Physiology of tooth movement and appliances overview Flashcards
2 types of tooth movement
physiological
orthodontic
physiological tooth movement
Tooth Eruption
- Pre-eruptive tooth movement (small, random)
- Intra-osseous eruption (after crown forms, slow, 1mm = 3/12-24/12)
- Mucosal penetration (fast, 1mm = 2/52)
- Pre-occlusal eruption (slow)
- Post-occlusal eruption (very slow)
not continuous - changes speeds
use interceptive orthodontics
5 stages in physiological tooth eruption
- pre-eruptive tooth movement
- intra-osseous eruption
- muscosal penetration
- pre-occlusal eruption
- post-occlusal eruption
3 phases in physiological tooth eruption
pre-eruptive phase
- pre-eruptive tooth movement
- intra-osseous eruption
pre-functional phase
- muscosal penetration
- pre-occlusal eruption
fuctional eruptive phase
- post-occlusal eruption
pre-eruptive phase
- Starts when the crown starts to form and ends when the crown formation complete/root formation about to start
pre-eruptive tooth movement
intra-osseous eruption
pre-functional eruptive phase
Starts as soon as the root start to form and ends when the teeth reach the occlusal plane
- Reduced enamel epithelium fuses with oral mucosa
- This breaks down and tooth erupts into oral cavity
- Tooth moves occlusally
muscosal penetration
pre-occlusal eruption
functional eruptive phase
Tooth movement/eruption continues as the root forms and throughout life in extremely small increments
- Tooth reached occlusal plane – appears fully erupted
- Further small movements
- Tooth wear, over eruption due to loss occluding
post-occlusal eruption
orthodontic tooth movements from
from externally generated forces
orthopantomogram
Not a static view
- Pre-eruptive movement in upper left (27)
- Rocks in crypt
- Intra-osseous phase lower left
- When roots form
- 1mm 3months-2 years
- Slow
- Resorbing bone and deciduous roots above it
- Mucosal phase
- Tooth breaches mucosa
- Fast – 1-2mm a month
- Wary – can worsen open bites
- Tooth breaches mucosa
- Once the tooth hits something hard, PDL established and post eruption slow
- Continuing to erupt
how to check OPT systematically
right pt,
right way round,
right time taken,
count teeth from back
- supernumerary in upper right
Caries
- right upper and lower – need BW
Root pathology - nil
Delayed eruption of upper left 6
- ALARM
possible tooth eruption theories
- Pulpal pressure
- Pulpal growth
- Fibroblast traction – PDL not formed yet
- Vascular pressure
- Blood vessel thrust
- Root elongation
- Alveolar bone remodel
- Periodontal ligament formation
Likely many work to erupt teeth – essential for life
3 key things in tooth eruption process
- genes
- apical blood flow
- dental follicle
tooth eruption process is
unknown exactly how it occurs
But
- Genes
- Apical blood flow
- Dental follicle
Have roles
does tooth eruption involve
bone resorption
yes
by dental follicle - mediator to bone resorption
tested - remove tooth and replace with metal replica - still erupts
does tooth eruption involve
deciduous tooth resorption
yes
if not cleidocranial dysplasia - affects bone and teeth
- delayed loss primary teeth
- shorter teeth
- no clavicles
does tooth eruption involve
cell proliferation for root lengthing
not critical for tooth eruption
- Remove apical area, tooth still erupts
- dental follicle pulls tooth
- Dilacerations occur if obstruction
- Hit hard then dilaceration
- Root still forms despite not erupting
- Hit hard then dilaceration
does tooth eruption involve
apical blood flow
very important
allows tooth to erupt
does tooth eruption involve
collagen fibres cross linking
no
only post eruption - when PDL forms
does tooth eruption involve
genes
yes
- Parathyroid hormone receptor gene (PTHR1 and PFE)
- Primary failure of eruption (OPT of 6 not erupting)
Genetic element
interceptive orthodontic treatment
- Orthodontists can utilise tooth eruption to minimise the impact of a developing malocclusion.
