arch length analysis Flashcards
palmer system
1) ortho usually use the palmer system
2) 1-8 and there is a quadrant system
review
1) spacing in the primary incisor region is the primate space
- mesial to canine in mx
- distal to canine in mn
incisor liability
1) difference between the amount of space needed for permanent incisors vs space available for
2) transitional stage of mandibular crowding at age 8-9
where did the extra space come from to align the lower incisors
1 )slight increase in width of dental arch
- across the canines
- 2 mm
2) labial positioning of the permanent incisors relative to the primary incisors
- 1-2 mm
3) repositioning of the canines in the mandibular arch
- move slightly back into primate space
leeway space
1) premolars are smaller than primary molars
- nance
- 0.9 mm on each upper quad
- 1.7 on each lower quad
2) proffit
- 1.5 mm on each upper quad
- 2.5 mm on each lower quad
—
1) used for correction of crowding and molar drift
correction of crowding
1) mesial migration closes spacing difference
2) by holding molars back, you can maintain the space
molar drift
1) occlusal relationships of the primary and permanent molars
space analysis
1) a comparison between the amount of space available for the alignment of the teeth and the amount of space required to align them
2) important to quantify the amount of crowding within the arches, because tx varies depending on the severity of the crowding
the amount of space available
1) measure arch perimeter
- one first molar to the other
- over the contact points of posterior teeth and incisal edge of anterior teeth
2) 2 ways to measure
- divide dental arch into segments that can be measured as straight line approximations of the arch
- by contouring a piece of wire to the line of occlusion and them straightening it out for measurement
amount of space required
1) measure the mesiodistal width of each tooth
- contact to contact
2) sum of the widths of the individual tooth
space analysis
1) space available > space required
- excess
2) vice versa (crowding)
mixed dentition arch length analysis
1) estimates if there will be enough space for the permanent canine and premolars if the molars are held in their current position
- helps to determine if it is a non extraction case
- determine post treatment stability of the incisors
- only done in the lower arch, as upper and lower arches are
4 common analysis
1) direct measurement
2) estimation from proportionality table
3) johnston - tanaka
4) hixon - oldfather
when to use these analyses
1) mixed dentition only
2) tell if there is enough space for canine and premolar eruption
3) severely crowding cases do not need analysis
4) to answer parent’s question
direct measurement
1) measurement of erupted teeth
2) measure space available
- distance from M of permanent first molar to the M of permanent first molar
3) measure the space required
- measure actual widths of erupted teeth on study model and unerupted teeth on radiograph
4) SA-SR = discrepancy for each side
measurement of teeth on radiograph
1) use PA
2) necessary to compensate for enlargement of the radiographic image => use proportional relationship
—
true width of primary molar/apparent width of primary molar = true width of unerupted premolar / apparent width of unerupted premolar
direct measurement factors
1) little predictive value
2) fair to good accuracy
3) contralateral teeth can estimate widths of unerupted teeth
4) lower canine and premolars need at least 23 mm of space
estimation from proportionality table
1) good relationship between erupted perm incisors and
- unerupted canines and premolars
2) moyer’s prediciton table
johnson tanaka
1) measure space available
- MD dimension of the 4 lower incisors plus the CDE space on each side
2) space required
- widths of four lower incisors + 21 = width of lower permanent canines and premolars
(then add this width of 4 incisors)
3) SA - SR = discrepancy
hixon - oldfather
1) measure space available
2) space required
- direct measurement of the permanent premolars from the PAs and incisors from the cast
- predict the size of unerupted canines
- use prediction graph
3 )SA - SR = discrepancy
space analysis notes
1) prediction tables work well only for the population group from which they are derived
- northern european descent
- best prediction: hixon oldfather
- followed by tanaka - johnston and moyers
- superior to measurement from radiographs
2) direct measurement from radiograph can be applied for all ethnic groups, however
practical application
1) if SA = Sr
- the leeway space must be maintained
- space maintenance appliance to prevent mesial migration
2) if SA < SR (1-4) mild crowding
- expansion, headgear, lip bumper
3) SA<SR (>5mm) very crowded
- consider tooth mass reduction by IPR or extraction in permanent dentition
expansion
1) incisors can be pushed facially
- small amount so it doesnt leave bone
2) posteriors can be pushed in transverse region
space analysis assumptions
1) A-P position of incisor is correct
- no protrusion/retrusion
- protrusion = crowding
2) space available will not change due to growth
- dentition shifted by jaw discrepancy
- less accurate for class II and class III skeletons
3) all teeth are present and normal in size
- check radiographs
