Whether a baby develops upper or lower teeth first does not indicate a high or low IQ, it is most likely determined by genes. If the parents develop the upper tooth germs before the lower tooth germs, the baby is also likely to develop the upper teeth first, so there is no connection between it and the IQ, which can be tested by later intelligence. However, the order in which the baby’s upper or lower teeth erupt first is not fixed. Normally, the lower teeth erupt first, but there are some babies who are affected by genes or races and grow their upper teeth first, which is normal. X-ray examination, as long as the embryo of milk teeth and permanent teeth are completely present in the jawbone, it will not affect the baby’s teething situation.