From the buccal aspect the crown is shaped like a pentagon. The tip of the buccal cusp is slightly mesial to the vertical axis line of the tooth. Therefore: The mesial slope of the buccal cusp is shorter than the distal slope. Except for tooth 14, 24 where the tip of the buccal cusp is slightly distal to the vertical axis line. Therefore the mesial slope of the buccal cusp is longer than the distal slope. This mark is characteristic for this tooth only. The buccal surface is convex, with a buccal ridge that is most prominent on the maxillary first premolars.
First Maxillary Premolars
The apical third of the root is usually bent distally. The first maxillary premolar has two roots or a divided root in the apical third in 61%, with buccal and lingual roots. The root of the second premolar is nearly twice as long as the crown, with a root to crown ratio 1, 8/1 which is the highest for any maxillary tooth.
The lingual cusp is shorter than the buccal cusp, more noticeable on the first premolar. The tip of the unworn lingual cusp of both maxillary premolars always bends toward the mesial. This makes it easy to tell right from left. The lingual roots of maxillary first premolars are shorter than the buccal roots. From the proximal side, the crown shape is trapezoid-like. Maxillary first premolars have a prominent mesial depression continuing onto the root! Second premolars do not have such concavity depression.
The distal marginal ridge of both premolars is more cervical in position than the mesial marginal ridge. This phenomenon is true of all posterior teeth, with the exception of the mandibular first premolar. From the occlusal aspect, maxillary premolars are considerably wider faciolingually than mesiodistally. The buccal and lingual triangular ridges extend from the tips of the cusps to the central groove.
Combined, these 2 triangular ridges make up the transverse ridge. The central developmental groove runs mesiodistally across the occlusal surface and ends mesially and distally in the mesial and distal triangular fossa. In the distal triangular fossa, the distal end of the central groove meets the distobuccal and distolingual supplemental or developmental grooves, sometimes forming a distal pit.
The mesial end of the central groove meets the mesiobuccal and monolingual developmental or supplemental grooves, forming a mesial pit in the mesial triangular fossa. An important mark to distinguish first and second premolars is the number of the supplemental grooves. There are fewer supplemental grooves on maxillary first premolars.
Second Maxillary Premolars
On the second premolars, there are many supplementary grooves radiating buccally and lingually from the depth of each triangular fossa. On the first premolar, a mesial marginal groove crosses the mesial marginal ridge. This is one of the distinguishing characteristics of the first premolar with a frequency of 97%.
From the occlusal aspect, the shape of the buccal surface is a wide and inverted V because of the prominent buccal ridge. The lingual portion of the tooth seems to be bent mesially. This asymmetrical occlusal design is a distinguishing feature of first premolars and is not found on second premolars. The second premolars are less angular, more oval shaped and much more symmetrical.
Distal contacts are in the middle third on second premolars, located more lingually than mesial contacts. Just the opposite is true on first premolars with their asymmetry, where the distal contact is more buccal than the mesial contact.