What does a notch at the gum line look like, and is it abrasion or abfraction?

What the drawing is measured from

1. Size: in a clinical study of 171 notches chosen for filling, 91% were 1 to 2 mm deep and 74% had walls meeting at 45 to 135 degrees, so the ordinary wedge is close to a right angle. Aw and colleagues, J Am Dent Assoc 2002. DOI 1
2. Shape: depth to height ratios measured over years in patients were 0.49 to 1.01 for wedges and 0.13 to 0.44 for rounded notches, so a wedge is at most about as deep as it is tall. Sugita and colleagues, a pilot study of 10 notches, J Dent 2017. DOI 2
3. Position: in 50 teeth scanned by micro-CT, the edge of every notch on the crown side lay at or below the junction of enamel and root, which is why none is drawn cut high into the enamel. Hur and colleagues, J Oral Rehabil 2011. DOI 3
4. Face-on: notches seen from the cheek side are crescents, wide in the middle and pointed at both ends, following the gum line. Worawongvasu, electron microscopy of 10 premolars, J Oral Maxillofac Pathol 2021. DOI 4
5. Floor: the floor of a notch is smooth and hard, honey-coloured to dark brown and darkest along its deepest line; fine lines along the walls were seen on wedges, not on rounded notches. Stanusi and colleagues, 27 teeth under the stereomicroscope, Diagnostics 2023. DOI 5
6. Brushing alone: in the laboratory, brushing with paste and no bite produced 9 wedged, 5 mixed and 4 rounded notches in 18 teeth. Litonjua and colleagues, Am J Dent 2004. PubMed 6
7. Acid: on extracted premolars brushed for the same number of strokes, brushing alone made wedges in 94% at a mean angle of 59 degrees; with acid as well, more tooth was lost and the notches were open, at about 145 degrees, none of them a wedge. Denucci and colleagues, Arch Oral Biol 2025. DOI 7
8. Cause: a review of the literature concluded that the shape of a notch does not predict its cause. Wood and colleagues, J Dent 2008. DOI 8
9. Under the notch: in 139 notches scanned by micro-CT, each extra millimetre of depth left about 0.64 mm less dentine over the pulp, because the tooth lays down new dentine behind a notch; that is the darker band drawn beside the pulp. de Abreu and colleagues, J Dent 2026. DOI 9
10. The tooth is an upper second premolar traced from Wheeler's Dental Anatomy (11th edition, Figs 9.17 and 9.20) and scaled to its measurement table: crown 8.5 mm, root 14 mm, 9 mm from cheek to palate. The depth and height of each notch follow the studies above; none is a measurement of one patient.