dh156alveolarbone

8/3/2019 DH156Alveolarbone

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Periodontium soft and hard dental tissues between and

including the tooth and alveolar bone (AB)

figure 14-1

cementum

AB

periodontal ligament (PDL)

gingiva?? (minor role)


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Cementum

attaches the tooth to the AB by anchoring the PDL and AB to thetooth

should NOT be visible in the healthy patient

thickest at the tooth apex in multirooted teeth thicker in the interradicular area

thinnest at the cementoenamel junction (CEJ)

no innervation

avascular receives nutrition from the PDL

forms throughout the life of the tooth

65% mineral, 23% organic, 12% water mineral hydroxyapatite (most similar to that seen in bone

apposition of cementum over the root dentin creates thedentinocemental junction or DCJ


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Formation

see previous lectures

but to remind you: disintegration of Hertwigs root sheath is followed by cementogenesis

allows direct contact of the cells of the dental sac with the root dentin

cementoblast differentiation results (cementoblasts) the differentiating cementoblasts disperse to cover the root and undergo

cementogenesis

results in the formation of unmineralized cementoid

many CBs become entrapped in the mineralizing cementoid = cementocytes

once the cementoid reaches full thickness it begins to mineralize initially aroundthe cementocytes

now called cementum the cementocytes are located in lacunae similar to bone

connected by canaliculi unlike bone they do not contain nerves/vessels also they do NOT radiate out but are directed toward the PDL

the cellular processes of the cementocytes take up nutrients that have diffused from thePDL into the cementum

see figures 14-2 and 14-11


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Microscopic appearance

figure 14-2 and 14-11

made of a matrix + cells

matrix consists ofSharpeys fibers portion of collagen fibers from the PDL that

partially insert into the outer part of the cementum at a 90 angle and into thealveolar bone

these function as a ligament between the tooth and AB

Figure 14-2

fibers collage fibers made by the cementoblasts

non-organized

but they do run parallel to the DCJ cells

cementoblasts Figure 14-7

located in lacunae and connected by canaliculi


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Cementoenamel

Junction (

CEJ)

3 patterns may be present

1) 60% show cementum overlapping the enamel at theCEJ

Figure 14-8 2) 30% show an end-on-end meeting of cementum and

enamel

3) 10% show a definitive gap between the cementumand enamel

can result in dental hypersensitivity as the gingiva recedesexposing the underlying root dentin

new study 1993 76% edge to edge, 14% overlap and10% gap with no exposed dentin


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Repair of

Cementum

resorption occurs by the odontoclasts results in the formation of reversal lines with a a scalloped

appearance

occurs at a rate less than bone

repair apposition of cementum by CBs at the adjacentPDL creates arrest lines smooth growth rings (like a tree)

these can be prominent due to trauma from occlusal trauma or totooth movement as well as the shedding of primary teeth and

eruption of the permanent dentition unlike bone the cementum is not continuously remodelled and

repaired


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Types ofC

ementum Acellular

first layers that are laid at the DCJ

formed at a slow rate

no embedded cementocytes seen

once continuous layer covers the root many layers are found covering the cervical 1/3rd of the tooth near the CEJ

Figure 14-3

Cellular or secondarycementum

last layers deposited over the acellular layers

mainly at the apical 1/3rd of the tooth

deposited at a faster rate therefore the presence of many cementocytes at the periphery are CBs - found within the PDL

allow for the future production of more secondary cementum

therefore the width of these layers changes with the life span of each tooth

especially at the apex


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Alveolar bone

part of the maxilla and mandible

point of attachment for the cementum via the periodontalligament

same composition as regular bone

but is remodelled at a higher rate

also remodelled at a higher rate when compared to thecementum allows for tooth movement

when stained alveolar bone shows areas of arrest lines

and reversal lines as seen in all bone tissue (figure 14-13) 60% mineralized, 25% organic, 15% water

mainly hydroxyapatite similar to dentin and enamel

very similar to that seen in cementum


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each jaw is composed of two types of bone tissue

different physiological functions

these can lead to different clinical considerations

density of alveolar bone can determine the efficacy of local anesthesia and the spread of dental infection

can also determine the most convenient areas of bony fracture during extraction

1. alveolar bone

or alveolar process or alveolar ridge

contains the roots of the teeth

divided into the

a. alveolar bone proper

lining of the tooth socket or alveolus (Figure 14-15)

compact bone

bone is also called the cribriform platebecause of the many holes through which Volkmanns canals pass (from the alveolar

bone into the PDL)

also called bundle bonebecause Sharpeys fibers insert into this bone (Sharpeys fibers = portion of the fibers of the PDL)

these fibers are inserted at a 90 angle into the ABP but are fewer in number than those found at the cemental surface

consists of plates of compact bone that surround the tooth

varies in thickness from 0.1 to 0.5mm

known in radiographs as the lamina dura (figure 14-17)

most cervical rim = alveolar crest (figure 14-18) slightly apical to the CEJ in healthy patients

the crests of neighboring teeth are uniform in height

can see portions of the alveolar crest between teeth on radiographs also (Figure 14-17)

b. supporting alveolar bone

has the same components as ABP

spongy or cancellous bone

considered to be comprised ofcortical and trabecular bone different arrangement of bony plates, different locations

cortical bone is made up of cortical plates found on the facial and lingual surfaces (Figure 14-15)

trabecular bone is located between the ABP and the plates of the cortical bone (Figure 14-15C cross section of mandible)


