For this column, I wanted to share the history and science of orthodontic retention, so I knew I had to reach out to Brian Gray, DDS, for my chat. He is a scholar in 3 academies and a postgraduate in the Academy of General Dentistry (AGD). At AGD, he was awarded the Lifetime Leadership and Service Recognition Award—less than 1% of dentists have received this award since its inception. Dr. Gray is chief dental officer at Candid, and when he took on that role, one of his goals was to develop the next generation of retainers. Candid is a dental company that provides CandidPro clear alignment solutions. Our discussion of the science of retention leads to an understanding of why the right materials and protocols are needed for lasting orthodontic results.
Lou Shuman (LS): Why did you start looking at a next-generation retention solution as an important part of the entire orthodontic process?
Brian Gray, DDS: In the past, when patients finished orthodontic treatment, they would take their retainer and return to their GP [GP] for their regular dental check-ups. If the patient was not adhering and noticed that a tooth was starting to recede, the general practitioner would usually send him back to the orthodontist. This extra appointment was just another inconvenience in their day, so often they let it slide and the teeth moved even more. Retention must be lifelong. But it must be based on science to produce lasting results. General practitioners now represent such an important part of alignment therapy that understanding retention has become an integral part of long-term patient care.
LS: How has conservation evolved over time?
BG: We want a retainer to act as a gentle reminder to keep the teeth in their final position after treatment. The real standard of care for a removable retainer has been the Hawley retainer—it has a long life unless lost or eaten by the dog—and can be adjusted in the event of a simple relapse. A Hawley maintains the position of the teeth because the combing of the acrylic on the lingual surface locks the teeth in place. But the problem is, when you wear this type of fixation, it’s like going back to high school. After patients have straightened their teeth with a clear aligner system, they don’t like wearing Hawley because it looks and feels weird.
LS: So, scientifically speaking, what makes a good retainer?
BG: An ideal retainer has 2 important components: It must fit very well and retain its shape. In other words, a clear plastic retainer needs to be precise and know where to stay. In the past, some doctors used the final aligner as a retainer. The plastic would fatigue very easily and then the teeth would start to move a bit in the retainer. If the plastic does not hold the teeth in place, they tend to move in a transverse direction, sideways. But the right retainer is a game changer.
Studies have shown that some first generation plastic aligners and retainers would begin to fatigue in as little as 1 week after being worn for 8 hour days. Based on this information, Candid began looking for a new, more reliable material. We saw improvement but still observed excessive fatigue with second generation materials. For effective maintenance, patients had to update their aligners approximately every 6 months. So we continued to analyze the data to deliver the best plastic retainer available. And we nailed it. We chose the latest transparent, stain-resistant Zendura FLX material because of how well it resists cracking and warping.
Candid performed rigorous stress analysis tests on plastic materials to see which would have the best memory and last the longest. We performed fatigue tests for strength, memory and stiffness. We then conducted a double-blind clinical trial to verify the best padding and thickness that patients found to be most comfortable.
LS: Why not use an aligner as a retainer?
BG: There is a big difference between pure alignments and retainers. Clear aligners are designed to move the teeth. Retainers are designed to prevent teeth from moving—to maintain a certain position. The fit must be very intimate with the teeth so that they have less opportunity to initiate movement under the plastic. A poorly made retainer will allow the teeth to drift or move, but a well-made retainer will hug the teeth and hold them in place.
Also keep in mind that a retainer will wear faster if the patient is a heavy grinder or bruxer. This causes the plastic to bend and not hold on the sides of the teeth as well.
It is important to know that a precision fitting retainer relies on 2 precision elements for success. First is the accuracy of the impression or scan. Second is the validity of the model used to thermoform the clean retainer. The scan, which gives us data on the position of the teeth, is converted into a compact lithographic model. When the models are made, they must be made with a high precision printer. We found the Carbon printers to be the best in this regard. Highly accurate models allow our thermoforming units to deliver the fidelity we were looking for when we started this mission.
The most important part is the type of plastic used to form over the model. The material must be in place [reach] in the interosseous spaces to help retain the teeth. Without it, the teeth will be allowed to move. When Candid created the next-generation holder design, we looked for these key things: the right material, the ability to capture the best data from the scan, and the highest print accuracy.
The next generation of retainers that Candid has just released is not gum-based, and that’s very important. It is designed to be supragingival, so it does not impinge on the soft tissue at all. But because it extends lower, the retainer can now leverage physics to grip more teeth and lock into the spaces between the teeth to prevent them from moving. And that helps prevent that cross-motion.
LS: What about rotary motion?
BG: Teeth actually relapse by wanting to return to their previous position. This has a lot to do with the periodontal ligament. Without further ado, there are 3 main theories of stem-based bone remodeling in orthodontic movement. Almost all of them are related to twisting relapse, which can happen because the round circular fibers act like a rubber band. [Before orthodontic treatment], the tooth is out of position, but the circular fibers are passive. Now we move the tooth, and even though it’s in an ideal position, these circular fibers are stretched and want to return to their original passive pre-rotated position. The longer the aligned tooth is held in its ideal position, the fibers begin to relax and become passive in their new position. This change happens over a long period of time, which is why adherence and the best retainer are so critical. This is also why Candid has spent so much research and development time to create a retainer that will allow the denture to remain in an ideal position.
LS: What does the future hold?
BG: The exciting part of working at Candid is their cutting edge technology [research and development team]. The company is fast, agile, and has a ton of game-changing innovations underway. The next 18 months will see great disruption and change in our incredible profession. Candid already has a sustain update coming in July, adding a few extra features. You must be a CandidPro provider to purchase retainers through the CandidPro website. But patients do not need to have undergone CandidPro alignment treatment to receive PermaForm retainers.
conclusion
The research and science that went into creating this next generation of condoms from CandidPro provide significant upgrades in fit, comfort and longevity. Patients spend a lot of time and money straightening their teeth, and Dr. Gray and Candid are determined to keep those teeth in place.
