Damshtra means the incisor teeth on either side of the mouth.
Chaturdamshtrah Narasimha Vigrahah meaning that this Nama speaks about Lord Narasimha says Sri Adi Shankaracharya.
The presence of Catur Damshtrah indicates that the person is a Mahapurusha. Hanuman describes Sri Rama to Sita Devi as follows
catuSh kalaH catuH lekhaH catuSh kiShkuH catuH samaH |
caturdasha sama dvandvaH catuH daShTaH catuH gatiH || 5-35-19 (Valmiki Ramayanam Sundara kandam).
He has fourteen other pairs of limbs (viz. the eye brows, nostrils, eyes, ears, lips, nipples, elbows, wrists, knees testicles, lions, hands, feet and thighs) equally matched. The four large teeth at both the ends of his upper and lower jaws are very sharp. He walks in four gaits (resembling the walks of a lion, a tiger, an elephant and a bull). He is endowed with excellent lips, chin and nose. He has five glossy limbs (viz. the hair, eyes, teeth, skin and soles). He has eight long limbs (viz. the arms, fingers and toes, eyes and ears, thighs and shanks).
Lets chant the Holy Name of the one who has the strong four incisor teeth, by which He lifted Bhumi Devi from the depts. Of the ocean and saved her from the demon- Hiranyaksha in His Varaha avatara. May He protect us from the four fold miseries with His sharp four teeth always.
Nama 141 – Vishnusahasranama