Unit 3c - Development of Roots Flashcards
Describe the sequencing of crown and root development
- 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
What is HERS
- 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
What are the stages in root development?
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
How is root dentin formed?
- 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
Describe how cementum forms
- 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
How are enamel pearls produced?
- 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
What are the different types of cementum?
- acellular
- cellular
What is acellular cementum?
- thin: completely surrounding root/DCJ * focussed on cervical 1/3
- no change in thickness
- no cementocytes
- sharpey’s fibers mostly mineralized
What is cellular cementum?
- 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
What are the three patterns that may be present at points along the CEJ?
- 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
How are single rooted teeth produces?
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
How are multirooted teeth roots developed?
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
How is a single rooted tooth with 2 canals developed?
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
How are roots lengthened?
- 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
What are some abnormalities in tooth roots?
- altered shape or size
- supernumerary roots
- lack of roots: rare but occurs due to no apical proliferation of HERS
What is the function of cementum?
- attachment of PDL to bone (via sharpey’s fibers)
- outermost hard tissue of tooth root: seals dentinal tubules
What is the composition of cementum?
35% organic
65% inorganic
significance: less mineralized than enamel therefore prone to erosion/abrasion/caries
What is the histological structure of cementum?
-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
Discuss the resorption and repair of cementum
- 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
What is the clinical importance of cementum?
- ortho tx
- age and function: thickness of cementum changes
- caries: if cementum is exposed
What are some anomalies that may occur with the formation of cementum?
- 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
Describe the process of pulp formation
- 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
Describe innervation and vascularization of pulp
- 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
What is the composition of pulp?
-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
