Ortho level 2 unit B module 3 4 5 Flashcards
What is the purpose of using cephalometric superimposition?
To evaluate the changes in jaw and tooth relationships in the same indiviudal from one time point to another.
To evaluate whether changes are due to growth, dental maturation, or orthodontic tooth movement.
To evaluate changes from orthognatic surgery.
How are cephalometric superimposition techniques done?
1 method is to make comparisons using angular and linear measurements from a ceph at one time point to another.
A better strategy is to compare tracings by overlaying them. This reduces the amount of information to a manageable level and provides visual overview of the changes that occurred between 2 time points.
What regions are used for ceph tractings?
Ceph tracings are superimposed on 3 regions:
Cranial base
Maxilla
Mandible
Why is the cranial base superimposition used?
Cranial base follows the neural growth curve and is completed by age 7 so it doesn’t change much making it a stable reference area.
How is the maxillary superimposition done?
The maxillary superimposition cancels out the skeletal changes and only the dental changes relative to the maxilla are seen.
How is the mandibular superimposition done?
It’s done anteriorly on the lingual outline of the symphysis and posteriorly on the canal that contains the mandibular neurovascular bundle.
What is used for tracing patient cephalometric radiographs?
Original tracing from patient’s initial ceph. (green lines)
Original tracing from patient’s final ceph. (blue lines)
How is cranial base sperimposition tracing patient cephs done?
Intiial tracing is taped to smooth surface.
Final tracing superimposed over initial tracing so that S-N lines match
Tape acetate tracing paper over the superimposed tracings.
Retrace initial tracing onto clean acetate paper including soft tissue profile including sella-nasion line.
Trace the final tracing onto the same paper. Use red for areas that are different.
Why are the 3 references used for superimpositions in cephalometric radiographs?
Cranial base: to demonstrate growth of the face and jaws, and any growth modification induced by treatment, relative to cranial base structures that are not growing during the time period of greatest interest clinically (>7 years)
Maxilla: to demonstrate movement of maxillary teeth relative to the maxilla
Mandible: to demonstrate movement of mandibular teeth relative to the mandible, and also growth changes in the ramus (both remodeling and condylar growth
How can space required for succedaneous teeth be measured?
Space within arches after the permanent incisors and first molars have erupted must be measured and compare to the space required to align the unerupted permanent teeth.
What is the space available in a dental arch defined as?
Distance around the arch circumference from the mesial of one permanent first molar to the mesial of the other permanent first molar.
It is measured as a series of straight-line segments, as shown here. Two lateral segments, from the mesial of the first molar to a point on the alveolar process in the canine region, and two anterior segments, from the canine region point to the midline, are used.
What is the space required defined as?
The sum of the width of the incisors that have erupted plus the width of the canines and premolars that have not erupted
How are the incisor widths measured?
Measured directily on the casts.
How is space required for the unerupted permanent teeth measured?
Measurement of the unerupted teeth on radiographs
Estimation of the width of unerupted teeth from a correlation with the width of the erupted lower incisors.
A combination of measurement on radiographs and correlation statistics.
How is radiographic prediction measured?
Accurate measurement of teeth width is hard to achieve because OPGs distort the teeth non-uniformly.
PAs are usually the best method however they are hard to do without distorting the canines (especially the lower ones) This inevitably reduces accuracy.
How is the problem with radiographic distortion countered?
The radiograph measurement is compared to the cast measurement. The difference in size between radiograph and cast indicates the percentage magnification which can be used to correct the magnification of the unerupted permanent teeth.
What are the advantages and disadvantages of using proportion of true to radiographic image to measure the crown of teeth on a radiograph?
The advantages are:
It can be used in maxillary and mandibular arches for all ethnic groups
The disadvantages are:
The additional radiation required
Questionable accuracy in some instances
Potential behavior problems with young children.
How is the size of unerupted teeth measured?
Radiograph measurement compared to cast (proportionality)
Moyers prediction (Proportionality tables) Uses the estimations from proportionality tables.
Tanaka-Johnson prediction (2 simple formulas that determine the size and tends to overestimate eruption size)
Hixon-Oldfather Prediction: Combination Method
What are the tanaka-johnston prediction value formulas?
One half of the mesiodistal width of the lower 4 incisors +10.5mm (mandibular) and +11mm (maxillary)
What is the Hixon-Oldfather Prediction: Combination Method?
A combination of radiographic and proportionality table methods.
Size of permanent incisors measured via dental casts, size of unerupted premolars measured from PA radiographs and canines can be calculated from there.
What are the disadvantages of the Hixon-Oldfather prediction method?
Only accurate for the Northern European children but not so much for African or Asian people.
It can only be used for the mandibular arch.
Requires PA radiographs.
What method of prediction is used most often for space prediction?
Tanaka-Johnston
what are the advantages ot the Tanaka-Johnston prediction?
Requires no radiographs
Requires no lengthy prediction tables, graphs or equations
Can be used for both arches
Is reasonably predictable
What are the assumptions that go with the Tanaka-Johnston measure?
Assumption 1: Correlation between size of erupted mandibular incisors and the size of the remaining unerupted maxillary and mandibular canines and premolars.
Assumption 2: Caucasian populations. Tooth size and morphology are different in Asian and African groups.
Assumption 3: Normal development.
Assumption 4: Space is available. (Arch dimensions can increase during growth in unpredictable ways but usually doesn’t)
Assumption 5: Stable position of incisors.
Assumption 6: The space analysis procedure assumes that the mesial shift of the first molars can be predicted accurately, at least in a child with a Class I skeletal pattern.
