3rd year lectures key points Flashcards
AP class 1
mandibular base 2-3mm behind maxillary base
AP class 2
maxilla more than 3mm in front of mandible
AP class 3
maxilla less than 2-3mm in front of mandible (mandible may be in front)
tx for skeletal discrepancies
growing pts - growth mod
completed growth - orthognathic surgery
aims of tx
stable
fct
aesthetic
risks
decalcification
relapse
root resorption
benefits
fct aesthetics dental health reduce risk of trauma facilitate other dental tx
why ortho assess?
determine if any malocclusion present
identify any underlying causes
decide if tx indicated
when assess?
brief at 9yrs - interceptive ortho
comprehensive 11-12yrs - when 3s and 4s erupt
when older pts first present
if a malocclusion develops later in life
ideal occlusion - Andrews 6 keys
molar relationship crown angulation crown inclination no rotations no spaces flat occlusal plane (no curve of Spee)
normal occlusion
more common than ideal
minor deviations that do not contribute an aesthetic or fct problem
malocclusions
more significant deviations from the ideal that may be considered unsatisfactory (aesthetically or fct)
may require tx but pt factors may influence decision
PMH
allergy - Ni or latex
epilepsy - if not well-controlled avoid URA
drugs - some induce e.g. gingival overgrowth
imaging - delay tx until had scans
PDH
freq attendance
prev tx
cooperation
trauma - RR
dentoskeletal relationships
teeth on individual skeletal bases which are attached to the cranial base
- maxilla - maxillary teeth and alveolus
- mandible - mandibular teeth and alveolus
ideal FMPA
meet at occipuit
lateral skeletal assessment ref line
mid sagittal plane
assessing skeletal pattern
visual
palpate skeletal bases
effect of lip trap
may procline U incisors
may lead to relapse of OJ if persists at end of tx
effect of hyperactive L lip
may retrocline L incisors
indicates likely instability at end of tx
lips
competent/incompetent
trap
lower lip activity
which type of tongue thrust may cause a relapse of AOB?
endogenous
tongue thrust associated with
AOB
angulation of U incisors to Frankfort plane
110 degrees
angulation of L incisors to mandibular plane
90 degrees
types of tooth movement
physiological - tooth eruption - mesial drift - U better orthodontic - from externally generated forces
tooth eruption stages
pre-eruptive tooth movement intra-osseous eruption mucosal penetration pre-occlusal eruption post-occlusal eruption
pre-eruptive tooth movement
small random movement
rocks in crypt
intra-osseous eruption
when roots begin to form
slow
1mm/3m to 1mm/3yrs
mucosal penetration
fast
1-2mm per month
pre-occlusal eruption
slow
stops when tooth hits something hard - when PDL begins to form
post-occlusal eruption
v slow
tooth eruption theories
root elongation alveolar bone remodel PDL formation apical blood flow important PTH receptor gene
interceptive tx
utilise tooth eruption to minimise impact of a developing malocclusion
interceptive tx - ectopic U C
remove c - 10-13yrs
permanent teeth can be encouraged ti erupt if extract primary tooth at correct stage - 1/2 to 2/3 root development
prevalence of ectopic U3
1-2%
when should you palpate for U3?
9-10yrs
buccal sulcus
things to assess when looking at ectopic U3
height
closeness to midline
- doesn’t overlap adjacent incisor by >1/2
- angle between vertical and canine ideally <30 degrees
physiological basis of tooth movement ortho
if external force applied to tooth - will move as bone around it remodels
bony remodelling mediated by PDL
- if ankylosed/no PDL will not move (will cause movement of other healthy teeth)
cementum much more resistant to resorption than bone
- but some RR after ortho expected
OBs and OCs
- appliances transmit force to PDL and bone
- phagocytosed by macrophages when stop functioning
theories for ortho tooth movement
differential pressure theory
Piezoelectric pressure theory
mechano-chemical pressure theory
differential pressure theory
force =
tension areas - deposition
compression areas - resorption
Piezoelectric pressure theory
Piezoelectric currents generated when crystalline structures such as bone are deformed
compression side more +, tension side more -
- OB and OC get preferentially recruited to certain sides
mechano-chemical pressure theory
mechanical stress
release of neuropeptides from nerve endings
stimulate FBs, endothelial cells and alv bone
FBs also comm with OBs and OCs
alv bone and PDL remodelling = tooth movement
force for tooth movement - tipping
35-60g
force for tooth movement - bodily movement
150-200g
force for tooth movement - intrusion
10-20g
force for tooth movement - extrusion
35-60g
force for tooth movement - rotation
35-60g
force for tooth movement - torque
50-100g
what movement do fixed appliances produce?
