Changes in compressive strength of glass ionomer restorative materials with respect to time periods of 24 h to 4 months

Sesame Oil (Sesamum Indicum L.) as a New Challenge for Reinforcement of Conventional Glass Ionomer Cement, Could It Be?

Purpose

Despite the advantages of glass ionomer cement (GIC) including chemical bonding to the tooth structure and fluoride release, its low-grade mechanical properties make it a topic for research. Accordingly, this study was conducted to assess the ability of sesame oil as a natural bioactive additive to reinforce conventional glass ionomer cement.

Materials and Methods

Sesame oil was blended into the liquid component of the cement in ratios of 3 and 5 (v/v%). One control and two experimental groups were enrolled in the study; I: unmodified GIC (control), II: 3 (v/v%) sesame oil-modified GICs, and III: 5(v/v%) sesame oil-modified GICs. Compressive strength, shear bond strength, diametral tensile strength, surface microhardness, surface roughness, and color stability were the parameters assessed. A representative specimen of each group was analyzed for its chemical structure by Fourier transformation infrared spectroscopy. One-way ANOVA followed by Tukey test was used to analyze the collected data of all evaluated parameters except the color stability results, which were analyzed by Student t-test at p < 0.05.

Results

Three and 5 (v/v%) sesame oil-modified GICs exhibited significant increase in their compressive strength, shear bond strength, diametral strength, and surface microhardness. Concurrently, there was a significant decrease in surface roughness (p < 0.05) in both formulations of the modified cement. Both 3 and 5 (v/v%) sesame oil-modified GICs showed a clinically acceptable color change.

Conclusions

Sesame oil seems to be a promising natural bioactive product for reinforcement of conventional GIC with a clinically agreeable esthetic.

An in vitro assessment of the physical properties of manually- mixed and encapsulated glass-ionomer cements

Objectives

The last decade has seen a variety of modifications of glass-ionomer cements (GICs), such as inclusion of bioactive glass particles and dispensing systems. Hence, the aim was to systematically evaluate effect of mixing modes and presence of reactive glass additives on the physical properties of several GICs.

Materials and methods

The physical properties of eight commercial restorative GICs; Fuji IX GP Extra (C&H), Ketac^TM Fill Plus Applicap (C&H), Fuji II LC (C&H), Glass Carbomer Cement and Equia® Forte Fil, capsulated versus manually mixed were assessed. 256 cylindrical specimens were prepared for compressive strength and microhardness, whilst 128 disc-shaped specimens were prepared for biaxial flexural strength tests. Fluid uptake and fluoride release were assessed. Data were analysed using one-way ANOVA and Games-Howell post-hoc tests (alpha = 0.05).

Results

Both encapsulated GIC/RMGICs exhibited significantly improved mechanical properties in comparison to manually mixed equivalents, which in turn showed higher fluid uptake and early fluoride release (p < 0.05). The glass carbomer cement exhibited improved mechanical properties post ageing and evidence of mineral deposits were apparent in the microstructure.

Conclusions

The mixing mode and inclusion of reactive glass additives in cements had a statistically significant effect on physical properties of the selected GICs-RMGICs.

The Influence of Mixing Methods on the Compressive Strength and Fluoride Release of Conventional and Resin-Modified Glass Ionomer Cements

Objective

To evaluate the compressive strength and fluoride ion release of conventional and resin-modified glass ionomer cement mixing methods (hand mix and mechanical mix) compared to ready-to-use ones.

Materials and Methods

Two conventional glass ionomer cements (GICs) (Fuji II and Fuji II Caps), two resin-modified GICs (Fuji II LC and Fuji II L Caps), and one ready-to-use GIC (Ionoseal, Voco) were used. For the compressive strength test, cylindrical specimens (6 mm × 4 mm) of each group were prepared. The test was performed in a universal testing machine (EMIC DL2000). For the fluoride release test, specimens were prepared in the form of discs and placed in deionized/distilled water, which were replaced daily for 15 days. The fluoride ion release readings were performed on an electrode (Orion 96-09) connected to a digital ion analyzer (Quimis 0400ISE). The compressive strength data were analyzed with one-way ANOVA, and the ion release data were submitted to repeated measures ANOVA (material vs. time) and Holm-Sidak post test (α = 5%).

Results

The one-way ANOVA showed statistical difference between the tested materials (p < 0.001). Ionoseal showed the highest values of compressive strength (p < 0.001). Mechanical manipulation increased the compressive strength only for conventional GIC, and resin-modified GIC did not present any statistical difference. Conventional GIC (mechanical mix) showed higher fluoride release on first day than the other groups tested.

Conclusion

There was influence of the mixing methods of the materials on the compressive strength and fluoride release pattern of the glass ionomer cements.

Comparative evaluation of compressive strength and surface microhardness of EQUIA Forte, resin-modified glass-ionomer cement with conventional glass-ionomer cement

PURPOSE

The study aimed to evaluate and compare the compressive strength and surface microhardness of EQUIA Forte, light cure, and conventional glass-ionomer cement (GIC).

METHODOLOGY

Fifty-four pellets of G-Coat (GC) Gold Label 2, GC Gold Label light-cured universal restorative material, and EQUIA Forte GIC were prepared of dimensions (6 × 4) mm and were divided into three groups (18) each and were stored at 37°C for 1 h and then immersed in 20 ml of deionized water, artificial saliva, and lactic acid six each, respectively, over 30 days. Samples were subjected to surface microhardness and compressive strength test on the 1^st day, 7^th day, and 30^th day. Results were subjected to ANOVA and Bonferroni post hoc test.

RESULTS

Comparing the compressive strength of EQUIA Forte from day 1 to 30 when placed in artificial saliva, there was a significant increase on day 30 (P = 0.007); compared to other groups. The surface microhardness of EQUIA Forte from day 1 to 30 when placed in artificial saliva nonsignificantly decreased comparing to other groups.

CONCLUSION

Surface microhardness and compressive strength of EQUIA Forte were significantly high in comparison to the other groups.

