Yellowing of teeth is mainly due to deposition of plaque on teeth..Which can b easily removed through professional cleaning by dentist..Cold sensitivity has many reasons n cavities is one of dem..But hot sensitivity​ is becoz of only one reason ie deep cavity involving d nerves of teeth..Usually these king of teeth require root canal treatment n can b saved..

Please check with your Dentist whether you are having any Enamel deformative..i.e Amelogenesis imperfecta or any other Tooth related problems.. Generally if teeth are healthy than simple cleaning and polishing of teeth will be sufficient with any desensitizing tooth paste.