The best "internship" would be to start shadowing a dentist. Look at the nearest dental offices in your area, and visit them in person. Ask the front desk (and dentist) about ur goals (interested in dentistry n want to do volunteer shadowing) ... some offices u wouldnt be able to get pass the front desk but other office.. dentist will be happy to help u.. dont expect to be paid , first ask to volunteer. .... after weeks, months (depending on ur situation and interest), u may gain dentist's trust and start to work partime doing sterlization or something... then later start to get hands on experience with chair side dental assisting (which would look amazing on ur app imo)..
There are other "internships" as well for dentistry such as gateway programs/introduction to the 9 specialities etc, with some basic hands on experiences such as 2 week "gateway to dentistry" (in newark nj w/ umdnj) and i know penn has a 1 week program as well.
I would recommend to get shadowing experience first b4 "internships"
Ateeb