Microtomographic Analysis of Resin Composite Core Material Porosity.

PURPOSE: To nondestructively evaluate the porosity of ten contemporary resin composite core materials using microtomographic (microCT) analysis. MATERIAL AND METHODS: Resin composite core material samples (n = 12) including dual-cure, visible light cure only, and a self-cure material were fabricated using a standardized mold following manufacturer's recommendations. After storage in phosphate buffered saline for one week, specimens were analyzed using a microCT unit at 5.3-µm resolution over a rotational range of 360°. Image 3D recombination and analysis was accomplished using microCT software. Evaluated parameters included material volume investigated, closed pore number and volume, as well as closed pore percentage. Parameter mean values were evaluated with Kruskal-Wallis/Dunn at a 95% confidence level (α = 0.05). RESULTS: Mean percent total porosity with standard deviation identified significant differences in decreasing order as Ti-Core: 2.2 (0.4) > Ti-Core Auto E: 1.3 (0.3) = Ti-Core Flow Plus: 1.1 (0.02) > Clearfil Photo Core: 0.94 (0.5) = Clearfil DC Core Plus: 0.6 (0.18) = MultiCore Flow: 0.58 (0.1) > Fluorocore 2+: 0.14 (0.2) = Build-It FR: 0.068 (0.02) = Gradia Core: 0.03 (0.02) = Rebilda DC: 0.02 (0.01). A pilot microCT evaluation evaluating a mixing tip revealed incomplete mixture between the two resins with porosity introduced from turbulence as the materials are forced through the tip during preparation. CONCLUSIONS: A wide range of porosity was identified between the ten materials evaluated. These preliminary results warrant more investigation evaluating additional resin composite core materials, the preparation capabilities of automix tips, and porosity presence in the unmixed materials.

Physical property investigation of contemporary glass ionomer and resin-modified glass ionomer restorative materials.

OBJECTIVES: The objective of this study was to investigate selected physical properties of nine contemporary and recently marketed glass ionomer cement (GIC) and four resin-modified glass ionomer cement (RMGI) dental restorative materials. MATERIALS AND METHODS: Specimens (n = 12) were fabricated for fracture toughness and flexure strength using standardized, stainless steel molds. Testing was completed on a universal testing machine until failure. Knoop hardness was obtained using failed fracture toughness specimens on a microhardness tester, while both flexural modulus and flexural toughness was obtained by analysis of the flexure strength results data. Testing was completed at 1 h, 24 h, 1 week, and then at 1, 3, 6, and 12 months. Mean data was analyzed with Kruskal-Wallis and Mann-Whitney (p = 0.05). RESULTS: Physical properties results were material dependent. Physical properties of the GIC and RMGI products were inferior at 1 h compared to that at 24 h. Some improvement in selected physical properties were noted over time, but development processes were basically concluded by 24 h. A few materials demonstrated improved physical properties over the course of the evaluation. CONCLUSIONS: Under the conditions of this study: 1. GIC and RMGI physical property performance over time was material dependent; 2. Polyalkenoate maturation processes are essentially complete by 24 h; 3. Although differences in GIC physical properties were noted, the small magnitude of the divergences may render such to be unlikely of clinical significance; 4. Modest increases in some GIC physical properties were noted especially flexural modulus and hardness, which lends support to reports of a maturing hydrogel matrix; 5. Overall, GIC product physical properties were more stable than RMGI; 6. A similar modulus reduction at 6 months for both RMGI and GIC produced may suggest a polyalkenoate matrix change; and 7. Globally, RMGI products demonstrated higher values of flexure strength, flexural toughness, and fracture toughness than GIC materials. CLINICAL RELEVANCE: As compared to RMGI materials, conventional glass ionomer restorative materials demonstrate more stability in physical properties.

Fracture resistance of all-ceramic crowns based on different preparation designs for restoring endodontically treated molars.

