True Intrusion in Periodontal Patient | Essential Biomechanics


Welcome to our educational platform.
This is your place to learn scientific biomechanics with a clinically useful
approach. Today, we’re going to talk about a very challenging situation: how to
get a pure intrusion in a periodontally compromised dentition? this problem
is quite common in adult patients and the discussion about a mechanical
solution for it constitutes a great opportunity to learn and practice some
essential concepts in biomechanics. If you want to be updated in orthodontic
biomechanics don’t forget to subscribe to our website, YouTube channel and other
social medias. But let’s jump into our challenge. Our goal today is to learn how
to intrude and retract the upper anterior teeth with a reduced periodontium. Here is the real clinical scenario: the patient’s main complaint was the
left lateral upper incisor she said “her tooth was disappearing
behind the other teeth”, which were moving forward and to the left, as you can see
in this upper line deviation in relation to the facial midline. In fact, the
patient’s complainy is only one sign reflecting a much more complex case.
Besides the significant bone loss due to a past periodontal disease, the patient
also has tooth loss, a deep curve of Spee, significant migration of upper
teeth and a dysfunctional occlusion because both anterior and lateral
guidances are not appropriate. Unfortunately, this situation tends to
worsen over time because the non-physiological distribution of
occlusal forces, especially in a reduced periodontium, will favor the continuous
migration of teeth. Two main changes occur in theses cases: first, the loss of
marginal bone level displaces the center of resistance to a more apical region
and this increases the shearing forces caused by occlusal loads dissipated into
a more oblique alveolar wall,
favoring the tipping and extrusion of this teeth. These cases in which
malocclusions has developed or has worsened in adulthood are called
secondary malocclusions according to Dr. Meslen. Theses case are common in
orthodontics and the problem gets worst as the time goes on. Unfortunately, in several of these cases the patient has not been appropriately
diagnosed by the dentist, or he may have been misinformed about his problem. This
can happen to anyone even a president of a country. This misinformation occurred
in the present case. The patient sought out several orthodontists and they
states that she would lose her teeth if she underwent orthodontic treatment. Come on! She will lose her teeth if she does not undergo orthodontic treatment. Yes,
the orthodontic correction is needed in this interdisciplinary case. We don’t
need to achieve a perfect occlusion but we need a functional onem in which the
occlusal loadings will keep the teeth and bone in good physiological
conditions. If you want to learn more about secondary malocclusions and how
orthodontic treatment can benefit these cases, we suggest the reading of our
recent systematic review on this topic. And now that I hope you are convinced
that this case needs an orthodontic correction, let’s discuss the
biomechanical details of HOW we are going to perform
at true intrusion in this significant reduced periodontium. First of all, it’s
obvious that we will never apply an orthodontic force in a patient with
active periodontal disease. This would be an iatrogenic orthodontics. The
orthodontic treatment will begin only if periodontal tissues are healthy and IF oral hygiene is maintained during the treatment. We need to constantly check if there are no bleedings or pockets of more than three
millimeters probing depth. I mean, if you have a healthy periodontium, even a
reduced one, we can move teeth! To understand some of the difficulties of
this case, let’s start by the differentiation between a real and a
false or pseudo intrusion. A true intrusion means the apical movement of the CR of a
tooth or group of teeth, as in our case. Remember that the CR is considered the
“heart” of a tooth or group of teeth, in a sense that the resultant force system
perceived by the CR will dictate the resultant tooth movement. In this picture
A, you can see a TRUE intrusion, in which the CR has moved upwards and following
the long axis of the teeth. This intrusive translational movement occurs
when the resultant force system paths through the CR. On the other hand, in this
picture B, you can see what happens if an intrusive force is applied at the
bracket level. Although the incisal edge and the bracket have moved upwards, the
CR had not moved, because in this case the force applied distant to the CR will
provoke a significant counter clockwise moment at this region. Therefore, in this
picture, basically a tipping is being produced, which reduces the overbite but
increase the overjet. This is called a pseudo-intrusion. This is the type of
movement that we would achieve if you use a straight wire or a continuous
intrusion arch in this case, and this is NOT our goal. In fact, in our case, things
will be worse than in this picture. Remember that we are dealing with a
reduced bone support, and these conditions provoked different tooth
displacements and different load distributions when an orthodontic force
is applied. Take a look at this experiment, for example. During my postdoc stage in Denmark, we have made a finite element study to analyze these differences.
By simulating different degrees of bone loss we have found that the same
intrusion force applied to the bracket of a central incisor leads to
different dental displacements when a normal bone condition is compared with a
bone loss condition. The protonation in a moderate bone loss
for example is around three times higher than in a normal condition! Not only the
tooth movements are different, but also the strains induced in the periodontal
ligament of these teeth. As more bone we lose as higher are the strains in the
periodontal ligament. These higher forces can be a problem for both the
bone and root resorption processes. To sum up, our results have claimed our
