This document discusses the development of dentition and occlusion from embryonic development through adulthood. It describes the stages of tooth development from the dental lamina to bud, cap, and bell stages. It also outlines the periods of occlusal development from pre-dental through deciduous, mixed, and permanent dentition. Key details include the eruption schedule and sequencing of primary teeth, physiological spacing in deciduous dentition, transition from deciduous to permanent molars, and factors that influence deep bite in early development.

1. Development of Dentition and Occlusion
PROF (Dr.) SAIBEL FARISHTA

2. Development Of Teeth
The embryonic oral cavity is lined by stratified squamous epithelium
known as oral ectoderm. Around the 6th week of intra-uterine life the
infero-lateral border of the maxillary arch and supero-lateral border of
the mandibular arch show localized proliferation of the oral ectoderm
resulting in the formation of horse-shoe shaped band of tissue called the
dental lamina.
The dental lamina plays an important role in the development of the
dentition. The dec. teeth are formed by direct proliferation of dental
lamina. All teeth originate from the dental lamina.

3. The ectoderm in certain areas of the dental lamina proliferates and forms
knob-like structures that grow into the underlying mesenchyme. Each of
these knobs represent a future dec. tooth and is called the enamel organ.
The enamel organ passes through a number of stages ultimately forming
the teeth. Based on the shape of enamel organ, the development of
teeth can be divided into 3 stages – bud, cap and bell stage.

4. Bud Stage -
This is the initial stage of tooth formation where the enamel organ
resembles a small bud. In this stage, the enamel organ consists of
peripherally located low columnar cells and centrally located polygonal
cells. The surrounding mesenchymal cells proliferate resulting in their
condensation in two areas. The area of condensation below the enamel
organ is the dental papilla. The ectomesenchymal condensation that
surrounds the tooth bud and dental papilla is the dental sac. The dental
papilla and dental sac is not well defined during this stage. The cells of
the dental papilla form the dentine and pulp while the dental sac forms
cementum and periodontal ligament.

5. Cap Stage -
The tooth bud continues to proliferate resulting in a cap shaped enamel
organ. This is characterized by a shallow invagination on the under
surface of the bud. The outer cells of the cap covering the convexity are
cuboidal and are called the outer enamel epithelium. The cells lining the
concavity of the cap become tall columnar and are called as the inner
enamel epithelium. The central area of the enamel organ between the
outer and inner enamel epithelium, which initially consisted of polygonal
cells, acquire more intercellular fluid and form a cellular network called
the stellate reticulum. The staellate reticulum has a branched network of
cells.

6. Bell Stage -
Due to continued uneven growth of the enamel organ, it acquires a bell
shape. The cells of the inner enamel epithelium differentiate prior to
amelogenesis into tall columnar cells called ameloblasts which lay down
enamel. The cells of the inner enamel epithelium eert a strong influence
on the underlying mesenchymal cells of the dental papilla.
A few layers of flat squamous cells are seen between the inner enamel
epithelium and stellate reticulum. This layer is called the stratum
intermedium.
The stellate reticulum expands due to continued accumulation of intra-
cellular fluid. The cells of this area are star shaped, having large
processes that anastamose with adjacent cells. As the enamel formation
starts, stratum reticulum collapses to a narrow zone, thereby reducing
the distance between the outer enamel and inner enamel epithelium.
The cells of outer enamel epithelium flatten to form low cuboidal cells.
The outer enamel epithelium is thrown into folds which are rich in
capillary network. This provides a source of nutrition for the enamel
organ.

7. Before the inner enamel epithelium begins to produce enamel, the
peripheral cells of the dental papilla differentiate into odontoblasts. These
are cuboidal cells that later assume a columnar form and produce dentin.
The dental sac exhibits a circular arrangement of its fibers and resembles
a capsule around the enamel organ. The fibers of the dental sac form the
periodontal fibers that span between the root and bone.
The junction between the inner enamel epithelium and odontoblasts
outlines the future dentino-enamel junction.

8. Root Formation -
Root development begins after the dentin and enamel formation reaches
the future cemento-enamel junction. The outer and inner enamel
epithelium join and form a sheath that helps in molding the shape of the
root. This sheath is called the Hertwig’s epithelial root sheath.

