Shrinkage behaviors of dental composite restorations-The experimental-numerical hybrid analysis.

OBJECTIVES: To investigate the effects of light curing protocols on the shrinkage behaviors, contraction stress, and microleakage in composite restorations by an experimental-numerical hybrid analysis. METHODS: Three groups of human molars were collected to receive different light-curing protocols: vertical or oblique curing at regular intensity, and vertical curing at reduced intensity. For each tooth, the composite fillings were consecutively placed under unbonded and bonded states, and their shrinkage behaviors were examined with a digital image correlation (DIC) technique. The strains of the unbonded restorations were input into two finite element analysis (FEA) models with settings of the composite as either homogeneous or hardened along polymerization gradients. The preliminary solutions were verified by their individual deformations in the bonded restorations. The interfacial microleakage of restorations was also determined by micro-CT scanning and compared with the FEA results. RESULTS: The bonded restorations showed centripetal shrinkage patterns with greater downward displacements than their unbonded restorations. Vertical curing at regular intensity caused the greatest shrinkage strain, contraction stress, and microleakage among the three protocols. Low-intensity curing reduced overall shrinkage strain and displacements at cervical margin, but did not prevent the formation of microleakage. Oblique curing caused asymmetric shrinkage with the tooth-shielded side revealing less deformation. Setting the polymerization-dependent elastic moduli of the composite enhanced the reliability of FEA. SIGNIFICANCE: This hybrid analysis comprehensively examined the polymerization shrinkage behaviors. Both the light intensity and direction affect the shrinkages and contraction stress. Oblique curing decreases shrinkage due to the attenuated irradiation by tooth-shielding rather than modulations of shrinkage direction.

Transactivation of protein expression by rice HSP101 in planta and using Hsp101 as a selection marker for transformation.

Plant HSP101 has dual activities, first, in conferring thermotolerance, and secondly, in serving as a translational activator. In this study, we introduced Oryza sativa Hsp101 (osHsp101) cDNA into tobacco by Agrobacterium-mediated transformation. Stable integration and expression of the transgene into the tobacco genome was demonstrated by Southern and Western blot analysis. Overexpression of osHSP101 had no noticeable effect on growth or development of the transgenic plants. Homozygous T(2) transgenic plants with overexpressed osHSP101 survived heat treatment better than untransformed control plants. In addition, taking advantage of conferring basal thermotolerance by plant HSP101, we were able to demonstrate the feasibility of using osHsp101 as a selection marker and select the transformants under high temperature in tobacco leaf disc transformation mediated by Agrobacterium. Furthermore, transgenic tobacco plants with overexpressed osHSP101 were able to enhance luciferase expression up to 2.9-fold more than untransformed plants in the progeny of reciprocally crossed with omega-luciferase reporter lines.