bodily movement
intrusion
pressure on supporting structures
resorption of bone
extrusion
tension in supporting structures
bone deposition
functional appliances mechanism by which they work
skeletal changes 30%
- growth of mandible, restraint of maxilla
dentoalveolar changes 70%
- facial musculature stretched which generates forces transmitted to teeth and alveolus
- retroclination U teeth
- proclination L teeth
light force
hyperaemia within PDL OB and OC appear resorption of LD from pressure side apposition of osteoid on tension side remodelling of socket - frontal resorption PD fibres reorganise gingival fibres appear not to become reorganised but remain distorted slow tooth movement
mod force
occlusion of PDL vessels on pressure side
hyperaemia of PDL vessels on tension side
cell-free areas on pressure side (hyalinisation)
- no cells, not dead but nothing going on so can’t resorb
period of stasis
increased endosteal vascularity
undermining resorption
increased OC activity
= get OC coming in and nibble from below
sudden movement of tooth CLUNK
- tooth may become slightly loose
healing of PDL - reorganisation and remodelling
rotation
need a force couple - 2 forces in opp directions
excessive force
necrosis undermining resorption resorption of root surfaces pain permanent change
factors affecting response to ortho force
magnitude
duration
age
anatomy
deleterious effects of ortho forces
pain and mobility pulpal changes RR loss of alveolar bone support relapse
rotational relapse
tend to rotate again due to supercrestal fibres
fibres will gradually move the tooth back after the appliance is removed
aetiology of skeletal variation
genetic
env - MM, mouth breathing, head posture
class 1 ceph
SNA 81 +/- 3
SNB 78 +/- 3
ANB 3 +/- 2
class 2 ceph
SNA usually average but may be increased if maxilla prognathic
SNB usually decreased
ANB >5 degrees
class 3 ceph
expect SNA decreased if maxilla deficient
SNB often average but may be increased if mandible prognathic
ANB <1 degree or negative
dento-alveolar compensation
dento-alveolar structures may disguise underlying skeletal discrepancy
forces from STs - incline teeth towards a position of ST balance
Frankfort plane clinical
lower orbital rim to superior border of EAM
where do FMPA normally meet clinically?
EOP
vertical facial proportions clinical landmarks
glabella
subnasale
soft tissue menton
vertical facial clinical proportions
50%
Frankfort plane ceph
orbitale to porion
mandibular plane ceph
menton to gonion
FMPA degree
27 +/- 4
vertical facial proportions ceph landmarks
nasion
ANS
menton
vertical facial ceph proportions
45, 55
vertical jaw relationship - long facial height
LAFH >55% FMPA >31 degrees steeply inclined mandibular plane backward mandibular growth rotation AOB tendency
vertical jaw relationship - short facial type
LAFH <55% FMPA <23 degrees tendency to parallelism of jaws forward mandibular growth rotation deep overbite tendency
mandibular displacement
inter-arch width discrepancy causes posterior teeth to meet cusp to cusp
mandible forced to deviate to one side to achieve position of inter-cuspation
- association with TMD - one reason why you would treat it
transverse jaw discrepancies: arch width discrepancies
disproportion of M and M arches
maxillary arch too narrow is the most common
causes buccal CBs
often exaggerated by AP discrepancies
transverse dento-alveolar compensation
small maxilla - upper molars tend to flare outwards due to forces of tongue
moulding to compensate
facial asymmetry causes
dental cause
true mandibular asymmetry
arch size discrepancies - DA disproportion
discrepancy between size of teeth and jaws
crowding
- small jaws, normal teeth (most common)
- macrodontia
spacing
- large jaws, normal teeth
- microdontia
aetiology of malocclusion
skeletal
dental
STs
other e.g. habits
local causes of malocclusion
variation in tooth number variation in tooth size/form abnormalities of tooth position ST abnormalities local pathology
variation in tooth number
supernumeraries hypodontia variation of timing - retained primary - early loss primary - unscheduled loss of permanents
supernumeraries
tooth/tooth-like entity which is additional to normal series
where are most supernumeraries located?
