If you have the bare minimum why not think about getting a diverse range of dental placements like mentioned before. Have you looked up dental labs for example together with shadowing at different types of dental settings.
I think volunteer work in health care settings is preferable as you can translate it to the qualities you will require as a dentist. You will be directly engaging with patients and healthcare professionals as well. However, other types of volunteering will still be beneficial if you can manage to get them.
You can also start to read up on dental news and researching some recent issues. It will get you familiar with dental terminology and certain codes of conduct etc. that you will benefit from knowing when you get to the interview stage. You may also find an interesting area of Dentistry that you can talk about in your personal statement and it will generally help in making your personal statement personal.
The longer you can keep your placements and volunteering going, the better as it shows commitment and gives you a chance to build up your application in more ways.
You still have time but make the best use of it and it looks like you are trying to. I decided on Dentistry in June during the 2nd year of my degree and managed to get w/e placements sorted out for the application cycle last year. By this March I had 2 offers, so it is very possible and you definitely have time.