Develop a Gap Between my Teeth After Two Separate Crowns on Front Teeth? (photo)

I am in Korea and I am getting two permanent crowns done on my front 2 teeth. My Korean dentist wants to attach the crowns so that they are one unit. After doing much research, I decided that I want the teeth to have separate crowns so that it looks more natural and because it is the norm procedure in the US. The korean dentist said OK but that after some time the crowns will shift and create a gap btwn my teeth. Is this true? How much time before this happens? I have never had a gap before.