The crown of the mandibular second premolar is wider buccolingually by 0.5 mm than the mandibular first premolar. Its lingual cusps are more developed, and both marginal ridges are higher. This produces a more efficient occlusion with the maxillary
antagonist. Therefore, a mandibular second premolar functions more like molar than a canine.
There are two common forms which this tooth assumes;
- The three cusp type, which is the most common and appears more angular from the occlusal aspect.
- The two-cusp type appears more rounded from the occlusal aspect.
The single root of the second premolar is longer (by 0.5 mm) than that of the first premolar with developmental groove buccally in many cases.
From the buccal aspect the crown resembles a first premolar in its general shape. It presents shorter buccal cusp than the first premolar with the mesiobuccal and distobuccal cusp riges more rounded and less pointed cusp tip which is
little mesial to the tooth center. The mesial and distal contact areas are nearly at the same level but are broader and placed higher occlusally. The buccal ridge isles prominent that than that of the mandibular first premolar.
The root is longer and
broader mesiodistally than the first premolar and ends in more blunt apex. The single root may show a developmental groove.
- The lingual lobes are developed to a greater degree making the
cusp or cusps longer. In the three cusp type, there are a mesiolingual and a distolingual cusps. The former is the wider and longer of the two cusps. The cusps are divided by a lingual groove.
- In the two cusp type, the single lingual cusp is higher
than on a mandibular first premolar. There is no groove, but a developmental depression is seen distolingually where the lingual cusp ridge joins the distal marginal ridge.
- The lingual surface of the crown of all mandibular second premolars is smooth
and spheroidal, having a bulbous form above the constricted cervical portion.
- The root is much wider lingually than that of the first premolar. This results in less convergence towards lingual. It is smooth and convex.
The second premolar differs from the first from the mesial aspect in the following ways;
- The crown and root are thicker buccalingually than the first premolar.
- The buccal cusp is shorter and its tip located more to the buccal
- The lingual lobe or lobes development is greater. The tip of the lingual cusp is on line with the lingual border of the root.
- The marginal ridge is at right angle to the long axis of the tooth.
- Less of the occlusal surface
may be seen.
- There is no mesio-lingual developmental groove on the crown portion.
- The root is longer and in most cases slightly convex on the mesial surface with a more blunt apex.
- More of the occlusal surface can be seen because the distal marginal ridge is at a lower level than the mesial marginal ridge.
- As a general rule, the crown of all posterior teeth (maxillary and mandibular) are tipped distally to the
long acis of the root. So, much of the occlusal surface may be seen from the distal aspect.
- In the three-cusp type both lingual cusps are seen since the distolingual cusp is shorter than the mesiolingual cusp.
- The root is conical in shape
and may show deeper developmental depression.
In both the two and three-cusp forms, the buccal cusp is similar, however, the outline of each type shows some variations from the occlusal
The occlusal characteristics of the three cusp type:
- It appears square lingual to the buccal cusp ridge. It has three distinct cusps, the buccal cusp is the largest then the mesiolingual cusp. The distolongual cusp is the smallest.
- Each cusp has a well defined triangular ridges separated by deep developmental grooves. These grooves converge in a central pit and from a ‘’Y’’ shape on the occlusal surface. Three pits may be present, a central, a mesial and distal.
- The central pit is located in the center buccolingually and slightly distal to the midway point between the mesial and distal marginal ridges.
- From the central pit, a mesial and distal developmental grooves travel in a mesiobucal and distobuccal
directions respectively ending in the mesialand distal triangular fossae.
- The lingual developmental groove extends lingually between the two lingual cusps and ends on the lilnguall surface of the crown just below the lingual cusps. The mesiolongualcusp
is wider mesiodistally than the distolingual cusp.
- Supplemental grooves and depressions are often seen radiating from the developmental groove.
- The mesial and distal marginal ridges are confluent with the cusp ridges.
characteristics of the two-cusp type as compared with the three-cusp type are:
- The outline of the crown is rounded.
- The lingual surface of the crown is more convex and tapers toward the lingual side (lingual convergence)
mesiolingual and distolingual line angles are rounded.
- There is only one well-developed lingual cusp located directly opposite to th buccal cusp in a lingual direction.
- There is no lingual developmental groove.
A central developmental
groove is seen on the occlusal surface traveling in amesiodistal direction. This groove may be straight and often crescent-shaped. The groove pattern can be either a ‘’U’’ or ‘’H’’ groove pattern, depending on
whether the central developmental groove is straight mesiodistally or curves buccally at its ends. The central groove of the two-cusp from terminates in a mesial and distal fossae. There is usually no central pit, a mesial or distal pit is much more likely.
Usually the two cusp type shows a transverse ridge.
The pulp cavity
- In buccolingual section it resembles that of the mandibular first premolar, but is larger in size, and the roof of the pulp chamber is
pointed to accommodate more than one pulp horn. The lingual pulp horn is smaller than the buccal pulp horn.
- In mesiodistal section it resembles that of the mandibular first premolar except for the added size and length.
- The pulp chamber has
three pulp horns in the three cusp type. The largest is the buccal pulp horn then the mesio lingual then the distolingual.
- In cervical cross section the outline of the pulp cavity follows that of the root and most commonly is rectangular.■