NEET MDS Lessons
Dental Anatomy
Mandibular Second Deciduous Molar.
-This tooth resembles the lower first permanent molar that is d
istal to it in the dental arch.
-There are two roots and five cusps. The three buccal cusps are all about the same size. This is in contrast to the lower first molar where the 'distal' cusp is smaller that the mesiobuccal and distobuccal cusps.
-The distal of the three buccal cusps may be shifted of onto the distal marginal ridge.
NOTE
-Upper molars have three roots, lowers have two roots.
-Upper and lower second deciduous molars resemble first permanent molars in the same quadrant.
-Upper first deciduous molars vaguely resemble upper premolars. -Lower first deciduous molars are odd and unique unto themselves.
-First deciduous molars (upper and lower) have a prominent bulge of enamel on the buccal at the mesial. These help in determining right and left.
Clinical importance of cementum
1) Deposition of cementum continues throughout life.
The effects of the continuous deposition of cementum are the maintenance of total length of the tooth (good) and constriction of the apical foramen (bad).
2) With age, the smooth surface of cementum becomes more irregular due to calcification of some ligament fiber bundles. This is referred to as spikes.
Behavior of cementum in pathologic conditions
MANDIBULAR SECOND MOLAR
Facial: When compared to the first molar, the second molar crown is shorter both mesiodistally and from the cervix to the occlusal surface. The two well-developed buccal cusps form the occlusal outline. There is no distal cusp as on the first molar. A buccal developmental groove appears between the buccal cusps and passes midway down the buccal surface toward the cervix.
Lingual: The crown is shorter than that of the first molar. The occlusal outline is formed by the mesiolingual and distolingal cusps.
Proximal: The mesial profile resembles that of the first molar. The distal profile is formed by the distobuccal cusp, distal marginal ridge, and the distolingual cusp. Unlike the first molar, there is no distal fifth cusp.
Occlusal: There are four well developed cusps with developmental grooves that meet at a right angle to form the distinctive "+" pattern characteristic of this tooth.
Contact Points; When moving distally from first to third molar, the proximal surfaces become progressively more rounded. The net effect is to displace the contact area cervically and away from the crest of the marginal ridges.
Roots:-The mandibular second molar has two roots that are smaller than those of the first molar. When compared to first molar roots, those of the second tend to be more parallel and to have a more distal inclination.
Embryonic development
The parotid derives from ectoderm
The sublingual-submandibular glands thought to derive from endoderm
Differentiation of the ectomesenchyme
Development of fibrous capsule
Formation of septa that divide the gland into lobes and lobules
The parotid develops around 4-6 weeks of embryonic lofe
The submandibular gland develops around the 6th week
The sublingual and the minor glands develop around the 8-12 week
The periodontium consists of tissues supporting and investing the tooth and includes cementum, the periodontal ligament (PDL), and alveolar bone.
Parts of the gingiva adjacent to the tooth also give minor support, although the gingiva is Not considered to be part of the periodontium in many texts. For our purposes here, the groups Of gingival fibers related to tooth investment are discussed in this section.
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Maxillary (upper) teeth |
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Primary teeth |
Central |
Lateral |
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First |
Second |
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Initial calcification |
14 wk |
16 wk |
17 wk |
15.5 wk |
19 wk |
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Crown completed |
1.5 mo |
2.5 mo |
9 mo |
6 mo |
11 mo |
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Root completed |
1.5 yr |
2 yr |
3.25 yr |
2.5 yr |
3 yr |
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Mandibular (lower) teeth |
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Initial calcification |
14 wk |
16 wk |
17 wk |
15.5 wk |
18 wk |
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Crown completed |
2.5 mo |
3 mo |
9 mo |
5.5 mo |
10 mo |
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Root completed |
1.5 yr |
1.5 yr |
3.25 yr |
2.5 yr |
3 yr |
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Dental Formula, Dental Notation, Universal Numbering System
A. Dental Formula. The dental formula expresses the type and number of teeth per side
The Universal Numbering System. The rules are as follows:
1. Permanent teeth are designated by number, beginning with the last tooth on the upper right side, going on to the last tooth on the left side, then lower left to lower right
2. Deciduous teeth are designated by letter, beginning with the last tooth on the upper right side and proceeding in clockwise fashion