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BIOLOGICAL RISKS OF RESIN-BASED MATERIALS TO THE DENTIN-PULP COMPLEX

Department of Cariology and Endodontics, Departement of Dental Materials, School of Dental Medicine, University of Geneva, 19 Rue Barthélemy-Menn, CH-1205 Geneva, Switzerland; serge.bouillaguet{at}medecine.unige.ch

View larger version (57K): [in a new window]   Figure 1. Schematic of convergence of tubules toward the pulp. (A) Periphery of the dentin. Most surface area is occupied by intertubular dentin (), with a few tubules surrounded by hypermineralized peritubular dentin (). (B) Near the pulp, the increase in tubule diameter has occurred largely at the expense of the peritubular dentin. This substrate has a high protein content. As the remaining dentin is made thinner (from A to B), the permeability of the dentin increases, because both diameter and density of dentinal tubules are increased. Reprinted with permission from Elsevier.

View larger version (77K): [in a new window]   Figure 2. In vivo diffusion through dentin of a solution of silver nitrate. (A) Diffusion of silver particles (arrows) across dentinal tubules 35 min after the application of a silver nitrate solution () inside the cavity (HE staining x 40). (B) Penetration of silver particles () into the pulp area and into the capillary system active at clearing the pulp (HE staining x 40).

View larger version (144K): [in a new window]   Figure 3. The dentin-pulp complex. The dentin and pulp exist together as an integrated unit. The functional barrier that develops between the odontoblasts prevents the passage of macromolecules from the pulp into the predentin and dentin (HE staining x 40).

View larger version (146K): [in a new window]   Figure 4. Tertiary dentin. Tertiary dentin formation (arrows) is regarded as an important defense mechanism of the pulp-dentin complex in response to either pathological or physiological insults. The presence of tertiary dentin reduces dentin permeability.

View larger version (130K): [in a new window]   Figure 5. Bonding resin-based materials to enamel. Acid-etching of enamel prior to adhesive application allows for a good wetting of the surface by the hydrophobic resin and a good penetration into the microporosities created by the acid (orig. mag. x 2400).

View larger version (330K): [in a new window]   Figure 6. Modified SEM illustration of bonding to dentin with conventional (three-step) total-etching adhesives. (A) Acid etching of the dentin. The smear layer has been removed, and both peritubular and intertubular dentin is demineralized. The exposed collagen fibers are highly hydrophilic (blue) and particularly sensitive to dehydration. (B) Priming of the dentin. The water has been replaced by hydrophilic primers (orange) which have impregnated the collagen fibers. Priming with water-based primers is a slow diffusing process. The evaporation of the water solvent will leave the collagen fibers coated and stiffened by the resins. The substrate has changed from hydrophilic to hydrophobic. (C) Application of the adhesive resin. The hydrophobic resin (red) diffuses into the dentinal tubules and impregnates the entire depth of the demineralized dentin before being polymerized.

View larger version (211K): [in a new window]   Figure 7. Modified SEM image of bonding to dentin with one-bottle (two-step) total-etching adhesives. (A) Acid-etched dentin (blue). (B) Application of the primer/adhesive mixture. The organic solvents used in these mixtures (green) quickly displace water in the collagen network because of the diffusion gradient they create between the water of the collagen and solvent in the bonding agent. Therefore, the incorporation of the primer and the bonding resin inside the collagen network can occur simultaneously.

View larger version (326K): [in a new window]   Figure 8. Modified SEM image of bonding to dentin with (two-step) self-etching adhesives. (A) The smear-layer covering the dentin surface and the smear-plugs occluding the dentinal tubules are impregnated by the self-etching primer (light blue). (B) Application of the acidic primer. The acidic resin (blue) has dissolved and impregnated the smear layer. The resin has also penetrated the dentinal tubules. (C) Dentinal substrate after application of the adhesive resin. Theoretically, the adhesive resin (purple) infiltrates to the same extent as the acidic primer exposed the collagen.

View larger version (119K): [in a new window]   Figure 9. Defective bonding. SEM micrograph of a specimen that was overdried after the etching gel was rinsed off. In such cases, the adhesive resin cannot penetrate the demineralized dentin because of the collapse of the collagen network (arrows) (orig. mag. x 10,000).