Saroash Shahid

Glass ionomer cements: Effect of strontium substitution on esthetics, radiopacity and fluoride release

OBJECTIVE SrO and SrF2 are widely used to replace CaO and CaF2 in ionomer glasses to produce radiopaque glass ionomer cements (GIC). The purpose of this study was to evaluate the effects of this substitution on release of ions from GIC as well as its effect on esthetics (translucency) and radiopacity. MATERIALS AND METHODS Cements were produced from ionomer glasses with varying content of Sr, Ca and F. The cements were stored in dilute acetic acid (pH 4.0) for up to 7 days at 37°C. Thereafter, the cements were removed and the solution was tested for F(-), Sr(2+), Ca(2+), and Al(3+) release. Radiopacity and translucency were measured according to BS EN ISO 9917-1:2003. RESULTS Ion release was linear to t(1/2) suggesting that this is a diffusion controlled mechanism rather than dissolution. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium. Radiopacity shows a strong linear correlation with Sr content. All cements were more opaque than the C0.70 0.55 standard but less opaque than the C0.70 0.90 standard which is the limit for the ISO requirement for acceptance. SIGNIFICANCE This study shows that the replacement of calcium by strontium in a glass ionomer glass produces the expected increase in radiopacity of the cement without adverse effects on visual properties of the cement. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium.

Novel Formulation of Chlorhexidine Spheres and Sustained Release with Multilayered Encapsulation.

This work demonstrates the synthesis of new chlorhexidine polymorphs with controlled morphology and symmetry, which were used as a template for layer-by-layer (LbL) encapsulation. LbL self-assembly of oppositely charged polyelectrolytes onto the drug surface was used in the current work, as an efficient method to produce a carrier with high drug content, improved drug solubility and sustained release. Coprecipitation of the chlorhexidine polymorphs was performed using chlorhexidine diacetate and calcium chloride solutions. Porous interconnected chlorhexidine spheres were produced by tuning the concentration of calcium chloride. The size of these drug colloids could be further controlled from 5.6 μm to over 20 μm (diameter) by adjusting the coprecipitation temperature. The chlorhexidine content in the spheres was determined to be as high as 90%. These particles were further stabilized by depositing 3.5 bilayers of poly(allylamine hydrochloride) (PAH) and polystyrenesulfonate (PSS) on the surface. In vitro release kinetics of chlorhexidine capsules showed that the multilayer shells could prolong the release, which was further demonstrated by characterizing the remaining chlorhexidine capsules with SEM and confocal microscopy. The new chlorhexidine polymorph and LbL coating has created novel chlorhexidine formulations. Further modification to the chlorhexidine polymorph structure is possible to achieve both sustained and stimuli responsive release, which will enhance its clinical performance in medicine and dentistry.

Therapeutic Ion-Releasing Bioactive Glass Ionomer Cements with Improved Mechanical Strength and Radiopacity

Bioactive glasses (BG) are used to regenerate bone, as they degrade and release therapeutic ions. Glass ionomer cements (GIC) are used in dentistry, can be delivered by injection and set in situ by a reaction between an acid-degradable glass and a polymeric acid. Our aim was to combine the advantages of BG and GIC, and we investigated the use of alkali-free BG (SiO2-CaO-CaF2-MgO) with 0 to 50% of calcium replaced by strontium, as the beneficial effects of strontium on bone formation are well documented. When mixing BG and poly(vinyl phosphonic-co-acrylic acid), ions were released fast (up to 90% within 15 minutes at pH 1), which resulted in GIC setting, as followed by infrared spectroscopy. GIC mixed well and set to hard cements (compressive strength up to 35 MPa), staying hard when in contact with aqueous solution. This is in contrast to GIC prepared with poly(acrylic acid), which were shown previously to become soft in contact with water. Strontium release from GIC increased linearly with strontium for calcium substitution, allowing for tailoring of strontium release depending on clinical requirements. Furthermore, strontium substitution increased GIC radiopacity. GIC passed ISO10993 cytotoxicity test, making them promising candidates for use as injectable bone cements.

Glass polyalkenoate cements based on simple CaO–Al2O3–SiO2 glasses

Abstract Glass polyalkenoate/ionomer cements formed from reacting CaO–Al2O3–SiO2 glasses with aqueous poly(acrylic acid) were investigated. Five glasses were investigated based on (1–X)CaO(1–X)Al2O3(2+2X)SiO2 (0≤X≤0·36) with varying Al/Si ratios. The cement properties were found to be highly dependant on the Al/Si ratio of the glass. The setting and working times of the cements decreased, while the compressive strength increased with Al/Si ratio. Fourier transform infrared spectroscopy showed that rate of set defined as change of the ratio of the carboxylate to carboxylic acid absorption bands up to first hour of the setting increased with increasing Al/Si ratio. 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) showed that the ratio of Al(VI)/Al(IV) in the cements increased with the Al/Si ratio of glass in presence of tartaric acid. The reactivity of these glasses increased with increasing Al/Si ratio consistently with the rate controlling role of acid hydrolysis of Al–O–Si bonds in the setting of the cements.

