Lesson 4 Flashcards
1
Q
List the stages of tooth development
A
- Initiation stage (6-7 weeks gestation)
- Bud stage (8 weeks gestation)
- Cap stage (9-10 weeks gestation)
- Bell stage (11-12 weeks gestation)
- Stages of apposition and maturation
(continued)
2
Q
Describe Odontogenesis
A
- Continuous process of physiological changes
- Initiation, proliferation, differentiation, morphogenesis and maturation
- Primary teeth begin to develop during embryonic and fetal stages
- Most of the permanent teeth begin forming during fetal period
- Tooth development continues after birth
3
Q
In what order do teeth develop?
A
- Mandibular anteriors
- Maxillary anteriors
- Teeth develop anterioposteriorly coinciding with growth of the mandible
4
Q
Describe the initiation stage
A
- This first stage of tooth development is the initiation stage.
- This involves the physiological process of induction, which is an interaction between the embryological tissue types.
- At the beginning of the sixth week, the embryo’s stomodeum, or primitive mouth, is lined by ectoderm.
- The outer part of the ectoderm gives rise to oral epithelium. The oral epithelium consists of two horseshoe‑shaped bands of tissue at the surface of the stomodeum, one for each future jaw or arch.
- At the same time, deep to the forming oral epithelium, there is a type of mesenchyme originally from the ectoderm, the ectomesenchyme, which is influenced by neural crest cells that have migrated to the area.
- A basement membrane separates the oral epithelium and the ectomesenchyme in the stomodeum.
- During the later part of the seventh week, the oral epithelium grows deeper into the ectomesenchyme and is induced to produce a layer called the dental lamina.
5
Q
Describe anodontia
A
- Developmental disturbance of the initiation stage
- Lack of initiation within the dental lamina results in the absence of a single tooth (partial) or multiple teeth (complete) produces anodontia.
6
Q
Partial anodontia (hypodontia) is more common than complete anodontia, and occurs most frequently in ___________
A
- Permanent maxillary lateral incisors
- Third molars
- Mandibular second premolars.
7
Q
Hypodontia can be associated with the syndrome of _____________ because many parts of the tooth are indirectly or directly of ectodermal origin
A
ectodermal dysplasia
8
Q
Describe supernumerary teeth
A
- Developmental disturbance of the initiation stage
- Abnormal initiation may result in the development of one or more extra teeth, or supernumerary teeth (hyperdontia).
- These extra teeth are initiated from the dental lamina and have a hereditary etiology.
9
Q
List the most common supernumerary teeth
A
- Between the maxillary central incisors (mesiodens)
- Distal to the maxillary third molars
- Premolar region of both dental arches
10
Q
Describe the bud stage
A
- The second stage of tooth development is called the bud stage and occurs at the beginning of the eighth week of prenatal development for the primary dentition.
- This stage is named for an extensive proliferation or growth of the dental lamina into buds or oval masses penetrating into the ectomesenchyme.
- At the end of the proliferation process involving the primary dentition’s dental lamina, both the future maxillary arch and the future mandibular arch will each have 10 buds.
- The underlying ectomesenchyme also undergoes proliferation.
- A basement membrane remains between the bud and the growing ectomesenchyme.
- Each of these buds from the dental lamina, together with the surrounding ectomesenchyme, will develop into a tooth germ and its associated supporting tissue types.
11
Q
What is a common developmental disturbance during the bud stage?
A
- Abnormal proliferation can cause a single tooth (partial) or the entire dentition (complete) to be larger or smaller than normal.
- Abnormally large teeth result in macrodontia; abnormally small teeth result in microdontia.
12
Q
Describe the cap stage
A
- The third stage of tooth development is called the cap stage and occurs for the primary dentition between the ninth and tenth week of prenatal development, during the fetal period.
- Not only does proliferation characterize this stage, but also various levels of differentiation, which is unequal growth in different parts of the tooth bud, leading to formation of a cap shape attached to the dental lamina.
- A depression results in the deepest part of each tooth bud of dental lamina and forms a cap, or enamel organ.
- The innermost margin of the cap shape of the enamel organ signals the tooth’s future crown form.
- In the future, the enamel organ will produce enamel for the outer surface of the tooth.
- A part of the ectomesenchyme deep to the buds has now condensed into a mass within the concavity of the cap of the enamel organ.
- This inner mass of ectomesenchyme is now called the dental papilla.
- The dental papilla will produce the future dentin and pulp for the inner part of the tooth.
- A basement membrane still exists between the enamel organ and the dental papilla and is the site of the future dentinoenamel junction (DEJ).
- The remaining ectomesenchyme surrounding the outside of the cap or enamel organ condenses into the dental sac.
- In the future, the capsule‑like dental sac will produce the periodontium, the supporting tissue types of the tooth: cementum, periodontal ligament, and alveolar bone.
- A basement membrane still separates the enamel organ and dental sac.
13
Q
List and describe the tooth germ components during the cap stage
A
- Enamel organ: Formation of tooth bud in a cap shape with deep central depression—Future enamel
- Dental papilla: Condensed mass of ectomesenchyme within the concavity of the enamel organ—Future dentin and pulp
- Dental sac: Condensed mass of ectomesenchyme surrounding the outside of the enamel organ—Future cementum, periodontal ligament, alveolar bone
14
Q
Describe dens in dente (dens invaginatus)
A
During the cap stage, the enamel organ may abnormally invaginate into the dental papilla
15
Q
Describe gemination
A
- Developmental disturbance of the cap stage
- Gemination occurs as the single tooth germ tries unsuccessfully to divide into two tooth germs, which results in a large single‑rooted tooth with a common pulp cavity.
