Resin Modified Glass Ionomer Cements

Glass Ionomer Cements is produced when ion-leachable calcium alumino-silicate glass powder that has fluoride is reacted with polyalkenoic acid. In recent times, the utilizing of Glass Ionomer Cements has been widespread in dentistry since GIC can be adapted by joining it with a number of materials and its properties may be additionally enhanced. Generally, Glass Ionomer Cements are categorized into three major classes: conventional, metal-reinforced along with resin-modified.

Glass Ionomer Cement was at first developed in 1972 by Wilson and Kent in England38. These were the Conventional glass ionomer cements and are made from aqueous polyalkenoic acid like polyacrylic acid as well as a glass constituent that is typically a fluoroaluminosilicate. When the powder along with the liquid are put together, an acid-base reaction takes place. When the metallic polyalkenoate salt starts to precipitate, gelation commences and goes on up to the point when the cement sets solid. In recent times, a number of more rapidly setting, high-viscosity Conventional Glass Ionomer cements have been made accessible. Referred to as viscous or condensable glass ionomer cements by some, these restorative substances were initially made in the early 1990s for utilization with the atraumatic restorative cure in several 3rd world nations. These materials set more rapidly and are of high viscosity due to the finer glass granules, anhydrous polyacrylic acids of higher molecular mass as well as a higher powder-to-liquid combination ratio. The reaction is the equivalent of the acid-base reaction characteristic of conventional glass ionomer cements. At the time of its making, the Conventional Glass Ionomer Cement was not an aesthetic substance and lacked any clearness or luminously. It was used to fill just small category V abrasive lesions. However, it has gradually tailored and may be utilized in a number of clinical procedures for instance luting, as a lining as well as a base, et cetera.

Metal-reinforced glass ionomer cements were initially established in 1977. They were fashioned by adding the silver-amalgam alloy fine particles to the conventional Glass Ionomer Cement materials and this improved the strength of the cement and offered radiopacity. Next, silver particles were sintered to the glass, and a variety of products then surfaced where the amalgam alloy substance had been preset at a plane maintained to generate optimum mechanical traits for a glass cermet cement.

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In the year 1992, resin-modified glass ionomer cements were made that is light cured. In the resin-modified glass ionomer cements, the basic acid-base reaction is complemented by a second resin polymerization typically kick off by a light-curing procedure.6, 7 In their most basic form, they are glass ionomer cements that have a minute amount of a water-soluble, polymerizable resin constituent. Additional compound substances have been created by transforming the polyalkenoic acid with side series that could polymerize through light-curing mechanisms in the presence of photo initiators, but they stay glass ionomer cements by their capacity to set through acid-base reaction.

In general, glass Ionomer cements posses a number of extraordinary properties that may not be found in any additional material. Glass Ionomer Cements aids to preserve the tooth formation, and it directly attaches to the tooth. The cement directly joins to the dentine that is in the tooth. This assists to remineralise caries; therefore, it can be used for conserving the tooth material. The Glass Ionomer Cements gradually discharges fluoride throughout a long time. This advantage can also be utilized in the prevention of caries and in patients who have a high threat of getting caries. The powder that is found on the resin-modified Glass Ionomer Cements cement is quite similar to the conventional Glass Ionomer Cement’s. The liquid has monomers as well as polymers to make sure the strength of the Glass Ionomer Cement is augmented. The Glass Ionomer Cement has two constituents, one powder, and the other liquid. The powder is an ion-leachable alumina-silicate glass while the liquid has polymers as well as copolymers of acrylic acid in water. In the setting reaction, Aluminum as well as calcium, the glass sets ions free and polymers discharge acid groups.

The setting reaction occurs gradually, and its outcome is the creation of a cross-linked gel matrix. Aluminum ions might be exchanged gradually in the gel matrix, which aids in strengthening it. This progression takes place very gradually until the last set. The calcium that is in the gel matrix might combine with the uncovered Glass Ionomer Cement bonds utilizing both diffusion as well as the adsorption phenomenon. When the newly engraved tooth surface is smeared with Glass Ionomer Cement, the polyalkenoic acid plays an extremely central part in starting adhesion. The carboxyl ions that are in the acid dislodge the phosphate ions that are in the apatite crystals. The Calcium phosphate-polyalkenoate crystalline compound that is formed at the meeting point of the tooth surface and the Glass Ionomer Cement material plays an extremely central role in the bond. This phenomenon is generally referred to as diffusion-based adhesion. When the intermediary compound stage is subjected to acid etching, it is additionally resistant to etching than the other part of the tooth.

