. PRF + CM showed a statistically significant DBF compared to OFD and L-PRF groups at follow up. Quantitative analysis of PDGF-BB and VEGF levels demonstrated a statistically significant (P < 0.001) decline between measurement intervals for all groups with no statistically significant differences between the three groups. CONCLUSION: Within the limitations of this study, L-PRF coverage with CM may augment defect base fill through its mechanical protective effect without enhancement in the release profile of VEGF and PDGF. The non-significant intergroup differences question the validity of the claimed extra physiologic concentration of GF offered by L-PRF harvests. TRIAL REGISTRATION: The present study was registered at ClinicalTrials.gov (NCT05496608), (11/08/2022).


Asunto(s)
Fibrina Rica en Plaquetas , Humanos , Factor A de Crecimiento Endotelial Vascular , Becaplermina , Colágeno/uso terapéutico , Leucocitos
3.
Clin Oral Investig ; 27(7): 3949-3960, 2023 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-37083985

RESUMEN

OBJECTIVES: This study evaluated clinically and histologically the efficacy of modified perforated collagen membrane (PCM) and/or leukocyte- and platelet-rich fibrin (L-PRF) in combination with xenogeneic block bone graft in the vertical alveolar ridge augmentation. MATERIALS AND METHODS: Six adult mongrel dogs were enrolled in this randomized blinded study. After defect preparation, xenogeneic screw-fixed block graft was covered by an occlusive collagen membrane in group 1 that represented the control group (Block + CM). In group 2, L-PRF membrane was added first before top coverage by occlusive collagen membrane (Block + L-PRF + CM). Groups 3 (Block + PCM) and 4 (Block + L-PRF + PCM) were identical to the first two groups except that the occlusive collagen membrane was replaced by a perforated one. Following a healing period of 2 months, the dogs were submitted to the surgical reentry phase for clinical and histological evaluation. RESULTS: Clinically, no significant differences were found among all groups regarding vertical and horizontal ridge dimensions (p = 0.155, 0.492, respectively). Histomorphometric analysis revealed that the percentage of the total bone area and mature bone was significantly higher in group 4 (69.36 ± 2.72, 33.11 ± 5.18) compared to the control group (59.17 ± 4.27, 21.94 ± 2.86) (p = 0. 027, p = 0.029). CONCLUSION: The use of xenogenic block grafts in combination with a double-layered perforated collagen L-PRF membrane in vertical ridge augmentation appeared to improve the inductive power of this challenging defect type. CLINICAL RELEVANCE: Size and number of perforations may affect the mechanical and handling properties of the membrane.


Asunto(s)
Aumento de la Cresta Alveolar , Fibrina Rica en Plaquetas , Animales , Perros , Aumento de la Cresta Alveolar/métodos , Regeneración Ósea , Trasplante Óseo/métodos , Colágeno
4.
J Periodontal Res ; 55(3): 441-452, 2020 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-32080858

RESUMEN

BACKGROUND: Defective cellular elements constitute an important challenge to achieve predictable periodontal regeneration. In an attempt to improve the cellularity of periodontal defects, gingival fibroblasts were implanted without their associated extracellular elements in periodontal defects to expose them to periodontal tissue mediators. In order to investigate the regenerative potential of gingival fibroblasts translocated into periodontal defects, the present study was designed to clinically and biochemically investigate the use of gingival fibroblasts (GF) and their associated mesenchymal stem cells (GMSC) in the treatment of intrabony periodontal defects. METHODS: A total of 20 subjects were randomly divided into two groups (n = 20). Group I: ten patients were included with ten intrabony periodontal defects that received ß-calcium triphosphate (ß-TCP) followed by collagen membrane defect coverage, while group II: (10 patients) ten periodontal defects received cultured gingival fibroblasts (GF) on the ß-TCP scaffold and covered by a collagen membrane. The clinical evaluation was carried out at the beginning and at 6 months. Gingival crevicular fluid (GCF) samples were collected directly from the test sites for the quantitative measurement of PDGF-BB and BMP-2 using the ELISA kit at 1, 7, 14, and 21 days after surgery. RESULTS: Group II reported a significantly greater reduction in vertical pocket depth (VPD) and CAL gain compared with group I after 6 months. Radiographic bone gain was statistically higher in group II compared with group I. A significantly higher concentration of PDGF-BB was observed in group II on days 1, 3, and 7 compared with group I. CONCLUSIONS: Translocation of gingival fibroblasts from gingival tissue to periodontal defects could be a promising option that increases cellular elements with regeneration potential. The concept of total isolation of gingival fibroblasts using occlusive membranes must be re-evaluated.


