For many years Dr. John R. Thompson has been cautioning orthodontists about moving the maxillary incisors posteriorly too far in growing patients. He continues this admonition in his recently published book entitled The Triad of Dentistry Diagnosis and Treatment, published by Northwestern University Dental School.

Dr. Thompson has made a tremendous contribution to orthodontics in his lifetime career as a clinician, researcher, teacher and practicing orthodontist.

The reason it is so important to observe this precaution is that moving the maxillary incisors too far posteriorly causes anterior interference and malfunction of the temporomandibular joints as evidenced by clicking of the joints.

Most orthodontists pay very little attention to whether lower incisors and cuspids are intruded in treatment and many pay insufficient attention to proper torquing of upper incisors. Also upper incisors oftentimes are not intruded (when needed) and overbite is not reduced to 1 mm. This often results in bite closure in the post treatment period. If there is post treatment condylar growth, as there usually is, this can lead to incisal interference and clicking of joints.

Fig. 1. This shows the effect of post treatment growth on tooth and jaw position.

For many years we have been advocating the correction of overbite to 1 mm. This is so post treatment condylar growth can tip the upper incisors forward. (Fig. 1) If the lower incisors contact the upper incisors 3 to 5 mm up the lingual surface of the upper incisors, the mechanical disadvantage will not allow the upper incisors to tip forward, but instead the lower incisors tend to move lingually and the overbite tends to increase.

Also for many years we have strongly advocated the avoidance of lower incisor intrusion for the reason that they have a strong tendency to move upward toward their former positions—increasing the overbite. The careful observance of the above precautions will go a long way toward producing permanent treatment results.

If there is careful attention to avoiding intrusion of lower incisors and cuspids, to properly intruding upper incisors (if needed), proper torquing of upper incisors and reducing overbite to 1 mm, then post treatment condylar growth will usually translate the upper molars and bicuspids forward and tip the incisors forward thus avoiding the possibility of incisor interference cause clicking of joints. (Again see Fig. 1)

Conclusions:

1. Do not intrude lower incisors in growing patients if it can be avoided
2. Do not fail to intrude upper incisors if this is needed
3. Do not fail to sufficiently torque upper incisors (24° to 25° to line NA)
4. Do not move upper incisors too far posteriorly in growing patients, and
5. Reduce overbite to 1 mm in most cases.

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