The process through which sugar causes a cavity in a tooth involves a series of biochemical and microbial reactions.

Here's a breakdown of this process:

Presence of Oral Bacteria: Your mouth is home to a variety of bacteria, some of which are harmful and contribute to tooth decay. The most notable among these is Streptococcus mutans.

Consumption of Sugars: When you consume foods or drinks containing sugars (like sucrose, fructose, glucose), these bacteria feed on these sugars. It's not the sugar itself that directly causes cavities, but rather the action of bacteria on these sugars.

Bacterial Metabolism and Acid Production: As bacteria metabolize these sugars, they produce acids as a byproduct. This primarily includes lactic acid.

Demineralisation of Tooth Enamel: These acids start to demineralize (dissolve) the enamel, which is the hard, outer layer of the tooth. Enamel is made of hydroxyapatite, a crystalline structure composed of calcium, phosphorus, and hydroxide. The acid in the mouth creates an environment where calcium and phosphate are lost from the enamel in a process called demineralization.

The chemical reaction can be simplified as:

Acid (from bacteria)

+

Hydroxyapatite (in enamel)

→

Demineralisation

Acid (from bacteria)+Hydroxyapatite (in enamel)→Demineralisation

Formation of Cavities: Over time, this demineralisation leads to the weakening of the enamel. If the process continues without being counteracted (by remineralisation from saliva and fluoride), it eventually leads to the formation of a cavity (dental caries).

Role of Saliva: Saliva plays a crucial role in counteracting this process by neutralising acids and providing minerals (like calcium and phosphate) that can help remineralise the enamel. Fluoride, from toothpaste or water, is also important as it helps to remineralise and strengthen the enamel.

It's important to note that this process doesn't happen overnight. It's the frequent consumption of sugars and poor oral hygiene that typically lead to the development of cavities. Regular brushing with fluoride toothpaste, flossing, and limiting sugar intake can significantly reduce the risk of this process leading to cavities.