Development of the Dentition

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Development of the deciduous and permanent dentition.Alexandria University, Egypt

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    Development of The Dentition

    Prof. Nadia el Harouni

    By the end of this lecture you should be able to:

    1- Recognize the normal features of the mouth of the neonate

    2- Discuss features of normal occlusion of the primary dentition

    3- Understand normal development of the primary to permanent dentition.

    4- Recognize the normal pattern of eruption of the permanent dentition.

    Humans have two dentitions, the deciduous (primary) and permanent

    (secondary)

    Dental arches constantly change from birth to adulthood, these changes can

    be divided into four stages:

    1. Gum pad stage

    2. Deciduous dentition stage

    3. Mixed dentition stage

    4. Permanent dentition stage

    A) The Mouth of the Neonate

    1. The Gum Pads

    The maxillary arch is horseshoe shaped, and the gum pads extend buccally

    beyond those in the mandible (wider in every way)

    At birth the alveolar processes are covered with gum pads , soon

    segmented by transverse grooves into 20 sites of developing teeth

    At birth the gum pads are not wide enough to accommodate the

    developing incisors which are rotated and crowded in their crypts but

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    during the first year of life the jaws grow rapidly in width. This allows

    the incisors to erupt in good alignment guided by the pressure of the

    tongue and lip.

    The lateral sulcus is the groove marking the distal of the canine

    segment

    The gingival groove is the horizontal groove separating the max.

    gum pads from the palate.

    The dental groove extends from the incisive papilla to meet the

    gingival groove at the canine region then lateral to the molar region

    The lower arch is U shaped and the lower gum pad is slightly

    everted labially it shows:

    The lateral sulcus

    The gingival groove: the lingual extension of the gum pads

    The dental groove: joins the gingival groove at the canine

    region

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    2. Neonatal Jaw Relationships.

    No precise relationship is seen

    Anterior open bite is normal. The tongue fills the space between the gum

    pads and rests on the lower lip

    3-Precociously erupted primary teeth Natal teeth:A child may be born with teeth already present in the Oral

    cavity

    Neonatal teeth erupt within the first month of life

    Pre-erupted teeth appear within the second and third months of life

    85% are deciduous (estimated) (management ?)

    tooth age

    Mand. centrals 7 months

    Max. centrals 9 months

    Max. laterals 11 months

    Mand. laterals 11 months

    Max. & mand. Ds 18 months

    Max. & mand. Cs 2 Years

    Mand. Es 2 years

    Max. Es 2 years

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    B) The Primary Teeth and Occlusion.

    1. Development of the primary teeth

    a) Calcification.

    At the fourth month IU

    At birth - of the crowns are formed

    b) Eruption.

    Always a range

    c) Teething Only trivial symptoms

    d) Size and shape of primary teeth. not much variability as in

    permanent

    e) Ankylosis of primary teeth:

    More common than permanent, Lower more than upper not truly submerged

    2- Development of the primary occlusion

    a) Primary dental arches.

    Ovoid

    Generalized spacing

    Primate spacing

    Slight increase anteriorly from birth till 12 months

    Posteriorly more increase

    b) Occlusal relations.

    No 3 dimensional reln until the eruption of the first molars ,

    The normal signs of normal deciduous occlusion include

    -Spaced anteriors

    -Primate spaces; The deciduous teeth are usually spaced as they erupt.

    The spaces mesial to the maxillary canines and distal to the mandibular

    canines are slightly wider and known as primate spaces. The spaces that

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    exist between the deciduous molars usually close by the time of eruption of

    the 1st permanent molars, whereas the spaces between the deciduous

    incisors remain till these teeth are replaced by their successors.

    -Shallow overbite and overjet

    -Almost vertical anteriors

    -Ovoid arch form

    -CLASS I molar and cuspid relation

    -Straight /flush terminal plane which changes into a mesial step by

    the age of 6 due to

    a) cuspal attrition so the mandible moves forward

    b) greater spacing in the mandible than the maxilla

    d) Disorders of the primary occlusion.

    Variable according to ethnic group and culture

    Class III and anterior crossbite

    Bruxism: a functional malocclusion.

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    The mixed Dentition stage

    Transition from deciduous to permanent dentition

    It is the period from 6 to about 12 years of age .During this

    period both the deciduous and the permanent teeth are

    present.

    The permanent teeth which follow the deciduous teeth are called

    successional teeth ( incisors, canines and premolars) while the

    permanent molars are called accessional teeth.

    Calcification of the permanent dentition All start after birth except 6s (might)

    As the permanent teeth are calcified after birth, they are susceptible to local

    and general environmental changes

    Eruption:

    a) Interrelationships between calcification and eruption.

    Eruption is a developmental process that moves the tooth

    from its crypt position through the alveolar process into the

    oral cavity.

    During eruption, the root elongates, the primary root resorbs,

    the permanent tooth moves occlusaly and the alveolar

    process grows.

    Permanent teeth begin their eruptive movement when their

    crown is completed.

    It takes 2 to 5 years for the posterior teeth to reach the

    alveolar crest following completion of their crowns and from

    12 to 20 months to reach occlusion after reaching the alveolar

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    margin. Roots are completed a few months after occlusion is

    attained

    It may appear that the incisor erupts first, whereas, in truth, the

    molar has preceded it in starting eruption, but is moving so slowly

    that the incisor passes by it

    b) Factors regulating and affecting eruption.

    1- Racial

    2- Genetic

    3- Mechanical

    4- Nutritional (to a lesser extent).

    5- Gender differences; Girls usually ahead

    c) Timing and variability of eruption

    Very variable, no set rules.

    N.B. Recently It has been observed that eruption occurs only from 8 pm till

    midnight or 1 am (growth hormone release?!) stops during the day or the

    tooth intrudes.

    d) Sequence of eruption.

    Also variable but most common;

    maxilla: 6,1, 2, 4, 5, 3, 7, 8

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    6,1, 2, 4, 3, 5, 7, 8

    mandible: 6, 1, 2, 3, 4, 5, 7,8

    6, 1, 2, 4, 3, 5, 7, 8

    Unfavorable where 7 erupts before 5

    First molars 6 years

    6 y

    7 y

    7 y

    8 y

    9 y

    10 y

    11 y

    11 y

    11 y

    12 y

    12 y

    rs 16-25 y

    Mandibular teeth erupt ahead of maxillary teeth except the maxillary

    premolars.

    e) ectopic eruption: The eruption of a tooth in an abnormal position in the

    permanent dentition, usually upper 6 or lower 1,2,3

    NB impaction :Failure of a tooth to emerge usually due to insufficient

    space ,or supernumerary tooth blocking its path or for no local reasons as

    in syndromes.

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    f) Factors Determining the tooths position during eruption.

    I-intra-alveolar stage:

    1-heridity

    2-presence of adjacent teeth

    3-early loss of deciduous

    4-pattern of resorption

    5-local pathological conditions

    6-general pathology affecting growth.

    7-mesial drifting tendency.

    II- Pre-occlusion stage

    1-lips, cheeks, muscles.

    2-objects brought in the mouth.

    3-caries and extractions of adjacent Teeth

    III- Occlusal stage

    All previous in addition to muscles of mastication through forces of

    occlusion and the anterior component of force

    Uses of the dental arch perimeter

    A) Alignment of the permanent incisors

    b) space for the cuspids and premolars

    c) adjustment of the molar occlusion.

    First permanent molar:

    1st permanent molars are the keys of the dental arches.

    The upper molar is located at the base of the key ridge that descends from

    the zygomatic arch.

    It is guided into place through

    1. the position of the second deciduou