Dentin bond strength of light-cured glass-ionomer cements

Evaluating dentin surface treatments for resin-modified glass ionomer restorative materials

This in vitro study evaluated the effect of six surface treatments on the shear bond strength of three resin-modified glass ionomers (RMGIs) to dentin. Occlusal surfaces of caries-free third molars were reduced to expose only dentin. Surface treatments were smear layer intact (negative control), Cavity Conditioner, EDTA, Ketac Primer, Self Conditioner, and etching with 35% phosphoric acid followed by the application of Optibond Solo Plus. Filtek Z250 composite resin bonded with Optibond Solo Plus served as a positive control. Conditioning agents were used according to the manufacturers' instructions. After surface treatments, Fuji II LC, Riva LC, Ketac Nano, and Filtek Z250 were placed in copper-band matrices 5 mm in diameter and 2 mm in height and were light-cured for 20 seconds. Specimens were stored in 100% humidity for 24 hours, after which they were placed in deionized water for 24 hours at 37°C. They were then tested under shear forces in an Instron Universal Testing Machine at a crosshead speed of 0.5 mm/min. A two-way analysis of variance and Tukey honestly significant difference statistical analyses (p<0.05) indicated significant interaction between RMGIs and conditioning agents. Acid etching followed by Optibond Solo Plus provided highest bond strengths for all three RMGIs, which were not statistically different from the positive control.

Effect of ultrasonic excitation on the microtensile bond strength of glass ionomer cements to dentin after different water storage times

The application of ultrasound waves on glass ionomer cement (GIC) surface can accelerate the early setting reaction and improve the mechanical properties of the material, resulting in higher resistance to masticatory forces within a short period of time and thus increasing the clinical longevity of the GIC restoration. In this study, the microtensile bond strength (μTBS) of two high-viscosity GICs (Fuji IX GP and Ketac Molar Easymix) and one resin-modified GIC (RMGIC-Vitremer) to dentin was tested after ultrasonic excitation and water storage. GIC blocks were built up on coronal dentin either receiving or not receiving a 30-s ultrasound application during the material initial setting. After storage in water for either 24 h or 30 d, beam-shaped specimens with a cross-sectional area of approximately 1.0 mm(2) were cut perpendicular to GIC/dentin interface and tested to failure. At 24 h, the ultrasonically set Ketac Molar had significantly higher (p < 0.05) μTBS than the cement set conventionally. Chemically set Ketac Molar presented significantly higher μTBS after the longer water storage (p < 0.05). The RMGIC presented the highest μTBS regardless of ultrasonic excitation and storage period. In conclusion, ultrasound application to Ketac Molar improved its adhesion to dentin, particularly within the first 24 h after setting. Clinically, it seems that ultrasonic excitation can contribute to prevent retention loss of restoration at early stages of GIC setting reaction.

Comparison of failure mechanisms for cements used in skeletal luting applications

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr-Ca-Zn-SiO(2)) 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).

Longevity of a resin-modified glass ionomer cement and a polyacid-modified resin composite restoring non-carious cervical lesions in a general dental practice

BACKGROUND

Long-term prospective survival studies of resin-modified glass ionomer cements (RMGICs) and polyacid-modified resin composites (compomers) placed in non-carious cervical lesions (NCCLs) are lacking from general dental practice. Short-term studies have shown an unsatisfactory clinical performance for several materials.

METHODS

One practitioner placed 87 compomer (Compoglass, Vivadent-Ivoclar) and 73 encapsulated RMGIC (Fuji II LC, GC Int.) restorations in NCCLs for 61 adults. Compoglass was placed using SCA primer, and Fuji II LC using GC Dentin Conditioner. No cavity preparation was undertaken. The Kaplan-Meier method was used for estimating the cumulative survivals for those restorations that were replaced, with the probability level set at alpha = 0.05 for statistical significance.

