SHEDDING OF SHEDDING OF PRIMARY TEETHPRIMARY TEETH..

PROF. AHMED HELMY PROF. AHMED HELMY

Definition:Shedding is a natural physiological elimination of the deciduous teeth as

a result of the resorbtion of their roots prior to the eruption of their permanent successors.

Definition: Shedding is the physiological elimination of primary teeth at specific ages.

Contributing factors: 1- Increased masticatory forces. 2- Weakened supporting structures e. g. loss of cementum, alveolar bone and periodontal attachment. 3- Pressure due to erupting successor.

•trauma and inflammation…occlusal stress, caries .. Etc.

Pattern:

Resorption of the roots of primary teeth starts at the lingual apical areas in the anterior teeth and in the interradicular areas of molars. It is related to where the erupting permanent successors are located.

Shedding of Primary Teeth

Histological features of teeth undergoing shedding:

Root surfaces exhibit resorption lacunae and clast cells are often associated with these concavities. It is significant that periodontal fibroblasts in the area show signs of impaired function. 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. 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.

Clast cells: Cytological features: Clast cells are large multinucleated cells with a ruflled border and numerous lysosomes and mitochondria. Osteoclasts and odontoclasts are morphologically similar and seem to have the same origin and mechanism of action. The rationale for using different names for these cells is to reflect the specific tissue that is being resorbed.

Mechanism of action during resorption of mineralized tissues:

Clast cells act by isolating an area of hard tissue (bone, cementum, dentin or even enamel) using clear cytoplasmic areas (no organelles) and through plasma membrane associated enzymes that act as proton pumps, the isolated area's pH is lowered making it acidic. This acidity breaks down the hydroxyapatite crystals of the inorganic content and also denature the collagenous organic matrix. Essentially denaturing makes the tightly assembled collagen fibrils looser. The proteolytic enzymes both secreted and within lysosomes in the clast cells are then able to break down this collagenous organic matrix.

Shed incisor Shed incisor (dentin)(dentin)

                                                                                                        

Shedding of teeth usually Shedding of teeth usually entails complete entails complete destruction of the root. destruction of the root. Resorption lacuna can Resorption lacuna can be seen in cervical be seen in cervical region of the shed region of the shed tooth. In this tooth. In this micrograph note the micrograph note the reparative dentin reparative dentin below the worn incisal below the worn incisal

edge.edge. A, Resorption lacunae; B, Incisal edge of shed tooth; C, Reparative dentin.

After termination of their resorption function, the odontoclasts lost their ruffled borders and became detached from the resorbed surface. Most of the detached odontoclasts had numerous large pale vacuoles and secondary lysosomes and appeared to be in the process of degeneration.

The pattern due to physiological root resorption of a deciduous upper front The pattern due to physiological root resorption of a deciduous upper front tooth (a) shows very regular polycyclic shallow lacunae representing a uniform tooth (a) shows very regular polycyclic shallow lacunae representing a uniform longterm ongoing process (b).longterm ongoing process (b).

Tissue and cellular changes:

Shedding is an intermittent process with periods of resorption involving alveolar bone, cementum and root dentin resorption by clast cells, osteoclasts and odontoclasts, respectively and recovery periods when osteoblasts and cementoblasts replace part of the resorbed tissues. Eventually more resorption takes place and when the tooth loses its supporting periodontal tissues, it is shed. During this process the primary teeth become loose during the periods of resorption and tighten during the brief periods of apposition.

Intermittent resorptionIntermittent resorption

                                                                                                        

During root resorption, During root resorption, periods of resorption periods of resorption are alternated by are alternated by periods of cementum periods of cementum repair. repair. CementoblastsCementoblasts deposit cementum in deposit cementum in areas of resorption areas of resorption forming a forming a reversal reversal lineline. Some . Some cementoblasts cementoblasts become embedded in become embedded in the cementum and the cementum and are then called are then called cementocytescementocytes..

A, Reversal line; B, Cementoblasts; C, Cementocyte.

Retained, ankylosed, shortened and submerged teeth:

-A retained tooth is one that remains in the dental arch beyond the age at which it is supposed to be shed. Many conditions cause primary teeth to be retained for example root ankylosis or the absence of a permanent successor. -An ankylosed tooth is one that have its root( s) fused to the alveolar bone. -A shortened tooth is a retained primary tooth which is smaller than the adjacent larger permanent teeth. -A submerged tooth is a retained tooth that becomes surrounded by alveolar bone. This condition is created by the loss of adjacent primary teeth and the accompanying resorption of their alveolar bone. When the permanent successors erupt they have their own alveolar bone which covers the retained tooth.