Maturation processes in glass-ionomer dental cements

Glass-ionomer cements are used for a variety of tooth-repair functions in clinical dentistry. They are formed by reaction of a basic glass powder with a solution of polymeric water-soluble acid, usually polyacrylic acid. After the initial neutralization reaction, by which the cement hardens, various maturation reactions occur. Changes induced by these maturation reactions are identified as: increase in strength; reduction in plasticity; improvement in opacity; and increase in proportion of tightly bound water. In addition, in contact with the tooth, an ion-exchange interfacial layer is gradually formed. This is mechanically strong and chemically-resistant. These changes are described in the current paper, which reviews the extent to which they occur, and reports what is know about the chemistry that underlies them. Processes involving slow diffusion of various ions and of water through the set cement bring about these changes. They include a secondary setting reaction to form a phosphate-based phase, binding of water to co-ordination sites around metal cations and to a hydration sheath around the polymer molecules, and possibly reaction of water with glass particle surfaces to form silanol groups. Evidence from a wide range of literature sources is used to be build up a detailed picture of the chemistry of the maturation processes, and gaps in our understanding are highlighted. The article concludes that, given the importance of glass-ionomers in contemporary dentistry, it is important to know the extent to which such maturation processes occur in current cement formulations, and also to determine how rapidly they take place.

Thermo-cured glass ionomer cements in restorative dentistry

Numerous positive properties of glass ionomer cements including biocompatibility, bioactivity, releasing of fluoride and good adhesion to hard dental tissue even under wet conditions and easy of handling are reasons for their wide use in paediatric and restorative dentistry. Their biggest drawbacks are the weaker mechanical properties. An important step forward in improving GIC’s features is thermo-curing with the dental polymerization unit during setting of the material. Due to their slow setting characteristics the GIC is vulnerable to early exposure to moisture. After thermo curing, cements retain all the benefits of GIC with developed better mechanical properties, improved marginal adaptation, increased microhardness and shear bond strength. Adding external energy through thermocuring or ultrasound during the setting of conventional GIC is crucial to achieve faster and better initial mechanical properties. Further clinical studies are needed to confirm these findings.

The role of poly(acrylic acid) in conventional glass polyalkenoate cements

Glass polyalkenoate cements (GPCs) have been used in dentistry for over 40 years. These novel bioactive materials are the result of a reaction between a finely ground glass (base) and a polymer (acid), usually poly(acrylic acid) (PAA), in the presence of water. This article reviews the types of PAA used as reagents (including how they vary by molar mass, molecular weight, concentration, polydispersity and content) and the way that they control the properties of the conventional GPCs (CGPCs) formulated from them. The article also considers the effect of PAA on the clinical performance of CGPCs, including biocompatibility, rheological and mechanical properties, adhesion, ion release, acid erosion and clinical durability. The review has critically evaluated the literature and clarified the role that the polyacid component of CGPCs plays in setting and maturation. This review will lead to an improved understanding of the chemistry and properties of the PAA phase which will lead to further innovation in the glass-based cements field.

An Invitro Comparative Evaluation of Compressive Strength and Antibacterial Activity of Conventional GIC and Hydroxyapatite Reinforced GIC in Different Storage Media

BACKGROUND

GIC is the most commonly used restorative material in pediatric dentistry since it has got various advantages like fluoride release, anticariogenic property and chemical adhesion to tooth but a major disadvantage is its contraindication in posterior teeth because of poor mechanical properties.

AIM

The purpose of this study is a modest attempt to explore the influence of the addition of 8% hydroxyapatite to conventional GIC on its compressive strength when immersed in different storage media and antibacterial activity.

MATERIALS AND METHODS

One hundred and twenty six pellets of the specific dimension of 6 x 4 mm were prepared and divided into 6 groups and were immersed in deionized water, artificial saliva, lactic acid solution respectively for three hours everyday over 30 days test period. The compressive strength was measured by using a universal testing machine (AG-50kNG) at cross head of 1mm(2)/min and strength was determined after 1 day, 7 days, 30 days respectively and the antibacterial activity evaluated against Streptococcus mutans strain in brain heart infusion broth using serial dilution method.

STATISTICAL ANALYSIS

Group wise comparisons were made by one-way ANOVA followed by post-hoc Tukey's test, Intergroup comparison was done with Mann-Whitney test.

RESULTS

GIC±HAp showed significantly greater antibacterial activity against Streptococcus mutans when compared to GIC group. There was no statistically significant change in the compressive strength among the groups except for group 3 and group 6 when immersed in lactic acid had shown significant difference at the end of 24 hours.

CONCLUSION

The addition of 8% hydroxyapatite to GIC showed marked increased in the antibacterial activity of the conventional GIC against caries initiating organism without much increase in the compressive strength of the GIC when immersed in the different storage media.

Conventional glass-ionomer materials: A review of the developments in glass powder, polyacid liquid and the strategies of reinforcement

OBJECTIVES

The development of glass-ionomers (GIs) from the earliest experimental GI formulations to the modern day commercially available GIs was reviewed. The aim of the review was to identify the developments in the glass powder and polyacid liquid constituents of GIs since their inception in the late 1960s.

DATA

The glass powder has undergone major changes from the earliest GI powder formulation (G200) in an effort to enhance the reactivity with the polyacid liquid. The GI liquids have also been optimised by the manufacturers in terms of polyacid composition, molecular weight and concentration to improve the handling characteristics. Despite these developments in the glass powder and polyacid liquid constituents, GIs cannot 'truly' be advocated for the restoration of posterior dentition due to the poor mechanical properties when compared with dental amalgam and resin-based composites (RBCs).

SOURCES

Various attempts to improve the mechanical properties of GIs through substitution of reinforcing fillers to the GI powder or modification of the GI liquid were identified in the dental literature. Despite the claimed improvements in mechanical properties of the modified GIs, a wide variation in mixing and testing conditions was identified which prevented a valid assessment of the reported reinforcement strategies. When investigating a GI reinforcement strategy it is crucial that the mixing and testing conditions are standardised to allow a valid comparison between studies.

STUDY SELECTION

The dental literature reporting the earliest experimental GIs to modern day commercially available GIs (1969-2015) was reviewed. In addition, full-text publications and abstracts published in English reporting various GI reinforcement strategies were included.

CONCLUSION

Nevertheless, major improvements in GI formulations through a reinforcement strategy have yet to be made to enable clinical usage of GIs for the restoration of posterior dentition.

CLINICAL SIGNIFICANCE

GIs chemically are inherently weak but bond to sound tooth structure without the need for preconditioning or removal of sound tooth structure such that improvements in the mechanical properties of GIs would be desirable. Although advances have been made through different GI glass powder and polyacid liquid formulations over the past 40 years, further improvements in the mechanical properties of the current GIs are required to be indicated for the restoration of posterior dentition. The literature is replete with reports on GI reinforcement, however, improved reporting and control of mixing and testing conditions are required for a valid assessment of the reinforcement strategies.

