Can glass polyalkenoate (glass-ionomer) dental cements be considered bioactive? A review

Objectives

This paper reviews the chemical behaviour of glass polyalkenoate (glass-ionomer) dental cements, both conventional and resin-modified, in contact with natural tissues, with the aim of determining whether these materials can be considered to be bioactive.

Data

Relevant papers describing the behaviour of bioactive glasses and ceramics, and glass-ionomer (glass polyalkenoate) cements have been identified using PubMed and Science Direct. This has allowed a comparison to be made between the behaviour of glass-ionomers and the speciality glasses and ceramics that are widely classified as bioactive, a designation considered valid for over fifty years. More recent papers concerning bioactive metals and polymers have also been studied and both in vitro and in vivo studies are included.

Sources

Have included general papers on the chemistry and biological behaviour of bioactive glasses and ceramics, as well as papers on glass-ionomers dealing with (i) ion release, (ii) bonding to the surface of teeth, (iii) influence on surrounding pH and (iv) interaction with bone.

Conclusion

The literature shows that glass-ionomers (glass polyalkenoates) have three types of behaviour that are similar to those of bioactive glasses as follows: Formation of direct bonds to living tissue (teeth and bones) without fibrous capsule; release of biologically beneficial ions; and change of the local pH. However, in in vitro tests, they do not cause calcium phosphate to precipitate from solutions of simulated body fluid, SBF. Despite this, studies show that, in patients, glass-ionomers interact chemically with hard tissues and this suggests that may indeed be considered bioactive.

Fluoride exchange by glass-ionomer dental cements and its clinical effects: a review

The topic of fluoride release and uptake by glass-ionomer (glass polyalkenoate) dental cements is reviewed. The study was based on a literature search carried out using PubMed. The main key words used were glass-ionomer and fluoride, and further refinements were made by adding the keywords anti-microbial, anti-caries and remineralization. Papers were selected from the initial search, which concentrated on fundamental aspects of fluoride release, including kinetics and the influence of the cement composition, and resulting clinical performance against caries. Other relevant papers were cited where they added useful and relevant data. From these published papers, it was possible to explain the detailed mechanism of fluoride release by glass-ionomer cements and also its uptake. Fluoride release has been shown to be a two-step process. In neutral solutions, the steps can be divided into early wash-out and long-term diffusion. In acid conditions, the early wash-out remains, though with greater amounts of fluoride released, and the long-term release becomes one of slow dissolution. The effect of fluoride on the viability of oral micro-organisms has been described, and glass-ionomers have been shown to release sufficient fluoride to reduce the size and viability of adjacent populations of oral bacteria. The effect of low levels of fluoride on the remineralization of tooth tissue has been considered. Levels needed to increase remineralization are much lower than those needed to adversely affect oral bacteria, from which we conclude that glass-ionomers release sufficient fluoride to promote remineralization. Despite this, there remains uncertainty about their overall contribution to sound oral health, given the widespread use of other sources of fluoride, such as toothpastes.

Computational study of the relative stability of some glass-ionomer cement-forming molecules

This work is part of a larger study whose main objective was to find a series of promising molecules to be used as glass-ionomer-type materials. The project was divided into 3 successive stages; the results of the first stage have been previously published and were used to continue the study. The molecules evaluated in the second stage were constructed by adding a glycidyl methacrylate molecule to the carboxylic groups of the polyacids selected in the previous stage. The modeling was done using the density functional theory for M06-2X/6-311G(d,p). The results indicate that the addition over the carboxylic groups of the fraction of the molecule, corresponding to itaconic acid, is thermodynamically favored. The final stage was modeled with the M06 functional and consisted of obtaining basic structures of glass-ionomer-type materials, by acid–base reaction between the molecules resulting from the second stage with individual ions of Ca (2 +), Zn (2 +), or Al (+ 3). It was concluded that aluminum atoms generate more compact structures that would correlate with more resistant materials.

Chlorhexidine to improve the survival of ART restorations: A systematic review and meta-analysis

OBJECTIVES

Our aim was to systematically assess the efficacy of chlorhexidine (CHX) as a cavity pre-treatment or restoration mix-in on the survival of ART restorations.

DATA

We included randomized controlled trials that assessed the effect of cavity pretreatment with CHX or the restoration mix-in of CHX on the survival of ART restorations (test group) versus a similar restorative approach without CHX. Risk of bias was assessed using Cochrane's randomized trial quality assessment Tool (RoB 2.0). Random-effects meta-analysis was conducted, with mean Odds Ratios and 95 % confidence intervals (OR, 95 % CI) as effect estimates. The certainty of the evidence was assessed according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system.

