Extractions and Clear Aligners

The content of this article was developed with Dr. Gabriel Dolci of PUSH Dental Learning.

For information regarding extractions and clear aligners, refer to the following:


 

Overview

When clear aligner therapy was introduced, there were limitations regarding its indications in extraction cases, specifically cases which would require major root movements or movements of larger teeth over greater distances.

However, advances in the quality of aligner plastic (ClearQuartz™ tri-layer material) and of digital treatment planning tools (ClearPilot™), have expanded the range of treatment possibilities to include difficult extraction cases.1

One of the challenges when treating patients with extractions using clear aligner therapy is knowing the type of tooth movements that are required to close the space generated by an extraction (e.g., tipping, translation, torque, etc.).

The answer to this challenge can provide an understanding of case complexity, optimum treatment time and the necessity of revisions in treatment, with the ultimate goal of achieving the best possible clinical outcomes.

 


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Application

Contemporary orthodontics tends to consider tooth extractions as an ordinary method of treatment, which can be an elected strategy to improve dentofacial esthetics and function for several clinical conditions.

Extractions have been used as a method of treatment for decades in the orthodontic field, allowing orthodontists to directly address specific patient needs for malocclusions and conditions, such as:

  • Crowding (crooked teeth)
  • Protrusive profiles (proclined incisors, sometimes creating a gap between upper and lower lips),
  • Excessive overjet (e.g., overjet associated with the protrusion of the upper jaw and upper teeth) 
  • Anterior crossbites

Two of the more common conditions which can lead to the decision to extract are:


 

 

Severe Crowding

Crowding is a malocclusion associated with a lack of available space in the arch to properly align the teeth (Figure 1). lt's one of the most prevalent conditions in orthodontics. After its diagnosis, the clinician should examine and classify the magnitude of crowding and based on their findings, determine if extractions are a plausible treatment strategy for that patient.

Fig._1A.jpg Fig._1B.jpg Fig._1C.jpg

Fig._1D.jpeg Fig._1E.jpeg

Figure 1: Intra-oral views of severe crowding. Crowding can be classified as mild, moderate or severe, when we need to gain, respectively, 1-3mm, 4-6mm and more than 6mm of space in the arch to allow for the proper alignment of teeth.

 


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Skeletal Discrepancies

lf the patient has a skeletal discrepancy, such as a Class lI with maxillary/mandibular protrusion, or bimaxillary protrusion (Figure 2), the orthodontist may choose to accept the skeletal discrepancy and attempt to "camouflage" the issue by extracting the tooth/teeth and moving the adjacent teeth into the space created by the extraction (Figure 5 in the Premolar Extraction section below).

A Fig._2A.jpeg  B Fig._2B.png  C Fig._2C.jpg

Figure 2A, B, C: Clinical case with protrusion of maxilla and mandible, skeletal and dental. The diagnosis is based on the clinical exam and lateral cephalometric evaluation (A and B). In C, it’s observed the results after ClearCorrect treatment and anterior retraction.

 


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Clinical Considerations

The most common teeth extracted in orthodontics are the premolars and lower incisors, and there are specific indications for the clinician to consider when selecting their method for extraction.

Lower Incisor Extraction

Usually performed in very specific cases, when the orthodontic diagnosis has the following clinical characteristics (Figure 3):

  • Severe deficiency of space in the anterior region of the lower arch (canine to canine).
  • Class I molars and canines on both sides.
  • Absence of a deep bite and increased overjet.
  • Presence of Bolton discrepancy with an excess of dental material in the anterior region of the lower arch.

A Fig._3A.jpeg B Fig._3B.png

C Fig._3C.png D Fig._3D.jpg

Figure 3: Clinical case of extranumerary lower incisor extraction. Clinical occlusal view (A) and setup view (B) before extraction. Observe the gray incisor on the right, indicating extraction and the presence of a pontic. Figures 3B and 3C are the clinical and setup views after treatment was finished and the extraction space was closed.

