I had dental implant surgery 13 years ago, the two teeth on either side of the front teeth never grew in, my implants were and had been a sucess up until a few years ago. My crowns are significantly shorter than they were originally. I did all the wrong things. Smoking(quit), not seeing the dentist since I lost insurance, poor dental hygiene for awhile due to severe depression(better). Why have my crowns sinking into the top of my mouth? How often are crowns on implants supposed to be changed?