SOURCES

Medline, Web of Science, Cochrane Central were searched. Eligible studies were in- or excluded and data extracted for included studies by two reviewers independently.

STUDY SELECTION

Four studies with 261 patients (mean age 3.8-14.6 years) and 467 ART restorations were included. All studies showed some concerns about the risk of bias. Three studies involving a total of 167 restorations in the CHX group and 188 restorations in the control group, followed up for one year, were submitted to meta-analysis. There were no significant differences between CHX vs. control (OR = 0.79, 95 % CI [0.26, 2.40], P = 0.68, I² = 3%, P = 0.35). The strength of the evidence was estimated as low.

CONCLUSIONS

Based on very limited data, CHX pre-treatment or restoration mix-in did not have any significant benefit for survival of ART restorations.

CLINICAL SIGNIFICANCE

There is a lack of evidence regarding the influence of chlorhexidine on the survival of ART restorations. Our results revealed that there was no significant difference in the survival of ART restorations when CHX was used as a cavity pre-treatment or mix-in.

Synthesis of poly(acrylic-co-itaconic acid) through precipitation photopolymerization for glass-ionomer cements: Characterization and properties of the cements

OBJECTIVE

The aim of this study was to synthesize poly(acrylic acid-co-itaconic acid) (PAA-co-PIA) ionomer through a novel precipitation photopolymerization technique. The ionomer was characterized and the effect of its structural parameters, such as molecular weight and copolymer composition were investigated on the mechanical properties of glass-ionomer prepared using the ionomer.

METHODS

Design of experiment (DOE) was used to examine the effect of monomer ratio and the amount of chain transfer agent on the molecular weight and final conversion of the ionomers synthesized through the precipitation photopolymerization. The copolymer compositions were identified using FTIR and ¹H-NMR spectroscopy. The molecular weights of the copolymers were evaluated by GPC. A series of PAA-co-PIA copolymers were then synthesized via the photopolymerization technique in three monomer ratios and two molecular weight ranges (high and low) to study the properties of the glass ionomers thereof. Experimental dental glass-ionomer cements were prepared by mixing the synthesized polymers with glass powder and their compressive properties were determined according to ISO 9917-1:2007 after storing for 0, 1, 7 and 28 days in distilled water. The scanning electron microscopy (SEM) was used to study the fracture surface morphology of the cements.

RESULTS

The PAA-co-PIA polymers were synthesized by the photopolymerization method in a short time and high purity. The DOE showed that by decreasing the acrylic acid/itaconic acid ratio and increasing the amount of transfer agent, the molecular weight and final conversion decreased significantly. By increasing the itaconic acid content in the copolymer composition and increasing the molecular weight in a constant copolymer composition, the compressive strength and modulus were increased. Microstructures revealed that cements made of the higher molecular weight poly acids showed lower cracks and voids.

SIGNIFICANCE

The precipitation photopolymerization technique provides a promising and facile method in the synthesis of ionomers which are used in dental cements and other application.

Effect of Intracanal Glass-Ionomer Barrier Thickness on Microleakage in Coronal Part of Root in Endodontically Treated Teeth: an In Vitro Study

Statement of the Problem:

The most common cause of endodontic treatment failures is improper coronal sealing. Therefore, besides to proper root sealing, coronal sealing which is supported by a proper restoration has a major role in endodontic treatment success, and coronal microleakage should be considered as an etiologic factor in endodontic treatment failure. Glass-ionomer (GI) has been proposed as a coronal barrier for microleakage after endodontic treatment.

Purpose:

This study aimed to evaluate the coronal microleakage in GI-obturated root canals in endodontically treated teeth using different thicknesses of GI.

Materials and Method:

In this in vitro study, forty-five single-rooted extracted human teeth with single canals were collected and disinfected with 0.5% chloramine solution. After endodontic treatment, teeth were divided into 3 groups. In the group 1 to 3, 1 to 3mm of gutta-percha was removed and GI was replaced at 1-, 2- and 3-mm thicknesses respectively. Then subgroups were placed in methylene blue dye and the microleakage was assessed using dye penetration.

