The crowns of 60 permanent human molars were sectioned transversally. The exposed dentin surface was divided into different parts: a first part was kept as control, a second part was immediately varnished, and a third part was irradiated with a CO₂ laser using the same irradiation conditions as those applied for caries removal (10 impulses of the same energy; 0.2 s/impulse; energy density/ impulse 280-715 J/cm². After irradiation, a small portion of this area was varnished. The teeth were immersed for 4 weeks in a cariogenic gel (pH = 4.5) at 36 °C. Twenty teeth were studied by scanning electron microscopy, and longitudinal sections of the other teeth were prepared for microradiography and microdensitometry measurements. The lased dentin surface appeared smooth for energy densities lower than 425 J/cm². Longitudinally fractured samples revealed a layer of dentin devoid of tubular structure (20-70 µm thick, depending on the energy density used), whereas below the sealed layer, the dentinal tubules retained their normal aspect. Although the sealed layer showed no demineralization when exposed to acid, demineralization of the underlying dentin occurred, but to a much lesser extent than in the unlased dentin.

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SynopsisThe properties relevant to nonradiative energy transfer have been computed in the unperturbed chain model for oligopeptides composed of from 4 to 21 residues of the formula Tyr-(Ala),,-Tyr and Trp-(X),,-Tyr, X being either Ala o r Gly. A Monte Carlo method has been used for the generation of the chains.The relation between the distribution functions of the distances between the luminophores and the various properties in energy transfer has been examined for chains of different lengths and compositions.The average of the orientation factor K') has been computed as a function of chain length both for molecules in a randomly coiled state and for molecules with backbones in a welldefined three-dimensional structure.The various averaging regimes of energy-transfer efficiency and of fluorescence decay are compared. Theoretical curves relating experimental efficiencies to the mean distance between the luminophores are proposed.

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