Glass ionomer cement
Afavourable restorative material that can adhere to the tooth and helps for further prevention of caries by continuous fluoride release is nothing other than Glass ionomer Cement and reading this section gives a clear picture of the material and its types, manipulation and clinical technique and all other related doubts.
1. What are the functions of the other acids co polymered with polyacrylic acid in GIC?
The other acids like itaconic, malleic and tricarboxylic acids tend to increase the reactivity of the liquid, decrease the viscosity and reduce the tendency for gelation.
Ref: Science of Dental Materials, Skinner, Prism books private limited, 9th Edn, 453
2. What is the set cement of GIC composed of?
The set cement of GIC is composed of an agglomeration of unreacted powder particles surrounded by silica gel in an amorphous matrix of hydrated calcium and aluminium polysalts.
Ref: Science of Dental Materials, Skinner, Prism books private limited, 9th Edn, 455
3. What is loosely bound and tightly bound water in GIC?
Loosly bound water is the one that is readily removed by dessication.
Tightly bound water cannot be removed by dessication. Tightly bound water increases with time reducing the risk of cracking of the cement.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,456
4. Why is a cool glass slab preferred for mixing of GIC?
When the glass slab is cooled, it maintains the temperature for a longer period of time and it permits incorporation of all the powder, maintaining the plasticity of the mix. But it should not be cooled below the dew point, to preserve the acid- water balance.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,459
5. What does a ‘Glossy mix’ of GIC indicate?
The glossy surface of the mix of GIC indicates the presence of polyacid that is not used in the setting reaction and this residual acid helps for the adhesive bonding to the tooth. Prolonged mixing leads to a loss of the glossy surface and adhesion does not occur.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,459
6. Why is matricing of GIC restorations important?
Matricing in GIC restorations is essential because it provides maximum contour with minimal finishing, restricted only to the removal of excess cement. Matricing ensures surface integrity and most important is that it protects the setting cement from the environment during the initial set.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,459
7. Why does the surface of the set cement of GIC need protection?
The surface of the restoration is immediately protected with a coat of varnish because it gets dehydrated when exposed to air, producing cracks.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,459
8. What is conditioning of tooth in GIC restorations?
After a pumice prophylaxis is done on the preparation, polyacrylic acid is swabbed for 5 seconds minimum and rinsed. The surface is then dried but it is not dessicated. This is called conditioning.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,458
9. What are the main requirements for a successful GIC restoration?
The main requirements are:
- Conditioning the tooth surface
- Proper manipulation of the cement
- Well protected cement while setting
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,460
10. What is Silver Alloy Admix?
There are modified forms of GIC in which some filler particles are included to improve the strength , fracture toughness and resistance to wear. Silver alloy admix the mixing of spherical silver amalgam alloy powder to type II Glass Ionomer powder. It is also called as Miracle Mix.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,461
11. How is Cermet differentiated from Silver alloy admix?
In Cermet cement, silver particles are bonded by fusion to the GI powder particles through high temperature sintering of the mixture of 2 powders. Whereas in silver alloy admix, spherical silver amalgam alloy powder is mixed to the GI powder.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,461
12. Why is the release of fluoride more in the admix cement?
This is because, the metal filler particles which is the spherical silver alloy powder, are not bonded to the cement matrix and this creates pathways for fluid exchange and the surface area for leaching of fluoride is also increased.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,462
13. What are Resin Modified Glass Ionomers?
Resin Modified Glass Ionomers are hybrid GI where modifications are made to replace the part of the original glass ionomer formulation with alternative fillers or matrix setting reactions. They are usually light cured, less technique sensitive and finished at the time of placement.
Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002; 209
14. How does fluoride release contribute for caries inhibition?
The fluoride ions released during the setting and dissolution of the cement react with the adjacent tooth structure, to form a structure that is most resistant to decalcification by acids. Also fluoride acts as an enzyme inhibitor, preventing carbohydrate metabolism.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,451
15. What are the precautions taken while cementing a restoration with GIC?
Precautions while cementing are taken like, the smear layer on the cut surface of the cavity preparation should be left intact to act as a barrier to the penetration of the tubules by the acids in the cement and all the deep areas are protected with calcium hydroxide cement.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,496
16. How does GIC bond to collagen?
GIC can adhere to the organic component of dentin through hydrogen bonding between the carboxyl groups on the polyacid and collagen molecules of dentin.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 78
17. Why is type I GIC used for luting?
Type I GIC has a thin film thickness, low solubility, fluoride release and biocompatible with the pulpal and gingival tissues. These properties favour the usage of Type I GIC as luting cement.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 85
18. How can GI cement be made radiopaque?
GI cement can be made radiopaque by incorporation of barium, strontium on lanthanum or by fusing metal to the glass particles as in cermet powders or by mixing with dental amalgam alloy or zinc oxide.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 72
19. Why is GIC not used in stress bearing areas?
GIC when compared to hybrid composites and amalgam, lack rigidity and are weak. They are more susceptible to fracture when subjected to heavy occlusal load. So it is not used in such areas and resins are added to the GI cement to make it stronger.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 83
20. What makes Type II GIC to be used as restorative cement?
Type II GIC provides adequate esthetics and transluscency, adheres to the tooth structure by ion exchange mechanism, continuous fluoride release helps for caries prevention and remineralisation of demineralised tooth structure. So it is favourable to be used as a restorative material.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 86
21. What are lining cements?
Lining cements have a low powder content and used only as a lining under any restoration to act as a thermal insulator and to seal the dentinal tubules. It should be entirely covered by the restorative material and should not be left exposed to the oral cavity.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 88
22. What is Sandwich Technique?
GIC can be used as a substitute for dentin in deeper cavities over which the final restoration can be done that can be a composite or amalgam restoration. GIC used as a sandwich between the restorative material and the tooth structure is called as Sandwich Technique.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 89
23. How is Sandwich Technique beneficial clinically?
By using a sandwich technique, the amount of composite resin used is less thereby the shrinkage of the resin is also minimized. Also the number of increments to be placed is reduced, thus saving time.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 89
24. Why is a sub base avoided in sandwich technique?
In a sandwich technique, GIC is sandwiched between the tooth and the restoration. GIC bonds to the tooth structure by ionic exchange. When a sub base such as calcium hydroxide is placed, it will reduce the area of adhesion on the GIC to the dentin. So it is generally avoided.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 89
25. When Resin Modified GIC is used for lamination, why is it not necessary to etch the cement?
The Resin Modified GIC has HEMA, incorporated in the cement which can adequately bond with the composite resin. So etching is not necessary.
Ref: Preservation and Restoration of tooth structure, Graham.J.Mount,Mosby,1998, 90