Chronology And Development Of The Dentition
Human dentition consists of the primary dentition, the mixed dentition and the permanent dentition. The first evidence of tooth formation occurs by the sixth week of intrauterine life within the developing jaws. During the intrauterine periods of development, the jaws harbour the tooth buds of all the teeth that belong to both the primary and permanent dentition in various stages of their development.
Table of Contents
Stages Of Tooth Development
- At about the 4th week of intrauterine life: The dental lamina is formed.
- Around 5–6 weeks of intrauterine period: The tooth buds of primary teeth begin to form.
Read And Learn More: Oral Anatomy Notes
The development of the tooth bud can be grossly described in the following stages:
- Bud stage
- Cap stage
- Bell stage
Bud stage:
- The ectodermal cells rapidly proliferate and form swellings/knobs in 10 sites on the dental lamina in the maxilla and the mandible representing the future primary tooth buds. These epithelial thickenings resemble buds; hence, this stage of tooth development is called bud stage.
- The mesenchyme then reciprocally differentiates underneath these ectodermal thickenings. The mesenchymal cells proliferate under the concavity of the enamel organ and represent the formation of the dental papilla.
- The dental sac or the dental follicle develops around the enamel organ and the dental papilla.
Thus, the tooth germ consists of the enamel organ, dental papilla and dental follicle
Origin of the tissues of the tooth:
Cap stage:
- The tooth bud continues to proliferate but not uniformly. It forms a shallow invagination along the deeper surface resembling a cap. Hence, this stage of tooth development is called the cap stage.
- The cells of the enamel organ now differentiate into the
- Outer enamel epithelium
- Inner enamel epithelium
- Stellate reticulum
- Stratum intermedium
- The dental papilla and the dental follicle proliferate simultaneously.
Bell stage:
- As the enamel organ continues to grow, it assumes a bell shape due to the pressure exerted by the growing dental papilla and the stellate reticulum.
- It is in bell stage that
- The shape of the crown is determined by the differential growth of the Cells of enamel organ.
- The cells of the inner enamel epithelium differentiate into ameloblasts And initiate amelogenesis.
- As the crown structure is formed the cells of the stellate reticulum and stratum intermedium collapse reducing the distance between the active ameloblast and nutrient capillaries.
- At the cervical portion of the crown, the cells of the inner enamel epithelium and outer enamel epithelium unite to form the cervical loop.
- The peripheral cells of the mesenchyme of the dental papilla differentiate into odontoblast and deposit dentin.
As the bell stage advances, the mineralization of the crown is completed and root formation begins.
Root formation:
In the bell stage, the enamel organ of the primary teeth show the successional lamina.
The successional laminae are lingual extensions that give rise to enamel organs of the permanent successor teeth. Hence, when the enamel organs of the primary teeth are in bell stage, one can see the dental lamina and enamel organ of the respective permanent successor teeth in the bud stage (permanent incisors, canines and premolars).
Predentate Period
The period from birth till the eruption of the first primary teeth is called the predentate period.
- At birth, the dental arches are called gum pads. They are usually non-dentate or edentulous and facilitate suckling. At times, some teeth tend to erupt prematurely and are referred to as neonatal or natal teeth. The natal teeth are usually hypermobile and sharp. They may hamper feeding in infants.
Primary Dentition
The primary dentition consists of 20 primary teeth also called deciduous teeth or milk teeth.
- With the eruption of the first teeth into the oral cavity, the primary dentition comes into existence (between 6 months to 1 year of age).
- By the age of 3 years, the complete compliment of the primary dentition is established.
Thus, the primary dentition period extends from eruption of the first primary teeth till the eruption of first permanent teeth (approximately 6 months to 6 years of age).
The primary dentition in each arch has:
- Two primary central incisors
- Two lateral incisors
- Two canines
- Four molars in each arch
Hence, the dental formula for the primary dentition stands as follows:
ICM/ICM = 212/212
Unique features of the primary dentition:
- Primary teeth are overall smaller in size and whiter in colour compared to permanent teeth.
- The primary teeth appear cup shaped due to the marked cervical constriction of the crowns.
- The roots of the primary teeth are narrow and slender. The roots of the molar teeth flare in order to accommodate the underlying permanent successor teeth.
- Primary dentition characteristically shows the presence of spaces between the primary teeth. These spaces play an important role in accommodating larger permanent teeth and ensure proper alignment of these teeth.
- The contact area between the adjacent primary molars is wide and broad
- The occlusal table is shallow and not as wide as in permanent posterior teeth.
