A . DEVELOPMENT OF THE DENTAL ORGAN (ENAMEL ORGAN):

AS EARLY AS THE SECOND MONTH OF FETAL LIFE, THE DEVELOPMENT OF THEAS EARLY AS THE SECOND MONTH OF FETAL LIFE, THE DEVELOPMENT OF THEDECIDUOUS TEETH MAY FIRST BECOME EVIDENT.

1. Dental lamina and Bud stage At about six weeks of prenatal life, an

epithelial thickening occurs in the region p g gwhere the teeth will form.

This thickening is termed the dental lamina. Shortly after the dental lamina y

differentiates, twenty tooth buds begin to appear on the dental lamina in the approximate location of the twenty

primary teethprimary teeth. The individual tooth buds are somewhat

round, or ovoid, and this stage is appropriately known as the bud stageappropriately known as the bud stage.

2. Cap stage2. Cap stageThe basal portion invaginates, and the structure thus

formed gives the appearance of a cap, and hence g pp p,this phase is termed the cap stage.

3. Bell stageAs the concavity in the basal area of the cap continues to deepen, development of the tooth enters the bell stage and the tooth's crown development of the tooth enters the bell stage and the tooth s crown can be recognized, and the dentinoenamel junction is identifiable. During the latter portion of the bell stage, the dental lamina connection with the deciduous tooth begins to break down, and eventually with the deciduous tooth begins to break down, and eventually disintegrates. As this portion of the dental lamina disappears, the bud of the succedaneous tooth is forming from it.

4. Root developmentpWhen enamel and dentin deposition have formed the area of the cementoenamel junction, the bell stage is regarded as ending, and the root development stage begins.

fThe enamel organ then proliferates a structure known as Hertwig's sheath, from which the root structure is formed.

The dentin and cementum of the root are then deposited

5. Chronology

The chronology of initiation of the tooth buds from the dental lamina occurs in three phases, over a total time period of about 5 1/2 years.

a .Deciduous dentition - As previously indicated, development of all deciduous teeth is initiated during the first few months of fetal life.

b Succedaneous teeth - All the permanent successors to theb. Succedaneous teeth All the permanent successors to the deciduous teeth begin to form in a time range between five fetal months for the central incisors, to about 10 months after birth for the second premolars.

c. Non-succedaneous permanent teeth - The initiation of the permanent molars occurs in a time period between four fetal months for the first molars to approximately five years for the third molars.

B. Eruption:Prior to the complete calcification of its root, the tooth normally originates eruption by pushing through the mucous normally originates eruption by pushing through the mucous membrane cover of the alveolar process, and into the oral cavity. The eruption process is considered complete when the tooth

i ( ) i h i j b I li contacts its opponent(s) in the opposite jaw member. In reality, the term eruption involves two entities:

I .Active eruptionActive eruption is the process just described, from the tooth's entry into the oral cavity, to its contact with an antagonist in the opposing arch.

II . Passive eruptionPassive eruption is the continuing process of adaptation of the t th t h i i i l d l l l ti hi ft ti tooth to changing incisal and occlusal relationships, after active eruption has ended. This adjustment to attritional wear and changing locations of adjacent and opposing teeth, continues throughout the life of the tooth. In fact, many times when a

h h b l h i ( ) ill i h tooth has been lost, the antagonist(s) will super-erupt into the space, and beyond the normal occlusal plane.

C. ROOT COMPLETION:THE ROOT APEX IS FUNNEL SHAPED SHORTLY AFTER ERUPTION. ROOT FORMATION IS THUS NOTCOMPLETE UNTIL ADDITIONAL DENTIN DEPOSITION REDUCES THE FUNNEL SHAPED OPENING TO ACONSTRICTED FORAMENCONSTRICTED FORAMEN. AT AGE 3 YEARS, ROOT FORMATION HAS ENDED FOR ALL DECIDUOUS TEETH.

D. Position of Developing Permanent Teeth:p gAll period that the child is in the deciduous dentition stage, the permanent teeth are beginning, and continuing, their growth process.The permanent incisor and canine buds are found in a position just lingual to the roots of their deciduousposition just lingual to the roots of their deciduous predecessors, while the premolar buds are located in the root furcation of the deciduous molars.Th t l t d t th d th iThe permanent molars are not succedaneous teeth, and their buds develop from the dental lamina in the alveolar process distal to the deciduous dentition.

E. Late Deciduous Stage and the Permanent First M lMolars:The mandibular first molar is normally the first permanent tooth to emerge, at about age six, thus ending the deciduous dentition stage, and initiating the mixed dentition stage.

The maxillary first molars follow shortly thereafter, and the four first molars are considered to be the cornerstones in the development of occlusion of the permanent co s de ed o be e co e s o es e de e op e o occ us o o e pe a edentition.

Because they erupt first, and because of their strategic location in the arches, the relationship of the maxillary and mandibular first molars to each other has arelationship of the maxillary and mandibular first molars to each other has a significant influence on the occlusion of the permanent dentition.

If any of the deciduous teeth are lost prematurely, the permanent first molar in that quadrant has a tendency to tilt or "drift" mesially thus reducing the space available forquadrant has a tendency to tilt or drift mesially, thus reducing the space available for the permanent canines and premolars.

This condition may result in impaction of permanent teeth, or crowding and l l i f th t d t l h imalocclusion of the permanent dental mechanism.

F. Resorption and Exfoliation:pResorption:

a .Shortly after the permanent first molars appear, thea .Shortly after the permanent first molars appear, the permanent mandibular central incisors are scheduled to erupt. However, before this can occur, the deciduous predecessors must be shed, or exfoliated. The processpredecessors must be shed, or exfoliated. The process by which the root of the deciduous tooth is "melted away" is termed resorption.

b. Generally, resorption begins at the apex and moves toward the cervical line. The actual process is due to

t l ti ti itosteoclastic activity.

c. The resorption phase normally begins at least a yearc. The resorption phase normally begins at least a year prior to exfoliation.

F. Resorption and Exfoliation:2. Exfoliation

When the root structure of the deciduous tooth is almost entirely resorbed the remaining crown almost entirely resorbed, the remaining crown becomes so loosened that it is lost. This phenomenon is known as exfoliation. Exfoliation usually occurs symmetrically, with the same teeth of the right and left sides being lost at about the same timesame time.Mandibular teeth generally precede the same maxillary teeth in exfoliation, with the exception of the second molars, where all four are lost simultaneously. The mixed dentition period ends with the exfoliation of the deciduous second molars with the exfoliation of the deciduous second molars at about age 12.

Incomplete resorption

Occasionally, root resorption is only partial, and the deciduous tooth does not exfoliate In this situation thedeciduous tooth does not exfoliate. In this situation, the permanent tooth must erupt in an abnormal position, or be entirely blocked from entry.

If this aberrant feature is present, it is the responsibility of the practitioner to diagnose it and perform the treatment whichpractitioner to diagnose it, and perform the treatment, which is extraction of the offending deciduous tooth.

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