Pediatric Tooth Development: Free INBDE Prep Course
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EMBRYONIC DEVELOPMENT
You will need to understand the different stages of tooth development, and how disturbances in each phase will affect patients clinically.
1. The initiation stage (bud stage) starts in the sixth week of embryonic development, with the dental lamina as the precursor. Permanent teeth originate from their deciduous counterparts, formed from the successional lamina. Failure at this stage leads to a congenitally missing tooth. Excessive budding causes supernumerary teeth. Fusion and gemination can result because of disruptions in the initiation stage.
2. The proliferation stage (cap stage) sees the inner and outer enamel epithelium form. Failure at this stage causes congenitally missing teeth. Excessive budding leads to a cyst, odontoma, or supernumerary tooth. Fusion and gemination can result because of disruptions in the proliferation stage.
3. The histodifferentiation and morphodifferentiation (bell stage) has the cells of the dental papilla differentiate into odontoblastic cells, and the cells of the inner enamel epithelium into ameloblasts. Disruption of histodifferentiation results in internal/structural faults (amelogenesis imperfecta, dentinogenesis imperfecta). Disruption of morphodifferentiation results in size and shape abnormalities (peg laterals, microdontia).
4. During the apposition stage ameloblasts and odontoblasts deposit a matrix of proteins. If this process is interrupted it leads to disturbances in apposition with incomplete tissue formation (e.g. hypoplasia).
5. Calcification begins at the cusp tips/incisal edges and proceeds apically. The basic composition of the enamel after calcification is 96% inorganic material and 4% organic material and water. There are many reasons calcification may be interrupted, including infection, trauma, or the presence of excessive systemic fluoride, often presenting clinically as hypocalcification. Tetracycline staining can be acquired during this stage.
The following is the order of the stages of development:
- Inner enamel epithelial cells of the enamel organ elongate, inducing differentiation of the mesenchymal cells on the outside of the dental papilla into odontoblasts.
- Odontoblast differentiation.
- Deposition of dentin, which leads to the:
- Deposition of enamel.
- Deposition of root dentin and cementum.
TOOTH CALCIFICATION & ERUPTION
You will need to know the calcification and eruption times of the teeth. If the calcification times are known, you can calculate when a problem occurred. Each different group of teeth begins to calcify about every 6 months. A 6 month variation in eruption times for a patient is normal. It takes 4-5 years for the crown to complete formation, and about 10 years for root formation (a little longer for the canines, it’s 6 years and 13 years respectively). When the crown has formed and the roots are two-thirds complete, the tooth will erupt through the bone. When the roots are ¾ formed, teeth typically make their way through the gingiva. For primary teeth it takes another 18 months for the roots to completely form. For adult teeth it’s another 3 years for the roots to become completely mature.
Calcification Times (Estimates)
Common calcification times are provided. Though the actual calcification time estimates are provided, it will be easier to memorize the approximate estimates for tooth calcification.
The sequence of calcification of primary teeth:
CENTRAL – FIRST MOLAR – LATERAL – CANINE – SECOND MOLAR
The sequence of calcification of permanent teeth, MANDIBLE:
FIRST MOLAR – CENTRAL – LATERAL -CANINE – FIRST PREMOLAR – SECOND PREMOLAR – SECOND MOLAR
The sequence of calcification of permanent teeth, MAXILLA:
FIRST MOLAR – CENTRAL – CANINE – LATERAL – FIRST PREMOLAR – SECOND PREMOLAR – SECOND MOLAR
Eruption Times (Estimate)
The sequence of eruption of primary teeth:
CENTRAL – LATERAL – FIRST MOLAR – CANINE – SECOND MOLAR
The sequence of eruption of permanent teeth, MANDIBLE:
FIRST MOLAR – CENTRAL – LATERAL – CANINE – FIRST PREMOLAR – SECOND PREMOLAR – SECOND MOLAR – THIRD MOLAR
The sequence of eruption of permanent teeth, MAXILLA:
FIRST MOLAR – CENTRAL – LATERAL – FIRST PREMOLAR – SECOND PREMOLAR – CANINE – SECOND MOLAR – THIRD MOLAR
Cleidocranial dysplasia, Chondroectodermal dysplasia, Achondroplasia, Osteogenesis imperfecta, Gardener’s syndrome, Down syndrome, DC Lange syndrome, Apert’s syndrome, Vit D resistant rickets, Hypothyroidism, Hypopituitarism, and Ichthyosis are associated with the delayed exfoliation of baby teeth and delayed eruption of adult teeth.
