Advances in glassionomer cement.

 

 

Glass ionomer cements (GICs) are getting used for a good range of applications in dentistry, so as to beat the poor mechanical properties of glass ionomers, several modifications are introduced to the standard GICs. Nanotechnology involves the utilization of systems, modifications or materials the dimensions of which is within the range of 1–100 nm. Nano-modification of conventional GICs and resin modified GICs (RMGICs) will be achieved by incorporation of nano-sized fillers to RMGICs, reducing the dimensions of the glass particles, and introducing nano-sized bioceramics to the glass powder. Studies suggest that the commercially available nano-filled RMGIC doesn't hold any significant advantage over conventional RMGICs as far because the mechanical and bonding properties are concerned. Conversely, incorporation of nano-sized apatite crystals not only increases the mechanical properties of conventional GICs, but can also enhance fluoride release and bioactivity. By increasing the crystallinity of the set matrix, apatites can make the set cement chemically more stable, insoluble, and improve the bond strength with tooth structure. Increased fluoride release also can reduce and arrest secondary caries. However, because of an absence of long-term clinical studies, the utilization of nano-modified glass ionomers continues to be limited in daily clinical dentistry. Additionally to the in vitro and in vivo studies, more randomized clinical trials are required to justify the utilization of those promising materials. The aim of this paper is to review the modification performed in GIC-based materials to boost their physicochemical properties.

 

Recent development Expansion of the concept of incorporation of polymerization and polyelectrolyte salt formation mechanisms within one molecule or a mixture of molecules has led to a spectrum of materials which range from classical acid-base GIC to modified polymer-ceramic (glass) composites with little polyelectrolyte character. The objectives sought in these latter materials are to enhance the strength, toughness and resistance to dissolution whilst retaining the basic attributes of adhesion, fluoride release and biocompatibility related to the GIC system. The requirement to produce adequate water within the system for polycarboxylate reactions to occur, i.e. adequate hydrophilicity, has led to difficulties in some materials in balancing this requirement against the hydrophobicity required in resin cement systems.

 

As is well-known, resin cement systems, even those containing monomers having potentially functional polar groups like carboxylate or phosphate, lack intrinsic adhesion to dentine unless a 'conditioning pretreatment to enhance surface penetration is utilized. as an example, Leung and Morris have demonstrated by Raman spectroscopy that 4-META during a methacrylate medium reacts too slowly with enamel for salt formation and first bonding is more likely because of improved wetting, enhanced surface penetration and micromechanical interlocking. Further, Ruse and Smith have shown previously that aciddemineralized surfaces of dentine contain little calcium or phosphorus thus reducing still further the possibility of calcium salt formation on subsequent application of functional resin bonding systems. Treatment of dentine by acidic primers containing hydrophilic solvents or monomers is thus required to also enhance penetration facilitating formation of the so-called 'hybrid layer' or 'resin diffusion zone'. The performance of resin-modified GIC in terms of intrinsic adhesion behavior to dentine is thus a sign of the contribution of polyelectrolyte character and/or penetration enhancement with micromechanical interlocking to their mechanistic behavior. Another aspect of resin-modified systems is important shrinkage on setting arising from monomer polymerization.

 

The current status of resin-modified glassionomer cements has been reviewed by Sidhu and Watson including the vexed question of the generic name. Classification of those materials is formed more confusing by the multiplicity and complexity of current formulations. Thus Vitremer (3M) luting cement relies on the Vitrebond (3M) copolymer developed by Mitra. The copolymer relies on an acrylic-itaconic acid chain having amide-linked methacrylate groups. The formulation also contains HEMA and tartaric acid and water. An acid-base reaction occurs on mixing but is overtaken by a polymerization reaction, both light and chemically initiated. Although there must be less -COOH and reduced chain mobility compared to a conventional GIC, there's evidently enough interaction with tooth tissue and enhanced penetration to produce adequate bonding without a requirement for primer treatment. We have shown recently that this technique interacts chemically with dentine but bonding is reduced by a delay between application and light-curing.

 

 Another current material, Fuji Duet (GC Corp.), supported a polyacrylic acid-itaconic acid) copolymer is stated to be 'water based' and 'resin reinforced'. It contains hydroxy acid and HEMA. It requires, however, the utilization of a 10/2 citric acid/ferric chloride conditioner so as to understand its bonding potential thus suggesting a greater proportion of non-ionic monomers and fewer polyelectrolyte character. (1) Between these materials which lay emphasis on the GIC characteristics and products that are essentially polymer composites containing F-containing fillers like GIC glass are several hybrid materials that contain relatively large amounts of acid monomers in polymerizable systems. These approaches are discussed by Hammesfahr. Samples of these materials include Advance(Dentsply-Caulk) Hybrid Ionomer Cement and Dyract(DentsplyCaulk).

