The Premolars. Chapter 17 Permanent Posterior Teeth (p )

Transcription

1 The Premolars Chapter 17 Permanent Posterior Teeth (p )

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3 General Information Function: u Hold and grind food u Work with molars in mastication. u Even without molars one may be able to chew well with the premolars. u There are two in each quadrant Fig 17-1

4 General Features All premolars u Develop from four lobes except the mandibular 2nd premolar which develops from five u Lingual lobe forms cusp rather than cingulum as in anterior teeth u Premolars have occlusal surface, bordered by marginal ridges. u Occlusal surfaces have cusps, grooves, ridges, and fossae.

5 General Information ucrowns are shorter than the anterior teeth. uthey have a vertical buccal ridge on the buccal surface (similar to the labial ridge on canines) uthe proximal contact areas are more cervically located than incisors. uthere are no premolars in the primary dentition. upermanent premolars are succedaneous teeth - they replace the deciduous molars.

6 CEJ uthe CEJ is less pronounced on the posteriors than on the anteriors. uthe CEJ is often quite straight for posteriors. Figure 17-6

7 Development Permanent Maxillary 1st Premolar o Evidence of calcification yrs. o Eruption yrs. o Root complete 13 yrs. Permanent Maxillary 2nd Premolar o Evidence of calcification - 2 yrs. o Eruption yrs. o Root complete 13 yrs.

8 Development Permanent Mandibular 1st Premolar o Evidence of calcification - 2 yrs. o Eruption yrs. o Root complete 13 yrs. Permanent Mandibular 2nd Premolar o Evidence of calcification yrs. o Eruption yrs. o Root complete 14 yrs.

9 Development

10 General Characteristics Maxillary Premolars Wider F-L than M-D dimensions Two major cusps on each Resemble each other Trapezoidal shaped proximal. Mandibular Premolars F-L and M-D dimensions almost equal Facial cusps much larger Do not resemble each other. Rhomboidal shaped proximal.

11 Comparing Proximal View of Crown Max Mand Trapezoid Shape Rhomboid Shape

12 Maxillary premolars Maxillary First PM Two roots (usually) Lingual cusp shorter and narrower than facial cusp Mesial marginal groove and depression Maxillary Second One root (usually) Cusps of nearly equal length and width. No mesial marginal groove or depression

13 Maxillary First Premolar Occlusal Aspect: Maxillary Second Premolar Occlusal Aspect: Long central developmental groove. Few supplemental grooves Hexagonal shape to occlusal outline. Shorter central developmental groove. Many supplemental grooves Ovoid shape to occlusal outline, rounder.

14 Mandibular Premolars Mandibular First There is one root with two pulp horns Small lingual cusp(nonfunctional cusp); facial cusp is twice as large. Occlusal anatomy can be seen from the lingual view. Mandibular Second There is one root with three pulp horns Well developed lingual cusp, with the possibility of two lingual cusp. Can see little of occlusal anatomy from lingual view.

15 Mandibular First Premolar Occlusal Aspect: Mandibular Second Premolar Occlusal Aspect: u Occlusal outline is diamond shape u M-L groove is present. u No central pit. u Occlusal outline is square. u No M-L groove. u Has Y groove pattern or an H groove pattern

16 Maxillary First Maxillary Second Mandibular First Mandibular Second

17 Maxillary First Premolars #5, #12 uhave buccal and lingual cusp; buccal slightly longer uusually have two roots*** (only premolar with this feature) utwo pulp canals most common, even if one root is present ubroader mesial and distal contact areas Fig *** check your tooth ID sheets from lab

18 Maxillary First Premolars #5, #12 Labial Aspect: ulooks similar to maxillary canine though narrower & shorter ucontact areas at same height mesially and distally uwell-developed middle facial lobe Fig 17-13

19 Maxillary First Premolar Fig 17-16

20 Maxillary First Premolars #5, #12 Has mesial marginal groove and concavity (depression). This requires special consideration when scaling. Fig 17-14

21 Maxillary First Premolar Root and Pulp cavity. ubifurcated root most common although single root possible ubuccal root larger and longer than lingual: utwo root canals present, even in single rooted tooth utwo pulp horns urarely, single rooted, single canal 1st premolar found Fig 17-12

22 Example of Possible Root Canal Configurations Two roots two canals One root two canals

23 Maxillary Second Premolars #4, #13 usimilar in form and function to 1st premolar, though more rounded uone root present most commonly uappearance varies more than 1st premolars uroot longer than 1st premolar Fig 17-17

24 Maxillary Second Premolars #4, #13 Lingual Aspect: o Buccal & lingual cusps are about the same length Mesial Aspect: o No deep developmental grooves and no depressions are present on the mesial surface o Groove on single-rooted tooth gives fused root appearance Lingual Distal Fig 17-17