OBJECTIVES: To evaluate endodontically treated molar fracture resistance restored with CAD/CAM lithium disilicate (LDS) crowns with different amalgam core preparation design. MATERIALS AND METHODS: Eighty-four recently extracted mandibular third molars were divided into seven groups (n = 12) and embedded in autopolymerizing resin. Coronal tooth structure was removed, pulp chamber exposed, and pulpal remnants removed. One group received LDS endocrowns, while three groups received amalgam cores with 2, 1, and 0 dentin axial wall heights (AWH). Three additional groups were likewise restored using an amalgam adhesive. Scanned preparations were restored with LDS crowns luted with a self-adhesive luting cement. After 24 hours, specimens were loaded to failure with results analyzed with Welch's Test/REGW Range Test at a 95% level of confidence (α = 0.05). RESULTS: The 1 mm-AWH amalgam core group had the highest failure load and was similar to the 2 mm-AWH amalgam, 2 mm-AWH bonded amalgam, and the 1 mm-AWH bonded amalgam core groups. The endocrowns had lower failure load than the 1 mm and 2 mm AWH amalgam groups but was similar to other groups. CONCLUSIONS: Adhesively luted LDS crowns with amalgam core preparations overall displayed similar failure load, as endocrown restorations. However, crowns based on amalgam cores demonstrated favorable failure modes. CLINICAL SIGNIFICANCE: The results of this in vitro test suggests that when suitable tooth structure and sufficient interact restorative space exists, endodontically treated molars restored with lithium disilicate complete crowns based on preparations with amalgam core foundations containing 1 mm and 2 mm of dentin axial wall height could serve as a suitable restorative option that may provide more recoverable failure modes than endocrown restorations.

Preparation Ferrule Design Effect on Endocrown Failure Resistance.

PURPOSE: To evaluate the effect of preparation ferrule inclusion with fracture resistance of mandibular molar endocrowns. MATERIALS AND METHODS: Recently extracted mandibular third molars were randomly divided into 3 groups (n = 12) with the coronal tooth structure removed perpendicular to the root long axis approximately 2 mm above the cemento-enamel junction with a slow-speed diamond saw. The pulp chamber was exposed using a diamond bur in a high-speed handpiece with pulpal remnants removed and canals instrumented using endodontic hand instruments. The chamber floor was restored using a resin core material with a two-step, self-etch adhesive and photopolymerized with a visible light-curing unit to create a 2 mm endocrown preparation pulp chamber extension. One and two millimeter ferrule height groups were prepared using a diamond bur in a high-speed handpiece following CAD/CAM guidelines. Completed preparation surface area was determined using a digital measuring microscope. Scanned preparations were restored with lithium disilicate restorations with a self-adhesive resin luting agent. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity and tested to failure after 24 hours at a 45° angle to the tooth long axis using a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunn (p = 0.05). RESULTS: Calculated failure stress found no difference in failure resistance among the three groups; however, failure load results identified that the endocrown preparations without ferrule had significantly lower fracture load resistance. Failure mode analysis identified that all preparations demonstrated a high number of catastrophic failures. CONCLUSIONS: Under the conditions of this study, ferrule-containing endocrown preparations demonstrated significantly greater failure loads than standard endocrown restorations; however, calculated failure stress based on available surface area for adhesive bonding found no difference between the groups. Lower instances of catastrophic failure were observed with the endocrown preparations containing 1 mm of preparation ferrule design; however, regardless of the presence of ferrule, this study found that all endocrown restorations suffered a high proportion of catastrophic failures but at loads greater than reported under normal masticatory function.

Failure load effect of molar axial wall height with CAD/CAM ceramic crowns with moderate occlusal convergence.

OBJECTIVES: To evaluate the significance of axial wall height (AWH) in molar fracture resistance involving CAD/CAM adhesively bonded, all-ceramic full coverage restorations on preparations with moderate total occlusal convergence (TOC) (16°). MATERIALS AND METHODS: 60 newly extracted maxillary third molars were divided into 5 groups (n = 12). Specimens were prepared for full-coverage, all ceramic restorations with occlusal cervical AWHs of 4, 3, 2, 1 as well as a flat preparation (0 mm AWH) with all preparations with AWH containing a moderate 16° TOC. Scanned preparations were fitted with a lithium disilicate restoration with a self-adhesive resin luting agent after intaglio surface preparation with hydrofluoric acid and silanation. Specimens were stored at 37°C/98% humidity for 24 hours and tested to failure at a 45° angle applied to the palatal cusp on a universal testing machine. Mean results were analyzed using ANOVA/Tukey's (P = .05). RESULTS: Preparations containing 2, 3, and 4 millimeters of AWH demonstrated similar and higher resistance to fracture than the 1 and zero millimeter AWH groups. CONCLUSIONS: Under the conditions of this study, results suggest that adhesive CAD/CAM technology may compensate for reduced axial wall height. However, more definitive results depend on fatigue testing. CLINICAL SIGNIFICANCE: These in vitro results suggest that adhesive CAD/CAM technology may compensate for less than optimal AWH.

