Smooth, flat, approximately trapezoidal

Mesial edge long and straight Distal margin short and protruding Curved neck edge Straight incisal edge

The mesial incisal angle is nearly right, and the distal incisal angle is slightly rounded and blunt; 2 developmental grooves; high point of appearance: labial cervical ridge

Shaped like lip surface, narrower

Incisal crest: straight Mesial marginal ridge: long and straight Distal marginal ridge: short, rounded process Tongue protuberance: large and prominent

Tongue fossa: wide and deep High point of appearance: lingual protuberance

triangle The mesial surface is large and flat, the distal surface is small and protruding The mesial curvature is larger and the distal neck curvature is smaller. Mesial contact area: cut 1/3 of the mesial angle; distal contact area: cut 1/3 of the distal angle

The labial side is flatter and curved - the incisal edge Lingual round process - incisal ridge Proximal view: the incisal ridge is located on the labial side of the long axis of the tooth

Narrow, short, rounded The mesial incisal angle is acute and the distal incisal angle is arc-shaped. Neck margin significantly narrowed The developmental groove is not obvious

Approximate triangle The marginal ridge is more obvious than the maxillary central incisor The tongue protuberance is more prominent The tongue fossa is narrow and deep, with a "V" shape

long and narrow triangle The mesial surface is wider and straight, contact area: cut 1/3 of the mesial angle Small round protrusion on the distal surface, contact area: cut 1/3 of the distal angle The mesial neck curvature is greater than the distal neck curvature

The distal lingual inclination is greater than that of the maxillary central incisors

The mesial incisal angle is sharp and the distal incisal angle is blunt (distinguish between left and right) The developmental groove is more obvious than that of the mandibular central incisor

The tongue protuberance is narrow The incisal ridge, marginal ridge, and lingual fossa are not obvious

long and narrow triangle, The mesial surface is large and flat, contact area: cut 1/3 of the mesial angle The distal surface is small and protruding, contact area: cut 1/3 of the distal angle

The incisal ridge slopes from mesial to distal and lingually Proximal view: the incisal ridge is located on the long axis of the tooth or slightly lingual

Long and narrow trapezoid, smooth and flat Nuchal diameter > mesial and distal diameter (obvious) The incisal edge is straight and the neck edge is slightly curved. The mesial and distal edges are symmetrical, and the mesial and distal incisal angles are equal (difficult to distinguish left and right) High point of appearance: Labial cervical ridge Labial cervical ridge and developmental groove are not obvious

The tongue fossa is shallow and not obvious The incisal ridge and mesial and distal marginal ridges are not obvious Tongue process is smaller Outward high point: lingual protuberance

long and narrow triangle The curvature of the tooth neck is small, and the mesial is larger than the distal. Mesio-distal contact area: cut 1/3 of the mesial angle

Straight, thin, symmetrical Proximal view: the incisal ridge is located on the long axis of the tooth or slightly lingual