diagnosis-正畸诊断PPT课件

Chinese 84° 80° 4° 28° 113° 98°
Soft Tissues Careful interpretation needed due to errors due to posturing, variable muscle tone and identification of points Common reference planes: 1. Harmony（H）line-should bisect nose 2. E-line-lips should be-2mm from line
6
Measurements
1. taken directly or indirectly (tracing) from cephalometric R/G
2. should also consider • validity-extent to which measurement represents structure under consideration •reproducibility-closeness of repeated measurements of the same structure •stability of points used to measure 3. means: •by hand •via digitizing computer programme •scanned by computer
8
Specific errors
1.Errors of Projection
● arise due to R/G being a 2 dimensional representation of 3dimensional object
● points not in the mid-sagittal plane are distorted according to the laws of perspective: i. angular measurements become too obtuse ii. linear measurements are fo·reshortened ● points on midsagittal plane are unaffected ● factors influencing errors: magnification-although standardized set-ups exists, magnification factor of approximately 10% should be taken into account ;R/Gic scales are often included to allow this factor to be accurately calculated
with rare earth metal intensifying screen
4
Uses
1. diagnosis and treatment planning-allows assessment of AP and vertical Sk pattern,dental bases,incisor positions and angulations,detection of unerupted teeth and soft tissue profile
assessment •errors may obscure Leabharlann Baiduifferences between values
Types of errors
1.Systematic-when a measurement is consistently under/ Overestimated
2. Random-variable error with no pattern
usually refers to use of lateral skull views
3
Equipment
1. collimated X-ray source-5 feet from midsagittal plane of patient
2. cephalostat-head positioned 3. aluminium wedge-increases soft tissue definition 4. film-placed 1 foot behind midsagittal plane of patient
2. during active treatment-e.g.end of functional Appliance treatment
3.end of treatment during/out of retention-assessment of relapse
4. assessing/monitoring growth-patient’s own growth (serial R/Gs) or comparing with “norms” for sex,age and race（use of templates e.g.Bolton）
5. (research)-Bjork’s implant studies
5
Norms
Hard Tissues
Common points:
SNA SNB ANB MMP U1 to MxP L1 to MnP
Caucasian 81° 78° 3° 27° 109° 93°
Afrocaribean 88° 84° 4° 28° 118° 101°
7
Advantages • time saving with 2 •‘wild’values more obvious immediately with 2 • Little difference in accuracy of methods Disadvantages •errors involved in recording values and result
Diagnosis
1
Cephalometrics
2
Definition
1.literally-measurement of the head 2. more commonly-means of using standardised skull R/G to assess facial and dento-Sk relationships
History
1.developed in 1930’s by Broadbent(USA)and Hofrath(Germany) 2.originally postero-anterior and lateral views
Recommended to allow 3 dimensional assessment 3. now, as features of greatest importance in sagittal plane,