Variability in cytotoxicity and fluoride release of resin-modified glass-ionomer cements

New-generation glass-ionomer cements contain resin to improve their restorative properties. These resin-modified glass-ionomer cements vary considerably in their chemistry, which could result in corresponding variability in their physical and biological properties. This study investigated the cytotoxicity and the fluoride release of two resin-modified glass ionomers, a conventional glass-ionomer cement, and a resin composite. Samples were prepared and extracted in distilled water for 1, 4, and 7 days; eluates were filtered and tested by means of 3T3 mouse fibroblasts. Cytotoxicity (MTT assay) values were low for all materials and extraction times, indicating minimal cytotoxicity of all materials (less than 30% inhibition). Cytotoxicity of one resin-modified glass ionomer was significantly higher than for the other materials (p < 0.001). One resin-modified glass ionomer and the conventional glass-ionomer cement released significantly more fluoride at each time interval (p < 0.001) than the other resin-modified glass-ionomer cement and the resin composite. Fluoride release and cytotoxicity were correlated (r2 = 0.60; p < 0.001), although the fluoride release does not account for the cytotoxicity observed. Cytotoxicity and fluoride release suggest that one hybrid behaved more like a conventional glass ionomer, and the other like a resin composite. These differences may have implications for material selection in specific clinical situations.     

Pulpal response to a resin-modified glass-ionomer material on nonexposed and exposed monkey pulps

OBJECTIVE: This study evaluated the biocompatibility of a resin-modified glass-ionomer material on monkey pulps. METHOD AND MATERIALS: Standardized Class V cavities were prepared in 112 teeth distributed in six healthy adult monkeys. The resin-modified glass-ionomer cement was placed in 24 nonexposed and 36 exposed pulps according to manufacturer's instructions. ZOE was used as a control in nonexposed pulps, while calcium hydroxide was used as a control for exposed pulps. Tissues were collected at 6 to 7, 21 to 27, and 90 to 97 days. After demineralization, the teeth were serially sectioned, stained, and observed by light microscopy. RESULTS: Except for one resin-modified glass-ionomer pulp at 6 days, there were no differences between the responses of nonexposed pulps to resin-modified glass-ionomer specimens and ZOE controls. In exposed pulps, eight of 36 resin-modified glass-ionomer pulps showed various grades of inflammatory response, all associated with stained bacteria. Pulpal healing was similar in both resin-modified glass-ionomer and calcium hydroxide direct-capped exposures. Twenty-two of 26 exposed pulps restored with the resin-modified glass-ionomer cement showed dentin bridge formation at 21 and 97 days. CONCLUSION: The resin-modified glass-ionomer material exhibited acceptable biologic compatibility in exposed and nonexposed cavities.     

Artificial caries formation around fluoride-releasing restorations in roots

Secondary caries is one of the most important factors leading to replacement of dental restorations. This investigation assessed the capacity of fluoride-releasing restorative materials to resist caries in vitro when used in roots. Class 5 cavities were prepared in the buccal and lingual surfaces of 30 extracted premolars. The six materials used were: glass-ionomer cement (Fuji), glass-ionomer cement with silver particles added (Ketac-silver), fluoride-containing composite resin (Tetric), composite resin (Silux plus), fluoride-containing amalgam (Fluor-Alloy) and high-copper amalgam (Dispersalloy). After 5 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that repair with glass-ionomer materials of a carious lesion may be of great importance in the prevention of secondary caries around the restorations in roots.     

Study on the relationship between vascular invasion and prognosis in patients with locally confined renal cell carcinoma

This study aimed to develop techniques to allow dynamic imaging of a cavity before, during and after placement of glass-ionomer restorative materials. Cavities were cut in recently extracted third molars and the teeth longitudinally sectioned. Each hemisected tooth surface was placed in green modelling compound at 90 to the optical axis of the microscope. The cavity surface was imaged using a video rate confocal microscope in conjunction with an internally focusable microscope objective. The sample on the stage was pushed up to the objective lens which 'clamped' the cover glass onto it. Water, glycerine or oil was placed below the coverglass, with oil above. Internal tooth structures were imaged by changing the internal focus of the objective. The restorative material was then placed into the cavity. Video images were stored either onto video tape or digitally, using a frame grabber, computer and mass memory storage. Software controls produced time-lapse recordings of the interface over time. Preliminary experiments have examined the placement and early maturation of conventional glass-ionomer cements and a syringeable resin-modified glass-ionomer cement. Initial contact of the cement matrix and glass particles was visible as the plastic material rolled past the enamel and dentine, before making a bond. Evidence for water movement from the dentine into the cement has also been seen. After curing, the early dimensional changes in the cements due to water flux were apparent using the time-lapse facility. This new technique enables examination of developing tooth/restoration interfaces and the tracking of movement in materials.     

Adhesive luting cements--classes, criteria, and usage

Clinical studies have shown that recurrent decay and lack of retention are the major causes of traditional crown and bridge failure. Optimal marginal accuracy and preparation retention form are important pre-requisites for longevity, as well as good patient oral hygiene. In an effort to provide improved clinical success, new classes of luting agents with improved physical properties and new therapeutic capabilities have been developed. Conventional glass ionomer cements provide fluoride release and adhesive properties. Recently introduced resin-modified glass ionomer luting materials add the potential for increased resistance to dissolution and improved physical and biological attributes. The resin luting cements are more difficult to use but provide greatly increased bonding capabilities and are necessary for strength requirements of all-ceramic restorations. This article describes the three classes of adhesive luting materials, provides a comparison of biological and physical properties, describes the indications and limitations of each class, and makes recommendations for clinical usage.     

The effect of dentin disinfectants on shear bond strength of resin-modified glass-ionomer materials

The purpose of this study was to investigate the effect of dentinal disinfection with a 2% chlorhexidine or a 0.11% I2-KI/CuSO4 solution on the shear bond strength of three resin-modified glass-ionomer cements: Fuji II LC, Photac-Fil, and Vitremer. The occlusal surfaces of extracted human teeth were flattened to dentin. Specimens were randomly assigned to one of nine treatment groups (n = 12). For each glass-ionomer material, there was a control group and two treatment groups in which the dentin was treated with either a 2% chlorhexidine or a 0.11% I2-KI/CuSO4 solution before the dentin was treated with the recommended dentin conditioner prior to glass-ionomer bonding. Specimens were stored for 1 day in water, thermocycled, and tested in shear until failure. The chlorhexidine solution did not significantly affect the shear bond strengths of any of the cements, but the I2-KI/CuSO4 solution significantly lowered the bond strengths of Vitremer and Fuji II LC compared to the controls.     

Resin-modified glass ionomers for luting posterior ceramic restorations

OBJECTIVES: Until recently, esthetic inlay restorations in posterior teeth have been limited to cavities surrounded by enamel. Dentin adhesive systems in combination with luting composites and light-cured resin-modified glass ionomer cements offer a possibility for bonding ceramic inlays to cavities when the cervical margin is in dentin. This study was designed to compare in vitro marginal integrity of ceramic inlays bonded to dentin to restorations placed in cavities with margins located entirely in the enamel. METHODS: In the present in vitro study, the sealing abilities of a dentin bonding agent/luting composite combination (Syntac/Dual Cement, Vivadent) and resin-modified glass ionomers (Photac Fil, Photac Bond, ESPE; Dyract, De Trey Dentsply; Fuji II LC, GC Dental Industrial Corp.; and Vitremer, 3M Dental Products) used as luting agents in cavities extending beyond the cemento-enamel junction, were compared to the sealing abilities of a conventional luting composite (Vita Cerec Duo Cement, Vita) in cavities within sound enamel. SEM analysis and dye penetration were performed to evaluate marginal integrity at the cervical cavity margins. RESULTS: The dentin bonding agent/luting composite combination (Syntac/Dual Cement) rendered a marginal seal within the dentin similar to the quality obtained with the conventional luting procedures within sound enamel. When three out of the five resin-modified glass ionomers were used as luting agents (Dyract, Fuji II LC and Vitremer), the results were comparable to those reported for the dentin bonding agents and the conventional method. SIGNIFICANCE: Light-cured resin-modified glass ionomer cements may be considered as an alternative to dentin bonding agents when the cavity margins of ceramic inlay restorations are within the dentin. However, further studies, e.g., wear resistance, must be performed.     

Wear resistance of four luting agents as a function of marginal gap distance, cement type, and restorative material

This study investigated the effect of marginal gap width, luting cement, and restorative material on the wear resistance of the luting cement in areas where no occlusal contact is present. Three types of resin luting cement and one resin-modified glass-ionomer cement were used with two inlay systems, a resin composite, and an all-ceramic system. Bovine enamel represented tooth structure. Toothbrush abrasion was the wear modality. Three predetermined gap widths were selected: 240 +/- 30 microns, 150 +/- 30 microns, and 60 +/- 30 microns. All specimens were thermocycled. Regardless of the luting cement or the restorative material, there was a significant difference (P < 0.05) in wear resistance of the cement among the three gap distances at both the enamel and restoration interface. Vertical wear of the luting cement at the enamel interface increased linearly with marginal gap distance when all four cements were considered together (r2 > 0.51), regardless of type of restorative material used. The resin-modified glass-ionomer cement showed the least amount of wear for all variables considered. Significant differences in wear were found between the four luting cements at wide gap distances (240 microns) at the enamel interface, regardless of type of restorative material used. No significant differences were found between the two restorative materials at the enamel interface at the three gap distances.     

Increased apoptotic cells in bone marrow biopsies from patients with aplastic anaemia

PURPOSE: To evaluate the 2-year clinical performance of two polyacid-modified resin composites and two resin-modified glass ionomers in Class V carious cavities. MATERIALS AND METHODS: A total of 120 Class V cavities were selected and 30 cavities were restored with one of two resin-modified glass ionomer materials (Fuji II LC Improved and Vitremer) and two polyacid-modified resin composites (Dyract and Compoglass) in Class V carious cavities after 2 years. The restorations were clinically evaluated after 1 and 2 years using the USPHS criteria. RESULTS: One-year findings revealed a significant difference in color match between Vitremer and other materials (P < 0.05) and no significant difference was found for the other criteria. Two-year results indicated a significant difference between resin-modified glass ionomers and polyacid-modified resin composite materials. The difference between Compoglass and Dyract was not statistically significant whereas the difference between Vitremer and Fuji II LC was statistically significant. Caries was not recorded at any evaluation period.     

The effect of pulpal fluid flow on tensile bond strength of a glass-ionomer cement: an in vivo and in vitro comparison

Previous studies of the bonding capabilities of glass-ionomer cements have concentrated on the use of in vitro testing conditions. Since early moisture contamination appears to have adverse effects on the physical properties of glass-ionomer cements, and with the probability of pulpally derived dentinal fluid being present under in vivo conditions, the objective of this study was to compare in vivo tensile bond strength with in vitro tensile bond strength of a glass-ionomer cement to dentin utilizing the same teeth under similar test conditions. A glass-ionomer lining cement was placed on freshly exposed labial dentin of the maxillary incisor on 10 Rhesus monkeys. Immediately following placement, an orthodontic button was placed over the cement and left undisturbed for 1 hour. The teeth were then extracted and stored in 100% relative humidity for 23 hours. An Instron testing machine was used to register in kilograms the force required to cause tensile bond failure of the cement. Identical methodology was then used on the same teeth for in vitro testing. The concluding results indicate that a statistically significant difference (P < or = 0.05) exists between in vivo and in vitro tensile bond strengths of the glass-ionomer lining cement and that the bond failure was cohesive in character for all cases both in vivo and in vitro. These findings suggest that clinically, tensile bond strengths of glass-ionomer cements to cut dentin can be expected to be weaker in vital teeth than in devital teeth.     

Bioavailability comparison between albendazole and albendazole sulphoxide in rats and man

Many restorative materials are claimed by their manufacturers to match the Vita shade guide. To verify this claim, 40 dental personnel were asked to color match five different restorative materials to their respective Vita shade tabs according to a 5-point scale (1 = very poor color match; 5 = excellent color match). Three shades were chosen for each restorative material (a mid-Value shade as well as the highest Value shade and the lowest Value shade present in each system). Pooled scores indicated that the resin composite materials had significantly better overall shade match than did the other materials evaluated and that one resin-modified glass-ionomer cement had significantly better shade match than did the "compomer" and another resin-modified glass-ionomer cement. Only 11% of the scores for all material and shade combinations were given a good or excellent rating (score greater than 3). Shade match to the Vita shade guide was not material dependent but tended to differ among the different Value shades evaluated.     

Marginal adaptation of resin-bonded light-cured glass ionomers in dentin cavities

PURPOSE: To investigate the marginal adaptation of resin-modified glass ionomer cements in dentin cavities placed with or without additional application of resin bonding systems. MATERIALS AND METHODS: Three resin-modified materials (Fuji II LC, Photac-Fil, Vitremer), one compomer (Dyract) and as reference an adhesively bonded resin composite system (Gluma CPS-Pekafill) were used. Flat peripheral dentin surfaces on human molar teeth were produced by wet grinding on SiC paper. Cylindrical cavities, 3.5 mm wide, were prepared in these dentin areas and restored with the individual materials. Sixty cavities were pretreated and restored as requested by the respective manufacturers. Following water storage of the specimens for 15 minutes or 24 hours, excess was gently removed by wet grinding for microscopic inspection of the marginal area. Additionally, in 30 cavities an experimental one-component adhesive resin system, a proprietary dimethacrylate and HEMA mixture dissolved in acetone, was combined with each of the restoratives for evaluation after 15-minutes water storage. Finally, in six cavities each, Dyract was combined with Prime and Bond 2.0, and Vitremer with Scotchbond Multi-Purpose Plus for assessment after 15 minutes. Maximum marginal gap widths (MGW) were measured. One-way ANOVA by ranks (Kruskal-Wallis-Test) followed by Wilcoxon's Two-Sample test were used to study the statistical difference of MGW among the treatment groups at a rejection level P = 0.05. RESULTS: Neither the conventionally placed material systems nor the restorations in combination with adhesives showed consistently gap-free margins after 15-minute water storage. After 24-hour storage with Vitremer 4 of the 6 restorations were gap-free, whereas with all other materials only perfect margins were registered. There was, however, no significant difference between the groups. Application of the experimental and/or the specific resin bonding agents had no effect on early MGW except for the Photac-Fil group, which was significantly reduced.     

The use of liners under amalgam restorations: an in vitro study on marginal leakage

OBJECTIVE: Marginal leakage of amalgam restorations may lead to secondary caries and pulpal damage. The purpose of this study was to determine the effect various cavity liners might have on microleakage. METHOD AND MATERIALS: Mesio-occlusodistal amalgam restorations with margins on enamel and dentin were treated with different liner materials (an adhesive system, a topical fluoride gel, a cavity varnish, and a glass-ionomer cement) in vitro. Following restoration, the teeth were submitted to thermocycling in a stained solution and sectioned to allow assessment of microleakage. RESULTS: On enamel, the control group (no liner) and the glass-ionomer-lined group had equivalent leakage scores and were superior to every other group. On dentin, only the glass-ionomer specimens had superior performance. The cavity varnish and fluoride-lined specimens exhibited the highest leakage scores. CONCLUSION: The use of liners does not reduce microleakage on amalgam restorations when the cavity margins remain on enamel. On dentin margins, a glass-ionomer liner can reduce microleakage.     

