9. Tooth Eruption and Exfoliation Flashcards
Dynamic replacement describes what?
the mixed dentition
- primary into permanent teeth
Teeth are displaced … and …
- anteriorly
- laterally
3 types of tooth movement
- pre-eruptive
- eruptive
- post-eeruptive
Explain pre-eruptive tooth movement
- movement of successional tooth germs
- developing anterior permanent teeth move into position behind the roots of primary teeth
- developing premolars move into position between roots of primary molars
- lack of space causes occlusal surfaces of maxillary molar germs to face backwards - once maxilla grows, repositioning occurs
When does eruptive tooth movement start?
while the crown is still being formed and eruption begins
Explain eruptive tooth movement
- requires remodelling of all periodontal tissue
- final tooth position in jaw is determined by muscle and occlusal forces acting on erupted teeth
- tooth eruption, emergence (through alveolar bone and gingiva - tooth partially erupted), clinical emergence
- in primary teeth, there is root reabsorption (in addition to alveolar bone resorption) and exfoliation - shedding of primary teeth
Define ‘exfoliation’
shedding of primary teeth
What influences the pattern of resorption of the primary teeth?
the developing permanent teeth
Give the root resorption patterns
- root resorption of primary incisors and canines occurs from lingual side, results in an intact pulp chamber at exfoliation
- root resorption of primary molars occurs in occlusal direction, results in resorption of pulp chamber, coronal dentine and sometimes enamel
Stages of exfoliation of anterior primary teeth
- permanent tooth germ moves into position
- resorption begins
- primary tooth is shed
- permanent tooth emerges
- root incomplete
Stages of exfoliation of primary molars
- permanent tooth germ moves into position
- resorption (almost complete)
- primary tooth is shed
- permanent tooth erupted and in occlusion
What happens in root resorption?
odontoclasts resorb dental hard tissues like root dentine
What happens in coronal dentine resorption?
- monocytes migrate from pulp to dentine surface and fuse with other cells to form odontoclasts
- begin to resorb dentine from pulp outwards
- odontoblasts regenerate towards end of root resorption
- resorption ceases before exfoliation occurs and cementum like tissue forms along coronal dentine
Explain PDL resorption
- occurs rapidly associated with cell death
-PDL fibroblasts undergo necrosis/apoptosis
Explain post-eruptive tooth movement
- maintenance of erupted teeth in occlusion while jaw grows and compensates for tooth wear
(like mesial and vertical drift, dento-alveolar compensation) - mechanisms is bone and PDL remodelling and compensatory formation of cellular cementum
Reasons for early primary teeth loss
How does this affect the permanent teeth?
- due to caries or extraction
- affects space distribution and symmetry
- leads to accelerated eruption of permanent teeth
Reasons for prolonged retention of primary teeth
- due to failure of successional tooth to resorb primary tooth
- or ectopic position of successor - impacted canines are common
Effect of primary teeth retention on permanent teeth
- lots of variation regarding exfoliation of primary teeth
- check radiograph when asymmetry in loss of contralateral teeth
3 categories of abnormal tooth eruption
- delayed
- accelerated
- impaction of teeth
Types of delayed eruption
- congenital (3rd molars)
- systemic (deficiencies)
- local (eruption cysts)
What happens in accelerated eruption?
- neonatal central incisors
Define ‘impaction of teeth’ in regards to eruption
- eruption failure
- caused by abnormal eruption pathway or lack of space
What is the role of successional teeth in exfoliation?
- retained primary teeth are common
- shedding is delayed if successional teeth are missing
- exfoliation determined by the successional teeth coming through
If successional tooth is missing, does the primary tooth shed?
eventually
Explain supernumerary teeth
How does this impact eruption?
- extra teeth (more than 32)
- can be an isolated trait or as part of a clinical syndrome
- normal teeth tend to be larger
- can prevent eruption of other teeth
Supernumerary teeth is more common in
- primary or permanent dentition?
- males or females?
- permanent
- twice as common in males
Define ‘hypodontia’
- absence of 1-6 teeth
- excluding 3rd molars
Define ‘oligodontia’
absence of more than 6 teeth
Most commonly missing teeth in hypodontia
Which are most likely to be congenital?
- 3rd molars
- lower 2nd premolar
- upper lateral incisor
above are the congenital - upper premolars
- lower central incisors
Localised Incisor-Premolar Hypodontia in common in what nationality?
European ancestry
Congenital absence of what teeth is rare?
How to confirm?
- canines, 1st and 2nd molars
-check evidence from clinical observation, a radiograph, clinical history from patient and patient records
In what percentage of people are 3rd molars missing?
