are there guidelines or rules for application of Eastman correction in cephalometrics? Or just because A point is abnormal and SN/Max plane is 5-11° means we need to correct all the time? Merci avous
The ‘Eastman correction’ by Mills 1982 was used to address the inaccuracies of the angle ANB . The correction states that for every 1 degree that the angle SNA falls below the standard value of 81 degrees, half a degree should be added to the ANB angle and vice versa. The correction is restricted for cases where the SN–maxillary plane angle is the standard 8 ± 3 degrees.
Dr. Natarajan thank you for your answer. I meant in cases where the SN-Max plane falls within 5-11 degrees but does N point play a part in the requirement? I believe as N point changes during growth, the ANB angle will also be affected. Also, I believe that , Mills 1982 as he stated in his book, the 3rd degree of standard deviation in SNA does not warrant doing an Eastman correction, but are there other reasons why not to do it if the SN-Max plane angle is within 5-11 degrees and SNA is 81 degrees? Many thanks.
Measuring jaw position in relation to the anterior cranial base can be problematic because alterations in the SN plane caused by erroneous positions of either sella or nasion can influence the SNA and SNB values. If the position of nasion is at fault, this will also influence ANB. The Eastman correction is available to overcome this:
For every degree SNA is greater than 81 degrees,
0.5 degrees° should be subtracted from the ANB
value
For every degree SNA is less than 81 degrees, 0.5
degrees should be added to the ANB value.
This correction for ANB can only be applied for changes in the position of nasion, which is indicated by a SN–maxillary plane within the normal range of 8 ± 3 degrees.
An SN–maxillary plane value outside this range indicates that the position of sella is at fault. Because this affects the SNA and SNB values to the same extent, the ANB value does not require correction.
However, the Eastman correction is associated with some overestimation of the true values as nasion moves both anteriorly and posteriorly in relation to sella and therefore, should only be used as a very approximate guide.
To avoid errors associated with discrepancies of the position of the cranial base within the skull it is advisable to carry out an additional analysis that is independent of this region. This is easily achieved by using the Wits appraisal of jaw disharmony.
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