Investigating the effect of SiO2-TiO 2-CaO-Na 2O-ZnO bioactive glass doped hydroxyapatite: characterisation and structural evaluation

The effects of increasing bioactive glass additions, SiO2-TiO2-CaO-Na2O-ZnO up to 25 wt% in increments of 5 wt%, on the physical and mechanical properties of hydroxyapatite (HA) sintered at 900, 1000, 1100 and 1200 °C for 2 h was investigated. Increasing both the glass content and the temperature resulted in increased HA decomposition. This resulted in the formation of a number of bioactive phases. However the presence of the liquidus glass phase did not result in increased densification levels. At 1000 and 1100 °C the additions of 5 wt% glass resulted in a decrease in density which never recovered with increasing glass content. At 1200 °C a cyclic pattern resulted from increasing glass content. There was no direct relationship between strength and density with all samples experiencing no change or a decrease in strength with increasing glass content. Weibull statistics displayed no pattern with increasing glass content.

Effects of oral hygiene, residual caries and cervical Marginal-gaps on the survival of proximal atraumatic restorative treatment approach restorations

Background:

Although Atraumatic restorative treatment (ART) approach has been in existence for a while, the reasons for the poor performance of multisurface ART restorations are not very clear.

Aim:

The aim of this study is to investigate the effects of oral hygiene, residual caries and cervical marginal-gaps on survival of proximal ART restorations.

Settings:

Two rural divisions in Kenya were selected for the study.

Design:

A randomized clinical trial.

Material and Methods:

The 804 children in the study had their baseline- and 2-year dental plaque levels documented. Each child received one proximal restoration in a primary molar using ART approach, together with trained and pre-tested operators/assistants, three glass ionomer cements (GIC)-brands and two tooth-isolation methods. The restorations were clinically evaluated soon after placement and after 2 years. Post-restorative bite-wing radiographs taken soon after restoration were also evaluated.

Statistical analysis:

Statistical Package for Social Sciences (SPSS) version 14 computer programme was used and results tested using Pearson's correlation, Cox Proportional Hazards regression analysis and Multiple Logistic regression models tests.

Results:

At baseline and after 2 years, the mean cumulative survival and plaque index changed from 94.4% to 30.8% and 2.34 (Standard Deviation, or SD of 0.46) to 1.92 (SD 2.1) respectively, with higher plaque indices associated with higher restoration failures. Of the 507 radiographs evaluated, 48 (9.5%), 63 (12.4%) and 9 (1.8%) restorations had residual caries (RC), cervical marginal-gaps (CMG) and both RC/CMG respectively. Survival of the restorations with RC/CMG was significantly lower (p = 0.003) compared to those with RC or without RC.

Conclusion:

Low survival of proximal restorations in the study was associated with the presence of cervical marginal-gaps.

Diametral tensile strength and water sorption of glass-ionomer cements used in Atraumatic Restorative Treatment

The purposes of this study were to evaluate the diametral tensile strength and the water sorption of restorative (Fuji IX and Ketac Molar) and resin-modified glass-ionomer luting cements (ProTec Cem, Fuji Plus and Vitremer) mixed at both manufacturer and increased powder: liquid ratio, for their use in the Atraumatic Restorative Treatment. A conventional restorative glass-ionomer (Ketac Fil) was used as control. Specimens (6.0 mm in diameter x 3.0 mm in height) were prepared and stored (1 hour, 1 day and 1 week) for a diametral tensile strength test. Data were subjected to two-way ANOVA and Tukey tests (p<0.05). For the water sorption test, specimens of 15.0 mm in diameter x 0.5 mm in height were prepared and transfered to desiccators until a constant mass was obtained. Then the specimens were immersed in deionized water for 7 days, weighed and reconditioned to a constant mass in desiccators. Data were subjected to one-way ANOVA and Tukey tests (p<0.05). Five specimens of each studied material and consistency were prepared for each test. The resin-modified glass-ionomer cements showed significantly higher strength than the conventional materials. Except for ProTec Cem, the diametral tensile strength of the resin-modified materials significantly increased from luting to restorative consistency. Except for ProTec Cem, the water sorption of the resin-modified glass ionomers was higher than the others. The water sorption of resin-modified materials at restorative consistency was significantly lower than at luting consistency. Resin-modified glass-ionomer luting cements mixed at increased powder: liquid ratio showed better properties than at luting consistency.

Bonding to glass ionomer cements using resin-based adhesives

OBJECTIVE

This study compared the microshear bond strengths (MSBS) of four self-etching adhesives (Adper Scotchbond SE [SSE], Clearfil SE Bond [CSE], Clearfil S3 Bond [CS3] and One Coat 7.0 [OC]) and an etch-and-rinse adhesive (Adper Single Bond Plus [SB]) when bonded to two conventional glass ionomer cements (GICs) (Fuji IX GP EXTRA and Riva Self Cure). The null hypothesis tested was there is no difference in the adhesive ability of an etch-and-rinse adhesive and self-etching adhesives when bonded to GIC for up to 6 months.

METHODS

The GICs were embedded in type III dental stone and wet ground with 1200-grit SiC paper. Twenty specimens were bonded for each adhesive according to manufacturers' instructions with a 1.5-mm bonding diameter. Specimens were stored at 100% humidity for 24 hours, 1 month, or 6 months. Microshear bond strengths were obtained using a crosshead speed of 1 mm/min. The results were calculated and analyzed using analysis of variance (ANOVA) and Tukey HSD test.

RESULTS

SB had significantly lower MSBS than the four self-etching adhesives for all storage periods. MSBS at 6 months for SB was significantly lower than at 1 month. There were no significant differences in MSBS among the self-etching adhesives. Cohesive failure within GIC was the most common failure mode observed.

CONCLUSIONS

SB showed a lower bond strength than the self-etching adhesives when bonded to conventional GICs for all storage periods. This might be a result of the phosphoric acid etching. However, cohesive strength of GIC was a limiting factor for the MSBS outcomes.