80% in anterior maxilla
prevalence of supernumeraries
1% in primary
2% in permanent
types of supernumerary
conical
tuberculate
supplemental
odontome
conical supernumerary
most common anterior maxilla small, peg shaped close to midline, mesiodens may erupt (extract) tend not to prevent eruption/cause impaction but may displace adjacent teeth parallax
supplemental supernumeraries
normal morphology
at end of a tooth series
often extract
tuberculate supernumeraries
tend not to erupt - often associated with a failure of eruption
cause impaction of teeth
paired
barrel-shaped
usually extracted
one of main causes of failure of eruption of permanent upper incisors
odontome
mass of P, D, E
can prevent eruption of teeth
compound/complex
hypodontia prevalence
4-6%
retained primary tooth
difference >6m between shedding of contralateral teeth
radiograph
why are primary teeth retained?
absent successor ectopic successor/dilacerated infra-occluded primary molars - trauma/idiopathic dentally delayed - may be medical causes pathology/supernumerary
retained primary tooth - absent successor
maintain primary tooth for as long as possible (if good prognosis)
or extract early - encourage spontaneous space closure
infra-occluded primary molar
tooth fails to achieve/maintain its occlusal relationship with adjacent teeth - MRs not same height often corrects temp ankylosis percussion sound
infra-occluded primary molar - prevalence
common 1-9%
slight infra-occluded primary molar
between occlusal surface and IP contact, <2mm
mod infra-occluded primary molar
within occluso-gingival margins of IP contact
severe infra-occluded primary molar
below IP contact point - likely extract
management of infra-occluded primary molar - successor present
usually self-correct so keep under review
consider extraction if
- contact points going subgingival
- root formation of successor near completion
infra-occluded primary molar management - successor absent
depends on potential of crowding
- retain if good condition (onlay)
- or extract and plan space management
early loss of primary teeth - localisation of crowding depends on:
which tooth extracted
when tooth extracted
pts inherent crowding
balancing ext
ext from opp side of same arch
minimise midline shift
compensating ext
extract from opposing arch of same side
maintain occ relationship
early loss of primary canines
consider balancing ext
as can get midline shift
when does the early loss of primary teeth have most effect?
when primary teeth extracted early - little effect if extracted late
more space loss in U>L
marked space loss in crowded pts
minimal/no space loss in spaced dentitions
compensating extractions if early loss of FPMs
U6 extracted - don’t compensate
L6 extracted - may need to compensate - depends on occlusal stops
when should the prognosis of FPMs be assessed if considered ext?
age 8-9yrs
balancing extractions if early loss of FPMs
consider if premolar crowding
factors influencing impact of loss of 6s
age at loss
- U less important
- L bifurcation development in 7s
- too late - poor space closure
- too early - distal drift of 5s
crowding
- U potentially rapid space loss
- L best results if crowded. if spaced/aligned - spaces
malocclusionloss of permanent central incisor
maintain space
- centre lines
reimplant
variation in tooth size/form
macrodontia microdontia abnormal form - aesthetics - pulp chamber morphology
abnormalities of tooth position
ectopic
transpositions
ectopic first molars
<5% U arch more common reversible <8yrs manage - separator - attempt to distalise 6 - extract E
incidence of ectopic canines
1-3% pop
80% palatal
what are ectopic canines associated with?
