Anatomy, Structure and Function Part 2

Question 1

What is the periodontal ligament and what is it composed of?

Answer 1

It connects the tooth root to the alveolar bone and is composed of highly cellular connective tissue and complex vascular tissue that communicates with bone marrow spaces

Question 2

what is the average width of the PDL space?

Answer 2

0.2mm
- smaller: unerupted or nonfunctioning teeth
- wider: teeth in hyperfunction

Question 3

What are the components of the periodontal ligament?

Answer 3

Fibers, cells, ground substance, blood vessels, lymph vessels, and nerves

Question 4

What are principal fibers in the PDL and their function?

Answer 4

Bundles of collagen fibers that form a network between tooth and bone, primarily composed of Type I collagen for tensile strength

Question 5

What are Sharpey’s fibers?

Answer 5

Terminal ends of principal fibers that insert into cementum and alveolar bone

Question 6

Which cells synthesize the principal fibers and collagen?

Answer 6

Mainly fibroblasts; collagen also chondroblasts, osteoblasts, odontoblasts

Question 7

How are collagen fibers formed in the PDL?

Answer 7

Fibroblasts synthesize tropocollagen → microfibrils → fibrils → overlapping gives striated pattern

Question 8

What are the types of principal fibers?

Answer 8

Transseptal, alveolar crest, interradicular, horizontal, oblique, and apical fibers

Question 8

What are oxytalan fibers and their role?

Answer 8

Elastic fibers synthesized by fibroblasts that run vertically along the root and regulate vascular flow

Question 9

What types of cells are found in the PDL?

Answer 9

Connective tissue cells, epithelial rests, immune cells, neurovascular cells

Question 10

What are the roles of fibroblasts in the PDL?

Answer 10

Main cell type; synthesize and degrade collagen; regulate turnover via enzymes; some produce collagenase

Question 11

Which other connective tissue cells are found in the PDL?

Answer 11

Cementoblasts, osteoblasts, osteoclasts, and odontoclasts

Question 12

What are epithelial rests of Malassez and their significance?

Answer 12

Remnants of Hertwig’s root sheath; may assist in repair or cause cyst formation; form a lattice near cementum interconnected by hemidesmosomes and surrounded by a basal lamina

Question 13

What immune cells are found in the PDL?

Answer 13

Neutrophils, lymphocytes, mast cells, macrophages, eosinophils

Question 14

What is the ground substance in PDL and its composition?

Answer 14

Fills space between fibers and cells; contains glycosaminoglycans, proteoglycans, glycoproteins, and 70% water

Question 15

What are glycosaminoglycans and what is the role of them in the PDL?

Answer 15

long linear polysaccharides with hyaluronic acid that regulate cell signaling, growth, adhesion, and wound healing

Question 16

What do the types of glycoproteins do in the PDL?

Answer 16

Fibronectin (adhesion/healing), laminin (differentiation), undulin (structure and function)

Question 17

What is the function of proteoglycans in the PDL?

Answer 17

Space-filling and regulating ECM; involved in adhesion, signaling, hydration, and tissue growth

Question 18

What are the main functions of the PDL?

Answer 18

Physical support, tissue remodeling, nutrition, and sensory roles

Question 19

What physical roles does the PDL perform?

Answer 19

Tooth attachment, force absorption, gingival support, protection of vessels and nerves

Question 20

What is the Tensional Theory of force resistance in the PDL?

Answer 20

Principal fibers unfold to transmit forces to alveolar and then basal bone

Question 21

What does the Viscoelastic Theory propose about occlusal forces?

Answer 21

Fluid in the PDL transfers force to bone marrow via foramina

Question 22

How does the PDL respond to axial forces?

Answer 22

Oblique fibers lengthen, root is displaced into alveolus, principal fibers absorb force

Question 23

What happens during horizontal/tipping forces on teeth?

Answer 23

Tooth shifts within PDL (Phase 1), then displaces facial/lingual plates (Phase 2)

Question 24

When and how does the PDL remodel?

Answer 24

During tooth movement, occlusal stress, or injury repair; forms/resorbs cementum & alveolar bone

Question 25

How is the PDL constantly remodeling?

Answer 25

High turnover of cells, collagen, and ground substance; mesenchymal cells form new fibroblasts, cementoblasts, and osteoblasts * PDL turnover rate is 2x as fast as the gingiva and 4x as fast as the skin

Question 26

What are the nutritional and sensory roles of the PDL?

Answer 26

Provides blood/lymph to periodontium; carries sensory nerves (free endings, Ruffini, Meissner, spindle-like)

Question 27

What is cementum and what is it composed of?

Answer 27

Cementum is a calcified, avascular mesenchymal tissue composed of collagen fibrils, calcified interfibrillar matrix, and cementocytes

Question 28

What are the types of fibers in cementum and their origins?

