1. TOOTH DEVELOPMENT: ODONTOGENESIS – Part II
Warren Tewes, DDS, MS, DABFO
Pauline Hayes Garrett,DDS
Department of Endodontics, Prosthodontics, and
Operative Dentistry
University of Maryland Dental School
Baltimore, Maryland

2. This material is from:
Essentials of Oral Histology and Embryology, third edition,
Gartner, 1999 with permission from Dr. Leslie P. Gartner
BCDS Learning Center sites

3. OBJECTIVES
Identify the parts of a tooth and cells that formed each part.
Identify the stages of tooth development.
Identify the cells, cell layers and their derivations for each stage of tooth development and eruption.

4. Deposition of Dentin
Primary Dentin forms first and ends at the start of root formation.
It is composed of:
A. Mantle Dentin – forms first before enamel and contains bundles of collagenous Korff’s fibers.
B. Circumpulpal Dentin – the bulk of primary dentin and is more mineralized than mantle dentin.
Illustration reprinted and modified from: Essentials of Oral Histology and Embryology, third edition, Gartner, 1999 pg. 25 with permission from Dr. Leslie P. Gartner

5. SEM Tooth Development
As dentinogenesis proceeds, more collagen fibers are formed in the area of matrix formation. Matrix vesicles (black dots / arrows) may be seen among the collagen fibers.

6. SEM Tooth Development
This high magnification electron micrograph shows the distinct axial periodicity of the collagen fibers (arrows) and the presence of a matrix vesicle(M) in the center of the field.

7. SEM Tooth Development
This electron micrograph shows a cross section of an odontoblastic process (small arrow on the right side of the field) in the dentinal tubule (white area).
Note that the dentin matrix displays numerous collagen fibers and many small black structures that represent matrix vesicles(M). The vesicles initiate mineralization which may be linear or globular.

8. Tooth Development Appositional Stage
Just prior to the beginning of root formation, the left hand side displays the bony capsule(B). Enclosed within the capsule is the dental sac(S) which surrounds the developing tooth germ. Note that the cusp region of the crown is finished. The enamel(E) is covered by a reduced enamel epithelium. About a third of the way apical from the cusp the ameloblasts are still columnar (arrow), indicating active enamel formation. Some enamel matrix is still evident between the postameloblasts and the enamel space. The reddish-pink dentin(D) extends almost all the way to the cervical loop. The dental papilla(P) occupies the center of the field and is almost completely surrounded by dentin.

9. Tooth Development Appositional Stage
In a tooth with two or more cusps, apposition begins at each cusp (arrows) and progresses apically down the slope toward the cervical loop as well as along the valley between the cusps. Note the bony capsule, dental sac(DS), outer enamel epithelium, cervical loop, and the dental papilla(DP).

10. Cervical Loop
The cervical loop(CL) in this tooth germ is near the end of the appositional stage. The lower half of the field displays the dental papilla, above which dentin(D) (and perhaps enamel) is evident. The stellate reticulum and outer enamel epithelium are visible, as the dental sac.

11. Developmental lobes
A tooth develops from 4 or more (depending on the type of tooth) growth centers known as developmental lobes. Each lobe formation continues until there is a coalescence of the lobes resulting in the final crown outline. Where each lobe coalesces with another, a developmental groove forms, and is seen on an erupted tooth. The number of lobes necessary for the formation of a tooth depends on how many cusps it has. Incisors and canines develop from 4 lobes. Premolars develop from four or five lobes. First molars develop from five lobes. Second molars develop from four lobes. The number of lobes necessary for third molar development is variable.
Odontoblastic process
Note: For Maxillary central incisors, the 4th lobe is on lingual surface.

12. Root formation
When dentin formation has reached the region of the cervical loop (red arrow) the appositional stage of tooth development ends. The cervical loop elongates in an apical direction, forming Hertwig's Epithelial Root Sheath (HERS) which is the epithelial extension between the red and black arrows. It signals the beginning of a new stage of odontogenesis, called root formation.

