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 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.

Cementum & Cementogenesis

Cementum formation is called cementogenesis and occurs late in the development of teeth. Cementoblasts are the cells responsible for cementogenesis. Two types of cementum form: cellular and acellular.

Acellular cementum forms first. The cementoblasts differentiate from follicular cells, which can only reach the surface of the tooth's root once Hertwig's Epithelial Root Sheath (HERS) has begun to deteriorate. The cementoblasts secrete fine collagen fibrils along the root surface at right angles before migrating away from the tooth. As the cementoblasts move, more collagen is deposited to lengthen and thicken the bundles of fibers. Noncollagenous proteins, such as bone sialoprotein and osteocalcin, are also secreted. Acellular cementum contains a secreted matrix of proteins and fibers. As mineralization takes place, the cementoblasts move away from the cementum, and the fibers left along the surface eventually join the forming periodontal ligmaments.

Cellular cementum develops after most of the tooth formation is complete and after the tooth occludes (in contact) with a tooth in the opposite arch. This type of cementum forms around the fiber bundles of the periodontal ligaments. The cementoblasts forming cellular cementum become trapped in the cementum they produce.

The origin of the formative cementoblasts is believed to be different for cellular cementum and acellular cementum. One of the major current hypotheses is that cells producing cellular cementum migrate from the adjacent area of bone, while cells producing acellular cementum arise from the dental follicle. Nonetheless, it is known that cellular cementum is usually not found in teeth with one root. In premolars and molars, cellular cementum is found only in the part of the root closest to the apex and in interradicular areas between multiple roots.

1. Errors in development. These are usually genetic.

a. Variability of the individual teeth. In general, the teeth most distal in any class are the most variable.

b. Partial or total anodontia. missing teeth in children,

c. Supernumerary teeth.

d. Microdontia

e. Macrodontia

F. Microdontia

2. Errors in skeletal alignment. Malpositioned jaws disrupt normal tooth relationships.

3. Soft tissue problems.

-Ocasionally, the proper eruption of a tooth is prevented by fibrous connective tissue over the crown of the tooth.

-In the mixed dentition, the deciduous second molars have a special importance for the integrity of the permanent dentition. Consider this: The first permanent molars at age six years erupt distal to the second deciduous molars.

-Permanent posterior teeth exhibit physiological mesial drift, the tendency to drift mesially when space is available. If the deciduous second molars are lost prematurely, the first permanent molars drift anteriorly and block out the second premolars.

An incisor diastema may be present. The plural for diastema is diastemata.

-Important: The deciduous anteriors--incisors and canines are narrower than their permanent successors mesiodistally.

-Important: The deciduous molars are wider that their permanent successors mesiodistally.

-This size difference has clinical significance. The difference is called the leeway space.

The leeway space in the lower arch is approximately 3.4 mm.

-The leeway space in the upper arch is approximately 1.8 mm. In normal development, the leeway space is taken up by the mesial migration of the first permanent molars.