 So today's topic of discussion is retention and relapse. Stability of orthodontic treatment outcome has been a topic of great interest because maintaining teeth in their corrected positions after treatment is often the most challenging part of an orthodontic treatment plan. Usually the corrected teeth tends to move back towards the original maleplusion. So this is called relapse. And relapse could be considered as any unfavorable change in tooth position after orthodontic treatment away from a corrected maleplusion. To prevent relapse we have to plan certain retention protocols. So retention and potential for relapse must form a key part of the orthodontic treatment plan. So I will be focusing mainly on the definition of relapse and retention, courses of orthodontic relapse, schools of retention, theorems of retention, six keys for lower retention and different types of retainers and some adjunctive procedures to aid in retention. So before going into the details of the retention and schools of retention and theorems of retention, let's see what is relapse. So according to Moyers, relapse is the loss of any correction achieved by orthodontic treatment. In low-stated, relapse is a histogenic and morphogenic response to some anatomical and functional violation of an existing state of anatomical and functional balance. According to Whitster, slipping back or falling back into form of bad state that is called relapse. So simply put, relapse is a rebound movement in which teeth recoil back somewhere close to their original positions. So to avoid any kind of relapse tendency, we plan retention protocols early in the treatment planning itself to halt the tooth and the corrected position for a longer period of time. And retention, it can be defined as the phase of orthodontic treatment which maintains the teeth in their orthodontically corrected positions following the cessation of active orthodontic tooth movement. For that, you can use various retention appliances called retainers that are different types of retainers like removable, fixed and aesthetic retainers. Also there are certain adjunctive procedures which will enhance the post-treatment stability. All these things will be discussed in detail later. Moving on, let's see what are the causes of relapse. Relapse basically compromises the post-treatment stability and there are several destabilizing factors which leads to relapse. To retain, categorize these destabilizing factors into four, they are soft tissue factors, supporting tissue factors, occlusion factors and facial growth and occlusion development. First one is the soft tissue factors. As we already discussed in the Muscular School of Thorn, there should be a balance between the intraoral and extrooral musculatures surrounding the jaws and teeth. If any abnormal muscular function or active soft tissue pressures will result in an abnormal skeletal configuration as well as dendroalveolar relationship. So for long-term stability, you should end up with a harmonious muscle function with passive soft tissue pressures. So next one is the forces from supporting tissues. Teeth are supported by alveolar bone, pyridontium and gingiva. So they are the supporting tissues. So they consist of several fibres such as pedontal fibres and gingival fibres. So when we move teeth, applying orthodontic force, not only the tooth moves but also the supporting structures such as the bone, pyridontal fibres and gingival fibres gets remodeled. And these structures require a certain period of time to adapt and reorganize within the new position. Otherwise, the stretch of these fibres can tend to move the teeth back to its original position. So to avoid this, we need to consider the time period required for them to reorganize. As you can see on the screen, the principal fibres of pyridontal ligaments require 83 days for reorganization and collagenous fibres of the gingiva require 147 days for reorganization and elastic fibres of the gingiva that is the supracrystall fibres. They require around 232 days for reorganization. So they are known to have the longest amount of time to reorganize. And alveolar bone, it takes 5 to 6 months for reorganization. So the important point to be noted here is that in case of severe derotated tooth, severely derotated tooth, the supracrystall gingival fibres are severely stretched. And after derotating the teeth, you have to use a long retention since these crystal gingival fibres are known to take the longest amount of time to reorganize. So the third one is the occlusion factors. It includes proper intercost patient, tooth size, arch length relationship, normal inclination and angulation of individual tooth and all these concerned occlusion factors. So if you are ended up with a proper, ended up the treatment with a proper occlusion with perfect intercost patient, near ideal or normal inclination and angulation of individual tooth without any societal, vertical or transverse discrepancies and with harmonious, tooth size, arch length relationship, you will not face much retention problems and post-treatment stability will be much better. Last category is the facial growth, especially the post-treatment facial growth. This is a reality that facial growth continues throughout other life and you can expect a certain amount of growth even after your treatment is over. So this post-treatment facial growth can alter the outcome of your treatment either in a favorable way or in an unfavorable manner. So you should be assessing the growth pattern and reminding growth beforehand and your retention protocol should be planned accordingly. Post-treatment occlusion responds to the growth changes, that's why you get an altered treatment outcome after two, three years of treatment. So why retention is necessary? So the major three points, these are already we discussed