Preparation, formulation and evaluation of novel photo-cured glass ionomers based on co-polymers of (meth)acrylated amino acids

Composition-structure-property relationships for non-classical ionomer cements formulated with zinc-boron germanium-based glasses

Non-classical ionomer glasses like those based on zinc-boron-germanium glasses are of special interest in a variety of medical applications owning to their unique combination of properties and potential therapeutic efficacy. These features may be of particular benefit with respect to the utilization of glass ionomer cements for minimally invasive dental applications such as the atruamatic restorative treatment, but also for expanded clinical applications in orthopedics and oral-maxillofacial surgery. A unique system of zinc-boron-germanium-based glasses (10 compositions in total) has been designed using a Design of Mixtures methodology. In the first instance, ionomer glasses were examined via differential thermal analysis, X-ray diffraction, and 11B MAS NMR spectroscopy to establish fundamental composition – structure-property relationships for the unique system. Secondly, cements were synthesized based on each glass and handling characteristics (working time, Wt, and setting time, St) and compression strength were quantified to facilitate the development of both experimental and mathematical composition-structure-property relationships for the new ionomer cements. The novel glass ionomer cements were found to provide Wt, St, and compression strength in the range of 48–132 s, 206–602 s, and 16–36 MPa, respectively, depending on the ZnO/GeO2 mol fraction of the glass phase. A lower ZnO mol fraction in the glass phase provides higher glass transition temperature, higher N4 rate, and in combination with careful modulation of GeO2 mol fraction in the glass phase provides a unique approach to extending the Wt and St of glass ionomer cement without compromising (in fact enhancing) compression strength. The data presented in this work provide valuable information for the formulation of alternative glass ionomer cements for applications within and beyond the dental clinic, especially where conventional approaches to modulating working time and strength exhibit co-dependencies (i.e. the enhancement of one property comes at the expense of the other) and therefore limit development strategies.

Synthesis of poly(alkenoic acid) with L-leucine residue and methacrylate photopolymerizable groups useful in formulating dental restorative materials

To develop resin-modified glass ionomer materials, we synthesized methacrylate-functionalized acrylic copolymer (PAlk-LeuM) derived from acrylic acid, itaconic acid and N-acryloyl-L-leucine using (N-methacryloyloxyethylcarbamoyl-N'-4-hydroxybutyl) urea as the modifying agent. The spectroscopic (proton/carbon nuclear magnetic resonance, Fourier transform infrared spectroscopy) characteristics, and the gel permeation chromatography/Brookfield viscosity measurements were analysed and compared with those of the non-modified copolymer (PAlk-Leu). The photocurable copolymer (PAlk-LeuM, ~14 mol% methacrylate groups) and its precursor (PAlk-Leu) were incorporated in dental ionomer compositions besides diglycidyl methacrylate of bisphenol A (Bis-GMA) or an analogue of Bis-GMA (Bis-GMA-1), triethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate. The kinetic data obtained by photo-differential scanning calorimetry showed that both the degree of conversion (60.50-75.62%) and the polymerization rate (0.07-0.14 s(-1)) depend mainly on the amount of copolymer (40-50 wt.%), and conversions over 70% were attained in the formulations with 40 wt.% PAlk-LeuM. To formulate light-curable cements, each organic composition was mixed with filler (90 wt.% fluoroaluminosilicate/10 wt.% hydroxyapatite) into a 2.7:1 ratio (powder/liquid ratio). The light-cured specimens exhibited flexural strength (FS), compressive strength (CS) and diametral tensile strength (DTS) varying between 28.08 and 64.79 MPa (FS), 103.68-147.13 MPa (CS) and 16.89-31.87 MPa (DTS). The best values for FS, CS and DTS were found for the materials with the lowest amount of PAlk-LeuM. Other properties such as the surface hardness, water sorption/water solubility, surface morphology and fluorescence caused by adding the fluorescein monomer were also evaluated.

Synthesis and characterization of a novel N-vinylcaprolactam-containing acrylic acid terpolymer for applications in glass-ionomer dental cements

In this study a novel N-vinylcaprolactam (NVC)-containing copolymer of acrylic-itaconic acid was synthesized, characterized and incorporated into Fuji IX conventional glass-ionomer cement (GIC). Subsequently, the effects of incorporation of synthesized terpolymer on the mechanical properties of GIC were studied. The synthesized terpolymer was characterized using (1)H nuclear magnetic resonance, Fourier transform infrared and Raman spectroscopy. The viscosity and molecular weight of the terpolymer were also measured. The compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural strength (BFS) of the modified GICs were evaluated after 24h and 1week of immersion in distilled water at 37 degrees C. The handling properties (working and setting times) of the resulting modified cements were also evaluated. One-way analysis of variance was used to study the statistical significance of the mechanical strengths and handling properties in comparison to the control group. The results showed that NVC-containing GIC samples exhibited significantly higher (P<0.05) DTS (38.3+/-10.9MPa) and BFS (82.2+/-12.8MPa) in comparison to Fuji IX GIC (DTS=19.6+/-11.4MPa; BFS=41.3+/-10.5MPa). The experimental cement also showed higher but not statistically significant values for CS compared to the control material (CS for NVC-containing sample=303+/-32.8MPa; CS for Fuji XI=236+/-41.5MPa). Novel NVC-containing GIC has been developed in this study, with a 28% increase in CS. The presented GIC is capable of doubling the DTS and BFS in comparison to commercial Fuji IX GIC. The working properties of NVC-containing glass-ionomer formulations are comparable and are acceptable for water-based cements.

