DENTAL ANATOMY 1st Semester 2008/2009 Academic Year Department of Stomatology

1. DENTAL ANATOMY 1st Semester 2008/2009 Academic Year Department of Stomatology School of Stomatology Wenzhou Medical College

2. Morphology of Premolars Kevin Yang Li Hong-qing

3. SECTION 1 OVERVIEW • Objectives • Describe the functions of premolars • List class traits common to all premolars • List arch traits that can be used to distinguish maxillary from mandibular premolars

4. A General description of premolars • What’s premolar ? • Pre- loanword from Latin, where it meant “before”; applied freely as a prefix, with the meanings “prior to,” “early,” “beforehand,” “before,” “in front of,” etc. • Any tooth in the permanent dentition that replaces a primary molar.

5. Locations and numbers

6. B Functions of premolars • Mastication of food • Maintain the vertical dimension of the face • Shearing or cutting food (first premolar) • Support the corners of the mouth and cheeks

7. C Class traits of premolars • Class traits similar to anterior teeth • Number of development lobes

8. Crowns taper toward the cervical • Widest proximal heights of contour • Cervical lines • Proximal view • Buccal or lingual view • Root shape • Roots taper apically • Apical third bends distally

9. Class traits that differ from anterior teeth • Tooth surface terminology • Occlusal cusps versus incisal edges • 1 buccal cusp 1 lingual cusp ( EXCEPTION)

10. Marginal ridges • Oriented in a horizontal plane (<45°) • ( EXCEPTION) (=45°) • Crown and root length • Crowns: shorter than anterior teeth • Roots: < canines, >=incisors • 1st premolars vs 2nd premolars: 1st pre crowns longer but roots shorter • Height (crest) of contour • Facial height of contour: cervical third • Lingual height of contour: middle third

11. Other class traits characteristic of most premolars • Buccal view • Crown outline shape: five-sided pentagon • Contact areas: distal contacts are more cervical than mesial contacts (EXCEPTION) • Cusp ridges size: buccal cusp is slightly mesial (EXCEPTION) • Lingual view • Crown shape: narrower than buccal side (EXCEPTION)

12. Proximal views • Mesial marginal ridges are more occlusal than distal marginal ridges • Occlusal view • Tooth proportions: faciallingual dimension wider than mesiodistal dimension • Ridges bound occlusal table: cusp ridges and marginal ridges • Transverse ridges: triangular ridges (EXCEPTION) • Grooves and fossae: mesialdistally from mesial fossa to distal fossa (EXCEPTION)

13. D Arch traits that differentiate maxillary from mandibular premolars • Relative shape and size • The maxillary premolars look more alike than the mandibular premolars • Lingual crown tilt in mandibular premolars • Tilt lingually relative to the roots • Fit & function both beneath and lingual to the maxillary buccal cusps

14. Cusp size and location • Difference of cusps • Distal crown tilt on mandibular premolars • Distal tilting from canine to molars • Buccal ridge prominence • Max 1st vs mand 1st • Crown proportions • Max oblong rectangular • Mand square

15. SECTION 2 TYPE TRAITS DIFFERENTIATE 1st FROM 2nd MAXILLARY PREMOLARS • Objectives • Class traits to distinguish maxillary 1st premolar from 2st premolar • Number any maxillary premolar

16. A type traits from the buccal view • Relative size of crowns • Crown: 1st >2nd in size • Root: 1st < 2nd in length • Shoulders • Crown taper

17. Location of proximal contacts • Mesial: middle third near the junction of the occlusal and middle thrids • Distal: more cervical • Location of the buccal cusp tip • Slightly to the distal for the1st premolar • Cusp ridges

18. Shape of the buccal cusp • 1st cusp angle: 100-110° long sharp • 2nd cusp angle: 125-130 ° obtuse • Buccal ridge and depression • 1st prominent than 2nd • Roots • 1st 61% 2 roots • 2nd mostly one root , long , root-to-crown ratio 1.8:1

19. B Type traits from the lingual view • Relative cusp size • shorter and narrower than buccal cusp • 1st premolar more prominent • Cusp ridges • Meet at a rounded angle • 2nd relatively sharper • Lingual cusp position • Tip is to the mesial of the midroot axis line

20. Marginal ridges • Distal ridge more cervical • Roots • 1st lingual root shorter than the buccal root • Root taper to the lingual

21. C type traits from the proximal views • Crown shape and morphology • Trapezoid • Mesial concavity cervical of 1st • Relative cusp height • 1st buccal longer • 2st equal • Height of contour • Buccal or lingual

22. Marginal ridge grooves • 1st marginal ridge groove: mesial 97% distal 39% • 2nd less • Cervical lines • Curvature of mesial & distal • Roots and root depressions • Concavity • Lingual root shorter • 1st only premolar that mesial depression deeper than distal

23. D type traits from the occlusal view • Relative size • 1st >= 2nd 82% • Grooves and fossae • 1st longer central groove • 2nd more Supplementary grooves • 1st mesial marginal ridge groove • Distal fossae always >= mesial ones in size

24. Relative proportions • Demention buccolingually > mesiodistally • Outline • Asymmetrical occlusal outline of 1st • 1st Marginal ridge • 2nd symmetrical • Contact areas & heights • 1st • 2nd

25. SECTION 3 TYPE TRAITS DIFFERENTIATE 1st FROM 2nd MANDIBULAR PREMOLARS • Objectives • Class traits to distinguish mandibular 1st premolar from 2st premolar • Number any mandibular premolar

26. A