The Permanent Mandibular Premolars
There are four mandibular premolars, two in each quadrant. It is the first posterior tooth in the lower jaw. They are located between the canine and the molars, the first premolar being distal to the canine and the second premolar distal to the first premolar.
Table of Contents
Development:
First premolar – develops from four lobes
Second premolar – in most instances, develops from five lobes (three buccal and two lingual)
Read And Learn More: Oral Anatomy Notes
Mandibular first premolar:
- Resembles a small canine as the buccal cusp occludes with the maxillary premolar
- Large, well-developed buccal cusp
- Small, nonfunctioning lingual cusp
- Supplements the mandibular canine in function
Mandibular second premolar:
- Resembles a small molar tooth as the lingual cusps are well formed and it occludes well with the antagonist
- Three well-developed cusps – one large buccal and two small lingual cusps.
- Works along with the mandibular first molar. The similarities between the mandibular first premolar and the mandibular second premolar are given in Box.
Similarities B Etween The Mandib Ular First Premolar And Mandib Ular Canine:
- Buccolingual dimensions are the same as the canine.
- Long, well-developed and sharp buccal cusp occluding with the antagonist.
- Lingually sloping occlusal surface.
- Distobuccal cusp ridge is longer than the mesiobuccal cusp ridge.
- Occlusal outline is similar to the incisal aspect of the canine.
Similarities B Etween The Mandib Ular First Premolar And Mandib Ular Second Premolar:
- Crown and root outline from the buccal aspect is similar
- Contact areas are located at the same level
- Curvature of the cervical line is the same on the mesial and distal aspect
The Mandibular First Premolar
The mandibular first premolar shares a few features with the canine and second premolar which are mentioned in Table below. The morphology of this tooth will be described from the buccal, lingual, mesial, distal and occlusal aspects. The nomenclature, chronology and the measurement of the mandibular canine are given in Tables.
Nomenclature: Mandibular First Premolar:
Mandibular First Premolar: Chronology and Measurements:
Buccal Aspect:
Buccal Aspect – Features of the crown:
Buccal Aspect – Shape and surface:
- Crown is trapezoidal and bilaterally symmetrical.
- Mesiodistal dimension of the crown is narrower at the cervix than at the contact areas.
- Middle buccal lobe is well developed, resulting in a large pointed buccal cusp; developmental depressions are seen on either side of the middle buccal lobe.
- The buccal ridge extends from the cervical line to the cusp tip.
- The surface is
- More convex at the cervical and middle third than the maxillary first premolar
- Smooth with no developmental grooves
Buccal Aspect – Mesial outline:
- The mesial outline is slightly concave or straight from the cervical line to the mesial contact area
- The mesial contact area is at the junction of the middle and occlusal third
- The mesial slope of the buccal slope has a concavity which might be obliterated due to wear.
Buccal Aspect – Distal outline:
- The distal outline is slightly concave from the cervical line to the distal contact area which is broad.
- The distal contact area is located at the junction of the middle and occlusal third.
- The distal slope might also exhibit a concavity.
Buccal Aspect – Cusp tip:
- The buccal cusp tip is pointed and often present mesial to the centre and formed by the union of the mesial and distal cusp ridges that meet at an obtuse angle.
- The distal slope is longer than the mesial slope.
Buccal Aspect – Cervical line:
- The cervical line is curved towards the root.
Buccal Aspect – Features of the root:
- The root is 3–4 mm shorter than the mandibular canine.
- The mesial outline is straight till the middle third and then tapers to the apex.
- The distal outline is slightly convex till the middle third and then tapers to the apex.
Lingual aspect:
Lingual aspect – Features of the crown:
- The cervical portion of the crown is narrow but the contact areas and marginal ridges extend beyond the narrow cervical portion.
- Due to the lingual taper of the crown, most of the mesial and distal surface is seen.
- The occlusal surface of the crown tapers towards the short lingual cusp in a cervical direction, thus most of the occlusal surface is seen.
- The lingual cusp is short, poorly developed with a pointed tip that is in line with the buccal triangular ridge.
- Mesiolingual developmental groove:
- The mesiolingual developmental groove is a characteristic feature of the mandibular first premolar.
- The mesiolingual developmental groove demarcates the mesiobuccal lobe and lingual lobe (present between the mesial slope of the lingual cusp and the mesial marginal ridge), present near the mesiolingual line angle extending into the mesial triangular fossa.
Lingual aspect – Features of the root:
- The root is narrow on the lingual side.
- A narrow ridge may be present along the length of the root.
- The root tapers evenly from the cervical third to the apex.
- Developmental depressions may be seen.
Mesial aspect:
Mesial aspect Features of the crown:
Mesial aspect Shape and surface:
- The crown is roughly rhomboidal (all the mandibular posterior teeth are rhomboidal from the mesial aspect).
