OPTION 3

Mills’ Eastman correction

• A potential problem of relating the maxilla and mandible to each other using the anterior cranial base is that any significant deviation in the position of this region within the skull will potentially affect interpretation of the jaw relationship.

• To compensate for the effect of an aberrant nasion position on ANB, a

modification called the ‘Eastman correction’ is suggested.

• This is only applied to cases with a change in the position of the nasion, indicated by a normal angle between the maxillary plane and sella-nasion line (8o ± 3o).

• An angle value outside this range indicates the position of the sella is at fault and because this affects the SNA and SNB values to the same extent, the ANB value does not require correction.

 

To perform the correction;

• If SNA is increased: for every degree that SNA is greater than 81o, subtract 0.5o from ANB.

• If SNA is reduced: for every degree that SNA is less than 81o, add 0.5o to ANB.

 

Key concept:

 

• To compensate for the effect of an aberrant nasion position on ANB, a modification called the 'Eastman correction' is suggested.

• This is only applied to cases with a change in the position of the nasion, indicated by a normal angle between the maxillary plane and sella-nasion line (8° ± 3°).

• An angle value outside this range indicates the position of the sella is at fault

and because this affects the SNA and SNB values to the same extent, the ANB value does not require correction.