RESULTS

Restorations were judged unsatisfactory (by the practitioner and the subjects) because of surface and marginal loss of material (68.8 per cent), dislodgement (18.8 per cent) and discoloration (12.4 per cent), these modes being similar for both materials (P = 0.35). Unsatisfactory restorations were replaced in 121 (75.6 per cent) instances. After periods of up to five years, cumulative survival estimates were 14.9 (5.8 Standard Error) per cent for Compoglass and zero per cent for Fuji II LC (P = 0.74). Median survivals were 30 months for Compoglass and 42 months for Fuji II LC.

CONCLUSION

Both materials had high long-term unsatisfactory performances when placed in non-prepared NCCLs in a general dental practice.

Effect of smear layer on root demineralization adjacent to resin-modified glass ionomer

The cariostatic effect of resin-modified glass ionomer (RMGI) on secondary root caries is well-documented. However, this beneficial effect may be dependent upon the mode of cavity surface treatment. To investigate this relationship, we studied 4 cavity surface treatments prior to the placement of RMGI: no treatment (None), polyacrylic acid (PAA), phosphoric acid (H(3)PO(4)), and Scotchbond Multi-Purpose adhesive (SMP) as a control. Specimens were aged for two weeks in synthetic saliva, thermocycled, and subjected to an artificial caries challenge (pH 4.4). Polarized light microscopy (PLM) and microradiography (MRG) showed significantly less demineralization with the H(3)PO(4) cavity surface treatment as revealed by ANOVA and Tukey's multiple comparisons (p < or = 0.05). Dentin fluoride profiles determined by electron probe microanalysis (EPMA) supported PLM and MRG findings. It may be concluded that removal of the smear layer with phosphoric acid provides significantly enhanced resistance to secondary root caries formation adjacent to RMGI restorations.

Water sorption and mechanical behaviour of cosmetic direct restorative materials in artificial saliva

OBJECTIVES

To evaluate the water sorption and mechanical behaviour of a compomer in comparison with those of its nominal forerunners, a filled resin restorative material and a conventional glass ionomer cement.

METHOD

Compomer (Dyract AP) (D-AP), filled resin (SureFil) (SF), and glass ionomer (ChemFlex) (CF) (all Dentsply, Addlestone, UK) restorative materials were tested. Forty bar specimens (26x1.5x1.0mm(3)) of each material were prepared according to the manufacturer's instructions and randomly distributed into eight groups: dry air (22% RH), saturated water vapour (WV) (100% RH), and five in artificial saliva (AS) at pH6, all at 37 degrees C, as well as untreated control (UC) (23 degrees C, 50% RH). Water sorption was assessed gravimetrically; flexural strength and elastic modulus were determined in three-point bend. The control group was tested at 24h; AS groups were separately tested after 0.5, 1, 3, 6 and 9 months; the other two at 9 months.

RESULTS

Mass gain for SF, D-AP and CF in AS was up to 0.17%, 1.2% and 7.0%, respectively. CF showed a marked decrease of strength in AS compared with other groups, followed by a gradual slight rise to a peak at 3 months. Unlike SF and CF, whose flexural strength remained relatively stable, that of D-AP showed a sharp decline from the 1 month peak (P=6x10(-7)) after 6 months in AS. D-AP also showed a slight decline in flexural modulus from a peak, that of SF was quite stable, while CF showed no peak. The values of flexural strength for both CF and D-AP at 9 months were significantly lower in AS than WV, but SF showed no such difference.

SIGNIFICANCE

Materials intended for service in the mouth must be stored in a realistic medium if the results of testing are to be interpretable. Dyract AP, a compomer, does not seem suitable for application in stress bearing areas as is currently recommended by its manufacturer. The rapid decline in flexural strength after 1 month of exposure to AS and its progressive fall in flexural modulus suggest a progressive deterioration of the material and this necessitates re-examination of the chemistry of compomers, if the behaviour is typical of the class.

