Penetration pattern of rhodamine dyes into enamel and dentin: confocal laser microscopy observation

Abstract

Enamel and dentin are susceptible to extrinsic and intrinsic stains. The purposes of this study were to determine the penetration pattern of Rhodamine B and dextran-conjugated Rhodamine B into the enamel and dentin as observed by confocal laser microscopy and to relate it to the penetration pattern of hydrogen peroxide commonly used as an active ingredient in tooth-whitening agents and high-molecular-weight staining molecules. Eighteen recently extracted human maxillary anterior teeth were used. Teeth were cleaned and painted with nail varnish except for the crown area above the cemento-enamel junction (CEJ). The painted teeth were then immersed in Rhodamine B and dextran-conjugated Rhodamine B (70 000 MW) for 4, 7, 10 and 15 days. Teeth were sliced to 3 mm thickness in transverse plane and mounted on a glass slide just prior to observation with confocal laser microscopy. Rhodamine B and dextran-conjugated Rhodamine B readily penetrated into the enamel and dentin when exposed for 4 and 7 days, respectively. Rhodamine B penetrated along the interprismatic spaces of the enamel into the dentin. The penetration was accentuated in sections with existing crack lines in the enamel. Rhodamine B was readily absorbed into the dentinal tubules at the dentino-enamel junction and continued to penetrate through the dentin via the dentinal tubules into the pre-dentin. Within the limitations of this study, it is concluded that Rhodamine B and dextran-conjugated Rhodamine B when applied to the external surface of the tooth readily penetrate into the enamel and dentin via the interprismatic spaces in the enamel and dentinal tubules in the dentin, suggesting that stain molecules and bleaching agents possibly exhibit similar penetration pathways.

Review of the Mechanism of Tooth Whitening

“…Tooth whitening is based on the premise that hydrogen peroxide penetrates into the enamel and dentin to interact with the organic chromophores. It is well known that the dental hard tissues are highly permeable to fluids, and that the greatest fluid flow in the enamel and dentin is in the interprismatic spaces and dentinal tubules, respectively . Therefore, enamel and dentin are expected to act as semipermeable membranes and that they allow hydrogen peroxide to move according to Fick's second law of diffusion, which describes that the diffusion of a molecule is proportional to the surface area, diffusion coefficient, and concentration, and that it is inversely proportional to the diffusion distance …”

Relationships Between Enamel Prism Decussation and Organization of the Ameloblast Layer in Rodent Incisors

“…It is worth noting that the precise mechanism of the molecular staining of enamel was uncertain at first, although as demonstrated by Kwon et al . () rhodamine can penetrate enamel deeply even without demineralization, so it is probable that our staining simply diffuses through enamel. This interpretation is supported by the fact that prisms are best distinguished with a TRITC staining rather than with a phalloidin‐TRITC one (used for staining cellular membranes), thereby suggesting that the size of the staining agent influences the staining's quality (a smaller agent diffusing more easily).…”

Photosensitizer and light diffusion through dentin in photodynamic therapy

“…[13][14][15] In fact, dentin has been considered a semi-permeable membrane, in which fluid movement through its structure is mainly driven by the tubular channels and the nature of the solute/solvent ratio specified by the solute molecular size, geometrical form, and chemical affinity. 14,15 The permeation of different solutions into dentin has been studied; however, no model was found that could predict a PS and light permeation profile and its concentration throughout the diffusion process.…”