Development of primary dentition:
Although the period of primary dentition becomes evident with the eruption of first primary teeth, more precisely the development of primary dentition begins with first evidence of calcification of the first primary tooth. Hence, it spans from first evidence of calcification of first primary tooth till the root completion of last primary teeth (i.e. 14 months in utero to 3.5 years of age after birth).
Stage of calcification:
- The calcification of primary tooth begins as early as 13–16 weeks in utero. By 18–20 weeks, the calcification of all the primary teeth begins and continues unto the formation of crown.
- Crown formation begins following calcification of the tooth. Passing through stages of tooth formation the as described before the crown takes the form of tooth it is intended to be.
Crown formation for each primary tooth:
Root formation and eruption:
Root formation begins with the completion of crown from the cervical region of the tooth.
- When two-thirds of root formation occurs, eruption of the tooth begins and the tooth traverses through the alveolar process.
- When three-fourth of root formation is complete, the tooth begins to erupt into the oral cavity. It continues to actively erupt until it establishes itself into occlusion with the tooth in the opposing arch.
The root formation completes within 1–2 years after the tooth first erupts into the oral cavity. The root formation of all the primary teeth is accomplished approximately by 3 years of age after which the development of primary dentition stops. The chronology of primary teeth is given in table.
Chronology of primary teeth:
The process of shedding then initiates exfoliation of primary teeth and its replacement by the permanent teeth.
Sequence Of Eruption Of Primary Teeth
The sequence of eruption of teeth can vary depending on race, ethnicity, etc. The most commonly evident sequence of eruption for primary teeth is presented here.
- The central incisors (a) are usually the first ones to erupt, followed by the lateral incisors (b), first molars (d), canines (c) and lastly second molars (e). This is abbreviated as abdce.
While the sequence is common to both the jaws:
- The eruption in maxilla is independent of the eruption in mandible.
- Most commonly the mandibular incisors are the first to erupt into the oral cavity.
- At times, the maxillary incisors erupt earlier than the mandibular incisors.
Eruption Of Primary Teeth
Before the teeth make their way into oral cavity, these undergo development within the jaws, which includes formation of crown and then the root.
- When the root formation is approximately two-third complete, the teeth traverse through the alveolar crest.
- The teeth emerge into the oral cavity when the root formation is about threefourth complete (fig. 18.3).
Eruption of primary teeth:
Primary Molar Relationships And Occlusion
The molar relation of primary molars greatly influences the development of occlusion in permanent dentition.
Three types of molar relations exist in primary dentition:
- Flush terminal plane
- Mesial step terminal plane
- Distal step terminal plane
.
Flush terminal plane:
- The distal surfaces of the upper second molar and lower second molar are in the same vertical plane.
- This type of molar relation in primary dentition allows for favourable class i molar relation to develop in the permanent dentition.
Mesial step terminal plane:
- The distal surface of the lower second molar is more mesial to distal surface of upper second molar. There exists a greater probability of a class i molar relation in permanent dentition.
- Sometimes a mesial step terminal relationship in primary dentition may also develop into a class iii molar relation in permanent dentition.
Distal step terminal plane:
- The distal surface of lower second molar is more distal to distal surface of the upper second molar. This kind of molar relation can lead to class ii molar relation in permanent dentition.
Shedding And Patterns Of Shedding
Shedding or exfoliation is a physiologic process of resorption of roots and supporting tissues of primary teeth leading to loss of the tooth. The primary triggering factor for resorption of primary teeth is believed to be the pressure exerted by the succedaneous permanent tooth.
- The resorption of primary incisors becomes evident by 4–5 years of age. The lingual surfaces of roots of primary incisor resorb first, and then, the apical portion of the roots demonstrates horizontal resorption. This is dictated by the path of eruption of the underlying permanent incisor .
- Resorption of primary first molar also starts by the age of 4–5 years of age. Resorption starts on the inner surface of the thin flared roots of the primary molars. As the permanent premolars moves coronally, the resorption in furcation area and coronal third of the inner aspect of root becomes evident.
- Upper canine is the last tooth to resorb. The resorption of canine is more horizontal in fashion than lingual unlike the incisors.
- The resorption of canines and molars take about 2.5–5.5 years and the incisors take about 1.5–2 years to resorb completely. The permanent successors may erupt consequently in about one to six months period.
At times, when the succedaneous tooth is missing, the resorption of the overlying primary teeth is delayed or absent. This leads to submerged over retained primary teeth.
