To prevent dental problem. Hygiene?

Unfortunately the number of times you brush isn't enough. The technique of brushing is important. Visit your dentist to make sure your brushing technique is proper Also, some mouthwashes tend to have alcohol, whch dry out the mouth, so while they provide temporary freshness, they might cause cavities in the long run. Make sure you get routinely 6-12 monthly cleanings from your dentist to ensure your teeth and gums are healthy. Professional care is required to maintain healthy teeth. And lastly, unfortunately some genetic pattern in teeth does play a role. Also, the quality of your saliva and food you eat. There isn't much you can do about these except a regular maintenance schedule on your part. Don't compare your teeth to others, they may be having other problems which you are spared of.