Evaluation of the antimicrobial activity and compressive strength of a dental cement modified using plant extract mixture

Literature lacks sufficient data regarding addition of natural antibacterial agents to glass ionomer cement (GICs). Hence, the aim of the study was to increase the antimicrobial properties of GICs through its modification with mixture of plant extracts to be evaluated along with an 0.5% chlorohexidine-modified GIC (CHX-GIC) with regard to biological and compressive strength properties. Conventional GIC (freeze-dried version) and CHX were used. Alcoholic extract of Salvadora persica, Olea europaea, and Ficus carcia leaves were prepared using a Soxhlet extractor for 12 h. The plant extract mixture (PE) was added in three different proportions to the water used for preparation of the dental cement (Group 1:1 PE, 2:1 PE, and 1:2 PE). Specimens were then prepared and tested against the unmodified GIC (control) and the 0.5% CHX-GIC. Chemical analysis of the extract mixture was performed using Gas chromatography-mass spectrometry. Antimicrobial activity was evaluated using agar diffusion assay against Micrococcus luteus and Streptoccocus mutans. Compressive strength was evaluated according to ISO 9917-1:2007 using a Zwick testing machine at a crosshead speed of 0.5 mm/min. Antimicrobial activity against Streptoccocus mutans was significantly increased for all the extract-modified materials compared to the unmodified cement, and the highest concentration was comparable to the CHX-GIC mixture. The activity against Micrococcus luteus was also significantly increased, but only for the material with the highest extract concentration, and here the CHX-GIC group showed statistically the highest antimicrobial activity. Compressive strength results revealed that there was no statistically significant difference between the different mixtures and the control except for the highest tested concentration that showed the highest mean values. The plant extracts (PEs) enhanced the antimicrobial activity against S. mutans and also against M. luteus in the higher concentration while compressive strength was improved by addition of the PE at higher concentrations.

Synthesis of belite cement from nano-silica extracted from two rice husk ashes

Nano-silicas extracted from a pure rice husk ash calcined in the laboratory (RHA) and ash from an impure industrial rice husk waste (BRHA), were used to form belite cement by firing with two different calcium sources (calcium carbonate and calcium nitrate). The nano-silica extracted from RHA was highly reactive due to its high pore volume and low activation energy of dehydration. The formation of belite cement from both nano-silicas was studied by firing with two different calcium sources, Ca(NO₃)₂ and CaCO₃ at 800-1100 °C. Both nano-silicas formed the principal phase in belite cement (larnite or β-C₂S) at temperatures as low as 800 °C, especially with calcium nitrate as the calcium source. Thus, highly impure BRHA is shown to be very suitable as a starting material for the low-temperature production of belite cement, especially in conjunction with calcium nitrate as the calcium source.

Aluminium-free glass polyalkenoate cements: ion release and in vitro antibacterial efficacy

Glass polyalkenoate cements (GPCs) have exhibited potential as bone cements. This study investigates the effect of substituting TiO₂ for SiO₂ in the glass phase and the subsequent effect on cement rheology, mechanical properties, ion release and antibacterial properties. Glass characterization revealed a reduction in glass transition temperature (T(g)) from 685 to 669 °C with the addition of 6 mol % TiO₂ (AT-2). Magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed a shift from -81 ppm to -76 pmm when comparing a Control glass to AT-2, indicating de-polymerization of the Si network. The incorporation of TiO₂ also increased the working time (T(w)) from 19 to 61 s and setting time (T(s)) from 70 to 427 s. The maximum compressive strength (σ(c)) increased from 64 to 85 MPa. Ion release studies determined that the addition of Ti to the glass reduced the release of zinc, calcium and strontium ions, with low concentrations of titanium being released. Antibacterial testing in E. coli resulted in greater bactericidal effects when tested in aqueous broth for both titanium containing cements.

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

A novel photo-cured amino-acid-constructed glass-ionomer cement system has been developed. Glutamic acid- and beta-alanine-based methacrylate and acrylate derivatives were synthesized, characterized and used to construct the polyalkenoic acids and formulated with water and Fuji II glass filler to form self-cured cement. Compressive strength (CS) of the cement and viscosity of the liquid were used as tools for evaluation. The effects of molar ratio and molecular weight (MW) were studied. The optimized co-polymer was further modified with glycidyl methacrylate (GM) and formulated with water, acrylic acid and Fuji II LC filler to form photo-cured cement. The effects of MW, GM tethering ratio, polymer liquid ratio and glass filler powder/polymer liquid (P/L) ratio were investigated. CS, flexural strength (FS) and viscosity were used as screening tools to find the optimal formulation. All the specimens were conditioned in distilled water at 37 degrees C for either 24 h or 7 days prior to testing. The results show that amino-acid-constructed polyalkenoic acids can be formed only from amino acid methacrylate derivatives or by co-polymerization of methacrylate with acrylate derivatives. Among the numerous co-polymers synthesized, poly(methacryloyl glutamic acid-co-acryloyl beta-alanine) or poly(MGA-co-ABA) with the molar ratio of 8:2 and MW of 19.5 kg/mol contributed the highest mechanical strengths and lower working viscosity to the cement. For photo-cured system, the effects of GM tethering ratio, polymer content and P/L ratio were significant. It is found that an appropriate ratio balance between these parameters is very important. The effect of molecular weight was not significant. The self-cured experimental cement was 32% higher in FS than Fuji II and the same in CS and DTS as Fuji II. The photo-cured experimental cement was 19%, 47% and 176% higher in CS, DTS and FS than Fuji II LC.

Preparation and evaluation of a novel glass-ionomer cement with antibacterial functions

OBJECTIVE

The objective of this study was to use the newly synthesized poly(quaternary ammonium salt) (PQAS)-containing polyacid to formulate the light-curable glass-ionomer cements and study the effect of the PQAS on the compressive strength and antibacterial activity of the formed cements.

