Once the patient has used their last aligner, we have hopefully achieved ideal occlusion and function. Just like the patient has a beautiful smile.
As the oral environment is a very dynamic environment. Now comes the challenge of keeping the teeth in their current position.
In this blog post we take a deep dive into retention after clear aligner treatment. Both bonded and removable retention will be addressed.
Biological challenges
From the delivery of the last aligner an onwards, the struggle against human nature begins: to keep stable something that is, in essence, unstable.
No matter how well we have carried out the orthodontic treatment, no matter how well all the teeth are properly positioned in relation to their bony bases and the occlusal contacts are balanced, in 99% of our patients the teeth will have a greater or lesser tendency to return to their initial situation.
To counteract this effect, we will place retainers which, supposedly, will prevent the undesired movements and will help us to maintain the results of the treatment in the medium to long term.
Golden standard.... or?
There is no consensus with supporting scientific evidence on the ideal retention protocol. Different types of fixed and removable retainers have been suggested, with different materials and protocols for use, but there is a lack of evidence on the superiority of a particular retention protocol for stability after orthodontic treatment.
Of course, the retention protocol will not be the same for all patients, it will be adapted to the initial malocclusion, the type of movements performed during treatment and the functional components that may affect the relapse of the case. We can classify the retentions used in orthodontics into two main categories: Fixed and removable.
Fixed retainers:
These are characterised by the fact that they do not depend on the patient's compliance, as they are cemented to the lingual surface of the anterior teeth (most commonly from canine to canine in the maxilla and from first premolar to first premolar in the mandible) and, if they are well cared for and there have been no major changes in the bicanine width or deleterious habits that could affect the position of the teeth, they are a good long-term retention strategy.
However, even if these conditions are present in the patient, fixed retainers can give rise to a series of complications that I will describe below.
Example of a case that has relapsed despite fixed retainers.
Complications with fixed retainers
As mentioned, fixed retainers, in addition to having a limited action, can cause numerous complications, such as:
Partial or total dislodgement
Unwanted tooth movement
Torque changes
Fenestrations
Dehiscence
Recession.
These problems can have a detrimental effect on the patient's periodontal health, especially in the lower canines. The wire we use for fixed retention will also favour the appearance of these complications if we do not follow the proper guidelines for its placement.
Choice of material
Braided wires are most commonly used as fixed retainers. However, the braids of which these wires are made will tend to unscrew over time. This unscrewing will occur slowly, moving the anterior teeth over the years. To avoid this problem, make sure you buy "passive" wires or, if you buy traditional braided wires, make them passive by burning the retainer with a blowtorch before fitting. In this way, the braided structure will remain stable in the long term.
Increase your clinical confidence with complimentary case selection and expert treatment planning support. Within 24 hours an expert dentist will send you an indexation of whether your case i easy, moderate, complex or should be referred to an orthodontist. Try it out today - click the button and follow the instructions.
Retainers made of braided wires should always be fitted to a model (Stone or printed resin model) and transferred to the mouth. If the braided wires are bend into position in the mouth of the patient there is an increased risk of activating the retainer material.
Even if the fixed retainers are placed correctly, they may not be sufficient to keep the teeth in position. It is relatively common to see patients who come for a re-treatment because their teeth have moved but they still have fixed retainers in their mouth, both those treated with brackets and those treated with aligners.
For this reason, if we reinforce the fixed retention with removable retention, we will be giving the patient a double guarantee. The challenge with a double retention like this is, that if we use an aligner. The aligner will typically wear the composite on the bonded retainer faster as it slides over the retainer every day.
Alternative retainer materials
Challenges associated with retainers made of braided wires have led to the evolution of alternative materials. This shift appears to be a response to the needs of general practitioners who may lack the knowledge and experience required to work with the traditional materials that have been used for decades.
Chain material
One of the more popular alternatives to the braided wire solution is a chain like material. It is rather easy to work with and place in a way that make it seem to be inactive. However the material is flexible in all areas not covered with composite. Which enables the teeth to move. We suspect that a deboning of such a retainer will result in a potential worse relapse compared to a stiffer material. In addition the chain materials are even more unhygienic than the braided wires (which we dislike for the same reason).
Glass fiber reinforced composite retainer materials
An easy and seemingly more hygienic solution (initially) could be the resin infiltrated glass fiber sticks that can be bonded directly to the teeth. They can be bend into the desired position. When cured they keep the shape they have been bend into. Initially this seems like an ideal material. However theses solutions tend to break after 1-2 years.
3D printed titanium wires
In recent years solutions with 3D printed titanium wires have become popular. The advantages are clear: A 3D printed wire mounted in a transfer jig will be completely passive… as long as the wire is not bend by accident.
The downside however is, that the titanium wires seem to be too brittle and as a consequence seem to break after 2-3 years.
