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Managing second molars

2011; Elsevier BV; Volume: 140; Issue: 2 Linguagem: Inglês

10.1016/j.ajodo.2009.10.048

1097-6752

Earl Johnson,

dental development and anomalies

Second molars can create great delays in orthodontic treatment if they are not managed intelligently. The purpose of this article was to describe common torque and position problems of the second molars and techniques for managing them. A simple technique for freeing mesially impacted second molars is presented. Second molars can create great delays in orthodontic treatment if they are not managed intelligently. The purpose of this article was to describe common torque and position problems of the second molars and techniques for managing them. A simple technique for freeing mesially impacted second molars is presented. Aligning second molars is a challenge for a clinical orthodontist. When these teeth erupt, they are often tipped, with the mandibular second molars tipped lingually and the maxillary second molars tipped buccally. Even if the crowns move into their correct positions in the normal arch form, the roots are often misplaced, producing excessive palatal root torque in the maxillary arch (with low-hanging lingual cusps) and excessive buccal root torque in the mandible (depressed lingual cusps). To add insult to injury, the mandibular second molars are often impacted; this can be a consequence of aggressive arch-length conservation in the mixed or transitional dentition. After preliminary leveling, the maxillary second molars often have extruded lingual cusps requiring intrusion and buccal root torque. The mandibular second molars are often depressed in relation to the first molars and need lingual root torque. The second molars often erupt late during treatment, tempting the practitioner to ignore them altogether. The purpose of this article is to present methods to prevent, minimize, or correct the problems listed above. Comprehensive treatment or phase 2 treatment should not be started until the mandibular second molars can be correctly banded (or bonded). Waiting for these molars before starting treatment will definitely shorten treatment time and better maintain patient cooperation, which wanes drastically when treatment drags on. The maxillary second molars usually erupt a bit later and can be banded at the quality-control reset appointment.1Carlson S.K. Johnson E. Bracket positioning and resets: five steps to align crowns and roots consistently.Am J Orthod Dentofacial Orthop. 2001; 119: 76-80Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar This will avoid the later time-consuming step of banding and releveling the second molars after the other teeth have been leveled. This is especially true if a second molar is impacted. Impactions can be dealt with easily with a minimal appliance before full fixed appliances. All remaining teeth can stay unbanded while the impacted molar is freed and allowed to erupt. If a distal operculum is preventing banding, it can be easily removed with an electro-surgery procedure by using local infiltration anesthesia (Fig 1). Most impacted mandibular second molars are tipped mesially and need to be tipped distally so that they can clear the mandibular first molar (Fig 2). Sometimes, the second molar’s distal movement is blocked by a mesially displaced third molar. If the third molar is impacted or incapable of ever erupting into a useful position, consider having it extracted when the oral surgeon exposes the occlusal aspect of the second molar. Oral surgeons do not like taking out third molars in 12- to 13-year-olds, but they are specialists, and this is a necessary part of their field. Please emphasize that only the occlusal aspect of the second molar needs to be freed of tissue. The attachment should be bonded just to the occlusal surface of the tipped second molar. 1.Surgically expose just the occlusal surface; extract the third molar at the same time, if indicated.2.Fabricate a custom eyelet and bond it in the second molar’s central groove with the vertical loop portion touching the distal portion of the first molar (Fig 3, A).3.Pass a light stainless steel ligature wire through the vertical custom eyelet loop.4.Fabricate the 0.018-in stainless steel sectional arch and adjust the arm length so that its terminal loop will lay directly distally to the custom eyelet loop (Fig 3, B).5.Place the 100-g superelastic open-coil spring over the 0.018-in stainless steel sectional arch.6.With a Mathieu needle holder, compress the open-coil spring 100% and lock the needle holder to hold the compressed spring in place.7.Holding the sectional spring assembly outside the mouth, thread the same stainless steel ligature wire (Step 3) through the sectional’s terminal loop.8.Thread the mesial end of