MATERIALS AND METHODS

The functional QAS and their constructed PQAS were synthesized, characterized and formulated into the experimental high-strength cements. Compressive strength (CS) and Streptococcus mutans viability were used to evaluate the mechanical strength and antibacterial activity of the cements. Fuji II LC cement was used as control. The specimens were conditioned in distilled water at 37°C for 24 h prior to testing. The effects of the substitute chain length, loading as well as grafting ratio of the QAS and aging on CS and S. mutans viability were investigated.

RESULTS

All the PQAS-containing cements showed a significant antibacterial activity, accompanying with an initial CS reduction. The effects of the chain length, loading and grafting ratio of the QAS were significant. Increasing chain length, loading, grafting ratio significantly enhanced antibacterial activity but reduced the initial CS. Under the same substitute chain length, the cements containing QAS bromide were found to be more antibacterial than those containing QAS chloride although the CS values of the cements were not statistically different from each other, suggesting that we can use QAS bromide directly without converting bromide to chloride. The experimental cement showed less CS reduction and higher antibacterial activity than Fuji II LC. The long-term aging study suggests that the cements may have a long-lasting antibacterial function.

CONCLUSIONS

This study developed a novel antibacterial glass-ionomer cement. Within the limitations of this study, it appears that the experimental cement is a clinically attractive dental restorative due to its high mechanical strength and antibacterial function.

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 TiO(2) which was also evident with analysis by X-ray photoelectron spectroscopy. Ion release from cements were determined using atomic absorption spectroscopy for zinc (Zn(2+)), calcium (Ca(2+)), strontium (Sr(2+)), Silica (Si(4+)) and titanium (Ti(4+)). Ions such as Zn(2+) (0.1-2.0 mg/l), Ca(2+) (2.0-8.3 mg/l,) Sr(2+) (0.1-3.9 mg/l), and Si(4+) (14-90 mg/l) were tested over 1-30 days. No Ti(4+) 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% TiO(2)) 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.

Synthesis of alpha'L-C2S cement from fly-ash using the hydrothermal method at low temperature and atmospheric pressure

The objective of this study was the synthesis of alpha'(L)-C(2)S (Ca(2)SiO(4)) belite cement, starting from fly-ash of system CaO-SiO(2)-Al(2)O(3)-SO(3), and using the hydrothermal method in alkaline solution. The lime deficit in these ashes was compensated by the addition of slaked lime from lime bagging workshops. The hydrothermal treatment of the mixture was carried out in demineralized water, NaOH or KOH solution, continually stirred at a temperature below 100 degrees C and atmospheric pressure. The dehydration and calcination of the mixtures at temperatures between 800 and 1100 degrees C allowed alpha'(L)-C(2)S-rich cement to be obtained. The optimization of the synthesis parameters (temperature and time of stirring, pH of solution, temperature and duration of mixture burning) was also studied. The phase formation during various synthesis stages was studied by X-ray diffraction (XRD). Other techniques, such as SEM and EDX, were used to characterize the cement minerals. The results obtained showed that these ashes could form belite cement composed of only one dicalcium silicate phase (alpha'(L)-C(2)S).

The influence of heavy metals on the polymorphs of dicalcium silicate in the belite-rich clinkers produced from electroplating sludge

The purpose of this study is to utilize an electroplating sludge for belite-rich clinker production and to observe the influence of heavy metals on the polymorphs of dicalcium silicate (C(2)S). Belite-rich clinkers prepared with 0.5-2% of NiO, ZnO, CuO, and Cr(2)O(3) were used to investigate the individual effects of the heavy metals in question. The Reference Intensity Ratio (RIR) method was employed to determine the weight fractions of gamma-C(2)S and beta-C(2)S in the clinkers, and their microstructures were examined by the transmission electron microscopy (TEM). The results showed that nickel, zinc, and chromium have positive effects on beta-C(2)S stabilization (Cr(3+)>Ni(2+)>Zn(2+)), whereas copper has a negative effect. The addition of up to 10% electroplating sludge did not have any negative influence on the formation of C(2)S. It was observed that gamma-C(2)S decreased while beta-C(2)S increased with a rise in the addition of the electroplating sludge. Moreover, nickel and chromium mainly contributed to stabilizing beta-C(2)S in the belite-rich clinkers produced from the electroplating sludge.

The effect of glass synthesis route on mechanical and physical properties of resultant glass ionomer cements

Glass ionomer cements (GICs) have potential orthopaedic applications. Solgel processing is reported as having advantages over the traditional melt-quench route for synthesizing the glass phase of GICs, including far lower processing temperatures and higher levels of glass purity and homogeneity. This work investigates a novel glass formulation, BT 101 (0.48 SiO(2)-0.36 ZnO-0.12 CaO-0.04 SrO) produced by both the melt-quench and the solgel route. The glass phase was characterised by X-ray diffraction (XRD) to determine whether the material was amorphous and differential thermal analysis (DTA) to measure the glass transition temperature (T (g)). Particle size analysis (PSA) was used to determine the mean particle size and X-ray photoelectron spectroscopy (XPS) was used to investigate the structure and composition of the glass. Both glasses, the melt-quench BT 101 and the solgel BT 101, were mixed with 50 wt% polyacrylic acid (M (w), 80,800) and water to form a GIC and the working time (T (w)) and the setting time (T (s)) of the resultant cements were then determined. The cement based on the solgel glass had a longer T (w) (78 s) as compared to the cement based on the melt derived glass (19 s). T (s) was also much longer for the cement based on the solgel (1,644 s) glass than for the cement based on the melt-derived glass (25 s). The cements based on the melt derived glass produced higher strengths in both compression (sigma(c)) and biaxial flexure (sigma(f)), where the highest strength was found to be 63 MPa in compression, at both 1 and 7 days. The differences in setting and mechanical properties can be associated to structural differences within the glass as determined by XPS which revealed the absence of Ca in the solgel system and a much greater concentration of bridging oxygens (BO) as compared to the melt-derived system.

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.

