Anatomy - Week 6 PP Flashcards
Odontogenesis
is the process of tooth development
Developmental disturbances
Developmental disturbances can occur within each stage of odontogenesis, affecting the physiologic process taking place
- These developmental disturbances can have
ramifications that may affect the clinical treatment
of a patient
When Does Tooth Development Begin?
Begins in the 7th week of embryonic development
- Continues until the late teens
◦ Exfoliation of primary dentitions
◦ Development and eruption of the permanent teeth
Tooth Tissues
All the tissues of the tooth are specialized forms of
connective tissue, except enamel * Each tooth is the product of two tissues that
interact during tooth development –ectoderm and
mesoderm (mesenchyme) ◦ Enamel - ectoderm
◦ Cementum - mesenchyme
◦ Dentin - mesenchyme
◦ Pulp - mesenchyme
5 Main Processes that Occur
- Induction - one group of cells directs the development of another group of cells.
- Proliferation - results in an increase of the number of cells
- Differentiation - when one cell begins to look different from another – cells become more
specialized. (specialized to do specific function - to do a their job) - Morphogenesis – causes a tissue or organ to develop its shape (cells are specialized to cause organ/tissue to change shape)
- Maturation – creates mature form (cells become mature)
6 Stages of Tooth Development
- Initiation (6-7th week) – ectoderm gives rise to the oral epithelium and then to the dental lamina with its dental placodes
- Bud stage (8th week) —growth of the dental placode into a bud shape that penetrates the
growing ectomesenchyme - Cap stage (9th-10th week)—future shape of the tooth becomes evident; cells specialize to form the enamel organ
- Bell stage (11th -12th week) —differentiation of the enamel organ into a bell shape with 4 cell types and the dental papilla into two cell types.
- Apposition (various times - happen back and forth, not necessarily 5th) — dental tissues secreted in successive layers as a matrix
- Maturation (various times - happen back and forth, not necessarily 6th) — dental tissue types fully mineralize to their mature form
Epithelial components (ectoderm)
- Enamel Organ - tooth germ becomes organized, develops into 4 layers
- proliferation, differentiation, & morphogenesis
- Bell Stage
Outer Enamel Epithelium (OEE) *
*Covers enamel organ
*Cuboidal cells
* One cell layer thick
* Outlines the shape of the
developing enamel *Organizes capillaries
(provides nutrition)
* Protects enamel orga
Stellate Reticulum (SR) (star shaped)
*Between OEE and IEE
*Star-shaped
*Many layers *Protects/Cushions
*Nourishes
Stratum intermedium (SI)
*Between SR and IEE
*Flat epithelial cell * 2-3 layers thick
*Lie on top of the IEE
*Helps ameloblast
formation
*Nourishes IEE
Inner Enamel Epithelium (IEE)
*The concave lining of the
enamel organ
*Cuboidal cells
*Become columnar cells
*One layer thick
*Becomes ameloblasts
*Nourishes
Mesenchymal Components - The Dental Sac
Dental sac (follicle)—surrounds the developing
tooth germ and provides cells that will form the
periodontal ligament, which, in turn, will produce
the cementum and the alveolar bone proper
The Bell Stage Layers of the Enamel Organ
Outer Enamel Epithilum (OEE)
Stellate Reticulum (SR)
Stratum Intermedium (SI)
Inner Enamel Epithelium (IEE)
Mesenchymal Components - The Dental Papilla
Dental papilla—condensed ectomesenchyme
located on the concave side of the enamel organ; peripheral cells facing the IEE will differentiate
into odontoblasts, dentin-forming cells
◦ The center of the dental papilla will become the dental
pulp
Enamel & Dentin Formation
-Apposition and maturation stages
* Induction, proliferation and maturation
* Begins at the dentino-enamel junction (DEJ)
Preameloblast Formation
- After the formation of
the IEE in the bell-shaped enamel organ - The innermost cells grow even more columnar as they
elongate and differentiate into preameloblasts
During this differentiation process, the nucleus in each cell moves away from
the center of the cell to the position farthest away from the basement membrane that separates the enamel organ from the dental papilla
- the preameloblasts will induce dental papilla cells to differentiate into dentin-forming cells (odontoblasts), and then will themselves differentiate into cells that secrete enamel (ameloblasts)
What are responsible for giving us dentin?
