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Aging Affects Two Modes of Nanoleakage Expression in Bonded Dentin

¹ Faculty of Dentistry, University of Hong Kong, Hong Kong SAR, China;
² Division of Pediatric Dentistry, Hokkaido University, Graduate School of Dental Medicine, Sapporo, Hokkaido, Japan;
³ Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA; and
⁴ Department of Cariology, Restorative Sciences and Endodontics, School of Dentistry, University of Michigan, Ann Arbor, MI, USA;

View larger version (975K): [in a new window]   Figure 1. TEM micrographs depicting the changes in silver tracer penetration within the hybrid layers of an experimental total-etch filled adhesive after aging in artificial saliva. (A) An overall view of the resin-dentin interface in a 24-hour specimen. High-magnification views of the hybrid layers are shown after aging for: (B) 24 hrs, (C) 1 mo, (D) 3 mos, (E) 6 mos, and (F) 12 mos. Reticular silver deposits (pointers) that were initially identified within the bulk of hybrid layers were gradually reduced, and were replaced by the accumulation of similar deposits along the hybrid layer-adhesive interface. Water trees (open arrowheads) that began to form along this interface at 6 mos were clearly evident after 12 mos. There was also an increase in the size and density of the isolated silver grains (arrows) during the entire storage period. C, resin composite; FA, filled adhesive; T, dentinal tubule; U, undemineralized dentin.

View larger version (637K): [in a new window]   Figure 2. High-magnification TEM micrographs showing the changes that occurred around the isolated silver grains (arrows) in the filled adhesive layer (FA) after aging in artificial saliva. (A) 24 hrs, (B) 1 mo, (C) 3 mos, (D) 6 mos, and (E) 12 mos. Isolated silver grains increased in size and density, and some were eventually surrounded by a secondary rosette of silver grains (C, D). The precursors of water-filled channels (i.e., water trees) that could be seen at 6 mos were attributed to the increase in density of these rosettes of silver grains. Frank water trees were evident at 12 mos (E). A siliceous hydrogel layer (arrowheads) could also be observed along the periphery of the fluoroaluminosilicate glass fillers (G) beginning at 3 mos.

View larger version (575K): [in a new window]   Figure 3. TEM micrographs showing the changes in silver tracer penetration along the resin-dentin interfaces after aging in oil (control). (A) 6 mos, (B-D) 12 mos. Pointer, reticular patterns of silver deposits; arrow, isolated silver grains; C, resin composite; FA, filled adhesive; H, hybrid layer; T, dentinal tubule; U, undemineralized dentin; G, fluoroaluminosilicate glass fillers. (A) Up to 6 mos, islands of heavy silver deposits could still be seen in the hybrid layers. (B) An overall view of a specimen examined after aging in oil for 12 mos revealed a considerable reduction of these bulk deposits to reticular silver patterns. (C) A high-magnification view of the hybrid layer in the 12-month specimen, showing that the extent of the reticular silver deposits within the hybrid layer was similar to that in the one-month specimen that was stored in artificial saliva (Fig. 1C). (D) A high-magnification view of the adhesive layer in the 12-month specimen revealed fine, sparsely distributed isolated silver grains that were devoid of rosettes or water tree formation.

View larger version (16K): [in a new window]   Figure 4. Percentage distribution of silver deposits within the hybrid layers of specimens aged in different media for up to 12 mos. Both modes of silver deposition in the hybrid layers are included, since we could not distinguish between the reticular patterns and the isolated silver grains during image analyses. Groups identified by different letter are significantly different (p < 0.05). M, month. In box plots, the distance between the upper and lower brackets includes 80% of the values. The box includes 50% of the values. The horizontal line in the box represents the median.