Asunto(s)
Pérdida de Hueso Alveolar/terapia , Fibroblastos/citología , Regeneración Tisular Guiada Periodontal , Estudios de Seguimiento , Encía/citología , Humanos , Membranas Artificiales , Resultado del Tratamiento
5.
Earth Syst Environ ; 4(3): 513-522, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-34723073

RESUMEN

The coronavirus pandemic has not only gripped the scientific community in the search for a vaccine or a cure but also in attempts using statistics and association analysis-to identify environmental factors that increase its potency. A study by Ogen (Sci Total Environ 726:138605, 2020a) explored the possible correlation between coronavirus fatality and high nitrogen dioxide exposure in four European countries-France, Germany, Italy and Spain. Meanwhile, another study showed the importance of nitrogen dioxide along with population density in determining the coronavirus pandemic rate in England. In this follow-up study, Aerosol Optical Depth (AOD) was introduced in conjunction with other variables like nitrogen dioxide and population density for further analysis in fifty-four administrative regions of Germany, Italy and Spain. The AOD values were extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites while the nitrogen dioxide data were extracted from TROPOMI (TROPOspheric Monitoring Instrument) sensor onboard the Sentinel-5 Precursor satellite. Regression models, as well as multiple statistical tests were used to evaluate the predictive skill and significance of each variable to the fatality rate. The study was conducted for two periods: (1) pre-exposure period (Dec 1, 2019-Feb 29, 2020); (2) complete exposure period (Dec 1, 2019-Jul 1, 2020). Some of the results pointed towards AOD potentially being a factor in estimating the coronavirus fatality rate. The models performed better using the data collected during the complete exposure period, which showed higher AOD values contributed to an increased significance of AOD in the models. Meanwhile, some uncertainties of the analytical results could be attributed to data quality and the absence of other important factors that determine the coronavirus fatality rate.

6.
J Periodontal Res ; 55(1): 85-95, 2020 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-31448832

RESUMEN

BACKGROUND: Perforated barrier membranes (PBM) were suggested to enhance periodontal regeneration by allowing positive charity of wanted elements from the gingival tissue side. The present study was designed to evaluate clinically and biochemically the use of PBM combined with simvastatin (SMV) gel with and without an associated EDTA gel root surface etching as a suggested option that could improve SMV availability and clinical outcomes of PBM. METHODS: Forty patients having moderate-to-severe chronic periodontitis with 40 intrabony defects were randomly divided into four treatment groups (10 sites each). Patients in group 1 received 1.2% SMV gel and covering the defect with occlusive membrane (OM). Patients in group 2 received 1.2% SMV gel and covering the defect with PBM. Group 3 received 24% EDTA root surface etching, 1.2% SMV gel, and defect coverage with OM (eOM). Patients in group 4 were treated as in group 3 but the defect was covered with PBM (ePBM). Clinical parameters were recorded at baseline before surgical procedures and were reassessed at 6 and 9 months after therapy. The mean concentration of SMV in gingival crevicular fluid (GCF) was estimated by reverse-phase high-performance liquid chromatography at days 1, 7, 14, 21, and 30. RESULTS: At 6- and 9-month observation periods, groups 3 and 4 showed a statistically significant improvement in PD reduction and CAL gain compared with groups 1 and 2. Group 4 showed a statistically significant more defect fill compared with groups 1, 2, and 3 (P ≤ .05). Group 2 showed statistically significant higher defect fill compared with group 1 and group 3 (P < .05). Bone density was significantly increased with no significant difference between the four groups at 6- and 9-month observation periods. SMV-GCF concentration in group 4 showed the highest mean concentration with no significant difference than that of group 3. CONCLUSION: The use of perforated barrier membranes in association with SMV enhances the clinical hard tissue parameters compared with occlusive ones in treating intrabony periodontal defects. Moreover, EDTA root surface treatment could enhance SMV availability in the defect area.


