When sending your transcripts and LOR's you only need to send one copy of your official transcipts with mathcing letter and one original for each LOR with a mathcing from. AADSAS will forward copies of all sent material to the schools you have selected. Since AADSAS is the application agency that the dental schools require students to apply through, they will accept the copied materials only from AADSAS.
As to your question about if your school will put a mathcing from in with the official transcripts, you can just take a matching form to your records office and request that they put the mathcing form in with your transcripts. If they will not, you can have them give you an official set of transcipts with a seal or signature across the seal, then you can take that envelope, put it in another envelope with a transcript mathing form and then just send it off to AADSAS yourself. I would recommend that if you send anything to AADSAS yourself, that you send it certified mail with a return receipt. Good luck.