Clinical performance of a bioactive dental luting cement--a prospective clinical pilot study

OBJECTIVE

To conduct a pilot study determining the clinical efficacy ofa new bioactive dental cement (Ceramir Crown & Bridge) for permanent cementation in fixed prosthodontics. The composition is a hybrid comprised of a calcium aluminate and a glass ionomer.

METHODS

This study examined the performance of Ceramir Crown & Bridge after cementation of high-gold alloy and porcelain-fused-to-metal (PFM) single crowns and bridges. A total of 38 crowns and bridge abutments were cemented in 17 patients; 31 were on vital, seven on non-vital teeth. Six were bridges with 14 abutment teeth (12 vital/two non-vital). One fixed splint comprising two abutment teeth was also included in the study. Preparation parameters were recorded, as well as working time, setting time, seating characteristics, and ease of cement removal. Baseline data were collected on dispensing, mixing, and handling of the cement; gingival inflammation index (GI), and a visual analog scale (VAS) and categorical assessment measured pre-cementation sensitivity. Post-cementation parameters were post-cementation sensitivity, categorical and VAS, gingival tissue reaction, marginal integrity, and discoloration. A one-week post-op telephone call recorded subjectively the patients' comfort level.

RESULTS

Working time (two minutes) and setting time (four minutes) were well within normal limits. Cement removal was determined to be very easy. Thirteen of 17 patients reported no post-cementation sensitivity after seven days; four reported a low-grade sensitivity. All 17 patients were seen for recall examinations at 30 days and six months. Of the four sensitivity cases, three were related to hyperocclusion, which disappeared spontaneously after adjustment. One case was due to post-cementation pressure from a three-unit bridge, which disappeared without intervention. After six months, no retentive failures were recorded, no sensitivity was subjectively reported, marginal integrity scored 38 alphas, one tooth had a 1 and two teeth a 0.5 GI score. Average VAS score for tooth sensitivity decreased from 7.63 mm at baseline to 0.44 mm at the six-month recall. Average GI score for gingival inflammation decreased from 0.56 at baseline to 0.11 at the six-month recall.

CONCLUSION

After six months, Ceramir Crown & Bridge performed favorably as a luting agent for permanent cementation.

Determination of the properties of an experimental glass polyalkenoate cement prepared from niobium silicate powder containing fluoride

OBJECTIVES

The purpose of this paper is to modify the conventional calcium fluoro-alumino-silicate glass, which is used in the formation of glass ionomer cements (CIGs) by the niobium addition and to study the properties of GICs obtained.

MATERIALS AND METHODS

Sol-gel process was used to prepare the powder at lower temperature than fusion method. Glass-ceramic powder obtained in this way was used to prepare the GICs. The properties such as working and setting times, microhardness and diametral tensile strength were evaluated for the experimental GICs and a commercial luting cement.

RESULTS

The ideal powder:liquid (P:L) ratio determined to prepare the experimental GICs was equal to 1:1. The cements prepared using this ratio showed working and setting times similar to the commercial GICs. In mechanical tests it was observed that microhardness and diametral tensile strength of the experimental GICs decreased significantly with the reduction of P:L ratio. On the other hand, the results obtained in microhardness tests indicated that the presence of niobium was a positive factor.

SIGNIFICANCE

The chemical process allows the development of glass-ceramic powder at 600 degrees C which is the goal of the present paper. It was concluded that GICs containing niobium might be used in dental applications and these results encourage further researches on other compositions.

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.

New polymeric materials for use in glass-ionomer cements

The polymeric materials currently used in GIC are based on poly(acrylic acid), poly(acrylic acid-co-itaconic acid), or poly(acrylic acid-co-maleic acid). For the visible light cured (VLC) type GIC, the polymeric material is chemically modified to have pendant free-radical polymerizable double bonds, with the aqueous formulation solution also containing a monomer having methacrylate groups. Exploring ways to improve both conventional and VLC GIC, routes to new acrylic acid copolymers have been explored, where acid groups are made more available for salt-bridge formation. In particular, amino acid modified acrylic acid copolymers have been prepared and shown to provide improved GIC. Also, it was discovered that the monomer N-vinylpyrrolidone (NVP) could be used to modify acrylic acid copolymers to provide a path to improved GIC. A new route to develop VLC GIC, based on the reaction of the acid copolymer, in water, with a cyclic imino ether (oxazoline) functionalized methacrylate monomer was developed. Looking for ways to change the microstructure of the acrylic acid copolymers, as a possible route to improve GIC, acrylic acid copolymers have been prepared under super critical conditions. A review of the aforesaid areas of research is provided in this manuscript.

MAS-NMR spectroscopy studies in the setting reaction of glass ionomer cements

OBJECTIVES

The main objective is the characterisation of the setting reaction in glass ionomer cements based on experimental ionomer glasses with different fluorine content and a commercial glass ionomer cement liquid by using 13C CP/MAS-NMR, 29Si, 27Al and 31P MAS-NMR spectroscopy in order to receive information specifically about the cross-linking process.

METHODS

Different fluorine containing glass compositions based on 4.5SiO2-3Al2O3-1.5P2O5-(5-z)CaO-zCaF(2) where z=0-3, were mixed with a commercially available polymer liquid to form glass ionomer cements. The cements were subjected to 27Al, 13C CP/MAS, 29Si, and 31P MAS-NMR analysis.

RESULTS

The 27Al spectra showed clearly the formation of six-fold coordinate Al(VI), that may crosslink the carboxyl groups in the poly-acid molecules. A shift towards to more positive values of the carboxyl peak in the 13C CP/MAS-NMR spectra showed clearly the proton dissociation of the carboxyl groups. A shift towards more negative values was observed in the 29Si MAS-NMR spectra, suggesting formation of hydrated silica gel and consequently formation of additional Si-O-Si bonds. 31P MAS-NMR spectra also reflected changes in the coordination state around a PO4(3-) tetrahedron. Increasing the fluorine content of the glasses resulted generally in increased reactivity during setting, due to promoting cross-linking and repolymerisation of the silicate phase, followed by clear changes in the MAS-NMR spectra.

