According to a report from the Manipal College of Dental Services in India was published in GreenMedInfo published in September of 2014, massaging your gums for 10 minutes a day for 4 weeks with olive, coconut, or sesame oil is slightly more effective in fighting plaque development and gingivitis as chlorhexidine. Chlorhexidine has toxic "side effects" that include staining teeth a brownish color, the potential of creating resistant strains of bacteria in the oral cavity, and having a foul taste.
This ancient Ayurvedia treatment has been around for 5000 years, but only recently was studied and compared to the standard treatment with chlorhexidine. Sesame oil had the greatest effect on reducing the levels of S. mutans, which is one of the causes of gum disease. Plaque scores and gingival scores were about the same with all of the treatments.
The basis of effectiveness of the oils has to do with how they "pull" toxins out of the tissues of the mouth...hence why it is called "oil pulling."