GAP Magazine Clear Idea Volume 5

12 www.acasociety.com | info@acasociety.com T oday, I have been given the difficult task of making retention sound interesting…or at least interesting enough that members will read enough of this article to take something from it. You see, dentistry is quick and exciting. A patient comes in with a chipped tooth and they can typically leave our chair with a semi-reasonable result within thirty minutes. A patient can’t sleep at night due to irreversible pulpitis and we can generally get them out of pain either by extirpating or extracting within one appointment. Orthodontics on the other hand is one of the slowest treatments in dentistry. So, for the average clinician, orthodontics is boring. And what is slower and more boring than teeth moving? Teeth NOT moving. But retention is just as important, if not more important, as active tooth movement. Steven Covey famously said that you must always begin with the end in mind. That is definitely true with retention. Firstly, your final tooth positioning must respect the principles of retention (more on this soon). And secondly, if a patient is not committed to long term retention, then they shouldn’t really be undergoing active movement. In fact, a large proportion of adult patients that we see in a general practice who are interested in aligners typically had orthodontics when younger and for one reason or another have stopped wearing their retainer and started to experience relapse. Let’s look briefly into principles of retention: According to Proffit’s textbook “Although a number of factors can be cited as influencing long-term results, orthodontic treatment results are potentially unstable and therefore retention is necessary for three major reasons: 1. the gingival and periodontal tissues are affected by orthodontic tooth movement and require time for reorganization when the appliances are removed; 2. the teeth may be in an inherently unstable position after the treatment, so that soft tissue pressures constantly produce a relapse tendency; and 3. changes produced by growth may alter the orthodontic treatment result. If the teeth are not in an inherently unstable position, and if there is no further growth, retention still is vitally important until gingival and periodontal reorganization is completed. If the teeth are unstable, as often is the case following significant arch expansion, gradual withdrawal of orthodontic appliances is of no value. The only possibilities are accepting relapse or using permanent retention.” In other words, tooth position is in a constant equilibrium between gingival and periodontal tissue forces, facial muscle forces, tongue forces, occlusal forces, skeletal changes as well as external forces. Any change to the above equilibrium can and generally will cases tooth movement to occur. Other principles of retention include: • The greater the tooth movement, the greater the likelihood and amount of relapse • Teeth will generally relapse in the same direction as their original position prior to movement • Changes to the lower intercanine width has been shown to be very unstable in the literature • Rotations are particularly unstable, especially for conical rooted teeth • Dental buccal expansion in non- growing adults requires lifelong retention Of course, each different treatment has its own principles in retention – ie retention for anterior openbite cases is different to retention for deep bite cases which is different to class III cases which is different to diastema cases and so on (these are beyond the scope of this article, but will be discussed in another edition of Clear Idea in the future). So, what do we do? Black and white rules for something that isn’t black and white is never a great idea. Retention for each case has to assessed and managed individually, and best to be assessed before active treatment as to minimise moving teeth into an “unstable” position. In saying that, a good starting point for retention is using thermoplastic retainers for 3-6 months full time after active movement has finished – and then wearing the retainer ongoing at night (for a great recent paper from excellent Australian orthodontists discussing retainer material – see Comparative assessment of two thermoplastic retainer materials using different wear regimes: a randomised controlled clinical trial by Cunning et al). A fixed retainer is best considered when: • There has been significant anterior tooth movement • Diastema closure • Maintenance of pontic or implant space Remember, you can always get the best of both worlds by having a fixed retainer and a removable retainer on top of it. Simply organise for the fixed retainer, place it, then take an impression/scan on top of it and the retainer will be made to accommodate the wire. Some clinicians have mentioned to me before that they find talking about retention awkward to patients and that discussing lifelong retention may cause patients not to go ahead with treatment. I don’t have all the answers to this, but two things I normally say to my patients are: 1. A (thermoplastic) retainer actually has three great benefits a. Keeps teeth in position b. Stops you from wearing out your teeth at night if you do any night time grinding c. Can comfortably act as your whitening trays 2. “You don’t have to wear your retainer for life, you just have to wear it for as long as you want to keep your teeth Retention George Abdelmalek By Dr George Abdelmalek