CONCLUSIONS

The cross-linking process during the setting reaction of glass ionomer cements can be followed by MAS-NMR spectroscopy observing the conversion of Al(IV) to Al(VI). The acid base setting reaction is completed in 1 day and no further significant changes in the MAS-NMR spectra can be observed. Further study is required in order to understand the role of phosphorus.

Ion processes in glass ionomer cements

Ion processes are involved in many aspects of glass-ionomer cements. The ions released from the glass take part in the formation of the cement matrix. Although this process has been investigated, particularly using model cement systems, no study provides a complete matrix composition. Combining results from different studies enables an approximate composition to be derived. The importance of Phosphorous in controlling ion release from the glass surface has been identified in a number of studies. The release of ions from the set cement into water (and other aqueous liquids) has been much reported, particularly for fluoride. Over most of the release periods studied (i.e. from >7 days up to 3 years), release of F ion is related to t1/2 indicating a diffusion-controlled process. Other ions, except possibly Na+ also show this relationship. The amount of cumulative F release whilst maintaining this relationship indicates that more F than is in the matrix is involved. Ion chromatography would probably elucidate the precise form of the ionic species released. Glass-ionomer cements take up ions from solutions in which they are immersed. The levels are much higher than required to produce as internal/external equilibrium. Studies using dynamic SIMS and XPS give some information on ion location and elemental association. It is suggested that ToF SIMS would elucidate these further. Re-release of uptaken ions can vary considerably for different cements and ion species. Surface disruption of glass ionomers is caused by both F ion and monofluorophosphate ion and occurs much more readily in F containing cements than in F free ones. The mechanism of this process has not been elucidated. Analysis of the ions released from the cement as disruption occurs should provide an indication of the site of attack.

A novel amphiphilic acrylic copolymer based on Triton X-100 for a poly(alkenoate) glass-ionomer cement

OBJECTIVES

The aim of this study was to synthesize a novel ampiphilic polyalkenoic acid copolymer based on acrylic acid and a methacrylic macromonomer of Triton X-100 and determine the efficacy of the novel copolymeric polyalkenoic acid in the formation of glass-ionomer cements.

METHODS

Two water soluble copolymers of acrylic acid (AA) and a new amphiphilic macromonomer derived from Triton X-100 (MT) were prepared via radical copolymerisation at 60 degrees C, using azobisisobutyronitrile (AIBN) as the initiator and used to formulate conventional glass-ionomer cements with reactive glass fillers. The acid-base reaction was carried out by reacting aqueous solutions of the new copolymer (40 and 50%) with a commercial aluminofluorosilicate glass as used in conventional glass-ionomer cements. The efficacy of the new copolymer in the formation of glass-ionomer cements was investigated and preliminary results on setting parameters, FTIR analysis, mechanical properties and SEM analysis are reported in this paper.

RESULTS

The copolymers were synthesized and characterized and further used to successfully prepare glass-ionomer cements. The experimental cements exhibited longer setting and working times in comparison to conventional glass-ionomer cements and the inclusion of tartaric acid enhanced the mechanical properties, which were comparable to the commercial glass-ionomer cement, Fuji IX.

SIGNIFICANCE

Glass-ionomer cements prepared using ampiphilic comonomers is expected to influence their behavior in both polar and non-polar environments. As bulky side chains have been incorporated within the polymeric chain it is expected to affect the reaction kinetics of the acid-base reaction.

Synthesis and preparation of novel 4-arm star-shape poly(carboxylic acid)s for improved light-cured glass-ionomer cements

OBJECTIVE

The objective of this study was to synthesize and characterize novel 4-arm star-shape poly(acrylic acid)s (poly(AA)s) via atom-transfer radical polymerization (ATRP) technique, tether in situ light-curable methacrylate functionalities onto the poly(AA) backbone, use these star-shape poly(AA)s to formulate the light-cured glass-ionomer cements (LCGICs), and evaluate the mechanical strengths of the formed cements.

MATERIALS AND METHODS

The 4-arm poly(AA)s were synthesized using ATRP and tethered with either 2-isocyanatoethyl methacrylate (IEM) or glycidyl methacrylate (GM). The polymers were formulated with 2-hydroxyethyl methacrylte (HEMA) or methacryloyl beta-alanine (MBA), water, initiators, and Fuji II LC filler. Compressive strength (CS) was used as a tool to evaluate the formed cements. The specimens were conditioned in distilled water at 37 degrees C for 24h prior to testing.

RESULTS

The 4-arm poly(AA) showed a lower viscosity as compared to its linear counterpart. Both IEM-tethered and GM-tethered 4-arm poly(AA) constructed LCGICs showed significantly high mechanical strengths. Both types of co-monomer and grafting agent dramatically affected the mechanical strengths. The MBA-containing poly(AA) cements exhibited much higher CS than the HEMA-containing cements. The IEM-tethered poly(AA) cements showed much higher CS and DTS than the GM-tethered cements.

CONCLUSIONS

This study developed a novel light-curable 4-arm star-shape poly(AA) system. The system was 13% in CS, 178% in DTS and 123% in FS, compared to Fuji II LC.

In vitro biocompatibility of a novel Fe2O3 based glass ionomer cement

INTRODUCTION

Since their invention in the late 1960s, glass ionomer cements (GICs) have been used extensively in dentistry but recently they have also been utilised in ear nose and throat (ENT) surgery. Unfortunately, Al3+, a component of conventional ionomer glasses, has been linked to poor bone mineralisation and neurotoxicity.

OBJECTIVE

The aim of the research was to modify a commercial ionomer glass composition by substituting Al2O3 with Fe2O3.

METHODS

Glasses with the following molar compositions were fabricated: 4.5SiO2*3M2O3*XP2O5*3CaO*2CaF2 (M = Al or Fe, X = 0-1.5). The glasses were characterised using X-ray fluorescence (XRF) and X-ray powder diffraction (XRD). Cements were prepared using a standard ratio of; 1 g of glass powder: 0.2 g of dried polyacrylic acid: 0.3 g of 10% tartaric acid solution. Cement formation was assessed using a Gilmore needle and in vitro biocompatibility was investigated for novel cement formulations.

