Oral Histo 9th Lec Pt1

8/2/2019 Oral Histo 9th Lec Pt1

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Cementum

its the least known among periodontium tissues and all mineralized tissues

,they are still having researches its not as well known as enamel and dentin

Thin layer of calcified tissue covering the root in the Humanteeth

we may sometimes see cementum covering the crown of some teeth in some

animals

E.g herbivorous, like cows ,horses, its important for them because its an

adaptation to their diet , they are continuous eaters thats why all the time

their teeth are worn out ,, and for these surfaces that are subject in

continuous wearing ,we need rough surfaces or irregular to make it easy to

grind so to have a rough surface we need cementum in addition to enamel and

dentin

Important.. Now How this happens ..?

The margins of enamel remain very raised because enamel is hard but the

areas of dentin are slightly depressed and the areas of cementum are very

much depressed that makes the surface very rough and irregular which gives

a good mechanical property for eating to these animals their diet which is

grass, and because grass has a very low nutritional value ,they want to get the

maximum benefit so in order for them to get the maximum benefit they have

to grind it to fine pieces thats why they have to continue grinding all the time

,if the surfaces become very flat or the crown of the teeth is made only of onematerial they will not be able to grind and die of hunger

It varies in thickness .. thick at the apex (50-200 micrometer) & inter radicular

regions (at the division of the roots) but it tends to be thin cervically (Look at

the previous picture)


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Its contiguous (continuous with the PDL) , its always in contact with the PDL

Its firmly attached to root dentin thats why its not easily separated from root

dentin, remember that cementum is thin cervically ,suppose that this tooth

has undergone some form of gum recession () then part of the rootwill be exposed if the person that has exposure of root uses a tooth brush

horizontally then it will erode the cementum , there will be areas of exposed

dentin in those people and dentin is innervated so it will cause pain and

sensitivity when they eat something cold or whatever, especially in old

females for example when they exposed to cold wind , because females brush

their teeth regularly which lead to removing part of the cementum then part

of the dentine will be exposed which is sensitive , its good for them to use

sensodine tooth paste which helps in blocking dentinal tubules that wereexposed ,which reduced the amount of sensitivity

Its also highly responsive mineralized tissue ,in contrast enamel is not responsive

because its a dead tissue

If you do something to enamel it will not respond but if you do something to

cementum it will respond

Which leads maintenance of root integrity, E.g if a tooth got subjected to

some trauma and part of the cementum was lost , this part can be replaced

because its able to build up the lost areas ,this happens when the trauma is

minor when there is a big area of cementum lost it will be difficult to be replaced

-maintenance of the functional position of the tooth ,because

cementum is responsive sometimes when the opposing tooth is lost, E.g we have

mandibular tooth and the opposing maxillary is lost so the tooth will not be in

contact with any tooth in the opposing arch , the tooth may erupt slightly and

becomes above the upper teeth or above the occlousal plane which is calledsupra eruption, for example when the tooth is 1 mm above its place because

the opposing tooth is lost, cementum will be build up at the apex we will find 1

mm of thickness at the apex because cementum is very responsive


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Similar to bone ,however

Bone is vascular while cementum is not

Bone is innervated while cementum is not ,although it contain cells but

cementum as cementum is not vascular

Cementum also less rapidly reabsorbed compared with bone , if theres a

movement for a tooth from one location to another the bone which is existing in

the area of movement will be reabsorbed but cementum will not be reabsorbed

as strongly as bone ,E.g if we have 5 mm reabsorption of bone but we may have

0.1 mm reabsorption of cementum and this is important in orthodontics because

if they both have the same rate , when the tooth moves there will be

reabsorption bone and also of reabsorption of cementum ,cementum will be lost

and there will be detached because centum play a major role in attaching the

tooth ..if the rate of reabsorption of cementum was equal to the rate of

reabsorption of bone orthodontics will not have existed ,because in orthodontics

there is just a little reabsorption of cementum which can be replaced later on

thats why the good orthodontist is the one who gives the tooth a very sufficient

time at least from one and half to two years!


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Cement-Enamel Junction

They are related in three patterns ..

