Comparison of polishing methods for two types of monolithic all-ceramic crowns after occlusal adjustments: Polishing paste versus glazed porcelain.

This study compared the effects of two surface preparation methods on two types of zirconia. Immediately prior to the placement of a monolithic zirconia crown, its morphology may be modified using a rotary cutting instrument for occlusal adjustments. The crown surface is scratched during the grinding process and, thus, requires polishing. Simplified zirconia crowns of 3Y and 5Y were fabricated and used as specimens. The surface roughness and gloss of the occlusal surfaces of specimens were measured and compared when a polishing compound was used after polishing points and when a silica-based coating was sintered. No significant differences were observed in surface roughness between 3Y and 5Y zirconia. The use of polishing compounds was effective because polishing points alone only resulted in a level of surface roughness that may cause wear on antagonist teeth. Although the silica-based coating improved surface properties, the polishing compound more effectively improved surface roughness.

Substituent Effect and Its Halogen-Atom Dependence of Halogen Bonding Viewed through Electron Density Changes.

Elucidating how the halogen-bonding ability and strength are controlled by the substituent effect and how this control depends on halogen atom will be essential for finely-tuned design of functionally important molecules. Here, this problem is tackled by analyzing the electron density differences/changes for variously substituted halobenzenes. It is shown that the anisotropy of the electron distribution around the halogen atom, which is an important factor for halogen-bonding ability, is not much affected by the substituent effect and rather simply depends on the halogen atom, while the partial charge on the halogen atom, which is related to the bond dipole of the C-X bond, is significantly modulated by the substituent effect and gives rise to enhancement of the electrostatic potential on the line extended from the C-X bond. The properties related to the polarization effect are also discussed.

Nature of hydrogen-bond-enhanced halogen bonding viewed through electron density changes.

Elucidating the mechanism of how we can achieve fine tuning of intermolecular interaction strength will be helpful for designing functionally important molecules. In the present study, a theoretical analysis is conducted, by examining the electron density changes, for two halogen-bonding iodinated systems whose halogen-bond strengths have been considered to be enhanced by the presence of a hydrogen-bond donating group (termed hydrogen-bond-enhanced halogen bonding). It is shown that, contrary to the expectation obtained from the enhancement of electrostatic potential along the line extended from the C-I bond, the anisotropy of electron distribution on the iodine atom remains nearly the same. This means that the hydrogen bond and halogen bond contribute almost independently and additively to the enhancement of electrostatic potential, indicating the nature of this enhancement and, in a more general sense, the relationship between the strength and the extent of directionality of halogen bonding.

Optical properties and flexural strength of translucent zirconia layered with high-translucent zirconia.

This study investigated the optical properties and flexural strength of translucent TZP layered with high-translucent PSZ using resin cement of various shades. Zirconia specimens (translucent TZP; Zpex and high-translucent PSZ; ZpexSmile) were 13 mm in diameter, layered at thickness ratios of 0.3/0.7, 0.5/0.5, and 0.7/0.3 mm (ZpexSmile/Zpex), and then luted using resin cement of 3 shades. Monolithic specimens of both were used as controls. CIE L*a*b* color coordinates and translucency parameter (TP) were evaluated as optical properties. Biaxial flexural strength was also determined as a mechanical evaluation. The a* and b* values of layered specimens varied depending on the shade of cement. TP values were not affected by shade of cement and thickness ratio. The biaxial flexural strength was intermediate value between both monolithic specimens. The layering method of zirconia with various translucencies using resin cement of different shades can improve color expression while maintaining clinically sufficient flexural strength.

Effect of Differences in Axial Thickness and Type of Cement on Fracture Resistance in Composite Resin CAD/CAM Crowns.

The purpose of this study was to investigate the influence of differences in axial thickness and type of cement on fracture load in CAD/CAM crowns. Assuming the mandibular first premolar to be the abutment tooth, 4 types of crown with different axial thicknesses and radii of curvature were prepared. To unify external design, the morphology of the crown margins was set at 0.15, 0.30, 0.45, or 0.60 mm, thus maintaining uniform axial form of the crowns. The CAD/CAM crowns and abutment teeth were bonded using each of 2 types of resin cement or polycarboxylate cement. The fracture load value was measured using a universal testing machine and the destruction phase observed.No significant difference was observed with change in axial thickness. The fracture load values with each of the 2 types of resin cement used were significantly higher than that with polycarboxylate cement (p<0.01). These results suggest that the fracture load values of CAD/CAM crowns are not influenced by differences in the axial thickness of the crown, and that they are higher when bonding is achieved with resin rather than polycarboxylate cement.

