My teeth are starting to look transperent, why?

Several possibilitis: You don't say where the transparency is. Have you been whitening your teeth. Overdone this can cause the teeth to have an overall transparent look. If it is just at the biting edge of your upper front teeth, it could be wear from grinding on the backside of your front teeth. You need to see a dentist to determine the cause and what to do about it.

Excessive wear: Your teeth may start to look transparent as the structure thins due to excessive wear from grinding or a malaligned bite. You should see your regular dentist and consider orthodontics to align your bite for a protected occlusion and then do any necessary restorative. The restorative part may be extensive and expensive so you may also want to consider a prosthodontist/specialist for treatment.