Retention

Introduction

Many dentists look at the topic of retention as which type of retainer should I use, but the first step for YOU is to establish a retention philosophy. You must know what you are retaining and what your policy will be when there is a relapse. Then you can choose the appliance.

It is my opinion that you should give the patient a retainer. It is “known” by all patients that they will get a retainer, since their friends all have one. I have known only one orthodontist who did not give retainers to his patients, and got away with it (Lee Boese). I first heard him at an AAO annual meeting, and after designing the IP appliance, I drove to his practice in Northern California to meet personally with him to confirm that he still was not giving retainers and that he was still doing the same. He was.

The principles used by Lee Boese to avoid retainers are:

  1. Full corrections of rotations established early in treatment. He made finishing bends in every archwire. IP rotation brackets do this with the first alignment wire.
  2. No expansion of the [lower] inter-canine width. He contoured all his archwires to fit the original archform of the patient, paying special attention to maintaining inter-canine width. In IP, we can do this with archwire diagnosis and selection since we have the 18 shapes available in preformed condition.
  3. Full correction of single tooth torque. If a tooth was blocked out, he would torque the nitie archwire (yes nitie) with a torquing key (single tooth) to move the root forward to be consistent with the adjacent teeth. In the IP appliance, we can do this with variable torque brackets.
  4. Stripping and fiberotomy: He is known for this, the orthodontists did not want to hear the first three, or maybe it was assumed that everyone does this (yeah, right). Stripping is done to reduce inter-canine width and to create flat contact points that will not “slip” into a tooth rotation. The fiberotomy is done to release the [circumferential] elastic fibers from the tooth that will rotate at tooth back to the original position after the forces are released (from the brackets and archwires).
  1. Advancement and retraction: Lee did NOT mention that he maintained the incisor near the starting position, not moving the incisors forward into the lip muscles nor back into the tongue muscle. Maintaining the starting position (AP), when possible, is of course part of maintaining the original archform, so this can be assumed.

As you can see, the IP appliance was partially influenced by the concepts of retention. Yes, we want to get the teeth to a great final position, making the patients smile and mouth look the best, but then we need to keep them there. As you mature in your ortho career, you will be faced with patients returning with retention problems, especially as a General practitioner. The topic becomes more and more interesting as the years pass.

*** Note: I will loosely refer to “retention” as being the time period following active orthodontics, including when the patient is wearing retainers and beyond.

What are you retaining?

Growth: Differential horizontal growth after the brackets are removed can force the lower incisor lingual (recrowding) and/or the upper incisor labial (spaces), a “collision”. If the upper teeth move forward with the extra mandibular growth, then the incisors should remain stable, but if the upper incisors do NOT move forward [enough], and there is good coupling of the incisors on the final occlusion, then there is “collision” pressure on the upper and lower incisors. The lower 3x3 retainer was invented to prevent the lower incisors from moving lingual and to maintain the inter-canine width.

Inter-canine width: It is accepted in the field of orthodontics that the LOWER cuspids cannot be expanded, and if they are, they will cause recrowding of the lower incisors. McGann feels that this may be due to tipping of the cuspid crowns over the crest of the labial cortical plate, which then ‘upright’ over the roots after the brackets are removed. To do something about this, McGann invented the Labial root torque bracket (La) to be used when expanded archwires are used in the lower arch. Assuming the archwires are eventually rectangular during treatment, and these archwires engage the bracket slot, the roots move labial, compensating for the labial crown tipping.

The archwire shape and size is the most important influence on inter-canine width. The patented concept of using the lingual shadow of the lower arch to determine the shape of the archwire, can also be important in retention. The lingual shadow represents the shape of the mandible, which could be the dento-alveolar bone (more superior shadow) or the basal bone (inferior shadow). It makes sense to match the shape of the mandible at the same time that you are diagnosing which shape is best for the dental arch. Matching the two should lead to improved retention.

Before the invention of the IP archwire system, nearly all archwire shapes were ‘ovoid’, this being because it is the easiest shape to manufacture. In the time before these preformed ‘generic’ shapes and sizes, each distributor must have their own shape, the orthodontist had to make an archwire for each patient, matching the dental archform and size. This was called the “diagnostic arch” concept. But that was time consuming, so preformed archwires quickly took over private practice, no matter what was taught in ortho school.

