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2-amino-1-methyl-6-phenylimidazole [4,5-b] pyridine (PhIP) is one of the higher levels of HAAs produced in protein foods during heating. The effects of heating temperature, time, and concentration of precursors on PhIP and related substances in the chemical model system and roast pork patty were studied using HPLC-Q-Orbitrap-HRMS and GC-MS. Results showed that the heating temperature, time, and concentration of four precursors significantly affected PhIP and its related substances (P < 0.05) in the chemical model system. Among them, PhIP production was greatest when heating at 200 min with 220 °C, and the concentrations of phenylalanine, creatinine, glucose, and creatine added were 10, 20, 20, and 20 mmol/L, respectively. Moreover, as the fat proportion of roast pork patties increased, PhIP and its intermediate-phenylacetaldehyde concentrations increased substantially (P < 0.05). PCA results showed that the samples of PhIP and related substances gradually dispersed as the temperature and time increased, and there were obvious effects among them.

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The effects of different heating conditions set to prevent food poisoning on the volatile components, lipid oxidation, and odor of yellowtail, Seriola quinqueradiata, were investigated. The heating conditions did not affect the lipid oxidation, fatty acid composition, and volatile compounds of each part of the flesh. High-temperature/short-time (90 °C for 6 min) heating led to significantly higher trimethylamine (TMA) contents in all muscle parts and higher odor intensity of TMA in dark muscle (DM) compared to those of lower temperature heating. Sensory evaluation showed that the odor intensities of all muscle parts heated at high-temperature/short-time were stronger than those at low-temperature/long-time (63 °C for 30 min). All DM samples had less odor palatability than the other flesh parts. Therefore, DM may have contributed to the unfavorable odor of steamed yellowtail meat and high-temperature/short-time heating may have enhanced the odor of all flesh parts compared with those subjected to low-temperature/long-time.

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Laminated custom-made mouthguards tend to delaminate with use; this is a problem in clinical use. Insufficient bonding strength causes delamination, and bonding strength is strongly affected by heating temperature during lamination. The present study aimed to evaluate the influence of heating temperature on the sheet lamination process. Seven mouthguard sheet products were laminated together at different heating temperatures. To evaluate the bonding strength, a delamination test (n = 6) was performed, and the fracture patterns were inspected visually. To evaluate the shock absorption capability, a falling impact test (n = 5) was performed, and the specimen thicknesses were measured. All recorded values were analyzed using two-way analysis of variance and Tukey's Honest Significant Difference Test (P < 0.05). The present study confirmed that bonding strength was dependent on heating temperature: In ethylene-vinyl acetate copolymer products, the bonding strength was almost constant at 130°C and above, and it was constant at 110°C and above in polyolefin products. The thickness of every specimen decreased and, in some specimens, the shock absorption capability decreased with increasing heating temperature. The present study concludes that the heating temperature during the sheet lamination process when laminated custom-made mouthguards are fabricated may not be less than 120°C in ethylene-vinyl acetate copolymer products and 110°C in polyolefin products.

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Physical properties of Alaska pollock surimi paste were investigated as affected by pH (4.0 and 6.0-10.0) and heating conditions (slow and fast). The highest values of gel strength and deformability, as shown by breaking force and penetration distance, were obtained at pH 7.5-8.0, while the lowest values were at pH 10.0 followed by pH 6.0 and pH 6.5, respectively. Two-step slow heating process increased the breaking strength value nearly two times higher than one-step fast heating. The effect of pH was strikingly high at pH 7.5 when gels were prepared using 2-step heating, indicating the pH dependence of endogenous transglutaminase. However, the highest gel strength was obtained at pH 8.0 when gels were prepared in fast heating. Whiteness value (L - 3b*) increased significantly (p < .05) as pH increased from 6.0 to 6.5, but thereafter decreased significantly (p < .05) as pH increased. L* value (lightness) and b* value (yellowness) continuously decreased as the pH is shifted from 6.0 to 10. Fast heated gels showed the lowest yellowness, resulting in whiter appearance, probably due to the effect of reduced browning reaction. PRACTICAL APPLICATIONS: The uniqueness of this study was to measure the combined effect of pH and heating conditions on the gel texture and color. There were various studies dealing with pH or heating conditions independently. As the primary character for surimi seafood is gel texture and color. The highest values of gel strength and deformability, as shown by breaking force and penetration distance, were obtained at pH 7.5-8.0, while the lowest values were at pH 10.0 followed by pH 6.0 and pH 6.5, respectively. Two-step slow heating process increased the breaking strength value nearly two times higher than one-step fast heating. Whiteness value (L - 3b*) increased significantly as pH increased from 6.0 to 6.5, but thereafter decreased significantly as pH increased. L* value (lightness) and b* value (yellowness) continuously decreased as the pH is shifted from 6.0 to 10. Fast heated gels showed the lowest yellowness, resulting in whiter appearance.