small/absent U laterals
assessment of canines
clinical - palpation - inclination of 2 - mobility of c/2 - colour of c/2 radiographic - 2 - parallax
tx options for ectopic canines
extract c - interceptive
retain 3 and observe
surgical and ortho
(surgical) extraction
reasons for ectopic upper centrals
dilacerated (trauma)
supernumerary
local abnormalities of STs
digit sucking
frenum
tongue thrust
transposition
interchange in position of 2 teeth
true transposition
apices in wrong place
pseudo transposition
only crowns crossed
treatment of transposition
extract one then close space
accept
(correct) if pseudo
labial frenum
may cause median diastema
tx
- ortho
- frenectomy
why shouldn’t you start tx straight after someone stops a non-nutritive sucking habit
might get some spontaneous correction
tongue thrust
may cause AOB
endogenous e.g. Down syndrome macroglossia
exogenous e.g. incompetent lips, struggle to get a seal to swallow
local pathology
caries
cysts
tumours
what does ectomesenchyme form?
P
D
C
PDL
how do the flat bones of the skull form?
IM ossification
how does the base of the skull form?
endochondral ossification
IM bone formation
bone deposited directly into primitive mesenchymal tissues
needle like bone spicules progressively radiate from primary ossification centres to periphery
vault of skull
maxilla
most of mandible
endochondral bone formation
hyaline cartilage precursor
centres of ossification
base of skull
get islands of cartilage remaining to allow growth
vault of skull growth
IM ossification in 3rd month in several centres
fontanelles
- anterior closes 2 years
- posterior closes 1 year
growth occurs at fibrous sutures in response to ICP
growth continues until 7 but some of the sutures remain open until adulthood
embryonic facial cartilages
M and M develop IM, but develop adjacent to pre-existing cartilaginous skeletons - nasal capsule and Meckels cartilage
6 weeks
associated but don’t form it
when does ossification of face and skull occur?
about 7-8 weeks
mandibular processes
condylar unit
angular unit - in response to MP and masseter
coronoid unit - in response to temporalis
alveolar unit - only forms if teeth are developing
body - forms in response to IAN
3 main sites of secondary cartilage formation in the mandible
condylar - disappears long before birth
coronoid - growth continues here until about 20yrs
symphyseal end of each half of bony mandible - disappears just after birth
appear 12-14 weeks IUL
development of M and M
both IM but are preceded by a cartilaginous facial skeleton
what precedes the mandible?
meckels cartilage
what precedes the primary skeleton of the upper face?
nasal capsule
primary abnormality
defect in structure/part of an organ that can be traced back to an anomaly in its development - spina bifida, cleft lip, CHD
secondary abnormality
interruption of normal development of an organ that can be traced back to other influences
- teratogenic agents: infection (rubella virus), chemical (thalidomide/lithium)
- trauma, amniotic bands
is a congenital abnormality always inherited?
