The objective of the present study was to test the hypothesis that the fracture strength of calcium hydroxide and mineral trioxide aggregate (MTA)-filled immature teeth decreased over time. Immature mandibular incisors from sheep were extracted and the pulps were extirpated using an apical approach with a barbed broach, and the teeth were divided into three experimental groups. Group 1: untreated teeth. Group 2: the root canals were filled with calcium hydroxide paste. Group 3: the root canals were filled with MTA. All specimens were kept in saline with 1% antibiotics at 4 degrees C for certain periods of time: 2 weeks, 2 months, and 1 year. Then they were tested for fracture strength in an Instron testing machine. The results were subjected to statistical analysis by the Tukey-Kramer tests. A P-value (<0.05) was considered statistically significant. One tooth from each group was selected randomly for a histological study, examining matrix metalloproteinases (MMP2 and MMP14) and tissue inhibitor of metalloproteinase (TIMP). The results showed the mean fracture strengths decreased over time for all the three groups. Although the untreated teeth showed the highest value (45.5 MPa) at 2 weeks, the fracture strengths decreased significantly after 2 months (P < 0.05). On the other hand, the teeth treated with calcium hydroxide or MTA decreased, but not significantly over time (P > 0.05). For the MTA-treated teeth, the fracture strengths were not found significantly different from the untreated or calcium hydroxide-treated teeth at 2 weeks or 2 months (P > 0.05). However, the strength was significantly higher in the MTA group compared with the other two groups after 1 year (P < 0.05). Immunofluorescence images revealed expression of collagen type 1, MMP-2 and MMP-14 in both untreated and endodontically treated teeth. However, TIMP-2 was only observed in the MTA-treated teeth. In conclusion, the teeth with root treatment with MTA showed the highest fracture resistance at 1 year (P < 0.05). An explanation could be that MTA induced the expression of TIMP-2 in the dentin matrix and thereby possibly prevented destruction of the collagen matrix.

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This research tested the hypothesis that active and arrested carious dentin lesions have distinct structural characteristics and differ in atomic force microscopy-based nano-mechanical properties of the identifiable zones found in hydrated coronal carious lesions. Eight carious molars were used in this study. After longitudinally bisecting all the samples through the centers of carious lesions, they were divided into two subgroups: moderately active caries and arrested caries. The samples were highly polished and stained by caries detector, which allowed identification of four zones: pink, light pink, transparent and apparently normal. The mechanical properties were studied wet using atomic force microscopy. The results show that both groups contained the same zones, regardless of activity status, and different zones have different mechanical properties. Generally, the more demineralized outer zones (pink, light pink) were larger and the mechanical properties of the zones were lower for moderately active caries. For arrested caries, the transparent zone occupied a larger portion of the lesion and the reduced elastic modulus was not significantly different from the underlying normal zone, although its hardness was lower than the apparently normal zone.

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Recent research in dentin bonding demonstrated the superiority of moist bonding over dry bonding on normal dentin, but it is unclear if this technique is also superior in bonding to caries-affected dentin. The purpose of this study was to evaluate the SEM appearance and bond strength of Scotchbond Multi-Purpose Plus (SMPP) to normal vs. caries-affected dentin bonded under moist vs. dry conditions, with and without polyalkenoic acid in the primer. Extracted carious human third molars were ground down by means of 600-grit SiC paper until the carious dentin no longer stained with caries detector solution. The flat surfaces were then primed, bonded, and built up with resin composite. After soaking in water for 1 day, the teeth were serially sectioned vertically into 5 or 6 slabs 0.7 mm thick. The bonded caries-affected areas were isolated by means of an ultrafine diamond bur to create an hourglass configuration with a cross-sectional area of 0.9 mm2. Bonded normal dentin was isolated the same way. Each specimen was attached to a Bencor device and tested in tension to failure. SMPP bonds to dry, normal dentin were only half as strong (21+/-10 MPa, x +/- SD) as those made to moist, normal dentin (42+/-9 MPa, p<0.01). There was no significant difference between bonds made to normal vs. caries-affected dentin by means of the moist technique (42+/-9 vs. 48+/-4 MPa, respectively). Removal of the polyalkenoic acid from the primer lowered (p<0.05) the bond strength of SMPP to caries-affected dentin (38+/-8 MPa). The benefits of moist bonding extend to caries-affected dentin. The polyalkenoic acid in the SMPP primer contributes to the high bond strength that can be achieved to caries-affected dentin.

Microbially produced alkanes are a new class of biofuels that closely match the chemical composition of petroleum-based fuels. Alkanes can be generated from the fatty acid biosynthetic pathway by the reduction of acyl-ACPs followed by decarbonylation of the resulting aldehydes. A current limitation of this pathway is the restricted product profile, which consists of n-alkanes of 13, 15, and 17 carbons in length. To expand the product profile, we incorporated a new part, FabH2 from Bacillus subtilis, an enzyme known to have a broader specificity profile for fatty acid initiation than the native FabH of Escherichia coli. When provided with the appropriate substrate, the addition of FabH2 resulted in an altered alkane product profile in which significant levels of n-alkanes of 14 and 16 carbons in length are produced. The production of even chain length alkanes represents initial steps toward the expansion of this recently discovered microbial alkane production pathway to synthesize complex fuels. This work was conceived and performed as part of the 2011 University of Washington international Genetically Engineered Machines (iGEM) project.

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In this paper, approaches for the realization of high-resolution periodic structures with gap sizes at sub-100 nm scale by two-photon polymerization (2PP) are presented. The impact of laser intensity on the feature sizes and surface quality is investigated. The influence of different photosensitive materials on the structure formation is compared. Based on the elliptical geometry character of the voxel, the authors present an idea to realize high-resolution structures with feature sizes less than 100 nm by controlling the laser focus position with respect to the glass substrate. This investigation covers structures fabricated respectively in the plane along and perpendicular to the major axis of voxel. The authors also provide a useful approach to manage the fabrication of proposed periodic structure with a periodic distance of 200 nm and a gap size of 65 nm.