Unit 3c - Development of Roots

Question 1

Describe the sequencing of crown and root development

Answer 1

• the development of the tooth root does not begin until enamel production is completed
• the develpment of enamel stops but dentin continues
• as this happens, the tooth begins to erupt but doesn’t enter the mouth until a considerable portion of the root is formed
• IEE and OEE meet at the cervical loop
• there is apical proliferation of this area = HERS

Question 2

What is HERS

Answer 2

• Hertwigs Epithelial Root Sheath
• guides the shape and number of roots
• stimulates root dentin formation
• grows down between the dental papilla and the dental sac and encloses all but the basal portion of the papilla
• the tip of HERS turns inward horizontally, this area is often referred to as the epithelial diaphragm
• HERS will guide the shape and number of roots

Question 3

What are the stages in root development?

Answer 3

a. cervical loop of a primary tooth, which is composed of the most cervical portion of the enamel organ and is responsible for root development. Note that the cervical loop is composed of the IEE and OEE
b. Hertwig’s epithelial root sheath is formed from elongation of the cervical loop, which is responsible for the shape of the root and the induction of root dentin

Question 4

How is root dentin formed?

Answer 4

• the peripheral cells of the papilla will differentiate into odontoblasts and induce the production of root dentin
• remember that IEE cells induced the poduction of dentin in the crown development
• in the root, once the odontoblasts adjacent to HERS are induced the dentin production begins, HERS proceeds to begin to break down and disintegrate
• the induction of dental sac cells to differentiate into cementoblasts happens at this time

Question 5

Describe how cementum forms

Answer 5

• the cemntoblasts begin to produce cementum matrix, or cementoid, after the HERS disintegrates and induces the dental sac cells to differentiate into cementoblasts
• some cells become entrapped during the later stages of apposition - these become teh cell rests of malassez seen in the periodontal ligament spaces
• note the developing periodontal ligament and alveolar bone adjacent to the cementum

Question 6

How are enamel pearls produced?

Answer 6

• if all the HERS cells do not pull away from the dentin, the remaining cells can differentiate into ameloblasts again
• bits of enamel may be produced, often in furcation areas with an inner core of dentin
• remember that HERS originates partially from enamel producing cells, these cells of the IEE that are also epithelial derived

Question 7

What are the different types of cementum?

Answer 7

• acellular

- cellular

Question 8

What is acellular cementum?

Answer 8

• thin: completely surrounding root/DCJ * focussed on cervical 1/3
• no change in thickness
• no cementocytes
• sharpey’s fibers mostly mineralized

Question 9

What is cellular cementum?

Answer 9

• thicker: middle 1/3 and apical; furcations
• continues forming
• 3-10x width of acellular
• cells trapped = cementocytes
• small spaces that house the cemtnocytes are lacunae
• sharpey’s fibers mineralize at periphery, but maintain a soft tissue core
• histologically: reversal lines evident
• this type of cementum will continue to form thoughout the life of the tooth

Question 10

What are the three patterns that may be present at points along the CEJ?

Answer 10

• cementum may overlap enamel
• the enamel and cementum may meet end to end
• there may be a gap between enamel and cementum, leaving dentin exposed

Question 11

How are single rooted teeth produces?

Answer 11

HERS simply grows apically as an epithelial cylinder from the cervical edge of the enamel organ, enclosing a tube of dentin and developing pulp tissue

Question 12

How are multirooted teeth roots developed?

Answer 12

Roots develop similar to the single rooted process until reaching the furcation area. at this site, there is a horizontal proliferation inward of 2-3 flaps of epithelial tissue across the opening. These flaps fuse at or near the center area. From teh 2-3 openings created a cylindrical root sheath continues to grow apically shaping the # of roots

Question 13

How is a single rooted tooth with 2 canals developed?

Answer 13

a single HERS presents. Odontoblats produce dentin towards the center at about the same rate, but because the root is more oval than circular and may be even slightly indented in the central region, obliteration of the dental pulp in the central region may occur and 2 canals are established

Question 14

How are roots lengthened?

Answer 14

• rate of root lengthening = rate of eruption
• with the root lengthening the tooth moves coronally or occlusally. the epithelial diaphragm remains in relatively the same position in the alveolar bone
• root compeltion = 1-4 years after eruption
• newly erupted teeth = large apical opening and roughly 2/3 root formed

Question 15

What are some abnormalities in tooth roots?