no
deformation
anomalies that occur due to outer mechanical effects on existing structures
agenesia
absence of an organ due to failed development during embryonic period
sequence
single factor results in numerous secondary effects
syndrome
group of anomalies that can be traced back to a common origin
facial syndromes arising from early problems with facial development (1-8 wks)
env - foetal alcohol syndrome genetic multifactorial - hemifacial microsomia - Treacher collins syndrome (mandibulofacial dysostosis) - clefts
FAS
high maternal alcohol intake day 17 microcephaly short palpebral fissures short nose low nasal bridge long and thin upper lip deficient philtrum small midface small mandible mild mental retardation
hemifacial microsomia
3D progressive facial asymmetry high arched palate malformed pinna ear tags unilateral mandibular and zygomatic arch hypoplasia normal intellect clinical spectrum of severity deafness, cardiac and renal problems
TC - mandibulofacial dysostosis
AD deformity of first and second branchial arches anti-mongoloid slant palpebral fissures coloboma of lower lid hypoplastic/missing zygomatic arches hypoplastic mandible deformed pinna, conductive deafness
CLP aetiology
genetic env - smoking - alcohol - anti-epileptics
dental features CLP
cleft lip that crosses over alveolus causes dental anomalies impacted teeth crowding hypodontia supernumeraries hypoplastic teeth caries
achondroplasia
problem with EC ossification
defects in long bones, short limbs = dwarfism
defects in base of skull, retrusive middle 1/3 of face, depressed nasal bridge
crouzon’s (CF dysostosis)
AD premature closure of cranial sutures esp C and L proptosis mild hypertelorism retrusion and vertical shortening of midface prominent nose class 3 distraction osteogenesis
Apert’s (acrosyndactyly)
AD premature closure of almost all cranial sutures maxillary hypoplasia class 3, AOB Parrot's beak nose syndactyly of fingers and toes CP association conductive deafness
differences between neonatal and adult skull
face small compared to cranium
eyes large
ears low set
forehead upright and bulbous
face appears broad
nasal region vertically shallow, nasal floor close to inferior orbital rim
- in adult mid face expands and nasal floor descends
growth of the cranial vault
expands in response to growing brain until age 7
growth at sutures - deposition in response to raised ICP
shape modified by surface resorption/deposition
after neural growth ceases forehead continues to expand due to pneumatisation of air sinuses
where does post-natal growth occur?
sutures
synchondroses - in cartilage
surface deposition
post-natal growth - sutures
periosteal lined contact areas
flat bones grow laterally and bone deposited where sutures are
post-natal growth - synchondroses
islands of cartilage remaining
between bones forming base of skull
in secondary cartilage of condyle and in cartilage of nasal septum
spheno-occipital synchondrosis
cartilage divides and areas pushed apart, turns to bone further away from the synchondroses
post-natal growth - surface deposition
over surfaces of cranial and facial bones, beneath the covering periosteum
growth of the cranial base
lateral growth completed by 3 years
sphenoethmoidal synchondrosis fuses at 6-7 yrs, after this the anterior CB is relatively stable and is used as baseline
growth ceases at SOS 12-15yrs and fusion by 20yrs
post-natal growth of maxilla
downwards and forwards
growth at sutures, between maxilla and skull
surface deposition mainly posteriorly and resorption anteriorly and inferiorly
post-natal growth of mandible
downwards and forwards
growth at condyle
surface resorption anteriorly and lingually with deposition posteriorly and laterally
timing of stopping of facial growth - M and M
order M and M growth stops: width, length, height
width growth completed before pubertal growth spurt
length growth continues throughout puberty
- girls slows to adult rate 2-3yrs after 1st period
- boys around 18yrs
vertical height continues longest, declines to adult rate around 17-18 girls, early 20s boys
sec difference in adolescent growth spurt
girls 1-2years earlier
for tx to coincide with growth spurt need to start earlier in girls
growth rotations
forwards - short face
downwards and backwards - long face AOB
crowding of lower labial segment in late teens/early 20s - growth rotation
adult facial growth
v variable
slowly throughout life
tendency to increased overall length and prominence of nose and chin and ears
general direction of growth
downwards and forwards
but variations with growth rotations
which skeletal problems can a lat ceph be used for?
AP and vertical
2D so can’t use for transverse problems
analysis of lat ceph
relationship between jaws and cranial base
relationship between jaws
position of teeth relative to jaws
ST profile
nasion
most anterior point of frontonasal suture
gonion
most posterior inferior point on mandibular angle
pogonion
most anterior point on mandibular symphysis
menton
most inferior point on mandibular symphysis
porion
upper midpoint on EAM
orbitale
most anterior inferior point on IO rim
ACB on lat ceph
sella-nasion
doesn’t change after age 7 so can use as ref point
A and B
hard tissue - deepest concavity
AP - class 1 ANB
2-4
AP - ANB what can ortho be done on
8 to -3
vertical MMPA angle
27
vertical MMPA what can ortho be done on
17-37
Ui/MxP
109 +/- 6
Li/MnP
93 +/- 6
Ui/Li
135 +/- 10
rule of thumb for angles you can achieve with braces
U 120
L 80
max movement with surgery
can only move M/M back/forward by 10mm
- if need >10mm do bimaxillary procedure
interceptive ortho - diastema
wait until Cs erupt
<2.5mm should close
ugly duckling stage
6 yrs 96% have diastema
canine crowns on distal of lateral roots
causes of UE central incisors
supernumeraries
trauma/dilaceration
other pathology
v unusual to be congenitally missing
UE central incisors due to supernumeraries management
usually palatal 1 - remove deciduous and supernumeraries 2 - expose/bond 3 - create space 4 - monitor >1.5yrs 80% will erupt over 16m
what does the effect of early loss of primary teeth depend on?
