Biomechanical analysis of pediatric injuries and child restraint system.

Airbag related injuries to infants in rear facing child seats are common in frontal crashes. Several vehicular modifications such as deactivated passenger airbags, manual cut-off switches, depowered airbags and smart airbags have been advanced to mitigate the effect of airbag deployment on child seats. However, there is limited research effort to address the biomechanics of airbag injuries due to modification in child restraint systems. The purpose of this research is to evaluate the biomechanical effects of a protective barrier between the rear facing child restraint and the frontal passenger airbag of the vehicle. An experimental study was conducted using an Anthropometric Test Dummy (ATD) in a vehicular partial structure (buck). The rear facing child seat was placed in the right front passenger seat of the vehicle. The child seat was restrained using the three-point restraint in the vehicle. The six-month-old instrumented ATD was restrained in the child seat. The ATD was instrumented with the head tri-axial and two uni-axial linear accelerometers. The uni-axial linear acceleration was used to calculate the angular acceleration. Two different rear facing child seats, the standard rear facing infant seat and the rear facing infant seat inside the protective barrier structure were tested. In each test, the Head Injury Criteria (HIC) and angular head acceleration were measured. Results show that the HIC was reduced by 95% and the angular head acceleration was reduced by 85% by the protective barrier. The head injury values were well below the tolerance limit for the child with the barrier. The protective barrier deflected the airbag away from the ATD’s head and also acted as a shield to minimize airbag force on the child seat. In the typical infant seat, the airbag contacted the ATD’s head and exerted significant force on the child seat which rotated the seat rearward. These kinematic responses may explain the clinical observation of severe head injuries by infants in rear facing seats due to forces transmitted through the child seat and downward force from the top of the head. The present study is a first step in better understanding the injury mitigating aspects of the safety protective structure in child restraints.

Choosing the esthetic angle of the face: experiments with laypersons and prosthodontists.

STATEMENT OF PROBLEM: Most faces are not symmetrical, and this complicates the task of aligning the anterior segment of the teeth for the restorative dentist, orthodontist, or oral and maxillofacial surgeon. The dental literature provides conflicting advice regarding guidelines for aligning the anterior teeth. PURPOSE: The purpose of this study was to determine the sensitivity of laypersons to variations in the alignment of the anterior segment within a symmetrical face, and to investigate which guidelines were preferred by laypersons and prosthodontists when aligning this segment. MATERIAL AND METHODS: Lay participants (21) were shown a series of 25 modified images of faces on a computer screen and asked to indicate 'noticeability' of tilt and, with another series of 19 images, preference for angulation of the anterior segment. Prosthodontists (14) were shown a further set of 7 images and asked to use a Clinometer to select an appropriate angle. Statistical comparisons were performed with multinomial goodness-of-fit tests and repeated measures ANOVA, followed by Sidak multiple comparisons tests (α=.05). RESULTS: The average angle at which the tilt of the anterior segment within a symmetrical face became noticeable to the laypersons was approximately 1 degree. No significant correlation (P=.15) was found between the laypersons' choice of angle for the anterior segment and the angle of the eyes, lips, or horizon, but an angle of 0 degrees was chosen significantly more often than the other angles offered (P<.001). The prosthodontists generally chose an angle close to zero. CONCLUSIONS: The results suggest that the threshold tilt within a symmetrical face, for noticeability by laypersons, is about 1 degree, and that for both laypersons and prosthodontists, the most important guideline is not any individual facial feature or the horizon but the face as a whole.

Biomechanical analysis of child restraint system - biomed 2009.

The purpose of the study is to test the hypothesis that potential for the head injury to child occupants is reduced with energy absorbing foam in a rear facing restraint system. The traffic safety of the pediatric population is improved with the child restraint system. However, the child restraint is effective only if advanced protective features are incorporated. One of the protective features is the energy absorbing padding on the side wings of the child seat wherein the child would interact during the crash. A hybrid computer model of the child restraint system was developed using the commercially available MADYMO and LS-DYNA software. A rear facing child seat in the rear compartment of the vehicle was simulated. The 9 months old anthropometric dummy was modeled. The dummy was restrained in the child seat and the child seat was restrained using the lap and shoulder harness. Two computer models with and without the padding on the side wing were simulated. The input included the acceleration at the center of gravity of the vehicle and the door intrusion into the vehicular interior and the child restraint system. Results indicate that the lack of padding allowed the child's head to interact with the side wing in a concentrated manner while the padding allowed distributed contact to the head area. The padding also retained the head within the confines of the child seat with no exposure to outside environment. The head injury parameters (Head Injury Criteria and Angular Acceleration) were reduced two to three times due to padding on the extended side wing. The present study is an additional step towards a better understanding of the injury biomechanics of pediatric population involved in motor vehicle crashes.

Why HIV infections have increased among men who have sex with men and what to do about it: findings from California focus groups.

A resurgence of sexual risk taking, STDs, and HIV incidence has been reported among men who have sex with men (MSM) in several countries. We asked 113 MSM in 12 focus groups conducted in five California cities to identify factors leading to increased risk taking and assess prevention messages to reduce risk in this population. Participants perceived that HIV risk taking has increased because (1) HIV is not the threat it once was due to more effective therapies, (2) MSM communicate less about HIV, and social support for being safe has decreased, and (3) community norms have shifted such that unsafe sex is more acceptable. The prevention messages ranked most likely to motivate risk reduction encouraged individuals to seek social support from friends. Themes ranked least likely to succeed were those that described the negative consequences of HIV or reinforced existing safer sex messages.