attention that we need a very careful mechanics in order to work with
compromised periodontal dentitions. So, let’s follow our five steps of a
force-driven planning to solve your problem and let’s discuss some biomechanical
details responsible for the success in the present case. As usual, in step one, we
identify the problem to be corrected which is the extrusion and proclination
of anterior teeth, and we draw the needed forces to achieve our final desired
position. Considering that we need not only to intrude but also to retract the
anterior teeth, the desired line of action should pass slightly behind the CR of
our active unit. I’m not enter in all the details of this
case but before performing this controlled intrusion, I have made a
progressive slenderizing technique in the upper right side of the mouth. You
can check the details of this procedure in chapter 18 of Sr. Melsen’s book. In
my case, a rigid TPA was used as anchorage and I had uprighted the
posterior teeth ONE BY ONE until I have space to align the anterior region.
This white wire you are seeing here is totally passive. When our individual
distalization have reached the right canine, we were able to initiate the
anterior alignment. After anterior alignment, a rigid anterior segment was
installed and now we can initiate the controlled intrusion and retraction. How can we apply a force behind the CR of active unit? By using a three piece base arch. If
you are not familiar with this type of appliance, I recommend reading the papers
of Dr. Burststone. You can also check our video demonstrating the
confection and activation of this appliance. Now, in step two, we will check
the equilibrium of the force system we want to apply. In our case, the desired
intrusive force that we will apply only in a single point will be accompanied by
an extrusive force and a clockwise moment that will be perceived by our
anchorage or reactive unit. In this case considering the fragility
of the patient’s dentition, I will certainly opt to use an absolute
anchorage. So, two mini-implants were installed in the buccal region as the
sources of anchorage. The step three is the choice of the appliance, a decision
that we have already made according to our desired force system. In step four,
we’ll activate the appliance. The two main ways to perform the activations is
by using bilateral tipback springs or cantilevers. I prefer cantilevers because we can control the force direction by changing
the angle of the ligature tie. Note that the angle of the ligature tie
represents the direction of our force. Besides the force direction, there are
more two force parameters you should control in order to get a physiological
and effective tooth movement. After choosing the line of action of the force,
you will check the magnitude of the force with a tensiometer. These are the
recommended values for the four or six upper anterior teeth. It’s very important
to keep force values as low as possible. And finally, you need to control
the constancy of the force. It’s advisable to use an appliance with a low
force-deflection rate, which means that a low and constant force will work over a
larger distance. This constancy is usually acquired by using cantilevers
made from TMA wires. The choice of the appliance also has an influence in the
step 5, where we evaluate the need of reactivations. Considering the constancy
of the system that I have just explained the three piece appliance usually
requires small reactivations and longer intervals between appointments. In the
present case, we have made only one or two reactivations during the four months
the appliance had been in place. In the before and after comparisons you can see
the great changes induced by the orthodontic treatment. In the frontal view, the dental midline is coincident with facial
midline , the crowding is solved, the patient is very happy because now she
can see her lateral incisor. The deep bite was reduced and the functional
guidances were reestablished. The arch form was improved and in the sagittal view
you can see the huge amount of real intrusion obtained. I didn’t explain the
lower arch chances, but basically the anterior teeth were intrude and proclined with a continuous intrusion archwire. Of course we didn’t reach an ideal
occlusion, but it is functional now! As a take-home message, I emphasize the need of controlling the force parameters, especially its line of action, whenever
we want to perform a complex dental movement Moreover, I hope the present
case can be an example that orthodontic treatment is not a contraindication in the
therapy of compromised periodontal patients. In fact the orthodontic
treatment in such case will enhance the chances of saving and restoring a
deteriorated dentition. The aesthetic and functional results obtained have a great
impact on patients appearance and motivation. The repositioning of teeth
can improve access for cleaning, establishes incisal guidance, improves
lip-seal and reduces the non-axial loadings which can negatively affect the
periodontal health. I hope you enjoyed this video. More challenges will come! Do
not forget to subscribe to our YouTube channel, Instagram and Facebook community. If you want a very detailed course with the main biological and mechanical
concepts needed to master the segmented arch techniques, I invite you to enjoy
our online course available at the Udemy platform. It’s a complete course, totally
online, you can see the lectures at your own time as many times you want and your
access is forever. This week we are offering a great
discount only up to Friday night. So I hope you enjoy this opportunity to
take your biomechanical knowledge and clinical practice to the next level. See
you in the next videos!

5 thoughts on “True Intrusion in Periodontal Patient | Essential Biomechanics”

  1. Que bom aprender, que exemplo de desapego ao disseminar conhecimento dessa forma. Parabéns meu recém conhecido novo mestre.

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