Title Failure of a glass ionomer to remineralize apatite - depleteddentin

Remineralization of demineralized dentin lesions adjacent to glass-ionomer cements (GICs) has been reported in the literature. This study tested the hypothesis that a strontium-based GIC can remineralize completely demineralized dentin by nucleation of new apatite crystallites within an apatite-free dentin matrix. Human dentin specimens were acid-etched, bonded with Fuji IXGP, and immersed in a calcium-and-phosphate-containing 1.5X simulated body fluid (SBF) for 1-4 months. Polyacrylic acid and polyvinylphosphonic acid biomimetic analogs were added to the SBFs to create 2 additional remineralization media. Specimens were processed by transmission electron microscopy (TEM). No apatite deposition could be identified in the completely demineralized dentin in any of the specimens immersed in the 3 remineralization media, despite TEM/EDX evidence of diffusion of ions specific to the strontium-based GIC into the demineralized dentin. The hypothesis was rejected; mineral concentration alone is not a sufficient endpoint for assessing the success of contemporary remineralization strategies. KEY WOrDs: glass-ionomer cement, demineralized dentin, remineralization, apatite, ion diffusion. INtrODUctION Glass-ionomer cements (GICs) have been widely used in restorative dentistry (Mount, 1998), due to their self-adhesive and fluoride-releasing properties (Naasan and Watson, 1998). Indirect evidence of the ability of GICs to remineralize artificial caries lesions was based on the results of microradiography and micro-computed tomography (Creanor et al., 1998; Exterkate et al., 2005; Lee et al., 2008). The use of energy-dispersive x-ray microanalysis (EDS) (Massara et al., 2002) and electron probe microanalysis (EPMS) (Kitasako et al., 2003; Ab-Ghani et al., 2007) further revealed changes in mineral profiles of specific elements across the GIC-tooth interface. Despite evidence of ion exchange between GICs and dentin at a chemical level (Coutinho et al., 2007), there is no direct ultrastructural evidence of interfibrillar or intrafibrillar remineralization of the demineralized collagen matrix. Intrafibrillar remineralization, in particular, is crucial for restoring the mechanical properties of partially mineralized dentin to those of mineralized dentin (Kinney et al., 2003). A recent report presented a successful strategy for in situ remineralization of phosphoric-acid-etched dentin in the presence of biomimetic analogs (Tay and Pashley, 2008). In that study, transmission electron microscopy (TEM) and electron diffraction were used to establish definitive evidence of interfibrillar and intrafibrillar apatite deposition within the collagen fibrils of the demineralized dentin matrix. These ultrastructural techniques were indispensible in discriminating the dimensions and ordered arrangement of apatite platelets in mineralized tissues (Traub et al., 1989). Incorporation of biomimetic analogs of non-collagenous proteins into the remineralization medium helped to stabilize amorphous calcium phosphate precursors in their nanoscale dimensions (Zhang and Webster, 2009). The analogs further served as templates that guided the self-assembly of the stabilized nanoprecursors along specific sites of the collagen fibrils (Gajjeraman et al., 2007), their subsequent transformation into nanoapatites, and fusion into conventional apatite crystallites. These phenomena were thought to proceed via the non-classic crystallization pathways of “bottom-up” nanoparticle assembly and mesocrystalline transformation (Niederberger and Cölfen, 2006). Fuji IXGP (GC International, Tokyo, Japan) is a strontium-based GIC developed for the Atraumatic Restorative Treatment of carious dentin (Massara et al., 2002; Amaral et al., 2006). It has been demonstrated that ions specific to Fuji IXGP penetrated deeply into caries-affected dentin (Ngo et al., 2006). Those Failure of a Glass Ionomer to remineralize Apatite-depleted Dentin rEsEArcH rEPOrts biomaterials & bioengineering at University of Hong Kong Libraries on January 5, 2011 jdr.sagepub.com Downloaded from J Dent Res 89(3) 2010 Fuji IXGP Did Not Remineralize Dentin 231 authors considered the presence of strontium and aluminum ions in the demineralized dentin matrix as evidence of a remineralization process. In this study, we challenged the ability of Fuji IXGP to remineralize completely demineralized dentin at an ultrastructural level by testing the hypothesis that the strontium-based GIC can successfully remineralize completely demineralized dentin by nucleation of new apatite crystallites within an apatite-free dentin matrix.