Definition:Shedding is a natural physiological elimination

of the deciduous teeth at specific ages as a result of the resorption of their roots prior to the eruption of their permanent successors.

Baby" teeth are important because:

•They hold the place for permanent teeth.

•Guide them into correct position.

"Baby" teeth play an important role in the development of speech and chewing.

Early primary tooth extraction leads to loss of its space.

This will cause great irregularities in the dental arch with high risk of caries and Periodontium diseases.

Thus space maintainer should be used to maintain this space.

Resorption of the roots of primary teeth starts at the lingual apical areas in the anterior teeth And in the interradicular areas of molars.

Pattern of shedding:

It is related to where the erupting permanent successors are located.

Anterior teeth:

First the pressure cause crypt wall resorption.

Then resorption of the root occurred lingo-apically.

Later, the developing permanent tooth germs occupy a position apical to the deciduous tooth, which permits them to erupt in the position formerly occupied by the deciduous tooth.

However frequently, this apical positioning of the permanent tooth germs does not occur particularly in the case of the permanent mandibular incisors where the permanent ones erupt lingual to the still functioning deciduous incisors.

These deciduous teeth are often shed with a considerable portion of the root remaining on their labial aspect and with much of their pulp chamber intact.

Shedding of Primary Teeth

Posterior teeth:

First, resorption of the roots of the deciduous molars often begins early on their inner surface facing the inter-radicular septum. This early resorption occurs long before shedding of deciduous molars.

As a result of the continued growth of the jaws and occlusal movement of the deciduous molars, the premolar tooth germs come to be apical to the deciduous molars.

This change in the position provides:

•The growing premolars adequate space for their continued growth.

•And also relieves the pressure on the roots of the overlying deciduous molars.

The areas of early resorption of the roots of deciduous molars are repaired by deposition of a cementum-like tissue but less mineralized and the alveolar bone is also repaired.

Later, when the premolars begin to erupt, root resorption of deciduous molars is again initiated and continued until the roots are completely resorbed.

•The resorption may even proceed far up into the coronal dentin and occasionally some areas of the enamel may be destroyed.

The process of tooth resorption is intermittent;

there are periods of resorption and periods of rest and repair.

However, in the long term, resorption predominates over repair

The primary teeth become loose during the periods of resorption and tighten during the brief periods of apposition.

Factors determining the pattern and rate of deciduous teeth shedding:

1- Genetic factors. 2- Local factors:A) Local pressure:Pressure from the erupting permanent successor plays a role in the shedding of deciduous dentition, If a successional tooth is congenitally missing or occupies an aberrant position in the jaw, shedding of the deciduous tooth is delayed. Yet the deciduous tooth is eventually shed.

Aberrant position.

Congenitally missing.

B) Masticatory forces:Increased force applied to a deciduous tooth can initiate its resorption. Growth of the face and jaws and the corresponding enlargement in the size and strength of the muscles of mastication probably increase the forces applied to the deciduous teeth to the point that they damage the supporting of the tooth, in particular the periodontal ligament and initiate resorption of the tooth.

Histology of shedding:

The fact that programmed cell death is seen during shedding that occurs at specific ages is consistent with the concept that shedding is a genetically determined process.

I- Resorption of hard dental tissues:The resorption of the hard dental tissues of deciduous teeth is achieved by highly specialized multinucleated cells called odontoclasts because of their involvement in the removal of dental tissues. These cells are identical to osteoclasts.

II- Histological characters of pulp during shedding:

It should be emphasized that the pulp tissue in teeth undergoing shedding appears histologically normal except that neural elements seem to be missing.

Thus the pulp does not contribute to the process of shedding and plays a passive role in this process.

P

Note:Odontoblasts degenerated and replaced by odontoclasts (internal resorption).

II- Histological characters of the PDL during shedding:

Loss of the periodontal ligament fibers is abrupt and programmed.

The cells show signs of death.

Cell death assumes at least two forms

• fibroblasts exhibit signs of interference with normal cellular processes

such as secretion as well

as other cytotoxic

alteration that eventually

lead to cell death. This

process is induced in

response to local cell

insult.

• the fibroblasts exhibit morphological features characteristic of apoptotic cell death including condensation of the cell with its ultimate phagocytosis by neighboring macrophages or adjacent fibroblasts

Clinical consideration:

•Ankylosis is a bony union between the alveolar bone and the roots of teeth. Thus the active eruption of an ankylosed tooth ceases.

•Mild trauma may result in damage to the periodontal ligament leading to ankylosis of a deciduous tooth rather than its loss.

1-Ankylosis and submerged deciduous teeth:

Because of the continued eruption of the neighboring teeth and increased height of the alveolar process, the ankylosed tooth may be either "shortened" or submerged in the alveolar process (below the plane of occlusion by 1 mm or more).

Clinical features:

Submerged deciduous teeth thus prevent the eruption of their permanent successors or force them away from their position. Submerged deciduous teeth should therefore be removed.

Side effects:

2-Retained deciduous teeth:

Deciduous teeth may be retained for a long time beyond their usual shedding schedule. Retention may be due to local or systemic causes. Congenital absence and impaction of the permanent successors are the common cause for this retention.

The most incidence teeth retained in the oral cavity:

Retained deciduous teeth are most often the upper lateral incisor, less frequently second deciduous molar and rarely, lower central incisor.

Fate of retained teeth:Retained deciduous teeth may remain for many years in a good functioning condition. However, resorption of the roots and continued active and passive eruption cause their loosening and final loss in most cases.

Retained canine.

3-Remnants of deciduous teeth:

Sometimes, segments of the roots of deciduous teeth are not in the path of erupting successors and may escape resorption.

These fragments are most frequently found in the region of the premolars, especially the lower second premolars. The reason is that the roots of the lower second molar are widely divergent; the mesio-distal diameter of the second premolar is much smaller than the greatest distance between the roots of the deciduous molar.

•Root remnants may remain embedded in the alveolar process.

•Completely surrounded by and ankylosed to the bone.

•Frequently they are cased in heavy layers of cellular cementum.

•When they are close to the surface of the jaw, they may ultimately be exfoliated.

•Progressive resorption of the root remnants and replacement by bone may cause disappearance of them.

Fate of root remnants:

Describe the pattern of anterior teeth shedding.

Describe the pattern of posterior teeth shedding.

Mention the factors that determine the pattern and rate of deciduous teeth shedding.

Describe the histology of shedding.

Define ankylosed tooth. Mention its predisposing factors, clinical features and side effects.

When can you consider the deciduous tooth retained one?Mention the supposed causes and the most affected teeth.Mention the fate of the retained teeth.

Describe tooth remnants, its predisposing factors and its fate.