Jun Sik Son

Drug delivery from hydroxyapatite-coated titanium surfaces using biodegradable particle carriers.

The goal of this study was to develop a functional titanium (Ti) implant loaded with bioactive molecules using biodegradable polymeric particles as drug delivery carrier for dental applications. In this study, dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) particles were electrostatically immobilized on a Ti disc surface coated with hydroxyapatite (HA) nanocrystals using a low temperature high speed collision (LTHSC) method. Resorbable blasting media (RBM) Ti discs (S1), HA-Ti discs (S2), and HA-Ti discs treated with DEX-loaded PLGA particles (S3) were fabricated in this study as sample discs. To facilitate surface immobilization, PLGA particles were coated with polyethyleneimine (PEI) to produce a positive surface charge. This modification of PLGA particle surfaces, allowed DEX-loaded PLGA particles to be immobilized on negatively charged S2 disc surface. It was found that DEX-loaded PLGA particles were well dispersed and immobilized onto the S3 disc surfaces. Release profile studies of DEX from S3 discs in a 4-week immersion study indicated an initial burst release followed by sustained release. In vitro evaluation of bone marrow derived mesenchymal stem cells (BMSCs) cultured for 1 and 2 weeks on S3 discs showed greater BMSC differentiation than on S1 or S2 discs, demonstrating that this innovative delivery platform potently induced BMSC differentiation in vitro, and suggesting that it could be exploited for stem cell therapy purposes or to enhance in vivo osteogenesis. In addition, the results of the present study shows that various bioactive molecules that promote bone regeneration can be efficiently incorporated onto HA-Ti surfaces using biodegradable polymeric particles.

Influence of surface energy parameters of dental self-adhesive resin cements on bond strength to dentin

The purpose of this study was to determine the surface energy parameters of dental self-adhesive resin cements (SRCs) and to measure their bond strength to dentin. Six dental SRCs (RelyX Unicem Clicker, RU; Maxcem Elite, ME; BisCem, BC; Clearfil SA Luting, SA; Multilink Speed, MS; seT PP, SP) and one resin-modified glass ionomer cement (RelyX Luting 2, RL; control) were tested. Smear layer-covered bovine dentin was used as bonding substrate. Using the dynamic sessile drop method, surface energy, surface energy components, degree of hydrophobicity/hydrophilicity (expressed as ΔG sws using thermodynamic notation), and apparent surface energies for each material were calculated. The luting cements were bonded to the dentin and stored in water at 37 °C for 24 h prior to shear bond strength test (n = 10). Pearson correlation analysis was applied to detect possible correlations between surface energy parameters and measured shear bond strength (α = 0.05). RU, SA, and MS produced negative ΔG sws values (hydrophobic), whereas ME, BC, SP, and RL yielded positive ones (hydrophilic). RU had the highest value among all six SRCs tested, the value for MS being statistically equivalent (p = 0.785). The base component, ΔG sws, and surface energy determined with water showed significant negative linear correlations with dentin bond strength (r/p = −0.801/0.030, −0.900/0.006, and −0.892/0.007, respectively). These results suggest that bonding to smear layer-covered bovine dentin was governed by the base component and the hydrophobicity/hydrophilicity of the SRCs.

Osteogenic evaluation of calcium phosphate scaffold with drug-loaded poly (lactic-co-glycolic acid) microspheres in beagle dogs

The goal of this study was to develop a bioactive hydroxyapatite (HA) scaffold as a calcium phosphatebased bioceramic using drug-loaded polymeric microspheres for bone regeneration. Dexamethasone (DEX) as a model bioactive molecule and poly (lactic-co-glycolic acid) (PLGA) microspheres as a carrier were employed. Polyethyleneimine was coated on DEX-loaded PLGA microsphere surfaces, resulting in a net positively-charged surface. With such modification of the PLGA microsphere surfaces, DEX-loaded PLGA microspheres were immobilized on the negatively charged HA scaffold surfaces. The release profile of DEX over a 4-week immersion study indicated an initial burst release followed by a sustained release. In vivo evaluation of the defects filled with DEX-loaded HA scaffolds indicated that new bone formation was enhanced when compared to defects that were either unfilled or filled only with HA scaffold. This innovative platform for bioactive molecule delivery more potently induced osteogenesis in vivo, which may be exploited in implantable bone graft substitutes for stem cell therapy or improved in vivo performance.