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BACKGROUND: The aim of this study was to identify suitable heating conditions of polyolefin-polystyrene co-polymer sheets in vacuum-pressure formation, monitor the sheet temperature during molding, and examine the thickness of the fabricated mouthguard. MATERIALS AND METHODS: Mouthguards were fabricated with polyolefin-polystyrene co-polymer sheets (4.0-mm thick) utilizing a vacuum/pressure-forming device, which was subjected to vacuum forming for 10 s and pressure molding for 2 min. Four heating conditions were compared, defined by the amount of sag distance of 5, 10, 15, or 20 mm from the center of the softened sheet below the clamp. The working model was trimmed to a height of 20 mm at the cutting edge of the maxillary central incisor and to a height of 15 mm at the mesiobuccal cusp of the maxillary first molar. The radiation thermometer was used to measure the sheet temperatures of the center of the heated and non-heated surfaces under each condition. The sheet thickness after fabrication was determined for the incisal and the molar portions, and dimensional measurements were obtained using a measuring device. The differences in the sheet thickness produced by the different heating conditions were analyzed by Games-Howell's multiple comparison tests. RESULTS: For condition of 5 mm sagged, the temperature on the non-heated surface did not reach a sufficient softening temperature and the thickness was smallest. Mouthguard thickness was largest in the order of 15 mm sagged condition, followed by 20 mm sagged condition and then by 10 mm sagged condition, but a statistical difference was not observed in the labial and the buccal surface among the three conditions. CONCLUSION: This study demonstrated that for sufficient softening, it was necessary to heat the sheet to obtain a sag of 10 mm or more, and that the mouthguard thickness decreased as the sag increased.

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BACKGROUND: The purpose of this study was to identify changes in sheet shape during thermoforming and the effect of the model position in the molding machine on fabricated mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate mouthguard sheets (3.8 mm thick) were used that had cross-stripes (10 × 10 mm), and the anteroposterior and bilateral lengths were used for measurements. Two forming machines were used: a vacuum- and a pressure-forming machine, and two heating conditions were investigated that defined as the time when sagging of the softened sheet was 15 mm (H-15) and 20 mm (H-20) below the clamp, and the length of each cross-stripes was measured. The area of each lattice was calculated using Bretschneider's formula to compare changes in sheet shape for each condition. Next, mouthguards were molded by forming machine where the working model was positioned under two different conditions: with the model anterior centered in the forming unit and with the model centered. The sheet thickness after fabrication was determined for the incisal and the molar portion, and dimensional measurements were obtained using a measuring device. Differences in the thickness were analyzed by two-way analysis of variance (anova). RESULT: In both molding machines, the change in the area under H-20 was greater than H-15. While the increase in area tended to expand from the center of the sheet in concentric circles, the difference between the central and surrounding areas was only approximately 5%. For both molding machines, differences in thickness after molding due to setting position of the model were not observed. CONCLUSION: The results showed that shape changes of the sheet during thermoforming tend to concentrically and almost uniformly expand from the center and that it is important to center the sheet and the model when positioning the model in the forming unit.