20-30%
Hypodontia can be associated with …
- reduced crown and root size
- conical crown shape
- enamel hypoplasia
- molar taurodontism
- delayed eruption
- retention of primary teeth
- impaction of maxillary canines
What is taurodontism?
shortening of the space between roots in molars
Explain dilaceration
- abnormal angulation between crown and root of tooth
- usually maxillary incisors
- often due to trauma of primary predecussors (tooth fails to erupt)
- trauma can cause cessation of root growth
- root so stunted and doesn’t properly support tooth
Which erupt first? Maxillary or mandibular teeth?
mandibular
Anterior teeth or posterior teeth erupt first?
anterior
Give 3 phases of tooth eruption
- first is 6-1-2 at 6.8 to 8.5 years
- second is 3-4-5-7 at 11-12 years (most variable)
- third is 8s at 17-21
Eruption dates of 1st and 2nd primary molars
- 1.5 years
- 2.5 years
Eruption dates of 1st, 2nd and 3rd permanent molars
- 6 yrs
- 12 yrs
- 18 yrs
There is variability between cultures in individuals and populations in eruption. Give 2
- some African populations erupts 3rd molars earlier than European, even though crown formation seems similar
- South African populations initiate anterior teeth at same age as Northern Europe but crown completion is earlier
4 important dates to look at in tooth formation
- calcification
- crown completion
- root bifurcation for lower permanent molar roots
- root coompletion
Moores, Fanning and Hunt’s stages of tooth formation are below. What do they mean?
Ci
Cco
Coc
Cr1/2
Crc
Ri
A1/2
Ac
- initiation
- cusp coalescence
- cusp outline complete
- crown one half complete
- crown complete
- root initiation
- apex 1/2 closed
- apex closed
What is the calcification date?
- first radiographic appearance of crown
Calcification dates for primary teeth
4-6 months in utero in womb
- front to back
Calcification date for permanent first molars, incisors, canines
- just before birth
- 3-5 months, except upper lateral at a year
- 6.5 months for lower, 9 months for upper
Calcification date for permanent premolars, 2nd and 3rd molars
- 1.85 to 2.65 yrs
- 3 yrs
- 8 years but unreliable
When is the crown completion date as a rule of thumb?
- usually little more than half of the time between first evidence of calcification and eruption
Upper lateral incisors have a calcification date of …, eruption date of … and crown completion of …
- 1 yr
- 8.5 yrs
- 4.5 yrs
Lower 1st molars have a calcification date of …, eruption date of … and crown completed of …
- just before birth
- 6 yrs
- 3 yrs
How can we see crown completion on an X-ray?
- denser enamel appears whiter than dentine
- dentine extends lower than enamel - initiation of root formation
Define ‘root birfurcation’
- first evidence of calcification of bifurcation of lower permanent molar roots
Root bifurcation date for
- lower 1st molar
- lower 2nd molar
- 4.5 yrs
- 8.5 yrs
Root completion in primary teeth is … years after eruption
1-1.5
Permanent teeth have root completion … to… after eruption
- less than 2 years for lower incisors
- to more than 3 years for 1st molars
Define ‘tooth eruption’
- process of tooth movement
- from within alveolar bone upward
- to reach functional occlusion
Emergence of the crown is through what?
- alveolar bone
- gingiva
Define ‘clinical emergence’
- tooth is visible in oral cavity
Mixed dentition begins at age … with appearance of … and ends at … age with appearance of …
- 6
- 1st perm molars
- 11+
- premolars
Time from clinical emergence to occlusion
- 3 months for incisors
- up to 6 months for molars
When does root resorption of primary teeth occur?
- anterior teeth is a year from onset of resorption to exfoliation
- molar teeth - 1.5 years
- i.e the Es commense resorption at 9.5+ years, exfoliate at 11+
What resorbs first? Mesial or distal roots?
distal
Root resorption occurs earlier in girls or boys?
girls
Give 2 examples of age determination from teeth
- dental panoramic tomograph
- age by tooth type graph
How to do age determination from a dental panoramic tomograph?
- find lower 6
- if crown complete, over 3
- bifurcation of root is around 4.5
- if unerupted less than 6
- if roots incomplete less than 9
- confirm by looking at upper 6
- find lower 7
- if crown complete, then more than 6.5 yrs
- root bifurcation calcifies at 8.5
- unerupted means more than 12 ish
- if root incomplete, around 15
- confirm by looking at upper 7
- look for evidence of calcification of 8 (around 8-10 years but crypt visible from 6)
- look degree of eruption of incisors (some variation) lower 1 and 2 can erupt at same time
- lower 1 6-7 yrs, lower 2 7-8 yrs, upper 1 erupts 7-8, upper 2 erupts 7.5-8.5 yrs
- confirm by checking degree of development or eruption of 5s, 4s and 3s
Why do dentists need to know eruption?
- knowing the normal to recognise the abnormal (age/sequence/position)
- estimate dental age (measure of growth) - number of erupted teeth indicates age