The restoration of carious teeth is among the main dental treatment needs. A restitution or restoration in the primary dentition (in Children) is dissimilar to the restoration in the lasting or permanent dentition owing to the restricted duration of the teeth’s life and the inferior biting powers of children. Going back as early as 1977, it was put forward that glass ionomer cements can present some advantages when used asa restorative material in the primary dentition owing to their capacity to discharge fluoride as well as to stick to dental tough tissues. In addition, owing to the fact that they only need a short time to fill a cavity, glass ionomer cements offer an extra when treating teeth in little children.

Resin Modified Glass Ionomer Cements

Notwithstanding the encouraging characteristics of Glass Ionomer Cements (GIC) that have been utilized by dentists ever since the 70s to date, to progress some of their traits and eliminate the disadvantages, resin modified glass ionomer cements (RMGIC) were created by the addition of resin into glass ionomer cements as aforementioned. Their make up is fundamentally 80 percent glass ionomer cement along with 20 percent resin although there are some changes in regards to variances in brand. HEMA (Hydroxy ethyl methacrylate) of which liquid is polymerized by light, methacrylate grouping (GMA, EGMA and Bis-GMA, et cetera.), tartaric, as well as polyacrylic acid and water, are used. Its powder, though, has fluoro aluminosilicate particles of glass. The traits of resin added glass ionomer cement range between conventional glass ionomer cements and composite resins, which indicates RMGIC is a crossbreed substance.

The polymerization of methacrylate components in cement may commence using light or chemical. In twofold treatment materials, HEMA’s polymerization begins with light activation along with a gradual acid base reaction, which continues to strengthen the cement as well as augment the resistance. In three-way cure materials; however, there is a chemical marker for HEMA and its polymerization begins chemically, subsequently a matrix toughened through progressive acid-base reaction occurs. In comparison to the twofold cure cements, the strong point of cements with tricure setting system are the additional chemical polymerization of resin as well as the happening of polymerization in areas where light would not reach. In this set of cement, there are two matrixes in each other; the first one is ionic matrix produced by acid-base reaction while the remaining one is resin matrix. These cement posses compressive as well as diametral tensile potency superior to those of zinc phosphate, polycarboxylate as well as several glass ionomers although have less compressive as well as diametral tensile potency than resin composite. Their bond to enamel and dentin, as well as their fluoride discharge pattern is analogous to glass ionomer cements. Owing to the carboxyl sets in the polyalcenoic acid in them, RMGIC has adhesive traits. Due to that, there is no requirement for an adhesive agent connecting the tooth to the material. The application of dentine polyacrylic acid conditioner before RMGIC is applied not just improves wettability of the dental surface, but it also makes it possible for hydrogen bond creation and reinforces the cement and ionic change.

Their abrasion resistance as well as fissure resistance are superior to those of convectional GICs;15 in addition, they also possess superior aesthetical features. In comparison to GICs, these cements are more resistant to water pollution in the setting reaction and boost diminished level of solubility. An additional strong point of resin modified GICs is their simplicity of mixing as well as use, since compound bonding steps are not a requirement. They also posses sufficiently low film breadth.14 removing the excess cement in resin ionomer cements following cementation is full of challenges. As such, shortly following the principal setting reaction, un-reacted materials under restoration margins require to be removed. The addition of resin in these cements has not considerably lessened the dehydration resistance of GIC materials.

On the other hand, the most significant disadvantage of resin added ionomers is that owing to poly-HEMA, which has hydrophilic quality water absorption, plasticity as well as hygroscopic growth is augmented. Water absorption at the start reduces the stress throughout polymerization contraction, but if water absorption continues, it creates a detrimental effect. As it exhibits noteworthy dimensional alterations, these cements are not appropriate to utilize in complete ceramic feldspathic-type restorations as well as post cementation. Resin ionomers may be employed in cementation of metal-porcelain, metal, supporting amalgam, crown, and bridges, composite along with glass ionomer cores, as well as base matter beneath composite fillings. They have diverse types created for orthodontic usage as well.14, 17 Resin added GICs are obtainable in the market as powder-liquid as well as automix capsule.

