Molar Control - An easier and effective approach by Tom Mulligan Tom started his lecture by explaining that orthodontists have routinely included second molars in their appliances, even if these molars are perfectly positioned. He suggested that the reason for including second molars in the strap-up is to avoid first molars from rotating as well as displacements to the buccal or lingual. He stated that to routinely include second molars in the appliance is to admit that the operator is unable to control first molar position. Tom mentioned that to avoid first molar displacements orthodontists also frequently use lingual and transpalatal arches to establish "rigidity for control". Tom suggested that the additional time and expense of banding second molars and of using lingual/transpalatal arches over a lifetime of practice is extremely expensive in terms of time and costs. He explained that although it is always best to prevent first molar rotation/displacements, these can be treated with minimal effort and time if the orthodontist has an understanding of the forces and moments involved in treatment. Tom then proceeded to discuss the mechanics he uses for first molar control. Mulligan uses .022" x .028" siamese brackets and tubes on the first molars. In order to control and/or correct first molar position Tom uses .020" SS arch wires with properly located bends on the arch wire to produce various angles according to need. He places these bends intraorally with a Tweed-loop plier, and only after bracket alignment is achieved. Tom explained that the bracket located closest to a bend (an off-center bend) contains the larger moment (the significant one). He showed that if the short section of the wire is placed into the bracket first, the long section will point in the direction of the force produced at the opposite bracket, and that if the long section is placed into the bracket first, the short section will point opposite to the direction of force produced at that bracket. Tom showed clinical examples of the three categories of bends he uses that allow him to maintain molar position, restore a correct position if lost, and allow crossbite correction without the use of inter-arch elastics (eliminating patient cooperation). Tom explained that most of the discrepancies in the first molar area occur inadvertently during treatment. He emphasized that if the second molars have not yet erupted the orthodontist misses the clues that would indicate that the first molars are being displaced by the appliances. Only when the second molars erupt does the orthodontist become aware that the central grooves of the first and second molars do not coincide. Tom explained that the vertical forces applied by our mechanics (intrusive or extrusive) result in moments that may cause the molars to tip buccally or lingually. Extrusive forces acting through the maxillary molar tubes produce lingual crown moments. If the forces of occlusion are such that the crowns are able to respond, the molars will tip to the lingual, narrowing posterior arch width and decreasing the Curve of Monson. Extrusive forces acting through the mandibular molar tubes produce lingual crown moments. If the forces of occlusion are such that the crowns are able to respond, the molars will tip to the lingual, narrowing posterior arch width and increasing the Curve of Wilson. Intrusive forces on the molars may do the exact opposite. The changes that take place in these functional curves of occlusion afford an opportunity to determine which arch is involved in the molar displacement. From a frontal view, any change in the curves of Monson or Wilson will offer the answer to the question of which molars need to be corrected. Tom stated that it is important for orthodontists to be aware that horizontal forces will generally produce greater moments than will vertical forces acting through the same molar tubes. This is because the perpendicular distance between a horizontal force and the center of resistance in the molar is greater than the perpendicular distance between a vertical force and the same center of resistance. Tom recommends using continuous arches because there will be fewer balancing forces when compared to sectional arches. He suggests bypassing the bicuspids to obtain sectional tooth movement with a continuous arch. He explained that equal and opposite forces cannot be avoided but that there is a clever way to prevent an equal and opposite response in the occlusal plane of space. Four or six anterior brackets provide an anterior area of relative rigidity while the molars are in an area of resiliency because the bicuspids are bypassed. With this partial strap-up horizontal forces are capable of producing significant posterior movement while the equal and opposite forces produce negligible response at the adjacent teeth, which lie in the anterior area. The first bend Tom described was the off-center bend. Tom recommends looking at the molars from the occlusal view to determine first, whether the molars need to be rotated, and second, whether they are displaced towards the buccal or the lingual. If the molars are rotated, Tom demonstrated how the toe-in and toe-out bends correct molar rotations while simultaneously displacing the molars towards the buccal or the lingual, respectively. Intermolar width increases with toe-in bends and decreases with toe-out bends (if the bicuspids are bypassed). If the molars are not rotated, only displaced towards the buccal or the lingual, Tom then recommends using an in-bend or out-bend, respectively. Tom explained that these 4 bends are off-center bends (cantilevers). The short sections of these bends are associated with the toe-ins/outs while the long sections are associated with the in/out-bends. Tom recommends that the toe-in/out bends be placed just mesial to the molar tubes while the in/out bends be located in the embrasures between the first bicuspids and cuspids. The second part of Tom's lecture dealt with another category of bend called the step bend. It is a variation of the off-center bend. The step bend consists of the combination of a toe-in bend with an out-bend, or a toe-out bend with an in-bend. The combination of either of these increases the force magnitude towards the buccal or the lingual, respectively. Tom suggested using these combinations of bends when a patient has steep cusps, a flat mandibular plane, a strong bite, or the orthodontist might be using .018" slots and would like to apply higher displacement forces on the molars. The third and final category of bend Tom discussed was the center bend. He explained that it is used to produce a moment for molar rotation. Tom mentioned that if we need to rotate a molar without displacing it, an in or an out-bend be used to counteract the buccal or lingual force associated with the toe bends. Tom explained that the combination of these two bends is the equivalent of a center bend. Tom used the term "neutral zone" to refer to the state of balance of the teeth in relation to the surrounding muscle environment. Tom emphasized that he does not know whether he has positioned the teeth in equilibrium with the surrounding tissues. Thus, when he is close to finishing a case he removes the archwires for 6 weeks to allow the teeth to find their neutral zone. In this way the degree of stability or instability may be determined for each patient before removing appliances. He stated that this method allows him to "listen to what the muscle forces want to do". He has found that this procedure has the added advantage of allowing the patients to understand and observe their tendency for relapse and thus, the importance of retainers. Tom finished his excellent lecture by showing clinical examples of the indications for the 3 categories of bends he uses for molar correction. For a more detailed explanation please refer to Mulligan's five part series published on Molar Control" in the JCO (Jan-May '02). Tom concluded by stating that we should bid farewell both to lingual arches (to prevent molar displacements) and to second molar bands. He asked that we do not misinterpret these statements to mean that lingual arches and second molar bands are contraindicated in orthodontic treatment but that they are used far more often than necessary, particularly if we understand how to control forces and moments.