Periodontium

Question 1

The Periodontium

Answer 1

1. Composed of:
   
   1. Cementum
   2. Periodontal ligament
   3. Alveolar bone
2. Also called “Gomphosis joint”
   
   1. “Vault” of the door
   2. Very fine movement, stiff

Question 2

Cementum

Answer 2

1. Cementum:
   
   1. A hard avascular connective tissue covering the roots of teeth
2. Role of cementum:
   
   1. Covers and protects the root dentin (covers the opening of the dentinal tubules)
   2. Provides attachment for the principal periodontal fibers; i.e. anchorage of the root
   3. Participates in maintenance of occlusal relationship (adaptation)
   4. Cementum also works as some protection over the sensitivity of dentin
3. Thickness
   
   1. Thickest in the apex and interradicular (between roots) areas of multirooted teeth (50 to 200 um, can exceed 600 um)
   2. Thinnest in the cervical area (10 to 15 um)
   3. Cementum gets thicker as we get older
4. Physical properties of cementum
   
   1. More permeable than other dental tissues
   2. Soft and readily abraded by the oral environment
      
      1. Critical pH 6.0 to 6.7 vs enamel 4.5 to 5.5 pH
      2. Critical pH is where the structure starts to demineralize; cementum easier to get demineralized
   3. Gingival recession→thin cementum exposed→root dentin exposed→sensitivity
      
      1. Root planning to clean between gums

Question 3

Development of Cementum

Answer 3

1. Initiates at root edge
2. Proceeds along the entire tooth with the onset of root formation and elongation
3. HERS → inductive signal to ectomesenchymal pulp cells to secrete predentin
4. Interruption of HERS
5. Ectomesenchymal cells from the inner portion of the dental follicle come in contact with predentin to differentiate into cementoblasts that lay down cementum→at least in theory.
6. Theories of cementoblasts activation to lay down cementum:
   
   1. Infiltrating dental follicle cells receive reciprocal signal from the dentin or the surrounding HERS cells and differentiate into cementoblasts
   2. HERS cells directly differentiate into cementoblasts (epitheliomesenchymal transition)
   3. Participation of epithelial cell rests of Malassez (HERS fragments in PDL)
7. Mineralization and formation of CDJ
   
   1. Collagen fibrils of dentin and cementum blend together.
   2. Mineralization spreads through dentin surface across the CDJ and into the cementum resulting in an amalgamated structure
      8.

Question 4

Classification of cementum

Answer 4

1. According to cellularity
2. According to origin of collagenous fibers in the matrix
3. Combined
4. Parts of the cementum:
   
   1. Cellular cementum
   2. Acellular cementum
   3. Hyaline layer (of Hopewell Smith [directly between cellular cementum and dentin])
   4. (Granular layer of Tomes in Dentin)
      5.

Question 5

Cellular and Acellular Cementum & Intermediate cementum

Answer 5

1. Acellular Cementum - Primary; Initial
   
   1. Coronal 2/3 of the root
   2. Covers root along adjacent dentin
   3. Slower deposition rate
   4. Incremental lines relatively close
   5. Apparently absent in intermediate cementum
   6. Used primarily for anchorage
2. Cellular Cementum - Secondary; after occlusion
   
   1. Apical (third), interradicular, and overlaying acellular cementum
   2. Fast rate of deposition
   3. Incremental lines relatively wide
   4. Apparent in intermediate cementum clearly demarcating cementum from dentin
   5. Occlussal adaptation to compensate for the enamel wear
   6. It gets greate in mineral deposition as we age
3. Hyaline layer of Hopewell Smith (Intermediate Cementum):
   
   1. Between the granular layer of Tomes and the cementum
   2. First layer of cementum by the inner cells of the HERS to seals of the dentin
   3. Mineralizes greater than the adjacent dentin or the seceondary cementum
   4. Approximately 10 um thick

Question 6

Nature and origin of collagen fibers

Answer 6

1. Extrinsic fibers
   
   1. From PDL –> Sharpey’s fibers
   2. Same direction as PDL fibers, i.e. perpendicular or oblique to the root surface
2. Intrinsic fibers
   
   1. Laid down by cementoblasts
   2. Parallel to root surface and perpendicular to extrinsic fibers
3. Mixed fiber cementum is where both extrinsic and intrinsic fibers meet

Question 7

Classification of collagen fibers

Answer 7

1. Acellular (AEFC)
   
   1. Extrinsic
   2. Bulk: from cervical margin to apical third increasing in thickness apically
   3. Main function is for anchorage
2. Cellular (CIFC) - bone-like
   
   1. Intrinsic
   2. Found in middle, apical thirds and furcation (after tooth comes in occlusion/fully functional, mainly premolars and molars)
   3. Main function is for adaptation and repair
3. Alternating cellular and acellular
   
   1. Mixed
   2. Found in apical and interradicular. Intrinsic fibers
      are uniformly mineralized but the extrinsic fibers are variably mineralized with some central unmineralized cores.
   3. Main function is for adaptation
4. Acellular afibrillar
   
