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Maxillary Premolars - BDS First Year Exam Summary

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OVERVIEW (General Points)

• Premolars are succedaneous teeth - they replace the deciduous molars
• There are 4 maxillary premolars (2 on each side): first premolar and second premolar
• FDI notation: 14, 15 (right) and 24, 25 (left)
• Universal notation: 5, 4 (upper right) and 12, 13 (upper left)
• Position: between canine (anteriorly) and first molar (posteriorly)
• Function: tearing and grinding (transitional between canines and molars)

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MAXILLARY FIRST PREMOLAR

Chronology (High-Yield!)

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Crown - Buccal Aspect

• Resembles a maxillary canine from buccal view - but crown is shorter (1.5-2 mm shorter than canine) and narrower mesiodistally
• Two cusps: buccal and lingual (both sharply defined)
• Buccal cusp is ~1 mm longer than lingual cusp
• Mesial slope of buccal cusp is longer than distal slope (opposite of the canine)
• Mesial and distal contact areas are at the same level (unlike canine where they differ)
• Buccal line angles are prominent - crown appears angular
• Buccal cervical ridge present

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Crown - Mesial Aspect (VERY IMPORTANT)

• Mesial concavity (mesial developmental depression) - a characteristic feature that distinguishes maxillary first premolar from the second premolar
• This depression extends from the cervical line onto the mesial root surface
• Mesial marginal developmental groove - another hallmark; groove cuts across the mesial marginal ridge from the occlusal surface onto the mesial surface
• Buccolingual width is greater than mesiodistal width

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Crown - Occlusal Aspect

• Outline is roughly hexagonal (6-sided)
• Widest in the buccal third
• Central developmental groove runs mesiodistally
• Mesial triangular fossa and distal triangular fossa present
• Buccal cusp is slightly offset toward the distal
• Two major cusps: buccal and lingual, separated by the central groove
• Marginal ridges are in a horizontal plane (part of the occlusal surface - unlike incisors/canines where they are part of the lingual surface)

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Crown - Lingual Aspect

• Lingual cusp is shorter and narrower than buccal cusp
• Crown tapers toward the lingual

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Root (HIGH YIELD!)

• Most maxillary first premolars have TWO roots (bifurcated) - buccal and lingual (palatal)
• This is the only premolar that normally has two roots
• Buccal root is larger and longer than the palatal root
• Even when only one root is present, two pulp canals are usually found - key exam point
• Single-rooted form has a prominent mesial root groove (giving appearance of root trying to divide)
• Root trunk = area between cervical line and bifurcation
• Bifurcation = junction of buccal and lingual roots

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Pulp Cavity

• Two pulp horns (one for each cusp)
• Two root canals (one for each root)
• If single root: usually still two canals, often combining into one apical foramen
• Rarely: one canal in a single-rooted tooth

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MAXILLARY SECOND PREMOLAR

Chronology

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Crown

• Slightly smaller than maxillary first premolar overall
• Buccal cusp is shorter and less pointed than in first premolar
• Cusps are more equal in size (buccal and lingual cusps are more symmetrically sized) - key differentiating feature from first premolar
• Markings (grooves, ridges) are less defined than in first premolar
• No mesial concavity - smooth mesial surface (vs. first premolar which has mesial depression)
• No mesial marginal groove cutting across the marginal ridge
• More efficient as a grinding tooth - functions like a molar
• Occlusal surface: cusps articulate with opposing teeth more efficiently

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Root (HIGH YIELD!)

• Usually ONE root (single rooted) - main difference from first premolar
• Root is longer than that of the first premolar
• Occasionally two roots can occur - not uncommon
• Root grooves present (less prominent than first premolar)

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Pulp Cavity

• Usually one root canal (corresponding to single root)
• Two root canals if two roots present

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KEY DIFFERENCES: First vs Second Premolar (Exam Favourite!)

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RELATIONS & CLINICAL IMPORTANCE

• Maxillary first premolar is close to the maxillary sinus (floor) - extractions can lead to oroantral fistula
• The posterior superior alveolar nerve (branch of maxillary nerve, V2) supplies molar and premolar teeth
• The middle superior alveolar nerve supplies premolar teeth primarily
• Important landmark for infraorbital nerve block and posterior superior alveolar nerve block
• The junction of first molar and second premolar is a landmark for the maxillary nerve approach

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INNERVATION

• Maxillary premolars are supplied by the posterior superior alveolar nerve and middle superior alveolar nerve (branches of the maxillary division of trigeminal nerve, CN V2)

