Your teeth are too big or too small for your jaw
Permanent teeth may be too large or too small for the jaw bone . For exemple, If you inherited a small jaw from your mother and larg teeth from your father, all of your teeth may not fit in your jaw ( crowding teeth). At the opposite teeth may be too small for the jaw. (see picture)
You may have bad a bad habit
Sucking your thumb can push your top teeth out and your bottom teeth in, as in the boy shown here. Breathing through yourmouth, or pressing your tongue against your front teeth ( tongue thrust) pushes both your top and bottom teeth apart ( shown in box). Both habits can cause an open bite.
Your teeth didn’t come in on schedule
Most people’s teeth grow in to the mouth according to a specific timetable. Sometimes the teeth do not erupt in the proper order. Permanent teeth that arrive too ealy may take up space that later teeth need. Permanent teeth that arrive too late may not have anywhere to go
Your molar are in the wrong positions
Teeth have trip (cusps), with valleys in between them (remember the saw blades?)./ The cusps of a lower toothshould fit in to the valley of the upper tooth. Like the teeth in a broken zipper. If the cusps and valleys of the very first molars do not meet, then all the teeth that come after them will not mesh either. Sometimes, a molar can be so far out of position that its tips meet the valleys of the wrong molar.
You are missing some teeth Sometimes teeth simply don’t develop. If this happens, there is too much space, and new teeth may drift into the extra space.
You have extra teeth Extra teeth can take up space, causing the other teeth to crowd
You lost a tooth accidentally
Injuries to your face can change how your jaw grows, and cause teeth to be crooked. Chipping your teeth or losing them accidentally will also affect the way your jaw and the rest of your teeth grow.