Physical property comparison of 11 soft denture lining materials as a function of accelerated aging,

Soft denture-lining materials are an important treatment option for patients who have chronic soreness associated with dental prostheses. Three distinctly different types of materials are generally used. These are plasticized polymers or copolymers, silicones, or polyphosphazene fluoroelastomer. The acceptance of these materials by patients and dentists is variable. The objective of this study is to compare the tensile strength, percent elongation, hardness, tear strength, and tear energy of eight plasticized polymers or copolymers, two silicones, and one polyphosphazene fluoroelastomer. Tests were run at 24 hours after specimen preparation and repeated after 900 hours of accelerated aging in a Weather-Ometer device. The data indicated a wide range of physical properties for soft denturelining materials and showed that accelerated aging dramatically affected the physical and mechanical properties of many of the elastomers. No soft denture liner proved to be superior to all others. The data obtained should provide clinicians with useful information for selecting soft denture lining materials for patients.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31019/1/0000695.pd

Tuning DNA compaction

DNA compaction is the collapse of long DNA chains into well-organized condensates of complex, hierarchical nanostructure induced by the presence of cationic agents. Although much progress has been made in understanding underlying interaction mechanisms of in vivo DNA compaction, the interplay of the myriad compaction agents and their types of interactions with DNA still raise a wealth of unanswered, fundamental questions. In particular, the hierarchical organization of chromatin is widely unclear. There, the DNA is first wrapped around histone cores and the formed beads-on-a-string structure is successively shifted towards higher order forms of chromatin structure. The latter process involves linker histones as major antagonists.Here, new results are presented that are derived from bio-mimetic investigations of the simplest possible DNA compaction model system containing only dendrimers, which can be viewed as uniformly charged cationic nanospheres, and unspecific, polydisperse DNA. Small angle X-ray (micro-)diffraction is employed as a principle method of analysis that accesses relevant molecular length scales. Targeting a quantitative understanding of compaction mechanisms, X-ray (micro-)diffraction measurements performed under laminar flow conditions in hydrodynamic focusing microfluidic devices provides microscale control of the self-assembly process. In addition, the method enables time-resolved access to structure formation in situ, in particular to transient intermediate states.Utilizing the high level of control over dendrimer size and charge, DNA compaction is systematically tuned and analyzed in detail. Results show that dendrimers bridge the entire spectrum of biological condensation agents from small cations, such as spermine/spermidine encountered in viruses, to the much larger histone proteins found in eukaryotic cells. Despite its simplicity, the dendrimer/DNA system reproduces characteristic features of DNA compaction in vivo. In particular, PAMAM 6 dendrimers (having a size and charge comparable to histone core proteins) induce a complete wrapping of the DNA around the cation. As such, PAMAM 6/DNA entities are structurally artificial equivalents of nucleosome core particles. For cationic dendrimers having an intermediate size and charge, which is conveniently between that of small multivalent organic cations and larger histone-like proteins, an alternate route of DNA compaction aside from the established salt or macroion condensation is observed in microflow below the isoelectric point, where DNA is in excess of dendrimers.In addition, the phenomenon of charge-induced dendrimer swelling has been experimentally quantified in detail over a wide range of generations. Results clearly show highly predictable, charge-induced changes of the dendrimer conformation and therefore eliminate the discrepancy between theory and experiments that previously existed in literature.Besides artificial model-proteins, the interaction of linker histones H1 and DNA has been studied in microflow. The time-resolved access to struture formation dynamics clearly shows that the interaction of H1 with DNA is a two step process: an initial unspecific binding of H1 to DNA is followed by a rearrangement of molecules in the formed complexes. Results suggest that the conformational transition of H1 tails from their rather extended conformation, in aqueous solution, to their fully folded state, upon interaction with DNA, is most likely the motor of the conformational phase transition of H1/DNA assemblies.Results obtained in this thesis are expected to have a direct bearing on the understanding of the hierarchical organization of chromatin in vivo. Underlying concepts and techniques may be generalized and used to experimentally address also other relevant protein/DNA systems. Moreover, the studied systems are of inherent importance to the field of biotechnology and are expected to contribute towards the design of new vectors for DNA gene delivery

Effect of mixed silanes on the hydrolytic stability of composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73694/1/j.1365-2842.1996.d01-194.x.pd

Simplification of Chrome-Cobalt Partial-Denture Casting Procedure

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67781/2/10.1177_00220345650440051101.pd

Immediate custom implant for the mandible

Recent advances in the technology of casting chrome-cobalt alloys for partial denture frameworks has resulted in a technic for fabricating a custom-made mandibular implant during a single surgical appointment. The fabricating procedures are performed during the initial surgery and therefore eliminates the necessity of the patient undergoing a second surgical procedure for attachment of the implant. The implant fits the bone abutments with a high degree of accuracy which offers greater support, rigidity, and immobility to the implant. This method of implant fabrication has practical application for patients suffering from cancer, traumatic injury, or gun shot wounds of the mandible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33072/1/0000458.pd