under causes of relapse. So what are the three major points? First one is the bone and adjacent tissues require time for reorganization. Soft tissue pressures constantly produce relapse tendency and changes produced by growth may alter the autonomic treatment results. So because of all these things, retention is necessary. So for many years, clinicians did not agree about the need for retention. But over the years, different people came up with different philosophies. They say that if you achieve any of these following characteristic features of post-treatment, then your results will be stable. So the set of these different philosophies are called schools of retention. So the first one is the occlusion school by Kingsley. So Kingsley stated occlusion is the most important factor in determining the stability in a new position. That is, when you have a perfect occlusion with perfect intracuspation, then your post-treatment stability will be much more than normal. Second school was the apical base school by Alex Lenstrom. So he suggested that the apical base was one of the most important factor in the correction of malocclusion and maintenance of a corrected occlusion. So many others also supported his view, that is, McClelland, who supported this by stating that intercanane and intermolar would should be maintained as originally presented to minimize retention problems. And so also stated, our strength cannot be permanently increased to a major extent. So basically, in this school, they say that maintaining intercanane and intermolar with that is the apical base with enhances the post-treatment stability. Third one is the mandibular incisors school by Grew and Twink. According to them, mandibular incisors should be placed and kept upright over basal bond to maximize the stability. So if it plays lower incisors upright over the basal bond, they are likely to remain in good alignment. So placing upright means when we draw post-treatment same, the long axis of the lower incisors should be perpendicular to the mandibular plane with plus or minus 5 degree variation is acceptable. So placing these mandibular incisors upright or 90 degrees to the mandibular plane, upright over basal bond gives you better stability. So the last school is the musculature school by Rogers. This philosophy is based on the equilibrium theory and Buxinator mechanism. As you all know that teeth are ideally should be placed in a neutral zone where pressures from outside that is by the cheeks and the lips and pressure from inside that is by the tongue should be equal and teeth should usually placed in a neutral zone. So if you place teeth in the neutral zone post-treatment then you don't need to worry about relapse. So these are the four schools of retention. These are very important. His first one is occlusion school by Kingsley where he stated that occlusion is the most important part in maintaining stability. Then second one was the apical base school by Lundstrom. So where he told that maintaining intercanine or intermolar with apical base is the key for retention. And third one is the mandibular school by Grieve and Till. According to them placing mandibular incisors upright over basal bone is the key for retention. And the fourth one is the musculature school by Rogers where he considered establishment of proper muscular balance is the key for stability. So the next one is one of the very important part of this topic that is theorems of retention. There are ten theorems in which first nine theorems are proposed by Richard Redill and the tenth one is proposed by Moyers. So let's see what is the first theorem. The first theorem states that teeth that have been moved tend to return to their former position. So as you can see in the first picture which is a pre-treatment photograph of a patient with lower anterior crowning with serial extraction has already done. Those are the second picture is the post-treatment photograph where you got a perfectly aligned lower anterior and the third picture is the retention period when the patient returned with a mild crowning in the anterior. So this is a perfect example of relapse because we didn't follow up with a proper retention protocol the case ended up like this. So this is what the first theorem says that is the teeth that have been moved tend to return to their former positions. This is what the first theorem says. And so basically first theorem is a reality check that we cannot achieve a perfect finish in every case because there are chances of relapse. So the second theorem states that elimination of the cause of malocclusion will prevent relapse. So malocclusion can have several etiologic factors and usually most of the malocclusion associated with abnormal habits such as tongue thrusting, mouth breathing, tongue sucking etc. So when you eliminate or break these habits before going for a corrective orthodontic treatment you can prevent relapse. If you're not bothered to eliminate or remove the cause or the etiology and do the rest of the treatment you will end up with the same problem again that is the patient will come to you with the same problem again. This is because the cause that etiology is still present. So elimination of the malocclusion is very important while treating the patient. The theorem 3 which emphasises on the overcorrection. It says that malocclusion should be overcorrected as a safety factor. As you can see in the picture there is a misolingally rotated lower canine on the left side. So your goal is to derotate the canine and make it in alignment with the other teeth. So instead of that what you can actually do is that you can slightly rotate the canine to the opposite side so that even if relapse happens it will be occupying the correct position. So this is called overcorrection. The point to be noted here is it's not