It is usual for a person to dream about a dead love one. One reason may be it's because we are missing the person so much. The dream you that you had where in you are supposed to meet your father somewhere with your dentist friend but sad to say, you weren't able to meet him, signifies that you may have this desire to prevent his death and you were thinking that if only there is something you could do then, he might still be around. You have some regrets about losing your father. Perhaps, you might have lost a huge percentage of your inner strength when he died. You feel the same way whenever his memories come back into your mind. At the back of your mind, you were thinking that if only you could turn back time, you might be able to do something to relieve your father from the burden he was feeling then. This is my dream interpretation for you.