hanarabi ga kirei desu.

歯並び（はならび） literally means the arrangement/alignment of teeth.

• 歯 = tooth/teeth
• 並び = lineup, arrangement

So 歯並び is not just teeth in general. It specifically refers to how the teeth are lined up.

が marks 歯並び as the subject of the sentence.

So the structure is:

• 歯並び = tooth alignment
• が = subject marker
• きれいです = is beautiful / is neat / is nice-looking

A natural literal breakdown is:

• As for the tooth alignment, it is nice/neat

In English, we often just say The teeth are nicely aligned or You have nice teeth, but Japanese often describes the alignment itself.

Because きれい is a na-adjective, and な is only used when the adjective directly modifies a noun.

So:

• きれいな 歯並び = beautiful/neat tooth alignment
• 歯並びが きれいです = the tooth alignment is beautiful/neat

In this sentence, きれい is the predicate at the end of the sentence, so you do not use な.

Yes. きれい is a na-adjective, not an i-adjective.

That can confuse learners, because it ends in い. But grammatically it behaves like a na-adjective:

• きれいな 歯並び
• 歯並びが きれいです
• 歯並びが きれいじゃないです

It does not conjugate like a true i-adjective such as 高い.

Here, きれい means something like:

• neat
• well-aligned
• nice-looking
• beautiful

With 歯並び, it usually suggests that the teeth are straight and aesthetically pleasing.

So this sentence is often closer to Your teeth are nicely aligned than to the broader English Your teeth are beautiful.

Japanese often leaves out information that is clear from context.

So 歯並びがきれいです could mean:

• Your teeth are nicely aligned
• Her teeth are nicely aligned
• His tooth alignment is nice
• The tooth alignment is nice

Who it belongs to is understood from the situation.

This is very normal in Japanese. You often do not need to say your, his, her, etc. unless it needs to be made explicit.

Yes, 歯並びはきれいです is also possible, but the nuance is a little different.

• 歯並びがきれいです: focuses on the fact that the tooth alignment is nice
• 歯並びはきれいです: sets tooth alignment as the topic, often with a contrastive or topical feel

For example:

• 歯並びはきれいですが、少し黄ばんでいます。
  The alignment of the teeth is nice, but they’re a little yellow.

If you are just making a straightforward observation, が is very natural.

です makes the sentence polite.

Compare:

• 歯並びがきれいです。 = polite
• 歯並びがきれい。 = plain/casual

It does not add tense by itself here beyond making the statement polite and complete. The sentence is present/non-past: is neat / are nicely aligned.

Yes, absolutely.

Japanese often uses very short sentences that are still complete:

• 歯並びがきれいです。

That is a full polite sentence meaning something like The tooth alignment is nice.

The subject’s owner and other details can be omitted if they are understood from context.

The spaces are just for learners. In normal Japanese writing, this would usually be written without spaces:

歯並びがきれいです。

Japanese normally does not separate words with spaces the way English does.

It is pronounced はならび.

Breakdown:

• 歯 = は
• 並び = ならび

So:

• 歯並びがきれいです
• はならび が きれい です

Not exactly.

• 歯がきれいです = The teeth are beautiful/clean/nice
• 歯並びがきれいです = The alignment of the teeth is nice

So 歯並び is more specific. It talks about how straight or well-arranged the teeth are, not just whether the teeth themselves look nice.

Yes, it can be.

歯並びがきれいです is a natural compliment meaning someone has nice straight teeth.

That said, as with any comment about appearance, whether it feels natural depends on the relationship and situation. In the right context, it sounds like a normal positive remark.