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PURPOSE: The purpose of this study was to investigate the differences of pressure-formed mouthguard thickness by varying the heating conditions within the proper heating temperature. MATERIALS AND METHODS: The material used in this study was a mouthguard sheet of 3.8-mm ethylene vinyl acetate. The sheets were formed by pressure forming using a vacuum-pressure former. Three heating conditions were varied as follows: the sheet was heated until the center was displaced by 10, 15, and 20 mm from baseline. We measured the mouthguard thickness at the labial surface of the central incisor, buccal surface of the first molar, and occlusal surface of the first molar. Differences in thickness by measurement region of the mouthguards formed under different heating conditions were analyzed by two-way analysis of variance and Bonferroni's method. RESULTS: We found that mouthguard thickness varied in different regions of the central incisors and the first molars (P < 0.01). The incisal (cusp) region was thinner than the cervical region. There were statistically significant differences among the heating conditions at the labial surface of the central incisor (P < 0.05), and the thickness became larger as the sheet was heated. Mouthguard thickness at the buccal surface and occlusal surface of the first molar did not differ among the three heating conditions. CONCLUSIONS: Our results suggest that the best heating condition of the pressure-forming method was the condition that the sheet was heated until its center displaced by 20 mm. This finding is an important fact when fabricating a mouthguard.

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The shapes of ethylene vinyl acetate (EVA) sheets are mainly square or round. The aim of this study was to elucidate a fabrication method that effectively maintains the thickness of the round sheet. Mouthguards were fabricated using EVA sheets (diameter 125 mm, thickness 4.0 mm) and a vacuum-forming machine. The sheet was pinched at the top and bottom and stabilized by the circle tray. Two heating conditions were compared: (i) the sheet was molded when it sagged 10 mm below the level of the sheet frame at the top of the post under normal conditions (N); and (ii) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use and molded when it sagged 10 mm from the sheet frame (L). Two EVA sheet shapes were compared: an ordinary sheet (O) and a sheet with a horizontal v-shaped groove 30 mm from the anterior end (G). The height of the working model was 20 mm at the incisor point and 15 mm at the first molar. The sheet temperatures of the heating and non-heated surface were measured by the radiation thermometer. Post-molding thickness was determined for the incisal and molar portion. Differences in the thickness were analyzed using two-way anova. The temperature difference among points was smaller under condition L than under condition N. Thickness after formation was higher in condition L than in condition N, and was higher in condition G than in condition O. At the labial surface and the cusp, L-G was thickest. With the present techniques, uneven softening during heating can be improved by lowering the sheet frame and consequently reducing the reduction in the thickness of the sheet. Additionally, the thickness reduction is reduced by creating a horizontal groove on the sheet, establishing the clinical efficacy of this method.

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The purposes of this study were to clarify the suitable heating conditions during vacuum-pressure formation of olefin copolymer sheets and to examine the sheet temperature at molding and the thickness of the molded mouthguard. Mouthguards were fabricated using 4.0-mm-thick olefin copolymer sheets utilizing a vacuum-pressure forming device, and then, 10 s of vacuum forming and 2 min of compression molding were applied. Three heating conditions were investigated. They were, defined by the degree of sagging observed at the center of the softened sheet (10, 15, or 20 mm lower than the clamp (H-10, H-15, or H-20, respectively)). The working model was trimmed to the height of 20 mm at the maxillary central incisor and 15 mm at the mesiobuccal cusp of the maxillary first molar. The temperature on both the directly heated and the non-heated surfaces of the mouthguard sheet was measured by the radiation thermometer for each condition. The thickness of mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in the thickness due to the heating condition of the sheets were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. The temperature difference between the heated and non-heated surfaces was highest under H-10. Sheet temperature under H-15 and H-20 was almost the same. The thickness differences were noted at incisal edge, cusp, and buccal surface, and H-15 was the greatest. This study demonstrated that heating of the sheet resulting in sag of 15 mm or more was necessary for sufficient softening of the sheet and that the mouthguard thickness decreased with increased sag. In conclusion, sag of 15 mm can be recommended as a good indicator of appropriate molding timing for this material.

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BACKGROUND: The goal of the present study was to examine the thickness of mouthguards molded under a variety of heating conditions to clarify suitable conditions during vacuum-pressure forming of ethylene vinyl acetate sheets. MATERIALS AND METHODS: Mouthguards were fabricated using ethylene vinyl acetate (EVA) sheets (thickness: 4.0 mm) using a vacuum-pressure forming machine. The sheet was pressed against the working model, followed by vacuum forming for 10 s and compression molding for 2 min. Three heating conditions were investigated in which the sheet was molded when the center of the softened sheet sagged 10 mm, 15 mm, or 20 mm below the clamp (H-10, H-15, or H-20 respectively). The temperature of the sheet surface was measured using a radiation thermometer under each heating condition. The thickness of the mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in thickness due to the heating condition of the sheets were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. RESULTS: The temperature difference between the heated and non-heated surfaces was lowest under H-15. The thickness differences at incisal edge, labial surface, and cusp were determined. The thicknesses for H-10 and H-15 were greater than that for H-20, and the thicknesses for H-10 and H-15 were equivalent at all measurement points. No differences in thickness at the buccal surface were observed for the various heating conditions. CONCLUSION: The present study demonstrated that a sagging distance of 15 mm provided the most suitable forming process. The results of the present study provide a standard heating condition for EVA sheet forming.

