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DEVELOPMENT OF DENTITION

Stages of tooth development
Chronology
Eruption
Shedding

OBJECTIVES
• Explain normal and abnormal dental
development
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(C5)

The development of the human dentition is a
highly orchestrated series of events under strict
genetic control
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The developmental timing, location, morphology, structure, and
composition of teeth are primarily determined by cascades of
molecular events that are regulated by hundreds of genes
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Because the development of dentition is prolonged, it is
susceptible to environmental influences for many years
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•By approximately 6 weeks of age (in utero), the oral ectoderm begins to
proliferate at the future sites of primary teeth
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Driven By Epithelium
• T he continued proliferation and expansion of the oral
ectoderm allow the epithelial cells to contact and interact
with the underlying ectomesenchymal cells, thereby initiating
the development of a tooth bud primordia
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• If these early, epithelial-driven developmental events do not
occur, then teeth do not form
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• After tooth formation has been initiated by the invagination
of the oral epithelium, the ectodermal cells and the
underlying ectomesenchymal cells engage in a complex series
of interactions and signaling mechanisms
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These
interactions result in the differentiation of highly specialized
cells that produce the unique dental tissues and establish the
tooth size and shape
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g
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The oral epithelium gives rise to the enamel organ, which
differentiates into the enamel-forming cells, called
ameloblasts
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The tooth root surface eventually is covered by cementum,
which is formed by cementoblasts, which are derived from
the mesenchyme
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All of these processes involve strict genetic control, so they
represent potential pathways for hereditary defects of teeth
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• Partially differentiated cells → secretory function → cyst formation
• Fully differentiated cells→ form enamel and dentine→ odontoma or
supernumerary
• Degree of differentiation leads to cyst/ odntoma /supernumerary
formation

BELL STAGE
(HISTODIFFERENTIATION)

• Histo differntiation:
• Cells differentiate into odontoblasts and ameloblasts,No more
proliferation,Forerunner for apposition
• Disturbances in differntiation →abnormal enamel and dentine
• Disturbance in ameloblasts → Amelogenesis imperfecta
• Disturbance in odontoblasts→ Dentinogenesis imperfecta

BELL STAGE
(MORPHODIFFERENTIATION)

• Formative cells are arranged to outline the form and size of
tooth
• Occurs before matrix deposition
• Morphology of tooth established when inner enamel
epithelium arranged in such a manner that the boundary
between it and odontoblasts becomes future DEJ
• Disturbances in this stage → abnormal form and size of tooth
like peg lateral, microdontia,macrodotia

APPOSITION
• Layer like deposition of non-vital extracellular secretion in the
form of a tissue matrix
• Deposited by ameloblasts, odontoblasts
• Deposited in a definite pattern and a definite rate
• Formative cells start this at a specific sites called growth
centers as soon as the DEJ is established
• Systemic disturbance or local trauma leading to ameloblasts
→ interruption / arrest in matrix apposition → Enamel
Hypoplasia
• Dentinal hypoplasia rare and occurs after severe systemic
disturbances

CALCIFICATION
• Follows apposition
• Precipitation of inorganic calcium salts within the deposited
matrix,
• A slow gradual process that starts at the cusp tips or incisal
edge of the tooth and progresses
• Starts with a nidus precipitation about which further
precipitation occurs- Calcospherites
• Original nidus increases by addition of concentric laminations
that eventually approximate and fuse to a homogenous
mineralised tissue
• Disturbances→ Lack of fusion of calcospherites, not seen
readily in enamel but in dentine as interglobular dentine
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• Parathyroid hormone related protein is
also said to be needed for tooth eruption
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half to two thirds of final length at
the time of gingival emergence
• Functional eruptive phase:
– After tooth is erupted and meets its antagonist
– Teeth continue to move and erupt as the body continues
to change throughout life
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Precursors of osteoclasts(Mononuclear cells) must be recruited
into dental follicle prior to onset of eruption
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NOLLA’S STAGES OF TOOTH DEVELOPMENT(1952)

Chronology
• Logan and Kronfeld’s chronology table of 1935 most accepted
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– Times of initial calcification of primary teeth earlier by 2-6weeks to
that given by Logan and Kronfeld
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– Sequence of calcification of deciduous teeth should be changed to
Central incisor, first molar, lateral incisor, canine and second molar
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Table 9-2, Eruption of teeth- Text book Mc Donald )
– Eruption age of primary teeth was revised
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Hatched
bar = mandibular;solid bar = maxillary
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J Am Dent Assoc 89:872-879,
1974
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Hatched bar = mandibular; solid bar =
maxillary
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In McDonald RE, Avery DR (eds):
Dentistry for the Child and Adolescent, ed 5
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Louis, Mosby, 1987, p 190
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• Dental age during the mixed dentition period
may be assessed on the basis of which teeth
have erupted, the amount of resorption of the
roots of primary teeth, and the amount of
development of the permanent teeth

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