Module Four: Posterior Teeth – Premolars (Vocabulary Flashcards)

Posterior Teeth: Premolars Overview

• Premolars succeed primary molars; there are eight total premolars in the permanent dentition (2 in each quadrant).

• They erupt anterior to permanent molars.

• All four premolar teeth develop from four lobes of development: 3 facial cusps and 1 lingual cusp.

• Variation: the mandibular second premolar can present a 3-cusp variety (1 facial cusp and 2 lingual cusps) that develops from 5 lobes.

• In summary: 2 premolars per quadrant; developmental lobes and cusp patterns influence morphology and function.

General Concepts and Key Characteristics

• Maxillary premolars have larger lingual cusps than mandibular premolars.

• Mandibular premolars have small/afunctional cusps (don’t function in occlusion).

• Premolar crowns and roots are shorter than canines.

• Root bifurcation incidence:

  • Maxillary first premolar bifurcated ~60 ext{\%} of the time.

  • Maxillary second premolar bifurcated ~25 ext{\%} of the time.

  • Mandibular premolars rarely bifurcated.

• Almost all premolar roots have proximal root concavities, even if not bifurcated.

Maxillary Premolars

Maxillary First Premolar

• Universal numbers: 5,\;12.

• Eruption: 10-11\text{ yrs}.

• Root completion: 12-13\text{ yrs}.

• Cusps: Buccal and Lingual cusps; Buccal cusp slightly longer than Lingual.

• Root anatomy: Usually has 2 roots (1 buccal, 1 lingual). If a single root, it may still have 2 canals; longitudinal grooves on mesial (M) and distal (D) surfaces of the root.

• Height of contour (HOC): M\text{-}D\text{ junction of middle and occlusal third},\; F\text{ cervical third},\; L\text{ middle third}.

• Facial surface: resembles maxillary canine but crown is shorter (CEJ to cusp tip) and narrower mesio-distally; Facial cusp tip is distal to the midline of the tooth.

• Key characteristics:

  • Mesial marginal groove crosses the occlusal surface onto the mesial surface.

  • Mesial developmental depression around the CEJ (a slight depression mainly on the root).

  • Occlusal anatomy: Facial cusp larger; Lingual cusp more pointed; central groove; facial/lingual cusp ridges run from cusp tips to the central groove.

Maxillary Second Premolar

• Universal numbers: 4,\;13.

• Eruption: 10-12\text{ yrs}.

• Root completion: 12-14\text{ yrs}.

• Cusps: Buccal and Lingual cusps; cusps are more equal in length and more rounded (resemble the first premolar but not as well defined).

• Root anatomy: Has a single root, slightly longer than the first premolar.

• Pulp: 1 root / 1 pulp canal; longitudinal grooves on M and D of the root.

• Height of contour (HOC): M\text{-}D\text{ junction of middle and occlusal third},\; F\text{ cervical third},\; L\text{ middle third}.

• Cusp alignment: Facial and Lingual cusps are more converged toward the middle of the tooth; occlusal surface is not as broad.

• Occlusal anatomy: Shallow; more supplemental grooves giving the occlusal a wrinkled appearance.

• Crown shape: Still more oval like the 1st premolar.

• Developmental depressions: No developmental depression on the mesial; no developmental depression on the root noted.

Similarities and Differences: Maxillary Premolars

• Similarities (implicit in shared premolar design): both possess buccal and lingual cusps; both contribute to posterior occlusion and function; both exhibit HOC near the middle third of the crown.

• Differences (not explicitly listed in the transcript beyond features above): First premolar tends to have two roots more often and more pronounced canine-like features; Second premolar tends to have a single root and more uniformly rounded cusps with shallower grooves.

• Note: The slide labeled “SIMILARITIES/DIFFERENCES – MAXILLARY PREMOLARS” exists in the transcript, but explicit points are not provided in the text.

Mandibular Premolars

Mandibular First Premolar

• Universal numbers: 21,\;28.

• Eruption: 10-12\text{ yrs}.

• Root completion: 12-13\text{ yrs}.

• Cusps: Buccal and Lingual cusps; Buccal cusp dominant in all dimensions; Lingual cusp is nonfunctional (does not occlude with maxillary teeth).

• Root anatomy: Usually 1 root, 1 pulp canal but may have 2; longitudinal grooves on M and D surfaces of the root; root is approximately 3\text{ mm} shorter than the corresponding mandibular canine root.

