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Tubular Occlusion Prevents Water-treeing and Through-and-Through Fluid Movement in a Single-bottle, One-step Self-etch Adhesive Model

¹ School of Dentistry, Medical College of Georgia, Augusta, GA, USA;
² Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, China;
³ Osaka University Graduate School of Dentistry, Osaka, Japan; and ⁴ Research and Development, Ivoclar-Vivadent AG, Schaan, Liechtenstein;

View larger version (70K): [in a new window]   Figure 1. TEM characterization of the unbonded, unstained, undemineralized, epoxy-resin-infiltrated, carious dentin substrate that remained after polymer bur amputation and silicon carbide paper abrasion. E: epoxy resin. (A) A low-magnification view of the first specimen, showing that the abraded surface corresponded with the transparent zone of carious dentin (TZ; i.e., caries-affected dentin). Transverse sectioning of the dentinal tubules in this zone indicated that the dentinal tubules were completely occluded by intratubular mineral deposits (open arrowhead). In contrast, dentinal tubules in the underlying sound dentin (SD) were either completely empty or contained remnant tubular contents that did not occlude the tubules (pointer). (B) A high-magnification view of the second specimen, showing the occlusion of dentinal tubules with fine, electron-dense intratubular mineral deposits (asterisk). Peritubular dentin cannot be readily discerned from the intertubular dentin in this specimen. (C) A high-magnification view of the transparent zone (TZ) from the third specimen. The dentinal tubules were occluded within intratubular mineral deposits (pointer) that can be distinguished from the peritubular dentin (P). In addition, larger discrete electron-dense caries crystals (arrows) can be identified within the tubular lumen.

View larger version (69K): [in a new window]   Figure 2. TEM micrographs of unstained, undemineralized, silver-impregnated sections, illustrating the application of the experimental single-bottle, one-step self-etch adhesive to carious dentin that remained after polymer bur amputation and SiC paper abrasion. C, resin composite; A, adhesive layer; H, hybrid layer. (A) A low-magnification view of a specimen that was bonded at 0 cm of H2O pressure. The hybrid layer varied from 2–5.5 µm thick. Both the hybrid layer and the adhesive layer were devoid of silver deposits. In contrast, the underlying transparent zone of caries-affected dentin (TZ) was highly porous, with discrete islands of heavy silver deposits (asterisks), and zones of reticular silver deposits (pointer) within the intertubular dentin, as well as within the intratubular mineral deposits located beneath the hybrid layer (open arrowhead). Dentinal tubular orifices (T) were completely occluded with intratubular mineral deposits. (B) A higher-magnification view of another carious dentin specimen that was bonded at 0 cm of H2O pressure, showing a well-sealed hybrid layer and an adhesive layer devoid of silver deposits. The highly porous nature of the transparent zone of carious dentin can be distinguished by the reticular streaks of silver deposits (pointer). The tubular orifice (T) was also completely occluded within intratubular minerals. Additional discrete caries crystals (arrow) can be identified farther down the dentinal tubule. (C) A specimen that was bonded under the application of 20 cm of water pressure. Some nanoleakage can be identified within the hybrid layer (arrows). However, that was relatively mild compared with the heavy reticular silver deposits identified from the transparent zone of carious dentin (TZ). Some of the tubules, probably from a region of sound dentin, were patent and were heavily filled with silver deposits after dentin perfusion. In contrast, the adhesive layer was completely devoid of silver.

View larger version (109K): [in a new window]   Figure 3. TEM micrographs of unstained, undemineralized, silver-impregnated sections, illustrating the application of the experimental single-bottle, one-step self-etch adhesive to sound dentin (SD). Bonding was performed under 0 cm of H2O pressure to permit only evaporative water flux. C, resin composite; A, adhesive layer; H, hybrid layer. (A) Bonded sound dentin taken from the same tooth as the bonded carious dentin in Fig. 2A. The 1-µm-thick hybrid layer was completely occupied by reticular silver deposits (nanoleakage). A layer of silver-impregnated water channels (i.e., water trees) can be seen arising from the surface of the hybrid layer and extending into the adhesive layer (pointer). Additional isolated silver grains (open arrowhead) can be discerned within the adhesive layer. (B) Bonded sound dentin taken from the same tooth as the bonded carious dentin in Fig. 2B. Apart from the presence of extensive nanoleakage within the hybrid layer (H), and the water trees that extended from the surface of the hybrid layer (pointer), extensive water-treeing could be identified throughout the adhesive (open arrowhead). The water trees that were in contact with the resin composite permitted through-and-through water movement and resulted in the entrapment of water blisters along the adhesive-composite interface (open arrow). These relatively smaller water blisters were completely filled with silver deposits.

View larger version (105K): [in a new window]   Figure 4. TEM micrographs of unstained, undemineralized, silver-impregnated sections, illustrating the application of the experimental single-bottle, one-step self-etch adhesive to sound dentin (SD). Bonding was performed under 20 cm of H2O pressure to permit both convective and evaporative water fluxes. C, resin composite; A, adhesive layer; H, hybrid layer. (A) Similar to the specimens bonded without dentin perfusion, the hybrid layer was extensively filled with silver deposits, with water derived from the evaporative water flux extending into the adhesive layer as a layer of water trees (pointer). The effect of convective water flux can be seen as the expression of a large water droplet (B), completely filled with silver deposits, from a patent dentinal tubular orifice (T) into the adhesive layer. Secondary water trees (open arrowhead) can be seen radiating from the circumference of the water droplet. (B) Bonded sound dentin taken from the same specimen from which Fig. 2C was taken. Extensive convective water flux from the array of dentinal tubules (arrows) resulted in the formation of water droplets (asterisk). Through-and-through water movement resulted in the extension of a large water blister into the resin composite. This water blister was partially filled with silver and was retained by the polymerizing composite during light-activation.