TOOTH CHARACTERISTICS AND ANATOMY
You will need to be familiar with the differentiating aspects of teeth to complete your diagnosis and treatment plan.
- Succedaneous tooth – a permanent tooth that moves into the space formerly held by a deciduous tooth.
- Nonsuccedaneous tooth – a permanent tooth that takes up a new space not held previously by a deciduous tooth.
- Anatomical crown – from the cementoenamel junction (CEJ) to incisal edge (the part that is/should be covered by enamel).
- Clinical crown – from the gingival margin to the incisal edge (visible portion of tooth).
- Lobe – center of enamel formation, can be cusps, mamelons, cingula. Separated by developmental depressions.
Deciduous Teeth
Deciduous teeth are not simply small adult teeth. There are key differences that affect how you approach the diagnosis and treatment of various pathologies. Compared to an adult tooth, primary tooth enamel is thinner (~1mm thickness occlusally) and is less calcified making it more prone to demineralization. The crowns are shorter and more bulbous, with constricted cervical areas, shallower occlusal anatomy and smaller occlusal tables. The root trunks are shorter and narrower, but the roots are more slender. Deciduous teeth have a smaller crown to root ratio compared to adult teeth.
The pulp chambers are larger relative to the tooth with less space between the pulp and the outside of the tooth (pulp horn sits closer to the surface). This means there is a shorter distance for bacteria to traverse in order to reach the pulp, and it is easier to find yourself with a pulpal exposure during a surgical procedure. In cross-section, the enamel rods at the gingival third slope occlusally (as opposed to cervically on adult teeth). The difference in orientation of the enamel rods influences the resin bonding system effectiveness around the gingival margin of a proximal box. The interproximal contacts are broader and flatter, and the teeth appear lighter compared to adult teeth.
Key Characteristics
- The maxillary central incisor has no mamelons, a straighter incisal edge compared to its successor, with prominent facial and lingual cervical areas.
- The maxillary lateral incisor also has a straighter incisal edge, no mamelons, and a prominent CEJ area.
- The maxillary canine is the only primary tooth with a pentagonal shape.
- The maxillary first molar is the smallest molar and generally resembles a permanent premolar. It has a rectangular occlusal outline and H shaped fissure configuration, with 4 cusps (MB is the largest, DL smallest).
- The maxillary second molar usually resembles a shrunk down permanent maxillary first molar. It has a rhomboidal occlusal outline and is the widest (primary) tooth in the bucco-lingual dimension. It has an oblique ridge. There are four cusps (MB largest, DL smallest). Some maxillary second molars may present with a fifth cusp, called a Cusp of Carabelli, like an adult first molar.
- The mandibular central incisor has a straighter incisal edge compared to its adult successor, with no mamelons, and a prominent cervical ridge.
- The mandibular lateral incisor has a straighter incisal edge compared to its adult successor, with no mamelons, and a prominent cervical ridge.
- The mandibular canine is unremarkable. Poor canine.
- The mandibular first molar is the most unique tooth and also the most difficult to restore. It has a rhomboidal occlusal outline with no central fossa, a prominent buccal cervical ridge, a well developed mesial marginal ridge, a prominent transverse ridge (MB cusp to ML cusp), and a sharp curve at the CEJ on the mesial surface that makes a Class II restoration difficult. There are 4 cusps, the MB is the largest, the DL the smallest.
- The mandibular second molar generally resembles the mandibular first molar with it’s rectangular outline. It is the widest primary tooth in the mesio-distal dimension, and has 5 cusps (an extra distal cusp).