ODONTOBLASTS - sits in the pulp, receives nourishment, able to reproduce dentin
Dentinogenesis
After the differentiation, the odontoblasts begin dentinogenesis, the
appositional growth of dentin matrix, or predentin, laying it down on their side of the now disintegrating basement membrane
Ameloblast, Enamel Matrix, and Dentinoenamel Junction Formation
This disintegration of the basement membrane allows the preameloblasts to contact the newly formed predentin, which induces the preameloblasts to differentiate into ameloblasts
With the enamel matrix in contact with the predentin, mineralization of the disintegrating basement membrane now occurs, forming the dentinoenamel junction (DEJ), the inner junction between the dentin and enamel tissue
- However, the odontoblasts (unlike the ameloblasts) will leave attached cellular extensions in the length of the predentin called the odontoblastic process
Each odontoblastic process is contained in a mineralized cylinder, the dentinal tubule
Amelogenesis
Ameloblasts begin amelogenesis, or the appositional growth of enamel matrix,
laying it down on their side of the now disintegrating basement membrane
Root Development
Roots can take 1-4 years to complete formation, doesn’t happen at same rate as other teeth tissues
Formation of root
dentin and cementum
follows after the
formation of the crown
of the tooth is complete
Cementum Formation - Hertwig Root Sheet (Hers)
- Hertwig’s root sheath is formed by the joining of the outer enamel epithelium and the inner
enamel epithelium; the sheath continues to grow down, shapes the root of the tooth and the
formation of root dentin, and is followed by differentiation of cells from the dental sac; these
cells produce: ◦ a Cementum
◦ b Periodontal ligament ◦ c Alveolar bone proper
Periodontal Ligament & Cementum
- Dental sac cells
◦ Surrounds root dentin
◦ Forms lamina dura
Cortical bone lining tooth socket ◦ PDL imbeds into
Lamina dura and the tooth root ◦ Cementum forms on root dentin
Active Eruption
Eruption of the primary dentition takes place in
chronologic order, as does the permanent
dentition. This process involves active eruption, which is the actual vertical movement of the tooth
Passive Eruption
passive eruption, which
occurs with aging when the gingival tissue recedes but no actual tooth movement takes place
Acellular Dental Cuticle
- After enamel appositional growth ceases in the crown of each primary or permanent tooth, the ameloblasts place an acellular dental cuticle on the newly formed outer enamel surface
Reduced Enamel Epithelium (REE)
The layers of the enamel organ become compressed, forming the reduced enamel epithelium (REE).
- The REE appears as
a few layers of flattened cells overlying the new enamel surface. - When this formation of the REE occurs the tooth can then begin to erupt into the oral
cavity.
To allow for the eruption process, the REE first has to fuse with the oral epithelium lining the
oral cavity. * Second, enzymes from the REE then
disintegrate the central part of the fused tissue, leaving a protective epithelial-lined
eruption tunnel for the tooth to erupt through the surrounding oral epithelium into the oral
cavity
As a tooth erupts, the coronal part of the fused epithelial tissue peels back off the crown,
leaving the cervical part still attached to the neck of the tooth
This fused tissue that remains near the CEJ after the tooth erupts then serves as the initial junctional epithelium of
the tooth
Primary Tooth Shedding
The process of shedding the primary tooth is intermittent because at the same time that osteoclasts differentiate to resorb bone and odontoclasts differentiate to resorb dental tissue, the always-ready odontoblasts and cementoblasts work to replace the resorbed parts of the root as well as the fibroblasts to repair the periodontic ligament
“Blast” at end of word means
means to create
“Clast” at end of word means
means to break down
“osteo” at front of word means
bone
Shedding -
The primary tooth is then lost, exfoliated, or shed, as the succedaneous permanent tooth develops lingual to it
Permanent Tooth Eruption
- The succedaneous permanent tooth erupts into the oral cavity in a position lingual to the roots of the
shedding primary tooth, just as it develops that way
The process of eruption
for a succedaneous
permanent tooth is the
same as for the primary
tooth
The process of the
nonsuccedaneous eruption of the permanent teeth is similar also, but no primary tooth is shed to allow for the process as with the succedaneous permanent teeth
Nasmyth Membrane
A residue may form on newly erupted teeth of both dentitions that may leave the teeth extrinsically stained.
- This green-gray residue, Nasmyth membrane, consists of the fused tissue of the REE and oral
epithelium, as well as the dental cuticle placed by the ameloblasts on the newlyformed outer enamel surface
Supraeruption
the condition in which a tooth is pushing too far out of the gums and bone
Ankylosis
occurs when a tooth fuses to the surrounding bone and slowly begins to sink or submerge into the nearby gum tissue
Ectopic Teeth
An ectopic tooth, also known as an impacted tooth, is a tooth that develops in an abnormal position (ectopia) and fails to erupt into its normal location in the oral cavity