Asunto(s)
Pérdida de Hueso Alveolar/terapia , Regeneración Tisular Guiada Periodontal , Membranas Artificiales , Simvastatina/uso terapéutico , Adulto , Pérdida de Hueso Alveolar/cirugía , Ácido Edético , Femenino , Estudios de Seguimiento , Líquido del Surco Gingival , Humanos , Masculino , Persona de Mediana Edad , Pérdida de la Inserción Periodontal , Bolsa Periodontal , Estudios Prospectivos , Resultado del Tratamiento
7.
J Liposome Res ; 29(4): 375-382, 2019 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-30633595

RESUMEN

Lycopene (LP), a naturally occurring carotenoid in red-coloured fruits, especially tomatoes, has a pivotal role in counteracting the deleterious effect of oxidative stress on periodontal tissues. The aim of this study is to prepare solid lipid microparticles (SLMs) encapsulating LP and to assess their biochemical and clinical effects in the management of chronic periodontitis. Optimization of SLMs was performed by assessing particle size and LP entrapment efficiency. Clinical study included 16 chronic periodontitis patients allocated into two groups, Group I was managed by scaling and root planing (SRP) and local delivery of LP loaded SLMs, while Group II was managed by SRP only. Protein carbonyl (PC) levels as a biomarker of oxidative stress and drug concentration in gingival crevicular fluid (GCF) were assessed at different time intervals. Results revealed that optimum formula of SLMs had a particle size of 77.28 µm and entrapped 98.03% of LP. SLMs recorded 30 d of drug release with no burst effect. Patients treated with LP SLMs showed significantly lower levels of PC after SRP compared to those treated with SRP only, in addition to improvement in the measured clinical parameters. In conclusion, locally delivered LP SLMs along with SRP could have a protective effect over periodontal tissues and it has the ability to decrease oxidative damage of proteins in diseased periodontium.


Asunto(s)
Antibacterianos/química , Periodontitis Crónica/tratamiento farmacológico , Líquido del Surco Gingival/metabolismo , Liposomas/química , Licopeno/química , Carbonilación Proteica/efectos de los fármacos , Adulto , Antibacterianos/farmacocinética , Biomarcadores/metabolismo , Raspado Dental/métodos , Composición de Medicamentos/métodos , Liberación de Fármacos , Femenino , Humanos , Lípidos/química , Licopeno/farmacocinética , Masculino , Persona de Mediana Edad , Estrés Oxidativo/efectos de los fármacos , Tamaño de la Partícula , Aplanamiento de la Raíz/métodos
8.
J Periodontol ; 89(6): 691-698, 2018 06.
Artículo en Inglés | MEDLINE | ID: mdl-29536543

RESUMEN

BACKGROUND: Because it is important to establish and maintain a firm blood clot to the surrounding tissues within the intrabony lesion; we have to investigate the potentials of different materials in resisting clot retraction that disrupt clot adhesion to the root surface. This study was designed to measure the gap distance created by clot retraction within the defect following intrabony defects grafting with and without root surface EDTA etching. METHODS: Eight mongrel dogs with surgically created acute-chronic bilateral mandibular interproximal intrabony defects in the premolar-molar areas were enrolled in this study (total 8 defects per dog). Intrabony defects were divided into four groups, the first group (OFD): control open flap debridement, the second group, (EDTA treated defects) in which debridement of the defects was followed by two minute root surface etching with a neutral 24% EDTA gel followed by two minute copious saline irrigation, the third group (only grafted defects): defects received closely packed ß-TCP of a particle size ranged from 150 to 500 mm, and the fourth group, (Graft + EDTA treated defects): defects were etched for 2 minutes with a neutral 24% EDTA gel and saline irrigation followed by intrabony defect fill of ß-TCP. Twenty four hours post treatment, animal euthanasia was carried out for histomorphometric analysis of the tooth and root side gap distances. RESULTS: EDTA treated group and EDTA + graft group showed statistically significant lower degree of clot shrinkage compared to both the control and only grafted group. Clot shrinkage in EDTA treated group showed no significant difference from that of the EDTA + graft group (p = 0.197). OFD and only grafted groups were found to show statistically higher clot retraction percnetage compared to both EDTA and EDTA+graft groups. CONCLUSION: following intrabony defect debridement, blood clot undergoes clot retraction creating a micro gap with the root surface. EDTA root surface etching before graft application into the defect area significantly reduced the amount of gap distance.


