Liners and cements

Liners and bases are materials placed as thin coatings that mainly act as a barrier against chemical irritation and the bases also provide thermal insulation.In this section, the various cements available, their properties, manipulation, precautions and uses are discussed through simple question and answers.

 

 

1. What are the differences between liners and bases?

Liners are materials placed as thin coatings that mainly act as a barrier against chemical irritation and does not provide thermal insulation. Bases are materials used as barriers against chemical irritation, provide thermal insulation and resist the condensation force.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 125

2. Why is an intermediate material used in a restoration?

An intermediate material stimulates pulp repair by production of secondary or reparative dentin near the site of irritation. Also it provides protection to the pulp from injurious toxic agents from restorative materials and blocks thermal diffusion through a metallic restorative material.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 126

3. How does a cavity varnish act?

Cavity varnishes are natural rosins or synthetic resins dissolved in a solvent such as ether or chloroform. When applied to the prepared cavity, the solvent evaporates and a this film is left in the cavity that provides a bandage over the fresh cut dentin.m it mainly reduces microleakage until the corrosion products form in amalgam restorations.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 126

4. Why varnishes do not provide thermal insulation?

When properly applied, the thickness of the varnish film is only 4um and hence it is too thin to provide thermal insulation.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 126

5. Why are varnishes not used under fluoride releasing cements?

In fluoride releasing cements, the varnish should be removed from the enamel so that the fluoride present in the cement interacts with it.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 126

6. Why are varnishes not used when composites or unfilled resins are used?

When the resins come in contact with the varnish, polymerization of the resin is inhibited, producing a softening at the varnish resin interface. Hence it is not used under resins.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 126m127

7. How is the varnish applied in the cavity?

The varnish should have a thin viscosity. A uniform and continuous layer is applied over all the prepared surfaces. A minimum of 2 thin layers are applied. The initial layer leaves small pinholes when it dries and the second coating will fill the voids created..

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 128

8. What happens when the varnish becomes too viscous?

A highly viscous varnish will not wet the cavity properly and hence results in microleakage.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 128

9. What is IRM?

IRM is a reinforced ZnOE product that makes use o0f a polymer for reinforcement. Also the ZnO powder particles have been surface treated to produce better bonding of the particle to the matrix resulting in greater toughness and longer durability.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 129

10. What are EBA cements?

In ZnOE cements, the eugenol is partially replaced by ortho ethoxy benzoic acid whose physical peoperties are superior to the conventional zinc oxide eugenol cements. They are called EBA cements designed particularly for permanent cementation of inlays, crowns and bridges.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 132

11. Why newly mixed Zinc phosphate cement may produce irreversible pulpal damage?

Newly mixed Zinc phosphate is highly acidic and irritating to the pulp. Without protection of a varnish, it may produce irreversible pulpal damage.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 132

12. Why is a cool mixing slab used while mixing Zinc phosphate?

A cool slab delays the setting and allows the operator to incorporate more powder before the crystallization proceeds to a point at which the mixture stiffens.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 134

13. What is the good consistency for luting of zinc phosphate cement?

The freely mixed cement is touched by the side of the spatula and lifted to form a strand of the cement. A good consistency will form a strand that extends upwards for ½ to ¾ inch. Less than ½ will need to add more powder and more than ¾ inch will need a new mix.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 134

14. Why is polycarboxylate cement more biologically acceptable when compared to Zinc phosphate?

The poly acrylic acid molecule has a macromolecule that restricts penetration through dentin or its attraction to protein,that limit the diffusion through the dentinal tubules. So the post operative sensitivity is low and is biologically acceptable.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 137

15. Why is the glossy appearance of the mixed cement important for polycarboxylate?

The glossy appearance of the mixed cement indicates the liquid is still available to bond to the tooth. If a dull or stringy appearance is present, it means that the set has progressed too far or a too high powder to liquid has been used.

Ref: Lloyd Baum,Ralph W.Phillips,Melvin R.Lund.Textbook of Operative Dentistry.W.B.Saunders company;1985; 139,140