Leishmania (Sauroleishmania) tarentolae versus pathogenic species: comparative evaluation of protease activity, glycoconjugates, resistance to complement and metabolome composition.

BACKGROUND: Leishmania tarentolae is a non-pathogenic species found in lizards representing an important model for Leishmania biology. However, several aspects of this Sauroleishmania remain unknown to explain its low level of virulence. OBJECTIVES: We reported several aspects of L. tarentolae biology including glycoconjugates, proteolytic activities and metabolome composition in comparison to pathogenic species (Leishmania amazonensis, Leishmania braziliensis, Leishmania infantum and Leishmania major). METHODS: Parasites were cultured for extraction and purification of lipophosphoglycan (LPG), immunofluorescence probing with anti-gp63 and resistance against complement. Parasite extracts were also tested for proteases activity and metabolome composition. FINDINGS: Leishmania tarentolae does not express LPG on its surface. It expresses gp63 at lower levels compared to pathogenic species and, is highly sensitive to complement-mediated lysis. This species also lacks intracellular/extracellular activities of proteolytic enzymes. It has metabolic differences with pathogenic species, exhibiting a lower abundance of metabolites including ABC transporters, biosynthesis of unsaturated fatty acids and steroids, TCA cycle, glycine/serine/threonine metabolism, glyoxylate/dicarboxylate metabolism and pentose-phosphate pathways. MAIN CONCLUSIONS: The non-pathogenic phenotype of L. tarentolae is associated with alterations in several biochemical and molecular features. This reinforces the need of comparative studies between pathogenic and non-pathogenic species to elucidate the molecular mechanisms of virulence during host-parasite interactions.

Experimental keratitis induced in rat by Acanthamoeba from distinct morphological groups/genotypes: a histological and immunohistochemical evaluation.

Species of the genus Acanthamoeba are free-living protozoans that occasionally act as parasites, causing a severe, progressive corneal infection termed Acanthamoeba keratitis (AK). The variable pathogenic potential among Acanthamoeba lineages has been shown by in vitro assays, but little is known about the behavior of different strains in animal models of AK. This work aimed to evaluate the infectivity of Acanthamoeba from distinct morphological groups and genotypes in a rat model of AK and apply an immunohistochemical technique for histological characterization of the lesions. Only a strain classified as group I/genotype T17, isolated from a soil source, caused ulcerated corneal lesions in two Wistar rats (n = 9) subjected to intrastromal inoculation. Two strains derived from AK human cases (group II/genotype T4 and group III/genotype T5) did not induce corneal lesions in the rats. A previous association of group II/genotype T4 trophozoites with lethally irradiated Escherichia coli did not influence the infectivity. A hyperimmune serum produced in Wistar rats was validated by an immunocytochemical technique using the three distinct strains and then applied for immunohistochemistry. The abundance of antigenic residues was observed in both corneas with keratitis, suggesting that the infectious process tended to resolve. Despite the low infection rate of the AK Wistar rat model, we produced an immunochemical tool with a potential diagnostic application. We also showed for the first time the ability of Acanthamoeba from T17 genotype to cause AK in experimental conditions.

Effects of parity order on performance, metabolic, and hormonal parameters of grazing beef cows during pre-calving and lactation periods.