Asunto(s)
Pérdida de Hueso Alveolar , Trombosis , Animales , Desbridamiento , Perros , Ácido Edético , Regeneración Tisular Guiada Periodontal
9.
J Orthod Sci ; 6(1): 28-35, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-28197400

RESUMEN

OBJECTIVES: To investigate the effect of using osteogenic induced gingival fibroblasts (OIGFs) and low intensity pulsed ultrasound (LIPUS) on root resorption lacunae volume and cementum thickness in beagle dogs that received orthodontic tooth movement. MATERIALS AND METHODS: Seven beagle dogs were used, from which gingival cells (GCs) were obtained and were induced osteogenically to produce OIGFs. Each third and fourth premolar was randomly assigned to one of the five groups, namely, LIPUS, OIGFs, bone morphogenetic protein-2 (BMP-2), OIGFs + LIPUS, and control. All groups received 4 weeks of bodily tooth movement, then LIPUS-treated groups received LIPUS for 20 min/day for 4 weeks, and OIGFs groups received an injection of OIGFs near the root apex. Microcomputed tomography analysis was used to calculate root resorption lacunae volume and histomorphometric analysis was performed to measure the cementum thickness of each root at 3 root levels on compression and tension sides. RESULTS: There was no significant difference in resorption volume between the treatment groups. OIGFs + LIPUS increased cementum thickness (P > 0.05) in third premolars near the apex, and LIPUS increased cementum thickness (P > 0.05) in fourth premolars near the apex. Furthermore, BMP2 increased cementum thickness at the coronal third at the compression side. CONCLUSION: OIGFs, LIPUS, and BMP-2 can be potential treatments for orthodontically induced root resorption, however, improvements in experimental design and treatment parameters are required to further investigate these repair modalities.

10.
J Periodontol ; 87(6): 654-62, 2016 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-26876351

RESUMEN

BACKGROUND: The open, usually contaminated nature of periodontal defects could negatively affect availability and activity of platelet concentrate-suggested growth factors (GF). The aim of this study is to test this hypothesis and investigate concentrations of: 1) vascular endothelial growth factor (VEGF) and 2) platelet-derived growth factor (PDGF-BB) in gingival crevicular fluid (GCF) from localized intrabony defects treated with platelets rich in growth factors (PRGF) or platelet-rich fibrin (PRF) compared with a control xenograft defect filling. METHODS: Thirty non-smoking patients suffering severe chronic periodontitis were allocated to this randomized, prospective, single-masked trial. Each patient had one interproximal defect randomly distributed to: 1) group 1: bone-substitute grafting control (n = 10); 2) group 2: experimental PRGF (n = 10); or 3) group 3: PRF (n = 10). Clinical parameters were measured at baseline and 6 and 9 months following therapy. GCF samples were obtained on days 1, 3, 7, 14, 21, and 30 after therapy for evaluation of VEGF and PDGF-BB levels. RESULTS: On days 1, 3, and 7 following surgery, mean levels of VEGF and PDGF-BB at sites treated with PRGF and PRF were not significantly different versus the control. Levels of PDGF-BB and VEGF were higher in the PRGF-treated group, but differences were not significant. Growth factor levels decreased significantly in samples collected on days 14, 21, and 30 with non-significant differences among the three groups. No significant clinical differences were reported among the three groups during the two observation periods (early period: days 1, 3, and 7; and later period: days 14, 21, and 30). CONCLUSIONS: Within the limits of the present study, it can be concluded that PRF and PRGF platelet concentrate failed to augment clinical effects achieved with the xenograft alone in treating intrabony defects. Periodontal defects could not retain extraphysiologic levels of GF suggested to be associated with platelet concentrate.


