Smoking cigarettes is more than the simple act of lighting little sticks of tobacco, and inhaling poisonous fumes. In many ways, it is a lifestyle. You identify and associate with people that are also smokers, and relate to celebrities you see smoking, as if you and them shared a special bond. Smoking cigarettes is also a deeply ingrained habit, one that is hard to break, and not only because of the powerful addictive effects of nicotine.
Think of all the habits you have, all you mannerism, your way of being. All of that is there for a reason, even if the reason for it no longer exists. It is the same thing with cigarettes. It is a scientific fact that after 3 weeks, there is not a molecule of nicotine left in your body. As you know, nicotine is what makes cigarettes and all tobacco products so addictive.
So why does the urge to start smoking cigarettes remain, long after the nicotine is gone? Because the habits and mannerism that come with smoking cigarettes are literally burned into you by months or years of repetition, it can be challenging if not very difficult to be rid of them. For many people, the strain of breaking these habits can be a lot harder than simply getting rid of the nicotine.
A lot of persons trying to quit smoking cigarettes report missing having something in their mouth; this is normal because as a smoker, you used to be sucking on a cigarette 15 or more times a day.
Try to replace the cigarette with something that will not rot your teeth, such as a toothpick, a pencil, or if you absolutely must, one of those fake cigarettes. I would personally refrain from using the ones that dispense nicotine for reasons that are obvious but too numerous to list here.