Effect of maturation on the fluoride release of resin-modified glass ionomer and polyacid-modified composite resin cements

The effect of an early water contact on the fluoride release is studied for the resin-modified glass ionomer cements (RM-GIC) GC Lining LC, PhotacBond, Vitremer and Vitrebond and for the polyacid-modified composite resins (PAM-C) Variglass and Dyract. Six months fluoride release profiles were determined in regularly renewed water (37 degrees C), for the products directly after light curing and after 24 h maturation in a humid atmosphere (85% RH). ANOVA shows that both the short-term and the long-term fluoride release of a RM-GIC are influenced by this maturation. This indicates that direct water contact for this material should be avoided. For the RM-GIC a correlation is found between the initial fluoride release process and the long-term process. For the PAM-C materials, no differences in the fluoride release are found as a function of maturation, indicating that early water contact has no effect. The amounts of fluoride released by PAM-C are low compared to RM-GIC, which can affect their caries preventive potential. The results are explained on the basis of the setting reaction of both types of materials.

Softening patterns of light cured glass ionomer cements

OBJECTIVE

The aim of this study was to determine the effects of commonly used food simulating solutions and sodium hydroxide on the softening of light cured glass ionomer cements.

METHODS

Four types of light cured glass ionomers (classified on the basis of the liquid component) as follows: (1) materials that combine a polymerizable monomer and polyalkenoic acid (PMPA); (2) use of a polymerizable polyalkenoic acid (PPA); (3) acid monomer (AM) in place of the polyalkenoic acid; and (4) replacement of polyalkenoic acid with polymerizable monomer (PMPR). A traditional glass ionomer and a microfil composite were used as controls. Disc-shaped specimens aged for a week at 37 degrees C and 100% relative humidity were stored in water, ethanol, heptane and 0.1 M sodium hydroxide for a period of 28 days. Barcol hardness measurements were made before immersion as well as at intervals of 24 h, 3 days, 7 days and 28 days after immersion.

RESULTS

In general the softening effect was lowest on the resin composite control. Hardness could not be measured for the traditional glass ionomer after 24 h due to breakage and dissolution of samples. The different solutions had varying effects on the different classes of light cured glass ionomers. The change in hardness after 28 days ranged from an increase of +6.7% for PMPA material in heptane to a complete disintegration of PPA amd PMPR in NaOH at 60 degrees C.

SIGNIFICANCE

The softening effect of food simulating solutions is dependent on the formulation of light cured glass ionomers. In clinical use, the role of softening in wear will consequently vary.

Failure of resin-modified glass-ionomers subjected to shear loading

The mechanism of bond failure of resin-modified glass-ionomers is unknown. This study examined the failure on shear loading at the dentine interface of these materials. Twenty-five teeth (embedded in acrylic blocks) were sectioned longitudinally to expose a flat dentine surface. Cylinders of materials were made by injecting into a tube placed on the dentine of each section surface. The materials used were Fuji Cap II and Fuji II LC (GC Corp., Japan), Vitremer (3M Dental Products, USA), Photac-Fil (original) and Photac-Fil* (new) (ESPE Dental-AG, Germany). After a week, a fluorescent dye was placed in the pulp chamber of each tooth and left for 3 h. The specimens were sectioned through the cylinders before both halves were tested in shear. The failure was observed using a confocal microscope, with video rate images (stored) digitally. The shear load at failure and locus of failure were recorded. All specimens had intact interfaces before testing, except the original Photac-Fil specimens which dislodged from their tooth surfaces even before testing, while being mounted on the device. An amorphous zone or absorption layer was noted at the dentine interface of 60% of Fuji II LC, 22% of Vitremer and all of the Photac-Fil* (new) specimens, but not in Fuji Cap II. Failure was cohesive in Fuji II LC, adhesive in Vitremer, cohesive/adhesive in Photac-Fil* (new) and cohesive in Fuji Cap II. In specimens with the absorption layer present, the failure was at the material/absorption layer interface, leaving it behind on the dentine surface. The mean stresses at failure (MPa) and standard deviations were 5.60, 2.46 (Fuji II LC); 4.82, 0.99 (Vitremer); 4.97, 2.10 MPa (Photac-Fil*); and 3.48, 1.06 (Fuji Cap II). All data were normally distributed as tested by the Shapiro-Francia test. One-way analysis of variance using exact inferential statistics indicated no significant difference between the mean failure stress for all the systems, p = 0.08. The mechanism of failure of resin-modified glass-ionomer materials to shear loading at the dentine interface varies between products. In materials in which the absorption layer is present, it appears to play an important role in mediating the bond of the glass-ionomer to dentine.