RESULTS

XRF revealed that the Fe2O3-based glasses had Al2O3 contamination from the crucibles and also had undergone substantial F- losses. XRD gave peaks that corresponded to magnetite Fe3O4 (JCPDS # 19-629) in all compositions. Apatite Ca5(PO4)3(OH,F) (JCPDS # 15-876) was identified in P2O5 containing glasses. It was possible to fabricate cements from all of the Fe2O3-based ionomer glasses. Good in vitro biocompatibility was observed for the Fe2O3-based cements.

CONCLUSION

Ionomer glasses may be prepared by entirely replacing Al2O3 with Fe2O3. Cement setting times appeared to be related to P2O5 content. Fe2O3-based cements showed good in vitro biocompatibility.

Novel amino acid-constructed polyalkenoates for dental glass-ionomer restoratives

Several methacrylate or acrylate derivatives of natural amino acids were synthesized and characterized. Based upon these derivatives, novel amino acid-constructed polyalkenoic acids were prepared and used to formulate glass-ionomer cements (GICs) with Fuji II glass filler. The effects of type of derivatives, molar ratio, molecular weight, and powder/liquid ratio were investigated. The results show that amino acid-constructed polyalkenoic acids can be formed only from amino acid methacrylate derivatives or by copolymerization of methacrylate with acrylate derivatives. Strong hydrogen bond interactions failed the polymer formation from acrylate derivatives. The cement composed of poly(methacryloyl glutamic acid-co-acryloyl beta-alanine) with the molar ratio of 8:2 demonstrated the best mechanical strengths along with a workable viscosity. By using the powder/liquid ratio of 3.0/1, the experimental cement exhibited a significantly higher FS (27.7 MPa), and nearly the same CS (198.5 MPa) and DTS (11.8 MPa), as compared to Fuji II (18.9 for FS, 189.1 for CS, and 11.4 MPa for DTS). During aging, the cement showed a significant increase in strength over 24 h, followed by a slow increase over 6 months.

The influence of environmental conditions on the material properties of setting glass-ionomer cements

OBJECTIVES

Aim of this study was to investigate the influence of temperature on the setting time and compressive strength of two conventional glass-ionomer cements (GIC's) and to determine the influence of storage medium, oil or water and storage time.

MATERIALS AND METHODS

Two conventional GIC's, Ketac Molar (3 M-ESPE Dental Products, Seefeld, Germany) and Fuji IX Fast (GC Corp., Tokyo, Japan) were used to perform flow property tests and compression tests. Flow property measurements were performed using a displacement rheometer at six different temperatures. From the results of the rheometer tests, the working times and setting times could be determined. The samples for the compressive tests were stored at four different temperatures and in two different media. Testing took place at five time intervals reaching from 1 h to 3 months.

RESULTS

The results of rheometer tests showed that a temperature increase speeded up the setting reaction significantly. The compressive strength results showed a jump in time as a result of the higher curing temperature but no long-term strength effect was observed. Materials curing in oil reached a significantly higher compressive strength compared to storage in water and Fuji IX Fast is significantly stronger than Ketac Molar.

SIGNIFICANCE

It was concluded that a temperature between 333 and 343 K almost sets conventional GIC's on command and improves the early compressive strength.

Effect of mixing method on the porosity of encapsulated glass ionomer cement

OBJECTIVE

To observe cement specimens mixed by various methods non-destructively using microfocus computerized tomography (micro-CT) and to evaluate the effect of mixing method on porosity.

METHOD

Five glass ionomer cements were used: two were hand-mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Fifteen cylindrical specimens were prepared for each material by each mixing method and stored in distilled water at 37 degrees C until testing. The specimens were observed and analyzed using micro-CT. 201 sliced images were obtained horizontally along the length of the specimens. Three-dimensional reconstructions were made and the sizes, numbers and total volume ratio of bubbles in the specimens were calculated.

RESULTS

Mixing method had a significant effect on porosity (P<0.05). For the luting/lining cement, mechanical mixing produced a significantly higher porosity (P<0.05). For the restorative cement, there were only small differences in porosity between specimens mixed by the two methods. More large bubbles were detected in specimens mixed mechanically than by hand for the fluid material. This suggested that for low-viscosity materials bubbles may combine until a certain viscosity is reached during setting.

SIGNIFICANCE

The strength of glass ionomer cement is affected by incorporated porosity and this depends on the mixing method. For low-viscosity cements, hand-mixing is favored in order to reduce porosity and increase strength, but this is not generally applicable to high-viscosity cements.

An amino acid-modified and non-HEMA containing glass-ionomer cement

It is known that unreacted 2-hydroxyethyl methacrylate (HEMA) in current resin modified glass ionomer cements (RMGICs) shows potential cytotoxicity to pulp and surrounding tissues. Elimination of HEMA could make RMGICs more attractive for dental applications. In this research, novel six acrylate and methacrylate derivatives of amino acids were synthesized, characterized and used for replace HEMA in RMGICs. The experimental RMGICs were formulated with vinyl-containing polymer, amino acid derivative, water, and commercial Fuji II LC glass. Among all the derivatives, methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high CS. Effects of polymer content and powder/liquid, P/L, ratio were significant. The formulation with liquid composition of 50/25/25 (polymer/MBA/water) and P/L ratio of 2.7/1 was found the optimal. It appears that this novel non-HEMA-containing RMGIC system based on amino acid derivatives will be a better dental restorative because it demonstrated improved mechanical strengths and may eliminate potential cytotoxicity in current RMGICs caused by leached HEMA. The optimal MBA-modified GIC were 20% higher in CS, 70% higher in DTS and 93% higher in FS, compared to Fuji II LC.

Synthesis and evaluation of HEMA-free glass-ionomer cements for dental applications

OBJECTIVE

The objective of this study was to synthesize and characterize amino acid acrylate and methacrylate derivatives, use them to formulate light-cured glass-ionomer cements (LCGICs), and evaluate their mechanical strengths.