- The surface is smooth except for the presence of the mesiolingual developmental groove.
- The surface at the mesial contact area is convex with the mesial contact area in line with the centre of the buccal cusp tip; a concavity is seen between the contact area and the cervical line.
- The outline of the lingual lobe is convex. The crown is projected in a lingual direction and outside the confines of the root. This is termed as the lingual overhang.
Buccal and lingual outline:
- The buccal outline is convex from the cervical line to the buccal cusp tip.
- The buccal crest of curvature is located at the junction of middle and cervical third.
- The lingual outline is less convex than the buccal outline.
- The crest of curvature approaches the middle third of the crown.
Occlusal outline:
- The buccal cusp tip is placed higher than the lingual cusp tip.
- It is often in line with the centre of the root; or may also be a little buccal to the centre.
- The lingual cusp tip is in line with the lingual border of the root.
- The lingual cusp tip is two-third the distance from the cervical line buccally to the tip of the buccal cusp.
- The mesiobuccal lobe is well developed and prominent; it forms the mesial contact area and the mesial marginal ridge.
- The mesial marginal ridge is lingually inclined in a cervical direction.
The lingual border of the mesial marginal ridge joins the developmental depression mesiolingually which harbours the mesiolingual developmental groove.- The mesial marginal ridge is parallel to the slope of the buccal triangular ridge.
Cervical line:
The cervical line is regular and curves occlusally with the crest being in the centre buccolingually.
Cervical line Features of the root:
- Buccal outline – convex
- Lingual outline – straight
- The root tapers from the cervix ending in a pointed apex in line with the buccal cusp tip.
- The surface is smooth and has flat with a deep developmental groove extending along the length of the root.
Distal aspect:
The distal aspect of the mandibular first premolar is similar to the mesial aspect with the following exceptions:
- The distal marginal ridge is placed higher and perpendicular to the crown–root axis.
- No developmental groove is present on the distal marginal ridge and thus the surface is smooth and convex.
- Distal contact area is in the centre buccolingually and mesiodistally too. It is broader than the mesial contact area.
- A concavity is present between the cervical line and the contact area.
- The curvature of the cervical line may be less or the same as on the mesial aspect.
- The root surface is convex with a shallow developmental depression on the centre
Occlusal aspect:
The occlusal form is diamond shaped and similar to the incisal aspect of the mandibular canine. Some of the mandibular first premolars might resemble the mandibular second premolar and have a circular form.
Features of the crown common to the mandibular first premolar:
- Prominent buccal ridge
- Well-developed middle buccal lobe that makes up majority of the crown
- More of the buccal surface and little of the lingual surface is seen
- Prominent and rounded mesiobuccal and distobuccal line angles
- Broad curvatures lingual to the buccal line angles
- The crown has a triangular outline due to the lingual convergence with the buccal cusp ridges being the base of the triangle and lingual cusp being the apex
- Small lingual cusp
- Well-developed marginal ridges
- Heavy buccal triangular ridge and small lingual triangular ridge
Cusps:
There are two cusps:
- Buccal (larger)
- Lingual (smaller)
Fossae:
Two fossae are present. They are the mesial and distal fossae and are irregular in shape.
- Mesial – linear in shape
- Distal – circular shaped
Groove:
Mesial developmental groove – The mesial developmental groove is continuous with the mesiolingual developmental groove and crosses the mesiolingual surface.
Distal developmental groove – The distal developmental groove is crescent shaped and may be seen extending from the distal fossa. The features that can help in identification of the mandibular first premolar.
Features To Identify The Mandib Ular First Premolar:
- Mesiolingual developmental groove
- Lingual overhang of the lingual cusp
- Buccal cusp is in line with the centre of the root from the proximal aspect
Differentiation Between The Right And Left Mandibular First Premolar
- Presence of the mesiolingual developmental groove
Development And Landmarks Crown And Root Of The Mandibular First Premolar
Variations And Developmental Anomalies
- Bifurcated root
- Dens evaginatus or Leong’s premolar
The Permanent Mandibular First Premolars Synopsis
Buccal aspect:
Buccal aspect Crown:
- Crown is trapezoidal and bilaterally symmetrical.
- The surface is more convex at the cervical and middle third than the maxillary first premolar and smooth with no developmental grooves.
- The mesial contact area is at the junction of the middle and occlusal third.
- The distal contact area is located at the junction of the middle and occlusal third.
- The buccal cusp tip is mesial to the centre and formed by the union of the mesial and distal cusp ridges that meet at an obtuse angle.
- The distal slope is longer than the mesial slope.
Buccal aspect Root:
- It is 3–4 mm shorter than the mandibular canine.
Lingual aspect:
Lingual aspect Crown:
- The cervical portion of the crown is narrow, but the contact areas and marginal ridges extend beyond the narrow cervical portion.
