Problem concerning copyright?

I am about to write a book in which i will use an invented language and an invented script. One of the ideas of this script is to write the vowels above the consonants as diacritics. Recently i found out that J.R.R. Tolkien (the one who wrote the lord of the rings trilogy) already used this idea in his tengwar alphabet. Letters in my alphabet are very different than in his, the same is for the language, but the idea of writing vowels as diacritics is common. So my question is: will it be a copyright issue if i use this mode of writing in some fragments of my book?