Lecture 2

Question 1

why is it important to have a good understanding of the sequence and biology of dental eruption when treating orthodontic patients?

Answer 1

because many orthodontic problems are related to abnormal dental development and eruption

Question 2

the first stage of eruption of the permanent teeth is seen at what age? what is it characterized by?

Answer 2

• 6 years old
• characterized by the near-simultaneous eruption of the mandibular central incisors, mandibular first molars, and maxillary first molars

Question 3

what is characterized by dental age 8?

Answer 3

• eruption of the maxillary lateral incisors

- the mandibular lateral incisors and maxillary central incisors have typically erupted between age 6 and age 8

Question 4

at what age do most ortho patients receive phase 1 orthodontic treatment if it is necessary?

Answer 4

dental age 8

Question 5

what is characterized by dental age 11?

Answer 5

more or less simultaneous eruption of the:

• mandibular canines
• mandibular first premolars
• maxillary first premolars

Question 6

what is typically considered the best stage of development to start full orthodontic treatment or phase II orthodontic treatment?

Answer 6

dental age 11

Question 7

what is characterized by dental age 12?

Answer 7

eruption of the remaining succedaneous teeth:

• maxillary canine
• maxillary second premolars
• maxillary and mandibular second molars a few months later (these teeth will typically erupt during the full orthodontic treatment, and are incorporated into the orthodontic treatment as they erupt

Question 8

what is characterized by dental age 15?

Answer 8

• roots of all permanent teeth (except 3rd molars) are complete
• crown formation of 3rd molars often has completed

Question 9

what are the two phases of tooth eruption?

Answer 9

1. pre-emergent eruption (eruption of the tooth until it emerges into the mouth)
2. post-emergent eruption (eruption of a tooth after it has broken through gingival tissues

Question 10

the post-emergent eruption phase is further characterized by what two periods?

Answer 10

1. juvenile post-emergent eruption

2. adult post-emergent eruption

Question 11

what supports the idea that metabolic activity within the PDL is necessary for tooth eruption to begin and continue?

Answer 11

the eruptive movement of the tooth begins soon after the root begins to form, and the roots are seen emerging from the dental follicle

Question 12

what are the two processes necessary for pre-emergent eruption to occur?

Answer 12

1. there must first be resorption of bone and the primary tooth roots, overlying the crown of the erupting tooth
2. next, there must be a propulsive mechanism to move the tooth in the direction where the overlying path has been cleared
   - these two mechanisms normally operate in concert with each other

Question 13

what is an example of a condition that interferes with the resorptive process of pre-emergent eruption?

Answer 13

cleidocranial dysplasia

Question 14

what are the characteristic features of cleidocranial dysplasia?

Answer 14

• underdeveloped or absent clavicles
• delayed closing of the fontanelles of the skull bones
• bulky forehead, hypertelorism, and midfacial hypoplasia
• dental abnormalities

Question 15

what are the dental abnormalities associated with cleidocranial dysplasia?

Answer 15

• delayed loss of the primary teeth
• delayed appearance of the secondary teeth
• unusually shaped, peg-like teeth
• misalignment of the teeth and jaws
• supernumerary teeth which are sometimes accompanied by cysts in the gums

Question 16

the failure of tooth eruption is thought to be caused by a failure of migration of the permanent teeth toward the oral cavity, which is thought to be caused by ___

Answer 16

defects in the osteoclastic and resorptive activity in the alveolar bone

Question 17

cleidocranial dysplasia is caused by a mutation in the ___ gene, a member of the ___ family of transcription factors located on chromosome ___

Answer 17

• core binding factor alpha 1 (CBFA1)
• RUNX
• 6p21
• the CBFA1 gene is responsible for the initial osteoblastic differentiation and osteogenesis to form skeletal structures

Question 18

what are the contributing factors for failure of eruption of permanent teeth in children with cleidocranial dysplasia?

Answer 18

• abnormal resorption of both the overlying bone and primary teeth
• presence of multiple supernumerary teeth can impede eruption
• fibrotic gingiva
• cleidocranial dysplasia patients are an example of a defect in a patient’s ability to remove the overlying structures during tooth eruption, which causes delayed eruption or the impaction of the involved teeth

Question 19

if the mechanical obstruction of eruption is removed in patients with cleidocranial dysplasia, what may happen to the teeth?

Answer 19

they may erupt spontaneously and can often be brought into the arch with orthodontic force

Question 20

T or F:

the rate of bone resorption and the rate of tooth eruption are controlled physiologically by the same mechanism

Answer 20

false
-this means that the tooth’s occlusal eruptive movement does not control the dissolution of the overlying bone and/or primary teeth

Question 21

completion of the crown does what two things in the eruption process?

Answer 21

1. signals for the resorption of overlying bone and primary tooth too begin
2. removes the inhibition of the genes that are necessary for root formation, causing root formation to begin

Question 22

T or F:
it has been shown that a tooth will continue to grow and form the tooth’s root regardless of whether the overlying bone and primary teeth are removed

Answer 22

true

• therefore, it would seem clear that resorption of the overlying bone and primary tooth is the rate-limiting factor in pre-emergent eruption
• if the overlying bone and primary tooth removal is delayed, then pre-emergent eruption will also be delayed or prevented, but root formation will typically continue

Question 23

normally, the rate of eruption is such that the ___ area where root formation begins remains in the same place, with the crown typically moving occlusally

Answer 23

-apical

Question 24

if eruption is mechanically blocked, what happens to the proliferating apical area?

