I suspect that you’re grinding your teeth in a protrusive grinding motion to the point where you are edging the incisal tips, which are the biting edges of teeth. Those edges are being worn from the back at an angle and the effect is almost prismatic – the worn edges are thinner and the effect is that you’re able to see right through them, creating the translucent appearance you mention.
The reason you may have been noticing this while using whitening strips is that whitening your teeth makes the contrast greater. See your dentist, who will tell you if you’re grinding your teeth.
The solution is to wear a night guard to protect your teeth from future grinding, or chipping away of the teeth. You should also troubleshoot the root cause of your grinding, which is a major symptom of sleep apnea, stress, and other conditions.
Mark Burhenne DDS