e. g. ectopic permenant canines
age for ectopic permanent canine interceptive orthodontics
ages 10-13
- Drift into right place
- If not – need surgical exposure and appliance to move into place 2-3 years
examples of interceptive orthodontic treatment
ectopic permanent canines
permanent teeth can be ‘encouraged to erupt’ if the deciduous toothis extracted at the correct stage
stage to remove deciduous tooth to encourage permanent to erupt
interceptive orthodontic
when perment root is 1/2 to 2/3 developed
any earlier will delay permanent eruption
key investigation for permanent canines
palpate for upper permanent canines from 9 years
check if ectopic
cause and prevalance of ectopic canines
genetic
1-2%
variation in difficulty to fix
best imaging technique for ectoptic canines
CBCT
check position, damage/resorption (follicle can dissolve away bone and cementum)
treatment for this case
Ignore ectopic canines – obvious
- One thing wrong with development likely to have other issues
go through methodically
- No additional teeth
- Caries – BW follow up
- Roots
- Lower right E – distal root partly resorbed, mesial root large – take long time to resorb
- 45 root is ½ - 2/3 formed – extract deciduous
- Same lower left E
- Lower right E – distal root partly resorbed, mesial root large – take long time to resorb
now maxillary ecotopic canines
- Palatally positioned – magnified (closer to midline)
- Follicle larger – cystic change
- No appearance of resorption of lateral – see full lamina dura
- Remove Cs – come into correct position
- Follicle pulls through bone
3 things to check on OPT in regards to ectopic canines
- height
- closeness to midline
- angle
assess ectopic canines on this OPT
High – above central apex
Good angle – compare to mid sagittal line (vertical plane), under 30 degrees = good
Midline - Doesn’t overlap adjacent incisor by more than half
Favourable -> interception will work, lining teeth up more successful
assess ectopic canines on this OPT
Still high
Angle now poor
very close to midline – fully covering lateral
no cystic change
- now need surgery and 2-3 years ortho tx
mesial drift of 6s more problematic in
mandible than maxilla
6 drift forward
5, 4, 3 still waiting to erupt – no space, reduced
what is happening in A, B, D, E, F (C ignore occlusal view)
Unusual tooth movement following interceptive extraction
Lower right buccal segment
- 46
- Submerging 85
- 45 – horizontal, no hope
Place a space maintainer – band and loop
- Within 6 months change position
- 2 years of space maintenance – erupt into space
Follicle pulling tooth through bone – not apical end
physiological basis for orthodontics
- if an external force is applied to a tooth, the tooth will move as the bone around it remodels
- bony remodelling is mediated by the periodontal ligament
- If a tooth has no PDL or is ankylosed, it will NOT move
- Cause intrusion of adj teeth with healthy PDL
- If a tooth has no PDL or is ankylosed, it will NOT move
- bony remodelling is mediated by the periodontal ligament
cementum Vs bone
resoprtion
Cementum is much more resistant to resorption than bone (1mm thick)
- although some degree of root resorption after orthodontics should be expected
orthodontic forces casue
osteoclasts (usually in lacunae) and osteoblasts appear
orthodontist role (2)
Manages the growth and development of the teeth, face and jaws
Corrects irregularities in these structures using
- Appliances to transmit force to PDL and bone
- ‘osteoclast herder’
- Thousands of workers, 24 hour shifts, no pay, no superannuation, no complaints, no sickness…
- Work not up to standard or any signs of slacking, macrophage will phagocytose!
3 theories for orthodontic tooth movement
- Differential pressure theory
- Piezoelectric pressure theory
- Mechno-chemical pressure theory
differential pressure theory
Pressure on tooth (e.g. here retrocline)
Tension on one side of PDL
Compression on other side of PDL
Tension = bone deposition
Compression = bone resorption
piezoelectric pressure theory (1)
Piezoelectric currents are generated when crystalline structures, such as bone, are deformed
These currents have been suggested as a mechanisms by which tooth movement is modulated
- Compression = +
- Tension = -
- May result in cells being recruited to sites (osteoclasts +, osteoblasts -)
Forces so small – unlikely alone
mechano-chemical pressure theory
Mechanical stress on tooth and bone ->
Release of neuropeptides from nerve endings ->
Stimulate fibroblasts, endothelial cells and alveolar bone ->
Fibroblast also communicate with osteoblasts and osteoclasts ->
Alveolar bone and periodontal ligament remodelling ->
Tooth movement
3 types of orthodontic appliance
- removable (URA)
- functionals
- fixed
6 types of orthodontic tooth movement
- tipping
- bodily movement
- intrusion
- extrusion
- rotation
- torque - root not crown
movement in URA
tipping
centre of rotation moves up as tipped
common use for URA
flat anterior bite plane – best, most efficient way at reducing overbite in growing pt
- Common URA and lower fixed – overbite reduced, and reduced the amount of time with fixed upper as start with URA
functional appliance changes (3)
- The mandible is postured away from its normal rest position
- Skeletal Changes - growth backwards (red arrows)
- The facial musculature is stretched which generates forces transmitted to the teeth and alveolus
- Dental changes
- Careful not to over procline lower anterior
- Posterior open bite – close naturally
- Dental changes
- There may be an effect on facial growth
- E.g. class II cases
- Restrict maxillary growth
- Promote mandibular growth
- Remodel the glenoid fossa
- E.g. class II cases
skeletal changes in functional appliance
growth backwards (red arrows)
mandible is postured away from its normal rest position
dental changes in functional appliance
- The mandible is postured away from its normal rest position
- Skeletal Changes - growth backwards (red arrows)
- The facial musculature is stretched which generates forces transmitted to the teeth and alveolus
- Dental changes
- Careful not to over procline lower anterior
- Posterior open bite – close naturally
- Dental changes
functional appliances potential affect on facial growth
E.g. class II cases
- Restrict maxillary growth
- Promote mandibular growth
- Remodel the glenoid fossa
how can functional appliance be used here
Significant jaw discrepancy – try and grow their jaw to save from surgery
functional appliance use in overjet
- Large 11mm overjet*
- 9months constant wearing functional appliance*
- 18 months after start Tx – wearing at night*
mode of action of functionals (%)
- Skeletal change (30%), growth of mandible, restraint of maxilla
- Dentoalveolar change (70%), retroclination of upper teeth, proclination of lower teeth
- Mesial migration of the lower teeth
- Distal migration of the upper teeth
Combination of the above achieves class I
mechanism of bodily movement
Note that there is a coordinated bone modelling and remodelling response leading and trailing the moving tooth.
