by Sanjivan Kandasamy, BDSc, BScDent, DocClinDent, MOrthRCS, MRACDS

The alignment of the second molars is one of the many occlusal goals of orthodontic treatment. According to the ABO, the permanent second molars need to be fully erupted, aligned, and in their final position at the end of treatment.1

Failure to align these teeth during orthodontic treatment may result in their eruption into an unfavorable transverse (bucco-lingual) or occlusal (vertical) relationship. This may lead to balancing or working side interferences and, in some cases, an unfavorable proximal contact relationship with the adjacent first molar. Failure to engage these teeth during orthodontic treatment may also result in greater anchorage loss, further extrusion of the lower first molars with Class II elastics,2,3 loss of control of nonfunctional second molars, and the significant displacement of the first and second molars following any type of distalising or tipping mechanics. This is commonly seen following the use of bite-repositioning appliances using the maxillary first molars as anchors, Class III elastics, reverse curve, and anterior intrusion or extrusion mechanics using the first molars as anchors.

How Second Molars Are (and Aren’t) Treated

Figure 1: Some orthodontists use bands with convertible tubes to overcome vertical and transverse discrepancies between the first and second molars.

Figure 2: When needed, the tube can be converted into a bracket permanently and the wire secured within the bracket by a steel ligature wire.

Second molars are commonly either banded with tubes welded on the buccal aspect or bonded with tubes. In the majority of cases, simply banding or bonding these teeth leads to their favorable alignment. This is especially helpful in patients who present with large deep bites, essentially facilitating the leveling of the Curve of Spee.

It may not, however, always be feasible or practical to level the posterior aspect of the Curve of Spee by engaging the second molars. In patients who present with a hyperdivergent facial pattern, a dental or skeletal open bite, or a moderate to severe Class II skeletal or convex profile, engaging the second molars may lead to undesirable side effects. These negative effects include downward and backward rotation of the mandible and significant bite opening, worsening the overall Class II dental occlusion and convex profile as well as increasing the anterior facial height.2-5

Many clinicians simply do not engage the second molars in these types of cases, or else they place the tubes further occlusally relative to the first molar tube. This may work in some cases, but if bands are placed this leads to excess band material at the occlusal aspect that needs to be trimmed away—and this can be time-consuming. If banding is impractical, these teeth are then usually bonded further occlusally instead, which (especially in the mandibular arch) can lead to the tube’s becoming an occlusal interference, resulting in bond failure. The buccal cusps also have less enamel to bond with given the different angulation and contour of the cusps compared to the tube base, which may also result in increased bond failures.

Figure 6: In cases where a rigid base archwire is present and a light overlay archwire needs to be placed into the first molars, the wire can be secured at the SL bracket with a rubber module or steel tie around the tie wings.

Using tubes, it is impossible to address the vertical and transverse discrepancies between the first and second molars with a step at the wire between the molars. To overcome this, bands with convertible tubes are commonly used (Figure 1). When needed, the tube can be converted into a bracket permanently and the wire secured within the bracket by a steel ligature wire (Figure 2). This allows the orthodontist to place various bends in the wires between the first and second molars.

The problems associated with this approach include getting adequate access, the time involved in the placement of the steel ligature tie, and the possibility of the steel ligature tie fracturing between visits (resulting in undesirable tooth movement). Also, if the wire needs to be taken out or replaced at the orthodontic visits, this means that the steel ligature tie needs to be removed and replaced as well, which again becomes time-consuming in the long term. Further, in busy clinical practices, delegating these tasks to auxiliaries may be too difficult or may not result in the full engagement of the wire in the bracket.

Figures 3-5: Using an SL molar bracket at the first molar (and even second molar, if needed) allows for the effective and efficient engagement and alignment of the second molars as well as the maintenance of a step to control the vertical dimension.

The Self-Ligating Solution

Using a self-ligating (SL) molar bracket at the first molar (and even second molar, if needed) allows for the effective and efficient engagement and alignment of the second molars as well as the maintenance of a step to control the vertical dimension (Figures 3 to 5). Bends in Nickel Titanium wires can also be placed with ease during the initial alignment and leveling stages. In cases where a rigid base archwire is present and a light overlay archwire needs to be placed into the first molars, the wire can be secured at the SL bracket with a rubber module or steel tie around the tie wings (Figure 6). I must mention that practices can incorporate these SL molar brackets without needing to use SL brackets on all the other teeth. They have a specific and defined purpose here, with no controversies associated with them such as an increased ability to “grow bone” or reduce friction. In terms of cost, the majority of SL brackets are actually the same price as the respective company’s bondable tubes.

It is important that orthodontists assess the type of SL molar bracket offered by each company prior to using them, as each one comes with its own set of advantages and disadvantages. Some brackets have a large base designed to provide better bonding, and some have a low profile designed not to interfere with the occlusion.

The perfect SL molar bracket is yet to be made, but when you weigh up all the factors, including clinical efficiency, better first and second molar occlusal treatment outcomes, better vertical and transverse control, and costs (in both money and time), their routine use is certainly indicated over standard tubes.


Sanjivan Kandasamy, BDSc, BScDent, DocClinDent, MOrthRCS, MRACDS, is in private practice in Midland, WA, Australia. He is a clinical senior lecturer in orthodontics in the Dental School of The University of Western Australia, Nedlands, WA, Australia. He is an adjunct assistant professor in orthodontics at the Center for Advanced Dental Education at St Louis University. He can be reached at /i>

Pros and Cons of SL Molar Brackets

Pros

  • Easy to place bends at the wire between the first and second molars.
  • Avoids the need for converting tubes.
  • Avoids the need for ligating the archwire with a steel ligature wire after converting the tube.
  • Allows for the control or maintenance of the vertical discrepancy between the first and second molars.
  • Allows orthodontists to more easily address the transverse discrepancy between the first and second molars.
  • Reduced likelihood of bond failures at these teeth.
  • Forestadent and GAC’s molar SL brackets have tie wings that allow for the placement of an auxiliary or overlay archwire.
  • Forestadent provides different bracket base sizes, which allows for maximizing the bonding surface of the molar that is being bonded.

Cons

  • Some manufacturers’ lower-molar SL brackets are too bulky and interfere with the buccal cusps of the opposing upper molars.
  • Some SL brackets do not have tie wings to facilitate the placement of an overlay archwire.

References
  1. American Board of Orthodontics. Case report preparation. St Louis; 2009. Available at: www.americanboardortho.com/professionals/clinicalexam/casereportpresentation/preparation/casts.aspx. Accessed February 14, 2012.
  2. Herzberg R. A cephalometric study of class II relapse. Angle Orthod. 1973;43:112-118.
  3. Schudy FF. Vertical growth versus anteroposterior growth as related to function and treatment. Angle Orthod. 1964;34:75-93.
  4. Creekmore TD. Inhibition or stimulation of the vertical growth of the facial complex, its significance to treatment. Angle Orthod. 1967;37:285-297.
  5. Schudy FF. The control of vertical overbite in clinical orthodontics. Angle Orthod. 1968;38:19-39.