Synthesis of a proline-modified acrylic acid copolymer in supercritical CO2 for glass-ionomer dental cement applications

Supercritical (sc-) fluids (such as sc-CO(2)) represent interesting media for the synthesis of polymers in dental and biomedical applications. Sc-CO(2) has several advantages for polymerization reactions in comparison to conventional organic solvents. It has several advantages in comparison to conventional polymerization solvents, such as enhanced kinetics, being less harmful to the environment and simplified solvent removal process. In our previous work, we synthesized poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone) (PAA-IA-NVP) terpolymers in a supercritical CO(2)/methanol mixture for applications in glass-ionomer dental cements. In this study, proline-containing acrylic acid copolymers were synthesized, in a supercritical CO(2) mixture or in water. Subsequently, the synthesized polymers were used in commercially available glass-ionomer cement formulations (Fuji IX commercial GIC). Mechanical strength (compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural strength (BFS)) and handling properties (working and setting time) of the resulting modified cements were evaluated. It was found that the polymerization reaction in an sc-CO(2)/methanol mixture was significantly faster than the corresponding polymerization reaction in water and the purification procedures were simpler for the former. Furthermore, glass-ionomer cement samples made from the terpolymer prepared in sc-CO(2)/methanol exhibited higher CS and DTS and comparable BFS compared to the same polymer synthesized in water. The working properties of glass-ionomer formulations made in sc-CO(2)/methanol were comparable and better than the values of those for polymers synthesized in water.

A novel light-cured glass-ionomer system for improved dental restoratives

A novel light-cured glass-ionomer cement (LCGIC) system based on the 4-arm star-shape poly(acrylic acid) (AA) tethered with glycidyl methacrylate has been developed. The 4-arm poly(AA) polymer was synthesized using atom-transfer radical polymerization. The purified polymer was used to formulate with water and Fuji II LC filler to form LCGICs. Compressive strength (CS) was used as a screening tool for evaluation. The effects of grafting ratio, polymer/water (P/W) ratio, filler powder/polymer liquid (P/L) ratio and aging on strengths were investigated. All the specimens were conditioned in distilled water at 37 degrees C for 24 h prior to testing. The results show that the 4-arm poly(AA) polymer exhibited a lower viscosity as compared to its linear counterpart that was synthesized via conventional free-radical polymerization. This novel LCGIC system was 13% in CS, 86% in diametral tensile strength (DTS) and 123% in flexural strength higher but 93.6% in shrinkage lower than Fuji II LC. Increasing P/W ratio significantly increased both CS and DTS. Upon increasing grafting ratio, the CS was increased from 35% to 50% but not from 50% to 70%. Likewise, when P/L ratio was increased, the CS was increased from 2.2 to 2.7 but not from 2.7 to 3.0. During aging, the ultimate CS (MPa) was significantly increased from 209.2 at 1 h to 329.7 at 1 week. It appears that this novel LCGIC system will be a better dental restorative because it demonstrated improved mechanical strengths as well as little shrinkage and may eliminate cytotoxicity in current LCGICs caused by leached HEMA.

A novel comonomer-free light-cured glass-ionomer cement for reduced cytotoxicity and enhanced mechanical strength

OBJECTIVE

The objective of this study was to develop a novel comonomer-free light-cured glass-ionomer system based on the 4-arm star-shape poly(acrylic acid). The mechanical strengths and in vitro cytotoxicity of the formed system were evaluated and compared with those of several representative commercial glass-ionomer cements.

MATERIALS AND METHODS

The 4-arm poly(acrylic acid) was synthesized using ATRP and tethered with glycidyl methacrylate (GM). The GM-tethered polymer was formulated with water, photo-initiators, and Fuji II LC filler. Fuji II, Fuji II LC and Vitremer were used for comparison. Compressive strength (CS) and MTT assay were used as tools to evaluate the mechanical strengths and in vitro cytotoxicity of the cements, respectively.

RESULTS

The experimental cement exhibited significantly high compressive, diametral tensile and flexural strengths as compared to commercial glass-ionomer cements, Fuji II, Fuji II LC and Vitremer. The effects of polymer/water (P/W) ratio, GM-grafting ratio, glass powder/polymer liquid (P/L) ratio and aging in water on strengths were significant. Similar to conventional glass-ionomer cement Fuji II, the eluates from the experimental cement showed little in vitro cytotoxicity to Balb/c mouse fibroblast cells, as compared to Fuji II LC and Vitremer that contain HEMA as a comonomer.

CONCLUSIONS

It appears that this novel comonomer-free light-cured glass-ionomer cement will be a promising dental restorative because it demonstrated significantly improved mechanical strengths and almost no in vitro cytotoxicity as compared to current commercial light-cured glass-ionomer cements.