BACKGROUND: Metabolic profile evaluation is a tool widely used in ruminant nutrition as metabolic cues that relate nutrition to physiology. Metabolic and hormonal traits change during pre-partum and lactation according to parity in dairy cows, but studies of beef cows under grazing are scarce. The present study aimed to evaluate how metabolic and hormonal traits change over time, their relationship to performance, and determine if these factors differ according to the parity order of grazing beef cows. Thirty-six pregnant Nellore cows (12 nulliparous, 12 primiparous, and 12 multiparous) were used. The study started at 60 d prepartum until 203 d of lactation. RESULTS: The initial body weight (BW) and final BW were higher for multiparous cows (P > 0.05). An interaction occurred between parity and day (P < .0001) for body condition score. Nulliparous and primiparous body condition score were reduced from - 60 prepartum to 30 postpartum, then stabilized 60 postpartum (P < 0.05), while multiparous maintained body condition score from - 60 days until 60 days postpartum (P > 0.05). Calf BW, final BW, and average daily gain did not differ between parities (P > 0.05). Effect of day (P < 0.05) was detected for non-esterified fatty acids, triglycerides, total cholesterol, LDL, VLDL, progesterone, and insulin. An interaction was observed between parity and days for glucose, HDL, ß-hydroxybutyrate, creatinine and IGF-1 (P < 0.05). Parity affected serum urea nitrogen, total proteins, albumin, and globulins (P < 0.05). Parity and day relative to calving did not impact total T3 and T4 (P > 0.05). CONCLUSIONS: Hormonal and metabolic profile is strongly influenced by the stage of lactation. Time effects (pre-partum and lactation period) were more pronounced in nulliparous since they displayed more unbalanced metabolic and hormonal traits and lowered BCS pre- and postpartum.

Factors influencing endothelial cell density of corneas for transplantation.

To evaluate factors affecting corneal endothelial cell density (ECD) under enucleation and preservation time studies at Eye Bank of the Federal District of Brazil. We conducted a case-control study collecting data from 1128 corneas where death-to-enucleation time and enucleation-to-preservation time were within 24 h. Low cell count were those corneas with an ECD less than 2000 cells/mm2 and high cell count was defined as those with ECD greater than 2000 cells/mm2. We calculated the independent risk factors related to: cause of death, donor age, death-to-enucleation time, enucleation-to-preservation time and primary graft failure. Correlation analysis was used to assess which parameters influence ECD: death-to-enucleation time, enucleation-to-preservation time, average cell area (AVE), coefficient of variation and percentage of hexagonal cells. Of the total number of corneas, 1004 had ECD data and were selected for the study. 87.4% (n = 877) had high cell counts with 2699 ± 412 cells/mm2. The mean donor age was 38.8 ± 16 years. The most common causes of death were external causes (48.6%, n = 488). Longer times from death-to-enucleation, up to 24 h were not associated with a decrease in ECD (OR 0.58; P = 0.44) or risk of graft survival (P = 0.74). Enucleation-to-preservation intervals greater than 12 h showed increased risk of graft survival (P = 0.04). AVE was the main parameter for ECD (R2 = 0.96, P < 0.001). The overall graft survival rate was 98.2% (n = 761). Donors with 40 years of age and above did not present a higher risk of graft survival (P = 0.09). We suggest that the maximum time from death-to-enucleation should be 24 h, assuming the body has been refrigerated after 6 h; and from enucleation-to-preservation time of 12 h, followed by proper processing and cornea morphology examination.

Production of xylanases by Bacillus sp. TC-DT13 in solid state fermentation using bran wheat.

Xylanases have gained increasing importance due to their diverse applications in the food, paper, and pharmaceutical industries, however, the production of these enzymes currently uses expensive substrates. It has already been estimated that more than 30% of the enzyme production cost originates from the substrate. The present study aimed to optimize the production of extracellular xylanases by the Bacillus sp. TC-DT 13 using solid-state fermentation with agro-industrial residues, with a view at reducing the production cost of these enzymes. All the agro-industrial residues were tested in submerged fermentation to select the best inductor to produce xylanase. Among these residues, wheat bran was selected as the best inducer of xylanase production with 1500 U/mL. Regarding solid-state fermentation, the use of wheat bran as the only fermentation substrate was used and a ratio of 1:4 moisture over a time of 144 hours induced higher amount of xylanase reaching 2943 U/g. The use of carbon and nitrogen sources did not result in the increase in production of xylanolitic enzymes. The use of agro-industrial residues in the solid-state fermentation, besides increasing the production of xylanase, reduces the cost of production and is an environmentally friendly alternative.

