NEET MDS Lessons
Dental Anatomy
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.
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.
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.
Gingiva
The connection between the gingiva and the tooth is called the dentogingival junction. This junction has three epithelial types: gingival, sulcular, and junctional epithelium. These three types form from a mass of epithelial cells known as the epithelial cuff between the tooth and the mouth.
Much about gingival formation is not fully understood, but it is known that hemidesmosomes form between the gingival epithelium and the tooth and are responsible for the primary epithelial attachment. Hemidesmosomes provide anchorage between cells through small filament-like structures provided by the remnants of ameloblasts. Once this occurs, junctional epithelium forms from reduced enamel epithelium, one of the products of the enamel organ, and divides rapidly. This results in the perpetually increasing size of the junctional epithelial layer and the isolation of the remenants of ameloblasts from any source of nutrition. As the ameloblasts degenerate, a gingival sulcus is created.
CEMENTUM vs. BONE
Cementum simulates bone
1) Organic fibrous framework, ground substance, crystal type, development
2) Lacunae
3) Canaliculi
4) Cellular components
5) Incremental lines (also known as "resting" lines; they are produced by continuous but phasic, deposition of cementum)
Differences between cementum and bone
1) Cementum is not vascularized
2) Cementum has minor ability to remodel
3) Cementum is more resistant to resorption compared to bone
4) Cementum lacks neural component
5) Cementum contains a unique proteoglycan interfibrillar substance
6) 70% of bone is made by inorganic salts (cementum only 46%)
Relation of Cementum to Enamel at the Cementoenamel Junction (CEJ)
"OMG rule"
In 60% of the teeth cementum Overlaps enamel
In 30% of the teeth cementum just Meets enamel
In 10% of the teeth there is a small Gap between cementum and enamel
SURFACES OF THE TEETH
Facial, Mesial, Distal, Lingual, and Incisal Surfaces
- The facial is the surface of a tooth that "faces" toward the lips or cheeks. When there is a requirement to be more specific, terms like labial and buccal are used. The labial is the surface of an anterior tooth that faces toward the lips. The buccal is the surface of a posterior tooth that faces toward the cheek.
- The mesial is the proximal surface closest to the midline of the arch. The distal is the opposite of mesial. The distal is the proximal surface oriented away from the midline of the arch.
- The lingual is the surface of an anterior or posterior tooth that faces toward the tongue. Incisal edges are narrow cutting edges found only in the anterior teeth (incisors). Incisors have one incisal edge
- Proximal Surfaces
A tooth has two proximal surfaces, one that is oriented toward the midline of the dental arch (mesial) and another that is oriented away from the midline of the arch (distal).
HISTOLOGIC CHANGES OF THE PULP
Regressive changes
Pulp decreases in size by the deposition of dentin.
This can be caused by age, attrition, abrasion, operative procedures, etc.
Cellular organelles decrease in number.
Fibrous changes
They are more obvious in injury rather than aging. Occasionally, scarring may also be apparent.
Pulpal stones or denticles
They can be: a)free, b)attached and/or c)embedded. Also they are devided in two groups: true or false. The true stones (denticles) contain dentinal tubules. The false predominate over the the true and are characterized by concentric layers of calcified material.
Diffuse calcifications
Calcified deposits along the collagen fiber bundles or blood vessels may be observed. They are more often in the root canal portion than the coronal area.
Histology of the Cementum
Cementum is a hard connective tissue that derives from ectomesenchyme.
Embryologically, there are two types of cementum:
Primary cementum: It is acellular and develops slowly as the tooth erupts. It covers the coronal 2/3 of the root and consists of intrinsic and extrinsic fibers (PDL).
Secondary cementum: It is formed after the tooth is in occlusion and consists of extrinsic and intrinsic (they derive from cementoblasts) fibers. It covers mainly the root surface.
Functions of Cementum
It protects the dentin (occludes the dentinal tubules)
It provides attachment of the periodontal fibers
It reverses tooth resorption
Cementum is composed of 90% collagen I and III and ground substance.
50% of cementum is mineralized with hydroxyapatite. Thin at the CE junction, thicker apically.