Bicuspid Axial Wall Height Effect on CAD/CAM Crown Fracture Mode on Preparations Containing Advanced Total Occlusal Convergence.

PURPOSE: To evaluate bicuspid axial wall height effect on the fracture mode of adhesively luted, all-ceramic CAD/CAM crowns with a 20° total occlusal convergence (TOC). MATERIALS AND METHODS: Recently extracted premolars were randomly divided into 4 groups (n = 12) with all-ceramic crown preparations accomplished using a high-speed handpiece inserted into a milling device. Specimens were prepared containing occlusogingival axial wall heights of 3, 2, and 1 mm as well as a group containing a flat preparation surface with no axial wall height. All preparations contained a 20° TOC. Completed preparation surface area was determined, and preparation features confirmed using a digital measuring microscope. Scanned preparations (CEREC) were fitted with milled and crystallized lithium disilicate full coverage restorations and luted with a self-etching adhesive resin cement after hydrofluoric acid etching and silanation. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity for 24 hours. Specimens were tested to failure at a 45° angle to the long axis of the tooth root on a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunn's (p = 0.05) RESULTS: The 3 mm preparation height specimens were similar to the 2 mm specimens, and both demonstrated significantly stronger failure load than the 1 mm axial wall height and flat preparation specimens. The flat preparation and 1 mm axial wall height specimens all failed adhesively, while the 2 mm and 3 mm specimens failed largely due to tooth fracture. CONCLUSIONS: Further evidence is provided that CAD/CAM adhesive techniques may compensate for less than ideal preparation features. Under the conditions of this study, bicuspid preparations with a 20° TOC restored with adhesively luted, CAD/CAM e.max CAD crowns require at least 2 mm of axial wall height, but further planned fatigue studies are necessary before definitive recommendations can be made.

Krokodile Injectors in Ukraine: Fueling the HIV Epidemic?

This study was designed to assess the characteristics of krokodile injectors, a recent phenomenon in Ukraine, and HIV-related risk factors among people who inject drugs (PWID). In three Ukraine cities, Odessa, Donetsk and Nikolayev, 550 PWID were recruited between December 2012 and October 2013 using modified targeted sampling methods. The sample averaged 31 years of age and they had been injecting for over 12 years. Overall, 39 % tested positive for HIV, including 45 % of krokodile injectors. In the past 30 days, 25 % reported injecting krokodile. Those who injected krokodile injected more frequently (p < 0.001) and they injected more often with others (p = 0.005). Despite knowing their HIV status to be positive, krokodile users did not reduce their injection frequency, indeed, they injected as much as 85 % (p = 0.016) more frequently than those who did not know their HIV status or thought they were negative. This behavior was not seen in non-krokodile using PWID. Although only a small sample of knowledgeable HIV positive krokodile users was available (N = 12), this suggests that krokodile users may disregard their HIV status more so than nonkrokodile users. In spite of widespread knowledge of its harmful physical consequences, a growing number of PWID are turning to injecting krokodile in Ukraine. Given the recency of krokodile use the country, the associated higher frequency of injecting, a propensity to inject more often with others, and what could be a unique level of disregard of HIV among krokodile users, HIV incidence could increase in future years.

Law enforcement practices associated with HIV infection among injection drug users in Odessa, Ukraine.

Despite HIV prevention efforts over the past 10 years in Odessa, Ukraine, HIV rates among injection drug users (IDUs) remain high. We explored whether IDUs' experiences with the police and court system in Odessa were associated with HIV serostatus, after controlling for other factors. Qualitative methods, including semi-structured interviews with the police and members of court (N = 19), and focus groups with IDUs (N = 42), were employed to aid in developing a survey instrument for a larger quantitative phase and to assist in interpreting the findings from the quantitative phase, which included 200 participants who were interviewed and tested for HIV. Overall, 55 % tested positive for HIV. Negative experiences with the police were noted by 86 % and included having preloaded syringes taken (66 %), rushed injections due to fear of the police (57 %), police planting drugs (18 %), paying police to avoid arrest (61 %) and threatened by the police to inform on other IDUs (23 %). HIV positive participants were more likely than those who were negative to report these experiences. In a multiple logistic regression, the most significant correlate of HIV infection was rushed injections due to fear of the police. Police actions in Odessa may be contributing to the continued escalation of HIV among IDUs, underscoring the need for structural interventions.