Resin-ionomer restorative materials for children: a review

Hybrid restorative materials comprising resins and components of conventional glass ionomers have been widely introduced and accepted by the dental profession in recent years. These include the resin-modified glass ionomer cements and the polyacidmodified resin composites or compomers. They are developed in an attempt to overcome the problems of traditional restoratives, such as moisture sensitivity and reduced early strength, while at the same time maintaining their clinical advantages of command setting, adhesion to tooth structures, adequate strength to occlusal load, fluoride release and aesthetics. This paper reviews the development, composition and properties of these new materials. Their clinical performance appears to be promising and they should be considered as good alternatives to amalgam and other conventional restorative materials in the future.

Direct core buildup using a preformed crown and prefabricated zirconium oxide post

This article describes a procedure that can produce a post and core in a reasonable chair time during a single session. With a preformed crown for core buildup, and being relatively rapid, this is a fairly simple procedure that has good results.

Effect of the application of dentin primers and a dentin bonding agent on the adhesion between the resin-modified glass-ionomer cement and dentin

OBJECTIVES

This study was designed to evaluate the influence of the application of dentin primer and/or dentin bonding agent on the adhesion of a resin-modified glass-ionomer cement to dentin.

METHODS

Bovine dentin was pretreated with Dentin Conditioner or EDTA 3-2 solution, primed by an experimental dentin primer, and applied with a dentin bonding agent. A resin-modified glass-ionomer cement, Fuji II LC, was then adhered to the dentin. The tensile bond strength between the light-cured glass-ionomer cement and the pretreated dentin was measured. The components of the experimental dentin primers were 2-hydroxyethyl methacrylate (HEMA), glyceryl methacrylate (GM) and a water-soluble photo-polymerization initiator, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N, N-trimethyl-1- propanaminium chloride (OTX). Significant differences in the data were examined by an analysis of variance and Scheffe's test for multiple comparisons between the means at p = 0.05.

RESULTS

A significantly higher mean bond strength between the Fuji II LC and dentin was obtained by EDTA 3-2 pretreatment, QTX/GM priming, and LB Bond application. This value was comparable with that obtained with the resin composite system. Scanning electron microscopy observation showed the formation of a hybrid layer with a thickness of 1-1.5 microns.

SIGNIFICANCE

The data obtained in this investigation suggest that the adhesion of Fuji II LC to dentin is closer to that provided by a resin composite system than to that of conventional glass-ionomer cements.

In vitro secondary caries inhibition around fluoride releasing materials

Objectives of the study were to compare the capacity of fluoride releasing materials to inhibit in vitro caries formation and to measure the width and height of the inhibition zones. Box-shaped cavities were prepared on bovine root dentine and restored with Fuji II, Fuji II LC. Vitremer, or Clearfil Liner Bond II system with a fluoride releasing composite. After immersion in a buffered demineralizing solution of 50 mmol/L acetic acid adjusted to pH 4.5 for 3 days, longitudinal sections were cut and imbibed in quinoline for analysis under a polarized light microscope (PLM). The contours of the lesions and inhibition zones were traced and their depth, width and height calculated. The data were analyzed by one-way ANOVA and Fisher's PLSD test at 95% level of confidence. The polarized light microscopy results showed a distinct inhibition zone adjacent to both conventional and resin-modified glass ionomer cements; however, it was not observed around the adhesive resin system. The width and height of this inhibition zone were significantly greater for Fuji II than for Fuji II LC and Vitremer. An inhibition zone was not observed adjacent to the adhesive resin system with fluoride releasing composite. The resin-modified glass ionomer cements produced less protection against in vitro secondary caries formation than the conventional glass ionomer cement. The recent bonding system that releases fluoride failed to produce an inhibition zone along the cavity wall adjacent to the restoration.

