By Björn Ludwig, DMD, MSD
Jan Hourfar, DMD, MSD
Bettina Glasl, DMD, MSD, and
Gregory Ludwig, PhD, MBA, BA (Hons), BBA

X-ray of impacted canine.

Apart from mandibular third molars, maxillary canines are most frequently affected by impaction, triggering the need for orthodontic treatment. Maxillary canines represent about 60% of impacted teeth (not including third molars). There are a number of etiologies for the impaction of canines including loss of space, eruption issues, and genetics. Particularly relevant in this context is the so-called guidance theory as it emphasizes the role of lateral incisors as a guide that allows normal eruption of canines.1-2

Physiologic eruption of upper canines usually takes place at about 11.5 years of age3 and in the majority of cases this occurs at about the same time on both right and left sides of the arch. In 10% of cases, however, there may be a differential in eruption of one side over the other of up to 1 year. The rate of impaction of maxillary canines is from 0.8 to 2.3%, with a slightly higher incidence for females.4 Moreover, 8% of them are affected by bilateral impaction. Finally, one third of impacted canines are located in a labial position within the alveolar process and about two thirds are located in the palate.5

Impacted canines are sometimes easy to identify, even without radiographs. For example, buccally impacted cuspids are often palpable high in the buccal alveolus. Further indicators are peg-shaped lateral incisors or their complete absence. Despite the often excess space for canines, congenitally missing lateral incisors increase the odds of impacted canines.

The use of 2D and 3D radiographs are often required to identify the precise location of palatally impacted canines. In a simple panoramic x-ray, a palatally impacted canine that is angled greater than 45° to the occlusal plane presents a better prognosis for directing this tooth’s eruption successfully. Certainly, successful orthodontic alignment of impacted canines permits the preservation of a functionally very important tooth.

Practical Considerations

Prior to any alignment of impacted canines, a surgical exposure of the tooth is usually required. This may be implemented by either so-called open or closed techniques; most often dependent on the location of the canine. In addition, prior to exposure, orthodontic space creation for the canine in the arch form should be completed. Active orthodontic movement of the uncovered canine should proceed immediately after the exposure.

In order to direct the eruption of impacted canines, orthodontists can choose from a large variety of biomechanical options; however, some offer striking disadvantages. If forces are applied to the canine from a small diameter super elastic archwire, the reciprocal forces will adversely affect the other teeth in the arch form, especially those adjacent to the impacted one. This may create an iatrogenic open bite, canted occlusal plane, crossbite, etc. On the other hand, if elastic chain or coil springs are used to provide traction to the canine, anchored by a rectangular stainless steel base arch, poor oral hygiene and limited biomechanical directional forces are possible.

Another option is to use an “overlay” or second parallel archwire (often a super elastic wire), in addition to a rectangular stainless steel base arch. The main disadvantage is increased friction due to the doubled archwires. Moreover, the force level also requires careful consideration as too much force may result in hyalinization and, in some cases, may even prevent the desired tooth movement. However, it should be noted that ankylosis is very rare for maxillary canines.6

Advantages of SL Bracket Usage with Auxiliary Slots

Figure 1.
Figure 1: Forestadent BioQuick bracket with auxiliary slot (dimension .016″ x .016″).

Self-litigating brackets with additional, auxiliary slots7 offer an alternative for the previously discussed treatment options. Not all SL systems are suitable. For instance, inserting “piggy-back” dual arches in the same slot is not feasible and would likely result in damage to the clip of the SL bracket. Forestadent’s Quick bracket system (Figure 1) and some others (e.g., Speed, Damon Q, etc.) address this issue by incorporating a parallel auxiliary slot (slot dimensions: 0.016″ x 0.016″). The auxiliary slot expands the “piggy back” technique by permitting the insertion of the second arch (e.g., 0.012″ NiTi) through that extra slot without disturbing the base wire.

 

Figure 2.
Figure 2: A diode laser was used to expose the crown of an impacted canine. The overlay superelastic wire was inserted into the auxiliary slots to be combined with the base archwire.

In this manner the secondary wire can move freely through the horizontal auxiliary slot. In turn, this permits more continuous, physiological forces to be applied to the impacted canine; thereby, reducing potential hyalinization and reducing treatment duration. Throughout the directed eruption of the impacted canine teeth, the base arch is still providing support and correction of other aspects of the malocclusion.

 

 Clinical Examples

Figure 3.
Figure 3: Healthy and natural-looking gingiva post-treatment.

In Figures 2 and 3, a diode laser (Sirona) was used to expose the crown of a buccally impacted canine (within attached gingiva). This was accomplished after the application of Forestadent BioQuick orthodontic brackets featuring horizontal auxiliary slots (.016″ x .016″) followed by levelling, alignment, and space creation for the canine. The “piggy back” or overlay superelastic wire (.012″ BioStarter) was inserted into the auxiliary slots to be combined with the base arch wire (.019″ x .025″ stainless steel). Initially, only the secondary light wire is inserted into either slot of the canine bracket to direct that tooth’s eruption into the arch form. Eventually, the base wire will encompass the canine’s main slot to provide more control.

