Casting Metals in Dentistry: Past - Present - Future

This article deals mainly with the development of dental casting techniques and formulation of the different groups of alloys used in the fabrication of ceramo-metal restorations. It is recognized that in order for the quality of dental cast restorations to be improved, having alloys with the proper composition is not enough. Biocompatibility, good mechanical and physical properties, longevity of the restoration, compatibility with porcelain, and a simple manipulative technique are as important. Researchers have contributed to different aspects of dental castings and have made cast restorations what they are today. Unfortunately, much of the original basic research has been overlooked by present investigators, who have duplicated studies conducted in the past without realizing that the study had already been performed and the research had been published. The main reason for this is that abstracts of articles published prior to 1975 are not available through a library computer-search system. To obtain copies of articles published prior to 1975, one has to search the literature to know where they were published. This article provides references for much of the past work in this area. Also, dental libraries do not carry copies of U.S. patents. This places the majority of researchers located at dental schools at a disadvantage. They are not familiar with what the patents claim, what is taught, and why certain elements are added or eliminated from alloys and investment materials. This article also provides the numbers of many U.S. patents. By having the patent number, one can obtain the text of the patent from the U.S. Patent Office in Washington, DC. Since esthetics plays an important role in today's society, emphasis will be given only to alloys designed for fabrication of ceramo-metal restorations. Many ceramo-metal alloys are available today, and they are classified differently by different individuals. In this article, classification will be based on the major components of these alloys, as well as on a chronological introduction of one group leading to the development of the next group. Based on this, one can classify these alloys into six major groups. Chemical composition, properties, and the developers of these alloys, along with their U.S. patents, are given. Recently, two types of all-ceramic restorations have been introduced. The main advantage of the all-ceramic restoration is its superior esthetic quality compared with that of ceramo-metal restorations. Their main disadvantages are low strength and ductility. Their strength, however, is sufficient for single-unit restorations, but not for bridgework. The use of titanium for dental restorations has also been studied, and it has been found to be suitable. Future Studies - Future work should be devoted to the following: (1) the development of stronger and more ductile ceramic materials: (2) further study of the promising palladium alloys from the noble metal group and titanium alloys from the base metal group; (3) the development of easier and less-time-consuming techniques for the fabrication of dental appliances; (4) the development of a powder technique rather than a cast technique for future fabrication methods; and (5) the development of new laboratory equipment, e.g., a single sintering oven capable of sintering both ceramic and metallic particles, which would be accepted if the powder technique is developed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67759/2/10.1177_08959374880020011701.pd

Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70-17 Ma) Grand Canyon models for Colorado Plateau drainage evolution

The provocative hypothesis that the Shinumo Sandstone in the depths of Grand Canyon was the source for clasts of orthoquartzite in conglomerate of the Sespe Formation of coastal California, if verified, would indicate that a major river system flowed southwest from the Colorado Plateau to the Pacific Ocean prior to opening of the Gulf of California, and would imply that Grand Canyon had been carved to within a few hundred meters of its modern depth at the time of this drainage connection. The proposed Eocene Shinumo-Sespe connection, however, is not supported by detrital zircon nor paleomagneticinclination data and is refuted by thermochronology that shows that the Shinumo Sandstone of eastern Grand Canyon was >60 °C (~1.8 km deep) and hence not incised at this time. A proposed 20 Ma (Miocene) Shinumo-Sespe drainage connection based on clasts in the Sespe Formation is also refuted. We point out numerous caveats and non-unique interpretations of paleomagnetic data from clasts. Further, our detrital zircon analysis requires diverse sources for Sespe clasts, with better statistical matches for the four “most-Shinumolike” Sespe clasts with quartzites of the Big Bear Group and Ontario Ridge metasedimentary succession of the Transverse Ranges, Horse Thief Springs Formation from Death Valley, and Troy Quartzite of central Arizona. Diverse thermochronologic and geologic data also refute a Miocene river pathway through western Grand Canyon and Grand Wash trough. Thus, Sespe clasts do not require a drainage connection from Grand Canyon or the Colorado Plateau and provide no constraints for the history of carving of Grand Canyon. Instead, abundant evidence refutes the “old” (70–17 Ma) Grand Canyon models and supports a <6 Ma Grand Canyon.Karl E. Karlstrom, Carl E. Jacobson, Kurt E. Sundell, Athena Eyster, Ron Blakey, Raymond V. Ingersoll, Jacob A. Mulder, Richard A. Young, L. Sue Beard, Mark E. Holland, David L. Shuster, Carmen Winn, Laura Crosse

Neptune’s zonal winds from near-IR Keck adaptive optics imaging in August 2001

We present H-band (1.4–1.8 ?m) images of Neptune with a spatial resolution of ?0.06?, taken with the W.M. Keck II telescope using the slit-viewing camera (SCAM) of the NIRSPEC instrument backed with Adaptive Optics. Images with 60-second integration times span 4 hours each on UT 20 and 21 August, 2001 and ?1 hour on UT 1 September, 2001. These images were used to characterize the overall brightness distribution on Neptune, and to determine rotations periods (which translate into wind speeds) of individual cloud features. The images show that the spatial brightness distribution of cloud features, in particular the bright bands at mid-southern latitudes and near 30°N, changed considerably between 1989 (Voyager era) and 2001. The brightest features extend latitudinally over several degrees, and despite the different velocities in different latitude bands, these bright features remain coherent. We show that these features are bright in part because of the foreshortening effect near the limb, which suggests that the features may be composed of small bright clouds that happen to line up near the limb. At certain latitudes (mid-southern and northern latitudes), there is considerable dispersion in relative rotation periods (and hence zonal velocities) of faint and moderately bright features, while there is essentially no velocity dispersion of features at 50°S. While the zonal speeds of the brightest features are consistent with the Voyager-derived zonal-mean wind profile, there are many cloud features that do not appear to move with the flow. The data are further suggestive of oscillations in longitude, with periods > 4 hrs. We suggest that tidal forcing by Triton could play a role in exciting the waves responsible for the velocity variations of the observed period.Space EngineeringAerospace Engineerin