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BLOOD SUPPLY

• Posterior superior alveolar artery (branch of maxillary artery) - descends on the infratemporal surface of the maxilla to supply molar and premolar teeth, adjacent bone, and maxillary sinus

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ADDITIONAL EXAM POINTS

1. Premolars are the only permanent teeth with no deciduous predecessors - FALSE; they replace deciduous molars. Premolars are succedaneous to deciduous molars.
2. Maxillary first premolar is the only premolar with 2 roots as a common occurrence
3. Even with a single root, 2 canals are almost always present in maxillary first premolar
4. Buccal root of maxillary first premolar is larger and longer than palatal root
5. The mesial concavity of the first premolar makes it the most difficult to clean and predisposed to periodontal disease on the mesial surface
6. Crown is wider buccolingually than mesiodistally in both maxillary premolars
7. Maxillary premolars are shorter in crown height than maxillary canines
8. Root length of maxillary premolars equals root length of molars

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Anatomy of Maxillary Premolars

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General Introduction

• FDI notation: 14 & 15 (upper right), 24 & 25 (upper left)
• Location: Between the maxillary canine anteriorly and the maxillary first molar posteriorly
• Function: Tearing and grinding - transitional between canines (tearing) and molars (grinding)
• Crowns are shorter than maxillary canines but longer than maxillary molars
• Crown is wider buccolingually than mesiodistally (a posterior tooth characteristic)
• Marginal ridges lie in a horizontal plane, forming part of the occlusal surface (unlike anterior teeth where marginal ridges are part of the lingual surface)

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MAXILLARY FIRST PREMOLAR

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Chronology

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Measurements (Wheeler's)

Note: Buccolingual (9 mm) > Mesiodistal (7 mm) - wider BL than MD

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Crown Anatomy - Surface by Surface

1. Buccal (Facial) Aspect

• Resembles the maxillary canine from the buccal view - but differences:
  • Crown is shorter by 1.5-2 mm than the canine
  • Crown is narrower mesiodistally than the canine
  • Contact areas mesially and distally are at the same level (in canine, mesial contact is more cervical)
  • Mesial slope of buccal cusp is longer than the distal slope (opposite of canine)
• Crown is angular with prominent buccal line angles
• Buccal cusp is tipped slightly toward the distal
• Shoulders: Prominent
• Buccal cervical ridge present at the cervical third
• Developmental depressions on either side of the buccal ridge demarcate the three buccal lobes (mesiobuccal, central buccal, distobuccal)
• Roots are 3-4 mm shorter than those of the maxillary canine but the buccal root outline resembles the canine root

2. Lingual Aspect

• Gross outline is the reverse of the buccal aspect
• Lingual cusp is shorter and narrower than the buccal cusp
• Crown tapers toward the lingual - lingual surface is narrower than buccal
• Lingual cusp tip is offset toward the mesial
• From lingual aspect, the buccal profile is visible (unlike the second premolar where the buccal profile is not visible from lingual - a siding aid)
• Lingual surface is smooth and convex

3. Mesial Aspect (Most Distinctive Surface)

• Mesial developmental depression (concavity) - a hallmark feature of the first premolar; a hollow or depression on the mesial surface of the crown and root
• Mesial marginal developmental groove - a groove that crosses the mesial marginal ridge from the occlusal surface onto the mesial surface (cuts across the marginal ridge)
• Mesial root depression present on root surface
• Cervical line shows more curvature on the mesial than on the distal
• Both buccal and lingual cusp tips are centered over the root
• Crown outline is roughly rhomboidal from this view

4. Distal Aspect

• Similar to mesial view but:
  • No groove crosses the distal marginal ridge (no distal marginal groove - or much less prominent)
  • No developmental depression on the distal surface
  • Crown surface appears more rounded and smooth
  • Cervical line is less curved than on the mesial
  • Some specimens show a faint distal marginal groove but it is shallower than the mesial marginal groove

5. Occlusal Aspect

• Outline form: Hexagonal (6-sided)
• Crown is widest in the buccal third and tapers toward the lingual
• Central developmental groove (CDG) runs mesiodistally across the occlusal surface
• Mesial triangular fossa (MTF) - depression on the mesial side where the mesiobuccal developmental groove lies
• Distal triangular fossa (DTF) - depression on the distal side where the distobuccal developmental groove lies
• Mesiobuccal developmental groove and distobuccal developmental groove radiate from the central groove
• Supplemental grooves: Usually NOT present (vs. second premolar which commonly has many)
• Lobes: 4 developmental lobes (3 buccal, 1 lingual)
• 2 pulp horns corresponding to 2 cusps
• Buccal triangular ridge and lingual triangular ridge meet to form the transverse ridge
• Marginal ridges: mesial and distal marginal ridges are sharp and prominent

