An assessment of encapsulated versus hand-mixed glass ionomer restoratives

Capsulation should enable uniform proportioning and mixing of dental restoratives so that functional properties of the cementitious mass will not be susceptible to clinically induced variability. Mechanical mixing induces a definite pore distribution determined by the viscosity of the system. This study evaluated the mixing process on the performance of a range of glass ionomer dental restoratives. Mean compressive fracture strengths and standard deviations and the associated Weibull Moduli (m) were determined for six glass ionomer restoratives that were either encapsulated or mixed by hand. Working characteristics were assessed using an oscillating rheometer. Scanning electron microscopy and image analysis was used to investigate the influence of the mixing method on pore distribution. The fracture strength data for some encapsulated restoratives resulted in significant differences compared with hand-mixing. Rotomix (compared with the Capmix mechanical agitator) resulted in increased Weibull moduli and 10% failure stress for the two restoratives that were investigated. Encapsulated restoratives that were prepared utilizing Rotomix or Capmix resulted in no significant differences for working characteristics; however, the setting time for the ChemFlex in Caps was extended compared with the hand-mixed ChemFlex. Not all restoratives had reduced porosity and improved performance following mixing with a Rotomix. This suggested that optimization of the initial viscosity of the system by manipulating the individual proportions of the constituents may not have been appropriate for all the restoratives investigated. The increased viscosity for hand-mixed ChemFlex prepared to a consistency of 3.8 g/ml compared with encapsulated ChemFlex in Caps prepared to a consistency of 3.5 g/ml was responsible for the reduced setting time.     

Preliminary study on chitosan modified glass ionomer restoratives.

OBJECTIVES: The aim of this study was to investigate the effect of chitosan (CH), a biocompatible polysaccharide, on the flexural strength of glass ionomer restoratives (GIR) and on the release of fluoride ions from GIR. METHODS: Commercial GIR (Vidrion, SS White) has been modified by adding chitosan (CH, Fluka). Samples containing 0.0044, 0.012, 0.025 and 0.045wt% CH were prepared, molded and weighed. For flexural strength, sets of 10 specimens 10mmx2mmx2mm of commercial and CH modified GIR were prepared. Differences were analyzed by the one-way analysis of variances (ANOVA) test, at significance level 0.05. The data were also analyzed by post hoc Tukey's HSD for unequal n (Spjotvoll/Stoline) test. Scanning electron microscopy analyses were performed on the composites cryo-fracture surfaces. For the fluoride release tests and medium pH determination, discs with 10mm diameter and 2mm height were prepared in a PTFE mold placed between two glass slides. Samples were weighed in order to normalize each material test group. At least 10 samples of each material were prepared. Approximately 5min after preparation the discs were transferred into individual glass flasks containing 50mL of distilled water. The concentration of released fluoride was determined as a function of time by means of a fluoride ion selective electrode Orion 94-09 SC connected to an Ionanalyser (Orion Research Inc., USA). The medium pH was monitored as a function of time at (25+/-1 degrees C), using a Digimed DM20 potentiometer (Digicrom Instrumentos, Brazil) equipped with a combined glass electrode. Ellipsometric measurements were performed to quantify the thickness of adsorbed polymer (poly(acrylic acid) or the mixture of poly(acrylic acid) with CH). RESULTS: The addition of 0.0044wt% of CH led to a significant increase in the flexural resistance. CH contents higher than 0.022wt% led to poor performance. For the same period of time the amount of fluoride ions released from CH modified GIR was much larger than that released from commercial GIR. CH catalyzed the fluoride release from GIR to the medium, especially from those with 0.0044wt% of CH. As a consequence, the medium pH increased from 5.0 to 6.3. A model based on the formation of a polymeric network around the inorganic particles was proposed to explain the experimental findings. The adsorption of CH and poly(acrylic acid) onto planar Si/SiO(2) substrates was quantified and supported the proposed model. SIGNIFICANCE: The results presented here showed that the flexural strength of a commercial GIR can be considerably improved by the addition of a tiny amount of CH. Moreover, in the presence of CH, the release of fluoride ions from GIR is catalyzed.     