Results:

The mean dye penetration in groups 1, 2 and 3 were 5.1, 3.7 and 2.9, respectively, with statistically significant differences. Group 1 exhibited the highest amount of dye penetration while group 3 showed the least one. Moreover, a significant difference between groups 1 and 2 (p= 0.002) and a non-significant difference between groups 2 and 3 (p= 0.098) was detected in mean dye penetration.

Conclusion:

Thicker layers of GI might decrease the coronal microleakage. GI at 3-mm thickness resulted in the best protective effect on coronal microleakage in endodontically treated teeth, though further studies are needed to confirm these results.

The effect of temperature and ionic solutes on the fluoride release and recharge of glass-ionomer cements

OBJECTIVE

To determine the effect of storage temperature and the presence of sodium chloride in solution on the fluoride uptake and release of glass-ionomer cements.

METHODS

Several commercial brands were used, and stored at either room temperature (21-23°C) or 37°C, in KF solution at a concentration of 1000ppm F^- with and without 0.9% NaCl present. Fluoride levels in the storage solutions after 24h were measured using a fluoride-ion selective electrode. Specimens were then stored in water, and fluoride release after 24h was determined. Studies were also carried out to determine chloride levels when specimens were stored in 0.9% NaCl, with or without 1000 ppm fluoride, again using an ion selective electrode.

RESULTS

All glass-ionomer specimens took up fluoride, and most of the fluoride was retained over the next 24 h when the specimens were stored in water. There was a slight variation in the amount of fluoride taken up with storage temperature and with the presence of sodium chloride. All specimens also took up chloride, with greater uptake at higher temperatures, but little or no effect when KF was also present in solution.

SIGNIFICANCE

The substantial retention of fluoride after 24h in deionised water confirms previous findings and suggests that an insoluble species, possibly SrF₂, forms in situ. Chloride uptake has not been reported previously, and its significance requires further investigation. Fluoride and chloride uptake were apparently independent of each other, which suggests that the ions are taken up at different sites in the cement. This may relate to differences in the respective sizes and hydration states of F^- and Cl^- ions.

The effect of antimicrobial additives on the properties of dental glass-ionomer cements: a review

Aim: The aim of this article is to review the literature on the use of antimicrobial additives in glass-ionomer dental cements.

Method: An electronic search between 1987 and the end of 2017 was performed using PubMed, Web of Science and Google search engines with the terms glass-ionomer, glass polyalkenoate, antibacterial and antimicrobial as the key words. The search was refined by excluding the majority of references concerned with cement antimicrobial properties only. Extra papers already known to the authors were added to those considered.

Results: A total of 92 relevant articles have been cited in the review of which 55 are specifically concerned with the enhancement of antibacterial properties of glass-ionomers, both conventional and resin-modified, with additives. In addition, information is included on the uses of glass-ionomers and the biological properties of the antibacterial additives employed. There are several reports that show that additives are typically released by diffusion, and that a high proportion is usually left behind, trapped in the cement. Additives generally increase setting times of cements, and reduce mechanical properties. However, smaller amounts of additive have only slight effects and the longer-term durability of cements appears unaffected.

Conclusion: Modified glass-ionomer cements seem to be acceptable for clinical use, especially in the Atraumatic Restorative Treatment (ART) technique.

Integrating the PILP-mineralization process into a restorative dental treatment

The addition of charged polymers, like poly-aspartic acid (pAsp), to mineralizing solutions allows for transport of calcium and phosphate ions into the lumen of collagen fibrils and subsequent crystallization of oriented apatite crystals by the so-called Polymer-Induced Liquid Precursor (PILP) mineralization process, leading to the functional recovery of artificial dentin lesions by intrafibrillar mineralization of collagen.

OBJECTIVE

To evaluate the feasibility of applying the PILP method as part of a restorative treatment and test for effectiveness to functionally remineralize artificial lesions in dentin.

MATERIALS AND METHODS

Two methods of providing pAsp to standardized artificial lesions during a restorative procedure were applied: (A) pAsp was mixed into commercial RMGI (resin modified glass ionomer) cement formulations and (B) pAsp was added at high concentration (25mg/ml) in solution to rehydrate lesions before restoring with a RMGI cement. All specimens were immersed in simulated body fluid for two weeks to allow for remineralization and then analyzed for dehydration shrinkage, integrity of cement-dentin interface, degree of mineralization, and changes in the nanomechanical profile (E-modulus) across the lesion.