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Root

• Most commonly 2 roots (bifurcated) - one buccal, one palatal (lingual)
• The maxillary first premolar is the only premolar that normally has two roots
• Buccal root is larger and longer than the palatal root
• Root trunk = area between the cervical line and the point of bifurcation
• Single-rooted form also occurs; the single root shows prominent longitudinal grooves (especially on the mesial surface) - "root trying to divide itself"
• Root grooves: Present on both buccal and lingual aspects, most prominent on the mesial
• Root length equals that of the molars

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Pulp Cavity

• Pulp chamber: Well-defined, with a distinct pulp chamber before the canals divide
• 2 pulp horns - buccal pulp horn (larger, under buccal cusp tip) and lingual pulp horn (smaller, under lingual cusp tip)
• 2 root canals in most teeth: buccal root canal and lingual (palatal) root canal
• Even when only 1 root is present, 2 pulp canals are usually still found - sometimes fusing to a single apical foramen
• Rarely: only 1 canal in a single-rooted specimen

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MAXILLARY SECOND PREMOLAR

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Chronology

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Measurements (Wheeler's)

Overall measurements are similar to the first premolar, but the second premolar has variations in crown features

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Crown Anatomy - Surface by Surface

1. Buccal (Facial) Aspect

• Similar general appearance to the first premolar
• Buccal cusp is shorter and less pointed than in the first premolar
• Cusp ridges are similar in length (mesial and distal cusp ridges are more equal)
• Buccal cusp is NOT tipped toward the distal (unlike the first premolar)
• Shoulders are narrow (first premolar shoulders are prominent)
• Markings (grooves, ridges, developmental depressions) are less defined than in the first premolar
• Contact areas: both mesial and distal contacts in the middle third

2. Lingual Aspect

• Buccal profile is NOT visible from the lingual view (unlike first premolar) - a useful siding feature
• Lingual cusp is more nearly the same size as the buccal cusp
• Cusps are more equal in height - less difference between buccal and lingual cusp lengths

3. Mesial Aspect

• No mesial developmental depression (concavity) - crown surface is convex on the mesial (key differentiating feature from first premolar)
• No mesial marginal developmental groove crossing the marginal ridge
• Mesial root depression is present (shallow groove on root surface)
• Buccal and lingual cusp tips are shorter, with greater distance between them - giving a wider buccolingual occlusal surface

4. Distal Aspect

• No outstanding variation from mesial aspect
• No distinct groove crossing the distal marginal ridge

5. Occlusal Aspect

• Outline form: Ovoid (vs. hexagonal in first premolar)
• Central groove is short (vs. long in first premolar)
• Many supplemental grooves often present - giving the occlusal surface a wrinkled appearance
• Lobes: 4 developmental lobes
• 2 pulp horns
• Cusps are more nearly equal in size - the tooth functions more efficiently as a grinding tooth
• Contact areas: centered at the middle third both mesially and distally

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Root

• Usually 1 root (single-rooted) - the major difference from the first premolar
• Root is longer than that of the first premolar
• Occasionally may have 2 roots - not uncommon
• No distinct root grooves (vs. first premolar with prominent mesial groove)
• Root tapers to a pointed apex

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Pulp Cavity

• Usually 1 root canal (when single root)
• 2 pulp horns (one buccal, one lingual)
• When 2 roots present: 2 root canals
• Pulp cavity is less complex than the first premolar

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KEY COMPARISON TABLE: First vs. Second Maxillary Premolar

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NERVES & BLOOD SUPPLY

Innervation

• Middle superior alveolar nerve (MSAN) - primary supply to upper premolars; a branch of the maxillary nerve (V2) that descends along the lateral wall of the maxillary sinus, ending in branches that unite with the superior dental plexus and supply rami to the upper premolar teeth
• Posterior superior alveolar nerve (PSAN) - also contributes
• Anterior superior alveolar nerve - minor contribution
• All branches of CN V2 (maxillary division of trigeminal nerve)

Blood Supply

• Posterior superior alveolar artery (branch of the third part of the maxillary artery in the pterygopalatine fossa) - descends on the infratemporal surface of the maxilla to supply molar and premolar teeth, adjacent bone, and the maxillary sinus

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RELATIONS

• Roots of maxillary premolars are in close proximity to the floor of the maxillary sinus - clinically important in extractions (risk of oroantral communication)
• The mental foramen of the mandible is located approximately opposite the mandibular first premolar (not maxillary, but a common association question)
• The second premolar-first molar junction is a landmark for the maxillary nerve block approach

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