MATERIALS AND METHODS

Acrylate and methacrylate derivatives of six amino acids were synthesized and characterized using FT-IR and 1HNMR spectroscopy. The LCGICs were formulated using a newly synthesized polymer having pendant methacrylate groups (in other words, a methacryloyl derived polymer or MDP), amino acid derivatives, water, and Fuji II LC glass. Compressive strength of the cements and viscosities of the resin liquids were used as screening tools in order to determine the optimal formulation. The specimens were conditioned in distilled water at 37 degrees C for 24 h prior to testing.

RESULTS

The measured compressive strengths (MPa) of the cements were found to depend on the amino acid derivative used: acryloyl aspartic acid (268.5) > methacryloyl beta-alanine (259.1) = methacryloyl glutamic acid (254.5) = acryloyl beta-alanine (251.9) > acryloyl glutamic acid (238.8) > methacryloyl aspartic acid (210.9). Methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high compressive strength. Effects of MDP content and power/liquid (P/L) ratio were significant. The formulation with a liquid composition of 50/25/25 (MDP/MBA/water) and P/L ratio of 2.7/1 was found to give optimal properties and handling of all the formulations studied.

CONCLUSIONS

A novel HEMA-free LCGIC system based on amino acid derivatives has been developed. This system may eliminate potential cytotoxicity in current LCGICs caused by leached 2-hydroxyethyl methacrylate (HEMA). The optimal MBA-modified cements were 20% higher in compressive strength, 70% higher in diametral tensile strength (DTS) and 93% higher in flexure strength (FS), as compared to Fuji II LC cement.

Reactive fibre reinforced glass ionomer cements

The mechanical properties of glass ionomer cements used in restorative dentistry reinforced by chopped glass fibres were investigated. Reactive glass fibres with a composition in the system SiO(2)-Al(2)O(3)-CaF(2)-Na(3)AlF(6) and a thickness of 26 microm were drawn by a bushing process. The manufacturing parameters were optimized with respect to maximum strength of the glass fibre reinforced ionomer cements. Powder to liquid ratio, pre-treatment of the glass, grain size distribution and fibre volume fraction were varied. Glass fibre and cement were characterized by X-ray diffraction, transmission electron microscopy and energy dispersive spectroscopy techniques, respectively. The highest flexural strength of the reinforced cement (15.6 MPa) was found by compounding 20 vol% reactive fibres and extending the initial dry gelation period up to 30 min. Microscopic examination of the fractured cements indicated a distinct reactive layer at the fibre surface. A pronounced fibre pull out mode gives rise to an additional work-of-fracture contributed by pulling the fibres out of the fracture surface.

Devitrification of ionomer glass and its effect on the in vitro biocompatibility of glass-ionomer cements

The effects of devitrification of an ionomer glass with a molar composition 4.5SiO(2).3Al(2)O(3).1.5P(2)O(5).3CaO.2CaF(2) on cement formation and in vitro biocompatibility were investigated. Differential thermal analysis was used to study the phase evolution in the glass, and to determine the heat treatments for production of glass-ceramics. X-ray diffraction patterns from glass frit heat-treated at 750 degrees C for 2h contained peaks corresponding to apatite (JCPDS 15-876), whereas for samples heat-treated at 950 degrees C for 2h apatite and mullite (JCPDS 15-776) were the major phases detected. Transmission electron microscopy (TEM) confirmed that apatite and apatite-mullite phases were present after heat treatments at 750 degrees C and 950 degrees C respectively. Glass and glass-ceramics were ground to prepare <45microm powders and glass ionomer cements were produced using a ratio of 1g powder: 0.2g PAA: 0.3g 10% m/v tartaric acid solution in water. In vitro biocompatibility was evaluated using cultured rat osteosarcoma (ROS) cells. Scanning electron microscopy (SEM) showed that cells colonised the surfaces of cements prepared using untreated ionomer glass and glass crystallised to form apatite (750 degrees C/2h). However, quantitative evaluation using MTT and total protein assays indicated that more cell growth occurred in the presence of cements prepared using ionomer glasses crystallised to apatite than cements prepared using untreated glass. The least cell growth and respiratory activity was observed on cements made with crystallised glass containing both apatite and mullite. It was concluded that the controlled devitrification of ionomer glasses could be used to produce GIC bone cements with improved biocompatibility.

A hybrid zinc-calcium-silicate polyalkenoate bone cement

A novel bone cement composed of sintered zinc-calcium-silicate phosphate and hybrid polyalkenoates has been developed. Synthesis and formulation of glass fillers, monomers and polymers as well as formulation of the cement were described. The effects of sintering, polymer content, glass powder/polymer liquid (P/L) ratio and comonomer on compressive strength (CS) and curing time (CT) were investigated. The effects of P/L ratio and comonomers on shrinkage as well as exotherm were also studied. Results show that the experimental cement was 61% higher in CS, 10% lower in diametral tensile strength, 35% lower in flexural strength, 62% less in exotherm, and 68% less in shrinkage, compared to conventional polymethylmethacrylate cement. With increasing polymer content and P/L ratio in the cement formulation CS of the cement increased but CT decreased. Curing time, shrinkage and exotherm of the cement decreased with increasing P/L ratio. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and formulation is optimized.

How storage and mixing affect a resin-modified glass ionomer

This study investigates how the storage time and mixing speed of an older (20+ years old), common brand triturator affect the working time of a resin-modified glass ionomer restorative material. To achieve consistent working times, the correct mixing speed should be used, especially for material near its expiration date.

Expulsion force, surface pH, and porosity of encapsulated glass-ionomer cements mixed with a Rotomix device

The aim of this study was to evaluate the Rotomix mixing device, used for mixing glass ionomer cements, in comparison with conventional mixing procedures including both hand and amalgamator methods. The properties examined were extrusion force, surface pH (indicating homogeneity), and porosity. The results indicated that the Rotomix device produced cement mixtures without compromising any of the examined properties relative to other mixing methods.

