Physiological Tooth Movement

Question 1

What happens at pre eruptive stage

Answer 1

Movement by tooth germs within tissues of jaw (intraosseous) before eruption, from initiation of tooth development to completion of crown

Question 2

How are permanent tooth germs positioned relative to deciduous teeth

Answer 2

Develop on lingual aspect of deciduous predecessors in same bony crypt. Eventually occupy own bony crypt. Anterior teeth lingual to roots. Premolars between divergent roots. Maxillary molar distal angulation. Mandibular molar medial angulation

Question 3

What is the rate of tooth eruption during intra osseous and extra osseous phase

Answer 3

1-10um/day and 75um/day

Question 4

For and against for root formation theory for eruption

Answer 4

For: increased root length, reciprocal upward force can accelerate eruption

Against: rootless teeth can erupt, root growth accommodated by bone resorption at base of socket and buckling of root, etc

Question 5

For and against PDL

Answer 5

For: ankylosis of teeth with damaged PDL show discrepancy at incisal edge (less vertical height)

Against: rootless (ie no PDL attached) teeth can still erupt, PDL present but failure of eruption

Question 6

For and against bone remodelling

Answer 6

For: teeth are moved via selective deposition and resorption during pre eruptive phase, eruption prevented in osteoporotic animals lacking csf 1

Against: base of crypt of first and third molars continually resorb during eruption, demonstration of eruptive pathway in bone does not mean bone remodelling is responsible

Question 7

What does dental follicle do

Answer 7

Produce csf-1 (colony stimulating factor) to stimulate osteoclast differentiation from monocytes. Express bone morphogenetic protein 6 to promote alveolar bone growth at crypt base. REE secrete proteases to facilitate connective tissue breakdown. Dental follicle required for eruption pathway to form

Question 8

Promoters of bone resoption and how

Answer 8

Monocyte chemotactic protein: attract monocytes along eruption pathway

Epidermal growth factor: enhance recruitment of mononuclear cells and osteoclastogenesis

CSF-1: promote differentiation to osteoclasts

interleukin 1a: induce dental follicle cells to produce csf 1

Transforming growth factor b: down regulate runx-2 which stimulates osteoblast differentiation

Question 9

What factor can inhibit bone resorption

Answer 9

Osteoprotegrin: inhibit osteoclast formation

Runx-2 stimulate osteoblast differentiation and function

Question 10

What is a gubernacular cord

Answer 10

Central strand of epithelium surrounded by connective tissue that connects fibrocellular follicle of successive tooth to lamina propria of oral mucosa, directing eruption pathway

Question 11

What happens to gubernacular cord as eruption occurs

Answer 11

Cord decreases in length and density, increases in thickness

Question 12

How does junctional epithelium form

Answer 12

Cells of outer layer of ree and basal layer of oral epithelium actively proliferate and unite to form epithelium lined pathway. Epithelium covering tooth degenerates and frown emerges through epithelium lined pathway into oral cavity. When tooth first erupts, ree is attached to unerupted part of enamel form an epithelial seal ie the junctional epithelium

Question 13

What are some factors that can affect final tooth position

Answer 13

Forward resting tongue/tongue sucking habit resulting in contact with erupted teeth, position of adjacent teeth, PDL actively stabilising teeth against unbalanced soft tissue resting pressures

Question 14

What is post eruptive movement for

Answer 14

Maintain erupted teeth in occlusion during jaw growth to compensate for occlusal and proximal tooth wear

Question 15

What 3 factors affect post eruptive movement

Answer 15

Accommodation for jaw growth: secondary to condylar growth, further eruption to maintain occlusion

Compensation for occlusal wear: maintain vertical dimension of face

Accommodation for interproximal wear: via mesial drift, increases with abrasive diet and considerable masticatory activity

Question 16

What is a dentigerous cyst

Answer 16

Epithelial lined developmental cyst that forms due to accumulation of fluid between ree and crown of an unerupted tooth. May block eruption pathway of adult tooth

Question 17

What is primary failure of eruption

Answer 17

Non ankylosed teeth fail to erupt despite clear eruption path, failure of eruption mechanism. All teeth distal to affected tooth will be affected. Only posterior teeth affected