9. Periods Of Occlusal Development
1. Pre-dental period
2. Deciduous dentition period
3. Mixed dentition period
4. Permanent dentition period
1. Pre-Dental period – Period after birth during which the neonate does
not have any teeth. It lasts for 6 months after birth.
Gum Pads
The alveolar processes at the time of birth are known as gum pads.
Gum pads are pink, firm and are covered by a dense layer of fibrous
periosteum. They are horse-shoe-shaped and develop in 2 parts.

10. They are the labio-buccal portion and the lingual portion. The two
portions of the gum pads are separated from each other by a groove
called the Dental groove.The gum pads are divided into 10 segments
by certain grooves called the teansverse grooves. Each of these
segments consists of one developing deciduous tooth sac.

11. The gingival groove separates the gum pad from the palate and floor
of the mouth. The transverse groove between the canine and first
dec. molar segment is called the lateral sulcus. The lateral sulcus of
the mandibular arch is normally more distal to that of the maxillary
arch.
The upper and lower gum pads are almost similar to each other. The
upper pad is wider and longer than the mandibular. Thus, when the
upper and lower gum pads are approximated, there is a complete
overjet. Contact occurs between the upper and lower gum pads in
first molar region and space exists between them in the anterior
region. This infantile open bite is considered normal and helps in
suckling.

12. Status Of Dentition
The neonate is without teeth for 6 months of life. At birth the gum
pads are not sufficiently wide to accommodate the developing
incisors which are crowded in their crypts. During the first year of life
the gum pads grow rapidly permitting the incisors to erupt in good
alignment.
Very rarely teeth are found to have erupted at the time of birth. Teeth
that are present at the time of birth are called Natal teeth.
Sometimes teeth eruptin an early stage. Teeth that erupt during the
first month of age are called the Neonatal teeth. The natal and
neonatal teeth are mostly located in mandibular incisor region and
show a familial tendency.

13. 2. Deciduous Dentition Period – the The initiation of primary tooth buds
occurs during the first 6 weeks of intra-uterine life. The primary teeth
begin to erupt at about 6 months. The eruption of all primary teeth is
completed by 2.5-3.5 years of age when the second dec. molars
come into occlusion.
Eruption Age And Sequence Of Deciduous Dentition
The mand. central incisors are the first teeth to erupt into the oral cavity
around 6-7 months of age. The timing of tooth eruption is highly
variable. A 3 month variation is considered normal. The sequence of
eruption of the dec. dentition is : A-B-D-C-E.
The primary dentition is established by 3 years of age on eruption of the
second dec. molars. Between 3-6 years of age, the dental arch is
relatively stable and very few changes occur.

15. Spacing Of Deciduous Dentition
Spacing exists between dec. teeth. These spaces are called as the
physiological spaces or the developmental spaces. Spaces in dec.
dentition is important for normal development of permanent dentition.
Absence of spaces in dec. dentition is indicative of crowding in
permanent dentition.
Spacing is seen mesial to max. canines and distal to mand. Canines.
These physiological spaces are called as the Primate spaces or Simian
spaces or Anthropoid spaces.

16. Flush Terminal Plane
The mesio-distal relation between the distal surfaces of the upper and
lower dec. molars is called the terminal plane. A normal feature of dec.
dentition is to find a flush terminal plane where the distal surfaces of the
upper and lower second dec. molars are in the same vertical plane.
Deep Bite
A deep bite may occur in the initial stages of development. Deep bite is
increased by the fact that the dec. incisors are more upright and the
lower incisal edges often contact the cingulum area of the max. incisors.
This deep bite is later reduced due to – eruption of dec. molars, attrition
of incisors and forward movement of the mandible due to growth.

17. 3. Mixed-Dentition period – This period begins around 6 years of age
with the eruption of the first per. Molars. Dec. teeth and some per.
Teeth are present during this period. This period can be classified into
3 phases – 1) First Transitional period 2) Inter-Transitional period and
3) Second Transitional period.
1) First Transitional period – is characterized by the emergence of the
first per. Molars and exchange of dec. incisors with the per. Incisors.
Emergence of the First permanent molars
The mandibular first molar is the first tooth to erupt at around 6 yrs of
age. The first permanent molars are guided into the dental arch by the
distal surface of the second dec. molars.

