NEET MDS Lessons
Dental Anatomy
Dentin
Composition: 70% inorganic, 20% organic, 10% water by weight and 45%, 33%, and 22% in volume respectively
Hydroxyapatite crystals and collagen type I
Physical characteristics: Harder than bone and softer than enamel
Yellow in color in normal teeth
Radiographic appearance: More radiolucent than enamel
Primary (circumpulpal) dentin: forms most of the tooth
Mantle dentin: first dentin to form; forms the outline of dentin in the adult tooth
Predentin: lines the innermost portion of dentin (faces the pulp)
Secondary dentin: after root formation dentin continues to form, continuous to primary dentin but with structural irregularities
Tertiary dentin: reactive or reparative dentin; may or may not have characteristics of primary dentin; produced in the area of an external stimulus; osteodentin
Dentin is formed by cells called odontoblasts.
These cells derive from the ectomesenchyme and produce the organic matrix that will calcify and become the dentin.
Formation of dentin initiates formation of enamel.
The formation of dentin starts during late bell-stage in the area of the future cusp.
First coronal dentin and then root dentin.
Completion of dentin does not occur until about 18 months after eruption of primary and 2-3 years after eruption of permanent teeth.
The rate of dentin development varies.
The role of the internal (inner) dental (enamel) epithelium
Cuboidal - Columnar (reverse polarization)
Ectomesenchymal cells of the dental papilla become preodontoblasts - odontoblasts
Acellular zone disappears
Histologic features of dentin
Odontoblasts
Dentinal tubules
Extend through the entire thickness of dentin
S-shaped (primary curvatures) path in the crown, less S-shaped in the root, almost straight in the cervical aspect
Secondary curvatures
Tubular microbranches
Presence of fluid
Intratubular dentin
Dentin in the tubule that is hypermineralized
The term peritubular dentin should not be used
Sclerotic dentin
Dentinal tubules that are occluded with calcified material
Most likely a physiologic response
Reduction of permeability of dentin
Intertubular dentin
Dentin between the tubules
Interglobular dentin
Areas of unmineralized or hypomineralized dentin
The defect affects mineralization and not the architecture of dentin
Incremental lines
Lines of von Ebner: lines associated with 5-day rythmic pattern of dentin deposition
Contour lines of Owen: Originally described by Owen they result from a coincidence of the secondary curvatures between neighboring dentinal tubules.
Granular Layer of Tomes
Seen only in ground sections in the root area covered by cementum
Originally, they were thought to be areas of hypomineralization
They are true spaces obtained by sections going through the looped terminal portions dentinal tubules
DE junction :Scalloped area
Enamel tissue with incremental lines of Retzius and dentin tissue with parallel, curved dentinal tubules are in contact at the irregular dentino-enamel junction. The junction often has a scalloped-shaped morphology
DC junction Dentin Cemental Junction
TYPES OF TEETH
The human permanent dentition is divided into four classes of teeth based on appearance and function or position.
Incisors, Canines, Premolars & Molars
MANDIBULAR SECOND BICUSPID
Facial: From this aspect, the tooth somewhat resembles the first, but the buccal cusp is less pronounced. The tooth is larger than the first.
Lingual: Two significant variations are seen in this view. The most common is the three-cusp form which has two lingual cusps. The mesial of those is the larger of the two. The other form is the two-cusp for with a single lingual cusp. In that variant, the lingual cusp tip is shifted to the mesial.
Proximal: The buccal cusp is shorter than the first. The lingual cusp (or cusps) are much better developed than the first and give the lingual a full, well-developed profile.
Occlusal: The two or three cusp versions become clearly evident. In the three-cusp version, the developmental grooves present a distinctive 'Y' shape and have a central pit. In the two cusp version, a single developmental groove crosses the transverse ridge from mesial to distal
Contact Points; Height of Curvature: From the facial, the mesial contact is more occlusal than the distal contact.The distal marginal ridge is lower than the mesial marginal ridge
Root Surface:-The root of the tooth is single, that is usually larger than that of the first premolar
the lower second premolar is larger than the first, while the upper first premolar is just slightly larger than the upper second
There may be one or two lingual cusps
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.
The very first histological evidence of tooth development appear during the second month of intrauterine life. Calcification of deciduous incisors begins at 3-4 months in utero.
MORPHOLOGY OF THE DECIDUOUS TEETH
Deciduous Anterior Teeth.
-The primary anteriors are morphologically similar to the permanent anteriors.
-The incisors are relatively simple in their morphology.
-The roots are long and narrow.
-When compared to the permanent incisors, the mesiodistal dimension is relatively larger when compared to axial crown length
-At the time of eruption, mamelons are not present in deciduous incisors
-They are narrower mesiodistally than their permanent successors.
Cementum
Composition
a. Inorganic (50%)—calcium hydroxyapatite crystals.
b. Organic (50%)—water, proteins, and type I collagen.
c. Note: Compared to the other dental tissues, the composition of cementum is most similar to bone; however, unlike bone, cementum is avascular (i.e., no Haversian systems or other vessels are present).
Main function of cementum is to attach PDL fibers to the root surface.
Cementum is generally thickest at the root apex and in interradicular areas of multirooted
Types of cementum
a. Acellular (primary) cementum
(1) A thin layer of cementum that surrounds the root, adjacent to the dentin.
(2) May be covered by a layer of cellular cementum, which most often occurs in the middle and apical root.
(3) It does not contain any cells.
b. Cellular (secondary) cementum
(1) A thicker, less-mineralized layer of cementum that is most prevalent along the apical root and in interradicular (furcal) areas of multirooted teeth.
(2) Contains cementocytes.
(3) Lacunae and canaliculi:
(a) Cementocytes (cementoblasts that become trapped in the extracellular matrix during cementogenesis) are observed in their entrapped spaces, known as lacunae.
(b) The processes of cementocytes extend through narrow channels called canaliculi.
(4) Microscopically, the best way to differentiate between acellular and cellular cementum is the presence of lacunae in cellular cementum.