Fabrication of spherical CaO-SrO-ZnO-SiO₂ particles by sol-gel processing

This study was concerned with the fabrication of ceramic CaO-SrO-ZnO-SiO(2) spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol-gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO-SrO-ZnO-SiO(2) particles by sol-gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H(2)O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3-5 mum homogenous spherical particles were obtained at a H(2)O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO(3)):Ca(NO(3))(2):Zn(NO(3))(2):Si(OC(2)H(5))(4) = x:0.12:(0.40 - x):0.48 (0 </= x </= 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.

A long-term study on the setting reaction of glass ionomer cements by (27)Al MAS-NMR spectroscopy

OBJECTIVES

The main objective is the characterization of the setting reaction in glass ionomer cements (GICs) based on experimental glasses using the (27)Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy in order to understand the crosslinking process during the setting reaction.

METHODS

Three types of GICs which are based on fluoro-alumino-silicate glasses (LG125, ART10, and LG26Sr) were studied using (27)Al MAS-NMR to monitor the setting reaction of the cements.

RESULTS

The result showed clearly the formation of six coordinate, aluminium Al(VI), that crosslink the carboxyl groups in the PAA. The deconvolution study was performed to quantify the amount of each Al species in the cements. The finding showed that composition of original glass has a substantial effect on the setting behavior of the cements.

SIGNIFICANCE

Our data demonstrate that the setting reaction of GICs can be followed by (27)Al MAS-NMR spectroscopy discovering the conversion of Al(IV) to Al(VI). Considerable amount of the five coordinate aluminium, Al(V), species was found in the cements aged up to one year. The presence of phosphorus has a strong influence on the setting reaction. The formation of Al-O-P species was postulated to be present in the cement.

The effects of heat treatment on selected properties of a conventional and a resin-modified glass ionomer cement

This study investigated the effects of application of heat alone and heat & pressure on the compressive strength and modulus, the stress relaxation characteristics and the fluoride release of a conventional and a resin-modified glass ionomer cement. Cylindrical specimens were made from both materials and divided into 3 groups. One group was heat treated in an oven at 120 degrees C for 20 min, another group was subjected to heat & pressure at 120 degrees C for 20 min at 6-bar pressure. The third group acted as a control. The compressive strength and modulus, stress relaxation and fluoride release were tested over 56 days. The results of this investigation indicate that heat treatment had no significant effect on the conventional GIC used but significantly affected the resin modified GIC by increasing both the compressive strength and modulus and reducing the stress relaxation characteristics and the fluoride release. The use of GIC to produce inlay or onlay restorations that adhere to tooth tissue and release fluoride would be highly desirable. The results of this study indicate that it is possible to improve the strength of RMGIC with heat to a limited extent, but fluoride release may decrease.

Zinc-based glass polyalkenoate cements with improved setting times and mechanical properties

The suitability of glass polyalkenoate cements (GPCs) for skeletal applications is limited by the presence, in the glass phase, of the aluminium ion (Al3+), a neurotoxin. The zinc ion (Zn2+), a bacteriocide, has been incorporated into aluminium-free GPCs based on zinc silicate glasses. However, these GPCs have considerably shorter working times and poorer mechanical properties than their Al3+-containing counterparts. Based on results for calcium phosphate cements, there is an indication that mixing a GPC with an organic compound, tricalcium citrate (TSC), may lead to cements with improved rheological and mechanical properties. We developed a range of Zn-based GPCs and determined their working times (Tw), setting times (Ts), compressive strength (CS) and biaxial flexural strengths (BFS). A GPC composed of 1g of a calcium-zinc silicate glass (BT100) mixed with a 50wt.% aqueous solution on polyacrylic acid (coded E9, Mw 80,800) at a powder liquid ratio of 2:1.5 exhibited the best combination of Tw, Ts, CS and BFS. We also found that the addition of TSC (over the range 5-15wt.%) to a GPC led to significant increases in both Tw (from 40+/-3 to 100+/-4s) and Ts (from 70+/-2 to 3000+/-4s) accompanied by changes in both CS and BFS that were affected by the duration of the aging time of the specimens in distilled water (for example, after aging for 7 days CS dropped from 62+/-2 to 17+/-1MPa, while after aging for 30 days, BFS increased 27+/-6 to 31+/-7MPa and then dropped to 17+/-1MPa). Future modification and characterization of the examined GPCs are needed before they may be considered as candidates for orthopaedic applications.

A review of bone substitutes

The use of bone grafts in the repair of defects has a long history of success, primarily with the use of autologous bone. With increasing technologic advances, researchers have been able to broaden the spectrum of grafting materials to allografts, xenografts, and synthetic materials, which provide the surgeon and patient with options, each with unique advantages. It is with the knowledge of each material that the clinician can present and suggest the best material and tailor treatment plans to fit each individual. In this article, we present an overview of the principles of bone grafting, the types of graft materials available, and an outlook to what the future holds in this area of medicine and dentistry.

The role of glass composition in the behaviour of glass acetic acid and glass lactic acid cements

Cements have recently been described, made from glass ionomer glass reacted with acetic and lactic acid instead of polymeric carboxylic acid. From their behaviour a theory relating to a possible secondary setting mechanism of glass ionomer has been adduced. However, only one glass (G338) was used throughout. In this study a much simpler glass ionomer glass (MP4) was compared with G338. This produced very different results. With acetic acid G338 formed cement which became resistant to water over a period of hours, as previously reported, MP4 formed cement which was never stable to water. With lactic acid G338 behaved similarly to G338 with acetic acid, again as reported, but MP4 produced a cement which was completely resistant to water at early exposure and unusually became slightly less resistant if exposure was delayed for 6 h or more. These findings indicate that the theories relating to secondary setting in glass ionomer maturation may need revision.

Compressive strength of glass ionomer cements using different specimen dimensions

The purpose of this study was to evaluate the compressive strength of two glass ionomer cements, a conventional one (Vitro Fil® - DFL) and a resin-modified material (Vitro Fil LC® - DFL), using two test specimen dimensions: One with 6 mm in height and 4 mm in diameter and the other with 12 mm in height and 6 mm in diameter, according to the ISO 7489:1986 specification and the ANSI/ADA Specification No. 66 for Dental Glass Ionomer Cement, respectively. Ten specimens were fabricated with each material and for each size, in a total of 40 specimens. They were stored in distilled water for 24 hours and then subjected to a compressive strength test in a universal testing machine (EMIC), at a crosshead speed of 0.5 mm/min. The data were statistically analyzed using the Kruskal-Wallis test (5%). Mean compressive strength values (MPa) were: 54.00 ± 6.6 and 105.10 ± 17.3 for the 12 mm x 6 mm sample using Vitro Fil and Vitro Fil LC, respectively, and 46.00 ± 3.8 and 91.10 ± 8.2 for the 6 mm x 4 mm sample using Vitro Fil and Vitro Fil LC, respectively. The resin-modified glass ionomer cement obtained the best results, irrespective of specimen dimensions. For both glass ionomer materials, the 12 mm x 6 mm matrix led to higher compressive strength results than the 6 mm x 4 mm matrix. A higher variability in results was observed when the glass ionomer cements were used in the larger matrices.

