second molar
[Fig 1 Pre-treatment Steep Mandibular plane]

Treatment planning in orthodontics includes evaluation of all three facial dimensions; Anterior-posterior, transverse and vertical. There are many appliances and mechanics strategies available for correction of the anterior posterior and transverse issues. Expanders, quad helix, transpalatal arches and archwires can assist in altering the transverse dimension. Elastics, Herbst appliance, Forus springs and head gears have been used with success to correct the Class II or Class III components of correction.

The challenge often lies in controlling the vertical dimension particularly in cases of excess vertical facial height. Vertical control is often linked with controlling the eruption of second molars. I have often heard the question asked why some orthodontists do not bond the second molars. In some cases the decision could be related to vertical control. As the most distal contact and hinge point, any increase in the eruption of the second molar can result in a discouraging anterior bite opening and increased overjet as the mandible rotates down and backward. A heavy wire extended to the second molar can easily accomplish this undesirable result in a vertical growth pattern. (Figure 1 and 2)

In contrast it is a welcome event when a deepbite forward rotator is in your hands. In some cases the second molars are well behaved and erupt into a gentle occlusion without the aid of the orthodontist’s well-meaning guidance. In too many other cases the upper second molars erupt to the buccal with a hanging lingual cusp. The opposing lower second molars can be found close to horizontal with the occlusal surface facing the tongue. Placed in a vertical growth pattern this situation brings stress the calmest among us.

[Fig 2 Open bite with full sized wire to the second molars]

Consulting some texts of mechanics and treatment it is advised if possible to avoid bonding the lower second molars when an openbite pattern exists. There are chapters devoted to the extraction of second molars to avoid issues of bite opening and partial impaction. In the final analysis all of us want a balanced occlusion without posterior interferences.

If your orthodontist is not bonding second molars and as a result the occlusion is not as balanced as you think possible, I would look at this as an opportunity for interdisciplinary collaboration. Call them and with photos in hand discuss the case and first ask what would happen if the second molars were bonded in that specific case. Hopefully by problem solving together you will both find a better understanding of the role of second molars in future cases.

I have done this with my referring doctors and now understand how they can help with equilibration post orthodontic treatment and when I need to keep working at improved alignment. It has also helped them to understand more ideal timing of patient referrals so I can better manage the second molars before they descend too far. It always leads to better results for the patients when we work together.

Donna J. Stenberg D.D.S., M.S., P.A. Spear Visiting Faculty and Contributing Author.


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