This is an ancient practice that is advised by ayurveda for improving health.
I use coconut oil. Around a teaspoon is taken in my mouth and swished and gargled for 15-20 minutes. Can be done daily. I wish I was more regular with it.
When you spit it out, it'll look like the foamy watery stuff you spit out after rinsing your mouth, when you finish brushing your teeth with toothpaste.
Works by disrupting the biofilms formed by bacterial colonies. Either through direct mechanical rinsing effect, or by exposing the biofilms to a wash with both a hydrophobic (oil) and hydrophilic (water in saliva). It also stimulates saliva production, which has it's own benefits for dental health and digestion. Some species of bacteria that colonize the mouth have been implicated in accelerated aging, heart disease and Alzheimer's. Bringing down their population will be beneficial in the long run. If you suffer from gingivitis(bleeding gums) or from halitosis(bad breath) you are probably at risk.
The other benefit is that the gargling and swishing of oil in the mouth is exercise for the muscles in the oropharynx and cheeks. This improves muscle tone in the area, and can help with obstructive sleep apnoea. Better sleep and oxygenation of the brain at night, again means a lower risk of Alzheimer's and neurodegenerative diseases.
The third benefit is the action, increases parasympathetic (rest,repair, regeneration) activity of the vagus nerve. I don't think anyone will say no to that either, in this day and age.
This is a low investment, low risk action that can have big dividends for your future health. Get started.
Questions are going to be-
1. Does it have to be coconut oil? No. Use whatever edible oil you want. I'm just telling you what I use.
2. Will sesame oil work? Yes. In fact that's the oil that I've seen recommended on some ayurveda blogs
3. Can it be 14 minutes instead of 15 minutes? Yes. Just, please, get it started.