possible to overcorrect every malocclusion. The fourth theorem explains the role of occlusion. So it says that occlusion is a potent factor in holding teeth in corrected positions. So this theorem is in accordance with the occlusion school of thought by Kingsley. So we have already discussed what is the role of occlusion and retention. That is if you have a proper occlusion with perfect intracuspation there is less retention problem post treatment. Moving on to the fifth theorem. This theorem emphasizing the role of supporting structures such as bone and adjacent tissues. This also we have discussed in detail under the causes of relapse. So it states that bone and adjacent tissues should be given enough time to reorganize. So the theorem 6 is in accordance with the Mandiblar incisals school by Quaid. That is this theorem states that lower incisals should be placed upright over basal bone. That is the inclination of lower incisals should be 90 degrees plus or minus 5 degrees to the Mandiblar plane or to the basal bone. So that you will have better stability. Theorem 7 is related to growth. It says correction carried out during periods of growth are less likely to relapse. It is actually telling us that due treatment on growth period that is in adolescence. It is actually easier to do treatment when growth is still present. And adult orthodontics is difficult and more challenging for orthodontists as well as for the patient himself. So it is also advocating you to go ahead with interceptive and preventive orthodontics rather than corrective and surgical orthodontics. Moving on to theorem 8. This is actually similar to theorem 3 that is over correction. It says that the further teeth have been moved, the less likelihood of relapse. So you can take the same example of rotated teeth where we do over correction. Means you rotate the tooth in the opposite direction fearing the relapse. So according to theorem 9, Mandiblar arch form cannot be permanently altered by treatment. Treatment should be directed towards maintaining the arch form presented by the malocclusion as much as possible. Any attempt to alter the mandibular arch form, there will be very high chances for relapse. So the two major dimensions to be considered here are the intercanine width and the intermolar width. So we should always establish them as fixed quantities and build the arches around them so that you get a better stability posturing. So move on to the last theorem which is proposed by Moyers. So it says that many treated malocclusions require permanent retaining devices. So the permanent retainers are the fixed bonded lingual retainers. So most commonly used for mandibular incisors and cases of midline dystema etc. So these type of retentions supposed to be there for lifelong. That's why it's called permanent retainer. So these are the 10 theorems of retention out of which 9 are proposed by a radial and the 10th one is proposed by Moyers. Apart from these, there is Raleigh-Williams keys for enhancing the lower retention. This actually relates to incisors and canines, inclinations and angulations. So the first key tells you about the labiolingual positioning of lower incisors in relation to apogonion line. So your lower incisor edge should be exactly on the apogonion line or one amount in front of it post-treatment. Not more than that so that you will get better stability post-treatment. The second key talks about the misiodistral angulation. How you should end up post-treatment to get maximum stability. The basic idea is to have enough bond between the roots. That is the lower incisor apisors should be spread distally to the crowns more than is generally considered appropriate and the apisors of the lower lateral incisors must be spread more than those of the central incisors. So there are three ways you can have your lower incisors. As you can see on the picture, out of the three, the third picture should be the appropriate positioning of lower incisors where the roots of incisors are slightly distally tipped or rather you can say it's in a diverging fashion. So you can get better stability. The third key is highlighting about the lower canines. So it emphasises that the apex of the lower canine should be positioned distal to the crown. The fourth key says that when you look from top or the occlusion view, all your incisor roots should be in the same labial ingot plane. So that you should not be seeing any root flaring or root apex going front or back or like that. And also the crowns should be straight. So the fifth key highlights the root apex of lower canines must be positioned slightly buckled to the crown. That is, root of the lower canine should slightly incline outwards and the crown should be slightly inclined inwards. So this is actually opposite to the fourth key where unlike the incisors mentioned in the fourth key where it says the incisors should be straight. That is, the roots of the incisors should be in the same labial ingot plane. So the sixth key says that the lower incisors should be slenderised as needed after treatment. So when you finish the case well-aligned, because of the shape of the lower incisor, you get point contacts between them. Due to this point contacts, they can slip past each other. So if you want more retention, it's always advisable to increase these contact areas. So the best way is to convert these contact points into contact areas by slenderisation or proximal stripling between the anteriors. When you do slenderisation in the finishing stage, you will get more stable relation. So these are the six keys for enhancing the lower retention, which is proposed by Rayleigh Williams. Thank you guys for watching. So that was the first part of this topic. And I'll be back with the second part soon. And I thank Dr. Sahi for giving me this opportunity. Have a good day.