Periodontal ligament (II)

牙周韌帶 (II)

何坤炎副教授：高醫醫學大學何坤炎副教授：高醫醫學大學 口腔醫學院牙醫學系口腔醫學院牙醫學系07-312110107-3121101 轉 轉 7004 , 70297004 , 7029 kuyeho@kmu.edu.twkuyeho@kmu.edu.tw

學習目標：學習目標：• 牙周組織細胞來源• 牙周組織的神經、血管• 牙周組織的功能

學習資源：學習資源： 1. Ten Cate’s Oral histology. sixth edition, pp 241-2741. Ten Cate’s Oral histology. sixth edition, pp 241-274 2. Berkovitz BK , Holland GR, Moxham BJ.: Color atlas & textbook of oral anatomy. 1978 3. Avery JK. Essentials of oral histology and embryology A clinical approach. 1992, p133 -140

1. Infiltrating dental follicle cells receive a reciprocal inductive signal from dentin or the surrounding HERS cells and differentiate into cementoblasts

2. HERS cells transform

into cementoblast

Initiation of cementum formation of cementum formation

Ten Cate’s Oral histology. sixth edition, pp 243 Fig.9-3 Ten Cate’s Oral histology. sixth edition, pp 243 Fig.9-3

1. The precursor cells for cementoblasts and PDL fibroblasts reside ( 駐在 ) in the dental follicle and that factors within local environment regulate their ability to function as cementoblasts that form ro

ot cementum or as fibroblasts of PDL.

Origin of Periodontal cells and differentiation Origin of Periodontal cells and differentiation of cementoblastof cementoblast

2. Cells involved in regenerating periodontal tissues include stem cells migrating from the vascular region, as well as local cells 3. Epithelial cells from HERS may undergo epithelial-mesenchymal transformation into cementoblasts during development

Origin of Periodontal cells and differentiation Origin of Periodontal cells and differentiation of cementoblastof cementoblast

• In rodents, initial formation of acellular cementum take place in the presence of epithelial cells, enamel organ-derived cells are capable of producing mesenchymal products such as type I collagen, bone sialoprotein and osteopontin ♣ Suggests that difference in cell types or factors controlling development of these two varieties of cementum (acellular vs. cellular)

• Compelling ( 令人信服的 ) evidence indicating that populations of cells within the PDL, during development and during regeneration, secrete factors that can regulate the extent of mineralization• Factors secreted by PDL fibroblasts may inhibit mineralization and prevent the fusion of tooth root with surrounding bone; for example, ankylosis

Key proteins proposed to regulate cementogenesis Bone morphogenetic proteins• Members of transforming growth factorβ superfamily, initiation of crown formation• BMP-2, BMP-4 and BMP-7 are to promote differentiation of preosteoblasts and putative cementoblast precursor cells• Induce periodontal regeneration

Epithelial factors

• Epithial-mesenchymal interaction are required for crown formation and root formation• Enamel matrix derivative consisting predominantly amelogenin molecules is used to stimulate repair and regeneration of periodontal tissue

Adhesion molecules

• Bone sialoprotein and osteopontin , promote adhesion of selecting cells to newly forming root. • Bone sialoprotein promote mineral formation o

n root surface• Osteopontin --- regulating mineral growth

Gla protein • A calcium-binding amino acid, may facilitate interacting with hydroxyapatite • Bone Gla protein (osteocalcin) is a marker of osteoblast, odontoblast, and cementoblast • Matrix Gla protein (MGP), identified in PDL, as an inhibitor of mineralization, may act to preserve the PDL width

Collagens• Type I collagen is predominant in cementum a

ccommodates mineral deposition • Type III collagen high amounts but is reduced

with maturation of this tissue • Type I and III collagen regulating periodontal

tissue during development and regeneration• Type XII collagen assist in maintaining the PDL space

Development of periodontal ligament

• At the commencement of ligament formation the ligament space consists of unorganized CT with short fiber bundles extending into it from bone and cemental surfaces

Ten Cate’s Oral histology. sixth edition, pp 271 Fig.9-32 Ten Cate’s Oral histology. sixth edition, pp 271 Fig.9-32

Development of principal fiberEruption and establishment of occlusion then modifythis initial attachment, before tooth erupts, the crest of alveolar bone is above CEJ, the developing fiber bundle of PDL is obliquely

Ten Cate’s Oral histology. sixth edition, pp 262 Fig.9-23Ten Cate’s Oral histology. sixth edition, pp 262 Fig.9-23

Blood supply of PDL A. Main blood supply from superior and inferior alveolar arteries →interalveolar arteries, penetrate the alveolar bone and enter PDL space, called perforating arteries

