The influence of lower extremity postures on kinematics and injuries of cyclists in vehicle side collisions.

OBJECTIVE: A cyclist assumes various cyclic postures of the lower extremities while pushing the pedals in a rotary motion while pedaling. In order to protect cyclists in collisions, it is necessary to understand what influence these postures have on the global kinematics and injuries of the cyclist. METHOD: Finite element (FE) analyses using models of a cyclist, bicycle, and car were conducted. In the simulations, the Total Human Model of Safety (THUMS) occupant model was employed as a cyclist, and the simulation was set up such that the cyclist was hit from its side by a car. Three representative postures of the lower extremities of the cyclist were examined, and the kinematics and injury risk of the cyclist were compared to those obtained by a pedestrian FE model. The risk of a lower extremity injury was assessed based on the knee shear displacement and the tibia bending moment. RESULTS: When the knee position of the cyclist was higher than the hood leading edge, the hood leading edge contacted the leg of the cyclist, and the pelvis slid over the hood top and the wrap-around distance (WAD) of the cyclist's head was large. The knee was shear loaded by the hood leading edge, and the anterior cruciate ligament (ACL) ruptured. The tibia bending moment was less than the injury threshold. When the cyclist's knee position was lower than the hood leading edge, the hood leading edge contacted the thigh of the cyclist, and the cyclist rotated with the femur as the pivot point about the hood leading edge. In this case, the head impact location of the cyclist against the car was comparable to that of the pedestrian collision. The knee shear displacement and the tibia bending moment were less than the injury thresholds. CONCLUSION: The knee height of the cyclist relative to the hood leading edge affected the global kinematics and the head impact location against the car. The loading mode of the lower extremities was also dependent on the initial positions of the lower extremities relative to the car structures. In the foot up and front posture, the knee was loaded in a lateral shear direction by the hood leading edge and as a result the ACL ruptured. The bicycle frame and the struck-side lower extremity interacted and could influence the loadings on lower extremities.

Aerial dispersal of blood-contaminated aerosols during dental procedures.

OBJECTIVES: Dental procedures with high-speed instruments produce large amounts of aerosols. The present study aimed to clarify whether blood-contaminated aerosols were existent and floating in air during dental procedures and to evaluate the effect of an extraoral evacuator system. METHOD AND MATERIALS: An extraoral evacuator system with a test filter was used for sample collection at distances from 50 cm (n = 102) and 100 cm (n =124) behind the patient. A leucomalachite green presumptive test was performed on the test filter. One or more positive reactions on the test filter was considered a positive result, and the positive ratio in each procedure was compared. To assess the effect of the extraoral evacuator, an additional extraoral evacuator was introduced, and the positive ratio during third molar extractions at 100 cm behind the patient was compared (n = 55). RESULTS: At 50 cm from the mouth of the patient during third molar surgery, full-crown preparation, inlay cavity (Black Class II) preparation, and scaling with an ultrasonic scaler, positive results were obtained in 92% (12/13), 70% (21/30), 35% (9/26), and 33% (11/33) of cases, respectively. At a distance of 100 cm, positive ratios sustained 90% (35/39), 48% (15/31), 29% (6/21), and 12% (4/33), respectively. When the second extraoral evacuator was utilized, the positive ratio, at a distance of 100 cm, decreased significantly from 90% (35/39) to 60% (33/55) (P = .0015, chi-square test). CONCLUSION: This study showed that blood-contaminated aerosols can be suspended in air, even in general dental settings, and that extraoral evacuators are useful for reducing contaminated aerosols.

Bone formation without lamina dura in the middle-aged and elderly: possible dependence on enamel.

Bone formation below the crown of mandibular horizontal incompletely impacted third molar is frequently seen in the middle-aged and elderly. The phenomenon shows lamina dura loss without radiolucency and we hypothesized the participation of mature enamel without any influence on the environmental oral status. In order to investigate the characteristics of the phenomenon based on the presence/absence of the lamina dura and radiolucency below the crown, we studied the relationship between 58 men and 43 women with a lamina dura without radiolucency, 12 men and 8 women without a lamina dura with radiolucency, 34 men and 16 women without a lamina dura without radiolucency, and the status of teeth in the ipsilateral mandible. Subjects without a lamina dura without radiolucency were significantly older than those with a lamina dura without radiolucency in both men (P < 0.0001) and women (P <0.01), indicating different chronological causes. Men without lamina dura with radiolucency showed significantly more tooth loss than those with a lamina dura without radiolucency (P < 0.00001) and those without a lamina dura without radiolucency (P < 0.0001), indicating the influence of poor oral health. Thus, the phenomenon without a lamina dura without radiolucency may show the clinical importance of bone formation in the elderly.

A comparison of the postnatal development of muscle-spindle and periodontal-ligament neurons in the mesencephalic trigeminal nucleus of the rat.

The trigeminal mesencephalic nucleus (Vmes) is known to include primary afferent neurons of jaw muscle spindles (MS neurons) and periodontal ligament receptors (PL neurons). The aim of this study was to clarify the postnatal development of Vmes neurons by comparing MS neurons with PL neurons using horseradish peroxidase labeling. We measured somal diameter and somal shape of MS and PL neurons in rats from postnatal day (P)7 to P70. No significant changes were seen between postnatal day P7 and P70 in somal diameter or somal shape of MS neurons. Conversely, PL neurons showed a larger somal diameter at P7 than at P14, and in terms of somal profile, multipolar neurons comprised 0% at P7, but 4.8% at P14 and 16.9% at P70. These findings suggest that PL neurons develop with the eruption of teeth, taking into account the fact that tooth eruption occurs from around P14 in rats. Conversely, the lack of postnatal changes in MS neurons is due to the fact that these neurons have been active since the embryonic period, as swallowing starts in utero.

Occupational safety among dental health-care workers.

Compared to other health-care workers, dental health-care workers come in close contact with patients and use a variety of sharp and high-speed rotating instruments. It is important to understand the characteristics of the occupational accidents that occur. We reviewed incident reports from April 1, 2005, to March 31, 2010, at Matsumoto Dental University Hospital. In addition, questionnaires dealing with identification of occupational safety issues, especially splash exposures, were conducted for dentists, dental hygienists, and nurses. Thirty-two occupational injuries were reported during the study period, including 23 sharp instrument injuries (71.9%), 6 splash exposures (18.8%), and 3 others. Of the six splash exposures, only two cases involved potential contamination with blood or other potentially infectious patient material. Of the 66 workers who experienced sharps injuries, 20 workers (30.3%, 20/66) reported them to the hospital work safety team. The questionnaire revealed high incident of splash exposures and conjunctiva exposures: 87.9% (51/58) and 60.3% (35/58) in dentists and 88.6% (39/44) and 61.4% (27/44) in dental hygienists. The compliance rate for routine use of protective eyewear was 60.3% (35/58) for dentists and 34.1% (15/44) for hygienists. Of the presented informational items included in the questionnaire, those that strongly persuaded respondents to use protective eyewear were 'splatters from the patient's mouth contain blood' (90%, 99/110) and 'dental operations at our clinic are performed based only on a questionnaire without serious examinations for HBV, HCV, and HIV' (71.8%, 79/110). The reason of low compliance of protective eyewear among dentists might relate to fine dental procedures. Appropriate information is important for the motive of wearing personal protective equipment, and an early educational program may have a potential to increase compliance with the use of that equipment.