An acid-etch technique and a proton probe were used to obtain profiles of changes in fluoride concentrations across enamel of 24 normal and 24 fluorotic porcine teeth. Polished and unpolished sections were used for probe measurements, and blocks of enamel cut from tissue adjacent to the sections were used for acid etching. Additional blocks were etched with acid containing dye to study penetration of acid beyond the sampling sites. Probe-derived values were characterized by wide fluctuations. They were also higher than acid-etch values, and this difference was reduced but not eliminated by polishing the sections prior to scanning. Profiles obtained with the two methods followed a parallel course in fluorotic and normal enamel. Thus, errors due to chemical estimations of enamel depth with the etch technique were not demonstrated, although penetration of acid deep to the surface of the porous fluorotic enamel was observed. Further development of the precision of the probe method is required to optimize the unique advantage provided by the potential accuracy, speed of data collection, and spatial resolution of this method.
The proton probe has been used to map F concentration changes in the enamel of 15 teeth showing clinical evidence of caries. Thin sections through the lesions were microradiographed and measurements made of the surface zone (radiodense) and body (radiolucent) areas. Each section was then scanned with a focused beam of 2.5 MeV protons, 2000 spot analyses being performed over areas up to 2 x 3 mm. F was determined by detecting gamma rays from a nuclear reaction and the data used to construct 3-D surface plots. The maximum F concentration in the lesion surface zone was extremely variable, ranging from 1750 to 21,700 ppm, and rarely occurred over the deepest part of the lesion. F levels were elevated in the lesion body but usually to a small extent only. A large increase in F throughout the lesion body was found in 3 lesions only, and was associated with a surface zone that was thin or of low x-ray density. Relatively small F increases in the lesion body were associated with either a thick, x-ray dense surface layer having a greatly increased F level (> 10,000 ppm) or, conversely, with a surface layer having a relatively small F increase. Since F uptake can be regarded as a "marker" of past remineralization events, this study shows that remineralization can and does occur in the body of natural enamel caries lesions, especially when the surface layer is thin or lost. Fluoride availability that encourages the formation of an extremely dense surface layer may result in under-achievement of this natural repair process in the lesion body.
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