Effect of early water exposure on the strength of glass ionomer restoratives

This study examined the effect of early water exposure on the shear strength of a spectrum of glass ionomer restoratives. The materials evaluated included conventional auto-cured (Fuji II [FT], GC), resin-modified light-cured (Fuji II LC [FL]) and, recently introduced, high strength auto-cured (Fuji IX GP Fast [FN], GC; Ketac Molar Quick [KQ], 3M-ESPE; Ketac Molar [KM], 3M-ESPE) cements. Sixteen specimens (8.7-mm in diameter and 1-mm thick) of each material were prepared in metal washers and randomly divided into 2 groups. The specimens were allowed to set for 6 minutes between polyester strips, to ensure completion of the initial set. The strips were subsequently removed, and the surfaces of Group 1 specimens were coated on both sides with resin (Fuji Coat LC, GC) and light cured for 10 seconds. Group 2 specimens were left uncoated. All specimens were then conditioned in distilled water at 37 degrees C for 4 weeks. After conditioning, the specimens were restrained with a torque of 2.5 Nm and subjected to shear punch testing using a 2-mm diameter punch at a crosshead speed of 0.5-mm/minute. The mean shear strengths of the materials were computed and subjected to Independent Samples t-test and ANOVA/Scheffe's tests at significance level 0.05. Mean strength ranged from 78.34 to 99.36 MPa and 79.88 to 95.78 MPa for Groups 1 and 2, respectively. No significant difference in shear strength was observed between the 2 groups. For both groups, KM and KQ were significantly stronger than FT. Contrary to current teaching, early exposure to water did not weaken glass ionomer restoratives. A marginal increase in strength was actually observed for some materials.     

Bond strengths of glass ionomer restoratives to primary vs permanent dentin

An in vitro experiment was conducted to evaluate the shear bond strength of a conventional GIC (glass ionomer cement) and a RMGIC (resin modified glass ionomer cement) when applied to dentin of primary and permanent teeth. Results show that the bond strength of the RMGIC was more than thrice that of the conventional GIC. Fracture analysis showed that the bond failures were cohesive in the cement.     

The physical-mechanical performance of the new Ketac Molar Easymix compared to commercially available glass ionomer restoratives

OBJECTIVES: To evaluate the time dependence of physical-mechanical performance of glass ionomer restoratives. METHODS: The physical-mechanical properties of Ketac Molar Easymix in comparison to four handmix glass ionomer restoratives were evaluated by testing the compressive and flexural strength, acid erosion and solubility. By testing the properties in the early and late setting phase it was determined how fast the level of material characteristics is achieved. IR spectroscopy was used for monitoring the acid-base reaction. RESULTS: The compressive strength after 1 and 24h setting time show that Ketac Molar Easymix and Fuji IX demonstrate a significantly higher performance. Ketac Molar Easymix exhibits by far the highest flexural strength 1h after start of setting. After 24h, it remains at this high level and only Vitro Molar and Fuji IX come close. Ketac Molar Easymix and Fuji IX show the lowest solubility in neutral media after 24h and 7d. It is remarkable that the solubilities of Ionofil Molar, Vitro Molar and Vidrion R stored in water for 24h are higher than those of Ketac Molar Easymix and Fuji IX obtained after 7d water immersion. In acidic media Ketac Molar Easymix is least prone to acid erosion. CONCLUSIONS: For clinical success of a filling material the early achievement of a high physical-mechanical performance is mandatory to minimize the risk of early damage to a restoration. With the high flexural strength reached after 1h combined with the lowest susceptibility for acid-attack and solubility in water, Ketac Molar Easymix, from 3M ESPE, provides the best performance of any materials tested.     

In vitro caries inhibition at the enamel margins of glass ionomer restoratives developed for the ART approach

OBJECTIVES: To assess the ability of conventional glass ionomer cements manufactured specifically for the atraumatic restorative treatment (ART) approach to inhibit the in vitro demineralization of enamel. METHODS: Twenty-four sound permanent premolar teeth, extracted for orthodontic reasons, had cervical cavities (4x2x1. 5mm(3)) prepared in enamel. These were restored with Fuji IX, Fuji IX GP, Ketac-Molar and Compoglass, and then thermocycled 300 times between 5-55 degrees C before being placed in a demineralizing solution (0.1M lactic acid with 1g/l dissolved hydroxyapatite at pH 4.7) for four weeks. Buccolingual planoparallel sections were cut axially through the restorations, and subsequently lapped to approximately 100 microm thickness. The sections were examined with a polarized light microscope, and lesion measurements made using image analysis software. ANOVA and coefficients of variance were used to compare the findings. RESULTS: Compoglass and Ketac-Molar showed significantly less surface erosion than did the other two cements (p<0.0001). Inhibition of enamel demineralization immediately adjacent to the restoration margins was more frequent with the glass ionomer cements (20.5-25.0%) than with Compoglass (13.0%). However, the widths of the inhibition zones varied between materials and sites. CONCLUSIONS: Fluoride ion release from the restorative materials afforded some degree of protection to the adjacent enamel against in vitro demineralization.     