Sign up for the blog and gain more knowledge, tips & tricks about clear aligner treatments.
We post 1-2 times a month free of charge.
3D printed CoCr retainers
We are aware of an alternative 3D printed wire made in CoCr. Theoretically this is a more interesting material as it has already been used with great success in dentistry for 100+ years. In addition it is strong and is somewhat flexible compared to titanium. Whether this is a success or not must rely on studies testing the product.
Removable retainers
Another option that exists, if we want to avoid complications with fixed retainers, is not to place them and use only removable retainers.
One advantage over fixed retainers is their ability to maintain the position of all teeth, both anterior and posterior, along with the arch form, a factor to be taken into account in cases with a lot of expansion.
This solution is practical and the most hygienic of all, but we depend entirely on the patient's cooperation. Moreover they can be lost or damaged.
However this is an inappropriate solution in cases with teeth that have been rotated (depending on the type of tooth and the amount of rotation) as the tooth can potentially rotate within the shape of the removable aligner - unless it is a bite appliance that has been relined directly in the mouth….
Vacuum formed plastic retainers.
There are several different options. Among the most popular and sturdy are the aligners.
The clear aligner retainers are easy for the patients to adapt to as they are used to wear them. In addition the aligner will guide the teeth into the desired end position and keep the teeth there.
It is also possible to use the clear aligner retainers in both arches and at the same time.
A drawback is the sturdiness of the material. Over time the aligner material is being deformed and thus can't prevent a little relapse to happen. Especially expansions may be challenged in this regard. This means the patient has to invest in new aligner retainers once or more every single year.
Depending on the clinical situation the clear aligner may have a hard time retaining rotated or extruded and intruded teeth in place.
Hawley and Hawley like retainers
This retainer is by far the most frequently used retainer. It consists of clasps on molars and a short labial round bow extending from canine to canine having adjustment loops.
The advantage of all the Hawley like retainers is that they let the teeth settle within the frame of the acrylic plate in the palate. The acrylic plate prevents any expansion from collapsing and is really durable. In combination with a bonded retainer in the maxilla, this retainer is really good at controlling the posterior setteling. Especially in treatments involving posterior expansion.
Jensen retainer
Is a Danish variety of the Hawley retainer. Here the short labial round bow has no adjustment loops and is made of a square metal bow. This is in an attempt to control the position of the anterior teeth better.
Begg's retainer
Consists of a labial round wire that extends all the way to the last erupted molar and curves around it to get embeded in acrylic that spans the palate.
Advantage: There is no
cross over wire that extends between the canine and premolar thereby eliminating the risk of space opening.
Disadvantage: The long span of the wire makes it difficult to control the exact position of the wire. Especially if the patient (easily) displaces or bends the wire by accident.
Acrylic splints
As with all the other retainers, bite splints come in numerous varieties.
The acrylic splints have a long durability and if it is an appliance that has been relined directly in the mouth of the patient, it will fit 100% passively enabling the patient to wear the same retainer for years.
These retainers are especially useful in the maxillary arch in ortho-restorative cases - after a setteling period as the splint will not allow any settling of the maxillary teeth and only limited settling of the mandibular teeth.
My personal favourite is the Tanner appliance relined directly in the mouth (Please do not try to utilise this kind of appliance without propper training!). Unlike the lab fabricated and 3D printet splints, the Tanner appliance works with 100% passive retention. In addition it can be made so thin, that it can be worn 24 hours a day... if needed. It is a very comfortable form of appliance. However it is hard to master from a technical perspective.
Biologic control - A bold holistic approach.....
Some doctors with a deep understanding of functional occlusion claim, that they are able to keep the patients teeth in a stable position lifelong as long as the occlusion is perfectly equilibrated and the teeth have been position in the neutral zone in the muscular envelope (Between the lips, cheeks and tongue).
As a restorative dentist having worked intensively with functional occlusion for 12+ years myself. I would not dare to think I was close to understanding nor able to control all the biologic, physical, chemical and psychological elements affecting the balance of the oral cavity. I may not be as intelligent and knowledgable as those colleagues stating they have control. I just would not dare to rely on this concept myself.
Retention after clear aligner treatment
It seems that there is no perfect retention... what is your preferred protocol? And why?
If you want more tips for your clear aligner workflow, sign up for the blog and get notified when we publish new posts.
It's easy - just press the button and follow the instructions.
Kind regards
Jesper Hatt DDSInternational key opinion leader for 9 years on CBCT and digital workflows for KaVo
Phone: +41 78 268 0078
AlignerService helps dentists create realistic, safe and predictable treatment plans with clear aligners.
Currently, we help approximately 1500 dental practices in 19 different countries. AlignerService is a preferred partner of ClearCorrect.
In addition AlignerService clear aligner experts work with Invisalign, SureSmile and Spark.
Σχόλια