Today we'll talk about fixed appliances which are the most common appliances are been used. Treatment of orthodontic patient can be either with removable appliance for periodontal movements or functional appliances for skeletal problems and the 3rd choice of treatment is the fixed appliance .
-Aims of this lecture:
–Definition of important terms
–Components of fixed appliances
–Types of fixed appliances
1. Correction of mild to moderate skeletal discrepancies
It's an appliance that usually deals with tooth movements and some camouflage treatment.
Camouflage treatment deals with compensatory movements. So if we have a severe skeletal problem we correct it by surgery, but if it wasn't severe and it's mild to moderate we could sometimes camouflage this skeletal problem. We accept this problem and try to achieve normal occlusion (class I occlusion In spite of the presence of skeletal problem and this is what we call camouflage treatment).However, we mask the skeletal problem by only correcting the occlusion like something called "the dental alveolar compensation" , which is the same concept of camouflage, but here the body itself tries to solve it (natural) , but in camouflage we use a dental appliances.
2. Multiple tooth movement.
3. Intrusion/Extrusion of teeth.
Patient has malocclusion with many types of tooth movements like intrusion/extrusion of teeth .Intrusion is usually hard and we use fixed appliances, Extrusion we can use a bite plane if tooth is erupted with a removable appliance. But we need to actively pull the tooth and we need some source of attachment on the tooth so we can use removable appliance to extrude the tooth but we need to fit bracket as an attachment to the tooth to pull it down .
4. Correction of rotation
We always need appliances to correct the rotation.
5. Space closure and space opening
We usually need bodily types of movement.
6. Lower arch treatment:
Usually removable appliances are reserved for upper arch treatment because in the lower arch retention is difficult and space is limited. So usually we don’t use removable appliances to move the teeth in the lower arch but a fixed appliance.
7. Orthognathic surgery:
You will take a lecture in details about this topic next year, but briefly those patients, who need a surgical procedure to their jaws' problems, would need an orthodontic treatment and this treatment is by fixed appliances.
Summary about biomechanics- that we took last semester- to be easy to understand how fixed appliances work:
Definition of Center of Resistance: Is an area of a tooth through which a force can be applied that will move the tooth in the same direction of the force without tipping or rotation (pure translation).
In other words; when we apply a force to the center of resistance,root and crown will both move in the direction of this force the same distance (root and crown move the same distance ) and usually this center of resistance in molars is on the area of furcation and in single rooted tooth on 1/3 distance of the crown or 2/3 distance of the root apex.
Moment: Tendency of rotation resulting from the application of force not through the center of resistance of a body >>tipping movement.
In other words if we have an object and we move it from one side, there will always be a tendency for rotation .
When does it happen ? When we apply a force away from the center of resistance.
So as we agreed on, when the force is applied on the center of resistance it would give a bodily movement,but if it's applied away from the center of resistance it would always be a tipping tendency (moment).
This moment is mathematically defined as : moment equals force multiplied by the perpendicular distance of this force from the center of resistance M=F*D
So as the force increases the tendency of rotation increases as well . And as the distance of this force from center of resistance increases the moment increases.
This is how the removable appliance works where we apply a force to the crown and this single force is away from the center of resistance, then a tipping movement will result and this tendency of rotation as we said increases as the distance or the force increase.
*Notice that the root moving in one direction and the crown in the opposite direction.
Center of rotation (CR): the point about which the rotation actually occurs when the object is being moved.
So notice that Center of rotation is not like center of resistance:
If we move the tooth bodily it would have a center of resistance, but there is no rotation so center of rotation here is infinity (no center of rotation). BUT if we are tipping a tooth it would have a center of rotation.
-If we apply a force on the center of resistance, would it be there a rotation? NO but if the center of tooth is being tipped, it would have a center of rotation.
So every tooth has got a center of resistance, but not a center of-
rotation unless this tooth is being tipped
-COUPLE: A pair of equal and opposite non –collinear forces (not acting on same plane) and this couple gives a rotation movement of the tooth.
For example: to move the tooth in a round and circular movement, we need a couple which is a two forces without any movement where the tooth stays in its place, but is being rotated as well (two equal forces acting in opposite direction not in the same one) .
Couple is the mechanism by which we get the fixed appliance application.
-It's very important to know that the application of forces and couple is the mechanism by which we get bodily movement or sometimes we get more root movement than the crown.
If we apply a force we get rotation and ideally if we want to move the tooth bodily we need to apply the force on the center of resistance, but it's difficult to apply the force directly on the center of resistance, since it's in the root area. So we need a way by which the tooth understands as the force is being applied to the center of resistance and here comes the fixed appliances.