Influence of glass composition on the properties of glass polyalkenoate cements. Part II: influence of phosphate content

The influence of phosphate content of the glass on the formation of glass polyalkenoate cements was investigated. Glasses were synthesised based on (4.5 - 2X)SiO2-3.0 Al2O3-(3.0 - X)CaO-(1.5 + X)P2O5-2.0 CaF2 and X was varied from -1.5 to 0.8. The setting and working time of the cement pastes increased with the phosphate content of the glass (X). Increasing the phosphate content resulted in an initial increase in compressive strength followed by a sharp reduction in strength. Young's modulus and un-notched fracture strength exhibited a maximum at intermediate phosphate contents. Fracture toughness reduced at high phosphate contents, whilst toughness increased. Phosphate in the glass is thought to aid glass degradation by providing additional phosphorus-oxygen bonds for hydrolysis, but may also reduce the amount of aluminium released by reducing the susceptibility of aluminium-oxygen-silicon bonds to acid hydrolysis. The released phosphate may also compete with the carboxylate groups in the polysalt matrix cement for cations inhibiting the crosslinking reaction.

Influence of glass composition on the properties of glass polyalkenoate cements. Part I: influence of aluminium to silicon ratio

Hydrolysis of aluminium-oxygen-silicon bonds is thought to be the first step in the setting reaction of polyalkenoate cements and the aluminium to silicon ratio of the glass is widely believed to be a dominant factor determining cement properties. The properties of glass polyalkenoate cements based on the generic glass composition (6 + X)SiO2 x (4 - X)Al2O31.5P2O5 x 4CaOCaF2 with varying aluminium to silicon ratio were studied. Setting and working times of the cement pastes, compressive strength, un-notched fracture strength, Young's modulus, fracture toughness and toughness were evaluated for the cements. In contrast to previous studies the aluminium to silicon ratio was not found to influence the cement properties significantly. The high phosphorus content of the glasses studied is thought to reduce the influence of the aluminium to silicon ratio of the glass, as a result of phosphorus locally charge balancing four coordinate aluminium ions in the glass network, as well as providing an additional mechanism of degradation in the form of hydrolysable phosphorus-oxygen bonds.

[The formulation of glass ionomer cements and the amount of fluoride]

The glass-ionomer cements (GIC) were developed in the late sixties. The set cement is the result of an acid-base reaction between an ion-leachable glass (the base) and a poly (alkenoic acid). Through the years, the number of applications of these GIC has increased steadily. The evolution has to be referred to the fact that the composition of both acid and base can be changed considerably. This has resulted in the marketing of GIC with different physical and chemical formulations. Furthermore resin-modified GIC were introduced in the late eighties. One of the major GIC advantages remains the fluoride release. The fluoride in GIC is a component of the material itself and is not added afterwards. Beneficial for the GIC in this respect is that the released fluoride is not of structural importance in the set cement. Furthermore the fluoride release does not result on itself in a reduction of physical properties or an increase in porosity.

[The formulation of glass ionomers and their degree of fluoride]

The glass-ionomer cements (GIC) were developed in the late sixties. The set cement is the result of an acid-base reaction between an ion-leachable glass (the base) and a poly (alkenoic acid). Through the years, the number of applications of these GIC has increased steadily. The evolution has to be referred to the fact that the composition of both acid and base can be changed considerably. This has resulted in the marketing of GIC with different physical and chemical formulations. Furthermore resin-modified GIC were introduced in the late eighties. One of the major GIC advantages remains the fluoride release. The fluoride in GIC is a component of the material itself and is not added afterwards. Beneficial for the GIC in this respect is that the released fluoride is not of structural importance in the set cement. Furthermore the fluoride release does not result on itself in a reduction of physical properties or an increase in porosity.

Preparation of glass ionomer cement using N-acryloyl-substituted amino acid monomers--evaluation of physical properties

OBJECTIVES

The objectives of this study were (1) to develop polyacid formulations through the incorporation of amino acid-derived monomers with carboxylic acid groups at various distances away from the polymer backbone to allow for greater flexibility, less rigid ionic cluster formation and improved solubility, and (2) to test selected physical and handling properties of experimental ionomers with a conventional glass ionomer as a control.

METHODS

The polycarboxylic acids prepared and used in glass ionomer formulation in this study included N-acryloylglutamic acid (AGA) and N-acryloyl-6-aminocaproic acid (AACA)- modified acrylic acid- ++itaconic acid copolymers, where the acrylic acid:itaconic acid:amino acid monomers were combined in different proportions. The characterization and purity of the monomers were determined by FTIR and their melting points. The characterization of synthesized polymers included molecular weight and relative viscosity determinations. The compressive strengths, diametral tensile strengths, flexural strengths and fracture toughness of the experimental ionomers and a commercially available ionomer (control) were measured after storage in water, at 37 degrees C for 1 h or 7 d. The working times and setting times of the experimental ionomers were compared to the control specimens. Separate analysis of variance and Tukey's tests were used to study the statistical significance of the physical strength parameters as a function of materials and storage times.

RESULTS

Significant increases (p< 0.001) in diametral tensile, compressive, flexural strengths and fracture toughness were observed in the AGA co-polymers, while significant increases were observed in diametral and flexural strengths in the AACA co-polymers compared to the control Fuji II. The working and setting times of all except one experimental ionomer studied were comparable to the controls.

SIGNIFICANCE

The use of amino acid-modified acrylic monomers to produce water soluble copolymers of acrylic-itaconic acid offers a new route of discovery to produce chemical-cured glass ionomers with improved physical properties. The spacer chain length, the hydrophobicity of the chains, the molecular weight and viscosity of the polymer all played important roles in determining the physical properties of the material.