Partial replacement of pork fat by Echium oil in reduced sodium bologna sausages: technological, nutritional and stability implications.

BACKGROUND: The present research aimed to evaluate the nutritional, technological, microstructural and sensory characteristics of bologna sausages made with pork fat replaced with Echium oil. Three different treatments were processed, all of them with approximately 35% less sodium than a regular bologna-type sausage: Control (only pork backfat addition) and T25 and T50 (replacement of 25 and 50% of the added animal fat with Echium oil respectively). RESULTS: Proximate composition, texture profile analysis, fatty acid profile and microstructure were evaluated to characterize the products. In refrigerated storage, the following characteristics were assessed: thiobarbituric acid-reactive substances (TBARS) index, objective color, pH value, microbiological counts and sensory acceptance. Both samples with Echium oil (T25 and T50) showed a healthier lipid profile, with high omega-3 content, mainly from α-linolenic and stearidonic fatty acids, consequently presenting better (P ≤ 0.05) values of nutritional indices than the Control. However, the replacement of 50% animal fat with Echium oil negatively affected (P ≤ 0.05) most of the technological characteristics and the sensory acceptance of bolognas. In contrast, the treatment with 25% replacement did not show significant differences in most of the evaluated parameters compared with the Control sample. CONCLUSION: Thus the replacement of 25% of pork backfat with Echium oil in bologna sausages can be recommended, representing a good balance between nutritional gains and sensory impairment. © 2019 Society of Chemical Industry.

Sodium reduction in enrobed restructured chicken nuggets through replacement of NaCl with CaCl2.

The present study aimed to reformulate chicken nuggets with reduced sodium content, replacing the NaCl with CaCl2 and assessing the physicochemical and sensory properties of the obtained products. Four treatments of chicken nuggets were processed: Control formulation (1.5 g NaCl/100 g) and three treatments containing CaCl2 substituting 25, 50 and 75% of the NaCl, considering an ionic strength equivalent to 1.5% NaCl. The four different chicken nuggets were similar (p > 0.05) for the variables oil absorption, lipid, protein and moisture contents, water activity, cooking yield, pick-up and texture profile analysis. However, a decrease in ash content (2.21-1.75 g/100 g) was observed. The replacement of 75% NaCl could reduce 34% sodium in chicken nuggets with a concomitant increase in the calcium content (10-130 mg/100 g). For objective colour, the brightness (L*) increased from 74.43 to 78.28 as CaCl2 contents increased in the chicken nuggets, but the a* and b*parameters did not show differences (p > 0.05) among all treatments. Sensory acceptance (texture, flavour and overall quality attributes) did not differ between Control and the 75% sodium reduction treatments (all values around 7.5 in the 9-point hedonic scale), despite the decrease in the salty taste observed in the just about right scale test. Thus, the maximum tested replacement of 75% NaCl by CaCl2 produced healthier chicken nuggets, for having provided a reduction in sodium content and increase in calcium content, besides maintaining sensory quality and most of the technological characteristics.

Modified atmosphere packaging for lamb meat: evaluation of gas composition in the extension of shelf life and consumer acceptance.

Convenience foods like chilled meat usually have a short shelf life. Modified atmosphere packaging (MAP) can be used together with refrigeration to retard meat degradation. This work evaluated the effect of MAP on the preservation and consumers acceptance of lamb meat. Lamb loins Longissimus lumborum were packed in five conditions: 15% O2 + 85% CO2 (O15), 30% O2 + 70% CO2 (O30), 45% O2 + 55% CO2 (O45), 60% O2 + 40% CO2 (O60), and Vacuum (control). Physicochemical, sensory, and microbiological analyses were carried out along 21 days of refrigerated (1 ± 1 °C) storage. Treatments O30, O45 and vacuum presented the lowest oxidation values: 0.60, 0.61 and 0.30 Malonaldehyde Kg-1 respectively. Treatment O45 showed the highest a* until the seventh day of storage (16.64). In the sensory preference ranking test, O30 and O45 received best scores in the first and second weeks of storage, respectively. Treatments O30 and O45 delivered products with lower microbial counts than the other ones. Considering a balance between consumer preference and microbiological results, we propose the use of 45% O2 + 55% CO2 gas composition to extend the shelf life of lamb loin.