Answer 24

it will move in the opposite direction, causing a distortion of the root in an abnormal direction (called a dilaceration)

Question 25

T or F: it has been shown that after a tooth has had its apical area removed (apicoectomy), the tooth cannot continue to erupt on its own

Answer 25

false -it can continue to erupt on its own, which shows that proliferation of cells associated with lengthening of the root is not an essential part of the propulsive eruption mechanism

Question 26

if a tooth's root formation is complete on an impacted tooth, can the tooth still erupt?

Answer 26

yes, but some situations may require surgical orthodontic eruption

Question 27

T or F: | the precise mechanism through which the propulsive force in pre-emergent eruption is generated remains unknown

Answer 27

true

Question 28

active formation of the root is not necessary for what two processes?

Answer 28

- continued clearance of an eruption path above the tooth | - propulsive movement of a tooth along the eruption path

Question 29

___ is a condition characterized by non-syndromic eruption failure of permanent teeth in the absence of mechanical obstruction, indicating that there is a defect in the propulsive mechanism of tooth eruption

Answer 29

primary failure of eruption (PFE)

Question 30

typically in PFE patients, the more _anterior/posterior_ teeth are, the more frequently they are affected

Answer 30

- posterior | - 1st and 2nd molars are more frequently affected than the premolars and canines

Question 31

in PFE patients, if a tooth in a further ___ position presents with an eruption disturbance, the ___ teeth are usually, but not always, affected as well

Answer 31

- anterior | - posterior

Question 32

in PFE patients, what happens to the affected teeth?

Answer 32

they resorb the alveolar bone above the crown, but then the teeth erupt only partially or fail to erupt at all

Question 33

T or F: | both deciduous and permanent teeth can be affected in patients with PFE

Answer 33

true

Question 34

is PFE typically seen as being symmetrical or asymmetrical?

Answer 34

asymmetrical, and primarily non-ankylosed teeth tend to become ankylosed as soon as orthodontic forces are applied

Question 35

when does the juvenile phase of post-emergent eruption begin?

Answer 35

once the tooth emerges into the mouth

Question 36

what is the juvenile post-emergent spurt?

Answer 36

the stage of relative rapid eruption from the time a tooth first penetrates the gingiva until it reaches the occlusal level

Question 37

instrumentation shows that the majority of tooth eruption occurs only during the critical period between what time of day? what does this cyclic rhythm of eruption correlate with?

Answer 37

- between 8PM and 1AM - it correlates with the cyclic release of growth hormone, which probably plays a role in post emergent juvenile tooth eruption

Question 38

experiments with the application of pressure against an eruption premolar suggest that eruption is stopped by a force applied for only ___

Answer 38

1-3 minutes

Question 39

what forces oppose the eruption of teeth?

Answer 39

- chewing forces | - soft tissue forces

Question 40

which forces controls tooth eruption the most and why?

Answer 40

-soft tissue pressure are probably more important in controlling tooth eruption than the heavy pressures that occur during chewing, because eruption typically occurs between 8PM and 1AM, during which most patients occlusal activities are not very active

Question 41

T or F: light pressures of long duration are more important in producing orthodontic tooth movement than heavy intermittent pressures like chewing

Answer 41

true

Question 42

are multiple teeth typically involved in ankylosis?

Answer 42

no, typically only one tooth is involved, but primary first and second molars can commonly both be seen to be ankylosed

Question 43

how can you tell if a second primary molar is ankylosed?

Answer 43

look for a step between the first permanent molar and the second primary molar

Question 44

how can you tell if a posterior openbite is caused by lateral tongue thrust?

Answer 44

- can involve multiple teeth, caused by the pressure of the tongue preventing the eruption of the teeth as the maxilla and mandible grow, creating a posterior openbite - you can typically see the patient pressing or resting the tongue in the openbite space - scalloped tongue

Question 45

what are 3 possible scenarios for an openbite?

Answer 45

- primary failure of eruption - ankylosis - lateral tongue thrust

Question 46

what are the treatment options if an adult tooth undergoes ankylosis during post-emergent eruption?

Answer 46

- extraction (with possible implant) - crowns - surgery (luxation or corticotomy and bone grafting)

Question 47

in what case is ankylosis especially problematic?

Answer 47

when the permanent tooth is missing underneath the ankylosed primary tooth

Question 48

if there is an adult tooth underneath the ankylosed primary tooth, do you HAVE to extract the ankylosed tooth?

Answer 48

not always, but the adult tooth will typically have a delayed eruption, which can be problematic

Question 49

when is extraction of a primary ankylosed tooth recommended?

Answer 49

- if the primary tooth drops below the height of contour of the adjacent teeth - you want to extract in this case even if there is not a permanent tooth underneath the ankylosed tooth - EXT of the primary ankylosed tooth in this case helps prevent periodontal and bone defects to the adjacent teeth and helps stop bone loss in the extraction site, which will typically require an implant later

Question 50

other than extraction, what are two other options for an ankylosed primary tooth, in the case where the permanent tooth is missing underneath?

Answer 50

- build up the primary tooth to place it into occlusion | - leave the primary tooth in place as it is

Question 51

T or F: | eruption of teeth stops in adulthood

Answer 51

false | teeth continue to erupt at an extremely slow rate during adult life

Question 52

the eruption mechanism remains active throughout life. what demonstrates this?

Answer 52

if a permanent tooth's opposing tooth is lost at any age, a tooth can begin to erupt again, causing occlusal interferences

Question 53

what might happen if extreme wear occurs and eruption rate is unable to compensate?

Answer 53

the vertical dimension of the face decreases

Question 54

typically, the wear of the teeth is compensated by ___

Answer 54

additional eruption