Nowadays, so many people don’t know how to effectively brush their teeth. Most people just rub the brush against the front surface of their teeth. However, you must change the angle of the brush as this brushing guide shows:
Note that once the front layer top row of teeth have been brushed at a 45 degree angle, you must change to a 90 degree angle from the horizontal meaning that the brush is facing completely up. This allows you to get the tough spots near the bottom of the teeth. The back of the teeth can be captured by angling the brush back even further to around 135 degrees so it’s facing in the direction your eyes look.
Don’t forget to brush the bottom row of the teeth in the same manner except with reversed angles!