Microhardness of in vitro caries inhibition zone adjacent to conventional and resin-modified glass ionomer cements

OBJECTIVE

This study was conducted to correlate Knoop and triangular hardness numbers by measuring the microhardness of in vitro caries-inhibited and -demineralized dentin adjacent to a conventional and two resin-modified glass ionomer cements.

METHODS

Box-shaped cavities were prepared on bovine root dentin and restored with either Fuji II, Fuji II LC, or Vitremer. The teeth were then decalcified in an acid buffered solution of 50 mmol l-1 acetic acid adjusted to pH = 4.5 for 3 days. Knoop and triangular microhardness indentations were performed perpendicular to the surface and parallel to the cavity wall, in the demineralized lesion and inhibition zone. Calcium and phosphorous contents of the outer lesions and inhibition zones were compared using energy-dispersive X-ray spectrometry (EDS). The correlation between Knoop and triangular hardness was analyzed by correlation coefficient. The statistical significance of hardness data was analyzed by one-way ANOVA and Fisher's PLSD test (p < 0.05).

RESULTS

Triangular hardness (HT) correlated well with Knoop hardness number (KHN) (r2 = 0.81, p < 0.05). The microhardness of the inhibition zone created by Fuji II was of 59.2 +/- 3.8 HT and was statistically significantly higher than the zone produced by Fuji II LC and Vitremer. Fuji II LC and Vitremer produced inhibition zones with similar microhardness [48.3 +/- 3.5 HT and 44.0 +/- 7.6 HT, respectively (p > 0.05)]. Calcium and Phosphorous were present in the inhibition zone, but did not exist in the demineralized lesion.

SIGNIFICANCE

Knoop and triangular hardness numbers correlated significantly (p < 0.05), and the latter seems to be a promising alternative method for measuring very narrow surfaces. Despite the fact that all glass ionomer materials used in this study were effective in producing an acid-resistant layer, microhardness and intensity of these layers were material dependent.

An update on fixed prosthodontics

The practice of fixed prosthodontics has continually evolved as a result of progress in laboratory and biomaterials science, clinical technologies and adjunctive multidisciplinary treatment advancements. This brief review describes those enhancements and how they affect the state-of-the-art practice of fixed prosthodontics.

Radiopacity of resin-modified glass ionomer liners and bases

STATEMENT OF PROBLEM

Lining and base materials for restorations have traditionally been autopolymerized and include conventional glass ionomer cements. Light-cured resin-modified glass ionomer cements have recently become available, but a lack of information exists regarding their radiopacity.

PURPOSE OF STUDY

In this study the radiopacity of glass ionomer cements was assessed with a standard method that related densitometric measurements to an equivalent thickness of aluminum.

MATERIAL AND METHODS

Radiographs were made of specimens with seven materials commonly used as liners and bases: two reinforced zinc oxide-eugenol cements (Kalzinol and Intermediate Restorative Material, De Trey Dentsply), a zinc phosphate cement (SS White, S.S. White Manufacturing), three resin-modified glass ionomer liners (Vitrebond [3M Dental Products], Fuji Lining LC [GC Dental], and Photac-Bond [ESPE Dental Medizin GmbH]), and a conventional glass ionomer liner/base (Ketac-Bond, ESPE Dental-Medizin GmbH), with dentin as a control. The radiopacity of all materials was compared with dentin.

