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Interaction of Glass-ionomer Cements with Moist Dentin

¹ Paediatric Dentistry and Orthodontics, Faculty of Dentistry, University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, China;
² Department of Oral Biology and Maxillofacial Pathology, Medical College of Georgia, Augusta, GA, USA;
³ Department of Restorative Dentistry, University of Newcastle, Newcastle upon Tyne, UK;
⁴ Department of Restorative Dentistry, National University of Singapore, Singapore;
⁵ Department of Dental Materials, University of Granada, Spain; and
⁶ Electron Microscopy Unit, University of Hong Kong, Hong Kong SAR, China;

View larger version (447K): [in a new window]   Figure 1. SEM images of fractured interfaces in dentin bonded with Fuji VII. Similar results were observed with the other GICs. (A) Dentin side of a representative beam fractured along the GIC-dentin interface. Despite the presence of artifactual cracks (arrow), numerous spherical bodies (pointer) could be seen within the fractured GIC. IL, intermediate layer; D, dentin. (B) Corresponding GIC side of fractured beam in (A), showing presence of similar spherical bodies (pointers). (C) High-magnification view contrasts the difference between spherical bodies (S) and angular fluoro-aluminosilicate glass (FASG) fillers (F). The spaces (asterisk) between the matrix and the spherical bodies are a result of shrinkage of the matrix (M) during specimen preparation of conventional SEM. (D) High-magnification view of (A), showing a partially fractured, hollow spherical body with evidence of brittle fracture (pointer) observed in the walls of the fractured eggshell-like structure. (E) When GIC beams were fractured 3 mm away from the GIC-dentin interface, only air-voids (pointer) could be identified. No spherical body could be seen. M, polyalkenoate matrix; G, FASG filler; arrow, dehydration crack.

View larger version (373K): [in a new window]   Figure 2. FE-ESEM images of fractured interfaces in dentin bonded with Fuji IX GP. The fractured specimens were examined wet and without further coating. (A) Similar to the conventional SEM images, the dentin sides of fractured beams examined in a FE-ESEM showed similar spherical bodies (arrows) closely adapted to the adjacent polyalkenoate matrix. At these very small vacuums, no cracks were seen in the fractured GIC. (B) A small crack (pointer) began to appear in the polyalkenoate matrix, adjacent to a spherical body, as the vapor pressure was reduced to 5.4 Torr. (C) Shrinkage of the polyalkenoate matrix resulted in irreversible separation of the latter from the spherical bodies, even after the vapor pressure was returned to 5.6 Torr. A fractured spherical body revealed the presence of a solid core that was probably due to the retention of water within the eggshell-like structure. (D) Fractured unbonded Fuji IX GP (control) showed the absence of spherical bodies within the polyalkenoate matrix. Only air-voids (arrows) could be observed. (E) EDX analysis of Fuji IX GP-bonded dentin that was fractured along the GIC-dentin interface and examined with FE-ESEM. The elemental composition included Ca and P within the polyalkenoate matrix and Si in the spherical bodies and FASG fillers.

View larger version (141K): [in a new window]   Figure 3. FE-ESEM images of polished, intact interfaces that were bonded with Fuji VII. The polished surfaces were briefly etched with phosphoric acid to remove the smear layer and to bring the interfaces into relief. (A) Representative example from specimens with the exposed GIC surface sealed with resin immediately after placement. A spherical body, still embedded within the polyalkenoate matrix, was seen 150 µm away from the bonded dentin (D). Another spherical body (open arrow) was probably dislodged from an adjacent air-void (arrow). No spherical bodies were observed from either the bonded enamel or along the exposed GIC surface (not shown). (B) Representative example from specimens in which the exposed GIC surface was not sealed and exposed to water for 10 min prior to storage at 100% relative humidity. The surface of the GIC was partially fractured during sectioning, exposing a spherical body (pointer) that was about 30 µm away from the unsealed GIC surface (US). Another partially intact spherical body (open arrowhead) could be seen further down the polished surface at about 180 µm from the unsealed GIC surface. Only air-voids could be identified further down the polished surface.

View larger version (269K): [in a new window]   Figure 4. TEM images of regions that were close to the GIC-dentin interfaces. (A). The GIC-dentin interface in ChemFlex showed the presence of a 3-µm-thick, partially demineralized, intermediate layer (IL; between open arrows) between the dentin (D) and the fractured GIC (GIC). The originally intact GIC was fractured during ultramicrotomy. FASG fillers (pointer) with a peripheral siliceous hydrogel layer (arrowhead) could be seen within the remnant GIC. T, dentinal tubule. (B) A high-magnification view of the polyalkenoate matrix (M) from a dentin specimen that was bonded with the experimental GIC K-136 (Dentsply DeTrey). Siliceous hydrogel layers (pointer) could be seen along the periphery of the FASG fillers (G). Within the siliceous hydrogel layer, numerous "seed-like", electron-dense fluoride-rich phases could be observed (open arrows). (C) A high-magnification view of the polyalkenoate matrix that was sectioned close to the GIC-dentin interface in ChemFlex. A portion of the wall of a hollow spherical body (S) could be seen. This wall resembled the adjacent polyalkenoate matrix (M) in ultrastructural appearance, but was separated from the latter. ESp, empty space that was occupied by the Formvar-coated copper grid.