   1. Found in spurs and patches over enamel and dentin close to CEJ.
   2. Unknown function; an anomaly

Question 8

Cementum vs. bone

Answer 8

1. Differences are present on 5 different levels
2. Function and location
   
   1. Bone as skeleton vs. cementum in periodontium
3. Structure of ECM
   
   1. Cementum lacks the lamellar organization of bone but still composed of collagen
   2. CIFC less cellular than bone but structurally and functionally non related to bone.
   3. Incremental lines (“resting” lines) by continuous phasic, deposition. (Incremental lines of Salter)
   4. Cementum is avascular hence more resistant to resorption and less remodeling ability
   5. Aneural, painless but covers sensitive dentin
4. Cells populations & their origin
   
   1. Bone: Osteoblasts , bone lining cells → osteocytes
   2. Cementum: Cementoblasts → Cementocytes
   3. (Alveolar) Osteoblasts origin: dental follicle, also periosteum and bone marrow.
   4. Cementoblasts origin :
      
      1. Dental follicle (classic theory)
      2. EM transition of HERS cells (more favorable to explain the phenotypic differences)
5. Biochemical composition of ECM
   
   1. Organic
      
      1. 45-50% in cementum vs. 70% in bone
      2. Similar organic fibrous framework (mainly Collagen Type I 90%, also III, V, VI, and VII)
      3. Non-collagenous proteins: AP, BSP, DMP1, DSP (not in AEFC), FN, OC, OP, ON)
      4. Ground substance (GAGs, GPs, Ch S)
      5. Unique cementum molecules has been identified: Cementum attachment protein (CAP, links cells to matrix)
   2. Inorganic
      
      1. Similar crystal type HA (50% in cementum vs. 30% in bone)
6. Functional cell regulation
   
   1. Cementum does NOT undergo physiologic remodeling as bone.
      
      1. Cementum is NOT supposed to resorb; if it does, it is pathological and usually ortho was done with too much pressure or also due to periodontal diseases
   2. Resorption is associated with periodontitis or orthodontic tooth movement.
   3. Regulated form the same bone- regulating pathways (RANKL/OPG)

Question 9

Cementoenamel Junction

Answer 9

1. Cementum overlaps enamel 60-65%
2. Edge to edge 30%
3. Gap between C&E 5%-10%

Question 10

Aging of cementum

Answer 10

1. Smooth surface becomes irregular due to calcification of ligament fiber bundles where they are attached to cementum
2. Continues deposition of cementum with age in the apical area.
   
   1. Pros.: maintains tooth length
   2. Cons.: obstructs the foramen
3. Cementum resorption. Active for a period of time and then stops for cementum deposition creating reversal lines
4. Resorption of root dentin occurs with aging which is covered by cemental repair
5. Cementicles - a small, discrete globular mass of cementum in the region of a tooth root.

Question 11

Cemental Repair

Answer 11

1. Protective function of cementoblast after resorption of root dentin or cementum; usually with acellular type
2. Occurs after:
   
   1. Trauma (traumatic occlusion, tooth movement, hyper-eruption)
   2. Loss of cementum accompanied by attachment loss; not much repair at this point i.e. compromised
3. Following reparative cementum deposition, the attachment is restored

Question 12

Cementicles

Answer 12

1. Calcified ovoid or round nodule in PDL
2. Single or multiple near the cement surface
3. Free in ligament; attached or embedded in cementum
4. Increase with aging and at sites of trauma
5. Origin:
   
   1. Calcifying nidus of epithelial cell.
   2. Composed of calcium phosphate and collagen to the same amount as cementum (45% to 50% inorganic and 50% to 55% organic)

Question 13

Hypercementosis

Answer 13

1. Abnormal thickening of normal (non neoplastic) cementum.
2. Could be diffuse or circumscribed,
3. Affecting a single or multiple teeth.
4. Cementoblastoma is when root is also resorbed and other complications are found
5. Etiology
   
   1. Pagets
   2. Gigantism‐Acromegaly
   3. Ideopathic
   4. Occusal Trauma
   5. Non functional tooth
   6. Periapical granuloma

Question 14

Periodontal Ligament (PDL)

Answer 14

1. A soft specialized connective tissue between cementum and alveolar bone proper.
2. Thickness range : 0.15 and 0.38 mm. (thicker with pathology)
3. Width decreases with age
4. High turnover rate

Question 15

Function of PDL

Answer 15

1. Supportive (Tooth, BV)
2. Shock absorber: Withstanding the forces of mastication
3. Formative : controlling synthesis and resorption of cementum, ligament and alveolar bone.
4. Nutritive: blood vessels provide the essential nutrients to the vitality of the PDL
5. Eruption by Contraction of fibroblasts in the dental follicle
6. Proprioception: Sensory receptor necessary for proper positioning of the jaw
   
   1. One tooth in each jaw in contact with each other to have a sense of proprioception; with any one misisng, proprioception is lost

