PCSO Bulletin: Spring 2000 Dr. Thomas Mulligan Lecture Summary

Dr. Mulligan gave his audience a familiar mix of physics and engineering, providing concise aphorisms meant to stick in the mind and plain entertainment. I have had the opportunity of hearing Tom speak many times, and his presentations have become only more polished and finely tuned over time. He now uses a computer to deliver his presentation, and he uses the medium with elegance.

This talk was specifically about using lever theory to move molars in all planes of space, while using appliances on first molars and anteriors. Tom is not against a full appliance, he simply advocates partial appliances for major movements of molars.

Tom always offers some interesting observations. My attention was first caught by his assertion that a trans-arch dimension discrepancy between first and second molars (e.g. the first molars lingual, the second molars buccal) is usually a problem with the first molars, not the second molars.

For this reason, he usually corrects arch form by first molar movement until the tooth aligns with the second molar. The first part of his presentation featured definitions of the center bend, cantilever bend, and the off-center bend.

Dr. Mulligan talked about the use of the off-center bend to rotate the molars and move the molars buccally or lingually. These two kinds of movement are produced by separate adjustments. The rotational bend is placed near the molar, while the buccal/lingual bend is near the incisor or canine. He emphasized one rule to help make the bends accurate: always place the rotational bends first and the displacement (buccal/lingual) bends second.

The images below will illustrate the application of off-center bends. Only a single quadrant is shown, but the illustrations involve the use of a continuous archwire with either a 2x4 or 2x6 strap-up. A full strap-up is contra-indicated.

In Figure 4, no rotations were present, so only an in-bend was used. This produces the necessary force system for correction – a lingual force on the molar. The same is true in Figure 5, except that an out-bend is used to produce a force in a buccal direction.

In Figures 6 and 7, toe-in and toe-out bends have been applied for the rotations present. The forces that accompany these bends are used to correct the lingual and buccal molar displacements.

Figures 8 and 9 show the previous molar problems, except that out-bends have been applied following placement of toe-in and in-bends have been applied following placement of toe-in and toe-out bends. Because this produces the step relationship, forces are at their highest magnitude. This can be done for adults, patients who are brachycephalic, steep cusps or .018 slots in order to provide greater forces with smaller slots.

Finally, rotation problems are resolved in Figures 10 and 11 by use of the toe-in and toe-out bends, with in-bends and out-bends used to provide forces in the opposite directions of those associated with the short section bends.

Spring 2000 Presentation Summary:

Common Sense Mechanics