Pattern one .. cementum overlaps enamel for a short distance this is the mostdominant pattern it occours in 60% of sections

Pattern two .. enamel meet cementum at butt joint (edge to edge) this happens in

30% of sections

Pattern three .. enamel fails to meet cementum so there will be an area of

exposed dentin this area is very sensitive thats why they have healthy

periodontium but they have sensitivity because dentin has dentinal tubules which

will be exposed to the environment it occurs in 10% of people

Remember ~ cementum covers enamel in 60% and not Enamel covers cementum

~


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Physical Properties

Pale yellow .. thats why when cementum is exposed due to gingival recession

with age and part of the root is exposed ,our teeth will start to look ugly because

the color of cementum is yellow which is not very acceptable it makes our teeth

uglier when we grow in age , also its softer than dentin, when we apply the same

force on dentine there will be less amount of reabsorb when we apply the same

force on cementum .. this important in herbivorous animals

Permeability

-varies with age and type of cementum

-decreases with age .. because we start to have the dentin that involves in

closure to the dentinal tubules

-cellular cementum is more permeable than Acellular cementum ..because

cellular contains cells and these cells have many processes that exist in canals that

can let fluids pass

-cementum is more permeable than dentine although dentine contain tubules

Readily removed by abrasion after gingival recession, after the recession of the

gingivae when the cementum is exposed it can be lost easily


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Chemical properties

Inorganic Organic Water

By weight 65% 23% 12%

By volume 45% 33% 22%

Compared with enamel that has 95 -96% by weight and dentine that has 70%

Hydroxyapatite crystals similar to those in bones

More concentration of trace elements Floride (F) at surface ,more than the deep

areas of cementum

Floride levels is higher in acellular cementum ,because usualy acellular cementumoccours in the cervical portion of the root in that area it can be exposed to saliva

to the outer atmosphere more than the deep areas at the apex thats why it

accepts more floride

Collagenous organic matrix , primarily type 1 ..which is similar to dentine and

bone but not enamel because the organic material in enamel is not collagenous

its enamlin and amelogenin

Molecules involved in PDL fiber reattachment

We have number of molecules that exist in cementum ..

Examples .. bone sialoprotin ,osetoponti & cementum specific elements these

function in the detached and reattachment remodeling of the PDL fibers

Classification of cementum

According to the presence or absent of cells .. >>Cellular cementum if it contains

cells

>>Acellular cementum if it

doesnt contain cells


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According to the nature and origin of organic matrix ..

>>Extrinsic fiber cementum if the fibers from extrinsic which means

from the periodontal ligament not from the cementoblast

>>intrinsic fiber cementum if the fibers arise from within or from the

cementoblast it self

>>mixed fiber cementum if the fibers are from external and internal

Note : we can have any type of combination between these types for instance we

can have cellular and extrinsic fibers at the same time

Acellular cementum ..

-Its the most common located adjacent to dentine ,usually this pattern located

cervically and also at the deep areas of cementum

-It doesnt have any structure because we dont see cells inside it , we can have

special type of Acellular cementum called Afibirllar in this time there is no cells

and also there is no fibers

Afibrillar cementum

-Exists between Acellular cementum and the hyaline layer (of hopewell -smith)

-it covers cervical enamel

-Mineralized GS

-results because of the loss of reduced enamel epithelium (REE), REE is a tissue

that covers enamel after enamel has been completed and this tissue is important

to prevent the exposure of the enamel to the surrounding ,when a part of enamel

which is still inside bone is exposed to the dental follicle cells, enamel as a tissue

will induce the undifferentiated cells of the dental follicle and become

cementoblast, and this will lay down cementum on the surface of enamel ,this

happens only on the cervical portion ,sometimes in the cervical portion we lose

REE,so we will see enamel in contact to the surrounding this will lead to the


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differention of the cementoblast and this is will lay down cementum on that

portion of enamel

Cellular Cementum


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Its the Most common pattern atThe Apical area of the tooth

In the Inter-radicular areas, between the roots

Also Overlying Acellular dentine

Note .. The Difference between cellular and Acellular is Cementocytes,these are

cells present within cellular cementum

These Cementocytes Are

Inactive Present In lacunae appear dark in ground section, GS They have Processes present in canaliculi Also these Processes connected via gap junctions

