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A Voice in the Arena: Simple but Powerful by Dr. Chad Foster

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A Voice in the Arena: Simple but Powerful

Proper positioning for maxillary molars

by Chad Foster, DDS, MS, editorial director

As a tooth nerd, one of my favorite things to do in life is discuss clinical concepts and mechanics with other tooth nerds. When I have the opportunity to lecture, one slide that I always linger on is the one pictured above.

Hard for me to imagine but I am entering my sixteenth year of practicing orthodontics (USC 2010 grad). In those 16 years, I’ve made plenty of mistakes. One mistake that I made far too often was not properly positioning my maxillary first and second molar tubes. When the maxillary molar tubes are not positioned ideally, a number of iatrogenic problems can develop.

First, and most obviously, it is very challenging to get a “socked-in” natural intercuspation if they are not positioned as nature intended. However, the most common and consequential problem created by improper placement is unfavorable eruption of the maxillary second molar, which can lead to a plunging palatal cusp, unintented bite opening via mandibular clockwise rotation, and a now significant iatrogenic occlusal challenge to overcome.

This is actually one reason why some orthodontists either don’t bond second molars or prefer a custom digital solution to avoid this simple problem altogether—though the fix is just as simple.

The solution is to bond the upper molars as nature intended. In naturally beautiful occlusions, what is most often found in the maxilla is a first molar that has distal root tip. This is where nature likes it, so leave it there! The upper first molar in this position is referred to in literature as a “stolarized” first molar.

To properly place a U6 tube to maintain this position, the orthodontist must position the tube so that there is a greater amount of disto-buccal cusp descending below the tube compared to the mesio-buccal cusp (there should not be an even and level amount of each of these cusps below the tube).

Look at the photo shared above. The U6 tube is positioned in this manner. If a straight wire is inserted, the U7 will not be erupted because of this proper placement of the stolarized U6 tube position.

Imagine now if the U6 tube were tipped slightly down in the distal so that an even and level amount of its mesio-buccal and disto-buccal cusps were below the tube. When a straight wire would be inserted, the wire extending from the U6 would need to deflect up to engage the U7, resulting in unfavorable extrusion of the U7 leading to the problems previously discussed.

The exact opposite positioning of the molar tube is needed for maxillary second molars. In naturally beautiful occlusions, what is most often found in the maxilla is a second molar that has mesial root tip. This is where nature likes it, so leave it there!

To properly place a U7 tube to maintain this position, the orthodontist must position the tube so that there is a greater amount of mesio-buccal cusp descending below the tube compared to the disto-buccal cusp (there should not be an even/level amount of each of these cusps below the tube). Look again at the photo. The U7 tube is positioned in this manner. When a straight wire is inserted, the U7 will not be erupted with its distal side tipping down.

Imagine now if the U7 tube were tipped slightly up in the distal so that an even/level amount of its mesio-buccal and disto-buccal cusps were below the tube. If a straight wire is inserted, the wire extending into the U7 would induce tipping down of its distal side, resulting in unfavorable extrusion of the U7, leading to the problems previously discussed.

Positioning molar tubes this way makes life much easier. You will suffer far fewer self-induced plunging U7 cusps with associated bite opening (clockwise mandibular rotation) and difficult molar settling. It is also one important reason why I routinely treat patients in three wires.

Another very important tip to help facilitate this technique is to use mini-tubes on the U7s. They allow you to place the U7 tubes much more occlusally compared to a traditional U7 tube—all the way down the mesio-buccal cusp. This will best allow you to mitigate any unintended disturbance/extrusion of the upper second molars.

[Editors note: View Dr. Foster’s free three-wire webinar by clicking here.]
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