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.