Inequalities in infant mortality among municipalities in Brazil according to the Family Development Index, 2006-2008.

OBJECTIVE: To describe inequalities in the infant mortality rate (IMR) according to socioeconomic indicators among geographic areas and municipalities in Brazil. METHODS: This was an exploratory ecological study of space aggregates that described IMR in 2006-2008 according to municipalities, states, and the Family Development Index (FDI), a socioeconomic indicator that ranges from 0 to 1. All the municipalities in Brazil were categorized according to four strata as defined by FDI quartiles, where stratum 4 included those with better FDI conditions, and stratum 1, worse conditions. The selected inequality measures were: Concentration Index, Attributable Risk Percent, Population Attributable Risk Percent, Rate Ratio, and number of avoidable events (number of infant deaths). RESULTS: The average IMR (per 1 000 live births) according to the FDI strata were: stratum 1 (FDI = 0.41-0.52) = 18.8; stratum 2 (FDI = 0.53-0.55) = 17.9; stratum 3 (FDI = 0.56-0.58) = 15.0; and stratum 4 (FDI = 0.59-0.73) = 13.4. Overall, the Concentration Index was 0.02. Moreover, stratum 1, with a proportion of 17% of all live births in the population, had a concentration of 20% of infant deaths. Additionally, the profile of causes and ages of infant mortality also differed qualitatively when stratum 1 was compared to stratum 4. CONCLUSIONS: The results suggest an association between the socioeconomic indicators, specifically the FDI, and the risk of infant death. These results call attention to the specific population groups in Brazil that are most vulnerable to infant mortality and demonstrate that the FDI can be used to identify these populations.

Does Parity Influence the Magnitude of the Stress Response of Nellore Cows at Weaning?

Most studies investigate the impact of stress at weaning on calves; however, little is known about the responses of cows, and whether they would differ according to parity. This study aims to investigate whether parity would influence the weaning stress response in beef cows. Thirty pregnant Nellore cows with their respective calves were randomly allocated to five paddocks and two females from each parity group were placed in the paddocks. There was an interaction (p < 0.05) between parity and evaluation days regarding cortisol, where on d + 7, the higher concentration was observed for multiparous cows. There was an interaction (p < 0.05) between parity and evaluation day for red blood cells (RBC), hematocrit (HCT), and hemoglobin (HB), whereby higher RBC counts on d + 4 were observed for multiparous cows. For HCT and HB, on all post-weaning collection days, higher values were observed for multiparous cows. The day of evaluation had an (p < 0.05) effect on all recorded behaviors, except for rumination (p > 0.05). Nellore cows, regardless of parity, underwent behavioral and physiological changes on abrupt weaning. Physiological parameters indicated that the magnitude of stress was greater in multiparous cows.

Increased interregional virus exchange and nucleotide diversity outline the expansion of the chikungunya virus ECSA lineage in Brazil.

The emergence and reemergence of mosquito-borne diseases in Brazil such as Yellow Fever, Zika, Chikungunya, and Dengue have had serious impacts on public health. Concerns have been raised due to the rapid dissemination of the chikungunya virus (CHIKV) across the country since its first detection in 2014 in Northeast Brazil. Faced with this scenario, on-site training activities in genomic surveillance carried out in partnership with the National Network of Public Health Laboratories have led to the generation of 422 CHIKV genomes from 12 Brazilian states over the past two years (2021-2022), a period that has seen more than 312 thousand chikungunya fever cases reported in the country. These new genomes increased the amount of available data and allowed a more comprehensive characterization of the dispersion dynamics of the CHIKV East-Central-South-African (ECSA) lineage in Brazil. Tree branching patterns revealed the emergence and expansion of two distinct subclades. Phylogeographic analysis indicated that the northeast region has been the leading hub of virus spread towards other regions. Increased frequency of C>T transitions among the new genomes suggested that host restriction factors from the immune system such as ADAR and AID/APOBEC deaminases might be driving CHIKV ECSA lineage genetic diversity in Brazil.