- This mechanism allows a tooth to move relative to basilar bone while maintaining a normal functional relationship with its periodontium
- Osteoclastic and osteoblastic activity are in red and blue, respectively*
More deposition on the outside of alveolus too – distant from tooth
- Secondary remodelling
5 types of tooth movement by fixed appliances specifically
- bodily movement
- intrusion
- extrusion
- rotation
- torque
wire for fixed appliances
must be active
cannot be bendy - tooth slides along
intrusion
- Pressure on the supporting structures is evenly distributed and bone resorption is necessary, particularly at the apical area at the alveolar crest
extrusion
- Tension is induced in the supporting structures and bone deposition is necessary to maintain tooth support
rotation
- Need a force couple – 2 forces in opposing directions
torque
- Apical root torque
- Hard to deliver – root moves most
- root uprighting
- Hard to deliver – root moves most
optimum force
tipping
35-60g
optimum force
bodily movement
150-200g
optimum force
intrusion
10-20g
optimum force
extrusion
35-60g
optimum force
rotation
35-60g
optimum force
torque
50-100g
histological changes during orthodontics
light forces
Hyperaemia within the periodontal ligament on both pressure and tension side
- Appearance of osteoclasts and osteoblasts
Resorption of lamina dura from pressure side (osteoclasts) frontal resorption
Apposition of osteoid on tension side (osteoblasts) deposition
Remodelling of socket – “frontal resorption”
Periodontal fibres reorganise
Gingival fibres appear not to become reorganised but remain distorted
histological changes during orthodontics
moderate force
Occlusion of vessels of periodontal ligament on pressure side
Hyperaemia of vessels of periodontal ligament on tension side
Cell free areas on pressure side (hyalinisation)
- Period of stasis
- not dead - but nothing happening
Increased endosteal vascularity – “undermining resorption”
Relatively rapid movement of tooth with bone deposition on the tension side – tooth may become slightly loose
Healing of periodontal ligament – reorganisation and remodelling
histological changes during orthodontics
excessive force
- Necrosis
- Undermining resorption
- Resorption of root surfaces
- Pain
- Permanent change
Extensive lateral root resorption (RR) and undermining resorption (UR), just to the left of an area of PDL necrosis (N), is associated with the lag phase of tooth movement
4 factors affecting respose to orthodontic force
- magnitude
- duration
- age
- anatomy
magnitude of orthodontic force impact
- Light forces – consistent movement*
- Heavy forces – no change for while as undermining resorption and then sudden*
- moderate and high forces – not wanted, bad histological movement process
- Main problem of heavy force – anchorage teeth are moving but not desired tooth so excessive movement by them*
duration of orthodontic force impact on tooth movement
Constant 24hrs of force to prevent teeth moving back into old position
age impact on orthodontics
works at any age
maybe slower in older ages
anatomy impact on orthodontic force
- no bone
- wasting/cleft
- e.g. alveolar encking - not possible to do ortho on as thin dence cortical plate bone
- wasting/cleft
- soft tissues
- tongue
- anterior open bite
- mid-palatal suture
alveolar necking
- 7, 5, 4*
- 6 extracted long time ago*
- 5 drifted mesial as no 6*
- Alveolar bone cortex plates together – knife edge*
- Hard to move through as dense
root treated teeth impact on ortho
No pathology = no problem as ortho deals with PDL
5 deleterious effects of orthodontic force
- Pain and mobility
- Pulpal changes
- Root resorption
- Loss of alveolar bone support
- relapse
ideal rate of tooth movement
1mm per month
treatment time 24 months for fixed appliances
3 most likely tooth eruption theories
combination of likely
- Remodelling of the alveolar bone
- Role of dental follicle
- Elongation of the root
- Pressure against the root surface in the apical part of the root pushing it towards the oral cavity
- Reorganisation of the periodontal membrane fibres
- Role of the fibroblasts both with their contractile properties and their ability to quickly turn over collagen fibres
most common and accepted theory of orthodontic tooth movement
mechano-chemical theory
removable and functional appliance
move teeth by
tipping forces
Functional can also act on MOM set up forces that influences dentition and growth of jaws
fixed appliances move teeth by
all forces
- tipping
- bodily movement
- intrusion
- extrusion
- rotation
- torque (uprighting root on top of crown)
tipping Vs bodily movement
Bodily 2 sides
- One deposition one resorption
Tipping
- Areas – not whole length
how long does it take for undermining resorption to be seen
7-14 days
4 factors on tooth movement and how they impact
- magnitude
- light - most efficient, get frontal resorption
- moderate - slower, get undermining resorption
- heavy/excessive - necrosis, root resorption, pain, loss of vitality (rare), alveolar bone loss (rare)
- duration
- most efficient with (light) continuous force
- age
- maybe sligtly slower in adults
- anatomy
- volume of bone
- effects of tongue
- digit habits
