Table 2.

Tooth Wear Index (TWI) according to Smith and Knight.

TWI	Tooth Surface	Criterion
0	Buccal/Lingual/Occlusal/Incisal Cervical	No loss of enamel surface characteristics. No loss of crown contours.
1	Buccal/Lingual/Occlusal/Incisal Cervical	Loss of enamel surface characteristics. Minimal loss of crown contours.
2	Buccal/Lingual/Occlusal	Loss of enamel exposing dentine for less than one third of examined surface.
	Incisal	Loss of enamel just exposing dentine.
	Cervical	Defect less than 1 mm deep.
3	Buccal/Lingual/Occlusal	Loss of enamel exposing dentine for more than one third of examined surface.
	Incisal	Loss of enamel and substantial loss of dentine.
	Cervical	Defect 1–2 mm deep.
4	Buccal/Lingual/Occlusal	Complete enamel loss or secondary dentin exposure or pulp exposure.
	Incisal	Exposure of pulp or secondary dentine.
	Cervical	Defect more than 2 mm deep or pulp exposure or secondary dentine exposure.