When the cell is becomes inside cementim is called cementocyte ,while its

outside its called osteoblast this location of the cells depends on the activity of

the cells ,when the cell is very active and produce cementum in different regoins

it will be surrounded by cementum because it secrets cementum in all directions

cementocyte, but when the cells gives cementum and moves back it will beaway from cementum cementoblast which is not very active as cementocyte


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Are more important because they are the actual fibers that function

in attachment

Intrinsic fiber cementumFibers derived from cementoblasts

Run parallel to the root surface at right angles to extrinsic fibers,

because they are not very important in attachment

Acellular extrinsic fiber cementum

its one of the different type of cementum that we can see ,it doesnt contain cells

and the fibers of this cementum is from the PDL

AEFC Its usually Over the cervical half or the cervical 2/3s of the root Usually the Bulk of cementum in premolars from this type Its First

formed cementum -

Its Thickness of 15 m All collagen are from Sharpys fibers,thats why all collagen are

involved in attachment of the tooth

GS from cementoblasts, cementoblast can only produce GS,but thefibers of this cementum is from the fibroblast (the cells in the PDL)

the Fibers are well-mineralized

Cellular intrinsic fiber cementumUsually when cementum is cellular its intrinsic fibers ,because sharpys

fibers are the fibers that are derived from PDL , are inserted to the deep

portion of cementum , at the outer portion of cementum usually

cementum provide some thickness without being involved in attachment ..


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CIFC Fibers deposited by cementoblasts Fibers run parallel to root surface ,so they dont function in attaching the

tooth

No role of tooth attachment , but they provide thickness for protection Its find In the apical 1/3 & inter-radicular areas May be

Temporary extrinsic fibers gain reattachment, they sometimes mayinter inside and gain attachment and with time the fibers will

penetrate to the cementum and become extrinsic fibers again

Permanent without attaching fibers , so no fibers will get inside soit will remain extrinsic all the time

Acellular intrinsic fiber cemetum

If cementum forms slowly CIFCCellular mixed stratified cementum

When there is an Alternating AEFC with CIFC,its called cellular mixedstratified cementum

It presents at the Root apex Also Fraction areas

Mixed-fiber cementum

When the Collagen fibers derived from


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Extrinsic fibers

Intrinsic fibers

Intrinsic fibers run between the extrinsic fibers, extrinsic fibers areperpendicular to the surface and between these them ,intrinsic

fibers are parallel to the surface

It can be divided to Two types depending on the rate of formation-Acellular mixed-fiber cementum

In this case its Well mineralized fibers-Cellular mixed-fiber cementum

Less well mineralized fibers

Incremental lines

Similar to enamel and dentine cementum is built incrementally increment

by increment between one increment and another we can identify a line called

incremental line ,but in a cementum they are very irregular not like enamel and

dentin where they are very regular


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So Irregular rhythm of deposition Its Not related to activity & quiescence ,in enamel and dentine

incremental lines are related to period of activity and periods of rest

Its Related to-Difference in the degree of mineralization , the area when we see

incremental line this means this area has different degree of

mineralization of the close area

-Difference in the Composition of organic matrix

Imprecise periodicity, it means we dont have the periodicappearance of these incremental lines and the measurement of the

distance will not be the same between another pair of incremental

lines ,due to the irregularity

Acellular tends to be closer, thinner & regular linesCellular tends to be farther apart, thicker & irregular lines,the rate

of deposition tends to be very fast thats why it tends to go

irregular

Resorption & repair of cementum

Less susceptibility to resorption than bone ,E.g if there is a newton force oncementum and the same Newton force on bone ,theres more resorption on

bone which is important in orthdodontics

Localized resorption areas occur


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Could be caused by micro trauma,(a minor trauma) May continue to root dentine Usually caused By multinucleated odontoclasts ,odotoclast are eater cells

that eat dentin and also cementum

Resorption can be repaired not like resorption in enamel which cannot berepaired ,also in dentine resorption cannot be repaired but in dentine if we

lose one layer from above another layer will form inside ,in cementum if

theres a loss for a small layer it can replace itself ,so Resorption areas filled

by mineralized tissue (resembles cellular cementum)