Answer 15

• altered shape or size
• supernumerary roots
• lack of roots: rare but occurs due to no apical proliferation of HERS

Question 16

What is the function of cementum?

Answer 16

• attachment of PDL to bone (via sharpey’s fibers)

- outermost hard tissue of tooth root: seals dentinal tubules

Question 17

What is the composition of cementum?

Answer 17

35% organic
65% inorganic
significance: less mineralized than enamel therefore prone to erosion/abrasion/caries

Question 18

What is the histological structure of cementum?

Answer 18

-cementoblasts produce cementoid
-cementoid is mineralized after initial formation: hyroxyapatite
-lamellae: each separated by slightly less calcified lines (incremental lines) indicated periodic formation
Matrix:
-ground substance: main function to hold matrix together
-crystalline part: as with all tooth tissues, the main crystal component is hydroxyapatite

Question 19

Discuss the resorption and repair of cementum

Answer 19

• 95% of teeth have come resorption
• presence of cementoblasts on surface *apical
• light pressure: no damage (ortho, impacted teeth, trauma)
• reversal lines indicate repair
• severe pressure=resorption *cementoclasts/odontoblasts
• cementum is more resistant to resorption than alveolar bone

Question 20

What is the clinical importance of cementum?

Answer 20

• ortho tx
• age and function: thickness of cementum changes
• caries: if cementum is exposed

Question 21

What are some anomalies that may occur with the formation of cementum?

Answer 21

• cementicles
• hypercementosis: at the root apex. This is due to traumatic occlusal forces of a tooth
• Concrescence: fusion of roots via the cementum (excess formation)
• Ankylosis: if primary tooth is not erupting assess

Question 22

Describe the process of pulp formation

Answer 22

• as the production of cementum continues and the odontoblasts differentiate along the pulpal boundary, cells of the dental pulp (embryonic dental papilla) form the pulp proliferative zone
• this is inside the epithelial diaphragm. These new cells will give rise to new odontoblasts and fibroblasts of the pulp
• as root dentin continues to be produced the structure of the pulp begins to become organized

Question 23

Describe innervation and vascularization of pulp

Answer 23

• capillaries and newer fibers surround the teeth at the earliest stages of growth. They invade the dental sac and papilla at the cap and bell stages of tooth development
• Once the odontoblasts start differentiating, many capillaries lie in and immediately underneath the odontoblastic layer
• the deposition of dental and enamel prevent the ameloblasts from receiving nutrition from the dental papilla any longer. Their nutrient supply will then come from the cells of the structure surrounding the tooth germ
• nerves in the dental papilla area (developing pulp) grow toward the odontoblastic layer and eventually nerve fibers from terminals on the odontoblasts

Question 24

What is the composition of pulp?

Answer 24

-100% organic

Cellular component:

• Fibroblasts: for collagen and ground substance and breaks down collagen fibers
• Histiocytes: defense mechanism = macrophages
• Lymphocytes/mast cells: defense system *CT
• Undifferentiated Mesenchymal cells:
• Odontoblasts: single layer to multiple as surface area gets smaller: process extends into tubules

Ground Substance:

• molecular sieve *CT
• Fibers: few types- collagen fibers
• BV’s: good blood flow especially in young and BP exists capillaries next to odontoblasts
• Lymph Vessel: follow pathway of BV’s

Nerves:
Autonomic: associated with BV’s
Sensory: associated with pain response

Question 25

What are the different between true and false pulp stones?

Answer 25

True: produced from odontoblasts *may form during development of tooth tissues and some form later
False: these calcifications occur later in life of the tooth *irregular calcification of minerals not dentin

Question 26

What is the function of pulp

Answer 26

• similar to CT
• formative
• nutritive
• physical/defensive
• sensory

Question 27

What are included in the theories of sensitivity?

Answer 27

Direct Innervation: belief that the nerve extends to the DEJ (NO)
Transduction: odontoblasts act as receptors and synapse occurs betwen cell and nerves (very close association) *organic and odontoblasts act as poor conductors
Hyrodynamic: most likely!! Stimulation of odontoblastic process causes movement, thus stimulating nerve ending *cold/heat/air. Induces osmotic pull inward or outward: movement of process and stimulation of nerve endings next to or on cells and then a pain response is registered