Definition: Shedding is a natural physiological eliminationof the deciduous teeth at specific ages as a resultof the resorption of their roots prior to theeruption 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 developmentof speech and chewing.
Early primary tooth extraction leads to loss of its space.This will cause greatirregularities in the dentalarch with high risk of cariesand Periodontium diseases.
Thus space maintainershould be used tomaintain this space.
Pattern of shedding:Resorption of the roots of primary teeth starts at thelingual apical areas in the anterior teethAnd in the interradicular areas of molars.
It is related to where the erupting permanentsuccessors are located. Anterior teeth:
First the pressure cause Then resorption of the rootcrypt wall resorption. occurred lingo-apically.
Later, the developing permanent tooth germs occupy aposition apical to the deciduous tooth, which permitsthem to erupt in the position formerly occupied by thedeciduous tooth.
However frequently, this apical positioning of thepermanent tooth germs does not occur particularly inthe case of the permanent mandibular incisors wherethe permanent ones erupt lingual to the still functioningdeciduous incisors.These deciduous teeth are often shed with aconsiderable portion of the root remaining on their labialaspect and with much of their pulp chamber intact.
First, resorption of the roots of the deciduous molarsoften begins early on their inner surface facing theinter-radicular septum. This early resorption occurslong before shedding of deciduous molars.
As a result of the continued growth of the jaws andocclusal movement of the deciduous molars, thepremolar tooth germs come to be apical to thedeciduous molars.
This change in the position provides:•The growing premolars adequate space for theircontinued growth.•And also relieves the pressure on the roots of theoverlying deciduous molars.
The areas of early resorption of the roots ofdeciduous molars are repaired by deposition of acementum-like tissue but less mineralized and thealveolar bone is also repaired.
Later, when the premolars begin to erupt, rootresorption of deciduous molars is again initiated andcontinued until the roots are completely resorbed.
•The resorption may even proceed far up into thecoronal dentin and occasionally some areas of theenamel may be destroyed.
The process of tooth resorption is intermittent;there are periods of resorption and periods of rest andrepair.However, in the long term, resorption predominatesover repairThe primary teeth become loose during the periodsof resorption and tighten during the brief periods ofapposition.
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.Congenitally missing. Aberrant position.
B) Masticatory forces:Increased force applied to a deciduous tooth caninitiate its resorption. Growth of the face and jaws andthe corresponding enlargement in the size andstrength of the muscles of mastication probablyincrease the forces applied to the deciduous teeth tothe point that they damage the supporting of the tooth,in particular the periodontal ligament and initiateresorption of the tooth.
Histology of shedding:The fact that programmed cell death is seen duringshedding that occurs at specific ages is consistent withthe concept that shedding is a geneticallydetermined process.
I- Resorption of hard dental tissues:The resorption of the hard dental tissues of deciduousteeth is achieved by highly specialized multinucleatedcells called odontoclasts because of their involvementin the removal of dental tissues. These cells areidentical to osteoclasts.
II- Histological characters of pulp during shedding:It should be emphasized thatthe pulp tissue in teethundergoing shedding appearshistologically normal exceptthat neural elements seem tobe missing.Thus the pulp does not Pcontribute to the process ofshedding and plays apassive role in this process.Note:Odontoblasts degenerated and replaced byodontoclasts (internal resorption).
II- Histological characters of the PDL duringshedding:Loss of the periodontal ligament fibers is abruptand programmed.The cells show signs of death.
Cell death assumes at least two forms• fibroblasts exhibit signs of • the fibroblasts exhibit interference with normal morphological features cellular processes characteristic of apoptoticsuch as secretion as well cell death includingas other cytotoxic condensation of the cell with its ultimatealteration that eventually phagocytosis bylead to cell death. This neighboringprocess is induced in macrophages or adjacentresponse to local cell fibroblastsinsult.
Clinical consideration: 1-Ankylosis and submerged deciduous teeth:•Ankylosis is a bony union between the alveolar boneand the roots of teeth. Thus the active eruption of anankylosed tooth ceases.•Mild trauma may result in damage to the periodontalligament leading to ankylosis of a deciduous toothrather than its loss.
:Clinical featuresBecause of the continued eruption of the neighboringteeth and increased height of the alveolar process, theankylosed tooth may be either "shortened" orsubmerged in the alveolar process (below the plane ofocclusion by 1 mm or more).
:Side effectsSubmerged deciduous teeth thus prevent the eruptionof their permanent successors or force them away fromtheir position. Submerged deciduous teeth shouldtherefore be removed.
2-Retained deciduous teeth:Deciduous teeth may be retained for a long timebeyond their usual shedding schedule.Retention may be due to local or systemic causes.Congenital absence and impaction of the permanentsuccessors 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 yearsin a good functioning condition. However, resorptionof the roots and continued active and passive eruptioncause their loosening and final loss in most cases.Retainedcanine.
3-Remnants of deciduous teeth:Sometimes, segments of the roots of deciduous teethare not in the path of erupting successors and mayescape resorption.
These fragments are most frequently found in theregion of the premolars, especially the lower secondpremolars. The reason is that the roots of the lowersecond molar are widely divergent; the mesio-distaldiameter of the second premolar is much smaller thanthe greatest distance between the roots of thedeciduous molar.
:Fate of root remnants•Root remnants may remain embedded in the alveolarprocess.•Completely surrounded by and ankylosed to the bone.•Frequently they are cased in heavy layers of cellularcementum.•When they are close to the surface of the jaw, theymay ultimately be exfoliated.•Progressive resorption of the root remnants andreplacement by bone may cause disappearance ofthem.
Describe the pattern of anterior teeth shedding.Describe the pattern of posterior teeth shedding.Mention the factors that determine the pattern and rate ofdeciduous 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.