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A modified Intra-oral Cariogenicity Test was used to study the influence of plaque on the reaction mechanism of sodium monofluorophosphate (MFP) or sodium fluoride (NaF) in either sound or demineralized enamel in vivo. Volunteer students, wearing mouth appliances holding enamel blocks, rinsed their mouths with MFP or NaF solution (1,000 ppm F-) three times a day. The amount of loosely-bound and acquired fluoride was determined after an experimental period of five days in plaque-covered, demineralized (PCD); clean, demineralized (CD); plaque-covered, sound (PCS); and clean sound enamel (CS). While no measurable loosely-bound fluoride could be found after MFP treatment, NaF caused deposition of a significant amount of alkali-soluble fluoride in all experimental groups. After MFP rinses, fluoride concentration in the enamel was increased in the following order: CS, PCS, CD, and PCD. After NaF treatment, demineralized enamel exhibited a higher fluoride acquisition when compared with sound enamel. Plaque had a minor effect on F- acquisition. It is concluded that demineralization of enamel enhances F- uptake from both NaF and MFP solutions. In the presence of plaque, F- acquisition was additionally increased only after MFP rinses in vivo.

Amorphous silicon films of a few hundred nm thickness on glass substrates have been crystallized by pulsed Nd‐YAG laser excitation of 6 to 8 ns duration at wavelengths of λ = 532 nm and λ = 1064 nm. The structural properties of the crystallized films obtained from Raman spectra, X‐ray diffraction data and transmission electron microscopy micrographs reveal crystallites of good structural quality and several hundred nanometers in size. The best quality and size of the crystallites is obtained by complete melting of the film. For λ = 532 nm excitation no sharp threshold for crystallization is obtained and incomplete melting of the films at low energy density leads to small crystallites and large strain in the films. For λ = 1064 nm pulses the threshold for crystallization is very sharp due to nonlinear absorption effects and the energy density coupled into the film is very sensitive to the film thickness because of interference effects. When films, crystallized at the two wavelengths under optimized conditions are compared, the gross structural properties and crystallite sizes differ only slightly but films crystallized with λ = 532 nm show much smoother surfaces and a larger tensile strain.

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