RESULTS

Kalzinol had the greatest radiopacity of the materials tested. The glass ionomer cements were substantially less radiopaque than other materials. The conventional glass ionomer cement, Ketac-Bond, was more radiopaque than the three resin-modified glass ionomer cements. Of the three resin-modified glass ionomer materials, Vitrebond was the most radiopaque and Fuji Lining LC was the least radiopaque.

CONCLUSION

Future resin-modified glass ionomer materials are recommended to be formulated to increase radiopacity for improved clinical detection.

The physical and adhesive properties of dental cements used for atraumatic restorative treatment

Atraumatic restorative treatment (ART), a recently reported field dentistry technique, involves removal of carious debris using only hand instruments and placement of a glass-ionomer cement (GIC) restoration. While small ART-GIC restorations are effective short-term replacements for lost tooth form, many larger ART-GIC restorations are defective after two years. Presently, resin-modified GICs (R-M GIC) are available which require no special activation equipment and handle easily in field settings. This study measured the compressive, tensile, and shear bond strengths to enamel and dentin of a conventional ART-GIC (Fuji IX) and two R-M GICs (Fuji Plus and Advance) at a powder-to-liquid ratio of 3.6:1. The compressive strengths of the GICs tested were significantly different. Fuji IX had the highest compressive strength, and Advance had the lowest strength (p < 0.05). The tensile strength of the R-M GICs was greater than that of the ART-GIC. Fuji Plus showed the highest shear bond strength to enamel and dentin and was significantly different from both Fuji IX and Advance. A clinical protocol is presented followed by case reports where the ART technique was used for management of acute caries in a modern dental setting.

SEM observations of the reactions of the components of a light-activated glass polyalkenoate (ionomer) cement on bovine dentine

OBJECTIVES

Glass ionomer cements are used in clinical dentistry as lining, luting and restorative materials. The precise nature of their bonding mechanism to dentine is unclear. This study is an SEM examination of the effect of the liquid contained in Vitrebond cement (3M Co., MN) on the surface of bovine dentine, with respect to delays in photocuring and washing off with water under pressure or as a gentle stream. The effects of delaying photocuring of the mixed and applied cement for up to 120 s were also examined.

RESULTS

The results of this study demonstrated that the liquid component of Vitrebond reacts chemically with dentine in a manner suggestive of an effervescent chemical reaction. This reaction produces plugs in the dentinal tubules which are resistant to dislodgement by water under pressure or by gentle washing. Similarly, a delay in photocuring the mixed and applied cements results in porosity of the cement at the dentine interface.

CONCLUSION

The findings in this study suggest that the adhesion of Vitrebond to dentine is primarily chemical in nature and that its mechanical strength is compromised if there are substantial delays in photocuring.

Effect of surface coatings on flexural properties of glass ionomers

The purpose of this study was to investigate the change in flexural strength and fracture toughness of light-cured glass ionomer cements after long-term immersion in water, and to investigate the effect of surface coatings on their properties. 2 resin-modified and 1 conventional glass ionomer cements were employed. For the flexural strength, a 25 x 2 x 2 mm stainless steel mold was used. For the fracture toughness (KtC), single edge notch specimens with dimensions 25 x 2.5 x 5 mm and a 0.5 mm notch (a/W = 0.5) were prepared in a stainless steel mold. Specimens were subjected to the 3 point bending at 0.5 mm/min after storage in 37 degrees C water for the periods of 1 h, 24 h, 1 wk, 1 month, and 6 months. The glass ionomer cements tended to exhibit an increase in mechanical properties over the 24-h period and then to maintain a constant strength. The surface protection of the resin-modified glass ionomer cement has some effect on the mechanical properties during early setting reactions, and it is desirable that the cement should be protected from direct water contact for at least 1 h after cement mixing.