The lingual shadow discovery formed the basis for an excellent archwire system. In general you want to maintain the original size and shape, but on occasion, we use non-coordinated archforms and shapes that are different than the lingual shadow. When this is done, we are changing the original starting condition of that individual patients mouth, which should be considered the most stable position…the teeth are in that position for a reason, in balance with the patients muscles, speech, and habits.

** lower 3x3 and clear overlay retainers maintain inter-canine width quite well.

  • Frontal cephs compared near the end of treatment versus 2 year retention with relapse. The cuspids uprighted.

Rotated teeth: 90% of all complaints from patients after treatment have to do with tooth rotations. Nearly 100% of those are due to under-correction of the original rotation, a problem that can be solved by diligent rotation diagnosis using model measuring, followed by the application of IP rotation brackets. It should be noted that rotation brackets must be properly used by the dentist, paying attention to detail in repositioning where position is incorrect and forcing the archwire into the bottom of the bracket slot (steel ligature ties, ligature director). Otherwise you do not get the full benefit of the precisely cut bracket slot.

As of this writing, there are no other brackets on the market except for the IP appliance that have rotation brackets. The zero degree slot (for rotation) in all straight wire type brackets will routinely result in an under-correction of the tooth rotation. To compensate for this, orthodontists will (I did too in the past),

a)Move the bracket off-center to the side of the [lingual] rotation

b)Vary the adhesive thickness on the bonding pad to compensate for the under-correction

c)Make second order wire bends to rotate teeth beyond where the bracket and archwire would take them. Most orthodontists are not going to do this, as it is very time consuming and stressful on the mind.

The period of time that the teeth are in their final (straight) position is important for stability in retention. Evidence can be pointed to cases that are treated in a short time period, maybe 6 months, and the experience of instability is very poor. I have a minimum of 1 year in my mind to treat an ortho case (with rotations), even if the case is perfect after 6 months. The supporting tissues of the teeth need this time to re-organize the tissue cells and fibers, the process is at least 6 months for the exchange.

With this in mind, the capability to FULLY correct tooth rotations on the first alignment wires is fantastic. Then during the mechanics and finishing, the tooth is fully corrected. This is similar to what Lee Beose was doing with his wire bending early in the case treatment, where most would only bend wires, if at all, at the end of the treatment in “finishing”. Correcting rotations in finishing is NOT good for retention as the brackets are likely removed the minute the rotation is finally corrected. Expect these teeth to be unstabile in retention.

Supracrestal circumferential fiberotomy (“fiberotomy”) was first presented by Edwards in 1981. He showed the elasticity of the gingival fibers surrounding the teeth (circumferential fibers) influenced if a tooth stayed straight or returned to the starting rotation position. He placed tattoo dots vertically on the labial of a rotated lower incisor, straightened the tooth (the tattoo dots moved to the side), and then released the archwire and the dots returned to the original position as the tooth relapsed.

In POS, I recommend the use of ‘fiberotomy’, separating the gingival fibers from the previously rotated tooth and then let them reattach in the new position. Yes, 360 degrees, “circumferential” and I put the blade into the sulcus and sever the fibers all the way to the bone (or PDL). Which teeth? The ones that a patient would “see” and complain if it rotated again, but for sure moderate to severe rotations. I feel “which teeth” should be decided at the original diagnosis, when you have the information from model measuring handy. The purpose is to improve the retention experience.

** notice that I have dealt with everything that the very skilled orthodontist Lee Beose was doing and YOU can easily to the same, with ¼ the effort and skill. From the retention experience shown on the “life change” reports in this seminar, the IP experience is definitely improved over the days of straight wire.

When selecting the type of retainer for tooth rotations, think of these concepts:

  1. Lower 3x3. These retainers are good to maintain inter-canine width, to prevent the constriction on the incisors, andto prevent the lingual drifting AS LONG AS the lingual bar is in contact with the mesial AND distal line angles of the tooth (or is bonded to the tooth). But what if a tooth rotates labial, away from the lingual bar? The concept is that the upper incisors are supposed to prevent that from happening. OK, in a perfect world. When a tooth rotates with the retainer securely in place, then YOUR retainer did not work and it is your responsibility to align the teeth again, for free, right? If one side or any bonding point debonds, and a tooth rotates, then your retainer ‘broke’, must not have been made right, so it is your responsibility to realign, right? NO, we want to shift the responsibility to the patient, off our shoulders, and this is best done with a removable retainer.
  2. Hawley: I used hawleys and 3x3s BEFORE inventing the current clear overlay retainer in 1984-85. Hawley’s were not routinely worn by the patient, even when they were well adapted (I used a biostar machine). They are simply too bulky and more difficult to wear than the brackets and bands were. The labial bow did NOT maintain rotations well, and I was a master at bending that bow to contact the key points on each tooth to maintain the rotation.
  3. Clear overlay: this is the best overall retainer to retain tooth rotations, assuming that you have a perfect adaptation of the acrylic to the teeth. The teeth simply cannot rotate if the retainer is being worn. Now, if a patient presents with a rotated tooth, you can simply say they did not wear the [clear] retainer enough, and sure enough the retainer does not fit anymore. Responsibility shifted to the patient for realignment.