Asunto(s)
Regeneración Tisular Guiada Periodontal , Pérdida de la Inserción Periodontal/terapia , Fibrina Rica en Plaquetas , Pérdida de Hueso Alveolar , Humanos , Péptidos y Proteínas de Señalización Intercelular/fisiología , Estudios Prospectivos , Factor A de Crecimiento Endotelial Vascular
11.
Front Microbiol ; 5: 6, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24478766

RESUMEN

The majority of risk factors for chronic inflammatory diseases are unknown. This makes personalized medicine for assessment, prognosis, and choice of therapy very difficult. It is becoming increasingly clear, however, that low-grade subclinical infections may be an underlying cause of many chronic inflammatory diseases and thus may contribute to secondary outcomes (e.g., cancer). Many diseases are now categorized as inflammatory-mediated diseases that stem from a dysregulation in host immunity. There is a growing need to study the links between low-grade infections, the immune responses they elicit, and how this impacts overall health. One such link explored in detail here is the extreme sensitivity of myeloid dendritic cells (mDCs) in peripheral blood to chronic low-grade infections and the role that these mDCs play in arbitrating the resulting immune responses. We find that emerging evidence supports a role for pathogen-induced mDCs in chronic inflammation leading to increased risk of secondary clinical disease. The mDCs that are elevated in the blood as a result of low-grade bacteremia often do not trigger a productive immune response, but can disseminate the pathogen throughout the host. This aberrant trafficking of mDCs can accelerate systemic inflammatory disease progression. Conversely, restoration of dendritic cell homeostasis may aid in pathogen elimination and minimize dissemination. Thus it would seem prudent when assessing chronic inflammatory disease risk to consider blood mDC numbers, and the microbial content (microbiome) and activation state of these mDCs. These may provide important clues ("the canary in the coal mine") of high inflammatory disease risk. This will facilitate development of novel immunotherapies to eliminate such smoldering infections in atherosclerosis, cancer, rheumatoid arthritis, and pre-eclampsia.

12.
J Periodontol ; 84(2): 239-47, 2013 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-22554294

RESUMEN

BACKGROUND: The objective of this study is to evaluate micro and nano-hydroxyapatite (NHA) blended clot adhesion to citric acid-conditioned peri-implantitis-affected surfaces. METHODS: Forty hopeless implants with peri-implantitis designated for removal were included in this study. Implants were divided into eight groups of five each: group 1 (G1) test areas were coated with hydroxyapatite of a microparticle size (MHA); group 2 (G2) test areas were coated with NHA; group 3 (G3) implants were coated with MHA after surface conditioning using citric acid; group 4 (G4) samples were treated in the same manner as in G3 except for the use of NHA; group 5 (G5) samples were coated without surface treatment with MHA mixed with whole human blood; group 6 (G6) implant samples were treated in the same manner as in G5 except for the use of NHA; group 7 (G7) implant samples were treated in the same way as in G5 plus surface conditioning using citric acid; and group 8 (G8) samples were treated in the same manner as in G7 except for the use of NHA. All implants in all groups were agitated for 3 minutes in phosphate-buffered saline. All samples were prepared for scanning electron microscopy evaluation. RESULTS: G1 and G2 non-etched implants coated with MHA or NHA sizes were devoid of any bone particle adhesion to the peri-implantitis-affected surfaces. Contrary to the lack of microparticle adhesion to the root surface that was seen in G3, G4 acid-treated and NHA-coated samples revealed nearly complete coverage of the peri-implantitis-affected parts by the graft material. G5 non-etched, clot-blended MHA showed some areas of clot-blended graft adhesion covering 6.7% of the examined surfaces. G6 non-etched, clot-blended NHA showed NHA retention within the fibrin strands in areas where the implant surface pores were exposed (24.3%). G7 acid-treated and clot-blended MHA-treated implant surfaces showed partial coverage of the implant surface with detached fibrin clot-blended graft material (31.4%). G8 acid-treated and NHA clot-blended graft-coated implants showed complete coverage of the implant surface by the clot-blended graft material (93.4%). CONCLUSION: Peri-implantitis-affected surface conditioning with citric acid improves NHA-blended clot adhesion to titanium implant surfaces.


Asunto(s)
Sustitutos de Huesos/química , Implantes Dentales , Durapatita/química , Nanopartículas/química , Periimplantitis/patología , Grabado Ácido Dental/métodos , Adhesividad , Adulto , Coagulación Sanguínea , Ácido Cítrico/química , Materiales Dentales/química , Fibrina/química , Fibrina/ultraestructura , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Microscopía Electrónica de Rastreo , Persona de Mediana Edad , Tamaño de la Partícula , Porosidad , Estudios Prospectivos , Método Simple Ciego , Propiedades de Superficie , Titanio/química
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA