Infrared spectrometric study of acid-degradable glasses.

J Dent Res. 2002 Aug;81(8):552-5

Authors: De Maeyer EA, Verbeeck RM, Vercruysse CW

The composition of glasses used in glass-ionomer cements affects their leaching behavior and hence the properties of the cement. The aim of this study was to correlate the composition and leaching behavior of these glasses with their infrared absorption characteristics. The wavenumber of the absorption band of the Si-O asymmetric stretching vibration shifts to a higher value with decreasing content of mono- and bivalent cations in the glass. This effect can be ascribed to the influence of these extraneous ions on the glass network order and connectivity. Preferential leaching of these ions induces an increase of asymmetric stretching vibration and a general modification of the band profile. The results can be correlated with the x-ray diffraction characteristics of the glass.

PMID: 12147746 [PubMed - indexed for MEDLINE]

Clinical performance of a condensable metal-reinforced glass ionomer cement in primary molars.

Br Dent J. 2001 Mar 24;190(6):317-21

Authors: Krämer N, Frankenberger R

OBJECTIVE: Aim of the present study was to evaluate the clinical suitability of the condensable metal-reinforced glass ionomer cement Hi-Dense in classes I and II cavities of primary molars. METHODS: Seventeen children received a total of fifty four Hi-Dense fillings (nineteen class I and thirty five class II). The restorations were clinically assessed at baseline, after one and after two years of clinical service according to modified USPHS codes and criteria. The restorations were replicated in each recall and representative samples were qualitatively analysed under a SEM. RESULTS: Over the observation period of two years, five restorations failed due to total retention loss, two fillings needed replacement because of persisting hypersensitivity, one filling was lost because of an unsuccessful endodontic treatment, and four restorations remained intact until natural exfoliation (Two year survival rate: 92% for Class I and 66% for Class II). The SEM analysis of surfaces and marginal areas exhibited an inferior adhesive performance primarily in proximal areas, whereas a negative step formation due to wear was frequently observed in occlusal parts. CONCLUSIONS: The results clearly indicate that the condensable, metal-reinforced GIC Hi-Dense reveals no enhanced performance and lifetime expectancy for class II restorations in primary molars when compared to other non-resin-modified GICs.

PMID: 11325157 [PubMed - indexed for MEDLINE]

Stoichiometry of the leaching process of fluoride-containing aluminosilicate glass-ionomer glasses.

J Dent Res. 1999 Jul;78(7):1312-8

Authors: De Maeyer EA, Verbeeck RM, Vercruysse CW

Dental glass-ionomer cements (GIC) set by an acid-base reaction between a polyalkenoic acid and an ion-leachable glass. The exact relationship between the glass composition and the setting and final properties of GIC is not yet fully elucidated. As part of a systematic study of this relationship, we studied the leaching stoichiometry of glasses used in commercial formulations to correlate the glass composition with its leaching properties. The leaching experiments were performed in acetic acid solutions at pH = 3.4 by means of a pH-stat method. After predetermined time intervals, the suspension was filtered and the filtrate was analyzed for the glass constituents. The usefulness of the pH-stat method for the determination of glass reactivity was corroborated. The deviation of the leaching stoichiometry with respect to the pure glass stoichiometry decreased with increasing relative content of mono- and bivalent glass network dwellers and modifiers. Indications were found that the latter can be leached out independently and preferentially, while the leaching of network dwellers is coupled with the aluminum release. The F content as well as the reactivity of the glass affect the amount of fluoride available for release from a set GIC. It could be concluded that the leaching stoichiometry of GIC glasses can be correlated with their absolute and relative composition.

PMID: 10403458 [PubMed - indexed for MEDLINE]

Early and long-term wear of conventional and resin-modified glass ionomers.