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the alveolar bone between two neighboring teeth = interdental septum

(Figure 14-15) or interdental bone

made up of ABP and trabecular (spongy) bone

easily seen on periapical and bite wing radiographs (Figure 14-17)

the alveolar bone between the roots of the same tooth = interradicular

bone or interradicular septum

both ABP and trabecular (spongy) bone

only a portion can be seen on radiographs

2. basal bone

apical to the roots of the teeth

forms the body of the maxilla and mandible


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alveolar bone can be resorbed with age

edentulous

the underlying basal bone is less affected with age because it does

not need the presence of teeth to remain viable

loss of teeth + alveolar bone can results in loss in the vertical

dimension of the face figure 14-22

Popeye facial appearance

can also affect the teeth and jaw line up functional consequences

dental implants can prevent this loss

core of titanium that is surgically implanted into the alveolar bone

implant can become integrated into the surrounding bone

no movement poor insertion of the PDL

after tooth extraction the clot is replaced with immature bone later remodelled as mature secondary bone

very similar process to fracture repair in skeletal bone


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Periodontal ligament part of the periodontium that provides for the attachment of

the teeth to the surrounding alveolar bone by way of thecementum Figure 14-25

PDL appears as the periodontal space (0.4 to 0.5mm) inradiographs between the lamina dura of the ABP and thecementum (Figure 14-17)

fibrous connective tissue - Figure 14-26

transmits occlusal forces from the teeth to the bone allowing for a small amount of movement

wider at the apex and cervical portion narrows betweenthese two points


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components made of matrix containing cells and fibers

also a vascular supply, lymphatics and nervous innervation enter the apicalforamen to supply the pulp

vascular supply is for the supply of nutrition for the cells of the PDL and surroundingcementum and alveolar bone

the nerve supply provides an efficient propriception mechanism allows thesensation of even the most delicate forces applied to the teeth

afferent and autonomic sympathetic (regulates blood vessel diameter)

afferent fibers transmit pain, touch, pressure and temperature

cells participate in the formation and resorption of the hard tissues of the periodontium

most common cell is the fibroblast similar to other fibrous connective tissues

also has cementoblasts along the cemental surface and osteocytes at the periphery ofthe ABP

also has odontoclasts and osteoclasts for resorption of cementum and bone

balance between the clasts and blasts maintain a certain level of AB andcementum depending on the need and environment adjacent to the PDL

also has epithelial rests of Malassezfigure 14-26

disintegration of Hertwigs root sheath during tooth formation

fibers all are collagenous in structure made up of multiple bundles of principal fibers


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PDL: Fibers principal fibers organized into groups or bundles

designed to resist the forces generated during mastication - because

the PDL fibers are anchored in both the cementum and AB 1) alveolodental ligament 5 fiber groups Figure 14-27

each of these have their own orientation as such they resist specific forces

a) alveolar crest group O: in the alveolar crest of the ABP I: fans out and inserts into the cementum at various angles

F: resists tilting, intrusive, extrusive and rotational forces

b) horizontal group: O: from the ABP I: into the cementum in a horizontal manner F: resists tilting and rotational

c) oblique group: most numerous covers the apical 2/3rd of the root Figure 14-28

O: ABP

I: more apically into the cementum in an oblique manner

F: resists intrusive/inward forces and rotational d) apical group: O: radiates from the apical region of the cementum

I: ABP

F: resists extrusive/outward forces and rotational

e) interradicular group multirooted teeth only O & I: runs from the cementum of one root to the cementum of the adjacent root

F: works with the alveolar crest group to resist intrusive, extrusive and rotational

forces


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2) interdental ligament -or the transseptal ligament I: mesiodistally into the cementum of the neighboring teeth over the

alveolar crest group fibers (Figure 14-27)

therefore travels from cementum to cementum without any bony

attachment F: resists rotational forces and holds teeth in interproximal contact

Figure 14-31

3) gingival ligament some clinicians disagree Figure 14-32

support the marginal gingival tissues and do NOT support the tooth

during mastication or speech separate but adjacent fiber groups within the lamina propria of the

marginal gingiva a) circular ligament lamina propria, encircles the tooth (pulling of

purse strings)

b) dentogingival ligament inserts into the cementum at the root andextends into the lamina propria, has one mineralized attachment to thecementum

c) alveologingival ligament extend from the AC and radiate into thelamina propria, role in attachement of the gingiva to the AB

d) dentoperiosteal ligament course from the cementum near the CEJacross the alveolar crest

dh156alveolarbone

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