Reversal line ,the area between resorption and depostion similar to thereversal line in bone,because we always have remodeling resorption and

deposition so theres always reversal lone which represents the end of

resorption and the begin of deposition

Reparative cementum vs. cementum

Usually reparative cementum is Wider uncalcified zone, which is calledprecementum

Also its Less mineralized Smaller crystals Sometimes we can see Calcific globules are present

Note : Differences are related to different speed of formation


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When we see the end of the teeth cementum is not covers the root from only

outside it also extends to cover the inside part(the last part) of the canal ,thats

why its called dental pulp ,that means that PDL is always associated withcementum ..so periodontal ligaments surrounds the tooth and also inters inside

area ,for that reason in endodontics when we cleen the pulp of the tooth we

have to consider this difference which is about 1mm

Remember , that the apex of the tooth doesnt contain pulp ,it contains

periodontal ligament ,so in dentistry so I always consider the distance that related

to cementum ,so theres an area that we dont clean because its not a pulp its a

periodontal ligament

Periodontal ligament PDL

Dense fibrous connective tissue Occupies the area between the root of the tooth and the walls of the

alveolar socket

Derived from the dental follicles Continuous with

the connective tissue of the gingiva above the alveolar crest The dental pulp at the apical foramen ,when theres a infection inside

the pulp it can spread and infect the Periodontal tissue ,in many of

the cases of many people that have pulpitis two or three days then

this pain disappears because the pulp got necrosis, these people

think that the problem is over which is not true! ,, necrosis ( means

there are germs and bacteria inside the pulp) and this can spread to

the outside and affect the periodontal ligament with pain while

biting ,if it is left without treatment there will be facial swelling

Periodontal ligament space


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Its the space where a periodontal ligament exists

Its Variable in width, the average is 0.2 mm It looks like hourglass ) ( in shape, the thinnest area of the

periodontal ligament is in the half way of the root

Its Reduced in (unerupted)& non-functional teeth , (non functional meansnot reach the opposing contact with the other tooth

Its Increased in teeth subjected to heavy occlusal stress, like bitingforcefully (clenching)

Narrows slightly with age Narrower in permanent teeth than in deciduous

Functions of PDL

Attachment the tooth to the bone this is the main function It Has a role in tooth eruption and support ,the remodeling (the attachment

and reattachment) has a force to push the tooth

Its cells repair the alveolar bone & cementum, because we always haveundifferentiated cells that differentiate to osteoblast to reabsorb bone or

to cementoblast to reabsorb cementum

The Neurological control of mastication through its mechanoreceptors thatsends information to the brain about the amount of load in the mandible ,

also in PDL ligaments there are receptors prpyoreceptor that sends

information to the brain about the position and the amount of load in the

mandible

Components of PDL

Fibers,which are collagen


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Ground substance Cells

Fibers of PDL

Collagen Type I (70% of fibers) Type III (20% of fibers) is

Found in the periphery of Sharpys fibers and the attachment

into alveolar bone

Small amounts of type V, VI as well as basement membrane collagenIV & VII associated with the epithelial rests

Highest turnover of collagen is in PDLTurn over its the break down and the rebuilt of fibers its:

Higher near apex because the apex is subjected toward theload

Even across the width of PDL The turnover rate is the same to the area close to the bone

and the area close to the apex

Rate could be related to the amount of occlusal stress

Oxytalan ( only in humans) ,which is another firber protein found or elastin

Attached into cementum May have a role in tooth support


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Important ,,, Principal fibers of PDL

Fibers exist as bundles (principal fibers) running in different orientations indifferent regions

These are..Dentoalveolar crest fibers

Dento means tooth, alveolar crest means the crest of the bone

They attach the tooth to the crest of the bone

We have Horizontal fibers as we go down Then they become Oblique fibers Then we have the Apical fibers Then Interradicular fibers,which are between the toots

From crest of interradicular septum to furcation

Note : we have another type of fibers but not related to

periodontal ligament ,these fibers connect the tooth to the

gingivae which is called dentogingival fibers

Sharpys fibers

they represent the end of the periodontal ligament fibers


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Principal fibers that either embedded into cementum or bone More numerous but smaller at cemental end They have Mineralized and unmineralized parts ,the mineralized are

embedded in cementum

Ground substance of PDL

60% of PDL by volume Main components

Hyaluronate GAGs Proteoglycans Glycoproteins

Functions of GS Ion and water binding & exchange

Control of collagen fibrillogenesis(the formation of the collagenfibers) & fiber orientation