Increased interregional virus exchange and nucleotide diversity outline the expansion of chikungunya virus in Brazil.

The emergence and reemergence of mosquito-borne diseases in Brazil such as yellow fever, zika, chikungunya, and dengue have had serious impacts on public health. Concerns have been raised due to the rapid dissemination of the chikungunya virus across the country since its first detection in 2014 in Northeast Brazil. In this work, we carried out on-site training activities in genomic surveillance in partnership with the National Network of Public Health Laboratories that have led to the generation of 422 chikungunya virus genomes from 12 Brazilian states over the past two years (2021-2022), a period that has seen more than 312 thousand chikungunya fever cases reported in the country. These genomes increased the amount of available data and allowed a more comprehensive characterization of the dispersal dynamics of the chikungunya virus East-Central-South-African lineage in Brazil. Tree branching patterns revealed the emergence and expansion of two distinct subclades. Phylogeographic analysis indicated that the northeast region has been the leading hub of virus spread towards other regions. Increased frequency of C > T transitions among the new genomes suggested that host restriction factors from the immune system such as ADAR and AID/APOBEC deaminases might be driving the genetic diversity of the chikungunya virus in Brazil.

Use of Focus Group as Selection Method of Descriptors for Check-All-That-Apply (CATA) for Sensory Characteristics of Hot Dogs.

Check-all-that-apply (CATA) is a methodology for sensory product characterization that can be used by consumers. These characteristics, on the other hand, are determined by a trained panel, and consumers are not asked how they perceive these attributes; as a result, some of the characteristics raised by the trained panel may not be relevant to consumers. In this study, the CATA test was applied to characterize three types of hot dogs, those with or without irradiation and salt reduction, and the focus group (FG) technique was employed to determine the CATA descriptors. Each participant in the FG provided five words (attributes) that, in their opinion, best defined each sample. Then, to understand the meaning and to assemble each of the different terms, a discussion of the defined attributes was conducted. The list of CATA descriptors was compiled using the most often cited attributes. The findings indicate that the major difference in hot dogs was between the formulations with and without sodium reduction. The consumers only noticed minor effects resulting from the irradiation process. The use of focus group as the method to select the CATA descriptors related to hot dogs was proven to be valid since the words that were listed for these samples were attributes that typically characterize hot dog sausages.

Evaluation of Non-linear Models to Predict Potential Milk Yield of Beef Cows According to Parity Order Under Grazing.

This study aimed to evaluate the effect of parity order on milk yield (MY) and composition over time of grazing beef cows and to evaluate non-linear models to describe the lactation curve. Thirty-six pregnant Nellore cows (12 nulliparous, 2 years; 12 primiparous, 3 years; and 12 multiparous, 4-6 years) were included in the study. With calving day assigned as day 0, milking was performed using a milking machine to estimate MY on days 7, 14, 21, 42, 63, 91, 119, 154, and 203. Dummy variable analyses were applied to estimate its effects on MY, composition (kg and percentage), afternoon/morning, and afternoon/total proportions. Since multiparous cows had higher MY than nulliparous and primiparous cows, two different groups were used for lactation curve analysis: Mult (multiparous) and Null/Prim (nulliparous and primiparous). The MY estimated by the last edition of BR-Corte (Nutrient Requirements of Zebu and Crossbred Cattle) equation was compared with the observed values from this study. Five nonlinear models proposed by Wood (WD), Jenkins & Ferrell (JF), Wilmink (WK), Henriques (HR) and Cobby & Le Du (CL) were evaluated. Models were validated using an independent dataset of multiparous and primiparous cows. The estimates for parameters a, b, and c of the CL equation were compared between groups, and the BR-Corte equation used the model identity methodology. Nulliparous and primiparous cows displayed similar MY (P > 0.05); however, multiparous cows had an average MY that is 0.70 kg/day greater than that of nulliparous and primiparous cows (P < 0.05). Milk protein and total solids were higher for multiparous cows (P < 0.05). Effect of days in milking was found for milk fat, protein, and total solids (P < 0.05). The yield of all milk components was higher for multiparous cows than for nulliparous and primiparous cows. The afternoon/morning and afternoon/total proportions of milk production were not affected by parities and days in milking (P > 0.05), with an average of 0.76 and 0.42, respectively. The BR-Corte equation did not correctly estimate the MY (P < 0.05). The equations of WD, WK, and CL had the best estimate of MY for both Mult and Null/Prim datasets. The equations had a very similar Akaike's information criterion with correction and mean square error of prediction.