After the decision to extract the lower incisor has been made, the clinician may select which tooth will be extracted based on:

  1. The clinical condition of the 4 incisors (e.g., decay, periapical/periodontal alterations, fractures)
  2. The position of the tooth (it's common to extract the tooth that has the worst positioning)
  3. The tooth anatomy (commonly the tooth with affected anatomy)

Treatment strategies and tactics for closing space created by lower incisor extraction

Some common strategies or tactics used for closing the space that is created after extracting a lower incisor are:

  • Use of vertical rectangular engagers (1.25 mm depth) on the two teeth adjacent of the tooth being extracted.
  • Using the ClearPilot™ Treatment Setup where a virtual pontic will be applied to the tooth being extracted, you can visualize how to proceed with reestablishing the esthetics in the region, while the space is being closed.

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Premolar Extraction

ClearCorrect® aligners are a good option for treating premolar extraction cases, because of the trimline that is above the gingival zenith (Figure 4), which provides more retentionand improved force application⁷ over the crown of the tooth.

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Figure 4: Trimline 1.5 mm above the gingival zenith.

When making the decision of which premolar to extract, the clinician should always consider the clinical and radiographic condition of the tooth, prioritizing extraction of teeth with restorations, decay and/or periodontal/periapical alterations.

The position of the tooth is another important point to consider. Pre-molars are usually the teeth elected for extraction, when their location is close to the problem area (anterior crowding). However, occasionally the second pre-molars can be extracted, instead of first premolars. If the lower dental arch does not present severe crowding or excessive buccal tipping of incisors, the decision of extracting only in the upper arch is another possibility to consider. Think about what reduces the treatment complexity and allows the achievement of excellent results.

A Fig._5A.JPG B Fig._5B.JPG

C Fig._5C.JPG D Fig._5D.JPG

Figure 5: Clinical case showing the extraction of upper first pre-molars, before (A, B) and after space closure (C, D).

Treatment strategies and tactics for closing space created by premolar extraction

For these challenging cases, detailed communication with the technician (in the prescription form) will help to ensure you receive the desired treatment setup for the case.

With this in mind, following are some common strategies or tactics used for closing the space that is created after extracting a premolar:

  • Reduce the rate of tooth movement in the "Treatment Preferences" section of the Doctor Portal to 0.2 mm and 2 degrees. (This is an option if you want to apply this preference to all cases. Otherwise, you'll make this request in the "Additional Information" section of the prescription form.)
  • Request for engagers (1.25 depth) to be placed on the teeth adjacent to the extraction tooth.
  • Apply buccal torque and intrusion to the incisors, intending to minimize the tendency of extrusion and lingual tipping during retraction/space closure.

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Auxiliaries Used for Extractions

Auxiliaries can be used to assist with treatment when teeth are being extracted.2 We will consider a few of these below.

Power Arm

Power Arms are bonded to the tooth crown so the line of force action will be near the center of resistance of the tooth/ group of teeth which are being moved distally by translation (without tipping of the crown). The force application can be done using power chains or closed NiTi springs (Figure 6 and 9 in Extractions with ClearCorrect section below).

An orthodontic power arm has a body with a bonding surface for attachment to a tooth. A blade-shaped arm extends gingivally from the body and has a width extending in a mesial-distal direction. The power arm is also equipped with a number of recesses in the mesial or distal edges of the arm for engaging a tractive device (elastics). Power_Arm_2_-_PUSH.jpg

 

PA_TADs_PC_-_PUSH_-_GIF.gif

Figure 6: Observe a power arm bonded in the buccal surface of canine, and how it’s possible to activate the system through power chains and TADs, intending to close the space of extraction.

From a clinical perspective, if you are planning to use power arms in your treatment, you can specify that a cutout be placed in the region of the canine and premolar in the "Additional information" section of the prescription form, or by adding them using the cutouts 3D editing tool in ClearPilot™.

 


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Cutouts and Elastics

Cutouts are cuts made in the aligner that allow the clinician to apply auxiliary mechanics, such as:

  • Class II intermaxillary elastics (Figure 7)
  • Class III intermaxillary elastics
  • Intramaxillary elastics
  • Elastic chains
  • Space for bonding a button or brackets

Cutouts_and_Elastics_-_Class_II_-_close_space_-_PUSH.png

Figure 7: Cutouts for Class II intermaxillary elastics

The use of cutouts and intermaxillary elastics is another good option to assist with space closure after extraction.  

 


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TADs

A temporary anchorage device (TAD) is a device that is temporarily fixed to bone for the purpose of enhancing orthodontic anchorage either by supporting the teeth of the reactive unit or by obviating the need for the reactive unit altogether. The TAD is subsequently removed after use (Figure 8).