-Tooth support & eruption because of high tissue fluid pressure in these

areas


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Cells of PDL

types of cells exist in the periodontal ligament ,They are derived from dental follicle..which is calcified in three zones

1-the zone close to the tooth ,the cells here become cementoblast

2-the intermediate zone ,the cells here become fibroblast

3-the outer layer ,the cells here bcome osteoblast

Fibroblasts,

Its smiliar to any fibroblast in a connective tissue

Fusiform cells with many processes Functions secretion and turnover of fibers

Regeneration of tooth support apparatus,(that means thefibers are resorbed and built again) that is important to

maintenance to the health of these fibers

Adaptive responses to mechanical loading,if there is amechanical loading this lead to resorption of some areas of

periodontal ligament, and building another area of periodontal

ligament so its under turnover all the time


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Cementoblasts

-Cement-forming cells lining cemental surface, These are the cells that

give cementum ,they occour in the surface because once they are integrated in

cementum they are called cementocytes

They are Cuboidal cellsOsteoblasts

Bone-forming cells lining tooth socket They Resemble cementoblasts

Cementoclasts & osteoclasts

Resorbing cells Located at Howships lacunae,because they resorbe

Epithelial rests cells,

-These cells is due to the break down of the epithelial rooth sheath due

to the exposure of newly formed root dentin , these cells are surrounded

by a basement membrane ,,anyy epithelial cell located insidemesenchayeml area should be surrounded by a basement membrane

because this basement membrane is a limiting membrane it prevents these

cells from interaction from the surroundings otherwise it will go interaction

They are Cuboidal cells that stain deeply They present Close to cemental surface

Defence cells.. Like

Macrophages Mast cells


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Eosinophils

Blood vessels of PDL

Separate from those entering pulp,so they are different groups Some from alveolar bone through foramina opening in the periodontal

ligament

Some from pulp through accessory canals Major vessels lie between principal fiber bundle close to alveolar

bone,usually the big blood vessels are close to the bone not to the tooth

Capillary plexus around the tooth Crevicular plexus of capillary loops,which is near the gingivae named

clevicular because that area between the gingivae and the tooth is called

clevicular groove

Veins do not follow arteries but drain into intraalveolar venous networks

Innervation of PDL

Sensory Nociception that receive stimuli of pain

Mechanoreception

Sensitivity to occlusal loads the proprioreceptors in the mandibular teeth that tells the

brain about the postion of the mandible , when the mandible is


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elevated up ..they guide the mandible into the correct

intercuspation

Autonomic Associated with blood vessels

Alveolar process

o The alveolar process develops during the eruption of teeth ,thissentence is related to primary teeth .. in primary teeth bone forms at

the same time and with the root and it can grow with little

surrounding bone but in permanent teeth bone is already existing

and it need to go inside bone

o Grows at a rapid rate at the free bordero Proliferates at the alveolar cresto No distinct boundary exists between the body of the maxilla or

mandible and the alveolar process, its difficult to determine the lines

o If teeth are lost the alveolar bone disappears they are present tomaintenance for the teeth one the tooth is lost the bone will be lost

,this means that the bone surrounding exists as long as the tooth

exist ,E.g if someone lost his teeth at 50 and didnt put a denturelater on there will be so much reabsorption


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Development of bony crypt

Reminder .. primary teeth when they erupt usually are not surrounded by too

much bone

Each primary tooth is related to lingual extension forming the permanent ,first the

permanent tooth is located lingual to the primary tooth ,then the tooth is going to

grow above and becomes bigger and bigger ,then it goes down until it remains

below the tooth ,but most of the time it remains lingual to the tooth for anterior

tooth but for posterior tooth it goes below or between the roots of that

deciduous molar

But always Deciduous tooth & permanent successor initially share crypt,butlater they both of them will have their own bony crypt

Bone subsequently forms to encase permanent tooth

Sorry for any mistakes ,,

Alaa Adas

Documents

Oral Histo 9th Lec Pt1