1. Early mouth cancer
2. Scurvy: In the mouth, scurvy can cause gums to swell, bleed and soften which can lead to tooth loss.
3. Eating disorder: regular bouts of vomiting covers the teeth in strong gastric acid from the stomach that can wear down the tooths protective layer of enamel, causing teeth to become discoloured, cracked and sensitive.
4. Anemia: Ulcers at the corner of the mouth. A change in color of the gums and tongue
5. Sinus infection: Infected sinuses can cause pain in the jaw and around the teeth, which can be mistaken for a toothache.
6. Vitamin D is needed to absorb calcium which helps to prevent tooth decay and gum disease.
7. Too little zinc can leave you open to gum disease, dry mouth and loss of sensation in your tongue.
8. Low levels of vitamin B3, or niacin, can cause the tip of the tongue to become red and swollen
9. Vitamin B2 - without it your tongue can become sore and your lips, red and shiny.
10. B12 levels which can prevent bad breath, loss of taste and a fissured tongue.
11. Diabetics are at a higher risk of early gum disease - gingivitis - and serious gum disease - periodontitis.
12. Biting your nails: If you like a nibble, you are putting undue stress on your teeth, causing them to crack, chip and wear down.

Jaw pain, recessed gums and even headaches are other side effects caused by the grinding and clenching involved in nail biting, as well as the germs being passed into your mouth every time you feel like a nibble.