Please explain if it is unhealthy to brush your teeth four times a day?

No: It does not. It helps and do not forget to floss.

Perhaps: It depends upon the hardness and design of the bristles of the toothbrush, your technique and how much time you spend brushing. You can wear away tooth structure and perhaps be too energetic for your gums. I would suggest you discuss this with your own dentist who can personally examine you and determine whether or not you are overdoing it.

Technique: What's important is technique, not frequency. Brushing teeth incorrectly 2x/day or 20x/day will still allow for problems. Ask your dentist/hygienist to review best oral hygiene techniques and instruments for your particular mouth. Everyone's different.

No: It takes plaque 24 hrs to develop on a clean tooth. A proper toothbrushing once a day is better than a poor toothbrushing 4times. Use a soft brush.