Question 16

Development of PDL

Answer 16

1. Mesenchymal in origin.
2. From the dental follicle shortly after root development begins
3. Soft tissue between two mineralizing structures
   
   1. Development through Hertwig’s Epithelial Root Sheath
   2. Maintenance theory: homeobox gene suppress Runx2 in PDL

Question 17

PDL Composition

Answer 17

1. Cells
2. Fibers
3. Ground substance: GAGs, GPs, GL (glycolipids)

Question 18

PDL Cells

Answer 18

1. Fibroblasts (mesenchymal in origin)
   
   1. Most abundant (65%)
   2. High turnover rate
      
      1. Prone to destruction
      2. Flexible adaptation to tooth movement
   3. Abundant secretory organelles (rER, Golgi ap., open-face nuclei); chromatins are visible meaning very active division going on
   4. Prominent Actin network (migration)
   5. Contractile properties: tooth eruption
2. Epithelial cells
   
   1. Epithelial cell rests of Malassez (ERM)
      
      1. PDL homeostasis
      2. prevent ankylosis
      3. maintain PDl space
      4. prevent root resorption
      5. cementum repair
      6. Unclear yet
3. Cementoblasts
   
   1. Cover the periodontal surface of cementum
4. Osteoblasts
   
   1. Cover the periodontal surface of alveolar bone
5. Macrophages
   
   1. Derived from blood monocytes
   2. Important defense cells
   3. Role:
      
      1. Phagocytosis dead cells
      2. Secreting growth factor
      3. Precursors of various immune cells
6. Osteoclasts
   
   1. Critical in PD disease
   2. Tooth movement
   3. Multinucleated
   4. Located within lacunae
7. Cementoclasts –> pathologic
8. Undifferentiated Stem cells
   
   1. Progenitors for fibroblasts, odontoblasts, and cementoblasts
   2. Perivascular
   3. Compensate for PDL cell apoptosis
   4. Two main properties:
      
      1. Pleuoripotent - can give rise to several lineages
      2. Self-renewing - upon division, one identical copy of mother and one daughter cells (asymmetrical division) –> establishment of stem cell niche
   5. Population of stem cells is reduced as we age; any sclerosis (cell deaths) e.g. ameloblasts are not found in adults
   6. Cancer is going the opposite way; normal cells that keep on dividng (self-renewing) without differentiating

Question 19

PDL fibers

Answer 19

1. Collagen fibers: I, III and XII. (Principal fiber bundles)
2. Continually remodeled.
3. End into acellular cementum or bone by Sharpey’s fibers
4. Principal Fibers:
   
   1. Dentoalveolar (between tooth and bone) and GIngival groups
      
      1. Alveolar crest group
      2. Horizontal group
      3. Interradicular group
      4. Oblique group
      5. Apical group
   2. Oblique group is subject to the most force during ortho treatment (as others are also going through strain); also the bulk of the tooth attachment; responsible for creating tension on the bone; maintaining teeth position even under pressure

Question 20

Orthodontic tooth movement

Answer 20

1. Creating tension = bone deposition
2. Creating pressure = bone resorption
3. Orthodontic relapse
   
   1. Orthodontic maintainer is wore to make sure that new position stays without putting any new pressure; teeth tend to go back to where they were originally

Question 21

Gingival Ligament Fibers

Answer 21

1. Gingival ligament fibers
   
   1. They are the principal fibers in the gingival area (not strictly related to periodontium).
   2. Present in the lamina propria of the gingiva.
2. Types:
   
   1. DentoGingival
   2. AlveoloGingival
   3. Circular (belt-like around the tooth)
   4. PeriosteoGingival
   5. Transseptal (tooth-to-tooth near cervical)

Question 22

Oxytalan Fibers

Answer 22

1. They are immature elastic fibers
2. Restricted to walls of blood vessels and are oriented obliquely in an axial direction from the cementum surface to the blood vessels.
3. Mostly numerous in the cervical area.
4. Function: Support BV and regulate vascular flow in relation to tooth function
5. Made of collagen but NOT part of the periodontal tissue
6. They support blood vessels, however, that pass into the periodontal ligament
7. Interstitial space allow for blood vessels to not get crushed

Question 23

Blood supply

Answer 23

1. From superior & inferior alveolar arteries.
   
   1. Apical vessels
   2. Gingival vessels
   3. Interalveolar arteries penetrating the cribriform plate.
2. A rich blood supply reflects the high turnover rate
3. The posterior teeth > anterior teeth
4. The mandibular teeth > maxillary teeth
5. Vessels occupy loose CT areas between the principle fibers (interstitial spaces)

Question 24

Nerve supply

Answer 24

1. The nerve supply originates from the inferior or the superior alveolar nerves.
2. Provide sense of
   
   1. Touch, pressure
   2. Pain
   3. Proprioception during mastication.
   4. Protective open jaw reflex.
3. The fibers enter from the apical region or lateral socket walls (with BV)
4. The apical region contains more nerve endings (except upper incisors)