Ossiculoplasty with Polymaleinate Ionomeric Prosthesis

With the continued concern over the possible transmission of viral infections through homologous middle ear implants, there is increasing pressure to develop a truly biocompatible alloplastic middle ear prosthesis. The polymaleinate ionomer, which has been used in dentistry as a filling and luting material for more than 15 years, has recently been used to construct total and partial ossicular replacement prostheses. In an attempt to evaluate these new implants, a multicenter prospective clinical trial was initiated. To date, 92 patients have undergone implantation. The follow-up interval ranged from 3 months to 22 months. Although it is premature to discuss the long-term results, the preliminary surgical experience and audio-metric data with these implants are reviewed. From a surgical perspective, the ionomeric prostheses were easily contoured with a diamond burr and were not prone to shattering. Preliminary follow-up audiometric data were available on 80 patients (59 partial ossicular replacement prostheses and 21 total ossicular replacement prostheses). Of the 59 partial ossicular replacement prostheses the air-bone gaps (average of 500 Hz, 1 kHz, 2 kHz and 3 kHz) were as follows: 0 dB to 10 dB, 15 (25%) of 59; 11 dB to 20 dB, 20 (34%) of 59; 21 dB to 30 dB, 11 (19%) of 59; and greater than 30 dB, 13 (22%) of 59. Of the 21 total ossicular replacement prostheses the air-bone gaps were as follows: 0 dB to 10 dB, 6 (29%) of 21; 11 dB to 20 dB, 6 (29%) of 21; 21 dB to 30 dB, 5 (24%) of 21; and greater than 30 dB, 4 (19%) of 21.

New aspects of the setting of glass-ionomer cements

For many years, glass-ionomer cements have been described as setting by the formation of a poly(acrylate) matrix. Recent research has suggested that a second reaction may be involved, namely, the formation of a silica matrix. So that this hypothesis could be tested, non-polymer cements, based on an ionomer glass plus acetic acid, were prepared and stored for up to six months. They were insoluble in water, and their compressive strength was found to increase rapidly over the period of storage. By contrast, the product of the reaction between ZnO and acetic acid was soluble in water. These results support the idea that there is a secondary setting reaction in glass ionomers and suggest that it is responsible for the increase in strength observed.

Effect of mixing speed on mechanical properties of encapsulated glass-ionomer cements

It is well established that the strength of encapsulated dental amalgam is affected by the speed of mixing. An investigation into the effects of mixing speeds on the compressive strength of three encapsulated glass-ionomer cements was carried out. The working and setting time and compressive strength at 24 hours and 7 days were evaluated for the three materials at four mixing speeds. There appeared to be little variation in working and setting times at the different mixing speeds. The early compressive strength of one material, Ketac-fil, increased as the speed of mixing increased. The variation in mixing speed did not appear to affect the early compressive strengths of the other two materials. Seven-day compressive strengths of all three materials were not affected by variations in mixing time.

The effect of using layered specimens for determination of the compressive strength of glass-ionomer cements

Compressive strength is widely used as the criterion of strength of glass-ionomer dental cements, despite the difficulties in interpretation of the findings. With the introduction of light-cured glass-ionomer cements, which can be used only in thin layers, the question arises of how test specimens should be prepared for the measurement of compressive strength. A suggested method has been to prepare test pieces by building them up in layers, an approach which is examined critically in the current paper. Two different conventional (acid-base) glass-ionomers were studied with the use of layered and unlayered specimens of dimensions 6 mm (height) x 4 mm (diameter) and 12 mm (height) x 6 mm (diameter). While smaller samples gave the same value of compressive strength as larger specimens, layered specimens gave significantly lower values of compressive strength for both sizes. In view of these findings, and since the layered specimens are tedious to prepare, we conclude that compressive strength is unsatisfactory as a criterion of strength for light-cured glass-ionomer cements.

Bending strength of Fuji and Ketac glass ionomers after sonication

Glass ionomer cements mixed by conventional methods contain voids that can decrease their overall strength. This study evaluated the effect of sonication on the reduction of air entrapment by measuring the bending strength in glass ionomer cements (Fujj-II and Ketac-fil). Glass ionomer cement was placed in identical-test vials and sonicated for 45s, 10s, or 0s. The bending strengths were measured (0.005 in min-1) after setting times of 1 or 2 weeks. Mean bending strengths (MPa +/- SD) for the 12 treatment both cements (P < 0.001) and sonication times (P < 0.001). The effect of setting time produced minimal increases in bending strength (P < 0.218). The sonication of freshly mixed glass ionomer cements is a possible solution for reducing voids to increase bending strength.

Development of novel dental cements. I. Formulation of aluminoborate glasses

Aluminoborate glasses were formulated as potential novel glass-ionomer cement components, and their reactivity with a polyalkenoic acid was assessed by means of working and setting time measurements. Of the 20 prepared formulations, some containing fluoride, eight were found to have acceptable manipulative characteristics, and three of these formed hard set materials.

Development of novel dental cements. II. Cement properties

Following earlier work, three novel aluminoborate glasses have been studied as potential cement components. Factors studied include the effect of batch size on composition and manipulative characteristics, and the effect of tartaric acid and conditions of storage on mechanical properties. It was concluded that two materials have potential for application as dental luting agents.

Phosphate glass cement bone graft

The objective of this study was to prepare cement-forming substances from phosphate glasses for use as a bone graft. The glass-forming system of CaO-SrO-Na2O-P2O5 was explored and ten phosphate glasses were prepared of varying compositions. Cements were made by reducing the glass to powders and reacting them with a water solution of calcium hydroxide or phosphoric acid. The cements were evaluated by X-ray diffraction, electron microscopy, density and porosity measurements, pH change during reaction and solubility in water. Because of the water solubilities of these cement materials, they may be useful as bone grafts containing drugs such as antibiotics which would be slowly released as the graft material degrades.

Glass-ionomer cement formulations. II. The synthesis of novel polycarobxylic acids

The synthesis of many polycarboxylic acids is reported. An account is given of their stability in aqueous solution and the properties of cements formed by their reaction with ion-leachable glasses. A copolymer of acrylic and itaconic acids was found to combine several favorable characteristics.