Periodontitis is an inflammatory disease of the tooth-supporting tissues caused by specific microorganisms. The idea of treating localised problem sites with local drug delivery seems appealing because the antimicrobial agent is delivered within periodontal pockets and the therapy is directed at specific pathogenic microorganisms. A novel in situ forming gel is introduced at the site, with the potential to overcome one of the main practical challenges associated with the treatment of local periodontitis: partial adhesion to the surrounding tissue, resulting in the accidental removal of at least parts of the implants from the patient's pockets. For the treatment of localised forms of periodontal destruction, controlled release antimicrobial agents should be considered as an adjunct to mechanical debridement. Local delivery of an in situ gelling system to periodontal pockets has the advantage of putting more drugs at the target site while minimising total body exposure to the drug The most appropriate type of formulation for the treatment of periodontitis has been found to be oral in situ gel because it delivers the drug locally, allowing the dose to be reduced while also reducing toxicity. In situ gel formation can be caused by a variety of mechanisms, including solvent exchange, UV irradiation, ionic cross-linking, pH change, and temperature modulation.Here we highlight about the methods of oral in situ hydrogel, polymers used in the preparation and also examines periodontitis pathogenesis as well as its diagnosis and treatment.