RESUMEN
OBJECTIVE: This in vitro study evaluated the shear bond strength of composite resin to deep dentin using a total etch adhesive after treatment with two collagen cross-linking agents at varying time intervals. MATERIALS AND METHODS: Thirty freshly extracted human maxillary central incisors were sectioned longitudinally into equal mesial and distal halves (n=60). The proximal deep dentin was exposed, maintaining a remaining dentin thickness (RDT) of approximately 1 mm. The specimens were randomly divided into three groups based on the surface treatment of dentin prior to bonding as follows: group I (n=12, control): no prior dentin surface treatment; group II (n=24): dentin surface pretreated with 10% sodium ascorbate; and group III (n=24): dentin surface pretreated with 6.5% proanthocyanidin. Groups II and III were further subdivided into two subgroups of 12 specimens each, based on the pretreatment time of five minutes (subgroup A) and 10 minutes (subgroup B). Shear bond strength of the specimens was tested with a universal testing machine, and the data were statistically analyzed. RESULTS: Significantly higher shear bond strength to deep dentin was observed in teeth treated with 10% sodium ascorbate (group II) and 6.5% proanthocyanidin (group III) compared to the control group (group I). Among the collagen cross-linkers used, specimens treated with proanthocyanidin showed significantly higher shear bond strength values than those treated with sodium ascorbate. No significant difference was observed between the five-minute and 10-minute pretreatment times in groups II and III. CONCLUSION: It can be concluded that dentin surface pretreatment with both 10% sodium ascorbate and 6.5% proanthocyanidin resulted in significant improvement in bond strength of resin composite to deep dentin.
Asunto(s)
Resinas Compuestas/química , Reactivos de Enlaces Cruzados/farmacología , Recubrimiento Dental Adhesivo , Materiales Dentales/química , Dentina/ultraestructura , Grabado Ácido Dental/métodos , Antioxidantes/química , Ácido Ascórbico/química , Colágeno/efectos de los fármacos , Análisis del Estrés Dental/instrumentación , Dentina/efectos de los fármacos , Humanos , Ácidos Fosfóricos/química , Ácidos Polimetacrílicos/química , Proantocianidinas/química , Resistencia al Corte , Estrés Mecánico , Factores de TiempoRESUMEN
OBJECTIVE: This in vitro study assessed the neutralizing effect of grape seed extract (oligomeric proanthocyanidin complexes [OPCs]) on the bond strength of bleached enamel. MATERIALS AND METHODS: Labial enamel surfaces of 70 extracted human maxillary central incisors were randomly divided into four groups based on the antioxidant used as follows: Group I (n=20): bleaching with 38% hydrogen peroxide gel for 10 minutes, without the use of an antioxidant; Group II (n=20): bleaching followed by the use of 10% sodium ascorbate solution; Group III (n=20): bleaching followed by the use of 5% proanthocyanidin solution; and Group IV (n=10): control group in which no bleaching was done. Groups I, II, and III were further subdivided into two subgroups of 10 teeth each, based on whether composite build-up was done immediately (subgroup A) or after a delay of 2 weeks (subgroup B) post bleaching. Shear bond strength of the specimens was tested under a universal testing machine. The data were tabulated and statistically analyzed. RESULTS: Significantly higher shear bond strength values were observed in teeth treated with 10% sodium ascorbate (Group II) and 5% proanthocyanidin (Group III) as compared with the control group (Group IV). Among the antioxidants used, teeth treated with proanthocyanidin showed significantly higher shear bond strength values than those treated with sodium ascorbate. CONCLUSION: It can be concluded that the use of grape seed extract prior to bonding procedures on bleached enamel completely neutralizes the deleterious effects of bleaching and increases the bond strength significantly.
Asunto(s)
Antioxidantes/farmacología , Recubrimiento Dental Adhesivo , Esmalte Dental/efectos de los fármacos , Extracto de Semillas de Uva/farmacología , Proantocianidinas/farmacología , Blanqueamiento de Dientes/efectos adversos , Análisis de Varianza , Ácido Ascórbico/farmacología , Análisis del Estrés Dental , Depuradores de Radicales Libres/farmacología , Humanos , Incisivo , Estadísticas no ParamétricasRESUMEN
The multidomain structure of soybean LOX1 was examined over the pH range 1-12. Lipoxygenase-1 activity was reversible over broad pH range of 4-10 due to the reversibility of conformational states of the molecule. Below pH 4.0, due to collapse in hydrophobic interactions, the enzyme unfolded to an irreversible conformation with the properties of molten globule state with a mid point of transition at pH 2.4. This intermediate state lost iron irreversibly. In alkaline pH at 11.5, LOX1 underwent partial unfolding with the exposure of cysteine residues with subsequent oxidation of a pair of cysteine residues in the C-terminal domain and this intermediate showed some properties of molten globule state and retained 35% of activity. Beyond pH 12.0, the enzyme was completely inactivated irreversibly due to irreversible conformational changes. The pH-dependent urea-induced unfolding of LOX1 suggested that LOX1 was more stable at pH 7.0 and least stable at pH 9.0. Furthermore, the urea-induced unfolding of LOX1 indicated that the unfolding was biphasic due to pH-dependent domain interactions and involved sequential unfolding of domains. The loss of enzyme activity at pH 4. 0 and 7.0 occurred much earlier to unfolding of the C-domain at all pHs studied. The combination of urea-induced unfolding measurements and limited proteolysis experiments suggested that at pH 4.0, the domains in LOX1 were less interactive and existed as tightly folded units. Furthermore, these results confirmed the contribution of ionic interactions in the interdomain contacts.
