Tarnish and corrosion
Tarnish and corrosion being a significant clinical finding in metallic restorations is discussed in detail in this section that will clear all doubts regarding the same.
1. What is Tarnish?
Tarnish is the surface discoloration on a metal or a slight loss of the surface finish. It occurs from the formation of hard and soft deposits on the surface of the restoration and it is an early indication of corrosion.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,291
2. What is Corrosion?
Corrosion is the actual deterioration of the metal by reaction with its environment which can be moisture, atmosphere, acid or alkaline solutions and chemicals.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,292
3. What is Electrochemical corrosion?
It is also called as wet corrosion since it occurs in the presence of water or other fluid electrolytes. The oral cavity is wet and most of the corrosion that occurs is of the wet type.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,293
4. Why does a sharp pain occur when 2 different metallic restorations, opposing each other come in contact?
When two metallic restorations like amalgam on the lower tooth opposing a gold inlay on the upper tooth comes in contact with each other in a wet environment with saliva, an electric couple exists and there is a sudden shot circuiting through the two alloys. This results in a sharp pain and it is an example for galvanic corrosion.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,296
5. Where does Concentration Cell Corrosion occur?
In the interproximal areas or in the crevices of a mouth with a poor oral hygiene, there is accumulation of food debris which produces one type of electrolyte and normal saliva produces another type of electrolyte. Electrolytic corrosion occurs in the metal surface underneath the food debris. This is concentration cell corrosion.
Ref: Science of Dental Materials, Skinner, Prism books private limited,9th Edn,298