Introduction
Clear aligners are a relatively new innovation in orthodontic treatment that only became commercially available in the late 1990s. Since then, clear aligners have rapidly gained popularity as an aesthetic and comfortable alternative to traditional braces made of metal wires and brackets.
Clear aligners are custom-made, clear plastic trays that fit over the teeth. They gradually move the teeth into proper alignment through sustained pressure. Each set of aligners is worn for 1-2 weeks before being replaced by the next set in the series, slowly moving the teeth incrementally with each tray. On average, treatment involves 10-20 sets of aligners over 3-6 months, but may comfortably treat cases significantly longer.
Compared to braces, clear aligners offer several key benefits:
Aesthetics - Clear aligners are practically invisible, allowing the patient to smile confidently during treatment. Braces are more noticeable with metal wires and brackets.
Removability - Aligners can be removed for eating, brushing, and special occasions, providing convenience and comfort. Braces remain fixed to the teeth 24/7.
Less irritation - Aligners are smooth plastic with no brackets or wires that could rub inside the mouth. This causes less irritation to the cheeks and gums.
Oral hygiene - Aligners are easy to remove for proper brushing and flossing. With braces, brushing and flossing must be done carefully around the brackets.
Shorter treatment times - Some cases, especially minor misalignments, can be treated faster with clear aligners than braces.
No emergencies - There are no broken wires or brackets associated with aligners that require orthodontic emergencies. If an aligner breaks or is lost, pt can wear previous aligner while that specific aligner is sent again.
Overall, clear aligners offer an attractive alternative to traditional braces using customized aligners that gradually move teeth into place. Their advantages in aesthetics, comfort, and convenience have fuelled their surging popularity.
Materials Used
Clear aligners are made from transparent thermoplastic materials that are durable yet soft enough to gently move teeth. The exact materials used can vary between different aligner brands, but they typically use a type of polyurethane plastic. Some of the key properties that make these plastics effective include:
Biocompatibility - The materials are non-toxic and do not cause adverse reactions in the oral environment. This allows for safe long-term wear.
Transparency - The clear plastic is aesthetically pleasing and discreet compared to traditional metal braces. The aligners can be removed for eating, brushing, and special occasions.
Thermoplasticity - The plastics soften when heated, allowing them to conform precisely to each patient's unique tooth morphology. The custom-fit design is enabled by vacuum molding production techniques.
Elasticity - Even after cooling and hardening, the plastics still demonstrate elasticity and flexibility. This allows gentle constant pressure to be applied to the teeth for gradual realignment.
Durability - The materials are resistant to staining, fractures, and damage from oral conditions. This allows for long-term wear and sustained force delivery.
Thin yet stiff - The optimal balance of thinness for comfort yet stiffness for tooth movement. The plastic must be rigid enough to actually move teeth rooted in bone without being too bulky.
The combination of transparency, custom-fit by thermoforming, flexibility, durability, and optimised stiffness makes polyurethane plastics well-suited for orthodontic tooth movement using clear aligner technology. The materials have been refined over decades to enable effective and convenient teeth straightening.
Custom-Fit Process
One of the key benefits of clear aligners is that each set is custom-fitted to the patient's teeth. This is accomplished through the following digital process:
Digital scan of teeth - Instead of taking traditional impressions, the orthodontist takes a 3D scan of the patient's teeth. This is done using an intraoral scanner, which is a handheld wand that captures precise digital images of the teeth and gums. The scan takes only minutes and is more comfortable for patients than having a tray of impression material held in their mouth.
Computer modelling of tooth movements - The digital scan is then sent to the clear aligner company, where specialised software models how the teeth will sequentially move over time. The orthodontist reviews this treatment plan and makes any necessary modifications. Adjustments can be made to the position of each tooth in millimetre increments.
3D printing of moulds - Once the treatment plan is approved, a series of customised moulds are 3D printed. Each mould corresponds to an exact stage of teeth straightening. These moulds are used to thermoform the clear plastic aligners. The result is a series of clear aligners tailored to the patient's teeth and treatment goals.
The custom-fit process enables clear aligners to move teeth in a gradual, controlled manner to the desired final position. The precision and personalisation of clear aligners are made possible by innovative digital scanning and 3D printing technology. This allows for a comfortable and customised treatment experience.
Please note conventional PVS impressions can still be sent to labs but will increase processing times!