Influence of enamel conditioning on bond strength of resin-modified glass ionomer restorative materials and polyacid-modified composites

This study evaluated enamel bond strength of restorative materials containing both glass ionomer and composite components. Three resin-modified glass ionomer restorative materials (Fuji II LC, Vitremer, Photac-Fil), three polyacid-modified composites (VariGlass VLC, Dyract, Ionosit Fil), a hybrid composite (blend-a-lux) and a chemical-cured glass-ionomer cement (ChemFil Superior) were tested for enamel tensile bond strength with and without conditioning of the tooth surfaces. Tensile bond strength was determined for five specimens each of conditioned and unconditioned bovine teeth. Specimen conditioning was performed as recommended by the manufacturers. The tensile bond strength was tested with a universal testing machine. Except for the enamel bond strength of ChemFil Superior, all materials showed greater adhesion to conditioned tooth surfaces than to unconditioned specimens. Enamel bond strengths of the polyacid-modified composites applied after a phosphoric acid etching technique (Ionosit Fit, Dyract, VariGlass) were greater compared with the materials applied after surface conditioning with polyacrylic acid-containing agents. No significant difference was observed between the hybrid composite and the tested materials attached with the phosphoric acid etching technique. To improve adhesion of the tested materials to enamel, following the manufacturer's instructions about tooth surface conditioning is recommended. Superior bond strength to enamel was obtained for polyacid-modified composites, which are attached with the phosphoric acid etching technique and thereby resemble the adhesion patterns of composites.

Shear bond strength of several new core materials

This study compared the shear bond strengths of three core materials: a light activated glass-ionomer cement (VariGlass VLC), a fluoride-release dual cure composite resin (Fluoro Core), and a conventional silver-reinforced glass-ionomer cement (Miracle Mix) when cured to dentin. Fifty-four noncarious molar teeth were extracted, cleaned, mounted in acrylic resin, and sectioned horizontally to expose the dentin surface. Each material was mixed according to manufacturer's instructions, applied in a premade mold to the exposed dentin, and then cured. The specimens were randomized into three group (six teeth from each material) and stored (37 degrees C, 100% humidity) for 15 minutes, 24 hours, and 24 hours and were then thermocycled (5 degrees to 55 degrees C) for 125 cycles. The specimens were tested for shear bond strength with the Instron universal testing machine. The differences among time groups were not statistically significant except for Miracle Mix and VariGlass VLC cements, which showed a greater improvement with thermocycling. This study indicated that the FluoroCore resin exhibited the greatest shear bond strength of the core materials and that VariGlass VLC cement had greater bond strength than Miracle Mix cement except after thermocycling, when VariGlass VLC cement and FluoroCore resin were not significantly different.

The Class V lesion--aetiology and restoration

The aetiology of non-carious cervical lesions is discussed. These have been variously described as 'abrasion', 'erosion', 'abrasion/erosion', and 'idiopathic cervical'. However, many lesions do not fit the classical appearance or location of an erosive and/or abrasive origin, and there is increasing interest in the possible role of occlusal stress in their aetiology. Non-carious cervical lesions often require restoration, and there are essentially three options using tooth-coloured materials: a restorative glass ionomer cement, a liner/base glass ionomer cement overlayed with a resin composite, or a resin composite bonded by an enamel/dentine-adhesive. The materials and techniques used in these options are discussed, indicating their advantages and disadvantages. Results of available clinical trials of these systems are given, and the link with the stress theory of cervical tooth loss is described. The preferred restorative approaches in order are: resin-modified restorative glass ionomer; resin-modified liner/base glass ionomer with a microfine resin composite overlay; enamel/dentine bonding agent with a microfine resin composite.

The influence of water sorption on the development of setting shrinkage stress in traditional and resin-modified glass ionomer cements

OBJECTIVES

The aim of this study was to determine the setting stress development for some traditional and resin-modified glass ionomer cements and to assess the effect of early water exposure to this stress.

METHODS

The development of the setting stress of the glass ionomer cements was determined in a tensilometer set-up as described earlier by Feilzer et al. (1987).

