A patient may have well-aligned upper teeth, a correct bite in the side teeth and very crooked lower front teeth. This can be due to what's known as a tooth-size discrepancy. The combined width of the upper front teeth and the combined width of the lower front teeth should be in the right proportion. The deviation from this relationship can be so marked that one lower front tooth (an incisor) has to be removed to make room for aligning the lower front teeth, while keeping the bite – which was correct to begin with – unchanged.
This answer is for general information. Your own case needs an examination by an orthodontist.