An update on glass-ionomer cements

It has been claimed that glass-ionomer cements possess properties that could make them the "ideal' restorative material. In the light of current disquiet about the safety of dental amalgam, are glass-ionomer cements likely to become the replacement materials of choice?     

Effect of restored and unrestored non-carious cervical lesions on the fracture resistance of previously restored maxillary premolar teeth

OBJECTIVES: The effect of non-carious cervical lesions (NCCL) on tooth fracture resistance has not previously been investigated. The aims of this in vitro study were to examine the fracture resistance of a group of extracted maxillary premolar teeth with mesio-occlusal-distal (MOD) restorations of amalgam, and restored or unrestored simulated NCCL. METHOD: Forty sound maxillary, premolar teeth were divided at random into four groups, each of 10 teeth, which were fixed crown uppermost and long axis vertical in stainless steel moulds. Groups 1,2,3 and 4 were prepared with standardized parallel-sided MOD cavities, then restored with amalgam. Groups 1, 2 and 3 were further prepared with standardized NCCL. The NCCL in Group 1 were restored using a resin-modified polyalkenoate (glass-ionomer) cement, and the NCCL in Group 2 were restored with an adhesive composite resin system. The NCCL in Group 3 were left unrestored. The specimens were loaded compressively at 1 mm min-1 using a universal testing machine. RESULTS: Mean fracture loads (KN) of 1.08, 1.03, 0.98 and 1.14, respectively, were recorded for Groups 1, 2, 3 and 4. Two-way ANOVA and Scheffe's Multiple Range Test showed no statistically significant difference between the groups. CONCLUSIONS: It is concluded that the presence of a standardized NCCL in an extracted maxillary premolar tooth does not reduce the fracture resistance of the tooth when loaded compressively at 1 mm min-1. The restoration of NCCL with the materials tested did not result in an increase in the fracture resistance of the previously restored premolar teeth, when loaded compressively at 1 mm min-1.     

Longevity in glass-ionomer restorations: review of a successful technique

It is just 20 years since glass-ionomer cements were introduced to the profession as a restorative material capable of an ion exchange adhesion to tooth structure as well as a continuing fluoride release. At the time of presentation there was considerable publicity, but, in retrospect, it is likely that the materials were marketed prematurely, before there had been a great deal of clinical investigation. The clinical short-term results were rather disappointing, particularly in relation to esthetics, because the original version lacked translucency. In the next few years, some manufacturers worked to refine the product and improve the properties and achieved reasonable results. In the early 1980s, it was shown that the main problem with both esthetics and physical properties was the need to maintain a proper water balance in the material during the early setting phase. Once this problem was identified and overcome, it became possible to achieve excellent results, but these have not been reported frequently. This article discusses a method of placement that will lead to acceptable glass-ionomer restorations and shows a series of restorations that are up to 15 years old.     

Tunnel restorations. A 3 1/2-year follow up study of Class I and II tunnel restorations in permanent and primary teeth

During 1988-89, 224 patients with approximal caries in the premolar/molar regions were provided with 318 tunnel restorations. In case of perforation of the enamel in the enamel/dentin border, (23%), complete Class II-tunnel restorations with glass ionomer cement and composite resin were made. In case of "intact" enamel, (77%), partial Class I-tunnel restorations were made. The restorations were controlled at annual routine recalls and the success rate after 3 1/2 years was 74% for permanent teeth, and 10% for primary teeth. Restorations in permanent teeth, made during the second year of the study were successful in 82%, as compared with 62% for restorations made during the first year, indicating a learning effect. Failures in the permanent dentition were due to marginal ridge fracture (35%), cavitation in the approximal enamel (31%), and recurrent caries (38%). Failures in primary teeth were predominantly due to marginal ridge fractures (84%). A comparison with the longevity of conventional Class II restorations is made and the possible advantages of the present method are presented.     

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.     

Interfacial characteristics of resin-modified glass-ionomer materials: a study on fluid permeability using confocal fluorescence microscopy

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.