- The occlusal surface of the crown tapers towards the short lingual cusp in a cervical direction.
- The lingual cusp is short, poorly developed with a pointed tip that is in line with the buccal triangular ridge.
- Mesiolingual developmental groove demarcates the mesiobuccal lobe and lingual lobe, present near the mesiolingual line angle extending into the mesial triangular fossa.
Lingual aspect Root:
- Narrow on the lingual side; a narrow ridge may be present along the length of the root
Mesial aspect:
Mesial aspect Crown:
- The crown is roughly rhomboidal and the surface is smooth except for the presence of the mesiolingual developmental groove.
- The crown is projected in a lingual direction and outside the confines of the root and is termed as the lingual overhang.
- The buccal crest of curvature is located at the junction of middle and cervical third.
- The lingual crest of curvature is located near the middle third of the crown.
- The buccal cusp tip is placed higher than the lingual cusp tip and is often in line with the centre of the root.
- The lingual cusp tip is in line with the lingual border of the root.
- The lingual cusp is two-third the distance from the cervical line buccally to the tip of the buccal cusp.
- It is regular and curves occlusally with the crest being in the centre buccolingually.
Mesial aspect Root:
- The root tapers from the cervix ending in a pointed apex in line with the buccal cusp tip.
Distal aspect:
- The distal aspect of the mandibular first premolar is similar to the mesial aspect with the following exceptions:
- The distal marginal ridge is placed higher and perpendicular to the crown–root axis.
- No developmental groove is present, and thus the surface is smooth and convex.
- Distal contact area is in the centre buccolingually and mesiodistally too. It is broader than the mesial contact area.
Occlusal aspect:
- The occlusal form is diamond shaped and similar to the incisal aspect of the mandibular canine.
- Features of the crown common to the mandibular first premolar:
- There are two cusps, i.e. buccal (larger) and lingual (smaller)
- Two fossae are present. They are the mesial and distal fossae.
- Mesial developmental groove is continuous with the mesiolingual developmental groove and crosses the mesiolingual surface.
- Distal developmental groove is crescent shaped and may be seen extending from the distal fossa.
The Permanent Mandibular Second Premolar
The permanent mandibular second premolar erupts distal to the mandibular first premolar. It resembles the first premolar from the buccal aspect and is larger and more well developed.
Permanent Mandibular Second Premolar are two types of this tooth:
1. The three-cusp type
- More common
- Has one buccal and two lingual cusps
- More angular from the occlusal aspect
2. The two-cusp type
- More rounded from the occlusal aspect
The morphology of this tooth will be described from the buccal, lingual, mesial, distal and occlusal aspects.
The nomenclature, chronology and the measurement of the mandibular canine are given in Tables.
Nomenclature: Mandibular Second Premolar:
Mandibular Second Premolar: Chronology and Measurements:
Features of the crown:
Shape and surface:
In comparison to the first premolar, the surface is more convex.
Mesial and distal outline:
- The mesial outline is convex from the cervical line to the contact area and then straight till the cusp tip.
- The mesial contact area is broad and located at the junction of the middle and occlusal third.
- The distal outline is more convex than the mesial outline.
- The distal contact area is located more cervical to the mesial contact area.
Occlusal outline:
- The buccal cusp tip is formed by the union of the mesial and distal cusp slopes.
- The angle between the two slopes is less than in the first premolar.
- The distal slope is longer than the mesial cusp slope.
- The buccal cusp is shorter than in the first premolar.
Cervical line: The cervical line is curved towards the root.
Features of the root:
- The root is wider mesiodistally along the entire length and the apex is more blunt than in the first premolar.
Lingual aspect:
The variation in the lingual aspect from the first premolar is as follows:
- The surface of the crown is smooth and spheroidal.
- The cervical part of the crown is constricted.
- Longer lingual cusps/cusp due to well-developed lingual lobes.
- Lesser lingual convergence.
- A part of the buccal portion of the occlusal surface is seen as the lingual cusp is shorter than the buccal cusp.
- Three-cusp type – There are two lingual cusps.
- The mesiolingual and the distolingual cusp.
- The mesiolingual cusp is larger and longer than the distolingual cusp with the lingual groove present in between the two cusps and centred over the root.
- Two-cusp type – This type does not have a groove but a developmental depression at the junction of the lingual cusp ridge and the distal marginal ridge might be present.
- The root is lesser in width.
- The degree of lingual convergence is less, and thus, lesser of the mesial and distal aspects is seen.
Mesial aspect:
Features of the crown:
Shape and surface:
- The buccolingual diameter of the crown is more than the first premolar.
- The crown is lingually inclined.
Buccal and lingual outline:
- The buccal outline
- It is less convex than the first premolar from the cervical line to the buccal cusp tip.