Analysis of vaccine loss due to temperature change.

OBJECTIVES: to analyze vaccine losses in a Health Region in the Northwest of São Paulo. METHODS: retrospective cross-sectional study with secondary data obtained from Temperature Change Notification Forms used by the Epidemiological Surveillance Group XXIX of São José do Rio Preto between 2010 and 2017. Descriptive and inferential analysis were performed using multiple linear regression and significance level of 95%. RESULTS: in total, 341 notifications of temperature changes were analyzed, of which 70.1% were caused by structural reasons, 57.8% in industrial refrigerators and 91.2% in primary care services. Of the doses that suffered a change in temperature, 41.4% were lost and 58.6% were administered to the population. The highest percentage of lost doses compared to those applied occurred in smaller municipalities, although they reported less. CONCLUSIONS: nursing workers who work in vaccination rooms should make efforts to prevent temperature changes and avoid losses and higher public expenses.

Effectiveness Analysis of the Immunization Against Hepatitis B in Liver Transplantation Patients.

OBJECTIVE: This article analyzes the effectiveness of a super-accelerated immunization schedule against hepatitis B in patients who have received a liver transplantation. METHODS: This is a quantitative and retrospective study based on secondary data of medical records from 177 patients who have received a liver transplantation at the Hospital de Base in São José do Rio Preto, São Paulo State, Brazil, between 1998 and 2016. RESULTS: From the total number of participants, 72.89% were male, 39.55% had a cirrhosis diagnosis with associated causes, 23.16% had hepatocellular carcinoma, 53.11% were classified according to Child-Turcotte-Pugh C score, 58.76% had the hepatitis C virus, 97.18% had received an unconventional immunization schedule, and seroconversion was 36.63% among those with an unconventional schedule. The fact that the patient had the hepatitis C virus was statistically significant considering the lack of protection of the vaccine against the hepatitis B virus; their chances were 5 times higher of not seroconverting at the end of the immunization schedule. CONCLUSION: The need for high immediate protection in a short term may justify using unconventional immunization schedules in patients who make it to the transplantation waiting list without any previous immunization.

Understanding salt reduction in fat-reduced hot dog sausages: Network structure, emulsion stability and consumer acceptance.

High sodium and fat contents are cause of concerns for industries and consumers of meat products. Direct reduction of NaCl and fat is a useful strategy to understand how these ingredients interfere with the quality parameters of an emulsified meat product and how to reduce them without significant changes from the original product. The aim of this work was to understand salt reduction in fat-reduced (10 g fat/100 g product) hot dog sausages. Five NaCl concentrations were tested: 1% (F1), 1.25% (F1.25), 1.50% (F1.50), 1.75% (F1.75) and 2% (F2 - control). Proximate composition, sodium content, water activity, pH, emulsion stability, color, texture, scanning electron microscopy results and sensory attributes (just-about-right and acceptance tests) were assessed. Emulsion stability decreased (P < 0.05) with salt reduction. Salt reduction increased water activity. Microscopic images showed a more compact matrix with the decrease in salt content. Sausages with the minimum (F1) and maximum (F2) amounts of salt were less accepted by consumers. A reduction of 26.8% of sodium can be obtained (with the formulation F1.25), allowing the labeling of sodium-reduced sausage and with acceptance by consumers.

