Why isn't there a structure of "express something (to somebody)" in the dictionary?

Question

Ok, now, in Oxford dictionary:

to express: to show or make known a feeling, an opinion, etc. by words, looks or actions source

so they got the structure "express something", ex: "Teachers have expressed concern about the changes".

However, there is no structure "express something (to somebody)". So, I am not sure I can say "Teachers have expressed concern about the changes to students"

In fact, there is a structure "express something (to somebody/something) (North American English)" which means "to send something by express post As soon as I receive payment I will express the book to you" source.

So, I think the dictionary got a shortcoming here.

So, Why isn't there a structure of "express something (to somebody)" in the dictionary?

Answer 1

In the first place, as stangdon says in the Comments, dictionaries cannot possibly catalog every conceivable or even every common use of a word. A dictionary will ordinarily only define those uses which are peculiar to the word, such as prepositions 'selected' by that word to signify particular semantic relationships. The use of to to indicate someone toward whom an expression is directed is not peculiar to express; it can be used with just about any verb involving utterance.

In the second place, we do not ordinarily use express in conjunction with an audience toward whom the utterance is directed. The metaphor which underlies the word—etymologically it means to "press out"—is concerned with the origin of an utterance, the person who uttered it, and the word is usually employed in contexts where the target of the utterance is unknown or irrelevant.

In fact, your example strikes me as awkward (I imagine it only arises because express is the stock verb used with concern), and I myself would not write this. If the point of the sentence is that students became aware of the teachers' concern, I would not use express but some term appropriate to the circumstances which explicitly embraces the notion of communication:

The teachers have told students about their concern.
The teachers have inadvertently revealed their concern to students.
The teachers have announced their concern to students.
The teachers have communicated their concern to students.
The teachers have made their students aware of their concern.
The teachers have shared their concern with students.

Answer 2

expressed concern is correct, why do you think it's not? Equivalent would be voiced concern, this is using express as a verb. Express post, is as an adjective for post, but I've never heard that next part of "express (send) something to you". Not to confuse the issue, but, when nursing mothers bottle their milk for babies, they express their milk...