Asunto(s)
Concentración de Iones de Hidrógeno , Lipooxigenasa/metabolismo , Naftalenosulfonatos de Anilina/metabolismo , Dicroismo Circular , Hidrólisis , Hierro/análisis , Lipooxigenasa/química , Pepsina A/metabolismo , Conformación Proteica , Desnaturalización Proteica , Glycine max/enzimología , Espectrometría de Fluorescencia , Espectrofotometría Ultravioleta , Compuestos de Sulfhidrilo/química , Urea/químicaRESUMEN
Mouse alpha(1-30)-horse alpha(31-141) chimeric alpha-chain, a semisynthetic super-inhibitory alpha-chain, inhibits beta(S)-chain dependent polymerization better than both parent alpha-chains. Although contact site sequence differences are absent in the alpha(1-30) region of the chimeric chain, the four sequence differences of the region alpha(17-22) could induce perturbations of the side chains at alpha(16), alpha(20) and alpha(23), the three contact sites of the region. A synergistic complementation of such contact site perturbation with that of horse alpha(31-141) probably results in the super-inhibitory activity of the chimeric alpha-chain. The inhibitory contact site sequence differences, by themselves, could also exhibit similar synergistic complementation. Accordingly, the polymerization inhibitory activity of Hb Le-Lamentin (LM) mutation [His20(alpha)-->Gln], a contact site sequence difference, engineered into human-horse chimeric alpha-chain has been investigated to map such a synergistic complementation. Gln20(alpha) has little effect on the O(2) affinity of HbS, but in human-horse chimeric alpha-chain it reduces the O(2) affinity slightly. In the chimeric alpha-chain, Gln20(alpha) increased sensitivity of the betabeta cleft for the DPG influence, reflecting a cross-talk between the alpha(1)beta(1) interface and betabeta cleft in this semisynthetic chimeric HbS. In the human alpha-chain frame, the polymerization inhibitory activity of Gln20(alpha) is higher compared with horse alpha(1-30), but lower than mouse alpha(1-30). Gln20(alpha) synergistically complements the inhibitory propensity of horse alpha(31-141). However, the inhibitory activity of LM-horse chimeric alpha-chain is still lower than that of mouse-horse chimeric alpha-chain. Therefore, perturbation of multiple contact sites in the alpha(1-30) region of the mouse-horse chimeric alpha-chain and its linkage with the inhibitory propensity of horse alpha(31-141) has been now invoked to explain the super-inhibitory activity of the chimeric alpha-chain. The 'linkage-map' of contact sites can serve as a blueprint for designing synergistic complementation of multiple contact sites into alpha-chains as a strategy for generating super-inhibitory antisickling hemoglobins for gene therapy of sickle cell disease.
Asunto(s)
Hemoglobina Falciforme/química , Proteínas Recombinantes de Fusión/química , Anemia de Células Falciformes/genética , Animales , Cromatografía por Intercambio Iónico , Hemoglobina Falciforme/genética , Caballos , Humanos , Cinética , Ratones , Modelos Moleculares , Mutación , Oxígeno/química , Fragmentos de Péptidos/síntesis química , Ingeniería de Proteínas , Análisis de SecuenciaRESUMEN
The unfolding of lipoxygenase-1 by urea and guanidine hydrochloride has been followed at the optimum pH of enzyme activity. The unfolding of lipoxygenase-1 by urea or guanidine hydrochloride was characterized by equilibrium transition curves for different parameters like (i) enzyme activity, (ii) change in ellipticity values at 222 nm, and (iii) relative fluorescence intensity at 332 nm could not be superimposed. The transition curves displayed more than one plateau region suggesting the presence of stable intermediates during unfolding. At urea concentrations less than 1 M there was no significant loss in activity although loss in secondary structure was approximately 20%. At 4.0 M urea concentration there was complete loss of activity with a midpoint concentration of 2.5 M urea. The loss in secondary structure was biphasic. The first transition had a midpoint concentration of 1.2 M, while the second transition which was complete at 8.0 M urea had a midpoint concentration of 3.5 M urea. The changes in relative fluorescence intensity and shift in emission maximum were complete at 8.0 M urea. The Stern-Volmer constant for acrylamide and potassium iodide did not change at urea concentrations less than 4 M and then at higher concentrations increased. The reactivity of sulfhydryl groups to Ellman's reagent increased during the course of unfolding. The kinetics of unfolding supported the presence of stable intermediates during unfolding. The unfolding was irreversible and complex because of the multidomain nature. The apparent irreversibility could be related to aggregation during unfolding which precluded the determination of thermodynamic parameters.