Applications of laser-based ultrasonics to the characterization of the internal structure of teeth.

Dental health care and research workers require a means of imaging the structures within teeth in vivo. For example, there is a need to image the margins of a restoration for the detection of poor bonding or voids between the restorative material and the dentin. In addition, a high-resolution imaging modality is needed to detect tooth decay in its early stages. If decay can be detected early enough, the process can be monitored and interventional procedures, such as fluoride washes and controlled diet, can be initiated to help remineralize the tooth. Currently employed x-ray imaging is limited in its ability to visualize interfaces and incapable of detecting decay at a stage early enough to avoid invasive cavity preparation followed by a restoration. To this end, nondestructive and noncontact in vitro measurements on "as-is" extracted sections of human incisors and molars using laser-based ultrasonics are presented. Broadband ultrasonic waves are excited in the extracted sections by using a pulsed carbon-dioxide (CO2) laser operating in a region of high optical absorption in the dental hard tissues. Optical interferometric detection of the ultrasonic wave surface displacements is accomplished with a path-stabilized Michelson-type interferometer. Laser ultrasonics is found effective in characterizing the anisotropic and inhomogeneous nature of dentin. In addition, time-of-flight analysis of the measured bulk transmission waveforms allows for detection of dentino-enamel and carious dentin-dentin junctions. These results are compared to those obtained for specially prepared tooth phantoms that mimic the mechanical properties of dental hard tissues.

Fatal unintentional occupational poisonings by hydrofluoric acid in the U.S.

BACKGROUND: Case reports have identified hydrofluoric acid (HF) as causing fatal work injury, and HF has both local and systemic toxicity. Surveillance for HF-related mortality is problematic because of the lack of unique coding for this acid in hospital records and vital statistics. METHODS: We identified HF-related fatal work injuries investigated by the Occupational Safety and Health Administration (OSHA) for 1984-94 from coding of Hazardous Substance 1460 (HF) and requested case investigation files under the Freedom of Information Act. We attempted to identify HF-related deaths in the US for the same period through literature case reports, the Consumer Product Safety Commission, and the American Association of Poison Control Centers (AAPCC). RESULTS: For the 11 year period, OSHA investigated nine deaths in eight incidents which involved HF. Four deaths were from skin contact with concentrated HF, and five deaths involved both skin contact and inhalation of vapor. Unsafe work practices were factors in all of the deaths. Calcium chloride or gluconate was noted to have been administered to five of the nine victims. Calcium was administered 90 min after exposure to two victims, and more than 6 h after exposure to a third. We were able to establish that the regional poison control center had been contacted in regard to only one victim. For the period 1984-94, we were able to identify no additional deaths from CPSC reports, one additional death from AAPCC annual reports, and four other deaths from case reports in the medical literature. CONCLUSIONS: For the period of this study, OSHA records identified the greatest number of HF-related fatalities. The limited information in the records suggest that some victims did not receive appropriate medical care, nor was the regional poison center contacted regarding care. The full extent of health problems related to HF could be better quantified if usual surveillance sources, such as vital records, included unique coding for this acid.