18. The mesio-distal relation between the distal surfaces
of the upper and lower second dec. molars can be of
three types -
1) Flush Terminal plane
2) Mesial Step Terminal plane
3) Distal Step Terminal plane

19. 1) Flush Terminal Plane – The distal surface of the upper and lower second
dec. molars are in one vertical plane. This is called flush or vertical
terminal plane. This is a normal feature of the dec. dentition. For the
transition of such an end on molar relation to a Class I molar relation, the
lower molar has to move forward by 3-5 mm relative to the upper molar.
This occurs by utilization of the physiologic spaces and Leeway space in
the lower arch and by differential forward growth of the mandible. The
shift in lower molar from a flush terminal plane to a Class I relation can
occur in two ways – a) Early Shift b) Late Shift.
a) Early Shift – This occurs during the early mixed dentition period. The
eruptive force of the first permanent molar is sufficient to push the dec.
first and second molars forward in the arch to close the primate space
and to establish a Class I molar relationship. As this occurs in the early
mixed dentition period, it is called early shift.

20. 2) Mesial Step Terminal Plane – The distal surface of the lower second
dec. molar is more mesial than that of the upper. Thus, the
permanent molars erupt directly into Angle’s class I occlusion. This
usually occurs due to early forward growth of the mandible.
3) Distal Step Terminal Plane – The distal surface of the lower second
dec. molar is more distal to that of the upper. Thus the erupting per.
Molars maybe in Angle’s Class II occlusion.
b) Late Shift – Many children lack the primate space and the erupting
permanent molars are unable to move forward to establish class I
relationship. In these cases, when the dec. second molars exfoliate,
the per. First molars drift mesially utilizing the Leeway space. This
occurs in the late mixed dentition period and is thus called late shift.

21. The Exchange Of Incisors
During the first transitional period the dec. incisors are replaced by the
per. incisors The man. Per. incisors are the first to erupt. The per.
incisors are considerably larger than the dec. teeth they replace. This
difference between the amount of space needed for the accomodation
of the incisors and the amount of space available for this is called ‘incisal
liability’. This is roughly 7 mm in max. arch and 5 mm in man. arch. The
incisal liability is overcome by the following factors –
a) Utilization of interdental spaces seen in primary dentition
b) Increase in inter-canine width
c) Change in incisor inclination
Inter-transitional Period
In this period, the max. & man. arches consist of sets of dec. & per. Teeth.
This phase is relatively stable and no change occurs.

22. The Second Transitional Period
This period is characterized by the replacement of the dec. molars and
canines by the premolars and per. cuspids. The combined mesio-distal width
of the per. Canines and premolars is usually less than that of the dec.
canines and molars. The surplus space is called ‘Leeway Space of Nance’. It
is greater in the mand. Arch [1.8 mm] than the max. arch [3.4 mm]. The
excess space available after the exchange of the dec. molars and canines is
utilized for mesial frift of the man. Molars to establish Class I molar relation.

23. The Ugly Duckling Stage [Broadbent]
This condition is sometimes seen during the eruption of per. Canines. As the
developing per. Canines erupt, they displace the roots of the lateral incisors
mesially. This results in transmitting of the force onto the roots of the
central incisors which also get displaced mesially. A resultant distal
divergence of the crowns of the two central incisors causes a midline
spacing.
This condition usually corrects by itself when canines erupt and the pressure
is transferred from the roots to the coronal area of the incisors.

24. The Permanent Dentition Period
The eruption sequence of the max. permanent dentition –
6 – 1 – 2 – 4 – 3 – 5 – 7 or
6 – 1 – 2 – 3 – 4 – 5 – 7
The eruption sequence of the man. permanent dentition –
6 – 1 – 2 – 3 – 4 – 5 – 7 or
6 – 1 – 2 – 4 – 3 – 5 – 7

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