NOW to apply a force, tipping movements will occur. But as a result of having fixed appliance (bracket) with a wire >>the interaction of the bracket with the wire generates a couple in the opposite direction of the moment (tipping) that the force gave. So this will prevent the tipping of the tooth.
Let's rephrase what we've just said : A part of the force gives moment (tipping of the tooth ) and when the rectangular wire comes inside the bracket ,they give a couple in the opposite direction of the moment preventing the tooth to tip back palately, but it allows the tooth to move in a bodily movement only .
Exam Question: What do we need for fixed appliances to move the tooth bodily?
We need A FORCE AND THE COUPLE (the force only is not enough as it gives a tipping movement ).However, always remember that the couple is as a result of the interaction between the bracket and the wire (specifically a rectangular wire).
So: Couple prevents the tipping movement and only allows the bodily movement of the tooth).
Sometimes we can move the root more than the crown .We mean that sometimes we could use this couple not only to prevent the crown of tipping palately, but we even could get a much more root movement as a result of the interaction and this is called a "Torque Movement " which is getting more root movement than the crown as a result of the interaction between the bracket and the rectangular wire.
The same thing in the tipping movement of intrusion,we could move the crown and the root in the same apical direction as a result of the bracket and the wire interaction and the same principle in the extrusion movement .
So in intrusion we do a bend in the wire in apical direction and the interaction of the wire and bracket prevent tipping baccolingually so the direction of force would be in the apical direction only and the opposite for extrusion .
-That is the principle of fixed appliances.
Componenet of fixed Appliances :
1) Attachments (brackets or bands ).
2) Arch wires (interaction between attachments and wires give a tooth movement).
3) Auxiliaries (these auxiliaries either help in tooth movement or fix the brackets on the tooth such as the elastics).
Attachments : 1) Bands: We can't insert them directly because of the tight contacts so we put a separators either metal or plastic separators for one week so there will be a space between the teeth and after that we can put the appliance.
2) Brackets :-
a) Metal stainless steel bracket: The most common one.
b) Plastic brackets : Not favorable since it has dimensional and color instability so we do not use it frequently .
c) Ceramic :It looks like plastic, but much better.
d) Titanium and Gold : In cases of patients who have got a metal allergies we can use titanium brackets.
Base and fitting surface of the steel bracket is done in way where the composite bonds to the mesh on the bracket.
It depends on the stage of treatment.
Usually in the initial stages of treatment a wire that is flexible with good resistance to a permanent deformation is desirable. So the displaced teeth can be aligned without the application of excessive forces . In contrast; in later stages of treatment rigid arch wires are required to engage the arch wire slot fully and to provide a fine control over the tooth position while resisting the unwanted effects of other forces,such as elastic traction.
The interaction between the wire and brackets influences the arch shape and tooth movement so the behavior of these arch wires and the force exerted by a particular material, is given by the formula :
F ∝ Me*d*r4
F: Force r:radious
Me: Modulus of elasticity(type of the wire)
I:length of wire d: Deflection
So from the above equation the more we deflect the wire the more force we get .
Types of arch wires :
1) Stainless steel wire : The wire could be stainless steel wire which is a rigid wire. However, if we want to increase its flexibility we could reduce the dimension and we put in it coils or loops.
3) Co/Cr wires : Its behavior looks like that of the stainless steel wire.
4)TMA wire : Its behavior is between the stainless steel and Ni/Ti wires .
So: - In the 1st stages of treatment we use Ni/Ti to align the teeth
- in the later stages we use stainless steel wire when we want to correct overbite ,space closure or bodily movement.
1. Elastomeric modules: Rubbers that fix the brackets on wires.
2. Elastics :Intra or inter arch elastics; inter maxillary elastics:- classII and classIII elastics and we use them for anchorage.
Class II elastics: The upper anterior (canine)is connected to the lower posterior teeth and as result of this connection we're pulling the anterior teeth back .So if we have an over jet we try to correct it.
Class III elastics: The opposite of class II elastics occurs. (from lower canine to posterior teeth of the upper arch).
3. Ligature wires: sometimes we do not use modules, so instead of using rubbers to fix the bracket on the wire we use a ligature wires
5. Transpalatal or lingual arches for anchorage
-There is a new generation of brackets such as Self ligating brackets, which are Damonbrackets and this bracket has got a door(slot) and as the wire is inserted, the door or the lock closes without a need for modules nor a ligature wires and the advantages of it :
1) The visit of the patient is quick (no need to change the rubbers).
2) The friction between the wire and the tooth is less.