Mixed Dentition/Transitional Dentition (6 – 12 Years Of Age)
Mixed dentition period refers to the period during which both the primary and permanent teeth are present in the oral cavity.
- The eruption of permanent first molar marks the beginning of mixed dentition period that is around 6 years of age and ends with the exfoliation of last primary tooth at about 11–12 years of age.
The mixed dentition phase is divided into stages as follows:
- The first transitional stage: The permanent first molar eruption and exchange of incisors.
- Intertransitional stage: Minor changes in already erupted teeth take place.
- The second transitional stage: The emergence of premolars, canines and second molars.
First transitional stage:
- The permanent first molar erupts around six years of age. Permanent molars are accessional teeth, and hence, the eruption of permanent first molar is not preceded by the exfoliation of any primary teeth. The first permanent molar erupts distal to the primary second molar.
- The primary second molar provides guidance to the eruption of the permanent molars in the arch. The transverse and vertical dimensions of the dental arch now increase to accommodate the permanent first molars.
In spaced type of primary dentition, the eruptive forces of permanent first molar exert a mesially directed movement of tooth. This leads to closer of space that exists between primary molars. This is called the early mesial shift. It also transforms the initial end-on molar relationship in permanent dentition to a more stable class i molar relation.
Incisal transition:
The replacement of primary incisors by permanent incisors takes place at around 7–9 years of age. The exfoliation of primary incisors is succeeded by the eruption of permanent incisors.
It is not unusual that mandibular incisors erupt lingual to primary mandibular incisor. In such situation, the primary incisor may not exhibit pre-shedding mobility until the permanent incisors move anteriorly.
The permanent incisors are much larger in size than their primary counterparts. The extra space required to accommodate and align the larger permanent incisor is called incisor liability. The factors responsible for accommodating permanent incisors are as follows:
- The increase in arch length
- The utilization of physiologic spaces present in between primary teeth
- The increase in inter canine width
- The anteriorly inclined eruption of permanent incisors
Intertransitional period:
- This period lasts for about 1.5–2 years.
- No major changes take place.
Under the influence of the circumoral musculature and continuous craniofacial development of orofacial skeleton, minor tooth alignments take place.
Asymmetry in emergence of teeth, minor tooth movements to equalize the clinical heights of the tooth, fixed intercuspation, etc. Are evident in this period.
Second intertransitional period:
- This period begins with the exfoliation of primary molar at around 9–10 years of age.
- There is exchange of lateral teeth during this period, which includes exfoliation primary canines and molars and eruption of permanent canines and premolars.
The combined width of the primary canine, first and second molar in both the upper and lower arch is greater than the combined width of permanent canine first and second premolars. This resultant space created by the exchange of lateral tooth is called ‘leeway space ofnance’.
With the appearance of excess space in the arch, the permanent first molar migrates mesially to close this space. This mesial movement of the molar is called the late mesial shift.
The appropriate alignment of canines and premolars largely depends on the sequence of exchange of these teeth.
The most favourable sequence of exchange is given in table.
Sequence of eruption of succedaneous teeth:
Eruption of maxillary canine marks the end of mixed dentition period.
Sequence Of Eruption Of Permanent Teeth
Permanent first molar erupts first followed by central incisors and lateral incisors.
Sequence of eruption of permanent teeth:
Permanent dentition:
Permanent dentition is called permanent as it does not exfoliate physiologically.
It consists of 32 teeth including
- 2 central incisors
- 2 lateral incisors
- 2 canines
- 4 premolars
- 6 molars in each arch.
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- The first permanent teeth to appear is the permanent first molar.
- The dental formula for permanent dentition is icpm/icpm = 2123/2123.
- Except for the molars all other teeth are succedaneous teeth.
- The eruption of permanent first molars, incisors, premolars and canines takes place during the mixed dentition period. The eruption of second molar and third molar takes place in the permanent dentition period.
- The second molar erupts posterior to first molar at the age of 12 years; hence, it is called the 12-year molar.
- When the jaw grows posteriorly after the age of 12 years, the third molars begin to erupt. This can take up to few years. The third molar erupts after 17 years, in the range of 17–25 years. In cases of insufficient growth of the jaws, the third molar either fails to erupt (impacted) or become malaligned. The chronology of the permanent teeth is described in table.
Chronology of permanent teeth:
Dental Age Estimation
Dental age estimation is a parameter to assess an individual’s developmental status based on the teeth present in the oral cavity:
- Dental age estimation is a useful tool in treatment planning in cases of Malocclusions.
- It plays a significant role in forensic evaluation also.