12-Month flexural mechanical properties of conventional and self-adhesive flowable resin composite materials.

The aim of this study was to investigate the 12-month flexural mechanical properties of 23 flowable resin-based composites (FRBC) that included 5 self-adhesive FRBC materials. Specimens were evaluated following ISO 4049:2019 guidelines, but additionally stored in physiologic 0.2M phosphate buffered saline solution being tested at 24 h, 1 week, 1 month, and at 3-, 6-, 9-, and 12-months. While some deviation and degradation were noted at testing intervals, conventional FRBC materials overall demonstrated greater flexural strength than the self-adhesive and compomer materials. Three self-adhesive materials and the compomer were below recommended ISO 4049:2019 flexural strength values at 24 h with another after 6 months storage. Conventional FRBC materials, except at 1 month, overall demonstrated increased flexural modulus than the self-adhesive FRBC materials. Although results were material dependent, conventional FRBC materials demonstrated overall greater flexural mechanical properties as compared to the self-adhesive FRBC materials and the compomer evaluated.

Individual and network interventions with injection drug users in 5 Ukraine cities.

OBJECTIVES: We evaluated the effects of an individual intervention versus a network intervention on HIV-related injection and sexual risk behaviors among street-recruited opiate injection drug users in 5 Ukraine cities. METHODS: Between 2004 and 2006, 722 opiate injection drug users were recruited to participate in interventions that were either individually based or based on a social network model in which peer educators intervened with their network members. Audio computer-assisted self-interview techniques were used to interview participants at baseline and follow-up. RESULTS: Multiple logistic analyses controlling for baseline injection and sexual risks revealed that both peer educators and network members in the network intervention reduced injection-related risk behaviors significantly more than did those in the individually based intervention and that peer educators increased condom use significantly more than did those in the individual intervention. Individual intervention participants, however, showed significantly greater improvements than did network members with respect to reductions in sexual risk behaviors. CONCLUSIONS: Social network interventions may be more effective than individually based interventions in changing injection risk behaviors among both peer educators and network members. The effectiveness of network interventions in changing sexual risk behaviors is less clear, probably owing to network composition and inhibitions regarding discussing sexual risk behaviors.

Shear Bond Comparison between 4 Bioceramic Materials and Dual-cure Composite Resin.

INTRODUCTION: Bioceramic materials have shown biologic and physical properties favorable for regenerative treatment. A key to treatment success is an adequate restoration to prevent microleakage; however, research is limited regarding the bond strength between restorative and bioceramic materials used in regenerative procedures. This study compared the bond strength between 4 bioceramic materials and a dual-cure composite resin. METHODS: Eighty wells in Teflon (ePlastics, San Diego, CA) blocks were filled with bioceramic materials representing 4 groups: White ProRoot mineral trioxide aggregate (MTA) (Dentsply Tulsa Dental, Tulsa, OK), Biodentine (Septodont, Saint Maur des Fosses, France), EndoSequence Root Repair Material Fast Set Putty (Brasseler USA, Savannah, GA), and NeoMTA (Avalon Biomed Inc, Houston, TX). After allowing samples to set according to the manufacturers' instructions, exposed surfaces of the bioceramic materials were prepared using ClearFil SE Bond (Kuraray America, Inc., New York, NY) followed by restoration with ClearFil DC Core Plus (Kuraray America, Inc.). To test shear bond strength, each block was secured in a universal testing machine, and the crosshead was advanced at 0.5 mm/min until fracture. Newton peak force was recorded and megapascals calculated followed by data comparison. RESULTS: The mean shear bond strengths between ClearFil DC Core Plus and the bioceramic materials were as follows: White ProRoot MTA, 7.96 MPa; Biodentine, 9.18 MPa; EndoSequence Root Repair Material Fast Set Putty, 4.47 MPa; and NeoMTA, 5.72 MPa. White ProRoot MTA and Biodentine were statistically similar, with a higher stress bond strength than NeoMTA, which had a statistically greater bond strength than EndoSequence Root Repair Material. All these values were lower than typical bond strengths shown for dentin-composite resin bonding. CONCLUSIONS: The choice of which bioceramic material to use in regenerative procedures should be based on factors other than the bond between that material and the overlying coronal resin restoration.

