Why in-out matters
Whilst, over the years, much focus has been given to both angulation and torque, significantly less attention has been given to the importance of in-out.
This may be because the general view was that in-out is not important, it could also be that doctors simply assumed the in-out of brackets they were using to be correct.
Unfortunately, it is not safe to make these assumptions. In-out should definitely be considered. If it is neglected, wire bending may be required. Sadly, in-out has been wrong on many brackets produced in the past.
What is in-out?
In his research Dr. Andrews used the term ‘prominence’ to describe what is commonly known as ‘in-out’. He measured it from an imaginary line known as the ‘embrasure line’, shown here in brown for the upper and lower arches. This illustration is redrawn from Dr. Andrews’ book pages 32 & 33. Andrews LF 1989 Straight Wire – The concept and appliance.
LA Wells Co. ISBN 0-9616256-0-0.
Bennett JC, McLaughlin RP, Fundamentals of orthodontic treatment mechanics.
2014 ISBN978-0-9564555-2-9 Page 44.
Making things better
More recently, careful work has been done to correct in-out on the entire Mini Sprint II bracket range.
Science from Andrews’ research sample found that the labial surface of upper lateral incisors was inset by 0.55mm compared with the centrals. However, experience has shown that whilst this degree of inset is scientifically correct, it does not give rise to an aesthetic outcome likely to please every patient.
For this reason, reduced inset on upper laterals is now a key feature, as we have found that this provides better smile aesthetics.