Tooth formation and development is considered as a sensitive tool to assess growth as well as to determine biological developmental status of an individual.
Based on the eruption status, dental age is calculated by two methods:
- The last erupted tooth in oral cavity is correlative of the approximate time of eruption of that particular tooth according the chronology of its eruption.
- Secondly dental age can also be estimated based on the number of teeth present in the oral cavity.
Dental age can also be estimated by radiological method:
- In an orthopantomogram tooth formation, stages of index/selected teeth are noted as per nolla’s stage of tooth formation.
- Dental age is calculated by the mean age estimate for the defined tooth
Formation stages.- 11,43,44,46 (tooth number as per fdi) are considered for dental age Estimation in children up to 9 years of age.
- 13,43,44,47 (tooth numbers as per fdi) are considered in children from 10 years onwards.
This system is not applicable on tooth after the root apex is closed.
Estimation Of Stages Of Tooth Development
Every tooth is in dynamic state of development from the stage of tooth follicle to its eruption into oral cavity and establishing itself into occlusion. The tooth formation is classified into various stages based on its development according to nolla (1952). The stage of development of tooth is determined with a radiograph.
Clinical Considerations
Predentate period:
- Some teeth tend to erupt prematurely they are referred to as neonatal or Natal teeth. The natal teeth are usually hypermobile and sharp. They May hamper feeding in infants.
Primary dentition:
- As the crown formation extend from prenatal life to birth and a few months after birth, disturbances in formative stages reflect as developmental disorders of crown in size, shape, colour and mineralization.
Variation in eruption:
- Variation in the sequence of eruption
This may exist in the form of ABCDE: The eruption of the central incisors, first molars, lateral incisors, canines and second molars.
Or A (B, D) CE that is eruption of central incisor followed simultaneous eruption of the lateral incisor and first molar, then the eruption of canines and second molars.
Impaction of canines
- As the upper canines form at the lower border of the orbit and must travel through dense bone of maxilla to erupt into oral cavity, impaction or ectopic eruption of canines is most common during this period.
Chronology And Development Of The Dentition Synopsis
- Human dentition consists of the primary dentition, the mixed dentition and the permanent dentition. The first evidence of tooth formation occurs by the sixth week of intrauterine life within the developing jaws. During the intrauterine periods of development, the jaws harbour the tooth buds of all the teeth that belong to both the primary and permanent dentition in various stages of their development.
- The development of tooth bud can be grossly described in following stages:
- Bud stage
- Cap stage
- Bell stage
- Predentate period is the period from birth till the eruption of first primary teeth is called the predentate period.
- Primary dentition: The primary dentition consists of 20 primary teeth also called deciduous teeth or milk teeth. Thus, the primary dentition period extends from eruption of first primary teeth till the eruption of first permanent teeth (approximately 6 months to 6 years of age).
- Sequence of eruption of primary teeth. The most commonly evident sequence of eruption for primary teeth is presented here.
- The central incisors (a) are usually the first ones to erupt, followed by the lateral incisors (b), first molars (d), canines (c) and lastly second molars (e). This is abbreviated as ABCDE.
- Primary molar relationships and occlusion: The molar relation of primary molars greatly influences the development of occlusion in permanent dentition.
- Three types of molar relations exist in primary dentition
- Flush terminal plane
- Mesial step terminal plane
- Distal step terminal plane
- Shedding and patterns of shedding: Shedding or exfoliation is a physiologic process of resorption of roots and supporting tissues of primary teeth leading to loss of the tooth. The primary triggering factor for resorption of primary teeth is believed to be the pressure exerted by the succedaneous permanent tooth.
- Mixed dentition/transitional dentition (6–12 years of age): It refers to the period during which both the primary and permanent teeth are present in the oral cavity.
- Sequence of eruption of permanent teeth: Permanent first molar erupts first followed by central incisors and lateral incisors.
- Lower arch: Canine erupts before the premolars followed by the second Molars and third molars. Eruption sequence is represented by the fdi system as 61234578.
- Upper arch: The first premolar erupts after the eruption of incisors, Followed by the second premolar then the canine and second, third molars. Eruption sequence is represented by the fdi system as 61245378.
- Permanent dentition is called permanent as it does not exfoliate physiologically.
- Dental age estimation: Dental age estimation is a parameter to assess an Individual’s developmental status based on the teeth present in the oral cavity. Dental age estimation is a useful tool in treatment planning in cases of malocclusions and plays a significant role in forensic evaluation also.
- Tooth formation and development is considered as a sensitive tool to assess growth as well as to determine biological developmental status of an individual.
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