The carious cavity - there are innumerable microorganisms that reside in our mouth. They are Invisible to the naked eye, but their reproductive rate is phenomenal producing colonies upon colonies of microbes. Small particles of food lodge between and within teeth when we eat. These food particles are used up as nutrition by the microbes living in the colonies which corrodes the tooth enamel (the hard outer covering), giving rise to cavities. Cavities are termed scientifically as "caries". A tooth is like a hollow cylinder consisting of nerves and veins collectively known as pulp enclosed within the hard enamel and dentin. The cavity formed in enamel eventually spreads deep through dentin to reach the pulp. A severe pain ensues with bacterial invasion of the pulp. Consequently there is an infection leading to pus formation and collection within the tooth. This phenomena is known as abcess formation. As long as the depth of the carious cavity is limited to hard tissue like dentin. The disease process can be stopped and damaged tooth structure restored by a process called "filling". Thus the tooth is salvaged. Infection of the soft pulp in deep cavities leads to severe pain making fillings ineffective. The only options available are either extraction (removal of tooth) or an RCT to save the tooth in a painless state.