- The buccal crest of curvature is located at the junction of middle and cervical third.
- The lingual outline
- It is less convex than the buccal outline.
- The crest of curvature is located near the middle third of the crown.
Occlusal outline:
- The buccal cusp is shorter and not near the centre of the root.
- The lingual lobe is well developed as compared to the mandibular first premolar.
- The marginal ridge is perpendicular to the long axis of the tooth.
Features of the root:
In comparison to the first premolar
- The root is longer.
- The apex is more blunt.
Distal aspect:
It is similar to the mesial aspect with the following exceptions:
- Most of the occlusal surface is seen due to the distal marginal ridge being lower than the mesial marginal and the crown being tilted distally in relation to the long axis of the crown of the tooth.
Occlusal aspect:
Occlusal Surface of the Mandibular Second Premolar:
Three-cusp type:
- The three-cusp type mandibular second premolar when well developed is square in shape, lingual to the buccal cusp ridges. The buccal cusp is the largest cusp, the mesiolingual being the next and the distolingual being the smallest.
- The triangular ridges are well formed and separated by deep developmental grooves.
- The grooves converge in the central pit to form a Y shape on the occlusal surface, and thus can be referred to as the Y-shaped groove pattern.
- The central pit is located halfway between the buccal cusp ridge and the lingual margin of the occlusal surface, and slightly distal to the centre of the tooth mesiodistally.
- The mesial developmental groove and the distal developmental groove start from the central pit and end in the mesial triangular fossa and distal triangular fossa, respectively. The lingual developmental groove between the two lingual cusps is distal to the centre of the crown, as the mesiolingual cusp is wider than the distolingual cusp.
- It extends on the lingual surface and ends below the convergence of the lingual cusp ridges.
- Supplementary grooves radiating from the developmental grooves are seen.
Two-cusp type:
- The two-cusp type is more round in shape because of the outline being rounded lingual to the buccal cusp ridges. A little lingual convergence is seen and rounded mesiolingual and distolingual angles are observed.
- One buccal cusp and a well-developed lingual cusp opposite to it are present.
- The central developmental groove extends in a mesiodistal direction and might be straight or crescent shaped.
Two groove patterns are observed:
- U pattern – The U is formed by the grooves that extend towards the buccal aspect, central groove, mesial and distal pits.
- H pattern – The grooves extend towards the lingual aspect in addition to the grooves in the U pattern.
The features that can help in identification of the mandibular second premolar are given in Box.
Features To Identify The Mandib Ular Second Premolar:
- It might have three cusps
- Y-shaped groove pattern in the three cusp form
- U- or H-shaped groove pattern in the two cusp form
- Larger mesiolingual cusp and smaller distolingual cusp
Differentiation Between The Right And Left Mandibular First Premolar
- Mesial slope of the buccal cusp is shorter than the distal slope.
- In the three-cusp type, the mesiolingual cusp is the largest lingual cusp.
Development And Landmarks Crown And Root Of The Mandibular Second Premolar
Variations And Developmental Anomalies
- Long or short root
- Dens evaginatus
The Permanent Mandibular Second Premolars Synopsis
Buccal aspect:
Crown:
- The mesial contact area is broad and located at the junction of the middle and occlusal third.
- The distal contact area is located more cervical to the mesial contact area.
- The distal slope is longer than the mesial cusp slope.
- The buccal cusp is shorter than in the first premolar.
Root:
- The root is wider mesiodistally and the apex is more blunt than in the first premolar.
Lingual aspect:
- The surface of the crown is smooth and spheroidal.
- The cervical part of the crown is constricted.
- Lesser lingual convergence.
- There are two lingual cusps, i.e. the mesiolingual and the distolingual cusp.
- Two-cusp type – This type does not have a groove but a developmental depression at the junction of the lingual cusp ridge and the distal marginal ridge might be present.
Mesial aspect:
Crown:
- The buccolingual diameter of the crown is more than the first premolar.
- The crown is lingually inclined.
- The buccal crest of curvature is located at the junction of middle and cervical third.
- The lingual crest of curvature is located near the middle third of the crown.
Root:
- The root is longer than in the first premolar.
Distal aspect:
- It is similar to the mesial aspect with the following exceptions:
- Most of the occlusal surface is seen due to the distal marginal ridge being lower than the mesial marginal and the crown being tilted distally in relation to the long axis.
Occlusal aspect:
- The pattern is U pattern: The U is formed by the grooves that extend towards the buccal aspect mesial and distal pits and the central groove.
- H pattern: There are grooves extending towards the lingual aspect in addition to the grooves in the U pattern.
- Y pattern: The Y shape is formed by the convergence of the mesial developmental groove, distal developmental groove and the lingual groove converge in a central pit.
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