Ultrasonically set glass polyalkenoate cements for orthodontic applications

There is an accepted clinical requirement for a luting cement that can be command set upon satisfactory placement of an orthodontic appliance onto dentition. This work evaluates the suitability of ultrasound, imparted from a dental scaler, as a potential mechanism for achieving this. The net setting times and subsequent compressive strengths of a range of commercial and experimental glass polyalkenoate cements (GPCs) were evaluated, using modified ISO 9917 methods, when set both chemically and by ultrasound. The ultrasound was applied to the GPC through an orthodontic brace. It was possible to command set GPCs by the application of five to ten seconds of ultrasound; the exact time required being dependent upon the composition of the GPC in question. The compressive strengths of these cements can be improved by around 90% with the command set when the optimum PAA molecular weight and tartaric acid content is employed.     

Kinetic studies of water uptake and loss in glass-ionomer cements

The water sorption and desorption behaviour of three commercial glass-ionomer cements used in clinical dentistry have been studied in detail. Cured specimens of each material were found to show slight but variable water uptake in high humidity conditions, but steady loss in desiccating ones. This water loss was found to follow Fick’s law for the first 4–5 h. Diffusion coefficients at 22 °C were: Chemflex 1.34 × 10⁻⁶ cm² s⁻¹, Fuji IX 5.87 × 10⁻⁷ cm² s⁻¹, Aquacem 3.08 × 10⁻⁶ cm² s⁻¹. At 7 °C they were: Chemflex 8.90 × 10⁻⁷ cm² s⁻¹, Fuji IX 5.04 × 10⁻⁷ cm² s⁻¹, Aquacem 2.88 × 10⁻⁶ cm² s⁻¹. Activation energies for water loss were determined from the Arrhenius equation and were found to be Chemflex 161.8 J mol⁻¹, Fuji IX 101.3 J mol⁻¹, Aquacem 47.1 J mol⁻¹. Such low values show that water transport requires less energy in these cements than in resin-modified glass-ionomers. Fick’s law plots were found not to pass through the origin. This implies that, in each case, there is a small water loss that does not involve diffusion. This was concluded to be water at the surface of the specimens, and was termed “superficial water”. As such, it represents a fraction of the previously identified unbound (loose) water. Superficial water levels were: Chemflex 0.56%, Fuji IX 0.23%, Aquacem 0.87%. Equilibrium mass loss values were shown to be unaffected by temperature, and allowed ratios of bound:unbound water to be determined for all three cements. These showed wide variation, ranging from 1:5.26 for Chemflex to 1:1.25 for Fuji IX.     

Ultra-fine cements for special applications

Ultra-fine cements produced on the basis of Portland cement are much finer than ordinary cement and have a steep grading curve. They are specially suited for rock and soil injection but nowadays also for filling and sealing of cracks in concrete.     

Ceramics for restorative dentistry: Critical aspects for fracture and fatigue resistance

Development of non-metallic restorative materials is a high priority due to biocompatibility issues and environmental concerns associated with metals waste and disposal. Ceramics are an ideal candidate for replacing metal-based restorative materials. Ceramics provide excellent chemical durability, wear resistance, biocompatibility, environmental friendliness and esthetics. However, widespread all-ceramic restoration use has been hindered by concerns related to marginal fracture resistance and clinical longevity. The recent introduction of higher toughness materials, especially partially stabilized zirconia, has expanded the range of clinically acceptable applications for all-ceramic restorative systems. In addition, advanced fabrication techniques such as CAD/CAM have reduced some of the problems associated with processing-induced flaws that can lead to short-term catastrophic failures in vivo. Some current research is focused on surface modification techniques (thin films, coatings, advanced adhesives) intended to minimize the effects of fabrication-induced defects.     

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 °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.     

Comparison of the material properties of PMMA and glass-ionomer based cements for use in orthopaedic surgery

The intrisic benefits of low exotherm and bioactivity have generated interest in utilizing glass-ionomer cements (GIC) as a bone cement replacement in orthopaedic surgery. This paper is concerned with evaluating the mechanical properties of compressive strength, flexural strength, and fracture toughness for two traditional GICs, one resin-modified GIC (an experimental bone cement) and two polymethylmethacrylate (PMMA) cement systems. To determine the suitability of a GIC system for use in the clinical orthopaedic setting, the additional characteristics of setting exotherm and setting time have also been evaluated. The characterization of these two vastly different cement systems has raised some concern as to the applicability of using the current orthopaedic standards for the testing of GIC systems. In particular, issues relating to the strain rate dependence of PMMA cement and the exothermic basis for determining setting time are not applicable as these factors are not characteristic of GIC systems. Whilst the intrinsic benfits of current GIC systems are well understood and generally accepted, this study has shown their intrinsic mechanical properties to be inferior to current PMMA cements. Improvement in the mechanical properties of traditional GICs have been achieved with the addition of a resin component (HEMA). © 2001 Kluwer Academic Publishers     

Ultrasonically induced in situ polymerization of PANI-SWCNT nanocomposites for electromagnetic shielding applications

Journal of Materials Science: Materials in Electronics - Electromagnetic interference (EMI) shielding has potential importance due to rapid growth in electronic technology. In recent days, carbon...     