the .018 sectional arch into the distal opening of the first molar tube and slide the sectional wire mesially through the first molar tube until the needle holder touches the distal aspect of the first molar tube (Fig 3, C).9.Take a second Mathieu needle holder and lock it onto the sectional wire where it emerges from the mesial side of the first molar tube. This will continue to hold the nickel-titanium (NiTi) spring compressed when the more distal needle holder is released and removed.10.Release and remove the more distal Mathieu needle holder (Fig 3, D).11.Tighten the prethreaded stainless steel ligature until the terminal end loop of the .018 sectional wire is firmly tied to the vertical loop of the custom eyelet. Cut the excess ligature free and tuck the remaining pigtail (Fig 4).Fig 4The 0.018-in stainless steel distal tipping assembly is tied in. The 100-g superelastic spring is severely compressed against the first molar tube because the arm end is tied snugly to the bonded custom eyelet.View Large Image Figure ViewerDownload Hi-res image Download (PPT)12.Release and remove the remaining Mathieu needle holder. This will allow the compressed NiTi spring to drive the sectional wire distally, and to apply a constant distal tipping force to the second molar.13.Adjust the length of the remaining sectional wire mesial to the first molar tube. Then bend the very mesial end 90° towards the teeth and away from the cheek. Make sure there is enough wire remaining mesial to the first molar tube to allow the sectional wire to slide distally enough as the spring expands and the second molar tips distally to clear the first molar. If the 90° bend is too close to the molar tube, the sectional will be prevented from tipping the second molar far enough. At the end of comprehensive orthodontic treatment, the maxillary second molar should be positioned with its occlusal surface slightly above the occlusal plane formed by the buccal-segment teeth mesial to it. The crown should be tipped slightly distally, with its root tipped slightly mesially, resulting in a slight curve of Spee in the second molar region (the occlusal plane should not be completely flat through the second molars; if so, the extruded second molar will open the bite excessively). The crown should follow the curve of Wilson exhibited by the first molar without a low-hanging lingual cusp. The crown should also be rotated so that a line connecting its buccal cusps is parallel to a similar line on the first molar. Andrews’s standard straight-wire torque prescription for the maxillary second molar is −10°.2Andrews L.F. Straight Wire, the Concept and Appliance. L.A. Wells Company, San Diego, CA1989Google Scholar However, this prescription is not always adequate to correct second molars that erupt flared buccally with excessive lingual root torque. Slot play, long interbracket distance, and lighter square finishing arches (0.017 × 0.017 inch in a 0.018 × 0.025-inch tube) routinely result in undercorrected second molars with the −10° prescription. Increasing the lingual crown torque to −30° reduces the need for adding lingual crown torque during the final finishing procedures. If you use heavier finishing arches, using less torque will still work, if you compensate for slot play and then some. (All nominal bracket prescriptions in orthodontic catalogs are in terms of crown torque [angulation of the facial surface]. However, the intent of a torque prescriptions or activation is to correctly achieve proper facio-lingual root position. When considering a change in a torque prescription, keep in mind that a larger plus or smaller minus means more lingual root movement, and a smaller plus or larger minus means more facial root movement.) The maxillary second molar tube placement should routinely produce an elevated and tipped second molar. Offset the second molar tube toward the occlusal margin to intrude the second molar in relation to the first molar. Tip the mesial aspect of the tube 3° toward the gingiva to produce a slight distal tipping of the crown. When banding the maxillary second molar, the following steps are necessary.1.Do not seat the band as far gingivally as you seated the first molar band. This will increase the vertical differential between the 2 teeth and tend to intrude the second molar.2.Seat the band a bit more mesially than distally. This will accentuate the distal tipping of the crown.3.Paying attention to Steps 1 and 2 will produce a more defined transition from a flat occlusal plane to a curve of Spee in the second molar region. This, along with the accentuated torque prescription, will lift the often present hanging lingual cusp out of the way. Andrews’s standard straight-wire torque prescription is −34°.2Andrews L.F. Straight Wire, the Concept and Appliance. L.A. Wells Company, San