NEET MDS Lessons
Dental Anatomy
ERUPTION
. Root completion (approximately 50% of the root is formed when eruption begins)
Generally mandibular teeth erupt before maxillary teeth,
Primary teeth
I. Emerge into the oral cavity as follows:
Maxillary Mandibular
Central Incisor 7½ months 6 months
Lateral incisor 9 months 7 months
Canine 18 months 16 months
First Molar 14 months 12 months
Second Molar 24months 20 months
The sequence of primary tooth development is central incisor, lateral incisor, first molar, second molar
3. Hard tissue formation begins between 4 and 6 months in utero
4. Crowns completed between 1½ and 10 months of age
5. Roots are completed between I½ and3 yearsof age 6 to 18 months after eruption
6. By age 3 years all of the primary and permanent teeth (except for the third molars) are in some stage of development
7. Root resorption of primary teeth is triggered by the pressure exerted by the developing permanent tooth; it is followed by primary tooth exfoliation in sequential patterns
8. The primary dentition ends when the first permanent tooth erupts
Time for tooth development
Entire primary dentition initiated between 6 and 8 weeks of embryonic development.
Successional permanent teeth initiated between 20th week in utero and 10th month after birth Permanent molars between 20th week in utero (first molar) and 5th year of life (third molar)
THE DECIDUOUS DENTITION
I. The Deciduous Dentition
-It is also known as the primary, baby, milk or lacteal dentition.
diphyodont, that is, with two sets of teeth. The term deciduous means literally 'to fall off.'
There are twenty deciduous teeth that are classified into three classes. There are ten maxillary teeth and ten mandibular teeth. The dentition consists of incisors, canines and molars.
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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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Permanent dentition period
-Maxillary / mandibular occlusal relationships are established when the last of the deciduous teeth are lost. The adult relationship of the first permanent molars is established at this time.
-Occlusal and proximal wear reduces crown height to the permanent dentition and the mesiodistal dimensions of the teeth
occlusal and proximal wear also changes the anatomy of teeth. As cusps are worn off, the occlusion can become virtually flat plane. -In the absence of rapid wear, overbite and overjet tend to remain stable.
-Mesio-distal jaw relationships tend to be stable,
With aging, the teeth change in color from off white to yellow. smoking and diet can accelerate staining or darkening of the teeth.
Gingival recession results in the incidence of more root caries . With gingival recession, some patients have sensitivity due to exposed dentin at the cemento-enamel junction.
Curve of Spee.
-The cusp tips and incisal edges align so that there is a smooth, linear curve when viewed from the lateral aspect. The mandibular curve of Spee is concave whereas the maxillary curve is convex.
-It was described by Von Spee as a 4" cylinder that engages the occlusal surfaces.
-It is called a compensating curve of the dental arch.
There is another: the Curve of Wilson. Clinically, it relates to the anterior overbite: the deeper the curve, the deeper the overbite.
lntraarch relationship refers to the alignment of the teeth within an arch
1. In an ideal alignment teeth should contact at their proximal crests of curvature. A continuous arch form is observed in occlusal view
Curves of the occlusal plane (a line connecting the cusp tips of the canines, premolars, and molars) are observed from the proximal view
Curve of Spee: anterior to posterior curve; for mandibular teeth the curve is concave and for maxillary teeth it is convex
Curve of Wilson- medial to lateral curve for mandibular teeth the curve is also convex and for the maxillary it is convex
2. Contact does not always exist Some permanent dentitions have normal spacing
Primary dentitions often have developmental spacing in the anterior area: some primary den titions have a pattern of spacing called primate spaces between the primary maxillary lateral incisors and canine and between the mandibular canine and first mo1ar
Disturbances to the intraarch alignment are described as
a. Qpen contact where interproximal space exist because of missing teeth oral habits, dental disease, or overdeveloped frena
b. where contact or position is at an unexpected area because of developmental disturbances, crowding, dental caries or periodontal ligament for their misplaced position: facial, lingual. mesial, supra(supraerupted) infra (infraerupted) and torso (rotated) version
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)