I hear both 残念ながら and 残念なことに when expressing that something was unfortunate before the actual sentence, much like the English "Unfortunately, ...".
However, I'm not sure on where these two phrases differ. Is their usage the same?
I believe the difference is:
残念ながら the focus is on the speaker's feeling while they tell you the information. It's like saying "I'm sorry to have to tell you, but..." The speaker's feeling of disappointment exists alongside the information.
残念なことに, the focus is on the thing the speaker is telling you, and is a cause of the disappointment. It's like saying "What's particularly disappointing is..." The speaker's disappointment comes from the information.
残念ながら、あなたと別れる。 (It's sad, but I'm going to break up with you.)
残念なことに、結婚しようかなと思っていた。 (What's sad is, I thought we maybe could have married.)
These two examples are subtley different. In the in the first case, you are being told that a breakup will happen, despite the fact the speaker is sad about it. In the second case, you are being given a fact which is itself a cause of disappointment.
Hope that helps.
I agree with Dave that the two seem very close. If we look at the core definitions, we can see this:
Although we usually stick this on the end of the verb stem (食べながら、見ながら、など), it can retain the same meaning in English here.
To me, the two are nigh identical. With
残念ながら ever so slightly less formal-sounding (and more common) than
According to this site:
Which I roughly interpret as 「〜ことに」giving more surprise/contradiction (but I must admit I'm not all that clear and could be wholly mistranslating that one... anybody care to confirm/infirm?).
At any rate, grammar is slightly different:
残念ながら 抜くことになる歯は このような歯です。