Dental fluorosis and caries prevalence in children residing in communities with different levels of fluoride in the water

OBJECTIVES

This study investigated the prevalence of dental fluorosis and caries in 7-14-year-old children residing in communities with negligible (NF: 0.2 ppm), optimal (OPF: 1.0 ppm), and four-times optimal (4X OPF: 4.0 ppm) naturally occurring fluoride in their water systems.

METHODS

Examinations were performed on 344 children who were lifetime residents of their communities.

RESULTS

Whether using the tooth surface index of fluorosis or Dean's index, children examined in the 4X OPF community had the highest prevalence of dental fluorosis. While the severity of fluorosis seen in the OPF and NF communities was mild in appearance, the results indicate that fluorosis does occur in optimally and negligibly fluoridated communities. Compared to the NF community, DMFT and DMFS scores in the OPF community were 9.2 percent and 21.2 percent lower, respectively.

CONCLUSIONS

The ingestion of water containing 1 ppm or less fluoride during the time of tooth development may result in dental fluorosis, albeit in its milder forms. However, in these times of numerous products containing fluoride being available, children ingesting water containing 1 ppm fluoride continue to derive caries protection compared to children ingesting water with negligible amounts of fluoride. Thus, the potential for developing a relatively minor unesthetic condition must be weighed against the potential for reducing dental disease.

Dielectric compound parabolic concentrating solar collector with a frustrated total internal reflection absorber

Coupling a dielectric compound parabolic concentrator (DCPC) to an absorber across a vacuum gap by means of frustrated total internal reflection (FTIR) can theoretically approach the maximum concentration permitted by physical laws, thus allowing higher radiative fluxes in thermal applications. The calculated optical performance of 2-D DCPCs with FTIR absorbers indicates that the ratio of gap thickness to optical wavelength must be <0.22 before the optical performance of the DCPC is superior to that of the nondielectric CPC.

Proposed frustrated-total-reflection acoustic sensing method

Modulation of electromagnetic energy transmission through a frustrated-total-reflection device by pressure-induced changes in the index of refraction is proposed for use as an acoustic detector. Maximum sensitivity occurs for angles of incidence near the critical angle. The minimum detectable pressure in air is limited by Brownian noise. Acoustic propagation losses and diffraction of the optical beam by the acoustic signal limit the minimum acoustic wavelength to lengths of the order of the spatial extent of the optical beam. The response time of the method is fast enough to follow individual acoustic waves.