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There is every indication that classical friction controls sliding mechanics below some critical contact angle, theta c. Once that angle is exceeded, however, binding and notching phenomena increasingly restrict sliding mechanics. Using geometric archwire and bracket parameters, the theta c is calculated as the boundary between classical frictional behaviour and binding-related phenomena. What these equations predict is independent of practitioner or technique. From these derivations two dimensionless numbers are also identified as the bracket and the engagement index. The first shows how the width of a bracket compares to its Slot; the second indicates how completely the wire fills the Slot. When nominal wire and bracket dimensions are calculated for both standard Slots, the maximum theta c theoretically equals 3.7 degrees. Thus, knowledge of the archwire or bracket alone is insufficient; knowledge of the archwire-bracket combination is necessary for theta c to be calculated. Once calculated, sliding mechanics should be initiated only after the contact angle, theta, approaches the characteristic value of theta c for the particular archwire-bracket combination of choice--that is, when theta approximately theta c.

Studies report increased rates of cigarette and substance use in youths with Attention-Deficit/Hyperactivity Disorder (ADHD), though the mechanism of risk remains unclear. The present study tests the hypothesis that ADHD individuals "self-medicate" with cigarettes and substances of abuse. As part of five- and ten-year case-control longitudinal family studies of ADHD, responses to the Drug Use Screening Inventory (DUSI) were examined for evidence of self-medication. DUSI data from 90 ADHD probands and 96 control probands were obtained. Thirty-six percent of subjects reported self-medication, 25% used to get high, and 39% had unknown motivation. No significant differences were found between ADHD and controls in motivation. ADHD symptoms did not differ between self-medicators and subjects using to get high. DUSI problem scores were higher in ADHD (versus controls), those using to get high (versus self-medicators), and subjects using alcohol (versus other substances). More than one-third of adolescents and young adults endorsed using cigarettes and substances for self medication. Studies clarifying the role of self-medication in substance use disorders are necessary.

Hematopoietic cell transplantation (HCT) is a life-saving treatment for patients with high-risk hematological malignancies. Prognostic measures to determine fitness for HCT are needed to inform decision-making and interventions. VO 2peak is obtained by measuring gas exchange during cycle ergometry and has not been studied as a prognostic factor in HCT. Thirty-two autologous and allogeneic HCT patients underwent VO 2peak and 6 Minute Walk (6MW) testing before HCT, and provided weekly symptom and health-related quality of life (HRQOL) assessments before HCT and concluding at Day 100. Twenty-nine patients completed pre-HCT testing. Pre-HCT VO 2peak was positively correlated with pre-HCT 6MW (r ¼ 0.65, Po0.001) and negatively correlated with number of chemotherapy regimens and months of chemotherapy. Patients with lower VO 2peak reported higher symptom burden and inferior HRQOL at baseline and during early post-HCT period. Patients with pre-HCT VO 2peak o16 mL/kg/min had higher risk of mortality post HCT (entire cohort: hazard ratio (HR) 9.1 (1.75-47.0), P ¼ 0.01; allogeneic HCT patients only: HR 6.70 (1.29-34.75), P ¼ 0.02) and more hospitalized days before Day 100 (entire cohort: median 33 vs 19, P ¼ 0.003; allogeneic HCT patients only: median 33 vs 21, P ¼ 0.004). VO 2peak pre-HCT is feasible and might predict symptom severity, HRQOL and mortality. Additional studies are warranted. Keywords: cardiopulmonary fitness; symptoms; health-related quality of life; hematopoietic SCT INTRODUCTIONFor patients with life-threatening hematological diseases, hematopoietic cell transplantation (HCT) offers the possibility of extended survival relative to standard conventional treatments. 1 The benefits of HCT are counterbalanced by the risk of treatmentrelated toxicity. Prognostic measures are needed to inform clinician and patient decision-making and to limit treatmentrelated risk. Direct cardiopulmonary fitness assessments such as VO 2peak are now available but have not yet been studied.Myeloablative allogeneic HCT has been associated with a 30-40% risk of treatment-related mortality (TRM). 2 Reduced intensity conditioning HCT is offered to older individuals and patients with comorbid illness, but this technique is still associated with a 20-30% risk of TRM. 3 Autologous HCT in older patients has been associated with a TRM risk exceeding 10%. 4 Subsets of patients after all types of transplants experience late health-related quality of life (HRQOL) deficits and functional impairment; 5 this effect is variable with other subgroups experiencing preserved patient-reported outcomes (PROs), relative to normative values. 6 Investigators and clinicians have attempted to determine who is 'fit' for transplant to inform pre-HCT counseling, selection of suitable HCT candidates and identification of vulnerable HCT recipients at risk for treatment-related complications. 7 Age remains the most commonly used surrogate variable for HCT

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