Raman Aulakh outlines the clinical rationale, planning approach, and practical techniques that enable a more reliable extrusion of a single tooth using Invisalign.
The discussion builds on evidence-based methods and real-world experience and should serve both GDPs and orthodontists striving for a more predictable method for this movement with aligners.
Why extrusion remains a challenge
The concept of combining vertical and horizontal forces to guide extrusion more predictably was first introduced by Dr Jonathan Nicozisis (2010). He advocated for synchronising extrusion with retraction movements, using force direction to optimise aligner biomechanics – a foundational idea we now refer to as retract and extrude mechanics.
Aligners push – they don’t pull. This fundamental truth is why single tooth extrusion ranks among the least predictable aligner movements (Rossini et al, 2015). The challenge is biomechanical: when the aligner attempts to pull a tooth down, the plastic often slips over the incisal edge, generating unintended tipping or no movement at all (Upadhyay et al, 2022).
Strategies for success
A force-driven approach begins with understanding that clear aligners need help to express vertical movements. Here are the clinical tools that improve extrusion efficacy:
Attachment design
Extrusion cannot happen without appropriate grip. Bonding a vertical rectangular or optimized extrusion attachment creates an undercut for the aligner to push against (Simon et al, 2014). For incisors, gingivally bevelled horizontal attachments increase surface engagement and minimise aligner lift-off.
Relative extrusion through tipping
Relative extrusion refers to changing the vertical position of a tooth not by moving it straight down, but by tipping it so the incisal edge appears lower. This movement is easier for aligners to express and more predictable method than attempting a pure vertical movement (Haouili et al, 2020).
Plan overcorrections
Due to low tracking rates, digital setups should include over-engineering. For instance, if 1mm of extrusion is required, consider planning 1.5-2mm. This ensures that even if movement under-expresses, the clinical outcome still meets the goal.
Extrusion with retraction
A powerful biomechanical concept is combining extrusion with slight lingual. This creates a diagonal vector that allows the aligner to push the tooth downward as it retracts – improving aligner engagement and vertical movement efficiency. I refer to this as retract and extrude mechanics.
Auxiliary support for stubborn cases
When attachments and over-engineering fails or is insufficient, auxiliaries like elastics can provide a direct vertical force. Buttons on the tooth with elastics to a cutout or opposing attachment offer the missing pull. In severe discrepancies, sectional braces or TAD-supported mechanics may be justified.
Case example: biomechanical application in practice
This 30-year-old male wished to align the UL3 to improve the aesthetics of his smile and function. The initial, predicted and actual outcomes are shown in Figure 1.
In Figures 2a, 2b and 2c, we can see planning of the ClinCheck, every movement was designed with control to achieve the planned movement shown in red:
- Create visible space between to teeth during alignment so there is no interproximal binding and serves as our start position of extrusion as we can see in Figure 2a
- Procline tooth (as shown by the green arrow in Figure 2b) to create a position that will allow for a push surface with the bevelled horizontal attachment
- Use equal amounts of extrusion for each increment of retraction. The resultant is the push vector of the slope (as shown in the blue arrow in Figure 2c)
- Attachment design: position in lower incisal third to maximise the gingival bevel attachment with aligner interface.
- Elastics optional lingual then buccal to aid the planned movements.
Final thoughts
Clear aligners have come a long way, but vertical control remains a frontier requiring respect for biomechanics. Predictable extrusion isn’t a software trick – it’s a treatment modality. Force-driven planning using retract and extrude mechanics, precise attachment selection, and proactive staging transforms extrusion from unreliable to routine.
To learn more about achieving this level of clinical precision and predictability, consider enrolling in the Postgraduate Diploma in Clear Aligner Therapy, where we dive deeply into force systems, advanced ClinCheck planning, and complex biomechanics.
References
- Boyd, R (2017). Clinical advances in Invisalign aligner technology. J World Federation of Orthodontists, 6(2), 81-89.
- Haouili, N, Kravitz, ND, Vaid, NR, Ferguson, D.J. and Makki, L., (2020). Has Invisalign improved? A prospective follow-up study on the efficacy of tooth movement with Invisalign. American Journal of Orthodontics and Dentofacial Orthopedics, 158(3), pp.420-425.
- Nicozisis, JL, (2010). Invisalign case report: anterior crossbite correction and extrusion mechanics. Orthotown Magazine, October 2010.
- Rossini, G, Parrini, S, Castroflorio, T, Deregibus, A and Debernardi, CL, (2015). Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. The Angle Orthodontist, 85(5), pp.881-889.
- Simon, M, Keilig, L, Schwarze, J, Jung, BA and Bourauel, C, (2014). Treatment outcome and efficacy of an aligner technique – regarding incisor torque, premolar derotation and molar distalization. BMC Oral Health, 14(1), pp.1-9.
- Upadhyay, M, Yadav, S, Neela, PK and Nanda, R, (2022). Biomechanics of clear aligner therapy: is there a standard protocol? Journal of Clinical Orthodontics, 56(5), pp.259-269.
This article is sponsored by the Aligner Dental Academy.
