65 Non-bacterial originated tooth wear is a normal process which occurs throughout lif. If the rate of loss is likely to prejudice the survival of the teeth, or is a source of concern to the patient, then it may be considered ‘pathological’. Robb reported that the prevalence of pathological loss of tooth tissue in patients less than 26 years of age was greater than in many older age groups. Tooth surface loss was classified into 4 groups: attrition, erosion, abfraction and abrasion. To find the prevalence of four different types of tooth wear among patients visited Digital Dental Office, Ulaanbaatar, Mongolia and investigate their dental attrition severity. Methods: From total of patients visited Digital Dental Office clinic between September 2016 and September 2017 adults aged 16-62 who was found with any type of tooth wear were explored by 4 types. Those patients with attrition were chosen and severity was determined by Bardsley’s simplified tooth wear index (TWI). There were total of 5432 patients examined and treated during this period of time. From them total of 1002 patients aged 16-62 presented some degree of tooth hard tissue wear/dental attrition. Most of the patients were with combination of 4 types of tooth wear: attrition, abrasion, abfraction and erosion. Attrition (At) was found in 68 patients which was only 6.7%, Abrasion (Ab) in14 people-1.3%, Abfraction (Abf) in 4-0.3%, Erosion (Er) in 2 -0.1% alone. The combination of these types of tooth hard tissue was dominant. At+ab+abf+er in 59 patients of total 1002 (5.8%). At+ab+er in 58 (5.7%). Ab+abf in 29 (2.8%). At+er in 25 patients (2.4%). Er+ab in 27 (2,6%). At+abf+er in 264 people (26.3%). At+abf in 452 (45.1%), which was the most prevalent combination. Dental attrition severity in these 1002 patients were shown as following: -0-0- No loss of contour. -1-229 people (22.8%) - Loos of enamel surface characteristics. Minimal loss of contour. -2- 505 people (50.3 %) - Loss of enamel exposing dentine for less than one third of surface.Loss of enamel just exposing dentine. Defect less than 1 mm deep. -3- 211 people (21 %) - Loss of enamel exposing dentine for more than one third of surface.Loss of enamel and substantial loss of dentine. Defect less than 1-2 mm deep. -4-57 people (5.6%) - Complete enamel loss - pulp exposure - secondary dentin exposure.Pulp exposure or exposure of secondary dentine. Defect more than 2mm deep - pulp exposure - secondary dentine exposure. In this descriptive study showed patients with some degree of tooth wear were around 19% from total patients visited during 1 year of period. Four types of tooth hard tissue wear shown as a different combination, very low percentage was in these types alone. Most of the attrition patients were with mild to moderate degree of enamel loss. This kind of study should be continued to explore harmful dentofacial change