Diego, CA1989Google Scholar However, mandibular second molars often erupt tipped lingually with excessive buccal root torque. Slot play, long interbracket distance, and lighter square finishing arches (0.017 × 0.017 inch in a 0.018 × 0.025-inch tube) routinely result in undercorrected second molars when the −34° prescription is used. Decreasing the lingual crown torque prescription to −10° consistently reduces the need for reducing torque with archwire bends during finishing procedures. If you use heavier finishing arches, using slightly more negative torque would work if you still compensate for slot play and then some. Mandibular second molar tube placement should routinely produce a second molar that is at the same height as the first molar with level marginal ridges. Often, after preliminary leveling, the mandibular second molar is somewhat submerged in relation to the first molar. This phenomenon occurs because most of us seat the mandibular first molar band more gingivally than is ideal, slightly below the marginal ridges to avoid premature contact between the maxillary molar’s buccal cusp and the mandibular molar’s buccal attachment. To compensate for this commonly observed phenomena, offset the second molar tube gingivally. This usually results in equal vertical distances from the archwire slots to the buccal cusps and marginal ridges of both teeth. Any minor discrepancies can be easily adjusted with a step bend in normal 0.017 × 0.017-in square stainless steel finishing arches. Nothing is more frustrating than trying to achieve extensive second molar torque correction late in treatment with conventional stainless steel finishing arches. Everything else is done, and you must spend another 3 to 4 months correcting the second molar torque. Ideally, this would have been finished earlier in treatment. Four factors can help minimize this problem: (1) use the prescriptions as described above, with maxillary molar torque of 30° and mandibular molar torque of −10°; (2) finish leveling with a full fit square wire; (3) correct severe torque problems early by using the turbo-torque technique; and (4) fine tune the torque with a 0.017 × 0.017-in stainless steel wire. My usual leveling wire sequence with an 0.018-in slot is 0.014-in NiTi, 0.016-in NiTi, and 0.018 × 0.018-in NiTi. Before placing the 0.018 × 0.018-in square NiTi wire, I check for second molar torque problems. If, for example, a maxillary second molar needs buccal root torque, I do the following.1.Hold the new archwire so that its occlusal plane is 90° to normal (vertical instead of horizontal with one buccal leg directly above the opposite buccal leg) (Fig 5).2.Place the distal end of the archwire into the second molar tube.3.Rotate the rest of the archwire until it is orientated in it normal fashion: parallel to the occlusal plane.4.Place the free end of the archwire in the contralateral second molar tube.5.Ligate all remaining teeth in the arch normally with 1 exception: bypass (buccally) the first molar just mesial to the second molar that is being torqued (Fig 6). Do not run the archwire through the first molar tube or bracket. Do not ligate the archwire to the first molar tube or bracket.Fig 6Turbo torque 2. The 0.018 × 0.018-in NiTi turbo-torqued wire in place. The wire is activated an additional 90° between the second premolar bracket and the second molar tube. The archwire bypasses the first molar tube assembly completely (no ligation or placement in tube) while all other teeth are fully tied in.View Large Image Figure ViewerDownload Hi-res image Download (PPT) The net result is that the archwire has an additional 90° of activation but has, at the same time, had its torsional stiffness effectively reduced by a third because the interbracket distance has been increased by a factor of 3 (by bypassing the first molar bracket or tube). This hyper-activated square NiTi wire will torque the second molar over a longer distance without repeated reactivations (Fig 6). This technique can be used equally well with lingually tipped mandibular second molars. When the torque problem has been resolved, remove the square archwire and then replace and retie it normally so that you can continue leveling the affected premolar, first molar, and second molar regions. The only side effect can be minor palatal tipping of the bypassed first molar. This can be easily taken care of with a lingual arch or a transpalatal arch. The net effect of turbo-torquing is to correct torque issues early and rapidly, thus drastically reducing overall treatment times. You can turbo-torque both second molars in the same arch at the same time. One side can finish torque correction earlier than the other side. If so, just remove the archwire, tie in the corrected side normally, and continue turbo-torquing the side that needs more correction.