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.

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

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.

ARTICULAR SURFACES COVERED BY FIBROUS TISSUE
TMJ is an exception form other synovial joints. Two other joints, the acromio- and sternoclavicular joints are similar to the TMJ. Mandible & clavicle derive from intramembranous ossificiation.

Histologic

1. Fibrous layer: collagen type I, avascular (self-contained and replicating)
2. Proliferating zone that formes condylar cartilage
3. Condylar cartilage is fibrocartilage that does not play role in articulation nor has formal function
4. Capsule: dense collagenous tissue (includes the articular eminence)
5. Synovial membrane: lines capsule (does not cover disk except posterior region); contains folds (increase in pathologic conditions) and villi
   Two layers: a cellular intima (synovial cells in fiber-free matrix) and a vascular subintima
   Synovial cells: A (macrophage-like) syntesize hyaluronate
   B (fibroblast-like) add protein in the fluid
   Synovial fluid: plasma with mucin and proteins, cells
   Liquid environment: lubrication, ?nutrition
6. Disk: separates the cavity into two comprartments, type I collagen
   anterior and posterior portions
   anetiorly it divides into two lamellae one towards the capsule, the other towards the condyle
   vascular in the preiphery, avascular in the center
7. Ligaments: nonelastic collagenous structures. One ligament worth mentioning is the lateral or temporomandibular ligament. Also there are the spheno- and stylomandibular with debatable functional role.

Innervations
 

HISTOLOGY OF THE ODONTOBLAST

Formation of Dentin

Mantle dentin: First formed dentin
Type I collagen with ground substance
Formation of the odontoblast process

Matrix vesicles
Appearance of hydroxyapatite crystals
 

Predentin
Primary physiologic (circumpulpal) dentin
All organic matrix is formed from odontoblasts
Smaller collagen fibers
Presence of phosphophoryn

Mineralization
Globular calcification
Interglobular dentin: Areas of incomplete calcification
Incremental lines of von Ebner: Daily, 4mm of organic matrix is deposited. Also every 5 days the arrangement of collagen fibers changes. This creates the incremental lines of von Ebner.
Intratubular dentin

Dentin tubules
S-shaped in the coronal aspect, straight in root dentin

Von Korff fibers
They are an artifact

The mixed dentition

I. Transition dentition between 6 and 12 years of age with primary tooth exfoliation and permanent tooth eruption

2. Its characteristic features have led this to be called the ugly duckling stage because of

a. Edentulated areas

b. Disproportionately sized teeth

c. Various clinical crown heights

d. Crowding

e. Enlarged and edematous gingiva

f. Different tooth colors