Ion processes in glass ionomer cements

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

The influence of accelerating the setting rate by ultrasound or heat on the bond strength of glass ionomers used as orthodontic bracket cements

Conventional glass ionomer cements (GICs) may be a viable option for bracket bonding when the major disadvantages of these materials, such as the slow setting reaction and the weak initial bond strength, are solved. The aim of this in vitro study was to investigate the influence of ultrasound and heat application on the setting reaction of GICs, and to determine the tensile force to debond the brackets from the enamel. A conventional fast-setting GIC, Fuji IX Fast, and two resin-modified glass ionomer cements (RMGICs), Fuji Ortho LC and Fuji Plus, were investigated. Three modes of curing were performed (n = 10): (1) according to the manufacturer's prescription, (2) with 60 seconds application of heat, or (3) with 60 seconds application of ultrasound. The tensile force required to debond the brackets was determined as the tension 15 minutes after the start of the bonding procedure. The mode of failure was scored according to the Adhesive Remnant Index (ARI) to establish the relative amount of cement remnants on the enamel surface. Curing with heat and ultrasound shortened the setting reaction and significantly (P < 0.05) increased the bond strength to enamel. The ARI scores showed an increase for all materials after heat and ultrasound compared with the standard curing method, most notably after heat application.

Compressive strength and surface characterization of glass ionomer cements modified by particles of bioactive glass

OBJECTIVES

The aim of this study was to determine compressive strength, Young's modulus of elasticity, and Vickers' surface hardness, of conventional cure and resin-modified glass ionomer cements after the addition of bioactive glass (BAG) particles into the cements.

METHODS

Experimental glass ionomer cement (GIC)-BAG materials were made by mixing 10- or 30-wt% of BAG particles with conventional cure and resin-modified GIC powders. Materials were processed into cylindrical specimens and immersed in water for 1, 3, 7, 14, 30 and 180 days before mechanical tests. SEM and EDS analysis was used to characterize the changes in surface topography and the main elemental composition.

RESULTS

The compressive strength of the test specimens decreased with the increasing amount of BAG. The compressive strength of resin-modified GIC increased during the immersion, but remained at a lower level than that of the other materials. The conventional cure GIC-based materials had on average 55% higher surface microhardness than the resin-modified materials. In the elemental composition, more Ca was detected in the BAG-containing materials than in the pure GICs. The amount of F was significantly higher (p < 0.001) on all resin-modified materials, being highest on resin-modified GIC with 30-wt% of BAG after 180d of immersion.

SIGNIFICANCE

The addition of BAG to GIC compromises the mechanical properties of the materials to some extent. Thus, their clinical use ought to be restricted to applications where their bioactivity can be beneficial, such as root surface fillings and liners in dentistry, and where high compressive strength is not necessarily needed.

Compressive and diametral tensile strength of glass ionomer cements

The aim of this study was to compare, in different periods of time, the compressive and diametral tensile strength of a traditional high viscous glass ionomer cement: Fuji IX (GC Corporation), with two new Brazilian GIC's: Vitro-Molar (DFL) and Bioglass R (Biodinamica), all indicated for the Atraumatic Restorative Treatment (ART) technique. Fifteen disk specimens (6.0mm diameter x 3.0mm height) for the diametral tensile strength (DTS) test and fifteen cylindrical specimens (6.0mm diameter x 12.0mm height) for the compressive strength (CS) test were made of each GIC. Specimens were stored in deionized water at 37º C and 100% of humidity in a stove until testing. Five specimens of each GIC were submitted to CS and DTS test in each period, namely 1 hour, 24 hours and 7 days. The specimens were tested in a testing machine (Emic) at a crosshead speed of 1.0mm/min for CS and 0.5mm/min for the DTS test until failure occurred. The data were submitted to two-way ANOVA and Tukey tests (alpha=0.05). The mean CS values ranged from 42.03 to 155.47MPa and means DTS from 5.54 to 13.72 MPa, with test periods from 1h to 7 days. The CS and DTS tests showed no statistically significant difference between Fuji IX and Vitro Molar, except for CS test at 1-hour period. Bioglass R had lowest mean value for CS of the cements tested. In DTS test Bioglass R presented no statistically significant differences when compared with all others tested GICs at 1-hour period and Bioglass R presented no difference at 24-hour and 7-day periods when compared to Vitro-Molar. Further studies to investigate other physical properties such as fracture toughness and wear resistance, as well as chemical composition and biocompatibility, are now needed to better understand the properties of these new Brazilian GIC's.

Strengthening effect of aluminum fluoride added to resin composites based on polyacid-containing polymer

OBJECTIVES

The study investigates the possible strengthening effect of aluminum ions liberated during long-time water storage of experimental resin composites containing a polymer with carboxylic acid groups.

METHODS

The organic part of the resin composites was formed by photopolymerization of methacrylate monomers. The monomer mixture was composed of UEDMA, HEMA or TEGDMA, and 0-40 mol% HEMAN (the adduct of HEMA and maleic anhydride). The filler part of the resin composites consisted of a conventional silanated glass filler and 1 or 5 wt% of AlF3 x 3H2O. The rupture strength and bending modulus were measured without water storage and after 1 month, 1 year, and 3 years of water storage at 37 degrees C of the resin composite.

RESULTS

The experimental composites that had been stored in water had lower rupture strength and modulus than the composites that were tested without water storage. Specimens containing 30 or 40 mol% HEMAN increased in strength, and specimens containing 20, 30, or 40 mol% HEMAN increased in modulus during the period of water storage. Depending on composition, values for strength and modulus obtained after 3 years of water storage was up to 50% higher than the values obtained after 1 month.

