Flow and Fracture of Dental Alloys Determined by a Microbend Tester
The microstructure of an alloy is the fundamental variable on which the mechanical properties of an alloy depend. For testing the mechanical properties, however, common tests, such as tensile strength or hardness, are generally used. This may be due to the fact that the microstructure study is more complicated and time-consuming. The common method of microstructure study is to perform a series of tensile tests and then obtain the microstructure of the specimens after the tests are completed so as to correlate the structure with the performance data. The actual contribution of each observable microstructure to flow and fracture is rather difficult to detect. When the structure is examined after the fracture has taken place, some of the evidence is lost that would have been available if continuous observation of the structure had been possible. In 1955 Flinn and Trojan' developed an apparatus by means of which the microstructure of an alloy under stress can be studied. The stress can be increased while the microstructure is under observation. Thus any changes that may take place can be detected in any of the phases. When an alloy with a complicated microstructure is studied, the microbend test shows its main advantage, since it is rather difficult to predict how the different phases of a complicated structure will behave under different stresses. With this test the effect of such stress on various phases may be continuously watched under the microscope. The purpose of this study was to observe the behavior of different phases of cobalt-base and gold alloys used in dentistry for partial denture framework when they were subjected to bending stresses.
MATERIALS IN RESTORATIVE DENTISTRY
Two major areas of practice are recognized in dentistry. One is directed toward the prevention of oral disease by the reduction of dental caries and the control of periodontal disturbances and oral lesions of all types in the mouth, the patient thereby being assured of the best possible oral health services from such preventive practice. The other area is the practice of restorative dentistry, which includes the treatment of localized infections and the preparation of restorations to replace lost tissue. It is with regard to this second area that an understanding of materials is important. The construction of dental restorations and the practice of restorative dentistry are a necessity while people continue to suffer from involvements of the oral tissues. When teeth and adjacent tissues are lost by accident or disease, the lost tissues must be replaced by functionally and esthetically effective artificial substitutes. A major portion-variously estimated at SO-70% -of dental service and time is devoted to these biomechanical procedures. Unfortunately, this condition is likely to continue throughout the present generation, or until research provides methods to assure a reduction of prevailing dental disorders. One should recognize, therefore, that restorative dental practice is important to the patient, is an accepted fact of the profession, depends on a knowledge and choice of available materials, and will continue to be needed in the future as a part of our dental health service. In restorative procedures, two major activities must be recognized as fundamental: The proper treatment, preservation and care of the remaining oral tissues, with an evaluation of tissue tolerance, compatibility or tissue reaction to the various restorations; and the understanding of the fundamental nature, the physical and mechanical properties, and the functional and esthetic performance of the materials employed in the restoration. Dental materials science is concerned with all facets of these activities, and restorative dental practice involves the attempt to replace with appropriate substitutes either hard or soft tissues of the mouth which has been lost through accident or disease.
Unicondylar femoral fractures: therapeutic strategy and long-term results. A review of 23 patients.
Unicondylar femoral fractures account for 0.65% of all femoral fractures; they have not been studied extensively in the orthopedic literature. Usually occurring following sports trauma or traffic accidents, these fractures involve the lateral condyle three times more frequently than the medial condyle. Conservative or surgical treatment has been advocated, depending on the fracture type. From 1986 to 1999, 19 patients with unicondylar femoral fractures were surgically treated at our institution: there were 15 males and 4 females, aged 36.2 years on average. According to the AO-ASIF classification, there were 7 B1, 6 B2 and 6 B3 fractures. We used Herbert screws in six cases, Barr screws together with cancellous screws in two, cannulated screws in five, cancellous screws alone in four, a compression screw and plate in one and a T-plate in one. In the same period of time, four patients were treated conservatively with a cast. Sixteen patients treated surgically were evaluated with a mean follow-up of 60 months, using Shatzker and Lambert's criteria: six results were rated as excellent, five good, four fair and one poor, while conservative treatment gave three fair and one poor results. In conclusion, we think that open reduction and internal fixation are essential in the treatment of such fractures.