** note: if the retainer is NOT well adapted, as can be with vacuum formers and even models that are processed when they are too wet (the heat creates steam that ruins the adaptation), the teeth can rotate within the retainer and now the retainer still ‘fits’ with the rotated tooth…ooops, your responsibility.

Maxillary expansion: Clear overlay and hawley retainers do NOT retain expansion well, so if you have expanded in a case (eg. RPE, not simply non coordinated archwires), then use a TPA (fixed retainer, straight wire soldered to blank bands) with a clear overlay retainer (retain tooth rotations) on top.

Hawley retainers would seem to do the job, being rigid in the cross palatal dimension, BUT patients generally do not consistently wear Hawley retainers, so they eventually come in saying the ‘retainer does not fit anymore’. The acrylic does not fully seat because the maxilla constricted. I even saw some patients that ‘wore’ the Hawley retainer, but the teeth still constricted. How does this happen? The patient has the retainer in their mouth, but it is not FULLY seated, so the teeth can constrict. Literature also agrees that you need FIXED retainers for maxillary expansion.

Clear overlay retainers are NOT rigid enough when you cut out the palate to maintain maxillary expansion. So you can leave the palate, but this still was not rigid enough. We then invented a way to put a rope of cold cure acrylic from 6-6 and then before it fully sets on the model, the clear retainer material is pressed. The clear material and acrylic stuck together, adding rigidity…this worked, and the patient wore that retainer (unlike Hawley).

Again, the safest is a fixed TPA retainer with a clear overlay made on top of that. Leave in the TPA for at least 4 years…recement every 1-2 years to prevent decalcification under the bands, and tell the patient to leave it in as long as they do not want to go back into braces!
*TPA + clear overlay

Both arch expansion: I am not sure the specialty is ready for the retention problems of the expanded Damon system, but is there and I am not sure what they are doing about it. Not only are the tooth rotations not fully corrected (due to wire slop in the slot, rotations are more under-corrected than zero degree straight wire by another 2 degrees when 19x25 archwire is inserted), but the expanded arches are not going to hold up long term, especially if they do not change their retention protocols. How do I know? Because I used expanded archwires for many years before IP.

The big difference is in the lower arch, and I am talking about using expanded archwires in the lower arch to reduce incisor advancement, making more non extraction cases. If you expand the lower arch with an archwire (not all will expand due to buccal cortical bone resistance), then will a 3x3 retainer hold that expansion? NO, that retainer does nothing for the posterior teeth. This is why I used LOWER HAWLEY retainers for many years when I was in the expanded archwire phase. Some patients would wear the upper Hawley, but not the lower, and what did we get then? The lower arch constricted and now we had arch coordination problems with the upper. Clear overlay retainers did well to retain total arch expansion upper and lower, even though they were not rigid enough to retain an RPE expansion of the upper arch.

Many of our cases we diagnose with archwires to maintain, but some we intentionally expand. Remember this come around the time to remove the brackets.

Deep bite: Retention of deep bite can take the form of maintaining a flat curve of spee (keep the lower incisors down) or preventing the upper incisors from extruding. As the bite deepens, then the lower incisors are pushed lingual, recrowding, and/or the upper incisors space. The same “collision” of incisors as with growth.

Hawley retainers were NOT good to maintain the vertical of the incisors, as the incisors could extrude through the opening between the acrylic and labial bow, and the posterior crossover wires and/or acrylic trim could intrude the posterior teeth, creating deep bite even if the incisors stayed. Lower 3x3 retainers also did not do much to hold down the lower incisors, as the entire segment 3-3 could extrude, the concept being that the perfect occlusion with the upper incisors would prevent this.