Sequential Alignment
Clear aligners work through a process of sequential alignment to gradually move teeth into their desired positions. Patients are provided with a series of custom-fit clear plastic aligners that are worn in a predetermined sequence. Each aligner applies carefully calibrated forces to the teeth for 1-2 weeks before being replaced by the next aligner in the series.
The aligners are programmed and customised to move the teeth incrementally, usually between 0.25mm to 0.33mm per aligner. However, the exact amount of programmed tooth movement varies depending on the types of tooth movements required and the clinical needs of the patient. At the beginning of treatment, the aligners may be changed more frequently such as every week.
The sequential series of aligners slowly move the teeth in small increments over a period of several months or longer, depending on the extent of realignment needed. This gradual process allows the teeth and bone to adjust to the changes comfortably and safely. The clear aligner therapy relies on patient compliance in wearing the aligners for the prescribed 22 hours a day to achieve the programmed tooth movements. With each new set of aligners, the teeth will have moved slightly closer to the desired final position.
Attachments
Attachments are small tooth-coloured bumps that are bonded to the teeth during Proligner treatment. They serve multiple important purposes:
a. Purpose of Attachments
Attachments help the aligners grip the teeth in order to apply the forces needed to move them. Certain tooth movements like rotation require the aligner to have something to "grab onto" so it can rotate the tooth.
Attachments are also used to help anchor teeth so other teeth can be moved. For example, attachments may be placed on molars to anchor them in place while front teeth are being moved.
In some cases attachments can help distribute the forces from the aligner more evenly across the tooth's surface.
They can also act as reference points or guides to help seat the aligner in place.
b. Types of Attachments
There are several types of attachment shapes that can be used:
Rectangular or square attachments provide the most surface area for grip and control. They are commonly used for rotations or extrusion movements.
Elliptical or oval attachments are rounded and smooth. They can be useful for movements that require lighter forces.
Vertical or horizontal attachments are longer in one dimension and can help tip or torque teeth.
Attachments can also be cut at an angle or be contoured to the shape of the tooth.
c. Placement on Teeth
Attachments are strategically placed on certain teeth where extra forces or control are needed. Common placement includes:
The front and back of canines for anchorage and rotations.
The edges of incisors when torquing or extruding front teeth.
Premolars and molars when intruding or extruding back teeth.
The number, shape and location of attachments is customised based on the patient's unique treatment plan. More complex tooth movements generally require more attachments. Overall attachments help enable the controlled, incremental movement delivered by clear aligners.
d. Movement Forces
Aligners move teeth through the application of light, constant forces. This is quite different from traditional braces, which apply heavy intermittent forces through wires and brackets.
With clear aligners, precise force calculations are done by the treatment software for each planned tooth movement. The forces generated by the aligners are gentle but persistent, allowing teeth to move gradually into their desired positions.
The software calculates the exact thickness required for each aligner to produce an ideal amount of force - not too heavy as to cause tissue damage or root resorption, and not too light as to stall movement. The forces are distributed evenly across all the teeth, rather than concentrated on individual brackets like with braces.
Each set of aligners is programmed to move teeth a small distance, typically between 0.25mm to 0.33mm. To achieve larger movements, new aligners are used in sequence, with each applying fresh forces to continue shifting teeth incrementally.
By using a series of custom-fabricated aligners and controlled constant forces, clear aligner treatment is able to move teeth efficiently while being relatively comfortable and gentle on tissues. The physics behind the forces are carefully calculated and managed digitally for safe, predictable orthodontic tooth movement.
e. Auxillaries
Power ridges are indented shapes placed near the gumline to give added root control.
Elastics for difficult extrusion or intrusion movements, bite corrections and complex rotations.
Tads for additional anchorage.
Types of Tooth Movements
Clear aligners can produce several types of tooth movements to gradually reposition teeth into proper alignment. The main types of movements include:
Tipping - Tipping teeth forward or backward by applying pressure against the crown. This is the easiest movement for clear aligners.
Torquing - Rotating teeth along their long axis to correct proper angulation and inclination. Attachments are often used to improve torque control.
Rotation - Turning a tooth clockwise or counter-clockwise around its centre axis. Aligners grip the sides of a tooth to slowly rotate into position.
Translation movement – Bodily movement of the entire tooth forward, back, sideways or vertically into position. Requires tight aligner fit for proper control.
