This is a step in adapting the preparation for receiving the final restoration material.
Sound dentin is the best barrier between a restorative material and pulp. So conservation of all sound dentin possible during cavity preparation should be beneficial.
When the thickness of remaining dentin is minimal, heat generated by injudicious cutting can result in pulpal burn lesion, abscess formation or pulpal necrosis. So water or air spray coolant should be used with high speed rotary instrument. The remaining dentin thickness is measured by using dentinometer.
Cutting of previously unexposed dentinal tubules will result in degeneration and death of affected primary odontoblast and their processes resulting in formation of dead tracts.
Other pulpal irritants are:
1. Some ingredients of various materials
2. Thermal changes conducted through restorative materials
3. Forces transmitted through materials to dentin
4. Galvanic shock
5. Injuries of noxious products and bacteria through microleakage.
To protect the pulp from these kinds of irritation cavity liners, varnishes, cavity liner suspension, intermediary bases, cement bases, etc. are used.
CAVITY LINER:
Liners are volatile or aqueous suspension or dispersion of Zinc oxide or calcium hydroxide that can be applied to a tooth surface in a relatively thin film. A few microns to about a millimeter in thickness.
Liners Provide:
- A barrier that protect the dentin from noxious agents.
- Initial electrical insulator.
- Some thermal protection.
A traditional liner is used to medicate the pulp when suspected trauma has occurred. The desired pulpal effects include sedation stimulation, later resulting in reparative dentin formation. If the removal of infected dentin does not extend deeper than 1-2mm from initially prepared axial or pulpal wall usually no liner is indicated. If the excavation extends into or closes pulpal tissue, Calcium hydroxide, Zinc oxide Eugenol liner is used. There liners in thickness of 0.5mm or greater have adequate strength to resist condensation forces of amalgam and provide protection against short term thermal changes. Then should be approximately 2mm of bulk between pulp and metallic restorative materials.
The ability of calcium hydroxide to stimulate formation of reparative dentin when it is in contact with pulpal tissue makes it is the material of choice in very deep excavations and known pulpal exposures.
CAVITY VARNISHES
There is no solution liner derived from natural gums, copal synthetic resins or rosin. When varnishes are applied to prepared tooth surface the solvent quickly evaporates leaving thin film of resinous materials (micro thickness). Two goals of varnish application are mandatory for complete seal. These are insoluble in oral fluids. These are applied to cavity wall using a small cotton pledge. Tooth varnishes usually applied just before the insertion of amalgam or cementation of cast gold restoration. These are the only material required in shallow preparations. These helps to prevent microleakage and reduce post operative sensitivity. These help to reduce pulpal irritation from leaking cement. They can be applied to enamel portion of the preparation. Tooth varnishes are not used under composite because solvent in the varnish reacts with resin component of composite and adversely affect the polymerization reaction. The free monomer of the resin can dissolve the varnish film. Varnishes will hamper the fluoride releasing property of glass ionomer cement. So they are not used under GIC also.
CAVITY LINER SUSPENSIONS
These are suspensions of calcium hydroxide, zinc oxide which are particularly used under tooth colored restorative material. The film deposited by these materials is thicker. They will dissolve & disintegrate in oral fluids, thus allowing severe marginal leakage if they are brought in to cavosurface. The whitish color also affects the aesthetic value of restoration. So they are confined to dentinal wall only.
INTERMEDIARY BASES.
There is no clear distinction between intermediary bases & cavity liners. Two forms of intermediary bases used are calcium hydroxide &modified zinc oxide eugenol.
Zinc oxide eugenol has topical anesthetic properties termed as obtudant effect. When a history of discomfort is found, zinc oxide intermediary base can be used.
They are contraindicated under composite because they will affect the polymerization reaction. Calcium intermediary bases are used as indirect pulp capping agents, protective chemical barrier under filled &unfilled resins. Calcium hydroxide has no otundant properties.
CEMENT BASES
Cement bases are relatively thick materials placed under the restorative material which will provide chemical &thermal insulation. They should be capable of providing support to the restoration that is subjected to occlusal function. Four types of base material used are Zinc phosphate, Reinforced Zinc oxide eugenol, Glass ionomer cement and Zinc polycarboxylate.
The level to which the base is built should never compromise the desired tooth preparation resulting in inadequate restorative material thickness. Since cement base materials are subjected to stress during insertion of restorative material and also they are indirectly supportive of masticatory functions, they also require their own specific retention in the prepared cavity. Retentive grooves are made using round burs directly laterally in the dentin.
In case of pin retained restorations, cemented pins are used for pulpal protection.
These are different methods of pulpal protection.
Regardless of the material used protecting the pulp appropriately is mandatory for the successful restoration of the teeth
REFERENCES-
•Sturdevant’s Art&Science of Operative Dentistry
•Principles&Practice of Operative Dentistry-Gerald T Charbeneau
•Textbook of Operative Dentistry-Vimal Sikri
•Textbook of Operative Dentistry-Satish Chandra
No comments:
Post a Comment