13. Root formation
After the outline of the crown has been established, root formation begins. The IEE meets the OEE, which becomes known as the cervical loop. These cells undergo rapid mitosis and form Hertwig’s Epithelial Root Sheath, which controls the formation of the root. As the root forms, the tooth moves toward the oral cavity. This is the first stage of eruption.
Illustration reprinted and modified from: Essentials of Oral Histology and Embryology, third edition, Gartner, 1999 pg. 33 with permission from Dr. Leslie P. Gartner

14. Root formation Epithelial Diaphragm Derived from HERS.
Controls size of roots.
Controls shape of roots.
Controls number of roots.
Illustration reprinted and modified from: Essentials of Oral Histology and Embryology, third edition, Gartner, 1999 pg. 33 with permission from Dr. Leslie P. Gartner

15. Root formation
The Epithelial Diagram shows the infolding pattern of a tooth with two roots.

16. Root and cementum formation
Cementum formation can only occur on the surface of dentin or preexisting cementum.
During the formation of the root breaks in HERS provide access for mesenchymal cells of the dental sac(DS) to the newly formed radicular dentin.
These mesenchymal cells, trapped between the newly formed dentin(D) and HERS, differentiate into cementoblasts, and elaborate cementum(C) on the surface of the dentin, thus establishing the dentinocemental junction. Note the following layers, starting on the left hand side of the field: dental papilla(DP), odontoblasts(O), dentin(D), cementum(C), cementoblasts(arrows), HERS, dental sac(DS), blood vessel(BV).

17. Root and cementum formation
The left side of this field displays the dental sac(DS) being organized into the periodontal membrane. Cellular cementum(C) is being elaborated on the surface of dentin(D). Observe that some of the cementoblasts have been entrapped in the matrix of their own formation, and these cells, sitting in lacunae, are known as cementocytes (arrow). Note the presence of dentinal tubules in the dentin.

18. Root and cementum formation
Cementum formation is not a continuous process. This lack of continuity is evidenced by the presence of resting lines. The parallel lines (arrows) appear in this image of cellular cementum.

19. Stages of eruption
Illustration reprinted from: Color Textbook of Histology, Gartner, L. and Hiatt, J,
Second edition. Saunders pg with permission from Elsevier.
Preeruptive Stage : the entire tooth germ shifts its position to accommodate a sudden increase in the size of the tooth germ and the lengthening of the upper and lower jaws.

20. Stages of eruption
Illustration reprinted from: Color Textbook of Histology, Gartner, L. and Hiatt, J,
Second edition. Saunders pg with permission from Elsevier.
Eruptive Stage : the tooth is moving in an axial direction, HERS moves apically and the base of the bony crypt becomes deeper. This stage concludes when the tooth is in occlusion with its counterpart on the opposing arch.

21. Stages of eruption
The cusp of an erupting tooth displays Reduced Enamel Epithelium (REE) at the arrow. [The white zone below the REE is the enamel space(ES), and is the location occupied by the enamel that was removed during decalcification in the preparation process.]
The connective tissue(CT) between the REE and oral epithelia is being displaced, broken down, and eventually will be absent in this zone when the two epithelia fuse.

22. Stages of eruption
As the succedaneous tooth(S) continues to erupt, the root of the deciduous tooth(D) is being resorbed (arrow) by odontoclasts; the deciduous tooth is much narrower on this surface. Similarly, the associated bone is being remodeled by osteoclasts.

23. Stages of eruption
Illustration reprinted from: Color Textbook of Histology, Gartner, L. and Hiatt, J,
Second edition. Saunders pg with permission from Elsevier.
Posteruptive Stage : can include some additional deposition of cementum at the apex and remodeling of the bony alveolus; some tooth movement due to occlusal and interpoximal wear.

24. Question #1 [Click mouse for answer.]
The very first layer of enamel that is produced is known as:
A. gnarled enamel
B. aprismatic enamel
C. prismatic enamel
D. Tomes’ process
E. enamel lamella

25. Question #2 [Click mouse for answer.] Primary dentin is:
A. synonymous with mantle dentin
B. deposited in response to occlusal forces
C. deposited prior to occlusion
D. deposited in response to trauma
E. deposited in response to pulpal injury

26. Question #3 [Click mouse for answer.] Cementogenesis occurs:
A. before amelogenesis
B. before dentinogenesis
C. due to cementoclastic activity
D. due to denticle formation
E. due to breaks in Hertwig’s epithelial root sheath

27. Question #4 [Click mouse for answer.]
One of the following is not a stage of tooth eruption:
A. pre-eruptive
B. eruptive
C. post-eruptive
D. root formation

28. Question #5 [Click mouse for answer.]
The first tooth to undergo exfoliation is:
A. maxillary central incisor
B. mandibular central incisor
C. maxillary lateral incisor
D. mandibular lateral incisor