Residual Microstrain in Root Dentin after Canal Instrumentation Measured with Digital Moiré Interferometry.

INTRODUCTION: Residual microstrain influences the resistance to crack propagation in a biomaterial. This study evaluated the residual microstrain and microdefects formed in dentin after canal instrumentation in teeth maintained in hydrated and nonhydrated environments. METHODS: Canals of 18 extracted human premolars with single-root canals were instrumented in accordance with 3 groups: the ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) group: ProTaper Universal (S1, S2, F1, and F2) used in rotation, the WaveOne Primary (Dentsply Maillefer) group: the WaveOne (Primary) used in reciprocal motion, and the control group: hand files. Half the specimens (3/group) were maintained in deionized water (hydrated) and half in ambient relative humidity conditions (22°C, 55% RH) for 72 hours (nonhydrated). Customized high-sensitivity digital moiré interferometry was used to qualitatively evaluate pre- and postinstrumentation dentinal microstrain. Subsequently, specimens were examined for dentinal microdefects with micro-computed tomographic imaging and polarized light microscopy. RESULTS: Digital moiré interferometry showed only minor changes in postinstrumentation microstrain in hydrated dentin in all groups, suggestive of a stress relaxation behavior. Nonhydrated dentin in all groups showed localized concentration of postinstrumentation microstrain, which appeared higher in the WaveOne group than in the other groups. No dentinal microdefects were detected by micro-computed tomographic imaging and polarized light microscopy in hydrated and nonhydrated specimens in all groups. CONCLUSIONS: This study suggested that the biomechanical response of root dentin to instrumentation was influenced by hydration. Reciprocating, rotary, and hand instrumentation of well-hydrated roots did not cause an increase in residual microstrain or the formation of microdefects in root dentin.

The influence of father criminality on juvenile recidivism: testing for delinquent behaviors as a mediator.

This study investigates the relationships between father criminality, prior delinquency, and recidivism using data from 382 incarcerated juveniles assessed in Singapore's Juvenile Court in 2005. The juveniles are aged 13 to 16 years, with a mean of 14.55 years (SD = 0.93). Using Baron and Kenny's framework, this study tests the prediction that the prior delinquent behaviors of the juvenile mediate the relationship between father criminality and recidivism in a four-step process. When the juvenile's prior delinquent behaviors are included in the model, the previous significant relation between father criminality and recidivism disappears. Implications of findings in terms of applied and practical intervention and prevention work for youths in schools and those in incarceration are discussed.