Comparative flow characteristics of selected dental materials with emphasis on thixotropic behavior.
Abstract Flow behavior of selected impression materials, dental cement liquids and fluoride gels were measured using a unique cup and bod viscometer. Programmable functions of the instrument allowed shear stress measurement during increasing and decreasing shear rates. Shear-dependent and time-dependent properties of plastic, pseudoplastic and thixotropic behavior were evaluated for these materials. The thixotropic index was also used to compare these materials. The impression materials tested showed pseudoplastic and thixotropic behavior, while the dental cements showed very little pseudoplastic or thixotropic behavior. The fluoride gels showed essentially plastic yield with minimal thixotropy.
Characterization of the Setting Process in Alginate Impression Materials
The functioning of an alginate impression material involves a change in its physical state from a viscous fluid to an elastic solid. (The paste obtained when water and the alginate powder are first mixed is a viscous fluid, since it flows irreversibly under the action of a force.) This change is effected by the reaction of calcium sulphate with the sodium or potassium alginate, thus forming a cross-linked molecular network.' The purpose of the present study has been to characterize the setting process in terms of easily measured physical parameters, and hence to make a rational study of the effect of those experimental variables that are of importance clinically.
Adolescent sexual offenders: incidence of childhood maltreatment, serious emotional disturbance, and prior offenses.
Adolescents incarcerated for sexual offenses were compared to those incarcerated for other crimes on measures of prior child abuse and neglect, serious emotional disturbance, and involvement in child welfare and the juvenile justice system. Sexual or physical abuse was more common than neglect among sexual offenders with fewer than three prior maltreatment reports. Sexual offenders were twice as likely to be receiving special education services for severe emotional disturbance, and were usually incarcerated later than other offenders. Implications for research and practice are discussed.