RESULTS

After the remineralization treatment, lesion shrinkage was significantly reduced for all treatment groups compared to demineralized samples. Pores developed in RMGI when pAsp was added. A thin layer at the dentin-cement interface, rich in polymer formed possibly from a reaction between pAsp and the RMGI. When analyzed by SEM under vacuum, most lesions delaminated from the cement interface. EDS-analysis showed some but not full recovery of calcium and phosphorous levels for treatment groups that involved pAsp. Nanoindentations placed across the interface indicated improvement for RMGI containing 40% pAsp, and were significantly elevated when lesions were rehydrated with pAsp before being restored with RMGI. In particular the most demineralized outer zone recovered substantially in the elastic modulus, suggesting that functional remineralization has been initiated by pAsp delivery upon rehydration of air-dried demineralized dentin. In contrast, the effectiveness of the RMGI on functional remineralization of dentin was minimal when pAsp was absent.

SIGNIFICANCE

Incorporation of pAsp into restorative treatments using RMGIs promises to be a feasible way to induce the PILP-mineralization process in a clinical setting and to repair the structure and properties of dentin damaged by the caries process.

Adhesion of resin-modified glass-ionomer cements may affect the integrity of tooth structure in the open sandwich technique

OBJECTIVE

To study the interfaces between model cavities prepared in teeth and four glass ionomer cements (two conventional and two resin-modified).

METHODS

Ten non-cavitated molars and premolars were used and, in each, two 3mm deep slot preparations were created on opposing sides of the tooth. The teeth were conditioned as appropriate, then restored using the open sandwich technique, using a conventional glass ionomer (Fuji IX, Ketac Molar) or resin modified glass ionomer (Fuji II LC or N100), followed by completion with composite resin. The teeth were then embedded in a transparent acrylic resin and cut parallel to the long axis through both restorations, using a low speed diamond wheel saw. Samples were evaluated using a metallographic light microscope (100×). Three areas were assessed: the axial wall, the axial gingival line angle and the cavo-surface line angle. Bonding was categorized as inadequate or adequate based on the appearance and inadequate bonding was further studied and classified. Data were analysed statistically using the McNamara analysis.

RESULTS

The majority of materials failed to make adequate contact with the axial wall, and there were also flaws at the axial/gingival line angle in several samples. By contrast, the cavo-surface line angle was generally soundly filled and the materials showed intimate contact with the tooth surface in this region. The most serious inadequacy, though, was not lack of intimate contact and/or adhesive bond, but the presence of perpendicular cracks in 30% of the Fuji II LC samples which extended into the underlying dentin.

SIGNIFICANCE

The problems of placement and dentin cracking experienced with these materials demonstrate that adhesive bond strength alone cannot be used as the criterion of success for restorative materials. In fact good adhesion can, in certain cases, promote cracking of the dentin due to stresses within the material, an outcome which is undesirable.

The Influence of Zinc Oxide Eugenol (ZOE) and Glass Ionomer (GI) Base Materials on the Microhardness of Various Composite and GI Restorative Materials

Objective:

Re-examining the well accepted concept that Zinc-Oxide-Eugenol bases (ZOE) have a negative effect on composite restoration materials microhardness, in light of the advancement in composite materials and newer publications.

Methods:

Five modern composite restoration materials were used, including hybrid (Xtra-fill and Z250), micro-fill hybrid (G-aenial and Gradia-direct) and methacrylate-free restorative material (Silorane- oxirane). Two base materials were used IRM (ZOE-base) and Fuji-IX (GI-base). Samples were made using a designed mold, in which composite discs were cured on top and in close relation to base materials. Micro-hardness testing was performed using a DMH-2 microhardness tester utilizing the Knoop method.

Results:

Statistic analysis demonstrated significantly better microhardness of three composite materials when IRM was used as base in comparison to control (G-aenial, Gradia direct and Filtek silorane), and no differences in two materials (Filtek universal Z250 and Voco Xtra-fil). Fuji-IX bases showed a significant positive effect on the microhardness of four composite materials, and a negative effect on one material (Voco Xtra-fill). In comparison with other tested restoration materials, both Voco Xtra-fill and Fuji-IX showed higher microhardness results (P<0.05).

Significance:

Related to microhardness, both ZOE and GI bases can be used safely as bases under composite restorations. The results of this study together with the results published recently showed that the concept of not using ZOE or GI bases under composite must be reconsidered. Fuji IX showed microhardness results similar to the best composite material and therefore it can be used as a restorative material.