J Dent Res. 1996 Aug;75(8):1613-9

Authors: de Gee AJ, van Duinen RN, Werner A, Davidson CL

Various studies have shown that glass ionomers are susceptible to brittle fracture and acid conditions and that they undergo long-term changes in their mechanical properties. Little information is available on how brittleness, acid susceptibility, and long-term changes are reflected in the wear characteristics of glass ionomers. The purpose of this study was to evaluate long-term changes in conventional glass ionomers, metal-reinforced glass ionomers (including a cermet), and (light-curing) resinmodified glass ionomers by wear experiments simulating the wear process in occlusal contact-free areas. The wear tests were conducted periodically over a period of one year. In addition, wear was determined after one year at a pH of 5 or 6, for assessment of acid susceptibility, and at a condition as found in the occlusal contact areas. All materials showed high early-wear rates which decreased significantly during the one-year test period. This long-term process may be related to a slow progression of the acid-base reaction extending over several months. At each stage, the resinmodified glass ionomers wore significantly faster than the acid-base setting glass ionomers. Most of these materials were not affected at a pH of 6.0, while at a pH of 5.0 only the conventional and the metal-reinforced glass ionomers showed increased wear. Direct contacts with the antagonist led to a significant increase in wear in comparison with contact-free wear, probably as a result of sub-surface fatigue phenomena. In view of the unfavorable wear characteristics of the resin-modified glass ionomers and the high early wear of the conventional glass ionomers, including the metal-reinforced glass ionomers, it was concluded that none of these materials can yet be recommended for use in high-stress-bearing situations.

PMID: 8906131 [PubMed - indexed for MEDLINE]

The effect of fluoride application on fluoride release and the antibacterial action of glass ionomers.

J Dent Res. 1993 Sep;72(9):1310-4

Authors: Seppä L, Forss H, Ogaard B

The aim of this study was to investigate whether the release of fluoride and the antimicrobial effect of freshly mixed glass ionomers could be prolonged by application of fluoride on aged material. Test slabs of freshly mixed and aged (14 d in water) conventional and silver glass ionomer (Ketac-Fil and Ketac-Silver, Espe, Seefeld, Germany) and composite (Silux Plus, 3M, St. Paul, MN) were fitted into the bottom of a test tube. A layer of S. mutans Ingbritt cells was centrifuged onto the test slabs, and the samples were incubated for 20 h in 1.7% sucrose solution. After the incubation, pH, F, and Ca contents of the fluid phase, and F, Mg, P, and K contents of the cells were determined. The aged glass-ionomer samples were then covered with toothpaste (0.1% F) or with fluoride gel (1.25% F), and the composite samples with fluoride gel. After being thoroughly rinsed, S. mutans cells were incubated on the samples as above. The pH fall was significantly inhibited by freshly mixed glass ionomers, and there were changes in cellular cation and phosphorus contents. Large amounts of fluoride were found in the fluid and cells. For old glass ionomers, no inhibitory effect on pH fall could be seen. Fluoride release had decreased to a low level.(ABSTRACT TRUNCATED AT 250 WORDS)

PMID: 8360380 [PubMed - indexed for MEDLINE]

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

J Dent Res. 1993 Aug;72(8):1257-62

Authors: Forss H

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.

PMID: 8360372 [PubMed - indexed for MEDLINE]

Dental composites/glass ionomers: the materials.

Adv Dent Res. 1992 Sep;6:44-9

Authors: Bowen RL, Marjenhoff WA

Most commercial dental composites contain liquid dimethacrylate monomers (including BIS-GMA or variations of it) and silica-containing compositions as inorganic reinforcing filler particles coated with methacrylate-functional silane coupling agents to bond the resin to the filler. They also contain initiators, accelerators, photo-initiators, photosensitizers, polymerization inhibitors, and UV absorbers. Durability is a major problem with posterior composites. The typical life-span of posterior composites is from three to 10 years, with large fillings usually fewer than five years. Polymerization shrinkage and inadequate adhesion to cavity walls are remaining problems. Some pulp irritation can occur if deep restorations are not placed over a protective film. Some have advocated the use of glass-ionomer cement as a lining under resin composite restorations in dentin. The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970's. Current GICs may contain poly(acrylic acid) or a copolymer. Higher-molecular-weight copolymers may also be used to improve the physical properties of some GICs. Stronger and less-brittle hybrid materials have been produced by the addition of water-soluble compatible polymers to form light-curing GIC formulations. The ion-leachable aluminosilicate glass powder, in an aqueous solution of a polymer or copolymer of acrylic acid, is attacked by the hydrated protons of the acid, causing the release of aluminum and calcium ions. Salt bridges are formed, and a gel matrix surrounds the unreacted glass particles. The matrix is adhesive to mineralized tissues. Provisions must be made for maintenance of the water balance of restorations for the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

PMID: 1292462 [PubMed - indexed for MEDLINE]

Mutans streptococci in plaque from margins of amalgam, composite, and glass-ionomer restorations.