X-ray microdiffraction on flow-controlled biomolecular assemblies

The study of liquid crystalline assemblies, with an emphasis on biological phenomena, is now accessible using newly developed microdevices integrated with X-ray analysis capability. Many biological systems can be described in terms of gradients, mixing, and confinement, all of which can be mimicked with the use of appropriate microfluidic designs. The use of hydrodynamic focusing creates well-defined mixing conditions that vary depending on parameters such as device geometry, and can be quantified with finite element modelling.We describe experiments in which geometry and strain rate induce finite changes in liquid crystalline orientation. We also demonstrate the online supramolecular assembly of lipoplexes. The measurement of lipoplex orientation as a function of flow velocity allows us to record a relaxation process of the lipoplexes, as evidenced by a remarkable 4-fold azimuthal symmetry. All of these processes are accessible due to the intentional integration of design elements in the microdevices

Shell casting of partial denture frameworks and universal aqueous acrylamide duplicating gel : final report

http://deepblue.lib.umich.edu/bitstream/2027.42/7071/5/bad2240.0001.001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/7071/4/bad2240.0001.001.tx

Evolution of DNA compaction in microchannels

Combining microfluidics with x-ray microdiffraction and Raman microscopy, the dynamic behaviour of soft matter, with specific consideration of the molecular structure, can be investigated. Microfluidic systems enable a reduction of sample volume and shorter reaction times. By performing experiments under continuous microflow, material damage is avoided and the influence of external stress on biomacromolecules can be analysed. The generated elongated flow induces alignment of the investigated materials, allowing for an improved structural characterization. Here, the dynamics of the compaction of DNA by polypropyleneimine dotriacontaamine dendrimers, generation 4 is studied. As a consequence of the laminar flow inside the microchannels, highly defined, diffusion-controlled compaction of the DNA occurs enabling the study of different states of the reaction during one measurement by varying the observation position in the channels. The evolution of a columnar mesophase with an in-plane square symmetry is monitored by x-ray microdiffraction and the molecular interaction between the two reactants is traced using Raman microscopy, leading to a more profound comprehension of the condensation reaction. The experimental results are in accordance with finite element method simulations of the flow and diffusion profiles in the elongated flow device

Sorption and solubility of 12 soft denture liners,

The long-term stability of a soft denture liner depends to a large extent on the sorption and solubility of the liner. Because sorption and solubility are accompanied by a volumetric change, bacterial infestation, hardening, and color change, it is a physical property of importance. The purpose of this investigation was to determine the sorption and solubility of 12 soft denture liners (Verno-Soft, Super Soft, ProTech, Soft-Pak, Flexor, Novus, Molloplast-B, Durosoft, Justi Soft, Velvesoft, VinaSoft and Prolastic). They include nine copolymers, two silicones and one polyphosphazene fluoroelastomer. The sorption and solubility test was performed as outlined in American Dental Association (ADA) specification 12 for denture base polymers. Five specimens of each material were tested and data were collected at 1 week, 1 month, 3 months, 6 months, and 1 year. Sorption data varied from 0.2 to 5.6 mg/cm2 at 1 week; 0.3 to 12.5 mg/cm2 at 1 month; 0.1 to 22.0 mg/cm2 at 3 months; 0,1 to 13.6 mg/cm2 at 6 months; and 0.1 to 35.7 mg/cm2 at 12 months. Solubility data varied from 0,0 to 0.4 mg/cm2 at 1 week; 0.1 to 0.8 mg/cm2 at 1 month; +0.1 to 1.2 mg/cm2 at 3 months; 0.0 to 1.9 mg/cm2 at 6 months; and +0.2 to 2.3 mg/cm2 at 1 year. A statistical analysis of the data by two-way ANOVA and calculated Tukey intervals showed significant differences between materials at all time intervals. The results of this study have clinical implications because the sorption and solubility may affect the long-term life expectancy of the soft denture liner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31265/1/0000171.pd

Dietary thyroid hormone replacement ameliorates hearing deficits in hypothyroid mice.

Thyroid hormone (TH) insufficiency causes variable hearing impairment and mental deficiency in humans. Rodents lacking TH have congenital hearing deficiency that has been attributed to physiologic, morphologic, and developmental abnormalities of the auditory system. We examined four genetically defined strains of hypothyroid mice for development of hearing and response to TH replacement initiated during late gestation and continued through six weeks of age. Auditory brain stem response studies showed variable hearing impairment in homozygous mutants of each strain at three weeks of age relative to normal littermates. Mutants from three of the strains still had hearing deficiencies at six weeks of age. TH-enriched diet significantly improved hearing in three-week-old mutants of each strain relative to untreated mutants. Differences in the level of hearing impairment between the Prop1df and Pit1dw mutants, which have defects in the same developmental pathway, were determined to be due to genetic background modifier genes. Further physiologic and morphologic studies in the Cgatm1Sac strain indicated that poor hearing was due to cochlear defects. We conclude that TH supplement administered during the critical period of hearing development in mice can prevent deafness associated with congenital hypothyroidism of heterogeneous genetic etiology