Yong Wang

Bio: Yong Wang is an academic researcher from University of Missouri–Kansas City. The author has contributed to research in topics: Dentin & Adhesive. The author has an hindex of 46, co-authored 145 publications receiving 6380 citations.

Adhesive/Dentin Interface: The Weak Link in the Composite Restoration

Abstract: Results from clinical studies suggest that more than half of the 166 million dental restorations that were placed in the United States in 2005 were replacements for failed restorations. This emphasis on replacement therapy is expected to grow as dentists use composite as opposed to dental amalgam to restore moderate to large posterior lesions. Composite restorations have higher failure rates, more recurrent caries, and increased frequency of replacement as compared to amalgam. Penetration of bacterial enzymes, oral fluids, and bacteria into the crevices between the tooth and composite undermines the restoration and leads to recurrent decay and premature failure. Under in vivo conditions the bond formed at the adhesive/dentin interface can be the first defense against these noxious, damaging substances. The intent of this article is to review structural aspects of the clinical substrate that impact bond formation at the adhesive/dentin interface; to examine physico-chemical factors that affect the integrity and durability of the adhesive/dentin interfacial bond; and to explore how these factors act synergistically with mechanical forces to undermine the composite restoration. The article will examine the various avenues that have been pursued to address these problems and it will explore how alterations in material chemistry could address the detrimental impact of physico-chemical stresses on the bond formed at the adhesive/dentin interface.

Adhesive phase separation at the dentin interface under wet bonding conditions.

Abstract: Under in vivo conditions, there is little control over the amount of water left on the tooth and, thus, there is the danger of leaving the dentin surface so wet that the bonding resin undergoes physical separation into hydrophobic and hydrophilic-rich phases. The purpose of this study was to investigate phase separation in 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane (BisGMA)-based adhesive using molecular microanalysis and to examine the effect of phase separation on the structural characteristics of the hybrid layer. Model BisGMA/HEMA (hydroxyethl methacrylate) mixtures with/without ethanol and commercial BisGMA-based adhesive (Single Bond) were combined with water at concentrations from 0 to 50 vol%. Macrophase separation in the BisGMA/HEMA/water mixtures was detected using cloud point measurements. In parallel with these measurements, the BisGMA/HEMA and adhesive/water mixtures were cast as films and polymerized. Molecular structure was recorded from the distinct features in the phase-separated adhesive using confocal Raman microspectroscopy (CRM). Human dentin specimens treated with Single Bond were analyzed with scanning electron microscopy (SEM) and CRM mapping across the dentin/adhesive interface. The model BisGMA/HEMA mixtures with ethanol and the commercial BisGMA-based adhesive experienced phase separation at ∼25 vol% water. Raman spectra collected from the phase-separated adhesive indicated that the composition of the particles and surrounding matrix material was primarily BisGMA and HEMA, respectively. Based on SEM analysis, there was substantial porosity at the adhesive interface with dentin. Micro-Raman spectral analysis of the dentin/adhesive interface indicates that the contribution from the BisGMA component decreases by nearly 50% within the first micrometer. The morphologic results in corroboration with the spectroscopic data suggest that as a result of adhesive phase separation the hybrid layer is not an impervious 3-dimensional collagen/polymer network but a porous web characterized by hydrophobic BisGMA-rich particles distributed in a hydrophilic HEMA-rich matrix. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 62: 447–456, 2002

Hybridization Efficiency of the Adhesive/Dentin Interface with Wet Bonding

Abstract: Although it is generally proposed that dentin bonding results from adhesive infiltration of superficially demineralized dentin, it is not clear how well the resin monomers seal the dentin collagen fibrils under wet bonding conditions. The aim of this study was to determine the quality and molecular structure of adhesive/dentin (a/d) interfaces formed with wet bonding as compared with adhesive-infiltrated demineralized dentin (AIDD) produced under controlled conditions (optimum hybrid). From each extracted, unerupted human 3rd molar, one fraction was demineralized, dehydrated, and infiltrated with Single Bond (SB) adhesive under optimum conditions; the remaining, adjacent fraction was treated with SB by wet bonding. AIDD and a/d interface sections were stained with Goldner's trichrome; corresponding sections were analyzed with micro-Raman spectroscopy. The histomorphologic and spectroscopic results suggest that, under wet bonding, the a/d interface is a porous collagen web infiltrated primarily by the hydrolytically unstable HEMA.

Role of Hyperphosphatemia and 1,25-Dihydroxyvitamin D in Vascular Calcification and Mortality in Fibroblastic Growth Factor 23 Null Mice

Abstract: Fibroblastic growth factor 23 (FGF23) regulates renal phosphate reabsorption and 1alpha-hydroxylase activity. Ablation of FGF23 results in elevated serum phosphate, calcium, and 1,25-dihydroxyvitamin D3 [1,25(OH)(2)D] levels; vascular calcifications; and early death. For determination of the independent roles of hyperphosphatemia and excess vitamin D activity on the observed phenotypic abnormalities, FGF23 null mice were fed a phosphate- or vitamin D-deficient diet. The phosphate-deficient diet corrected the hyperphosphatemia, prevented vascular calcifications, and rescued the lethal phenotype in FGF23 null mice, despite persistent elevations of serum 1,25(OH)(2)D and calcium levels. This suggests that hyperphosphatemia, rather than excessive vitamin D activity, is the major stimulus for vascular calcifications and contributes to the increased mortality in the FGF23-null mouse model. In contrast, the vitamin D-deficient diet failed to correct either the hyperphosphatemia or the vascular calcifications in FGF23 null mice, indicating that FGF23 independently regulates renal phosphate excretion and that elevations in 1,25(OH)(2)D and calcium are not sufficient to induce vascular calcifications in the absence of hyperphosphatemia. The vitamin D-deficient diet also improved survival in FGF23 null mice in association with normalization of 1,25(OH)(2)D and calcium levels and despite persistent hyperphosphatemia and vascular calcifications, indicating that excessive vitamin D activity can also have adverse effects in the presence of hyperphosphatemia and absence of FGF23. Understanding the independent and context-dependent interactions between hyperphosphatemia and excessive vitamin D activity, as well as vascular calcifications and mortality in FGF23 null mice, may ultimately provide important insights into the management of clinical disorders of hyperphosphatemia and excess vitamin D activity.