• Height of contour (HOC): M\text{-}D\text{ Junction of middle and occlusal third},\; F\text{ cervical third},\; L\text{ middle third}.

• Key characteristic: Mesial lingual developmental groove extends from the occlusal surface onto the lingual surface.

• Occlusal features: Two pits on the occlusal surface (mesial and distal pits); mesial lingual developmental groove extends onto the lingual surface.

Mandibular Second Premolar

• Universal numbers: 20,\;29.

• Eruption: 11-12\text{ yrs}.

• Root completion: 13-14\text{ yrs}.

• Size and morphology: Mandibular second premolar is always larger than the first premolar; the tooth begins to resemble a molar (boxier shape).

• Cusp anatomy: Buccal cusp shorter than the first premolar; the root is longer.

• Cusps and ridges: Facial and Lingual cusps are more developed; both Mesial (M) and Distal (D) marginal ridges are more occlusal; resembles shoulders.

• Occlusal function: Occlusal surface functions like a molar; Lingual cusp(s) are still nonfunctional with the maxillary arch.

• Variations: Two-cusp variety or three-cusp variety (two-cusp forms arise from 4 lobes of development; three-cusp forms arise from 5 lobes of development).

  • If a 3-cusp variation is present, the Mesial Lingual cusp is larger than the Distal Lingual cusp (mesial side is dominant).

• Root and canal anatomy: Single root, single pulp chamber; however, two pulp horns exist for each cusp in the 2-cusp form; the 3-cusp form has two lingual pulp canals.

• Height of contour (HOC): M\text{-}D\text{ Junction of middle and occlusal third},\; F\text{ cervical third},\; L\text{ middle third}.

• Key characteristic: Mesial lingual developmental groove extends from the occlusal onto the lingual surface.

• Occlusal groove patterns: 2-cusp type can show H or U occlusal groove patterns; 3-cusp type shows a Y occlusal groove pattern (the mesial lingual groove forms the tail of the Y).

Similarities and Differences: Mandibular Premolars

• Similarities (inferred from premolar anatomy): both first and second mandibular premolars have buccal and lingual cusps and participate in occlusion; both have defined HOC regions.

• Differences (as described): First premolar typically has a dominant buccal cusp and a nonfunctional lingual cusp; second premolar shows size and cusp development variations (2-cusp vs 3-cusp) and more complex occlusal groove patterns, with the 3-cusp form featuring a mesial lingual cusp larger than the distal lingual cusp.

• Note: The transcript includes a slide labeled “SIMILARITIES/DIFFERENCES – MANDIBULAR PREMOLARS” but does not provide explicit content.

Quick Reference and Key Terms

• Lobes of development for premolars: typically 4 lobes (3 facial, 1 lingual); mandibular second premolar may have 5 lobes in the 3-cusp form.

• HOC (Height of Contour) locations: middle third typically for occlusal function; positions differ by tooth surface as listed above.

• CEJ: Cementoenamel junction – noted in several descriptions (e.g., mesial developmental depression around CEJ).

• Occlusal groove patterns for mandibular second premolars:

  • 2-cusp type: could be H or U.

  • 3-cusp type: Y pattern (mesial lingual groove forms the tail of the Y).

Connections to Broader Concepts

• Functional implications: Cuspal size and cusp functionality influence occlusion and grinding efficiency; premolars bridge canine guidance and molar function.

• Root morphology and canals: Bifurcation and canal patterns affect endodontic considerations and root canal therapy planning.

• Developmental biology: Lobes of development and cusp formation explain natural variations (e.g., 3-cusp mandibular second premolars) and correlate with radiographic and clinical findings.

• Real-world relevance: Accurate identification of premolar types and variations is critical for accurate diagnosis, restorative planning, and occlusal analysis in dental practice.

Summary Takeaways

• Premolars are transitional posterior teeth with cusp patterns that vary by arch (maxillary vs mandibular) and by tooth (first vs second premolar).

• Maxillary premolars generally show distinct cusp lengths (first typically has a longer buccal cusp; second more symmetrical) and often have two roots (first premolar more so than second).

• Mandibular premolars emphasize a functional buccal cusp with a nonfunctional lingual cusp in the first premolar; the second premolar shows notable variation in cusp numbers (2 or 3) and a Y-shaped occlusal groove in the 3-cusp type.

• Height of contour, root morphology, and developmental grooves are key identifiers for each premolar type and have implications for endodontics, restorative dentistry, and occlusal therapies.