Predictors of HIV sero-status among drug injectors at three Ukraine sites.

OBJECTIVE: To assess the HIV serostatus of injection drug users (IDU) in Ukraine, as well as associations between serostatus and selected demographic and risk factors. DESIGN AND METHODS: IDU were recruited from the streets in Kiev, Odessa and Makeevka/Donesk. Participants were interviewed using an HIV risk behavior assessment and tested for HIV with a finger-stick rapid test. Multiple logistic regression was used to identify determinants of HIV infection. RESULTS: Of the 891 IDUs surveyed, one-third came from each site and 22% were female. Their mean age was 29 years and on average they had been injecting for slightly more than 10 years. Seven hundred and seventy-eight of the total sample did not know their HIV status when first interviewed; they are the participants in this investigation. Overall, 33% tested positive for HIV, including 34% in Kiev, 51% in Odessa and 17% in Makeevka/Donesk. Independent predictors of HIV included injecting a sedative/opiate mixture, female sex, having sex with a person who was HIV positive or whose HIV status was unknown and injecting daily. HIV-negative IDU were significantly younger than those infected, they were more likely to be from Makeevka/Donesk and they were more likely to have been sexually active. CONCLUSIONS: Rates of HIV infection among IDU vary considerably across Ukraine, although even in the site with the lowest rate nearly one in five was infected. The extent of drug and sex-related risk behaviors calls for interventions to reduce the spread of HIV and other infectious diseases.

Predictors of risky needle use following interventions with injection drug users in Ukraine.

This study was designed to assess factors associated with change in needle-related risk behaviors as well as predictors of continued high-risk behavior following intervention efforts among injection drug users (IDUs) in Ukraine. In each of three locations--Kiev, Odessa, and Makeevka/Donesk--100 IDUs were recruited using modified targeted sampling methods. Following a baseline interview, participants were offered free HIV testing and, over the course of the next 5 months, individualized interventions focusing on reducing HIV-related risk behaviors. Former IDUs conducted interventions through street outreach. The intervention model was based on the Indigenous Leader Outreach Model (ILOM) and stressed assessing an individual's unique risks and developing strategies by which to minimize those risks. Follow-up assessments showed significant reductions in every risk behavior measured. Following the intervention, however, approximately one of four participants reported front- or backloading, using drugs obtained from a common container or injecting with a used needle/syringe. Although the sample as a whole averaged only 28 years of age, those who were younger were significantly more likely to engage in each of these behaviors than those who were older. In light of the overall young age of the Ukrainian IDUs observed in this study, the consistent finding that younger IDUs were at highest risk foreshadows a worsening HIV epidemic in Ukraine.

HIV incidence among people who inject drugs (PWIDs) in Ukraine: results from a clustered randomised trial.

BACKGROUND: HIV prevalence among people who inject drugs (PWID) in Ukraine is among the highest in the world. In this study, we aimed to assess whether a social network intervention was superior to HIV testing and counselling in affecting HIV incidence among PWID. Although this was not the primary aim of the study, it is associated with reducing drug and sex risk behaviours, which were primary aims. METHODS: In this clustered randomised trial, PWID who were 16 years of age or older, had used self-reported drug injection in the past 30 days, were willing to be interviewed for about 1 hour and tested for HIV, were not too impaired to comprehend and provide informed consent, and, for this paper, who tested HIV negative at baseline were recruited from the streets by project outreach workers in three cities in southern and eastern Ukraine: Odessa, Donetsk, and Nikolayev. Index or peer leaders, along with two of their network members, were randomly assigned (1:1) by the study statistician to the testing and counselling block (control group) or the testing and counselling plus a social network intervention block (intervention group). No stratification or minimisation was done. Participants in the network intervention received five sessions to train their network members in risk reduction. Those participants assigned to the control group received no further intervention after counselling. The main outcome of this study was HIV seroconversion in the intent-to-treat population as estimated with Cox regression and incorporating a γ frailty term to account for clustering. This trial is registered with ClinicalTrial.gov, number NCT01159704. FINDINGS: Between July 12, 2010, and Nov 23, 2012, 2304 PWIDs were recruited, 1200 of whom were HIV negative and are included in the present study. 589 index or peer leaders were randomly assigned to the control group and 611 were assigned to the intervention group. Of the 1200 HIV-negative participants, 1085 (90%) were retained at 12 months. In 553·0 person-years in the intervention group, 102 participants had seroconversion (incidence density 18·45 per 100 person-years; 95% CI 14·87-22·03); in 497·1 person-years in the control group 158 participants seroconverted (31·78 per 100 person-years; 26·83-36·74). This corresponded to a reduced hazard in the intervention group (hazard ratio 0·53, 95% CI 0·38-0·76, p=0·0003). No study-related adverse events were reported. INTERPRETATION: These data provide strong support for integrating peer education into comprehensive HIV prevention programmes for PWID and suggest the value in developing and testing peer-led interventions to improve access and adherence to pre-exposure prophylaxis and antiretroviral therapy. FUNDING: The National Institute on Drug Abuse.