Answer 28

- Intrinsic fibers: Form the cementum matrix, made by cementoblasts (90% type I, 5% type III collagen). - Extrinsic fibers (Sharpey’s fibers): From principal PDL fibers, made by fibroblasts, mainly type I collagen.

Question 29

What is the interfibrillar ground substance of cementum?

Answer 29

Synthesized by cementoblasts; includes proteoglycans, glycoproteins, and phosphoproteins; regulates cell interactions during development and repair

Question 30

What are cementoblasts and what do they do?

Answer 30

Originating from the dental follicle, they form collagen and ground substance of cementum. When embedded, they become cementocytes in lacunae

Question 31

What distinguishes cellular from acellular cementum?

Answer 31

- Cellular: Contains cementocytes in lacunae, thicker - Acellular: No cementocytes, thinner * Both types form lamellae with incremental lines (rest periods), which are more mineralized

Question 32

What are the 4 types of cementum?

Answer 32

- Acellular afibrillar: No cells/fibers, coronal, 1–15 µm - Acellular extrinsic fiber: Sharpey fibers, cervical third, 30–230 µm - Cellular mixed stratified: Intrinsic + extrinsic fibers, apical/furcation, 100–1000 µm - Cellular intrinsic fiber: Intrinsic fibers only, fills resorption lacunae

Question 33

How does the permeability of cementum change with age?

Answer 33

Cementum is highly permeable when young, and permeability decreases with age

Question 34

What are the three CEJ relationships and their frequency?

Answer 34

- Cementum overlaps enamel (60–65%) - End-to-end (30%) - Do not meet (5–10%)

Question 35

Where is cementum thickest and how does it change with age?

Answer 35

Thickness increases with age, mainly at the apical third and furcation areas; thicker distally than mesially

Question 36

What are conditions affecting cementum thickness?

Answer 36

- Aplasia: No cementum. - Hypoplasia: Too little cementum; raises periodontitis risk. - Hyperplasia/hypercementosis: Too much; seen in Paget’s disease, acromegaly.

Question 37

What is cementum resorption and where does it occur most?

Answer 37

Very common (>90%), mainly in apical third (~77%), may reach dentin/pulp. Often painless, may alternate with repair.

Question 38

What causes cementum resorption?

Answer 38

- Local: Trauma, ortho movement, cysts, tumors, disease. - Systemic: Calcium deficiency, hypothyroidism, Paget’s. - Idiopathic: Unknown causes.

Question 39

What is needed for cementum repair?

Answer 39

Viable cementoblasts and connective tissue. Repair is blocked if epithelium invades. ECM macromolecules help regulate cementogenesis.

Question 40

Why is cementum repair important?

Answer 40

Needed for periodontium development and regeneration. Epithelial rests of Malassez may assist in repair

Question 41

What is ankylosis and its diagnostic signs?

Answer 41

Fusion of cementum to bone with PDL loss. Leads to root resorption, no tooth mobility, no eruption/drifting, and lost proprioception

Question 42

What are the parts of the alveolar bone?

Answer 42

- Outer plate: Haversian & compact bone. - Inner wall: Alveolar bone proper (lamina dura). - Cancellous bone: Between compact layers

Question 43

When does bone remodeling occur and why?

Answer 43

Continuous process involving osteoblasts/clasts; happens during shape changes, force application, wound healing, and mineral balance

Question 44

What factors influence alveolar bone remodeling?

Answer 44

- Local: Tooth biomechanics, age-related osteoblast/clast changes. - Systemic: Hormones (PTH, calcitonin, vitamin D3), diseases, and medications.

Question 45

What are the steps involved in the process of bone resorption by osteoclasts?

Answer 45

1. Attachment: Osteoclasts attach to the mineralized bone surface. 2. Acidification: They create a sealed acidic environment using proton pumps, which demineralizes bone and exposes the organic matrix. 3. Degradation: Enzymes (e.g., acid phosphatase, cathepsin) break down the organic matrix into amino acids. 4. Sequestration: Mineral ions and amino acids are absorbed into the osteoclast for further processing.

Question 46

What is the periosteum and what are its layers?

Answer 46

a differentiated osteogenic connective tissue covering bone surfaces where bundles of collagen fibers from the periosteum penetrate and anchor it to the bone - It has two layers: Inner layer: Contains osteoblasts and osteoprogenitor cells (which can become osteoblasts). Outer layer: Made of collagen fibers and fibroblasts, rich in blood vessels and nerves.

Question 47

What composes the endosteum?

Answer 47

Inner osteogenic layer: A single layer of osteoblasts. Outer layer: A small amount of fibrous tissue; lines internal bone surfaces and is thinner than the periosteum

Question 48

What is the difference between fenestration and dehiscence?

Answer 48

- Fenestration: Root is exposed (denuded of bone), covered only by periosteum and gingiva; Marginal bone remains intact. - Dehiscence: Root is exposed and covered only by periosteum and gingiva; Bone loss extends through the marginal bone