DENTAL PLAQUE is a soft deposit that forms a thin film and sticks on the surface of the tooth

CALCULUS (TARTAR): if dental plaque is not removed it gets mineralized to form a hard deposit on the tooth and gums called calculus 

• Dental plaque has a large amount of bacteria. Studies have shown that 1 gram of plaque contains 2 X 1011It is usually formed in pits and fissures of teeth. it is also formed around teeth that are not aligned properly.
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• It is more prominent on the inner surface of lower teeth and the outer surface of upper molars
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Role of plaque in causing gingivitis.

Plaque accumulation causes inflammation and irritation of the gums leading to a condition called gingivitis (gingiva means gums and it means inflammation)

In gingivitis, gums become red, edematous, and inflamed. the edge of the gums becomes rolled (image). It is associated with bleeding of the gums. People usually complain of bleeding gums when they brush or eat something hard like apples. 

But the unfortunate part is since there is no pain associated with it people either don’t notice these changes or just ignore it.

Role of plaque in Periodontitis

When gingivitis is not treated at the right time the infection from the gums proceeds to the supporting structures of teeth i.e the periodontium