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BACKGROUND: Unevenness in softening of the plastic sheet leads to a decrease in the mouthguard thickness during thermoforming. In this study, we examined the heating methods for reducing unevenness when softening mouthguard sheets during vacuum-pressure formation. MATERIALS AND METHODS: Ethylene vinyl acetate mouthguard sheets and olefin copolymer sheets (thickness: 4.0 mm) were used. The following three heating conditions were compared: condition A-the sheet was molded when it sagged 15 mm from the sheet frame (under normal condition); condition B-the heater was turned off when the sheet sagged by 10 mm from the frame, followed by the sheet molding when the sagging reached 15 mm below the frame; and condition C-the sheet was inverted after heating when the sheet sagged 10 mm and was molded when the sagging reached 15 mm below the frame. The sheet was heated and pressed over the model using a vacuum-pressure machine; then, 10 s of vacuum forming and 2 min of pressure molding were applied. The sheet temperatures were measured using a radiation thermometer. Thickness of the fabricated sheets was determined for the incisal and the molar portion using a measuring device. Thickness data for each condition were analyzed by one-way anova followed by Bonferroni's multiple comparison tests. RESULTS: On both sheets, condition B was smallest for temperature difference between the heated and the non-heated surface, and thicknesses after molding were greatest at all measuring portions. CONCLUSION: By comparing changes in sheet temperatures at molding and variation in thicknesses when applying the heating method using a vacuum-pressure molding machine, we found that reduced unevenness in sheet softening occurred when the heater was turned off when the sag distance of the sheet was 5 mm less than the conventional molding, and then, the sheet was pressed when the conventional sag distance was reached.

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The aim of this study was to investigate the influence of the thermal shrinkage to thickness of the mouthguard with the heating method by the setting position of a sheet and the working model using an ethylene vinyl acetate sheet prepared by extrusion. Mouthguards were fabricated with EVA sheets (4.0 mm thick) using a vacuum-forming machine. Two forming conditions were compared: the square sheet was pinched by the clamping frame attached to the forming machine (S); and the round sheet was pinched at the top and bottom and stabilized by the circle tray (R). The sheet was aligned to make the sheet's extrusion direction vertical (V) or parallel (P) to the midline of the working model. The following two heating conditions were compared: (i) the sheet was molded when it sagged 15 mm below the level of the sheet frame measured at the top of the post in condition S (S-0), or that sagged 10 mm in condition R (R-0) in the usual position; (ii) the sheet frame was lowered by 50 mm from the ordinary height (S-50, R-50). Postmolding thickness was determined using a measuring device. Measurement points were the incisal and molar portion. Differences in the change of thickness of mouthguards molded under different heating conditions and extrusion directions for each sheet shape were analyzed by two-way analysis of variance (anova). The results of this study showed that by lowering the height of the sheet frame, the difference of the sheet temperature of each part was reduced. Among all sheets, condition V produced under S-50 and R-50 had the largest thickness independently of shape sheet. Furthermore, thickness reduction is effectively suppressed by aligning the direction of the extruded sheet to be vertical to the midline of the model.

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AIM: The purpose of this study was to examine the differences of the vacuum-formed mouthguard thickness by the heating condition within the proper heating temperature. MATERIALS AND METHODS: The material used in this study was a mouthguard sheet of 3.8-mm ethylene vinyl acetate. The sheets were formed by vacuum forming using a vacuum-pressure former. Three heating conditions were prepared: The sheet was heated until the center was displaced by 10, 15, and 20 mm from baseline. We measured mouthguard thickness at the labial surface of the central incisor, buccal surface of the first molar, and occlusal surface of the first molar. Differences in thickness in different regions of mouthguards formed under different heating conditions were analyzed by two-way analysis of variance and Bonferroni method. RESULTS: We found that mouthguard thickness differed in different regions of the central incisors and the first molars (P < 0.01). The incisal (cusp) region was thinner than the cervical region. There was statistically significant difference among the heating conditions at the buccal surface of the first molar (P < 0.01), and the thickness became larger as the sheet was heated. Mouthguard thickness at the labial surface of the central incisor and occlusal surface of the first molar did not differ among the three heating conditions. CONCLUSIONS: Our results suggest that the best heating condition within the proper temperature was the condition that the sheet was heated until its center displaced by 20 mm. This finding is necessary knowledge when forming a mouthguard sheet.