Growth inhibition and differentiation of cultured smooth muscle cells depend on cellular crossbridges across the tubular lumen of type I collagen matrix honeycombs.

Although rabbit vascular smooth muscle cells (SMCs) showed a differentiated phenotype in three-dimensional type I collagen matrices (honeycombs, diameter of pores=200-500 microm), mouse vascular SMCs proliferated in honeycombs having the same pore size. Here we investigated the relationship between pore sizes of honeycombs and differentiation of SMCs using various pore sizes of honeycombs. Rabbit SMCs (length: 200+/-32 microm) and mouse SMCs (49+/-10 microm) formed crossbridges in honeycombs with 200-300 microm and less than 200 microm of pores, respectively. Both SMCs spread on the inner wall but did not form crossbridges in honeycombs with larger pores. [(3)H]Thymidine incorporation and cell number of both SMCs were decreased when the crossbridges were formed in honeycombs. Because proliferation inhibition and crossbridge formation were observed in the culture of rabbit and mouse SMCs using 200-300 microm and less than 200 microm pore sized honeycombs, respectively, these data suggested that forming crossbridges was important for the inhibition of proliferation of SMCs. Rabbit SMCs differentiation was accompanied by the expression of caldesmon heavy chain when cultured in honeycombs having less than 300 microm pores. Proliferation of mouse SMCs stopped in honeycombs having less than 200 microm pores, but caldesmon heavy chain was not detected despite the expression of its mRNA. Proliferation of SMCs stopped on plates when cells reached confluent state, however, caldesmon heavy chain was not expressed. These data suggested that an appropriate structure and suitable honeycomb pore size are important for the differentiation of SMCs.

Electronic structures of five-coordinate iron(III) porphyrin complexes with highly ruffled porphyrin ring.

The spin states of the iron(III) complexes with a highly ruffled porphyrin ring, [Fe(TEtPrP)X] where X = F-, Cl-, Br-, I-, and ClO4(-), have been examined by 1H NMR, 13C NMR, EPR, and Mössbauer spectroscopy. While the F-, Cl-, and Br- complexes adopt a high-spin (S = 5/2) state, the I- complex exhibits an admixed intermediate-spin (S = 5/2, 3/2) state in CD2Cl2 solution. The I- complex shows, however, a quite pure high-spin state in toluene solution as well as in the solid. The results contrast those of highly saddled [Fe(OETPP)X] where the I- complex exhibits an essentially pure intermediate-spin state both in solution and in the solid. In contrast to the halide-ligated complexes, the ClO4(-) complex shows a quite pure intermediate-spin state. The 13C NMR spectra of [Fe(TEtPrP)ClO4] are characterized by the downfield and upfield shifts of the meso and pyrrole-alpha carbon signals, respectively: delta(meso) = +342 and delta(alpha-py) = -287 ppm at 298 K. The data indicate that the meso carbon atoms of [Fe(TEtPrP)ClO4] have considerable amounts of positive spin, which in turn indicate that the iron has an unpaired electron in the d(xy) orbital; the unpaired electron in the d(xy) orbital is delocalized to the meso positions due to the iron(d(xy))-porphyrin(a(2u)) interaction. Similar results have been obtained in analogous [Fe(TiPrP)X] though the intermediate-spin character of [Fe(TiPrP)X] is much larger than that of the corresponding [Fe(TEtPrP)X]. On the basis of these results, we have concluded that the highly ruffled intermediate-spin complexes such as [Fe(TEtPrP)ClO4] and [Fe(TiPrP)ClO4] adopt a novel (d(xz), d(yz))3(d(xy))1(d(z)(2)1 electron configuration; the electron configuration of the intermediate-spin complexes reported previously is believed to be (d(xy))2(d(xz)), d(yz))2(d(z)(2))1.

Formation of the intermediate-spin iron(III) porphyrin complexes with (dxz, dyz)3(dxy)1(dz2)1 electron configuration.

On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermediate-spin iron(III) complexes with highly ruffled and highly saddled porphyrins have different electron configurations. While the latter has a conventional (dxy)2(dxz, dyz)2(dz2)1, the former adopts a novel (dxz, dyz)3(dxy)1(dz2)1.