J Dent Res. 1990 Mar;69(3):861-4

Authors: Svanberg M, Mjör IA, Orstavik D

Levels of mutans streptococci in plaque samples from margins of Class II amalgam (Dispersalloy), composite (P-10), and glass-ionomer (Ketac Silver) restorations were compared. Fifty-one children, each having one of the restorations in a permanent first molar, were part of an inter-individual comparison, giving 17 restorations of each material. The age of the children, the age of the restorations, and the salivary levels of mutans streptococci were comparable in the three groups. Another seven children--each having both a composite and a glass-ionomer restoration of the same age placed on contralateral premolar or molar teeth--were part of an intra-individual comparison. The percentage mutans streptococci of total CFU count in plaque was higher on composite (mean 13.7) and amalgam (mean 4.3) than on glass-ionomer (mean 1.1) restorations in the inter-individual comparison, and higher on composite (mean 4.2) than on glass-ionomer (mean 0.4) restorations in the intra-individual comparison. In both comparisons, the differences in values between samples from glass-ionomer restorations and samples from composite or amalgam restorations were statistically significant (p less than 0.05).

PMID: 2109000 [PubMed - indexed for MEDLINE]

In vitro caries-inhibitory properties of a silver cermet.

J Dent Res. 1989 Jun;68(6):1088-93

Authors: Swift EJ

Recurrent caries is one of the primary causes of failure of dental restorations. One method for reducing the frequency and severity of this problem is the use of fluoride-releasing restorative materials. The glass-ionomer cements are a type of fluoride-releasing material. They have been used extensively in recent years for a variety of clinical applications. However, in comparison with other restorative materials such as amalgam and composite resins, glass ionomers have relatively poor physical properties. Sintering of silver particles to glass-ionomer powder is a means of improving these physical properties. The sintered material is called a silver-glass ionomer or silver cermet. This study examined the in vitro caries-inhibitory potential of a silver cement by means of two methods. First, long-term fluoride release was measured. Second, an artificial caries system was used for evaluation of caries inhibition by cerment restorations in extracted teeth. In comparison with a standard glass-ionomer restorative material, fluoride release from the cermet material was significantly less throughout a 12-month period. The results from the artificial caries system indicated that this decreased fluoride release corresponded with a lesser degree of caries inhibition. Lesions around cermet restorations in both enamel and root surfaces were significantly more severe than those around conventional glass-ionomer restorations. However, in comparison with amalgam and composite resin restorations, the cermet did have some cariostatic activity.

PMID: 2509525 [PubMed - indexed for MEDLINE]

Wear and microhardness of a silver-sintered glass-ionomer cement.

J Dent Res. 1988 May;67(5):831-5

Authors: McKinney JE, Antonucci JM, Rupp NW

Knoop Hardness and pin-and-disc-wear measurements were made on a commercial silver-sintered glass-ionomer cement. The objective was to determine whether the incorporation of a bonded-metal-to-glass filler would enhance durability as determined by the above measurements. As with the previous work on conventional (non-metalized) glass-ionomer cements, the specimens were preconditioned at 37 degrees C in air, water, 0.02 mol/L lactic acid (pH 2.67), and heptane. The influence of these media on the microhardness of the silver-sintered material was about the same as that on the conventional materials. Storing in air produced dehydration, which increased the hardness considerably. Heptane storage increased the hardness less, but this increase is attributed to continued curing during storage. After storage in water, the hardness was essentially unchanged; the influence of increased cure is believed to be offset by softening or plasticization from water uptake. Lactic acid produced a decrease in hardness from chemical dissolution as seen from the SEM observations. In most cases, in particular for the air-stored specimens, the wear resistance was enhanced markedly over that of the conventional materials evaluated previously. The exception was the lactic acid-stored specimens for which little, or no, improvement was observed during early periods of wear. The incorporation of silver appeared to provide lubrication, thus reducing wear. However, catastrophic failure from brittle fracture was still a problem, but its occurrence was less frequent.

PMID: 2966819 [PubMed - indexed for MEDLINE]