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.
MANDIBULAR THIRD MOLAR
Facial: The crown is often short and has a rounded outline.
Lingual: Similarly, the crown is short and the crown is bulbous.
Proximal: Mesially and distally, this tooth resembles the first and second molars. The crown of the third molar, however, is shorter than either of the other molars
Occlusal: Four or five cusps may be present. Occlusal surface is a same as of the first or second molar, or poorly developed with many accessory grooves. The occlusal outline is often ovoid and the occlusal surface is constricted. Occasionally, the surface has so many grooves that it is described as crenulated--a condition seen in the great apes
Contact Points; The rounded mesial surface has its contact area more cervical than any other lower molar. There is no tooth distal to the third molar..
Roots:-The roots, two in number, are shorter in length and tend to be fused together. they show a distinct distal curve
Pulp
1. Four zones—listed from dentin inward
a. Odontoblastic layer
(1) Contains the cell bodies of odontoblasts.
Note: their processes remain in dentinal tubules.
(2) Capillaries, nerve fibers, and dendritic cells may also be present.
b. Cell-free or cell-poor zone (zone of Weil)
(1) Contains capillaries and unmyelinated nerve fibers.
c. Cell-rich zone
(1) Consists mainly of fibroblasts. Macrophages, lymphocytes, and dendritic cells may also be present.
d. The pulp (pulp proper, central zone)
(1) The central mass of the pulp.
(2) Consists of loose connective tissue, larger vessels, and nerves. Also contains fibroblasts and pulpal cells.
2. Pulpal innervation
a. When pulpal nerves are stimulated, they can only transmit one signal pain.
b. There are no proprioceptors in the pulp.
c. Types of nerves:
(1) A-delta fibers
(a) Myelinated sensory nerve fibers.
(b) Stimulation results in the sensation of fast, sharp pain.
(c) Found in the coronal (odontoblastic) area of the pulp.
(2) C-fibers
(a) Unmyelinated sensory nerve fibers.
(b) Transmits information of noxious stimuli centrally.
(c) Stimulation results in pain that is slower, duller, and more diffuse in nature.
(d) Found in the central region of the pulp.
(3) Sympathetic fibers
(a) Found deeper within the pulp.
(b) Sympathetic stimulation results in vasoconstriction of vessels.
ERUPTION OF THE PERMANENT TOOTH
- At the time at which the deciduous tooth erupts the tooth bud for the permanent tooth has already been building up enamel and dentin.
- When the permanent tooth starts to erupt, pressure on the root of the deciduous tooth causes resorption by the osteoclasts.
- Wolff's law states that when two hard tissues exert pressure on one another the softer of the tissues will be resorbed.
- The dentin and cementum of the root of the deciduous tooth is softer than the enamel of the permanent tooth that is why the root of the deciduous tooth is resorbed.
- Most permanent teeth have erupted and have been in use for 2 years before the root is completely formed.
Genetics and Environment: Introduction
The size of the teeth and the timing of the developing dentition and its eruption are genetically determined. Teeth are highly independent in their development. Also, teeth tend to develop along a genetically predetermined course.: tooth development and general physical development are rather independent of one another. Serious illness, nutritional deprivation, and trauma can significantly impact development of the teeth. This genetic independence (and their durability) gives teeth special importance in the study of evolution.
Teeth erupt full size and are ideal for study throughout life. Most important, age and sex can be recorded.
When teeth erupt into the oral cavity, a new set of factors influence tooth position. As the teeth come into function, genetic and environment determine tooth position.
In real life, however, girls shed deciduous teeth and receive their permanent teeth slightly earlier than boys, possibly reflecting the earlier physical maturation achieved by girls. Teeth are slightly larger in boys that in girls