Microstructures and Mechanical Properties of Co-Cr Dental Alloys Fabricated by Three CAD/CAM-Based Processing Techniques

The microstructures and mechanical properties of cobalt-chromium (Co-Cr) alloys produced by three CAD/CAM-based processing techniques were investigated in comparison with those produced by the traditional casting technique. Four groups of disc- (microstructures) or dumbbell- (mechanical properties) specimens made of Co-Cr alloys were prepared using casting (CS), milling (ML), selective laser melting (SLM), and milling/post-sintering (ML/PS). For each technique, the corresponding commercial alloy material was used. The microstructures of the specimens were evaluated via X-ray diffractometry, optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy, and electron backscattered diffraction pattern analysis. The mechanical properties were evaluated using a tensile test according to ISO 22674 (n = 6). The microstructure of the alloys was strongly influenced by the manufacturing processes. Overall, the SLM group showed superior mechanical properties, the ML/PS group being nearly comparable. The mechanical properties of the ML group were inferior to those of the CS group. The microstructures and mechanical properties of Co-Cr alloys were greatly dependent on the manufacturing technique as well as the chemical composition. The SLM and ML/PS techniques may be considered promising alternatives to the Co-Cr alloy casting process.

Effect of heat treatment of dental zirconia ceramic treated with three different primers on the bonding durability of resin cement

AbstractEstablishing a durable bond with dental zirconia ceramic remains difficult. This study investigated the effect of heat treatment of primer-coated dental zirconia on the bonding durability of resin cement to the zirconia. Each of three types of primers (silane primer, acidic monomer-containing primer, and silane/acidic monomer containing two-component primer) was applied to sandblasted zirconia surfaces. For subsequent heat treatment, half were then put in a furnace for 60 min at 150 °C. All specimens were bonded with resin cement and aged using thermocycling (0, 5,000, and 20,000 cycles) prior to a shear test. The surface energy parameters of the zirconia were also calculated from the contact angle measurements based on the acid-base theory. The heat treatment enhanced the bonding durability of the zirconia pre-treated with the silane primer and the acidic monomer-containing one, the shear test and Weibull analysis results showed that the former performed better than the latter. In contrast, the twocomponent primer-coated zirconia showed poor bonding durability after the heat treatment. The bonding performance was related to the surface characteristics of the zirconia. Thus, we suggest that heat treatment of zirconia pretreated with silane primer effectively improves bonding durability with resin cement.

A Simple 2-step Silane Treatment for Improved Bonding Durability of Resin Cement to Quartz Fiber Post

INTRODUCTION This study examined a clinically feasible protocol for improving hydrolytic stability using a 2-step silanization including a nonorganofunctional silane. METHODS The surfaces of 24 D.T. Light-Posts (Bisco Inc, Schaumburg, IL) were polished and assigned to the following 4 groups: M: 1-step silanization with Monobond-S (MS) (Ivoclar Vivadent, Schaan, Liechtenstein); BM: 2-step silanization with 5% 1,2-bis(triethoxysilyl)ethane and then MS; and HM and HBM: 1-step and 2-step silanization, respectively, after 24% H2O2 etching. Four resin composite cylinders (RelyX Unicem; 3M ESPE, St Paul, MN) were bonded on each surface according to a microshear testing protocol. All bonded samples were stored in water at 37°C for 24 hours, and half of them were then thermocycled 5000 times before microshear testing (n = 12). The failure modes were evaluated under an optical and scanning electron microscope. Water contact angles were measured on the post surfaces before and after silanization to estimate surface hydrophobicity. The results were statistically analyzed using 2-way analysis of variance and the Tukey test. RESULTS The bond strengths for the BM and HBM groups were significantly higher than the M and HM groups at 5000 thermocycles (P < .05), whereas no significant differences were found between the 4 groups before thermocycling (P > .05). All debonded samples showed some fractured fibers. No significant difference in the hydrophobicity was found between the 1-step and 2-step silanized post surfaces (P > .05). CONCLUSIONS The 2-step 1,2-bis(triethoxysilyl)ethane/MS treatment has potential as a silanization procedure for enhancing the hydrolytic stability of the fiber post/resin composite interface.