SIGNIFICANCE

The strengthening effect of aluminum fluoride may be interpreted as the result of increased crosslinking by aluminum ions and carboxylate groups. The results may serve as a basis for the improvement of the mechanical properties of polyacid-modified resin composites.

Flexural strength and modulus of a novel ceramic restorative cement intended for posterior restorations as determined by a three-point bending test

The aim of this study was to compare a new restorative cement intended for posterior restorations, Doxadent, with other types of tooth-colored materials as regards flexural strength and flexural modulus. The new restorative material consists mainly of calcium aluminate. Four hybrid resin composites, one polyacid-modified resin composite, one resin-modified glass ionomer cement, one conventional glass ionomer cement, one zinc phosphate cement, and an experimental version as well as the marketed version of Doxadent were investigated. Flexural strength and flexural modulus were tested according to ISO standard 4049 and determined after 1 d, 1 week, and 2 weeks. Together with the zinc phosphate cement, Doxadent had the lowest flexural strengths (13-22 MPa). The strongest materials were the resin composites and the polyacid-modified resin composite (83-136 MPa). The highest flexural modulus was found for Doxadent (17-19 GPa). The flexural strength of Doxadent decreased significantly from 1 week to 2 weeks, while flexural modulus remained unchanged. The other materials reacted in different ways to prolonged water storage. It can be concluded that the restorative cement Doxadent had significantly lower flexural strength and significantly higher flexural modulus than today's materials used for direct posterior restorations.

Physico-mechanical properties of a fast-set highly viscous GIC restorative

The fast-setting reaction of 'fast-set' highly viscous glass-ionomer cements (GIC) may result in superior mechanical properties and good wear resistance as the material can theoretically achieve sufficient strength to resist masticatory loads within a shorter time. The aim of this study was to determine the hardness, strength (compressive and diametral tensile) and wear resistance of a 'fast-set' highly viscous GIC (Fuji IX GP Fast). Its regular set counterpart (Fuji IX GP) was used for comparison. The glass powders of the two cements were also characterized. Hardness testing [Vickers' hardness number (VHN)] was performed with a digital hardness tester (load=50 g; dwell time=30 s) and compressive/diametral tensile strength testing (MPa) was conducted based upon British Standards specification for GICs (BS6039, 1981). Wear testing was conducted using a reciprocal compression-sliding wear instrumentation at 20 MPa contact stress against SS304 counter-bodies with distilled water as lubricant. All specimens were immersed in distilled water at 37 degrees C and tested 24 h after start of mixing. Further mechanical tests (hardness and strength) were conducted with specimens stored for 1 week in distilled water at 37 degrees C. The glass powders were characterized using laser particle sizing, standard electron microscope (SEM) and energy dispressure X-ray (EDX) analysis. Results were analysed using multiple analysis of variance (manova) and independent samples t-test at significance level 0.05. No significant difference in hardness, compressive and diametral tensile strength was observed between Fuji IX GP and Fuji IX GP Fast at 1 day. There was also no significant difference in wear at all cyclic intervals. Although the difference in strength was not significant between the two cements at 1 week, Fuji IX GP Fast was significantly harder than Fuji IX GP. Particle size of both cements ranged from 0.3 to 200 microm. The mean particle sizes were, however, different and were 13.43 and 7.13 microm for Fuji IX GP and Fuji IX GP Fast, respectively. Fuji IX GP Fast offers no other advantage over Fuji IX GP with the exception of improved hardness.

CLINICAL RELEVANCE

Besides being harder, the fast-set highly viscous GIC restorative offers no other physico-mechanical advantage over its regular set counterpart.

The glass ionomer cement: the sources of soluble fluoride

This study aimed to investigate certain processes of fluoride production which enable glass ionomer cements to leach fluoride. Two fluoroaluminosilicate glasses, G338 and LG26 were used. The free and total fluoride which could be dissolved from the glasses was measured, before and after acetic acid washing. Both glasses contained appreciable amounts of soluble fluoride prior to any acid treatment. The latter process reduced the amount to some 75% of the original levels. Replacing the customary polymeric acid with propionic acid produced a cement which disintegrated in water allowing the amount of fluoride generated by the cement forming process to be measured. Cement production increased soluble fluoride by a further 3%. Both glasses behaved similarly when undergoing the various processes. G338 produced significantly greater quantities of fluoride, of the order of 10, compared with LG26 although containing only three times the amount of fluoride in the glass formula. A substantial proportion, over half, of the total fluoride was complexed especially after contact with cement and when G338 was used. During the period of the experiment, 21 days, total fluoride release did not seem to depend on the square root of time.

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.

A preliminary comparison of the mechanical properties of chemically cured and ultrasonically cured glass ionomer cements, using nano-indentation techniques

There is a requirement for a dental cement with properties comparable or superior to conventional glass ionomer cements (GICs) but with the command set properties of the resin-modified GICs. The objective of this work was to show that the application of ultrasound to conventional Fuji IX commercial glass ionomer cement imparts a command set, whilst improving the short-term surface mechanical properties. Nano-indentation techniques were employed to highlight the improvements in hardness and creep resistance imparted to the cement through the application of ultrasound. The instant set imparted by the application of ultrasound provides improved surface hardness and creep, particularly within the first 24 h after setting. The surface hardness of the chemically cured Fuji IX (176 M Pa) increased by an order of magnitude when set ultrasonically (2620 M Pa), whilst creep reduced to a negligible amount. Rapid setting allows for shorter chair time and an improved clinical technique, making restorations more convenient for both the patient and clinician.

Influence of glass composition on the properties of glass polyalkenoate cements. Part IV: influence of fluorine content

The influence of fluorine content of the glass in a series of glasses based on: 4.5SiO2-3.0Al2O3-1.5P2O5-(5.0-X)CaO-XCaF2 was investigated on their cement formation with poly(acrylic acid). Increasing the fluorine content of the glass was found to reduce the glass transition temperature, as a result of fluorine replacing bridging oxygens by non-bridging fluorines. Working and setting times of the cement pastes reduced with increasing fluorine content of the glass. Compressive strength and Young's moduli increased with fluorine content initially and then remained approximately constant. Fracture toughness, toughness and un-notched fracture strength were not significantly influenced by fluorine content. The results are consistent with fluorine simultaneously disrupting the glass network and reducing the basicity of the glass.