玻璃离子黏固剂的粘接

玻璃离子黏固剂作为充填材料,具有很多优良的性能特点,在临床中得到广泛应用,但其粘接性能并未引起临床医生的重视。下面就玻璃离子黏固剂的组成、固化、粘接机制、影响粘接的因素以及牙表面预处理对玻璃离子黏固剂粘接力的影响等作一综述。     

The radiopacity of glass ionomer dental materials

Although some glass ionomer dental materials are described as radiopaque by the manufacturer, it is rare for the actual degree of radiopacity to be specified. Using a technique previously described for measurement of the radiopacity of enamel, dentine and composite resin dental materials, the radiopacity of a number of glass ionomer materials, including restorative, lining and luting cements, was determined.     

The properties of metal-reinforced glass ionomer materials

The physical properties and bond strengths of two glass ionomer materials reinforced with silver and amalgam alloy powders were compared with those of a conventional material from the same manufacture as well as two commercially available products. The diametral tensile strength, hardness and bonding strength are improved with the addition of either commercial available silver particles or fabricated high-copper amalgam alloy powders to the glass. Simple mixture of the metal or alloy powders with the glass ionomer cement seems to be feasible to improve the properties of the regular cement. However, further studies in formulating an optimal composition of metal or alloy, setting characteristics and long-term clinical evaluation are necessary before proposing uses for this new material.     

Microleakage of glass ionomer/composite resin restorations: A laboratory study. 1. The influence of glass ionomer cement

Acid-etching of enamel margins, often combined with bevelling and use of a low viscosity resin, has resulted in improved sealing of composite restorations. When enamel is absent and margins involve dentine or cementum, microleakage is more often observed. The use of glass ionomer cement, as both a restorative material and as a base combined with a veneer of composite resin, has been advocated as a means of minimizing microleakage where margins are placed in dentine or cementum. Four restorative techniques incorporating glass ionomer cement were used, in vitro, to restore cervical cavities. After thermal cycling, dye penetration was scored along occlusal and gingival margins. In all instances the gingival margin exhibited a less reliable seal than the occlusal margin. The sandwich restorations produced a superior seal at both occlusal and gingival margins when compared with glass ionomer restorative cement.     

Physical property investigation of contemporary glass ionomer and resin-modified glass ionomer restorative materials

Objectives

The objective of this study was to investigate selected physical properties of nine contemporary and recently marketed glass ionomer cement (GIC) and four resin-modified glass ionomer cement (RMGI) dental restorative materials.

Materials and methods

Specimens (n = 12) were fabricated for fracture toughness and flexure strength using standardized, stainless steel molds. Testing was completed on a universal testing machine until failure. Knoop hardness was obtained using failed fracture toughness specimens on a microhardness tester, while both flexural modulus and flexural toughness was obtained by analysis of the flexure strength results data. Testing was completed at 1 h, 24 h, 1 week, and then at 1, 3, 6, and 12 months. Mean data was analyzed with Kruskal-Wallis and Mann-Whitney (p = 0.05).

Results

Physical properties results were material dependent. Physical properties of the GIC and RMGI products were inferior at 1 h compared to that at 24 h. Some improvement in selected physical properties were noted over time, but development processes were basically concluded by 24 h. A few materials demonstrated improved physical properties over the course of the evaluation.

Conclusions

Under the conditions of this study:

1. 1.

   GIC and RMGI physical property performance over time was material dependent;

2. 2.

   Polyalkenoate maturation processes are essentially complete by 24 h;

3. 3.

   Although differences in GIC physical properties were noted, the small magnitude of the divergences may render such to be unlikely of clinical significance;

4. 4.

   Modest increases in some GIC physical properties were noted especially flexural modulus and hardness, which lends support to reports of a maturing hydrogel matrix;

5. 5.

   Overall, GIC product physical properties were more stable than RMGI;

6. 6.

   A similar modulus reduction at 6 months for both RMGI and GIC produced may suggest a polyalkenoate matrix change; and

7. 7.

   Globally, RMGI products demonstrated higher values of flexure strength, flexural toughness, and fracture toughness than GIC materials.

Clinical relevance

As compared to RMGI materials, conventional glass ionomer restorative materials demonstrate more stability in physical properties.

     

The use of glass ionomer cements in endodontics

Glass ionomer cements are currently used in endodontic therapy for sealing root canals (orthogradely and retrogradely), for sealing and restoring the pulp chamber, for repairing perforations and root resorption defects, and, rarely, for treating vertically fractured teeth. The successful use of these cements is the result of their particular characteristics: a chemical bond to dentin, which enhances the seal of the root canal and the reinforcement of the tooth; a good biocompatibility in the periradicular area and a fluoride release without loss of strength of the material. The fluoride release imparts an antimicrobial effect to combat root canal infection and attributes to bone mineralization after surgery. The present paper reviews the literature regarding the various applications of glass ionomer cements in present-day endodontics.