DH119-2NDexam-3RDppt

root formation begins

AFTER outline of crown has been formed

-WEEK 12 after Bell Stage

cervical loop is located where the

INNER ENAMEL EPITHELIUM (IEE) and OUTER ENAMEL EPITHELIUM (OEE) MEET

hertwigs epithelial root sheath undergoes

rapid division, grows deep into connective tissue below, extends from CEJ apically, and is the BEGINNING of root formation

Cervical loop forms (important)

HERTWIGS EPITHELIAL ROOT SHEATH

root sheath begins at the

cervical loop and made of OEE and IEE

epithelial diaphragm is where

downward growth continues so the root sheath turns inward horizontally

epithelial root sheath continues to grow

vertically to create the length of the root

epithelial diaphragm continues to grow horizontally towards the

middle of the tooth

the epithelial root sheath and epithelial diaphragm determine the

shape and number of roots the tooth will have

(IMPORTANT)

If circumference of diaphragm grows EVENLY, it will form

ONE root

if 2 areas opposite each other grow inwards and meet, it will form

2 roots

if 3 areas opposite each other grow inward and meet, it will form

3 roots

2 structures determine the number of roots a tooth will have (important-national board)

epithlial root sheath and epithelial diaphragm

tooth eruption is where

as root lengthens, tooth moves upwards the surface of oral cavity and eventually crown erupts thru gingival tissue

exfoliation is the shedding of

primary teeth CAUSED by permanent tooth under primary tooth that puts pressure on the primary root.

the pressure from exfoliation causes

osteoclasts to form that resorb the primary root. this resorptions happens ONE YEAR prior to exfoliation

attachment apparaatus is in the

dentinocemntal junction (DCJ)

The attachment apparatus of the DCJ includes the epithlial root sheath thats a

wall of cells surrounding the developing tooth root thats riddles w/holes. this barrier cant SEPERATE the odontoblasts and dentin on the inside from the cells of the dental sac on the outside

in the attachment apparatus of the DCJ, dental sac cells change into

cementoblasts that move thru holes and form cementum which is laid down againt the previously formed dentin and forms the DCJ

At the DCJ, the epithelial root sheath has broken up which is how the cementoblasts that contact

dentin are able to transform only where the epithelial root sheath has gaps

the remaining root sheath cells pull away from dentin, and the cementoblasts contact the entire dentin and establish

the rest of the DCJ

the epithlial rests of malassez is (important)

after the cells of the epithelial root sheath have broken up and away from dentin, the remaining root sheath cells are found in periodontal space next to tooth

in the epithelial rests of malassez, if the cells divide LATER, it will create

periodontal cysts in the jaw

cementum is where the epithelial root sheath has broken up the cells from the

dental sac which surround tooth change into cementoblasts. These cementoblasts form cementum as epithlial root sheath continues to break up until its gone.

cementum is laid down on the entire

dentinal surface and DCJ is formed

developmental disturbance is when ALL epithelial root sheath cells dont

break up and turn into ameloblasts and form small globs of enamel on the dentin called enamel pearls

enamel pearls (enamelomas) are usually found on the

CEJ and furcation areas that can create problems w/scaling teeth

cementum is a

hard, yellowish substance covering root of tooth

cementum is

45-50% inorganic hydroxyapatite crystals 50-55% organic components and water (national board question)

the organic component of cementum is primarlily

collagen fibers and mucopolysaccharide ground substance

cementum forms from the

CEJ down to apical

this destroys bone and may also destroy or resorb cementum (and dentin which lies beneath)

osteoclast (clast=destroy)

this proceeds slower in cementum and is not affected as quicky as trauma to bone.

