Accuracy of cone beam computed tomography in measuring thicknesses of hard-tissue-mimicking material adjacent to different implant thread surfaces.

BACKGROUND/PURPOSE: To evaluate the measurement accuracy of hard-tissue thicknesses adjacent to dental implants with different thread designs on images obtained from cone beam computed tomography (CBCT) using an in vitro model. MATERIALS AND METHODS: On 4 × 13-mm implant, the neck of the implant was designed with micro-threads, and the apical part was covered by macro-threads; these implants were placed in a vinyl polysiloxane block that mimicked hard-tissue. Models were prepared with various thicknesses of 2.0, 1.0, 0.5 and 0.3 mm adjacent to the dental implant. Each model was scanned using CBCT, and the thickness of the cortical bone from the outer surface of the micro-threads and macro-threads were recorded. Ground sections were prepared, and the thickness was measured with electronic calipers as the gold standard (GS) measurement. RESULTS: CBCT measurements of the micro-thread surface were consistently underestimated compared to the GS measurement when the thickness of the hard-tissue-mimicking material was ≤1.0 mm. In comparison, CBCT measurements of the macro-thread surface closely approximated the standard measurement, except when the thickness of the hard-tissue-mimicking material was 0.3 mm. The mean percentage errors from the standard measurement for the 2.0-, 1.0-, 0.5-, and 0.3-mm thickness groups were 4.8%, 16.4%, 37.8%, and 92.6%, respectively, for the micro-thread group, and were 0.6%, 2.9%, 9.5%, and 40.8%, respectively, for the macro-thread group. CONCLUSION: Within the limitations of this study, we conclude that CBCT may not produce sufficient resolution for thin sections of hard tissue-mimicking materials adjacent to micro-thread surfaces.

Evidence of formation of site-selective inclusion complexation between beta-cyclodextrin and poly(ethylene oxide)-block-poly(propylene oxide)- block-poly(ethylene oxide) copolymers.

A series of inclusion complexes of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) with beta-cyclodextrin (beta-CD) was prepared. Their formation, structure, and dynamics were investigated by solution two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY) and one-dimensional (1D) and 2D solid-state (13)C NMR. The inclusion complexes between the PEO-b-PPO-b-PEO copolymers and the beta-CDs were formed in aqueous solution and detected by 2D ROESY. The high efficiency of cross polarization and spin diffusion experiments in (13)C solid-state NMR showed that the mobility of the PPO blocks dramatically decreases after beta-CD complexation, indicating that they are selectively incorporated onto the PPO blocks. The hydrophobic cavities of beta-CD restrict the PPO block mobility, which is evidence of the formation of inclusion complexes in the solid state. The 2D wide-line separation NMR experiments suggested that beta-CDs only thread onto the PPO blocks while forming the inclusion complexes. The stoichiometry of inclusion complexes was studied using (1)H NMR, and a 3:1 (PO unit to beta-CD) was found for all inclusion complexes, which indicated that the number of threaded beta-CDs was only dependent on the molecular weight of the PPO blocks. 1D wide angle x-ray diffraction studies demonstrated that the beta-CD in the inclusion complex formed a channel-like structure that is different from the pure beta-CD crystal structure.

Injectable biomaterials for incontinence and vesico-ureteral reflux: current status and future promise.

Many injectable biomaterials have been produced as bulking agents for compression of urethral sphincter or ureteral orifice for treating adult stress incontinence or vesico-ureteral reflux in pediatrics. The agents being developed include glutaraldehyde crosslinked collagen, dextranomer/hyaluronic acid copolymer, pyrolytic carbon-coated zirconium oxide beads, polydimethyl-siloxane microparticles, polytetrafluoroethylene paste, autologous fats, autologous chondrocytes, and others. Though less invasive nature of these agents has gained their popularity as a quick solution of the disease symptoms, most of such treatments fail to produce good long-term efficacy. The failure is likely caused by the rapid degradation of material implants and the lack of tissue regeneration/integration properties. We thus believe that a good injectable biomaterial for incontinence should possess the following two properties: (1) to resist degradation and to reside in the implantation sites for a long period of time or (2) to enhance tissue regeneration and to establish permanent periurethral or subureteric tissue. Here we report some recent results for supporting this hypothesis.

Three-dimensionally packed nanohelical phase in chiral block copolymers.

Chirality-driven microphase-separated morphology, poly(l-lactide) (PLLA) left-handed nanohelices hexagonally packed in PS matrix, was obtained from chiral diblock copolymers, poly(styrene)-b-poly(l-lactide). This is perhaps for the first time; the helical superstructures of chiral block copolymers were generated in the bulk and self-assembled to a two-dimensionally (2D) packed lattice. Now, the analyses of block copolymer thermodynamics should be complicated by the chiral entities of constituted components. Orderly packed nanohelical channels can be obtained after hydrolysis, and this provides new opportunities for block copolymer applications in the fields of nanosciences.