The effect of storage in aqueous solutions on glass-ionomer and zinc polycarboxylate dental cements

Cylindrical specimens (dimensions 6 mm diameter×12 mm height) of glass-ionomer and of zinc polycarboxylate dental cement have been stored in aqueous solutions for periods of 24 h, 1 week and 1 month. The solutions were of varying composition and affinity for water, and storage in them resulted in fluctuations in mass of the cements, an effect which was attributed to differences in the partitioning of water between the solutions and the cement specimens. Unlike the zinc polycarboxylate, the glass-ionomer gained mass in most of the solutions examined (except Na₂SO₄), showing it to have a much greater affinity for water than the zinc polycarboxylate. Despite the fluctuations in water uptake by the glass-ionomer, and loss of water by the zinc polycarboxylate, no statistically significant differences in compressive strength were recorded in any solution at any storage time. This contrasts with results reported previously for zinc polycarboxylates using smaller specimens, showing that specimen size has an influence on the interaction of cements with storage solutions. ©2000 Kluwer Academic Publishers     

Clinical applications of glass-ceramics in dentistry

Glass-ceramics featuring special properties can be used as a basis to develop biomaterials. It is generally differentiated between highly durable biomaterials for restorative dental applications and bioactive glass-ceramics for medical use, for example, bone replacements. In detail, this paper presents one biomaterial from each of these two groups of materials. In respect to the restorative dental biomaterials, the authors give an overview of the most important glass-ceramics for clinical applications. Leucite, leucite-apatite, lithium disilicate and apatite containing glass-ceramics represent biomaterials for these applications. In detail, the authors report on nucleation and crystallization mechanisms and properties of leucite-apatite glass-ceramics. The mechanism of apatite nucleation is characterized by a heterogeneous process. Primary crystal phases of α - and β -NaCaPO₄ were determined. Rhenanite glass-ceramics represent biomaterials with high surface reactivity in simulated body fluid, SBF, and exhibit reactive behaviour in tests with bone cells. Cell adhesion phenomena and cell growth were observed. Suitable colonization and proliferation and differentiation of cells as a preliminary stage in the development of a material for bone regeneration applications was established. The authors conclude that the processes of heterogeneous nucleation and crystallization are important for controlling the required reactions in both biomaterial groups.     

Antibacterial activity of four glass ionomer cements used in atraumatic restorative treatment

The in vitro antibacterial activity of four glass ionomer cements (Fuji IX, Ketac Molar, Vidrion R and Vitromolar) indicated for Atraumatic Restorative Treatment (ART) was studied against strains of bacteria involved in the development of oral diseases, Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus and Actinomyces viscosus. The agar plate diffusion test was used for the cultures, which included chlorhexidine as a positive control. The results demonstrated that all the cements evaluated presented antibacterial activity. Based on the results of this study, it can be concluded that Fuji IX and Ketac Molar presented the most effective antibacterial activity considering the ART approach.     

Comparison of failure mechanisms for cements used in skeletal luting applications

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr–Ca–Zn–SiO₂) glasses and low molecular weight poly(acrylic acid) (PAA) have been shown to exhibit suitable compressive strength (65 MPa) and flexural strength (14 MPa) for orthopaedic luting applications. In this study, two such GPC formulations, alongside two commercial cements (Simplex^® P and Hydroset?) were examined. Fracture toughness and tensile bond strength to sintered hydroxyapatite and a biomedical titanium alloy were examined. Fracture toughness of the commercial Poly(methyl methacrylate) cement, Simplex^® P, (3.02 MPa m^1/2) was superior to that of the novel GPC (0.36 MPa m^1/2) and the commercial calcium phosphate cement, Hydroset?, for which no significant fracture toughness was obtained. However, tensile bond strengths of the novel GPCs (0.38 MPa), after a prolonged period (30 days), were observed to be superior to commercial controls (Simplex? P: 0.07 MPa, Hydroset?: 0.16 MPa).     

Investigation of the post-hardening reaction in glass-ionomer cements based on poly(vinyl phosphonic acid)

In this study the behaviour of two PVPA-based glass-ionomer cements was investigated. The first cement was prepared from PVPA homopolymer and glass, together with a reaction modifier. In the second cement a modified version of the polymer was used instead of the homopolymer. The modification was achieved by the treatment of the polymer with a small quantity of zinc fluoride. The effect of ageing under different conditions on the strength, mass and volume of the cements was determined. The ZnF₂-containing system behaved in a fairly straightforward manner, showing a gradual increase in strength with time (up to 3 months) that was similar to glass-ionomer cements based on poly(acrylic acid). By contrast the unmodified material did not increase in strength with time, a feature that was attributed to extensive crosslinking of the material, causing it to become more brittle and hence more sensitive to defects in the specimens. With regard to the effect on mass and volume, both types of cement behaved like typical set glass-ionomers, displaying a sensitivity to dessication but little, if any, sensitivity to aqueous media.     