A Fig._8A.JPG B TADs_-_PUSH.jpg

Figure 8: TAD insertion to allow the application of hybrid mechanics together with a power arm. For this case, a close coil spring (Niti) was used as active element of anterior teeth retraction.

Temporary Anchorage Devices (TADs) are also useful as auxiliaries, specifically in cases where you need assistance with movement mainly in one arch. Anchoring the elastic on the TAD, and not on a button or slit in the aligner in the opposing arch, can help prevent unwanted movement in the opposing arch.

PA_TADs_PC_Posterior_-_PUSH_-_GIF.gif

 


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Extractions and ClearCorrect®

One advantage of ClearCorrect® aligners with extraction treatment is that clinicians can plan the desired tooth movements using ClearPilot™. The clinician can design how much of the extraction space should be used to move molars forward, correct crowding, and/or retract anterior teeth, setting molar angulation and incisor torque according to their treatment goals. lt's important to note that there can be a discrepancy between digital treatment planning and clinical outcomes; in other words, actual anchorage and torque control may not always be achieved as planned.

If you are planning an extraction in your patient's treatment, you can indicate which teeth you plan to extract on the prescription form (on Step 4 - Additional Instructions) when creating your order in the Doctor Portal (Figure 9).

It is strongly encouraged that you provide additional treatment details (Figure 9) and information about the extraction in the "Additional Information" section of the prescription form. (E.g., requesting engagers to be placed on specific teeth or at a specific step of treatment, requesting sequential distalization 2 by 2, request for resizable pontics or bars, etc.)

Fig_9A.png

Fig_9B.png

Figure 9: Extractions treatments may require “full arch correction”, as observed in the figure. Also, you can select the teeth to be extracted and add specific information about the treatment on Step 4 in the "Additional Information" section.

 


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Tips for Extractions with Clear Aligners

  • When treating extraction cases with aligners, consider midcourse re-scans and case revisions as a normal treatment characteristic. To be prepared for this possibility, inform your patient from the beginning.
  • Auxiliary anchorage devices, power arm, different engager designs and sizes, intermaxillary elastics and overcorrection should be considered to help achieve treatment goals and desired clinical outcomes.
  • One of the most predictable tooth movements with clear aligners is tipping3,4, whereas one of the least predictable movements is torquing. Therefore, it's important for the clinician to identify the type of movement needed when closing the extraction space.
  • Extraction cases usually require challenging posterior tooth movements (i.e., torque, tipping, and rotation). For this reason, a 2-week wear schedule should be considered the ideal to allow the required tooth movements to occur and to achieve more predictable clinical outcomes.5
  • Request pontics or bars in your Treatment Setup to assist with space maintenance and help with aesthetics while opening or closing spaces.

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Sources and References

Cases and imagery courtesy of PUSH Dental Learning.

1. Ojima, K. Dan C., Nisiyama R., Ohtsuka S., Schupp W. Accelerated Extraction Treatment with Invisalig J Clin Orthod 2014 Aug;48(8):487-99.

2. Giancotti, A. and Di Girolamo, R.: Treatment of severe maxillary crowding using lnvisalign and fixed appliances, J. Clin. Orthod. 43:583-589, 2009.
3. Papadimitriou A, Mousoulea 5, Gkantidis N, Kloukos D. Clinicai effectiveness of invisalign®orthodontic treatment: A systematic review. Prog Orthod. 2078;79:37.

4. Simon et al.: Treatment outcome and efficacy of an aligner technique – regarding incisor torque, premolar derotation and molar distalization. BMC Oral Health 2014 14:68

5. Mays AI-Nadawia; Neal D. Kravitzb; lsmaeel Hansac; Laith Makkid; Donald J. Ferguson; Nikhilesh R. Vaid Effect of clear aligner wear protocol on the efficacy of tooth movement: A randomized clinical trial

6. The effect of gingival-margin design on the retention of thermoformed aligners” by Daniel P. Cowley, James Mah, and Brendan O’Toole
in the Journal of Clinical Orthodontics: JCO 11/2012; 46(11):697-702.

7. Elshazly, T. et al. Effect of Trimming Line Design and Edge Extension of Orthodontic Aligners on Force Transmission: An in vitro Study.
Journal of Dentistry (2022). doi: https://doi.org/10.1016/j.jdent.2022.104276 

 

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