Influence of glass composition on the properties of glass polyalkenoate cements. Part III: influence of fluorite content

The influence of fluorite content of the glass on the formation and properties of glass polyalkenoate cements was investigated. A series of glass powders based on 1.5SiO2 x 0.5P2O5 x Al2O3 x CaO x XCaF2 were synthesised. The glass transition temperature of the glass fell with increasing fluorite content. Setting and working times of the cement pastes decreased with increasing fluorite content of the glass. Compressive strength and un-notched fracture strength increased with increasing fluorite content of the glass. Fracture toughness and toughness of the cements were relatively insensitive to fluorite content.

Fluoride release profiles of mature restorative glass ionomer cements after fluoride application

This study investigates the fluoridation of four conventional glass ionomer cements (GIC) (ChemFil Superior encapsulated, Fuji Cap II, Ketac-Fil and Hi Dense) and three resin-modified GIC (RM-GIC) (Fuji II LC encapsulated, Photac-Fil and Vitremer). The fluoride release of matured restorative GIC was measured as a function of time, after four repeated fluoridations in a 2% NaF aqueous solution for 1 h. This release was corrected for the intrinsic release as determined with a control group. It was demonstrated that application of fluoride is capable of recharging GIC but the subsequent high fluoride release only lasts for one or a few days. Moreover, the fluoride release behaviour depends on the cement formulation. Comparable to the intrinsic release, the net fluoride release after fluoridation is composed of a short- and a long-term process, the former being predominant after fluoridation. The total amount of fluoride released according to the short-term process increases with consecutive fluoridations. This is especially pronounced for the RM-GIC, who exhibit a relatively slow release after fluoridation as compared to the conventional GIC. An explanation for these results is suggested on the basis of the physicochemistry of the setting reaction of the cements and of the fluoridation process.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.

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.

An in vitro investigation of a poly(vinyl phosphonic acid) based cement with four conventional glass-ionomer cements. Part 1: Flexural strength and fluoride release

OBJECTIVE

To investigate the flexural strength and fluoride release of four conventional glass-ionomer cements: Ketac-Molar (KM), HiFi (HF), Vivaglass Fil (VF), Ketac-Fil (KF) and a newly developed glass polyphosphonate cement, Diamond Carve (DC).

METHOD

Disc specimens (10 mm diameter, 1 mm thick) were prepared and mould stored at 37 degrees C. After one hour, the specimens were removed from their mould and immersed in 20 ml of deionised water until required for testing. Biaxial flexural strength was determined at 1 hour and at 1, 7, 30 and 90 days after the start of mixing. Measurements of fluoride release from the specimens were carried out at 2 hours and at 1, 3, 7, 14, 30, 60 and 90 days after the start of mixing using a fluoride ion selective electrode. The results were analysed using ANOVA and student 't' tests.

RESULTS

All the materials displayed different flexural strength patterns. KM and DC became stronger whilst KF and VF plateaued in strength with time. HF peaked in strength and then became weaker. At 90 days, the mean flexural strengths in decreasing order was as follows: KM > or = VF > or = DC > or = HF > KF. An initial fast rate of fluoride release followed by a slower but steady release of fluoride was observed in each of the materials. The mean cumulative fluoride release in decreasing order was as follows: VF > KF > or = HF > DC > KM. VF released significantly higher level and KM significantly lower level of fluoride than the other materials.

CONCLUSIONS

The acid used to form the cement could not be used to predict changes in cement strength behaviour with respect to time. DC increased in strength with time and its flexural strength at 90 days was comparable to that of HF and VF. The cumulative and rate of fluoride release varied for the materials. DC had a low fluoride release consistent with a fast setting material with good early resistance to water.

Structural integrity of resin-modified glass ionomers as affected by the delay or omission of light activation

Since light activation of resin-modified glass ionomers as a means of polymerizing the HEMA is usually done shortly after mixing occurs, the acid-base reaction will proceed mainly within a formed HEMA-polymer matrix. Delaying or omitting light activation may alter the structure and consequently its integrity. The aim of this study was to investigate the effect on the structural integrity of Fuji II LC, Photac-Fil, and Vitremer by delaying or omitting light initiation as compared with the integrity when light activation is performed 2 min after mixing occurs. We evaluated integrity by three-body wear experiments, conducted 8 hrs after sample preparation, to establish the integrity in the early phase of hardening, as well as after 1 wk and after 4 mos, to follow the materials throughout the process of maturation. When light activation was delayed for 1 hr, the structural integrity of Fuji II LC and Photac-Fil improved significantly in the early stages of hardening. In the case of Vitremer, an hour's delay of light activation significantly decreased integrity, which declined further when light activation was omitted. Fuji II LC was not affected by the omission of light activation, while Photac-Fil was markedly weakened. After 4 mos of aging, most of the samples of each product which had been cured by the different methods attained equal integrity, with the exception of the non-light-activated Vitremer samples, which remained weaker. We concluded that the structural integrity of resin-modified glass-ionomer cements benefits from a chemical integration of the polyalkenoate and poly-HEMA networks, as in Vitremer. Improvement in the structural integrity in the early phase for cements with a mechanical entanglement of the matrices, as in Fuji II LC and Photac-Fil, requires an acid-base reaction, a considerable portion of which may take place before activation of the HEMA polymerization.

Glass-ionomers in medicine and dentistry

This paper describes the current uses and future prospects for glass-ionomer cements in dentistry and medicine. Glass-ionomers divide into two chemical types, one is known as self-hardening and sets entirely by a neutralization reaction to give relatively brittle materials, the other is known as resin-modified and sets partly by polymerization and partly by neutralization to give slightly tougher materials. Compared with the self-hardening cements, these latter materials have improved aesthetics and easier clinical handling. Both types bond well to enamel and dentine, and release clinically useful amounts of fluoride. They have been used in a variety of applications in dentistry, including as liners/bases, luting cements for stainless steel crowns, and in various restorative procedures for both permanent and primary teeth. The resin-modified glass-ionomers are particularly promising for these latter uses, though it is too soon to be sure how durable they will prove to be over the longer term. Self-hardened glass-ionomers have been shown to have much better biocompatibility than resin-modified glass-ionomers in a variety of situations and consequently they have been used for various non-dental applications, such as ear, nose and throat surgery and craniofacial reconstruction.

Long-term flexural strength of three direct aesthetic restorative materials

OBJECTIVES

This investigation evaluates the long-term flexural strength behaviour of three different glass-ionomer cement (GIC) based materials.

