PubMed · 12183736
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David Kwee. 2002. Optimizing immunization--going beyond parent reminders.. https://doi.org/10.1067/mpd.2002.126007
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OBJECTIVES: The purpose of the study was to characterize long-term creep deformation behavior of selected dental composite resins. METHODS: Two hybrid composite resins (one midifill type Clearfill and the other minifill type Charisma) and one microfill type (Durafill) were evaluated. 25 mm x 10 mm x 2 mm rectangular bar specimens were subjected to single cantilever mode of flexural loading and their creep compliance changes determined over 10 min durations in the temperature range of 32-120 degrees C at 5 degrees C intervals. The reference temperature selected was the body temperature of 37 degrees C for the oral environment. All creep compliance curves at other temperatures were shifted along the log time axis to superimpose them on the reference temperature (37 degrees C) curve to generate an extended isothermal master curve over eight decades of time (seconds). The shift factors were determined as a function of temperature and fitted by the least square method to the William-Landel-Ferry model. RESULTS: The data showed excellent fit to the model, indicating the validity of the model to characterize the long-term behavior using the time-temperature superposition principle. The creep compliance changed from initial mean values of 76, 245 and 605 microm(2)/N to 3 year mean values of 217, 880 and 1653 microm(2)/N for Clearfill, Charisma and Durafill systems, respectively. These means were significantly different both as a function of composites and time (p<0.05). SIGNIFICANCE: The results indicate that resin volume fraction and filler parameters may play a critical role in the long-term deformation and energy release processes, and these processes may be an important influence on the long-term clinical durability of composite restorations.
Infection-control recommendations include the use of gowns and gloves to prevent horizontal transmission of vancomycin-resistant enterococci (VRE). This study sought to determine whether the use of a gown and gloves gives greater protection than glove use alone against VRE transmission in a medical intensive care unit (MICU). From 1 July 1997 through 30 June 1998 and from 1 July 1999 through 31 December 1999, health care personnel and visitors were required to don gloves and gowns upon entry into rooms where there were patients infected with nosocomial pathogens. From 1 July 1998 through 30 June 1999, only gloves were required under these same circumstances. During the gown period, 59 patients acquired VRE (9.1 cases per 1000 MICU-days), and 73 patients acquired VRE during the no-gown period (19.6 cases per 1000 MICU-days; P<.01). The adjusted risk estimate indicated that gowns were protective in reducing VRE acquisition in an MICU with high VRE colonization pressure.
The objective of this study was to use finite-element analysis to model tensilometer tests of polymerizing dental composites. A typical sample in polymerization shrinkage stress tests is shaped like a flat disk, that is, has a high aspect ratio (ratio of diameter to height). In the experimental literature it is implied that the induced stress state in the flat disk composite samples is uniaxial. Three published tensilometer tests of curing dental composite samples with similar high aspect ratios (varying from 3 to 5) were modeled, but with test configurations having low, intermediate and high relative compliance (a tenfold variation). With the use of linear elastic finite element analysis, an instantaneous volumetric shrinkage of 1% was applied to the composite via the thermal analogy and the following questions were addressed: 1. Does the numerically predicted state of stress in composite samples tested in this fashion differ substantially from the uniaxial stress state assumed in the experiments?2. How do the numerically predicted stresses compare with the experimentally determined nominal stresses?3. Does compliance of the mountings influence the numerically predicted stress state? The finite-element results predicted a complex triaxial stress state that was strongly influenced by the compliance of the mountings. For the low and intermediate system compliance the model overpredicted the polymerization contraction stress, as would be anticipated due to the inability of the model to account for viscoplastic flow. For high system compliance, the numerical and experimental stress values were in better agreement, mainly because the linear elastic mountings accounted for most of the measured system compliance.