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Water-dependent Interfacial Transition Zone in Resin-modified Glass-ionomer Cement/Dentin Interfaces
F.R. Tay1,*,
S.K. Sidhu2,
T.F. Watson3 and
D.H. Pashley4
1 Pediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, China;
2 Restorative Dentistry, School of Dental Science, University of Newcastle, Newcastle upon Tyne, UK;
3 Department of Conservative Dentistry & Biomaterials, Guy’s, King’s & St Thomas Dental Institute, King’s College London, Guy’s Hospital, London, UK; and
4 Department of Oral Biology and Maxillofacial Pathology, Medical College of Georgia, Augusta, GA, USA;
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Figure 1. Transmission electron micrographs and elemental analyses of the application of Fuji II LC to hydrated dentin (A–C) and dehydrated dentin (D). Both types of substrates were conditioned with GC Dentin Conditioner (10% polyacrylic acid) for 20 sec before placement of the RMGIC. In dehydrated dentin, conditioning was performed prior to the dehydration protocol. (A) A 7- to 10-µm-thick absorption layer (AL) can be seen between the partially demineralized dentin (i.e., hybrid layer [H]; between open arrowheads) and the RMGIC. Phase separation (arrow) can also be observed within the resin matrix (RM). D: mineralized dentin. (B) A high-magnification view showing electron-dense, multilocular phases (arrow) within the absorption layer (AL). A 2-µm-thick, partially demineralized hybrid layer (H; between open arrowheads) is present on top of the mineralized dentin (D). (C) Energy-dispersive x-ray analysis results comparing the elemental distribution and their relative concentrations in the absorption layer and the multilocular phases found in Fuji II LC. Cu originated from the copper specimen grids. (D) When bonded to dehydrated dentin, the RMGIC was in direct contact with the surface of the hybrid layer (H; between open arrowheads). No absorption layer could be identified. Multilocular phases were absent from the resin matrix (RM). D: mineralized dentin.
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Figure 2. Transmission electron micrographs showing silver deposition within the interfaces of Fuji II LC bonded to normal hydrated dentin, after immersion in ammoniacal silver nitrate. (A) An intricate pattern of water channels (water trees) (arrows) can be identified within the absorption layer (AL). H: hybrid layer. (B) Extension of the water trees (pointer) around the glass fillers (G) of the RMGIC. A siliceous hydrogel layer (open arrow) can be seen along the periphery of the glass fillers. Multilocular phases (arrow) within the resin matrix are devoid of silver deposition. Additional unconnected silver grains are identified (open arrowhead).
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Figure 3. Field-emission/environmental scanning electron microscopical images of Photac-Fil Quick bonded to hydrated dentin (A–C) and dehydrated dentin (D) and examined at different relative humidities produced by adjustment of the vapor pressure of the environmental chamber and with the temperature maintained at a constant temperature of 4°C. (A) Hydrated dentin at 100% relative humidity (6.1 Torr). A 7- to 10-µm-thick absorption layer (AL) is present between the RMGIC (C) and the dentin hybrid layer (H). No gap is present along the entire interface. D: dentin. (B). At 90% relative humidity (5.6 Torr), dehydration cracks begin to form between the RMGIC and the absorption layer (arrows). (C) At 75% relative humidity (4.8 Torr), apart from continuing enlargement of existing cracks, vertical cracks begin to form within the absorption layer (pointers), and between the glass filler particles and the resin matrix (open arrowhead). (D) Dehydrated dentin at 100% relative humidity (6.1 Torr). No absorption layer can be identified. A gap (pointer) is present between the RM-GIC (C) and dentin. Fractured glass filler particles (arrow) are seen adjacent to the dentin hybrid layer (H).
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Figure 4. (A) Microtensile bond test results of Fuji II LC and Photac-Fil Quick applied to hydrated dentin and dehydrated dentin. Twenty beams derived from 5 third molars were used for each group (N = 20). Means ± standard deviation for the 4 groups are: 17.6 ± 4.1 MPa (Fuji II LC, hydrated dentin), 0.0 ± 0.0 MPa (Fuji II LC, dehydrated dentin), 18.5 ± 4.9 MPa (Photac-Fil Quick, hydrated dentin), and 0.3 ± 1.4 MPa (Photac-Fil Quick, dehydrated dentin). Groups identified by different lower-case letters are statistically different (P < 0.001). [Note: In Photac-Fil Quick, dehydrated dentin group, 19 of the 20 specimens failed during specimen preparation. The only specimen that remained intact gave a tensile bond strength of 6.25 MPa or 6.25/20 = 0.3 ± 1.4 MPa. The null bond strengths from the other 19 specimens that failed prematurely were included in the statistical analysis to avoid the bias of only measuring "survivors".] (B) Representative scanning electron microscopic image of the dentin side of a fractured beam in hydrated dentin bonded with Photac-Fil Quick. The non-particulate nature of the absorption layer (AL) can be clearly observed, with the presence of artifactual dehydration cracks (open arrowhead) similar to those seen in Fig. 3D . C: fractured RMGIC. Similar features were observed in debonded specimens of Fuji II LC bonded to hydrated dentin (not shown). (C) Representative scanning electron microscopic image of the dentin side of a fractured beam in dehydrated dentin bonded with Photac-Fil Quick. The absorption layer is absent, and failure occurred between the RMGIC (C) and the surface of the hybrid layer (H). Note opening of the dentinal tubules. Similar features were seen in Fuji II LC bonded to dehydrated dentin (not shown).
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Journal of Dental Research, Vol. 83, No. 8,
644-649 (2004)
DOI: 10.1177/154405910408300812
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