Advantages

1. Adhesion

By attaching a restorative substance to the tooth structure, Resin added GICs hypothetically seals the cavity, protects the pulp, eliminates resultant caries, and prevents seepage at the boundaries. This too permits cavity forms to be additionally conformist and, to some extent, strengthens the residual tooth by incorporating restorative substance that has the tooth makeup.18 Bonding linking the cement and dental hard tissues is realized by an ionic exchange at the boundary.19, 20 Polyalkenoate chains penetrate the molecular plane of dental apatite, substituting phosphate ions. Calcium ions are dislodged uniformly with the phosphate ions to retain electrical symmetry.21 This leads to the creation of an ion-rich stratum of cement that is firmly attached to the tooth.22 In comparisons of convectional materials and resin-modified GICs, the latter shows to have a generally stronger shear bond strength; 23 however, they show an extremely low bond strength to unconditioned dentin in comparison to conventional materials.18 As such, conditioning plays a big part in realizing effective bonding with the resin-modified GICs. The effects of light curing along with the bonding mechanism of resin-modified GICs are better compared to that of traditional materials.

2. Margin Adaptation and Leakage

The resin-modified glass ionomer cements demonstrate superior bond strength to dental hard tissues as compared to the conventional substances; however, they display variable results in micro-leakage tests. Not all of them exhibit considerably less leakage against enamel and dentin than the conventional materials. This might arise because their coefficient of thermal expansion is greater than that of the conventional materials, although still way less than composite-resins. Debate still goes on as to whether the minor polymerization shrinkage is sufficiently momentous to upset the margin seal.

3. Fluoride Release

The fluoride discharge of most of resin-modified materials is at least the identical as that of conventional materials although it defers among dissimilar. However, the vital quantity of fluoride discharged from a restoration that is needed to be effectual in inhibiting caries is not until now determined. As such, there is no apparent advantage of resin added GICs over other convectional materials. Tyas studied cervical composite-resin and GIC restorations 5 years after it had been placed and found no noteworthy variation in recurring caries rates.

4. Esthetics

The addition of resin in the modified GIC materials additionally improves their translucency; however, they are still quite opaque and are not as esthetic like composite-resins. Additionally, surface finish is typically not very good. The color of resin-added materials varies with the last and polishing techniques utilized. All the same, the requirement or the need for esthetics in the primary dentition is typically lesser than in the lasting dentition.

5. Biocompatibility

Concerns have been raised as regards the biocompatibility of resin-modified materials owing to the fact that they have unsaturated groups. A cell culture examination showed reduced biocompatibility of a resin-modified liner31. On the other hand, Cox et al  demonstrated that a resin-modified GIC does not damage pulp curing when sited on bare pulps. Owing to this lack of certainty, application of resin-modified materials in cavernous unlined cavities is certainly almost ill advised.

Disadvantages

The use of resin-modified glass ionomer cements does have limitations in some particular conditions.

1. Physical Strengths

The major disadvantage of the glass ionomer cements in general is their comparative lack of strength as well as their diminished resistance to abrasion in addition to wear. The resin-modified glass ionomer cements have been found to have a considerably higher flexural as well as tensile strength, in addition to lesser modulus of elasticity, as compared to the conventional materials. As such, they are more fracture-resistant although their resistance to wear is not that good.33 Additionally, their strength capabilities are still way too inferior compared to those of composite-resins; therefore, they ought not to be subject to unwarranted occlusal load except if they are well shored up by adjacent tooth formation.

2. Water Sensitivity

Conventional glass ionomer restorations in general are hard to control as they are receptive to moisture inhibitions in the early setting reaction as well as hard to dehydration as the materials start to coagulate. Even though it was held that the incidence of the resin polymerization in the adapted glass ionomer restorations materials diminishes the early sensitivity to water, research has demonstrated that the properties of the resin added glass ionomer restorations materials altered manifestly after contact with water34. Whether it is obligatory to position a protective layer on resin-modified glass, ionomer restorations is still subject to debate.

Conclusion

Resin-modified glass-ionomer cements are helpful medical materials for restoration of teeth that have been affected by dental caries. They can be put into use as either liners or complete restoratives. Their mechanical traits are good enough for their use, and they possess the medically helpful traits of intrinsic bond to the tooth enamel and dentin surface as well as discharge of fluoride. Other clinical traits are; resistance to marginal micro-leakage, cariostatic potential and not as soluble as conventional glass-ionomer cements. Added properties include enhanced setting traits, reduced resistance to lasting buckle, small film thickness, and better clearness in comparison to conventional glass-ionomer cements of the restorative matter and easily manipulated. Disadvantages include sensitivity to lack of moisture, resulting in noteworthy contraction. Ruin from continuing contact with water and might upshot in an amplified water sorption and ensuing plasticity as well as hygroscopic extension. As evident, the advantages conveyed by resin addition to conventional glass ionomers overshadow or offset the disadvantages. The advantageous traits of resin-modified glass ionomer cements mean they are helpful materials in the restoration of carious lesions in less stress areas; for example, smooth surface as well as undersized front proximal cavities in primary teeth.