 

 In Advance (Dentsply-Caulk)

a GIC glass is mixed with a liquid containing polymerizable carboxylic acids, water and diluent monomer. The material sets by interaction between the glass and therefore the monomeric acid monomers within the liquid and by a chemically initiated ("self-curing') reaction. Thus this approach aims to create the polyacid structure in place. The novel acid monomer employed is termed OEMA monomer. The system as supplied is alleged to produce bond strength to dentine at conventional GIC levels but higher bond strength requires use of the Probond (Dentsply-Caulk) acid phosphate primer suggesting limited tooth interaction before setting of the composition. The degree of interaction with the glass is before setting and therefore the effect of setting contraction because of polymerization of the monomer component furthermore as changes in structure and cross-linking within the cement over time don't seem to be clear at the moment. Sufficient interaction occurs, however, to produce significant fluoride release.

 

Newer advances of Glass ionomer Cement

Conventional GIC lacks in sufficient strength and toughness, which has attracted focused research so as to enhance the mechanical properties of conventional GIC, Resinmodified glass-ionomers(RMGI) were introduced, which contains hydrophilic monomers and polymers like HEMA and that they have higher flexural strength compared to traditional GIC." Recently, a replacement restorative concept is marketed, a system application consisting of a posterior restorative GIC combined with a unique nanofilled coating material, the compounded nanofillers protect against the abrasive wear and therefore the coating acts as a glaze, enhancing its esthetic properties.9.10 Hybridization of GIC and Composites using prereacted glass ionomer technology, 'Giomer' was developed by Shofu. Newer bioreactive material "HAINOMER was developed using hydroxyappatite with glass powder and have shown a promising future during initial clinical trials as retrograde filling material. More recently, Zirconia containing GIC, Proline containing GIC, CPP-ACP GIC are synthetically manufactured to reinforce the remineralization potential and aimed toward improving the strength."

 

Resin-Modified GlassIonomer Cement as a Restorative Material

Resin-modified glassionomer cements are compatible as luting cements and tooth adhesives where thin layers are often photo-cured to polymerize the HEMA present within the cement. In deep cavities, the chance of unpolymerized HEMA at the floor of the cavity may end up in absorption of fluid from the tooth into the restoration or permeation of free HEMA into the dentine and pulp where postoperative sensitivity may develop (Watson1997 ). The scientific use of resin-modified glassionomer cements as a restorative fabric should be restrained to shallow cervical restorations where excessive aesthetics are required and center build-ups in non-vital enamel where there's adequate remaining teeth structure. Resin-modified glassionomer cements are well acceptable as dental adhesives, thin hollow space lining materials and luting of translucent ceramic restorations.(1)

 

Bioactive glass (BAG)

The first Bioglass was invented by Larry Hench etal10 at the Universidad Florida It considers the. indisputable fact that on Their acid dissolution is that the formation of a layer rich in glass Ca+ and PO4 + ions round the glass, a glass like which will Forms close bioactive connections with the bone cells and is fully Inbuilt with bone.2 Osteo-conductivity, thanks to its good bioavailability BAG has been used as a restorative, and biodegradability over a decade of material, and its degradation Products stimulate protein development, Cell proliferation and Gen Expression Activation Osteoblasts, also help to treat hypersensitivity to dentine And promoting remineralisation of enamel.

 

The BAG formed a stable bond or interface with biological tissues through the formation of an apatite layer. The primary commercially available BAG had a composition of 46.1 mol % silica (SiO 2 ), 24.4 mol aflaxen oxide (Na 2 O), 2.6 mol % phosphorus pentoxide (P 2 O 5 ), and 26.9 mol Nalfon oxide (CaO). This material was labeled as 45S5 or Bioglass. 12 supported the composition of BAG added to GIC, the modified GICs are shown to exhibit antimicrobial properties. It's said that a substance is bioactive if it gives an adequate biological response and ends up in Bonding of substance and tissue. (4) What's more, remineralisation. BAG has antibacterial effect, because it increases the pH Solutions Aqueous. Mixture of bioactive nano silica improves its biocompatibility with dental cement, which is helpful in overcoming small differences that are an enormous downside to several dental cements.

 

Clinical Applications of Bioactive Glasses in Dentistry

The compositional similarity to the bone and tooth structure combined with the bioactive properties and apparent antimicrobial properties inspired the research of baggage in clinical application in dentistry and were first used as bone substitutes in dentoalveolar and maxillofacial reconstruction, periodontal regeneration, and implants.