Great initiative! What schools like to see when it comes time to apply in a couple of years is longevity! They see tons of applicants who started volunteering in Sept of 3rd year to get the minimum hours in, but few people actually stick to a volunteer position for a solid couple of years.
I would echo what was written above. Get some good shadowing experience. This will show schools that you actually have an interest in the field, it will allow you to build a longer term relationship with the facility where you are shadowing and perhaps guarantee you a solid reference letter, you will learn about the field, and you might even learn that you don't want to do what you think you want to do...ideas of "who I think I want to be" as an 18 year old, don't always look the same at 22 years of age.
My specific suggestions:
1. Make a list of all the dental/oral surgery centers in your area. Look at their websites, read their mission, read about the doctors who work there, read reviews of the doctors. Make a list of all the clinics that are "good" clinics - ones where you would want to be a patient.
2. Look at your local hospital. All hospitals, esp those with trauma centers will have oral surgeons on call or even a department within the hospital. I would really really really stress looking into a hospital for several reasons - usually people who work in a hospital setting are used to having lots of residents and students around, so they are more keen to teach and provide observerships; you might also get the opportunity to observe some other health care professionals to get a better idea of other career options out there.
3. Is there a dental school near you? Can you contact any of the current students to ask questions etc. You could even ask them if they hold any "open house" events or talks for interested students, ask them about the program.
Basically reach out to a lot of people. Start by reaching out to say 5 people in different clinics and hospitals and ask them to spend even a half day or day. That's it. Use this as an opportunity to feel them out. Do they seem keen to have you around? are they good at answering questions? Do you "connect" with them? You want to find one or two people who you enjoyed shadowing, whom you connected with to build a longer shadow opportunity. You need to get along well and have someone who is interested in having you around if you plan to have this person like you enough to provide you a good reference later.
Good luck!