Influence of Curing Mode on the Surface Energy and Sorption/Solubility of Dental Self-Adhesive Resin Cements

This study investigated the influence of curing mode (dual- or self-cure) on the surface energy and sorption/solubility of four self-adhesive resin cements (SARCs) and one conventional resin cement. The degree of conversion (DC) and surface energy parameters including degree of hydrophilicity (DH) were determined using Fourier transform infrared spectroscopy and contact angle measurements, respectively (n = 5). Sorption and solubility were assessed by mass gain or loss after storage in distilled water or lactic acid for 60 days (n = 5). A linear regression model was used to correlate between the results (%DC vs. DH and %DC/DH vs. sorption/solubility). For all materials, the dual-curing consistently produced significantly higher %DC values than the self-curing (p < 0.05). Significant negative linear regressions were established between the %DC and DH in both curing modes (p < 0.05). Overall, the SARCs showed higher sorption/solubility values, in particular when immersed in lactic acid, than the conventional resin cement. Linear regression revealed that %DC and DH were negatively and positively correlated with the sorption/solubility values, respectively. Dual-curing of SARCs seems to lower the sorption and/or solubility in comparison with self-curing by increased %DC and occasionally decreased hydrophilicity.

A simple, sensitive and non-destructive technique for characterizing bovine dental enamel erosion： attenuated total reflection Fourier transform infrared spectroscopy

Although many techniques are available to assess enamel erosion in vitro, a simple, non-destructive method with sufficient sensitivity for quantifying dental erosion is required. This study characterized the bovine dental enamel erosion induced by various acidic beverages in vitro using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Deionized water (control) and 10 acidic beverages were selected to study erosion, and the pH and neutralizable acidity were measured. Bovine anterior teeth (110) were polished with up to 1 200-grit silicon carbide paper to produce flat enamel surfaces, which were then immersed in 20 mL of the beverages for 30 min at 37 °C. The degree of erosion was evaluated using ATR-FTIR spectroscopy and Vickers’ microhardness measurements. The spectra obtained were interpreted in two ways that focused on the ν1, ν3 phosphate contour: the ratio of the height amplitude of ν3 PO4 to that of ν1 PO4 (Method 1) and the shift of the ν3 PO4 peak to a higher wavenumber (Method 2). The percentage changes in microhardness after the erosion treatments were primarily affected by the pH of the immersion media. Regression analyses revealed highly significant correlations between the surface hardness change and the degree of erosion, as detected by ATR-FTIR spectroscopy (P<0.001). Method 1 was the most sensitive to these changes, followed by surface hardness change measurements and Method 2. This study suggests that ATR-FTIR spectroscopy is potentially advantageous over the microhardness test as a simple, non-destructive, sensitive technique for the quantification of enamel erosion.

Effects of Prepolymerized Particle Size and Polymerization Kinetics on Volumetric Shrinkage of Dental Modeling Resins

Dental modeling resins have been developed for use in areas where highly precise resin structures are needed. The manufacturers claim that these polymethyl methacrylate/methyl methacrylate (PMMA/MMA) resins show little or no shrinkage after polymerization. This study examined the polymerization shrinkage of five dental modeling resins as well as one temporary PMMA/MMA resin (control). The morphology and the particle size of the prepolymerized PMMA powders were investigated by scanning electron microscopy and laser diffraction particle size analysis, respectively. Linear polymerization shrinkage strains of the resins were monitored for 20 minutes using a custom-made linometer, and the final values (at 20 minutes) were converted into volumetric shrinkages. The final volumetric shrinkage values for the modeling resins were statistically similar (P > 0.05) or significantly larger (P < 0.05) than that of the control resin and were related to the polymerization kinetics (P < 0.05) rather than the PMMA bead size (P = 0.335). Therefore, the optimal control of the polymerization kinetics seems to be more important for producing high-precision resin structures rather than the use of dental modeling resins.