*Bayasgalan Ganbaatar1, Nomintsetseg Gantumur1, Gantuya Gansukh1, Oyungerel Tsevegmid1, Munkhjargal Gantumur1, Gunchinmaa Tsedev1, Ariungoo Ganbat1, Sapaar Bayarmagnai1 (1. Department of Prosthodontics, School of Dentistry, Mongolian National University of Medical Sciences)