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Microfilled composite resins have been introduced in clinical dentistry because of the difficulty in finishing conventional composite resins satisfactorily. Owing to the difference in coefficients of thermal expansion of the two resin systems, the objective of this in vitro study was to evaluate microleakage of a conventional and a microfilled composite resin. Class V cavities with butt cavosurface margins were prepared in the middle third of the facial surfaces of the crowns of 80 noncarious human premolar teeth; they were acid etched within the preparations only. Forty preparations were restored with Concise composite and forty with Silar microfilled resin. Ten teeth from each group were subjected to cyclic temperature changes between 5 and 55 degrees C for 1000, 2500, or 5000 cycles, respectively, and ten teeth from each group were not cycled (controls). After suitable preparation, the teeth were immersed in 45Ca solution for 18 h and contact radiographs were prepared. Microleakage was scored 0-3 at both the cervical and occlusal margins of the restorations. Microleakage was significantly greater at the cervical margins than at the occlusal margins. Differences within occlusal and cervical microleakages among the two resins were not significant.

The Prudhoe Bay field is recognized as the largest oil field in the United States. The Permian-Triassic reservoirs, estimated to contain reserves of 9.6 billion bbl of oil and 26 Tcf of gas, have overshadowed other known substantial accumulations of hydrocarbons in formations ranging in age from Mississipian to Cretaceous in the general area of Prudhoe Bay. This study is a summary of the geology of the Lisburne carbonate rocks, as well as the Kuparuk River sandstone reservoirs and their potential. The regional structure and stratigraphic relationships of other less significant Permian-Triassic and Cretaceous accumulations are also included. Perhaps unrecognized, except in retrospect, is the significance of the planned sequential availablility of both Federal and State lands on the North Slope beginning in 1958. An 11-year period of land availability followed a 14-year moratorium. The history of exploration that led to the discovery in 1968 is presented from that viewpoint. This period culminated with the (September, 1969) State of Alaska "Billion Dollar Sale." The post-discovery sequence of exploration, development, and production in the area has been characterized by environmental, social, legal, political, and economic complexity and controversy. Comparison of the status of petroleum exploration today on the North Slope of Alaska with the history of the 1950s through the early 1970s is an object lesson for explorationists.

Questionnaires requesting much data about oral surgeons and their practice of the specialty were mailed to the members of the American Society of Oral Surgeons. A total of 2,251 usable questionnaires were returned. The methods used in the survey and to summarize the data have been described and some general characteristics of the responding oral surgeons have been supplied in this report. Almost 76% (75.8%) of the oral surgeons returned usable questionnaires. Only 2.4% of the respondents were younger than 30 years and 60.5% were in the age range of 30 to 44 years. The average age of all respondents was 43.0 years. Slightly more than 80% participate in private practice either full-time or part-time teaching. Only 5.1% of the respondents aged 65 to 69 had retired. Almost 82% (81.7%) were active members of the Society. More respondents (24.7%) practiced in cities with populations larger than 500,000 and only 4.5% practiced in cities with populations less than 25,000. More than half of the 2,251 respondents (53.8%) practiced in cities with populations less than 150,000, and 44.4% were in cities with populations less than 100,000.

In this investigation heat-sealed gutta-percha (A) reinforced with Adaptic (B), ASPA (C), Cupralloy without (D) and with (E) varnish, Spheraloy without (F) and with (G) varnish were used as retrofilling materials. Seventy maxillary central incisors with Class I canal anatomy were selected. Marginal leakage at the apical filling/root canal interface was evaluated quantitatively by means of a fluorescent dye technique. All statistical tests were computed at the 5 percent level of significance. Analysis of variance revealed that differences in microleakage among retrofillings were significant. Tukey's test of multiple contrasts was used to isolate statistically significant differences between all pairs of means. The following results were obtained: D F A G E C B Retrofillings are ranked in descending order of microleakage. Means that are linked were not significantly different.