A novel acrylic copolymer for a poly(alkenoate) glass-ionomer cement

The interest in the clinical use of polyalkenoate cements stems mainly from their behavior as bioactive adhesive materials with therapeutic action. Glass-ionomer cements set by an acid-base reaction between a degradable glass and a poly(alkenoic acid) and the therapeutic action is related to the release of fluoride ions which are present in the hardened cement that show a sustained release over years, responsible for caries inhibition in teeth. Conventional glass-ionomers, however, suffer from some disadvantages such as short working time, initial moisture sensitivity and prone to desiccation after setting and are generally brittle. In the present study, a poly(alkenoic acid) copolymer was synthesized based on acrylic acid and 2-hydroxyethylmethacrylate (HEMA) using azobisisobutyronitrile as the initiator and characterized. The acid–base reaction was carried out by reacting aqueous solutions of the new copolymer (40 and 60%) with a commercial aluminofluorosilicate glasses as used in conventional glass-ionomer cements. The results showed that the copolymer of HEMA and acrylic acid was a viable poly(alkenoic) acid for formation of glass-ionomer cements.     

Development of multi-walled carbon nanotubes reinforced monetite bionanocomposite cements for orthopedic applications

In this study, we present results of our research on biodegradable monetite (DCPA, CaHPO₄) cement with surface-modified multi-walled carbon nanotubes (mMWCNTs) as potential bone defect repair material. The cement pastes showed desirable handling properties and possessed a suitable setting time for use in surgical setting. The incorporation of mMWCNTs shortened the setting time of DCPA and increased the compressive strength of DCPA cement from 11.09 ± 1.85 MPa to 21.56 ± 2.47 MPa. The cytocompatibility of the materials was investigated in vitro using the preosteoblast cell line MC3T3-E1. An increase of cell numbers was observed on both DCPA and DCPA-mMWCNTs. Scanning electron microscopy (SEM) results also revealed an obvious cell growth on the surface of the cements. Based on these results, DCPA-mMWCNTs composite cements can be considered as potential bone defect repair materials.     

Mechanical properties of bio compatible functional prototypes for joining applications in clinical dentistry

In the presented research, work investigations have been made for mechanical properties of the functional prototypes prepared from biocompatible filament of fused deposition modelling (FDM), comprising of hydroxyapatite (HAp), polypropylene (PP) and polyvinyl chloride (PVC). The functional prototypes will be used in clinical dentistry (mainly for joining application for job-type production activities). The filament has been prepared in house using twin screw extrusion process. For evaluation purpose, standard tensile specimens as per ASTM D-638 have been prepared on FDM. This study highlights the effect of three parameters of FDM (namely: infill percentage, layer thickness and speed of extrusion head) on the mechanical properties (namely: load at peak and load at break). The results of the study suggest that infill density has majorly contributed, 92% on load at peak and 89% for load at break, and deposition speed has very less contribution i.e., 1% towards the mechanical strength of the specimen. Further, the results are supported with thermal analysis using differential scanning calorimeter (DSC), which ensures that the specimen prepared are thermally stable and can be put in for joining applications for job-type production activities in clinical dentistry.     

Calcium phosphate bone cements for clinical applications. Part I: Solution chemistry

Calcium phosphate cements have been the subject of many studies in the last decade because of their biocompatibility, their capacity to fill bone cavities and their hardening properties; properties which are desirable in a broad range of surgical applications. The setting and hardening of these materials are controlled by dissolution–precipitation chemical reactions at room or body temperature and involve crystalline phase transformations. © 1999 Kluwer Academic Publishers     

The bioactivity and ion release of titanium-containing glass polyalkenoate cements for medical applications

The ion release profiles and bioactivity of a series of Ti containing glass polyalkenoate cements. Characterization revealed each material to be amorphous with a T _g in the region of 650–660°C. The network connectivity decreased (1.83–1.35) with the addition of TiO₂ which was also evident with analysis by X-ray photoelectron spectroscopy. Ion release from cements were determined using atomic absorption spectroscopy for zinc (Zn²⁺), calcium (Ca²⁺), strontium (Sr²⁺), Silica (Si⁴⁺) and titanium (Ti⁴⁺). Ions such as Zn²⁺ (0.1–2.0 mg/l), Ca²⁺ (2.0–8.3 mg/l,) Sr²⁺ (0.1–3.9 mg/l), and Si⁴⁺ (14–90 mg/l) were tested over 1–30 days. No Ti⁴⁺ release was detected. Simulated body fluid revealed a CaP surface layer on each cement while cell culture testing of cement liquid extracts with TW-Z (5 mol% TiO₂) produced the highest cell viability (161%) after 30 days. Direct contact testing of discs resulted in a decrease in cell viability of the each cement tested.