Intrusion and extrusion - Moving teeth up into the bone or downward out of the bone. Challenging movements that may require attachments, elastics or more stages.
a. Limitations
While capable of producing a variety of tooth movements, clear aligners do have some limitations compared to braces:
Less ability to control root torque or rotation of rounded teeth
Difficulty achieving large vertical movements of teeth
May require attachments, elastics or additional aligners for challenging movements
Depends on patient compliance with 22 hour daily aligner wear
Proper case selection and realistic treatment planning help ensure clear aligners can achieve the desired tooth movements for each patient. But orthodontists need to understand the limitations and account for difficult movements during treatment planning.
b. Treatment Times
Clear aligner treatment times can vary greatly depending on the severity of the case and how well the patient complies with the recommended wear times. On average, treatment with clear aligners takes around 6-12 months for adults, but can be longer or shorter than this depending on several factors.
c. Average Length of Treatment
For adults with simple or mild to moderate malocclusion cases where teeth only need to be moved a small amount, treatment can take as little as 6-9 months. However, more complex cases involving significant tooth movements or bite corrections may take 18-24 months.
Teens and kids usually complete their treatment faster than adults since their teeth tend to move quicker. However, their treatment times are also dependent on the case complexity and compliance.
d. Factors Affecting Treatment Duration
Some of the key factors that determine how long clear aligner treatment will take include:
Case complexity - Simple, mild crowding or spacing cases take less time than severe crowding, underbites, or large gaps which require more movements.
Amount of movement needed - If teeth only need to be moved a millimetre or two, it takes less time than several millimetres of movement.
Patient compliance - Wearing aligners for the prescribed hours per day and not missing any aligners.
Bone density - Younger patients with less dense bones respond faster than mature adults.
Tooth roots - Shorter roots allow faster movement than long established roots.
Metabolic factors - Some studies show hormones like oestrogen can affect speed of movement.
Attachment issues - If attachments fall off it can prolong treatment.
Mid-course corrections - If further refinements are needed it adds time.
So, while most adults complete clear aligner treatment within 12-18 months, there are many variables that can shorten or lengthen the timeframe. Regular aligner changes and sticking to proper wear protocol helps ensure the shortest and most efficient treatment time possible.
Retention
Retention is a critical part of orthodontic treatment with clear aligners. After the teeth have been moved into their ideal positions, they have a tendency to relapse back towards their original positions. This is why retainers are necessary to hold the teeth in their new alignment.
There are two main types of retainers used after clear aligner treatment.
The first is a removable plastic retainer that is custom-made to fit the teeth. This type of retainer is similar to the clear aligner trays worn during treatment, but is thicker and sturdier. Patients are instructed to wear the removable retainers full-time for the first 6 months after treatment, then transition to night-time wear. Wearing the retainers at night prevents teeth from shifting back while sleeping. Removable retainers are typically worn at night for at least a year after treatment, and often indefinitely.
The second type of retainer is a fixed wire retainer. This consists of a thin wire that is bonded to the back of the front 6 teeth. The wire keeps the front teeth from shifting, while allowing the back teeth to settle. Fixed retainers are convenient since they don't require compliance from the patient. However, they do limit access for cleaning between the teeth. Fixed retainers are commonly kept in place for 1-3 years after clear aligner therapy.
Proper retention is imperative to prevent relapse after clear aligners. Both removable and fixed retainers play important roles in retaining the results of treatment long-term. Patients should closely follow their orthodontist's recommendations regarding retainer use to protect their investment in a beautiful smile.
Conclusion
Clear aligners are an excellent alternative to traditional braces for straightening teeth that utilise a series of custom-fit, clear plastic aligners to incrementally move teeth into position over time. The aligners are fabricated using 3D modelling based on the intended treatment plan, ensuring precise control over the direction and amount of force applied to each tooth.
The aligners are worn in a sequence, each applying light, constant pressure to gradually shift the teeth into alignment. The technology allows for highly customised treatments tailored to each patient's unique teeth and goals. Attachments bonded to the teeth provide anchors for the aligners to grip and apply targeted forces.
Compared to braces, clear aligners offer advantages like enhanced comfort, easier hygiene and diet, and aesthetics. Aligners are removable, resulting in fewer lifestyle interruptions and less irritation of oral tissue. Continued innovation in aligner materials and 3D modelling will open up new capabilities, with shorter treatment times on the horizon.
Overall, clear aligners represent an excellent system for realigning teeth efficiently and discreetly. When paired with advanced digital treatment planning, aligners provide an innovative alternative to accomplish many orthodontic goals. Patients can transform their smiles with the convenience and flexibility of this modern approach to teeth straightening.
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