1. from apical vessels

2. from interalveolar vessels

3. from gingival vessels

* 在齒槽骨端較牙骨質端多* 在韌帶之尖端及頸部有 豐富血管網

♣ Perforating arteries more abundant in PDL of posterior teeth than that of anterior teeth• Greater numbers in mandibular than maxillar

y teeth• Single-rooted teeth, more frequently in gingival third of ligament, followed by apical third

♣ Once within the ligament, these arteries occupy areas of loose connective tissue called interstitial areas between the principal fiber bundles

Avery JK. Essentials of oral histology and embryology A clinical approach. 1992, p133 Fig. 11-2B

LymphaticsLymphatics

* They are following the part of the blood

vessels

* From the ligament toward and into the

adjacent alveolar bone

Nerves supplyNerves supplyRunning from apical region toward gingival margin anRunning from apical region toward gingival margin an

d jointed by fiber entering laterally through foramina od jointed by fiber entering laterally through foramina o

f socket wallf socket wall

Apical region of ligament containing more nerve endinApical region of ligament containing more nerve endin

g than elsewhere ( except for upper incisors ) g than elsewhere ( except for upper incisors )

♣ Nerve terminal is demonstrated by immuno♣ Nerve terminal is demonstrated by immunohistochemistryhistochemistry

Nerves ending in human Nerves ending in human

periodontal ligamentperiodontal ligament

Ten Cate’s Oral histology. sixth edition, pp 270 Fig.9-31 Ten Cate’s Oral histology. sixth edition, pp 270 Fig.9-31

Four types of nerve ending:1. Treelike ramifications (most frequent), locate

d along the length of root, originate largely from unmyelinated fiber, are thought to be nociceptor and mechanoreceptors

2. Ruffini’s ending, found around root apex, ensheathing, function as mechanoreceptor

Ten Cate’s Oral histology. sixth edition, pp 272 Fig.9-33

Four types of nerve ending:

Ten Cate’s Oral histology. sixth edition, pp 271 Fig.9-32 Ten Cate’s Oral histology. sixth edition, pp 271 Fig.9-32

Four types of nerve ending:

3. Coiled ending found in middle of PDL, function have not been determined yet

4. Spindle-like ending surrounded by fibrous capsule

♣ Autonomic supply of PDL , close associated with blood vessels are sympathetic , to affect regional blood flow

NervesNerves 2. Two types of nerve fibers : 1) Large and myelinated( 髓鞘 ), have

knob- like ( 節瘤狀的 )endings

2) Small and may not be myelinated, and

end in branch

3) The larger fiber appear to be concerned

with touch and the small one with pain

Berkovitz BK , Holland GR, Moxham BJ.: Color atlas & textbook of oral ana

tomy. 1978, p119 Fig. 306B

Functions of the PDLFunctions of the PDL * Supportive

• During mastication the compressed PDL provides support for the loaded tooth. 咀嚼時被壓縮的牙周韌帶提供牙齒的支持

• Collagen fibers and ground substance act as a cushion for the displaced tooth. 膠原纖維及基質作為位移牙齒之襯墊

Functions of the PDLFunctions of the PDL * Supportive

• Pressure of blood vessels provides a hydraulic mechanism for support of the tooth. 血管的壓力提供支持牙齒的水力

學機轉

Functions of the PDL (cont’)Functions of the PDL (cont’)

* Sensory

Through nerve supply, it can detect the most

delicate forces to the tooth and very light

displacement of the tooth, and protects the

tissue from the effects of excessively

vigorous masticatory movement.

Functions of the PDL (cont’)Functions of the PDL (cont’)

* Nutritive Blood vessel provide anabolites （養分） and remove the catabolites （廢物）

Functions of the PDL (cont’)Functions of the PDL (cont’)

* Homeostatic （恆定）1. The cell of the periodontal ligament have a capacit

y to resorb and synthesize extracellular substance of the connective tissue of the ligament.

2. If homeostatic mechanism are upset will result in ankylosis bone and tooth

3. If the balance between synthesis and resorption is disturbed, the quality of the tissue will be change.

Homeostatic (cont’)Homeostatic (cont’)

4. If loss of homeostasis function, much of

extracellular substances of the ligament is lost,

the width of the periodontal space is decreased.

Clinical considerationsClinical considerations1. The thickness of PDL seems to be maintained by

the functional movement of the tooth

2. Thin in functionless and embedded teeth

wide in teeth that are under excessive occlusal

stresses

3. Pulp inflammation apical granuloma ( 肉芽腫 )

or cyst ( 囊腫 )

結論結論1. The balance between formation and maintenance

of mineralized tissue versus soft connective tissue

of PDL require finely regulated control over cells

in the local area.

2. Equally important to the process of cell maturation

and function are the timed expression of specific cell

surface receptors and the ability of certain factors to

regulate their expression