Synergistic effect of Cordia curassavica Jacq. essential oils association against the phytopathogen Xanthomonas campestris pv. campestris.

The increased use of pesticides applied to treat diseases caused by bacteria has caused serious environmental problems. There are few fungicides/bactericides for the treatment of plant diseases caused by Xanthomonas campestris pv. campestris (Xcc), and only two natural products with general bactericidal/fungicidal use are available on the market. Thus, this study evaluated the antimicrobial activity of essential oils (EOs), and their combinations, from five distinct genotypes of Cordia curassavica (Jacq.) Roem. & Schult (Syn. Varronia curassavica Jacq.) (CCUR) against Xcc. GC/MS chemical analysis revealed α-pinene, sabinene, (E)-caryophyllene, ar-curcumene, ß-sesquiphellandrene, 7-cyclodecen-1-one, and ar-Turmerone as the major compounds of the five EOs of CCUR. All EOs showed growth inhibition of Xcc with minimum inhibitory concentration between 500 and 1000 µg mL-1. The associations between two EOs from different CCUR genotypes showed that 70% of the total combinations had an additive effect. However, the combinations between CCUR-002 × (-302, -202) and CCUR-302 × (-601) showed a synergistic effect, with mean fractional inhibitory concentration FIC50 values of 0.28, 0.42, and 0.40, respectively. This study demonstrates that combinations of C. curassavica EOs have antimicrobial activity and a potential to be used in the control of black rot. Graphical abstract.

Effect of Abutment Screw Design and Crown/Implant Ratio on Preload Maintenance of Single-Crown Screw-Retained Implant-Supported Prostheses.

PURPOSE: New solutions need to be developed for cases in which implants that were placed years ago are now presenting prosthetic complications. A conical head screw design for a single-tooth abutment was developed to preserve the initial applied torque. The aim of this study was to assess the preload maintenance of different screw design sets (a conical head screw set and a flat head screw set) for single-tooth abutments in external hexagon implants, verifying whether reverse torque changes after mechanical loading at different crown/implant ratios and to understand if the use of the tested conical head screw set design can help clinicians solve loosening torque. MATERIALS AND METHODS: Forty external hexagonal implants, 40 single-tooth abutments, 20 conical head screws, and 20 flat head screws were split into four groups with different crown/implant ratios (crown/implant ratio > 1 or crown/implant ratio < 1). The abutments were attached to the implants by applying a torque of 35 Ncm; the specimens were mechanically loaded for 1 million cycles, and the loosening torque was checked and recorded with a digital torque wrench. The Kruskal-Wallis test (P = .05) and Wilcoxon test were performed to assess the results. RESULTS: In all groups, at least one specimen kept 100% of the initial applied torque before mechanical loading (t0). After mechanical loading (t1), all specimens presented torque reduction. The Kruskal-Wallis test was performed, and the flat head screw t0 group presented lower torque maintenance and a significant difference (P < .05) compared with the initial applied torque and with the conical head screw t0 group. The conical head screw t0 group presented a higher torque maintenance and no significant difference (P > .05) compared with the initial applied torque. For the flat head screw, the crown/implant ratio affected the torque maintenance. For the conical head screw, the crown/implant ratio did not affect the torque maintenance (P > .05). CONCLUSION: The conical head screw set presented a higher maintenance of applied preload than the flat head screw set. As far as reverse torque is concerned, the crown/implant ratio affects the torque maintenance only in association with a flat head screw set. The use of the tested conical head screw set can help clinicians solve loosening torque, mainly in a situation with a crown/implant ratio > 1.