Interfacial Chemistry of the Dentin/Adhesive Bond

Abstract: To date, the dentin/adhesive (d/a) bond has primarily been studied by morphologic analysis in conjunction with bond strength measurement. Although these analyses have enhanced our understanding, numerous questions about the chemistry have not been answered. The purpose of this study was to determine, at the molecular level, quantitative differences in the composition of the d/a interface formed under "wet" bonding conditions. The occlusal one-third of the crown was removed from 10 extracted, unerupted human third molars. The prepared dentin surfaces were treated, per manufacturers' instructions, with either Single Bond (3M) or One-Step adhesive (Bisco). Three-micron-thick sections of the d/a interface were cut and stained with Goldner trichrome for light microscopy. Companion slabs were analyzed with micro-Raman spectroscopy; the sample was placed at the focus of a 100x microscope objective, and spectra were acquired at 1-microm intervals across the d/a interface. Reference spectra were collected on model compounds of type I collagen and adhesive; the relative ratios of the integrated intensities of spectral features from adhesive and collagen were determined and plotted as a function of wt% adhesive. The same ratios were determined for the interface samples; by comparing these ratios with the calibration curve generated from the model compounds, we determined the percent of adhesive as a function of spatial position across the d/a interface. The relative percent of Single Bond adhesive was or = 50% throughout most of the hybrid. The results from this study provide the first direct chemical evidence of phase separation in a dentin adhesive and its detrimental effect on the dentin/adhesive bond.

The Amazing Osteocyte

Abstract: The last decade has provided a virtual explosion of data on the molecular biology and function of osteocytes. Far from being the “passive placeholder in bone,” this cell has been found to have numerous functions, such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. The osteocyte is a source of soluble factors not only to target cells on the bone surface but also to target distant organs, such as kidney, muscle, and other tissues. This cell plays a role in both phosphate metabolism and calcium availability and can remodel its perilacunar matrix. Osteocytes compose 90% to 95% of all bone cells in adult bone and are the longest lived bone cell, up to decades within their mineralized environment. As we age, these cells die, leaving behind empty lacunae that frequently micropetrose. In aged bone such as osteonecrotic bone, empty lacunae are associated with reduced remodeling. Inflammatory factors such as tumor necrosis factor and glucocorticoids used to treat inflammatory disease induce osteocyte cell death, but by different mechanisms with potentially different outcomes. Therefore, healthy, viable osteocytes are necessary for proper functionality of bone and other organs. © 2011 American Society for Bone and Mineral Research.

Fibroblast growth factor 23 and mortality among patients undergoing hemodialysis.

Abstract: BACKGROUND Fibroblast growth factor 23 (FGF-23) is a hormone that increases the rate of urinary excretion of phosphate and inhibits renal production of 1,25-dihydroxyvitamin D, thus helping to mitigate hyperphosphatemia in patients with kidney disease. Hyperphosphatemia and low 1,25-dihydroxyvitamin D levels are associated with mortality among patients with chronic kidney disease, but the effect of the level of FGF-23 on mortality is unknown. METHODS We examined mortality according to serum phosphate levels in a prospective cohort of 10,044 patients who were beginning hemodialysis treatment and then analyzed FGF-23 levels and mortality in a nested case-control sample of 200 subjects who died and 200 who survived during the first year of hemodialysis treatment. We hypothesized that increased FGF-23 levels at the initiation of hemodialysis would be associated with increased mortality. RESULTS Serum phosphate levels in the highest quartile (>5.5 mg per deciliter [1.8 mmol per liter]) were associated with a 20% increase in the multivariable adjusted risk of death, as compared with normal levels (3.5 to 4.5 mg per deciliter [1.1 to 1.4 mmol per liter]) (hazard ratio, 1.2; 95% confidence interval [CI], 1.1 to 1.4). Median C-terminal FGF-23 (cFGF-23) levels were significantly higher in case subjects than in controls (2260 vs. 1406 reference units per milliliter, P<0.001). Multivariable adjusted analyses showed that increasing FGF-23 levels were associated with a monotonically increasing risk of death when examined either on a continuous scale (odds ratio per unit increase in log-transformed cFGF-23 values, 1.8; 95% CI, 1.4 to 2.4) or in quartiles, with quartile 1 as the reference category (odds ratio for quartile 2, 1.6 [95% CI, 0.8 to 3.3]; for quartile 3, 4.5 [95% CI, 2.2 to 9.4]; and for quartile 4, 5.7 [95% CI, 2.6 to 12.6]). CONCLUSIONS Increased FGF-23 levels appear to be independently associated with mortality among patients who are beginning hemodialysis treatment. Future studies might investigate whether FGF-23 is a potential biomarker that can be used to guide strategies for the management of phosphorus balance in patients with chronic kidney disease.