RESULTS

The results of this study show the influence of water sorption on the development of setting shrinkage stress in bonded glass ionomer cements. When curing took place under isolated conditions (no hydration or dehydration), all the traditional glass ionomer cements investigated fractured spontaneously, either adhesively and/or cohesively, due to the developing stress. Early exposure to water led to stress relief and prevented spontaneous fracturing. For the light-cured products, no spontaneous failures were observed under isolated conditions. Stress relief due to water sorption reversed the contraction stress into an expansion stress.

SIGNIFICANCE

Exposure of traditional glass ionomer cements to water at an appropriate time by the use of permeable matrix systems is advised. Whether the conversion of contraction stresses into expansion stresses as observed for the resin-modified products, is beneficial for a restoration requires further study.

Operative dentistry considerations for the elderly

As the mean age of an older dentate population increases, so does the incidence of dental caries in its primary and secondary forms. Primary and secondary root decay gingival to existing restorations are significant operative problems prevalent in the elderly. Treated root decay is prone to recurrence if the etiology is ignored. Effective, customized prevention must parallel operative intervention. The dentist today has a wider selection of techniques and materials than ever before to treat the elderly patients. Use of preventive restorative materials such as conventional and hybrid glass ionomer materials for the treatment of root decay are discussed.

Bond strength to dentine of two light-activated glass polyalkenoate (ionomer) cements

The effects of sample thickness on the in vitro bond strength of two light-activated glass polyalkenoate cements to dentine have been investigated. The buccal and/or lingual surfaces of non-carious human third molar teeth were used for bonding. The tensile bond strengths to dentine of samples of the cements of 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm were measured 10 min after bonding. For one of the materials bond strength and reliability were found to decrease as the sample thickness increased. The bond strength to dentine of the second material was also affected by changes in the thickness of the cement but as the bond strengths were all very low for this material, any differences are probably of little clinical relevance.

Release of fluoride and other elements from light-cured glass ionomers in neutral and acidic conditions

The purpose of this study was to measure the release of fluoride, sodium, silicon, calcium, strontium, and aluminum from light-cured glass ionomers. The materials tested were: (1) Baseline VLC thick mix; (2) Baseline VLC thin mix; (3) Fuji Lining LC; (4) Vitrebond; and (5) XR-Ionomer. A conventional glass ionomer, Ketac-FilAplicap, and a silver-reinforced glass ionomer, Ketac-Silver, were used as controls. Each test specimen was first stored for 16 days in de-ionized water, followed by a further 16 days in 0.01 mol/L lactic acid (pH 4.0); both solutions were replaced at predetermined intervals. After that, the specimens were immersed for up to 122 days in de-ionized water. During the immersion, light-cured glass ionomers showed considerable variation in the release of fluoride and other elements. In lactic acid, all cements eluted the matrix-forming cations, aluminum and calcium or strontium. This suggests that light-cured materials are as equally susceptible to erosion as are chemically cured glass ionomers. During the immersion, some of the light-cured materials showed a considerable weight gain.

In vitro characterization of visible light-cured glass ionomer liners

The purpose of this study was to characterize the in vitro performance of three visible light-cured glass ionomer liners. The liners containing 2-HEMA showed significantly higher compressive strength, diametral tensile strength and Vickers hardness than the liner without 2-HEMA. Statistically significant differences were found in the optical properties of the materials tested. The liners containing 2-HEMA manifested higher shear strength at liner/composite than at dentin/liner interfaces. The acid-base reaction was significantly delayed after light exposure in all the liners tested. The liner without 2-HEMA presented the greatest maximum gap at the liner/dentin interface. Significant correlations were detected between the optical properties of the liners and the top-bottom differences in the extent of conversion, as well as between the maximum marginal gap at the dentin/liner interface and the bond strength with dentin and composite. These correlations suggest the following areas for further developments: incorporation of low molecular weight polyalkenoic acids or accelerating agents to increase the initial carboxylate yield, increase in total transmittance and reduction in diffuse reflectance to improve the in-depth conversion, and reinforcement of the dentin liner interface to prevent gap formation.