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This study examines the thickness and fit of mouthguards by notching thermoplastic copolymer ethylene vinyl acetate (EVA) sheets and then heating them to various degrees. The material used was a 3.8-mm-thick sports mouthguard. Notches with a length of 90 and 80 mm were cut into an EVA sheet 20 mm from the anterior and posterior margins and 15 mm from the right and left margins, respectively, and the sheet was compared with the original. The sheets were formed using a vacuum former when the sheets were heated until they hung 1.5, 2.0, 2.5, and 3.0 cm from the baseline. We measured the thickness and fit of the mouthguard at the central incisor and first molar. Differences in thickness and fit according to the measurement parts, sheet type, and heating conditions were analyzed by three-way anova. The measurement parts and sheet type significantly differed (P < 0.01), and the notched sheet maintained the required thickness. Fit differed among the measurement parts and by heating conditions (P < 0.01), but was not affected by the notching. The mouthguard fit was optimal when the sheets were heated to a hanging distance of 3.0 cm. These results suggest that the thickness and fit of the EVA sheet could be maintained by notching and heating the sheet to a hanging distance of 3.0 cm. These findings could be useful for fabricating appropriate mouthguards.

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PURPOSE: The aim of this study was to determine the optimal heating conditions for sheet forming using a circle tray by comparing the thickness and fit of mouthguards formed under different conditions. METHODS: Mouthguards were fabricated using ethylene vinyl acetate sheets (4.0mm thick) and a vacuum forming machine. The working model was trimmed to a height of 20mm at the incisor and 15 mm at the first molar. Two forming conditions were compared: square sheets were pinched by the clamping frame attached to the forming machine; and round sheets were pinched at the top and bottom and stabilized by a circle tray. Each condition was defined when the sheet sagged by 10-mm or 15-mm below the level of the clamp. The thickness of the sheet was determined for the incisal and molar portion. Additionally, the difference in fit according to the forming conditions was measured by examining the cross section. Differences in the thickness or the fit due to forming conditions were analyzed using two-way analysis of variance (ANOVA) followed by Bonferroni's multiple comparison tests. RESULTS: The thickness after formation was thicker at the 10-mm condition than that of 15-mm, and the fit at the 15-mm condition was better when that of 10-mm with square and round sheets. CONCLUSION: Within the limitation of this study, it was suggested that when forming a mouthguard using a 4.0-mm EVA sheet and a circle tray on a vacuum forming machine, the sheet should be formed at a sagging distance of 10-mm.

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The aim of this study was to examine the difference of the thickness and fit of the mouthguard sheet according to the holding conditions and the heating conditions. The material used in this study was Sports Mouthguard (3.8 mm thickness). Two holding conditions of the sheet were undertaken: One was the condition that the sheet was held all around the periphery, and the other was that the sheet was held at only four points. The sheets were formed using a vacuum former when the sheets were heated until they hung 2.0, 3.0, and 4.0 cm from the baseline. We measured the thickness of the mouthguard and calculated the ratio of changes. The fit of the mouthguard was also investigated. The differences of the ratio of changes in the thickness and the fit according to the holding conditions, heating conditions, and measurement areas were analyzed by three-way anova. The results showed that the thickness differed significantly among the holding conditions, heating conditions, and measurement areas (P < 0.01). The condition that the sheet was held at only four points could maintain the thickness especially on the heating condition set at a hanging distance of 4.0 cm. The fit of the sheet differed among the heating conditions and measurement areas (P < 0.01), but not by the holding conditions. The thickness of the sheet could be maintained by holding the sheet only at four points without being inferior to the sheet held all around the periphery in the fit, and this result could be useful on fabricating proper mouthguard.

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