Fractal ventilation enhances respiratory sinus arrhythmia.

BACKGROUND: Programming a mechanical ventilator with a biologically variable or fractal breathing pattern (an example of 1/f noise) improves gas exchange and respiratory mechanics. Here we show that fractal ventilation increases respiratory sinus arrhythmia (RSA) -- a mechanism known to improve ventilation/perfusion matching. METHODS: Pigs were anaesthetised with propofol/ketamine, paralysed with doxacurium, and ventilated in either control mode (CV) or in fractal mode (FV) at baseline and then following infusion of oleic acid to result in lung injury. RESULTS: Mean RSA and mean positive RSA were nearly double with FV, both at baseline and following oleic acid. At baseline, mean RSA = 18.6 msec with CV and 36.8 msec with FV (n = 10; p = 0.043); post oleic acid, mean RSA = 11.1 msec with CV and 21.8 msec with FV (n = 9, p = 0.028); at baseline, mean positive RSA = 20.8 msec with CV and 38.1 msec with FV (p = 0.047); post oleic acid, mean positive RSA = 13.2 msec with CV and 24.4 msec with FV (p = 0.026). Heart rate variability was also greater with FV. At baseline the coefficient of variation for heart rate was 2.2% during CV and 4.0% during FV. Following oleic acid the variation was 2.1 vs. 5.6% respectively. CONCLUSION: These findings suggest FV enhances physiological entrainment between respiratory, brain stem and cardiac nonlinear oscillators, further supporting the concept that RSA itself reflects cardiorespiratory interaction. In addition, these results provide another mechanism whereby FV may be superior to conventional CV.

Mathematical modelling to centre low tidal volumes following acute lung injury: a study with biologically variable ventilation.

BACKGROUND: With biologically variable ventilation [BVV--using a computer-controller to add breath-to-breath variability to respiratory frequency (f) and tidal volume (VT)] gas exchange and respiratory mechanics were compared using the ARDSNet low VT algorithm (Control) versus an approach using mathematical modelling to individually optimise VT at the point of maximal compliance change on the convex portion of the inspiratory pressure-volume (P-V) curve (Experimental). METHODS: Pigs (n = 22) received pentothal/midazolam anaesthesia, oleic acid lung injury, then inspiratory P-V curve fitting to the four-parameter logistic Venegas equation F(P) = a + b[1 + e-(P-c)/d]-1 where: a = volume at lower asymptote, b = the vital capacity or the total change in volume between the lower and upper asymptotes, c = pressure at the inflection point and d = index related to linear compliance. Both groups received BVV with gas exchange and respiratory mechanics measured hourly for 5 hrs. Postmortem bronchoalveolar fluid was analysed for interleukin-8 (IL-8). RESULTS: All P-V curves fit the Venegas equation (R2 > 0.995). Control VT averaged 7.4 +/- 0.4 mL/kg as compared to Experimental 9.5 +/- 1.6 mL/kg (range 6.6 - 10.8 mL/kg; p < 0.05). Variable VTs were within the convex portion of the P-V curve. In such circumstances, Jensen's inequality states "if F(P) is a convex function defined on an interval (r, s), and if P is a random variable taking values in (r, s), then the average or expected value (E) of F(P); E(F(P)) > F(E(P))." In both groups the inequality applied, since F(P) defines volume in the Venegas equation and (P) pressure and the range of VTs varied within the convex interval for individual P-V curves. Over 5 hrs, there were no significant differences between groups in minute ventilation, airway pressure, blood gases, haemodynamics, respiratory compliance or IL-8 concentrations. CONCLUSION: No difference between groups is a consequence of BVV occurring on the convex interval for individualised Venegas P-V curves in all experiments irrespective of group. Jensen's inequality provides theoretical proof of why a variable ventilatory approach is advantageous under these circumstances. When using BVV, with VT centred by Venegas P-V curve analysis at the point of maximal compliance change, some leeway in low VT settings beyond ARDSNet protocols may be possible in acute lung injury. This study also shows that in this model, the standard ARDSNet algorithm assures ventilation occurs on the convex portion of the P-V curve.

