Why are the end of my teeth translucent after whitening?

Normal: Teeth are normally somewhat translucent at the edges. In fact, cosmetic dental labs try to create that translucency to resemble natural tooth structure. It is possible that you may see the translucency more immediately after whitening because of the dehydration of the tooth structure that occurs with bleaching with peroxides. One can whiten too much, so have your dentist evaluate your concerns.

Deep bite: If take home whitening or bleaching was done, it will give you a better answer if you see your dentist. Some cases i've seen with remarkable translucency (to gray) was due to attrition of the back of the biting surfaces of the teeth due to deep bite plus hyperacidity - either from the diet, gastroesophageal reflux disease, and sometimes a mild form of bulimia.