- At screening a minimum of 20 natural teeth and at least two accessible, non-adjacent teeth (incisors, canines or pre-molars) preferably in different quadrants with a signs of facial/cervical gingival recession and/or signs of erosion or abrasion (EAR),tooth with modified gingival index (MGI) score =0 adjacent to the test area (exposed dentine) only and a clinical mobility of ≤1 and tooth with signs of sensitivity measured by qualifying evaporative air assessment (Y/N response).