Convexity, Jensen's inequality and benefits of noisy mechanical ventilation.

Mechanical ventilators breathe for you when you cannot or when your lungs are too sick to do their job. Most ventilators monotonously deliver the same-sized breaths, like clockwork; however, healthy people do not breathe this way. This has led to the development of a biologically variable ventilator--one that incorporates noise. There are indications that such a noisy ventilator may be beneficial for patients with very sick lungs. In this paper we use a probabilistic argument, based on Jensen's inequality, to identify the circumstances in which the addition of noise may be beneficial and, equally important, the circumstances in which it may not be beneficial. Using the local convexity of the relationship between airway pressure and tidal volume in the lung, we show that the addition of noise at low volume or low pressure results in higher mean volume (at the same mean pressure) or lower mean pressure (at the same mean volume). The consequence is enhanced gas exchange or less stress on the lungs, both clinically desirable. The argument has implications for other life support devices, such as cardiopulmonary bypass pumps. This paper illustrates the benefits of research that takes place at the interface between mathematics and medicine.

Interventions with injection drug users in Ukraine.

AIMS: To assess the effectiveness of a brief human immunodeficiency virus (HIV) testing and counseling intervention compared to a more time-consuming and expensive street-based intervention with injection drug users (IDUs). DESIGN: Cross-over experimental design in which 900 IDUs were recruited, followed by a 'wash-out' period with no recruitment, a reversal of intervention assignment areas and an additional recruitment of 900 IDUs with baseline and 6-month follow-up assessments. SETTING: Kiev, Odessa and Makeevka/Donesk Ukraine. PARTICIPANTS: A total of 1798 IDUs. MEASUREMENTS: HIV testing and audio computer-assisted self-interview (ACASI) data on socio-demographics, drug use and injection and sex-related risk behaviors. FINDINGS: Participants in both conditions reduced their injection and sex risks significantly; however, there was little difference in outcomes between conditions. IDUs who knew they were HIV-infected at baseline were significantly more likely to practice safe sex than those unaware or HIV-negative; those who first learned that they were infected at baseline changed their safe sex practices significantly more than those who already knew that they were infected at baseline and those who were HIV-negative. Younger IDUs and those injecting for a shorter period of time reported higher injection and sex risk behaviors following interventions. CONCLUSIONS: Awareness of HIV infection by street-recruited drug injectors is associated with reduced sex risks. Additional interventions are required for younger IDUs and those injecting for shorter periods of time.

Stimulant injectors in Ukraine: the next wave of the epidemic?

This study was designed to assess differences in drug and sex-related risk behaviors between injectors of opiates only, opiate/sedative mix only and stimulants only. Participants were current out-of-treatment injection drug users (IDUs), unaware of their HIV status, recruited through street outreach in Kiev, Odessa and Makeevka/Donetsk, Ukraine. Overall, 22% tested positive for HIV, including 39% among opiate/sedative injectors, 19% among opiate injectors and 17% among stimulant injectors. Despite these differences, stimulant injectors were at higher risk than other IDUs in sharing a used needle/syringe, always injecting with others, injecting a drug solution drawn from a common container, having an IDU sex partner, not using condoms during vaginal or anal sex and on composite measures of injection and sex risks. After controlling for age differences, stimulant injectors remained at higher risk in their needle and sex risk behaviors. Without intervention, it is likely that HIV will increase among stimulant injectors.