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Objective To investigate the variations of elastic modulus and hardness of human dentin with aging and location.Methods The non-carious third molars were collected and divided into youth group,middle-aged group and elderly group.Nanoidentation test was conducted on the dentin specimens from multiple regions to test their mechanical properties.Results The elastic modulus and hardness in outer and middle dentin were greater than those in inner dentin;the elastic modulus and hardness increased with the aging in each region of the dentin.Conclusions The dentin shows a gradient mechanical property.The stiffness and hardness in middle and outer dentin are greater than those in inner dentin.The deformation resistance in middle and outer dentin is stronger than that in inner dentin.Meanwhile,elastic modulus and hardness of the dentin increase with the aging.
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Objective To investigate the variations of elastic modulus and hardness of human dentin with aging and location. Methods The non-carious third molars were collected and divided into youth group, middle-aged group and elderly group. Nanoidentation test was conducted on the dentin specimens from multiple regions to test their mechanical properties. Results The elastic modulus and hardness in outer and middle dentin were greater than those in inner dentin; the elastic modulus and hardness increased with the aging in each region of the dentin. Conclusions The dentin shows a gradient mechanical property. The stiffness and hardness in middle and outer dentin are greater than those in inner dentin. The deformation resistance in middle and outer dentin is stronger than that in inner dentin. Meanwhile, elastic modulus and hardness of the dentin increase with the aging.
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Objective To analyze the contact failure of monolithic lithium disilicate CAD/CAM crowns by experiment and numerical simulation, and explore the influences of adhesives aging in water on load-bearing capacity of the crowns. Methods The specimens of sectioned monolithic lithium disilicate crowns were designed and manufactured, and evenly divided into two groups and stored in the air and in the distilled water for 30 days, respectively. The specimens were then subjected to monotonic contact loads to compare and analyze their load-bearing capacity. The fractured surfaces and adhesive interfaces of the specimens were observed by scanning electronic microscope. Meanwhile, the stress distribution on the crowns was calculated by numerical simulation to analyze the adhesives aging influence on load-bearing capacity of the crowns. Results The fracture loads on crowns stored in the air and in the water were (561.51 ± 65.66) N and (398.09 ± 90.20) N, respectively, indicating a significant difference. The tensile stress increased considerably at lower surface of the ceramic crown due to the reduction of adhesive strength at the interface of ceramic crown and substrate, which could increase the propensity of contact failure. Conclusions The adhesives aging in water reduces the bonding strength, and accordingly changes the tensile stress distributions, which can lower the load bearing capacity of the lithium disilicate crowns. The research finding provides references for the design and manufacturing of all-ceramic CAD/CAM restored crowns in clinic.
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Objective To investigate the changes of plasma decorin in patients with acute ischemic stroke and its clinical significance. Methods The plasma levels of decorin were assessed in 102 patients with acute ischemic stroke (< 7 days) and 120 control subjects using ELISA. Then we evaluated the relationship between decorin level and the TOAST subtypes of stroke, so as to analyze the role of decorin level in diagnosis and treatment of acute ischemic stroke. Results Compared with the control group, the decorin level was significantly decreased in acute ischemic stroke group (P<0. 001), and that in the large-artery atherosclerosis group was lower than those in other groups of the same level. According to the receiver operating characteristic curve, decorin level was a diagnostie marker for acute ischemic stroke (P<0. 001). Decorin levels
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Objective To investigate effects of aging on the fracture mechanical behavior of human dentin with finite element numerical method. Methods The finite element model was established according to the typical compact tension specimen in the experiment. The stable crack growth in human dentin was simulated with the cohesive zone model to compare the crack extensions of the young and aged dentin. Results The growth toughness and plateau toughness of the aged dentin were 0.51 and 1.19 MPa•m1/2, respectively, which were significantly lower than those of the young dentin (7.48, 1.71 MPa•m1/2). However, the initiation toughness of the young and aged dentin showed no significant difference with 0.51 and 0.38 MPa•m1/2, respectively. Conclusions The crack growth resistance of human dentin is decreased significantly with aging. Based on the cohesive zone model, the crack growth behavior of biological hard tissue, whose mechanical properties are related with age (such as the human dentin), can be well predicted by using numerical methods.
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<p><b>OBJECTIVE</b>To explore the curative effects on surgical methods for the prevention of Frey syndrome and a concave facial deformity after parotidectomy.</p><p><b>METHODS</b>A literature search was performed using the Wianfang Database, Chinese Biomedical Literature Disk Database, Chinese Digital Hospital Library and Chinese Scientific Journals Database of VIP from January 1989 to December 2008. Twenty-six Chinese language controlled studies involving surgical techniques for prevention of Frey syndrome and the concave facial deformity after parotidectomy were identified. Review manager 4.2 software was applied for Meta analysis.</p><p><b>RESULTS</b>Meta-analysis for surgical techniques to prevent symptomatic Frey syndrome, a positive starch-iodine test, and contour deformity, favored intervention with a cumulative odds ratio (OR) of 0.14 [95% confidence interval (CI), 0.07-0.25]; OR, 0.21 (95% CI, 0.17-0.26); and OR, 0.09 (95% CI, 0.04-0.19), respectively. There was a significant difference in the incidence of these complications between surgical treatment groups and control groups (Z = 6.42, Z = 13.70, Z = 6.43, all P < 0.05). The application of a sternocleidomastoid muscle flap decreased the incidence of symptomatic Frey syndrome (Z = 2.33, P < 0.05), positive starch-iodine test (Z = 7.48, P < 0.05) and contour deformity (Z = 7.78, P < 0.05). The application of acellular dermal matrix decreased the incidence of symptomatic Frey syndrome (Z = 6.02, P < 0.05) and positive starch-iodine test (Z = 5.72, P < 0.05) but did not decrease the incidence of contour deformity (Z = 1.27, P > 0.05).</p><p><b>CONCLUSIONS</b>Meta-analysis of operative techniques to prevent symptomatic Frey syndrome, a positive starch-iodine test, and facial asymmetry suggests that such methods are likely to reduce the incidence of these complications and improve the quality of life after parotidectomy.</p>
Assuntos
Humanos , Seguimentos , Glândula Parótida , Cirurgia Geral , Complicações Pós-Operatórias , Cirurgia Geral , Sudorese Gustativa , Cirurgia Geral , Resultado do TratamentoRESUMO
Objective To analyze the compressive strength and fracture mode between four kinds of dental zirconia CAD/CAM ceramic materials by Hertzian contact test. Methods Four CAD/CAM ceramic materials including Cercon smart, Lava, Porcera, and CEREC 3 were selected. Six zirconia sectioned flat specimens were prepared in each group. The critical load and fracture load as well as the fracture mode for each specimen were analyzed with digital image correlation (DIC) technique. Results It was found that cracks were initiated at the middle level of the veneer below the contact zone and propagating along an arc curve into the core/veneer interface, which eventually caused the debonding of the core/veneer layers. For the four ceramic systems, there were no significant differences in the critical load（P＞0.05）, while there were significant differences in the fracture load（P＜0.05）. Conclusions The compressive strength of the four zirconia CAD/CAM ceramic materials could substantially meet the clinic requirement for oral functions regarding the maximum occlusal load. Crack initiation and complete fracture only occurred in the veneer, which indicated that the strength of the veneer should be further reinforced.