One of the main characters in best-selling Irish author Sally Rooney's new novel 'Intermezzo' wears fixed braces.

On the very first page of the novel, we are told that Ivan Koubek, a 22-year-old Irish/Slovakian competitive chess player, has braces. We later learn he has "the new white ceramic braces that young people have now", and there are further references as the novel goes on. 

Do we suspect that Sally Rooney has a thing for guys in braces?

I don't think so. I'm unfamiliar with Rooney's other work, but I can't find any references to characters in her other novels with braces. She appears to have used Ivan's braces as a physical manifestation of his "youth and inexperience" compared to his more worldly older brother. Pleasingly, his ceramic smile doesn't stop a female character from taking a shine to him in the opening chapter.