Just checked it in the Charaka Samhita and he doesn't specify the type of oil at all, but generally in Ayurveda, we would want to use the type of oil that is the opposite of predominating characteristics of the person. Just because someone has inflamed gums, doesn't mean it is necessarily a fire (pitta) imbalance, it could just as well be due to an air or earth imbalance. Generally, there is a conception, even among Ayurvedic professionals that sesame oil is good for people of all constitutions and can only do good and remove disease and never have any negative effects. This is absolutely false. Sesame oil is a great oil and can remove disease when used by someone of a constitution that is appropriate to sesame oil, especially for those of an air constitution (vata) and to a lessor extent those of an earth constitution (kapha). Those of fire constitution, especially those that have an imbalance of fire, using sesame oil in preparation of food, oil pulling or even in massage oils can be of great harm and be the cause of disease. Pitta types should use sunflower seed oil (or possibly coconut oil) for oil pulling, food preparation and massage oils.