Resorption

what are the enamel cementum relationship percentages (important)

60% cementum overlap at CEJ of enamel

30% cementum MEET at CEJ of enamel

10% gap at CEJ and DONT meet

Acellular cementum is as the cementoblast begin laying down cementum, it

moves away from DEC and secreting maxtrix behind it

the secretion of the acellular cementum is when ALL of the cementoblasts remain on the

surface rather than being trapped in cementum

in the acellular cementum, cementoblasts not only build cementum, but also aid in

rebuilding cementum when its damaged

acellular cementum is

2/3 cervical of root

but not in apical 1/3 of root

cellular cementum (cellular=alive) is as root formation and cementum formation proceed from the cervical line to the apex of root,

cementoblasts surround themselves and become entrapped as they secrete matrix

(entrapped cells=cementocytes)

cellular cementum is

MORE VITAL and receive nourishment from blood vessels of periodontium

In the middle and apical 1/3 of the root, cellular cementum can be seen

overlapping acellular cementum

in sharpeys fibers, the outer layer of cementum is lined with

cementoblasts which will form cementum through a LIFETIME

In sharpeys fibers, as the periodontal ligament forms from the middle layer of cells in the old dental sac, the ends of the periodontal fibers become surrounded by

cementoblasts where the secretion hardens around the ends of the fibers attaching them to cementum

the parts of the periodontal ligament (PDL) embedded in cementum are which fibers

sharpeys fibers

The periodontal fibers surrounded by albeolar bone on the other side of the tooth socket are also known as

Sharpey’s Fibers (periodontal)

alveolar bone is also the alveolar process and it is the bone of the max/man jaw that compromised the sockets for the teeth and has percentages of

Adult bone: 65% inorganic crystals

35% organic composition is about 89% collagen and 11% non collagenous material (National Board Question)

alveolar bone is mesodermal in origin and bone has

embedded parts of the PDL in which are sharpeys fibers and better blood supply

Bone changes in response to

stress which can be seen during orthodontic treatment and teeth movement

The ends of the Periodontal Ligament (PDL) entrapped in bone and cementum and the entrapped fibers are

Sharpey’s Fibers

alveolar bone involves the cortical plate that has

compact bone on the buccal/lingual w/normal periosteum

in the cortical plate, the SOCKET for the tooth is

compact bone but NOT normal periosteum

the alveolar bone has spongy cancellous bone thats in b/w the

cortical and cribiform plate and made up of bone marrow

spongy cancellous bone cant be seen radiographically because its only on the

buccal/lingual sides of the socket

the alveolar crest can be seen at the interproximal area and is a good indicator of

periodontal health

the alveolar bone proper of the cribiform plateis a compact layer w/

holes that allow passage for blood vessels connecting deeper part of the bone w/vessels of periodontal space

the cribiform plate is also referred as the

lamina dura radiographically and ORIGINATES from the outer layer of the dental sac

the PDL develops from the

middle layer of mesodermal cells of the dental sac after cementum forms.

in the PDL, as the dental sac cells change, they 1st become

fibroblasts and form collagen fibers

Collagen fibers of the PDL are

around the tooth and parallel with the root surface in the middle of the periodontal space.

The collagen fibers of the PDL that are forming adjacent to cementum and alveolar bone are initially more

oblique oriented. Later they band into groups of fibers that span the periodontal space

While the collagen fibers are forming, the PDL components start to appear:

blood vessels, lymphatic vessels, nerves, connective tissue cells

the nerves of the PDL allow the feeling of

light touch/pressure and heat/cold

the blood vessels of the PDL are branches of the same vessels that go to the

pulp and penetrate holes in the wall of the cribiform plate that join w/the vascular channels in the spongy part of the alveolar bone. Others come from the gingival blood supply and interconnect w/other vessels

the PDL has FIBERS that arrange themselves in a definite pattern:

gingival fibers, transseptal fibers, alveolodental fibers

gingival fibers function is to

hold gingiva against the tooth that run from cementum into free and attached gingival areas and support gingiva

gingival fibers are have

circular gingival fibers that run around the tooth in free gingiva

transseptal fibers function is to

hold the teeth in interproximal contact that run from cementum of the interproximal of one tooth across the alveolar crest of bone to the cementum of the interproximal portion of the adjacent tooth

alveolodental fibers run from

cementum to alveolar bone

alveolar crest group is a runs from

cementum, slightly apical to the alveolar crest of bone

horizontal group runs from

cementum horzontally to the alveolar crest

function of both the alveolar crest group and horizontal group helps resist

horizontal movements of teeth (IMPORTANT)