Gold Nanorod Mediated Chlorhexidine Microparticle Formation and Near-Infrared Light Induced Release

Gold nanorods (GNR) are good light harvesting species for elaboration of near-infrared (NIR) responsive drug delivery systems. Herein, chlorhexidine microparticles are grown directly on the surface of gold nanorods and then stabilized with polyelectrolyte multilayer encapsulation, producing novel composite drug-GNR particles with high drug loading and NIR light sensitivity. Crystallization of chlorhexidine is caused by the ionic strength of the chloride solution that has been demonstrated via formation of a homogeneous porous spherical structure at 0.33 M CaCl2. By introducing GNRs into the CaCl2 solution, the nucleation of chlorhexidine molecules and size of produced spheres are affected, since GNRs act as sites for chlorhexidine nucleation. Similarly, when GNRs are replaced by chlorhexidine seeds (5.2 ± 1.7 μm), a core-shell crystal structure is observed. The encapsulated GNR/chlorhexidine composites are responsive to NIR light (840 nm) that increases the temperature at the chlorhexidine crystals, followed by microparticle dissolution and rupture of capsules which is illustrated with confocal microscopy and SEM. Furthermore, a stepwise burst release of chlorhexidine can be induced by multiple cycles of NIR light exposure. The GNR/chlorhexidine composites show good biocompatibility and antimicrobial activity. The proposed method of antibacterial drug release may therefore indicate that this NIR responsive chlorhexidine composite may be useful for future clinical applications.

Apatite Glass-Ceramics: A Review

This article is a review of the published literature on apatite glass-ceramics (GCs). Topics covered include crystallization mechanisms of the various families of the apatite GCs and an update on research and development on apatite GCs for applications in orthopedics, dentistry, optoelectronics and nuclear waste management. Most apatite GCs crystallize through a homogenous nucleation and crystallization mechanism, which is aided by a prior liquid-liquid phase separation. Careful control of the base glass composition and heat-treatment conditions, which determine the nature and morphology of the crystal phases in the GC can produce GC materials with exceptional thermal, mechanical, optical and biological properties. The GCs reviewed for orthopedic applications exhibit suitable mechanical properties and can chemically bond to bone and stimulate its regeneration. The most commercially successful apatite GCs are those developed for dental veneering. These materials exhibit excellent translucency and clinical esthetics, and mimic the natural tooth mineral. Due to the ease of solid solution of the apatite lattice, rare earth doped apatite GCs are discussed for potential applications in optoelectronics and nuclear waste management. One of the drawbacks of the commercial apatite GCs used in orthopedics is the lack of resorbability, therefore the review provides a direction for future research in the field.

Synthesis of novel chlorhexidine spheres with controlled release from a UDMA–HEMA resin using ultrasound

OBJECTIVE Establish the release kinetics of new chlorhexidine particles incorporated in a dental resin, and with the application of ultrasound. METHODS Spherical chlorhexidine particles (SCP) were synthesized (5wt%), freeze dried and incorporated into UDMA-HEMA resins. Chlorhexidine diacetate (CDP) (5wt%) was similarly incorporated in separate resins. Resin discs were immersed in deionized water, and a release profile established (650h). Ultrasound was used to trigger chlorhexidine (CHX) release from the resin discs at specific durations (10-30s) and time intervals (1-425h). Chlorhexidine content was determined by UV-vis absorption. The chlorhexidine particles/polymer composites were characterized using TGA, SEM, and confocal microscopy. RESULTS SCP exhibited structures with high chlorhexidine content (90-95%), and a Mean (SD) diameter of 17.2 (2.5)μm which was significantly (p<0.001) smaller than the CDP crystals at 53.6 (33.7)μm. The SCP discs had a lower (7.7%) CHX release compared to the CDP group (16.2%). Ultrasonication of the resin discs with increasing durations (10-30s) resulted in higher drug release rates. CDP release rates (CHX) over 650h were: 23.5% (10s), 42.6% (20s), 51.2% (30s), and for SCP (CHX) were; 9.8% (10s), 12.3% (20s), and 14.0% (30s). SEM/confocal microscopy revealed CDP discs exhibited dissolution associated with the particle surface and SCP from the interior. SIGNIFICANCE Chlorhexidine spheres incorporated in a dental resin demonstrated a responsive and lower CHX release. Ultrasound enhanced CHX release and is useful in clinical situations where the drug is required on demand to treat severe or persistent infections.