Ankylosis is caused by the fusion of the cementum of the root to the bone and accompanying loss of periodontal ligament attachment. Prevalence is between 7-14% in the primary dentition. The most commonly affected teeth are mandibular primary first molar, mandibular primary second molar, maxillary first molar and maxillary primary second molar in that order.  

Ankylosis can lead to: Loss of arch length. Extrusion of teeth of the opposite arch. Interference with the eruption of succedaneous teeth.

Remnants of deciduous teeth:Parts of the roots of deciduous teeth which

are not in the path of erupting permanent teeth may escape resorbtion. e.g. The lower E have widely divergent roots, where the mesiodistal diameter of lower 5 is smaller than the distance between the roots of lower E, so part of roots found deep in the bone ,and their fate is;

a- Surrounded by cellular cementum. b- Ankylosed to bone.e-Resorbed. d- Exfoliated.

Incompletephysiologic rootresorption resulting inretained root tips ofdeciduous secondmolar.

Retained deciduous root tips

Physiologic resorption

of deciduous second

molar in the absence

of the second

premolar. Resorption

of a deciduous tooth

can occur even in the

absence of an

underlying permanent

tooth. However, the

resorption may be

delayed.

Congenitally Missing TeethCongenitally Missing TeethHypodontia - usually a single tooth missingHypodontia - usually a single tooth missing

Frequency: 2-9%Frequency: 2-9%

Usually occurs with lateral incisors, second Usually occurs with lateral incisors, second premolars, and third molarspremolars, and third molars

Key to diagnosis - count the teeth!!!Key to diagnosis - count the teeth!!!

Missing teeth!!!

If the root of the primary tooth is resorbed by neighbouring permanent teeth If the root of the primary tooth is resorbed by neighbouring permanent teeth instead of the respective successor, we speak of undermining resorption. instead of the respective successor, we speak of undermining resorption. This occurs more frequently in the upper than in the lower jaw and more This occurs more frequently in the upper than in the lower jaw and more often in boys than in girls. often in boys than in girls.

In descending order, this happens to In descending order, this happens to a) the distal roots of the upper second primary molars  by the first a) the distal roots of the upper second primary molars  by the first permanent molars permanent molars b) the lateral primary incisors by the permanent central incisors b) the lateral primary incisors by the permanent central incisors c) the primary canines by the lateral incisors, more rarely by the permanent c) the primary canines by the lateral incisors, more rarely by the permanent first bicuspids. first bicuspids. This is caused mainly by a lack of space, but also by an unfavourable This is caused mainly by a lack of space, but also by an unfavourable inclination of the erupting teeth.inclination of the erupting teeth.

The consequences of undermining resorption are similar to those of premature The consequences of undermining resorption are similar to those of premature loss of the primary teeth or breakdown of the buccal segment (Stuetzzone) loss of the primary teeth or breakdown of the buccal segment (Stuetzzone) due to caries (tooth migrations, tipping, rotations), i.e., lack of space in the due to caries (tooth migrations, tipping, rotations), i.e., lack of space in the front teeth segment or in the buccal segment (Stuetzzone).front teeth segment or in the buccal segment (Stuetzzone).

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Odontoclastic resorption at the pulpal surface of coronal dentin prior to the shedding of human deciduous teeth. odontoclastic resorption as a rule takes place at the pulpal surface of coronal dentin. The process of this internal resorption of coronal dentin of deciduous teeth clearly showed time-related histological changes. During the time the roots were actively being resorbed, the pulpal tissue retained its normal structure. However, when root resorption neared completion, inflammatory cells started to gradually infiltrate into the pulp, and odontoblasts began to degenerate. After that, multinucleate odontoclasts appeared, and resorption proceeded from the predentin to the dentin. The odontoclastic activity was initially detected only on the pulpal surface at the bottom areas of the crown. It gradually spread towards the pulpal horn regions along the wall of the pulp chamber. However, this internal resorption of coronal dentin did not continue until the teeth were finally shed. After the elimination of resorption, the resorbed dentin surface was repaired by a cementum-like deposition or covered with fibrous connective tissue.

Histological change of pulp tissue during shedding of the deciduous tooth.

1. While the root was resorbed more than one half way, some normal pulp was replaced by the connective tissue as in inflammation. Internal resorption could be seen. 2. By the time deciduous root resorption was essential as complete, normal pulp tissue was no longer present. 3. Because the nerve degenerated during initial tooth resorption, there was no evidence that deciduous root resorption was under nervous control. 4. in addition to odontoclasts, several other cells such as fibroblast-like cells and macrophages, were actively involved in root resorption during the shedding of deciduous teeth.