 

Figure 4.
Figure 4: Closed exposure of an impacted canine accompanying congenitally missing lateral incisors (its position can be seen in the CBCT image). The main archwire was joined by the superelastic overlay inserted into the auxiliary slots and through the links of the chain on the canine.

Figure 4 demonstrates closed exposure of an impacted canine accompanying congenitally missing lateral incisors (its position can be seen in the CBCT image). Levelling, aligning, and space creation was accomplished prior to surgical exposure of the canine. A bonded attachment with attached chain links was applied. The main arch wire (.019″ x .025″ SS) was then joined by the superelastic overlay (.012″ BioStarter) inserted into the auxiliary slots and through the links of the chain on the canine. As the impacted tooth was directed into the arch from, a bracket was applied onto it with +17° of palatal root torque. The appropriate root torque was required to move the canine root into the alveolar bone.

 

Figure 5.
Figure 5: A closed exposure was accomplished for this buccally impacted canine. The main arch was combined with a superelastics overlay wire placed in the auxiliary slot and through a link in the chain applied to the impacted canine.

Figure 5 reiterates this auxiliary slot technique for a patient with impacted right canine and associated congenitally missing third molar. A closed exposure was accomplished for this buccally impacted canine. Levelling, alignment, and space closure had been previously accomplished prior to the exposure. The main arch (.019″ x .025″ SS) was combined with a superelastics overlay wire (.012″ BioStarter) placed in the auxiliary slot and through a link in the chain applied to the impacted canine. The final result could have been improved with additional palatal root torque for the canine.

 

Figure 6.
Figure 6: Bilateral, palatally impacted canines that were exposed using a diode laser. A bonded attachment with chain was attached to the problem teeth, and a “piggy back” superelastic wire was placed through one of the links of the chain to begin directing the eruption.

The final example (Figure 6) demonstrates bilateral, palatally impacted canines that were exposed using a diode laser after initial levelling, alignment, and space creation was accomplished to a rectangular (.019″ x .025″ stainless steel) base wire. A bonded attachment with chain was attached to the problem teeth and a “piggy back” superelastic wire (.012″ BioStarter) was placed through one of the links of the chain to begin directing the eruption.

 

Later, appropriate root torque was applied with continuous arch mechanics. The marginal gingival contours are favourable post-treatment (Figure 7).

 

 Conclusion

The use of SL brackets with additional auxiliary slots offers a number of advantages for the direction of eruption and alignment of impacted canines. These benefits may include the appropriate application of traction while maintaining base archwire support, potentially shorter treatment and clinical management of “dual wire” scenarios, and reduced friction. OP

Figure 7.
Figure 7: The marginal gingival contours are favourable post-treatment.

 

Authors’ note: Special thanks to S. Jay Bowman, DMD, MSD, for his assistance with this article.


 

Image of authors.
Björn Ludwig, DMD, MSD, is in private practice in Traben-Trarbach, Germany. He is scientific coordinator at the University Homburg/Saar. He can be reached at [email protected]

Jan Hourfar, DMD, MSD, is in a private practice in Reinheim, Germany. He can be reached at [email protected]

Bettina Glasl, DMD, MSD, has a private practice together with Björn Ludwig in Traben-Trarbach, Germany. She can be reached at [email protected]

Gregory Ludwig, PhD, MBA, BA (Hons), BBA, is senior lecturer in the faculty of business and law at Northumbria University in the United Kingdom. He can be reached at [email protected]

 


References

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  2. Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod. 1994;64(4):249-256.
  3. Proffit WR, Fields HW, Sarver DM. In: Proffit WR, ed. Contemporary Orthodontics. 4th ed. Oxford: Elsevier; 2007.
  4. Becker A, Smith P, Behar R. The incidence of anomalous maxillary lateral incisors in relation to palatally-displaced cuspids. Angle Orthod. 1981;51(1):24-29.
  5. Johnston WD. Treatment of palatally impacted canine teeth. Am J Orthod. 1969;56(6):589-596.
  6. Jacoby H. The “ballista spring” system for impacted teeth. Am J Orthod. 1979;75(2):143-151.
  7. Kokich. VG, Mathews DA. Impacted teeth: surgical and orthodontic considerations. In: McNamara JA, Brudon WL, Kokich VG, eds. Orthodontics and Dentofacial Orthopedics. Ann Arbor: Needham Press; 2001.
  8. Ludwig B, Bister D, Baumgaertel S. Self-Ligating Brackets in Orthodontics. Current Concepts and Techniques. New York: Thieme; 2012.