METHODS

The materials under investigation were a conventional GIC (Opusfil), a metal-reinforced GIC (Opus Silver) and a resin-modified GIC (Fuji II LC). Flexural strength specimens of the materials were prepared according to the relevant manufacturers' instructions for clinical use. After 10-min maturation at 37 degrees C, the specimens were placed in water, also at 37 degrees C, until required for testing. Specimens were tested under four-point bend at intervals between 7 and 130 days after manufacture.

RESULTS

Opusfil increased in strength up to day 56, but was significantly weaker after this time. Opus Silver was strongest on day 7, although there was no further decline in strength after day 14. Fuji II LC increased in strength up to day 14, but there was deterioration in strength after day 100. Opus Silver had the highest early strength of the three materials, but after day 7 there was no significant difference in strength between the three materials under test.

CONCLUSIONS

The three cements tested did not exhibit the continued increase in strength with time that has been attributed to glass-ionomer cements. Each material behaved differently, but they all appeared to be adversely affected by storage in aqueous media. Materials formed by the inclusion of metal or the incorporation of resins into the glass-ionomer cement formulation should be regarded as separate sub-classes of materials in their own rights.

Long-term strength of aesthetic restoratives

Glass-ionomer cements have established an important role in clinical dentistry since their introduction over 20 years ago. More recently, in an attempt to enhance the strength of the material, resin additions have been made to conventional glass-ionomer cements. This study established the long term flexural strength of two hybrid glass-ionomer cements, by use of a bi-axial flexural strength test (Shell test), and compared the values with those obtained for a light curing composite resin and a conventional glass-ionomer cement. The results demonstrated that those materials with a high resin component relying on polymerization as the main method of setting had a greater initial flexural strength than those with little or no resin addition. Those materials where the glass-ionomer acid-base reaction provided a substantial contribution to the setting reaction showed an increase in strength as they matured, whereas a decline in strength with time was observed for those materials where the resin setting reaction predominated.

Capsulated versus hand-mixed glass-ionomer luting cements for post retention

OBJECTIVES

Glass-ionomer luting cements are supplied in two forms, as loose powder and liquid to be hand-mixed (HM) or pre-proportioned in a capsule to be mechanically mixed (MM). This study was to determine if post retention in pull-out tests was affected by the method of mixing the cement.

METHODS

Two hundred stainless steel posts of diameter 1.75 mm were cemented within post-channels prepared in stainless steel cylinders using two hand-mixed cements FJL and KCL (Fuji I Luting Cement and Ketac-Cem Luting Cement) and two capsulated cements FJC and KCM (Fuji Cap I and Ketac-Cem Maxicap). Three groups of test specimens were prepared. In Group I each cement was mixed as recommended by the manufacturer, Group II cements were placed within a capsule and mechanically mixed and in Group III cements were removed from the capsule and mixed by hand. Specimens were stored for 1 h at 37 degrees C and 100% humidity prior to post pull-out tests at a crosshead speed of 10 mm min-1. The maximum loads at failure were subjected to Weibull analysis and Mann-Whitney tests to determine probabilities of survival and significant differences between the groups.

RESULTS

Significant differences (P < 0.05) were found between all pairs of cements tested except KCM(MM) vs FJL(HM), FJL(MM) vs KCL(HM), KCL(MM), vs KCL(HM), FJC(HM) vs FJC(MM), KCL(MM) vs FJL(MM).

CONCLUSIONS

The capsulated cements as supplied by the manufacturers are preferable to the equivalent hand-mixed formulations, as they give higher probabilities of survival when subjected to a given load. Both capsulated and hand-mixed formulations of Fuji had higher probabilities of survival compared to the corresponding Ketac cements. The probability of post survival can be altered by the method of mixing the cement.

Comparison of the porosity of hand-mixed and capsulated glass-ionomer luting cements

The strength of dental glass-ionomer cements will be influenced by defects present within its structure. This study measured the surface area porosity, percentage surface area porosity, and mean surface area of small bubbles (<0.01 mm2) and the surface area porosity, percentage surface area porosity and diameter of large bubbles within 40-microm-thick layers of four cements, using image analysis software. Two hand-mixed cements (Fuji I and KetacCem) and two capsulated cements (Fuji Cap I and KetacCem Maxicap) were viewed under transmitted light at x117.6 magnification. For each selected area (64.75 mm2) of each cement sample, five independent measurements were made of each of these parameters. Analysis of variance (ANOVA) indicated that there were no significant differences between the four cements in the small bubble parameters measured, whilst there were significant differences in the surface area porosity, percentage surface area porosity and diameter of the large bubbles. It was concluded that the hand-mixed cements tested had a greater number of larger diameter bubbles compared with the capsulated cements.

Changes in compressive strength on ageing in glass polyalkenoate (glass-ionomer) cements prepared from acrylic/maleic acid copolymers

Previous studies have shown that glass-ionomers made from acrylic/maleic copolymers stored in water reach a maximum strength at about 1 week, and after 4 months have become significantly weaker. This finding, which contrasts with the behaviour of glass-ionomers based on poly(acrylic acid), was originally attributed to hydrolytic instability. This interpretation has been tested in the current work. Specimens of glass-ionomer prepared from acrylic/maleic acid copolymer have been stored for up to 4 months in different media, namely deionized water, dry air and vegetable oil, then tested for compressive strength. Specimens were in the form of cylinders of dimensions 6 mm high x 4 mm diameter, and storage temperature was 37 degrees C. Data were analysed using two-way analysis of variance (ANOVA) and in all three media specimens became weaker at 4 months than they had been at 1 week (P < 0.05). However, for the specimens stored in dry air and in water, the 1-week values were not the maximum. The fact that there was a loss of strength under all conditions led to the conclusion that it is not, after all, due to hydrolysis.

The use of organic compounds of phosphorus in clinical dentistry

Organic compounds of phosphorus have been developed for a range of applications in clinical dentistry. These include dentine bonding agents, restorative materials and therapeutic agents, such as active ingredients in anticaries mouthwashes. A characteristic feature of all of these applications is the good bonding of the phosphorus compound to the tooth. This review highlights the progress that has been made to date in preparing functional and durable organophosphorus bonding agents and cements, and includes coverage of recent synthetic work aimed at preparing improved organophosphorus molecules for this application. The review concludes that this remains a promising field of chemistry to explore in the search for improved, clinically useful dental materials.