Tooth in art refers to the grain of canvas or paper. In general, the more tooth, the more rough the texture is.
Tooth is what allows paint, pastel or whatever to bind to the surface.
Tooth and texture are not necessarily interchangeable. Texture is the feel, appearance or consistency of a surface or a substance. Tooth measures how well a medium binds to the surface.
For example, you could have a smooth and bumpy surface which has texture but no tooth. Or you could have a surface with even texture but a high level of tooth.