Open coil springs and closed coil springs are two common orthodontic auxiliaries used to move teeth in different ways. Although they may look similar, they perform opposite functions.
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✅ Introduction
Orthodontic treatment often requires more than brackets and wires. Small accessories such as coil springs provide controlled forces that improve tooth movement.
The two main types are:
▪️ Open coil springs
▪️ Closed coil springs
Both are placed on orthodontic archwires, but they have different designs, indications, and biomechanical effects.
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What is an Open Coil Spring?
An open coil spring is a compressed spring placed between two brackets. When compressed, it pushes adjacent teeth away from each other.
Main Purpose
To create or maintain space between teeth.
Common Clinical Uses
▪️ Creating space for impacted or crowded teeth
▪️ Opening space before implant placement
▪️ Making room for prosthetic restorations
▪️ Correcting mild crowding
▪️ Preparing space for erupting canines
Advantages
▪️ Produces continuous and gentle force
▪️ Creates predictable space
▪️ Simple to place and adjust
▪️ Works with most fixed orthodontic appliances
Limitations
▪️ Requires sufficient anchorage.
▪️ Space creation may be slower in dense bone.
▪️ Improper activation can produce unwanted tooth movement.
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What is a Closed Coil Spring?
A closed coil spring has loops or eyelets at both ends. Instead of pushing, it stretches between two attachment points and continuously pulls teeth toward each other.
Main Purpose
To close existing spaces between teeth.
Common Clinical Uses
▪️ Closing extraction spaces
▪️ Retracting anterior teeth
▪️ Maintaining constant traction
▪️ Space closure after orthodontic alignment
Advantages
▪️ Delivers continuous force over long distances
▪️ Requires fewer reactivations
▪️ Efficient for controlled space closure
▪️ Can be used with elastomeric or metal ligatures
Limitations
▪️ Anchorage control is essential.
▪️ Force levels should be monitored.
▪️ Excessive tension may slow efficient tooth movement.
✅ Key Differences
| Feature | Open Coil Spring | Closed Coil Spring |
|---|---|---|
| Primary Action | Pushes teeth apart | Pulls teeth together |
| Main Goal | Create space | Close space |
| Activation | Compression | Stretching |
| Direction of Force | Outward | Inward |
| Typical Indication | Crowding, impacted teeth | Extraction space closure |
| Design | Open spiral | Closed spiral with loops |
| Force Delivery | Expansive | Contractile |
Neither spring is better than the other. The correct choice depends entirely on the treatment objective.
▪️ If space needs to be created, an open coil spring is indicated.
▪️ If spaces need to be closed, a closed coil spring is the appropriate option.
Both appliances are highly effective when properly selected and activated according to the patient's orthodontic treatment plan.
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Modern orthodontics emphasizes light, continuous forces because they promote more efficient tooth movement while reducing discomfort and minimizing undesirable biological effects. Both open and closed coil springs are designed to provide these controlled forces. Advances in nickel-titanium (NiTi) alloys have further improved their performance by offering greater elasticity and a more consistent force over time compared with traditional stainless steel springs. Proper diagnosis, anchorage management, and regular follow-up remain essential for achieving predictable clinical outcomes.
✍️ Conclusion
Open coil springs and closed coil springs serve opposite but complementary roles in orthodontic treatment. Open coil springs create space by pushing teeth apart, whereas closed coil springs close spaces by pulling teeth together. Selecting the correct spring depends on the desired tooth movement, anchorage requirements, and overall treatment goals. When used appropriately, both appliances provide predictable, efficient, and biologically sound orthodontic tooth movement.
📚 References
✔ Burstone, C. J., & Koenig, H. A. (1976). Optimizing anterior and canine retraction. American Journal of Orthodontics, 70(1), 1–19.
✔ Graber, L. W., Vanarsdall, R. L., Vig, K. W. L., & Huang, G. J. (2023). Orthodontics: Current principles and techniques (7th ed.). Elsevier.
✔ Proffit, W. R., Fields, H. W., Larson, B. E., & Sarver, D. M. (2023). Contemporary Orthodontics (7th ed.). Elsevier.
✔ Thurow, R. C. (1982). Edgewise Orthodontics (4th ed.). Mosby.
✔ Uribe, F., & Nanda, R. (2015). Biomechanics in Orthodontics: Principles and Practice. Quintessence Publishing.
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