25 Maxillary Second Premolars #4, #13 Occlusal Aspect of Maxillary Second Premolar: umore rounded outline than 1st premolar, appears ovoid. umany supplemental grooves. umore wrinkled in appearance. Fig 17-19

26 Maxillary Second Premolars #4, #13 Root & Pulp Cavity: usingle root most common with groove on mesial and distal surfaces uone canal most common though divided canal occurs frequently utwo pulp horns Fig 17-18

27 Mandibular First Premolars #21, #28 ushare characteristics with mandibular canine ugenerally smaller than mandibular 2nd premolar (opposite pattern for maxillary premolars) ufour lobes contribute to this tooth with lingual cusp small, non-occluding and, therefore, afunctional Fig 17-20

28 Labial Aspect: ulooks similar to canine usingle sharp buccal cusp ubuccolingual dimension similar to adjacent canine uwell developed buccal ridge umesial cusp ridge shorter than distal umesial and distal contact areas at same height ushorter root than canine

29 Occlusal Aspect of Mandibular premolars: umore variation in occlusal anatomy is present on mandibular premolars than maxillary premolars usharp convergence from buccal to lingual cusp ularge buccal triangular ridge w/ mesial and distal fossae ufossae may contain pits Fig 17-23

30 Mandibular First Premolars Lingual Aspect: o Severely tapers toward the lingual o Very small lingual cusp o Occlusal pits in fossae on either side of triangular ridges o Prominent mesiolingual developmental groove separates mesial marginal ridge from lingual cusp Figure 17-22

31 Mandibular First Premolars Figure 17-24

32 Mandibular First Premolars Root & Pulp Cavity usingle-rooted form most common, although buccallingual two-rooted 1st premolar possible uif bifurcated, a longitudinal groove found proximally utwo pulp horns, one canal most common Fig 17-21

33 Mandibular Second Premolars #20, #29 ularger than 1st premolar ucontact areas at same height mesially and distally ushorter buccal cusp and longer root than 1st premolar umore developed lingual cusp(s) function as molar umarginal ridges higher than 1st premolar utwo forms: two-cusp type three-cusp type

34 Mandibular Second Premolars Labial Aspect: o Shorter buccal cusp than 1st premolar o Mesial and distal cusp ridges more rounded o Wider, longer root Fig 17-26

35 Mandibular Second Premolars Lingual Aspect uvaries due to cusp variety uat least one lingual cusp (in 3- cusp variety) is longer than 1st premolar umesiolingual cusp usually larger in 3-cusp form ularge single cusp in 2-cusp form compared to 1st premolar uwider lingual surface than 1st premolar Fig 17-26

36 Mandibular Second Premolars Occlusal Aspect of Mandibular 2 nd Premolar: Two-cusp form (U or H-shaped) o u Occlusal outline more rounded than 3-cusp form u No lingual developmental groove u U shape groove pattern and a H shape groove pattern u No central pit u Mesial and distal pit may be present Fig 17-32

37 Mandibular Second Premolars Occlusal Aspect of Mandibular 2 nd Premolar: o Three-cusp form( Y-shaped) ubuccal largest, then mesiolingual, then distolingual u Each cusp has triangular ridge umesial, distal and lingual developmental grooves separate cusps umesial, distal and central pit may be present as well as mesial and distal triangular fossae udevelopmental grooves more common and less deep Fig 17-27

38 Mandibular Second Premolars Root & Pulp Cavity usingle-rooted udistal root depression in middle third of root usingle pulp canal most likely Fig 17-28

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40 Clinical Considerations for Premolars Fehrenbach, MJ. Slide Collection. Single, permanent premolars can be extracted in each quadrant during orthodontic therapy to improve dental arch spacing. If a premolar has been extracted, the distinctive pit and groove patterns on the occlusal surface will help in identifying the remaining premolars when the arch space from the extraction is lost if the remaining molars are not restored. However, orthodontic therapy tends instead to include expansion of the jaw, if needed, instead of removing premolars to retain a more natural rounded curved shape to the arches. If still needed, first premolars are usually extracted more often than second premolars.

41 Specific Overall Features A distinct mesial root concavity is present on the root trunk of maxillary first premolar, extending from the contact area to the bifurcation. Fehrenbach, MJ. Slide Collection. Surgical access facilitates debridement of the root surface.

42 Clinical Considerations for Maxillary Second Premolars With premature loss of the primary second molars, the developing permanent maxillary first molar inclines and drifts mesially. The developing permanent tooth is prevented from normal eruption because its arch leeway space is nearly closed. Figure 20-3

43 Impacted Mandibular Second Premolar Darby ML, Walsh M. Dental Hygiene: Theory and Practice, ed 2. Mosby, St. Louis, 2003