Describe how and why varnishes are used in the restoration process

A cavity varnish provides a barrier against fluid penetration into the underlying dentin. When applied to dentin, a varnish may reduce postoperative sensitivity and limit migration of corrosion products into dentin, thereby reducing tooth discoloration. RMGI liner/base products seal the tooth and strongly bond to the restoration to reduce the incidence of microleakage between the tooth and the restoration. ... Reduces postoperative sensitivity — RMGI liner/bases offer a strong bond to the tooth, sealing the tooth structure to protect against microleakage.

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they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.