Oblique group runs from cementum

coronally into alveolar bone and their function is the MAIN fiber group for resisting occlusal stresses

apical group runs from the apex into the

adjacent alveolar bone and their function is to resist forces trying to pull tooth from its socket

alveodental fibers include the

alveolar crest group, horizontal group, oblique group, and apical group

functions of root include

-sensory function

-house nourishment system of teeth. internal/external reparative methods to respond to pathology, pressure or trauma

-support/anchorage for teeth

sensory function of root is the

inner part of tooth roots composed of dental pulpal tissue where pulp nourishes and contains nerves that can have pain response

ex. dehydration, rootdecay, abrasion, resorption, friction

in the sensory function, the dentin that surrounds the pulpal tissue of the tooth is covered by an

imperfect layer of cementum (IMPORTANT)

in the sensory function, If the tooth root is exposed because of periodontal disease, recession, trauma or pathology the exposed dentin can stimulate the

pulpal nerves through their tubules.

Roots are a warning system that indicates external or internal trauma

pressure/temp are NOT a response by the

pulpal tissue, it is from the NERVE tissue w/in bone, gums and periodontal ligament. *****

Root canal tissue does NOT have

nerves that can stimulate sensations of temp/pressure, it can ONLY respond to pain ****

what houses the nourishment system of the tooth

pulp canals*******

the root canal houses arteries,veins,and lymph tissue which

nourish tooth internally

in the reparative/nourishment function, this enters/exits through apex of the root called

apical foramen

the apical foramen allow

nutrients and oxygen to circulate throughout the pulp chamber and provide a system to remove harmful products and carbon dioxide from the tooth

Inside the tooth the odontoblasts allow

secondary and reparative dentin to be formed in response to trauma—this process is not only occurring in the root but in the entire pulp chamber

Apical 1/3 of the root can continue to form cementum outside of the root called

hypercementosis and forms a cementoma at the apex of the root

Shape & Length of the roots have a direct effect on how much

anchorage and support they have.

The longer and wider the root, the more

support the tooth receives

The longer the root the more firmly embedded into bone the tooth is

The greater the surface area of the root, the more the

periodontal fibers can attach the root to the bone and the better the root can resist displacement

A tooth with multiple roots has its periodontal ligaments more

disbursed in different directions compared with a single rooted tooth—this allows resistance to displacement

Concavities and grooves also allow for more

attachment surface area which increases strength & resistance

The width, shape, length, curvature, number of roots, concavities and direction of the periodontal fibers all affect the amount and direction of

resistance a tooth can offer to withstand the forces exerted on it

Teeth are NOT embedded into bone but are

supported between the root and bone by a hammock of periodontal fibers attached to cementum on the root on one end and to alveolar bone

The Periodontal Ligament (PDL) is living tissue composed of

collagenous fibers of connective tissue and is capable of being tensed or compressed

The PDL fills the thin area of space that is between the tooth and bone. Pressure on the tooth compresses the PDL fibers on one side and tenses them on the other. This movement is called

MOBILITY

A slight amount of mobility is healthy and normal, but If pressure is too extreme, both bone and root can be

resorbed. if root is resorbed then mobility will increase

if bone is resorbed we have

reduced strength and periodontal problems

Even without external forces, a tooth will still move

If all occlusal forces are removed from a tooth and it has no opposing tooth to occlude with the tooth will continue to erupt and is called

SUPER ERUPTION

If a tooth moves mesially because it doesn’t make contact with a tooth on its mesial it is called

MESIAL DRIFT

The grooves & depressions on the roots make these areas harder to clean and more susceptible to

periodontal disease