NEET MDS Lessons
Dental Anatomy
Root Formation and Obliteration
1. In general, the root of a deciduous tooth is completely formed in just about one year after eruption of that tooth into the mouth.
2. The intact root of the deciduous tooth is short lived. The roots remain fully formed only for about three years.
3. The intact root then begins to resorb at the apex or to the side of the apex, depending on the position of the developing permanent tooth bud.
4. Anterior permanent teeth tend to form toward the lingual of the deciduous teeth, although the canines can be the exception. Premolar teeth form between the roots of the deciduous molar teeth
Nutrition and tooth development
As in other aspects of human growth and development, nutrition has an effect on the developing tooth. Essential nutrients for a healthy tooth include calcium, phosphorus, fluoride, and vitamins A, C, and D. Calcium and phosphorus are needed to properly form the hydroxyapatite crystals, and their levels in the blood are maintained by Vitamin D. Vitamin A is necessary for the formation of keratin, as Vitamin C is for collagen. Fluoride is incorporated into the hydroxyapatite crystal of a developing tooth and makes it more resistant to demineralization and subsequent decay.
Deficiencies of these nutrients can have a wide range of effects on tooth development. In situations where calcium, phosphorus, and vitamin D are deficient, the hard structures of a tooth may be less mineralized. A lack of vitamin A can cause a reduction in the amount of enamel formation. Fluoride deficency causes increased demineralization when the tooth is exposed to an acidic environment, and also delays remineralization. Furthermore, an excess of fluoride while a tooth is in development can lead to a condition known as fluorosis.
Maxillary Second Deciduous Molar.
-The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somwhat rhomboidal in outline.
-They often have the Carabelli trait.
- the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.
Maxillary First Deciduous Molar.
-The notation is B or I.
-It looks a bit like an upper 1st premolar.
-There are three roots.
-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.
-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.
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Maxillary (upper) teeth |
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Primary teeth |
Central |
Lateral |
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First |
Second |
Initial calcification |
14 wk |
16 wk |
17 wk |
15.5 wk |
19 wk |
Crown completed |
1.5 mo |
2.5 mo |
9 mo |
6 mo |
11 mo |
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 |
Crown completed |
2.5 mo |
3 mo |
9 mo |
5.5 mo |
10 mo |
Root completed |
1.5 yr |
1.5 yr |
3.25 yr |
2.5 yr |
3 yr |
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Introduction. The Jaws and Dental Arches
The teeth are arranged in upper and lower arches. Those of the upper are called maxillary; those of the lower are mandibular.
- The maxilla is actually two bones forming the upper jaw; they are rigidly attached to the skull..
- The mandible is a horseshoe shaped bone which articulates with the skull by way of the temporomandibular joint the TMJ.
- The dental arches, the individual row of teeth forming a tooth row attached to their respective jaw bones have a distinctive shape known as a catenary arch.
The Transition from the Deciduous to the Permanent Dentition.
1. The transition begins with the eruption of the four first permanent molars, and replacement of the lower deciduous central incisors by the permanent lower central incisors.
2. Complete resorption of the deciduous tooth roots permits exfoliation of that tooth and replacement by the permanent (successional) teeth
3. The mixed dentition exists from approximately age 6 years to approximately age 12 years. In contrast, the intact deciduous dentition is functional from age 2 - 2 /2 years of age to 6 years of age.
4. The enamel organ of each permanent anterior tooth is connected to the oral epithelium via a fibrous cord, the gubernaculum. The foramina through which it passes can be seen in youthful skulls
The deciduous second molars are particularly important. It is imperative that the deciduous second molars be preserved until their normal time of exfoliation. This prevent mesial migration of the first permanent molars.
Use a space maintainer in the event that a second deciduous molar is lost prematurely