The two important modifications in the glass ionomer cement (GIC) are the metal and resin-modified glass ionomer cement. The resin-modified glass ionomer cement (RMIG) is developed to combine the advantages of glass ionomer cement and resin composites and at the same time to overcome the disadvantages of these two dental restorative materials. This cement is also referred to as a hybrid ionomer. Due to the fluoride-releasing ability, the glass ionomer cement and resin-modified glass ionomer cement are used in patients with high caries risk and where esthetics is not a major concern.
Dispensing and Composition of the Resin Glass Ionomer Cement
The cement-containing capsule is mixed on a device, and the mixed cement is extruded from the capsule into the prepared cavity.
The powder of this dental cement comprises Fluoroaluminosilicate glass, also known as ion leachable glass, due to its fluoride-releasing properties. The liquid of the cement comprises of polyacid, which reacts with the powder and enables setting by the acid-base reaction, methacrylate resin which enables the setting by polymerization, Hydroxyethyl methacrylate (HEMA), which take part in the polymerization reaction and enable both the resin and acid component to coexist in an aqueous medium, Water is an important component that is required for acid-base reaction to complete, Activators, initiators, and stabilizers are also important ingredients of this dental cement.
Setting reaction of the Resin Modified Glass Ionomer cement
Most resin-modified glass ionomer cement is supplied in powder and liquid bottles. The two components are mixed on a special mixing pad supplied with dental cement. Few manufacturers supply this cement in capsules in which the powder and the liquid are enclosed in a capsule. When the powder and liquid are mixed, the acid-base reaction begins immediately. The polymerization reaction starts as soon as sufficient free radicals are available to initiate the reaction.
The light source used to activate the polymerization of Resin modified glass ionomer cement is similar to that used for dental composites. The light-activated resin-modified glass ionomer cement does not possess a long working time like the resin composite filling material. The possible reasons for this rapid setting and short working time are
a) The acid-base reaction starts immediately before exposure to the curing light.
b) These materials contain chemical initiators and activators which enable the chemically activated polymerization to start before exposure to activating light.
c) These materials are sensitive to visible light and the setting reaction starts in presence of visible light.
Most of the resin-modified glass ionomer cement has a light-activated polymerization setting reaction. In comparison, some products used for the cementation of crowns, bridges, and orthodontic appliances are chemically activated.
Properties of the Resin modified glass ionomer cement
- The resin-modified glass ionomer cement undergoes expansion when it is in contact with water or moisture and this effect compensates for the initial shrinkage due to the presence of resin.
- The resin-modified glass ionomer cement is slightly stronger than the conventional glass ionomer cement.
- This dental cement forms a chemical bond with the tooth structure like the conventional glass ionomer cement.
- The amount of fluoride release is slightly lower in the resin-modified glass ionomer cement as compared to conventional glass ionomer cement.
- This restorative material is less soluble and brittle as compared to conventional glass-ionomer dental cement.
- These materials have a very short setting time as compared to the glass ionomer cement. Therefore, the resin-modified glass ionomer cement should be placed and shaped rapidly after mixing.
- The presence of resin in this type of glass ionomer cement protects the cement from contamination by moisture. Therefore, protective resin or varnish coatings are not required for these materials and can be finished immediately after setting.
Clinical Uses of the Cement
- The resin-modified glass ionomer cement is used as a luting cement for cementation of crown and bridges.
- This cement is also used for lining purposes in deep cavities for example under amalgam restorations.
- The resin-modified glass ionomer cement is also used to restore carious and other non-carious lesions at the cervical areas of the tooth.
- This dental cement is also used for the cementation of orthodontic bands and appliances.