Incompatibility of Oxalate Desensitizers with Acidic, Fluoride-containing Total-etch Adhesives
C.K.Y. Yiu1,
N.M. King1,
B.I. Suh2,
L.J. Sharp2,
R.M. Carvalho3,
D.H. Pashley4, and
F.R. Tay1,*
1 Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, 34 Hospital Road, Hong Kong SAR, China;
2 Bisco Inc., Schaumburg, IL, USA;
3 Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil; and
4 Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA, USA;
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Figure 1. SEM micrographs of the dentin side of a fractured beam following application of single-bottle total-etch adhesives to oxalate-desensitizer-treated acid-etched dentin. (A) Spherical globules (arrowheads) with sizes ranging from 2 to 4 µm were preferentially found at the orifices of the dentinal tubules in the PB-SS subgroup. Clusters of smaller globules (arrow) were found between the larger globules. Patent dentinal tubules (pointer) were frequently observed. (B) Spherical globules (pointers) up to 12 µm were also observed in the adhesive layer of the PB-BB subgroup. (C) The dentin side of the OB-BB subgroup was covered with a continuous layer of spherical globules with sizes ranging from 0.5 to 3 µm. Patent dentinal tubules (arrowheads) were evident from the dentin (D) below. (D) No spherical globules could be found on the dentin surface of the SB-SS subgroup. Numerous fractured resin tags (arrowheads) could be seen at the base of the hybrid layer (H).
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Figure 2. Unstained, undemineralized TEM micrographs of oxalate-desensitizer-treated acid-etched dentin specimens that were bonded with single-bottle total-etch adhesives. The bonded specimens were immersed in an ammoniacal silver nitrate tracer solution before laboratory dehydration and epoxy resin embedding. U: undemineralized dentin. (A) A specimen from the PB-SS subgroup, showing extensive nanoleakage (open arrowheads) in the hybrid layer (H) and the dentinal tubule (T). Electronlucent spherical globules (pointer) were depicted in the adhesive layer (A). Silver deposits were occasionally seen within the spherical globules. Discontinuous electronlucent structures with a scalloped margin could be identified along the adhesive-hybrid layer interface (open arrow). Electronlucent crystals, probably representing the calcium oxalate crystals (arrow), were also seen in the dentinal tubules at a position that was 8–10 µm from the dentin surface. (B) A specimen from the OB-BB subgroup, showing fairly extensive nanoleakage (arrowhead) within the hybrid layer (H). Discontinuous electronlucent deposits, with scalloped margins resembling conglomerates of spherical globules (pointer), could be identified along the adhesive-dentin interface. Subsurface electronlucent deposits (asterisk) were also observed in the dentinal tubules (T). (C) A high-magnification view of the hybrid layer in the SB-BB subgroup. Only isolated spots of silver grains (arrowhead) were observed in the hybrid layer (H). No globular structures were identified on the surface of the hybrid layer. The dentinal tubules (beneath the position of the hybrid layer) were blocked by subsurface electronlucent deposits (asterisk). P: polyalkenoic acid copolymer component of the adhesive. (D) A high-magnification view of subsurface angular crystalline deposits (asterisk) within the dentinal tubule (T) in the OS-BB subgroup. No surface globular structures could be identified. Silver deposits (arrowhead) were occasionally observed within the hybrid layer (H). A: adhesive.
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Figure 3. SEM micrograph of cryofractured phosphoric-acid-etched dentin following the application of an oxalate desensitizer. Bi-pyramidal calcium oxalate crystals (open arrowhead) were identified in the dentinal tubules, at 8–10 µm beneath the dentin surface, where calcium ions were available from the adjacent mineralized dentin (D). In contrast, the demineralized collagen matrix (asterisk) was almost completely devoid of these angular crystals. Since no acidic, fluoride-containing dentin adhesive was further applied to the desensitizer-treated dentin, the etched dentin surface was devoid of the spherical calcium-fluoride-like structures. Only demineralized collagen fibrils (pointer) were identified from the surface of the acid-etched dentin.
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