Controlled release of chlorhexidine from a HEMA-UDMA resin using a magnetic field

OBJECTIVES To functionalize novel chlorhexidine (CHX) particles with iron oxide (Fe3O4) nanoparticles and control their release kinetics in a dental resin using an external magnetic field. METHODS Fe3O4 nanoparticles were synthesized and incorporated into spherical CHX particles and the powder was freeze dried. Resin disc specimens were produced using a UDMA-HEMA resin mixed with freeze dried spherical Fe3O4-CHX particles (5wt.%), which were placed into a Teflon mould (10mm diameter×1mm depth) and covered with a Mylar strip. A MACS magnet was left in contact for 0min (Group 1), 5min (Group 2) or 10min (Group 3) and the resin discs subsequently light cured (Bluedent LED pen, Bulgaria) for 60s per side. The resin discs were immersed in deionized water at various time points up to 650h. UV-Vis absorbance was used to determine the CHX content. CHX released for each time point was determined. The functionalized CHX particles and resin discs were characterized using TEM, TGA, EDX and SEM. RESULTS Fe3O4 nanoparticles (20nm) incorporated into the spherical CHX particles led to a mean (SD) particle size reduction from 17.15 (1.99)μm to 10.39 (2.61)μm. The presence of Fe3O4 nanoparticles in the spherical CHX particles was confirmed with SEM, EDX, and TGA. SEM of Group 1 resin discs (no magnetic exposure) showed functionalized CHX spheres were homogeneously distributed within the resin discs. For resin discs which had magnetic exposure (5 or 10min) the particles started to cluster nearer the surface (Group 2: 43.7%, Group 3: 57.3%), to a depth of 94μm. UV-Vis absorbance revealed Group 1 resin discs had a cumulative CHX release of 4.4% compared to 5.9% for Group 2 and 7.4% for Group 3 resin discs, which had magnetic exposure (5, 10min). SIGNIFICANCE Fe3O4 nanoparticle functionalized CHX spheres demonstrated a magnetic field responsive property. A magnetic field responsive release of CHX may be useful in clinical situations where the drug can be directed to give a tailored release at the site of infection.

Predicting refractive index of fluoride containing glasses for aesthetic dental restorations

OBJECTIVE Dental restoration aesthetics, particularly the translucency of modern dental restorative filling materials depends on the refractive index (RI) match between the different components in the material. In the case of dental composites (DC), the RI of the polymer must match the RI of the filler otherwise the material is optically opaque and has limited depth of cure. In the case of glass ionomer cements (GICs), the RI of the ion-leachable glass must match the RI of the polysalts to engineer a smart material with a tooth-like appearance. The RI of oxide glasses can be calculated by means of Appen factors. However, no Appen factors are available for the fluoride components in dental glasses. Therefore, the objective of this study is to empirically derive composition-specific Appen factors for the metal fluorides in complex multicomponent glasses for use in dentistry. METHODS Two series of bioactive glasses and two series of ionomer-type glasses were produced for this study. Refractive indices of all glasses were then measured by the Becke Line technique. Thereafter, composition-specific factors for the metal fluorides were derived. RESULTS It was found that increasing metal fluoride content reduces the RI of multicomponent dental glasses linearly. A series-specific Appen factors for the metal fluorides were successfully derived and allow RI calculation to within 0.005. SIGNIFICANCE This paper proposes a modified Appen Model with composition-specific Appen factors for the metal fluorides for the development of dental restoratives with enhanced aesthetics and improved depth of cure of dental composites.

Validation of a Real-Time ISE Methodology to Quantify the Influence of Inhibitors of Demineralization Kinetics in vitro Using a Hydroxyapatite Model System

The aim was to validate a novel protocol to measure the cariostatic efficacies of demineralization inhibitors by repeating previous SMR (scanning microradiography) studies investigating the dose response of Zn²⁺ and F^– on demineralization kinetics in vitro using real-time Ca²⁺ ion selective electrodes (ISEs). In this study, Ca²⁺ release was used as a proxy for the extent of demineralization. Forty-eight hydroxyapatite (HAP) discs were allocated into 16 groups (n = 3) and adding either increasing [Zn²⁺], or [F^–], similar to those used in the previous SMR studies. Each HAP disc was immersed in 50 mL, pH 4.0, buffered acetic acid for 1 h, and real-time ISE methodology was used to monitor the rate of increase in [Ca²⁺] in the demineralization solution. Next, either zinc acetate or sodium fluoride was added into each demineralization solution accordingly. Then after each [Zn²⁺] or [F^–] addition, the HAP disc was further demineralized for 1 h, and ISE measurements were continued. The percentage reduction in the rate of calcium loss from hydroxyapatite (PRCL_HAP) at each [Zn²⁺] or [F^–] was calculated from the decrease in Ca²⁺ release rate, similar to that used in the previous SMR studies. A log-linear relationship between mean PRCL_HAP and inhibitor concentration was found for both Zn²⁺ and F^–, similar to that reported for each ion in the previous SMR studies. In conclusion, real-time Ca²⁺ ISE systems can be used to measure the cariostatic efficacies of demineralization inhibitors.