crowding
age
arch
anteriorly spacing so ok
posteriorly causes crowding as 6s come forward
early loss of primary c’s
balance to prevent centre line shift
tx of anterior CB
tend to tx early (2s through) z-spring 3 Adams clasps - need one at front PBP so occlusion doesn't interfere
extracting L FPM
need to compensate
don’t balance
extracting U FPM
don’t compensate - don’t get over eruption in lower arch
ideal time for ext of FPMs
7s furcation forming - less likely to get severe mesial tipping (8s present) class 1 mod L crowding mild/mod U crowding U space closure much better
when should you treat a posterior unilateral CB?
if displacement on closure
- distance between centre lines
tx of a unilateral posterior CB
PBP - disocclude
6m would get correction
turn screw x2 per week
reciprocal anchorage
when should habits be stopped by?
9yrs (within 3yrs of eruption)
retained primary teeth
extract
U canines development
palatal
migrate and lie labial and distal to root apex of U laterals
90% palpable by 11yrs
- if can’t then radiograph
slightly enlarged canine roots
palatally placed
diagnosis of infra-occluded primary teeth
percussion (hollow)
visually
radiograph (best)
tx of infra-occluded primary teeth
successor present and mild (2mm or less) - observe 1yr
no successor - extract as likely to get worse
consequences of leaving infra-occluded primary tooth
hard to keep clean
further submerged = harder to extract
management of ectopic U C’s
extract c’s 11-12yrs
- if 3 not past midline of 2 - 90% success
- if 3 encroaching on 1 (significantly past 2) - 60% success
ensure enough space
causes of a reverse OJ
dental e.g. retroclined uppers
skeletal e.g. class 3
both
comprehensive tx
full correction of malocclusion
Andrew’s 6 keys
class 1 canines, incisors, molars
compromise tx
correct certain aspects accepting others
e.g. accept buccal CB with no displacement - no fct problem
stages of tx planning
plan around L arch (LLS stable - just incisors) - plan everything around lower incisors tx in lower build U arch around L - canines must be class 1 molar relationship - class 1 or full unit class 2
crowding assessment
measure space available and space required
overlap technique
space required in L arch - mild
0-4mm
NE - stripping
E5s
space required in L arch - mod
5-8mm
E5s (5mm)
E4s (6,7,8mm)
space required in L arch - severe
8+ mm
E4s
stripping
metal sandpaper IP enamel reduction can get up to 3mm - 12 surfaces c to c - take off 0.5mm
extracting L4 or L5
extract L4 - less mesial drift
only take out 5s if at mild end of crowding - won’t get enough space if severe
L4 is 7mm wide so get 14mm space if ext both
- if all the space needed need to reinforce anchorage (HG) - usually front teeth come back 50% and back teeth forward 50%
if you ext in L arch what should you do in U?
E in U arch t get a MR class 1 (avoid class 3)
if you don’t ext in L arch what should you do in U?
1 - ext U arch - MR class 2 2 - distalise UBS with headgear (MR class 1)
tx options
accept malocclusions E only URA functionals +/- ext fixed +/- ext complex tx - ortho and restorative - ortho and orthognathic surgery
limitations
effects almost purely dentoalveolar and tooth movement
only remain stable where forces in equilibrium