Types of fixed components are generally divided into 1.Buccal appliances 2.Lingual appliances .
2.Decalcification is visible if oral hygiene is poor and patient doesn’t brush his teeth well
6.Less control in tooth movement and less types of movements that is achieved by fixed appliances (Buccal has got a much more range).
-There is a new assistance in finishing: You can now take an impression and send it to the company which gives you in return a series of wires to use them for the patient with a great results,but this system is usually made of gold and it's very expensive to the patient.
Fixed appliances techniques: (we mean labial/buccal fixed appliances)
3.Begg technique 6.Fixed-removable technique (for single tooth movement)
1)Standard Edgewise Technique:
-Edward Angle 1920s
-Why its name is edgewise ?
Because it's characterized by brackets with horizontal rectangular slot for engagement of an orthodontic wire .SO the wire enters the brackets "edgewise" (the wide part of the wire enters as edgewise "horizontal" and not as rectangular.
-Round wires are initially used and rectangular later.
- The orthodontic treatment before the 1970s using this technique used to take a very long time because a very excellent wire bending skills are needed and that includes :
1) 1st order bends : to control the tooth movement in the horizontal plane such the bucculingual and rotation .
2)2nd order bends : to fix the tipping of the teeth; Not only to fix the alignment of the teeth ,rotation ,extrusion and intrusion of the vertical plane of the tooth, but even the tipping of the tooth.
3)3rd order Bends : to fix the torque .that means if the tooth-for example- is bucally inclined we need to fix the inclination or if its palately inclined we need to fix the root inclination as well .
Disadvantages of Edgewise:
1. It depends on wire bending.
2.Anchorage demands : Edgewise mechanism depends on bodily movement to close spaces and move the tooth.And this bodily movement is the biggest force that affects the tooth , so due to Newton's 3rd law : "for every action there is an equal and opposed reaction" .When we increase the force to get bodily movement we increase the demand for anchorage, specially when we're moving the teeth there will be friction between the wire and bracket .
2) Pre-Adjusted Edgewise Technique:
-In 1970s Lawrence Andrews, who was a very intelligent orthodontist, brought 120 cast of a non-orthodontic patients with normal occlusion and he studied the alignment, inclination tipping and 1st order location (buccolingual location ) for each tooth and he called his technique "the straight wire technique" (AKA Pre-Adjusted Edgewise Technique) since it's a modified edgewise technique and honestly it's the one that we're still using nowadays.
So it's a variation of edgewise appliance where the details for each tooth position is programmed into brackets.
He designed the brackets for each individual tooth ,and each tooth is programmed as a result of the interaction between the wire and the bracket. So this bracket figures out where its position would it be as the 1st order location of the tooth; buccolingually,rotation, occluso-ginigvally ) ,and information about tipping of the tooth and the torque. So it reduced the need for wire bending (but didn’t eliminate it completely).
So in Edgwise the brackets for the teeth are the same bracket, but here in the pre-adjusted each set of teeth has got their own bracket design
So the bracket has got an "in and out" position of the teeth information by changing the bracket thickness. He also changed the tip by changing the angulation of the slot of the bracket (where the wire enters).
Torque:By changing the inclination of this slot so when the rectangular wire enters each tooth move bucculingually not like any other teeth.
So in Edgwise there is a wire bending, but here we have a straight wire.
In/out info (by changing bracket thickness) Variable bracket thickness
*Change in/out position of different teeth. Bracket Slot Inclination
(mesiodistal tip)>slot angulation
Stages of treatment:
Leveling and alignment (round flexible ).
We usually use a rectangular wire, Ni/Ti wire (round flexible wires) and then stainless steel wire
*This stage uses "a round flexible wire".
Overbite reduction (rectangular).
Overjet and space closure (using rectangular wire ).
Friction between wire and brackets has got an anchorage demand
More expensive than edgewise system
3) Begg technique
-It's introduced by the Australian Raymond Begg in 1956.
He changed the shape of the brackets and didn’t depend that much on the bodily movements, but he thought to depend more on the tipping movement to decrease the anchorage demand so he changed the shape of the slots and it's usually used in class 2 malocclusion. So they tip the teeth to the correct position and then into extraction space followed by uprighting the root. So tipping is followed by uprighting the root and there is no significant bodily movement .But usually this movement depends on the auxiliaries, I mean the wires don't move the teeth, but here the auxiliaries that are been inserted move the teeth instead.
This technique is based upon tipping teeth with light forces, followed by root movements with auxiliary springs.
-It mainly depends on round wires and doesn’t depend that much on the rectangular wires
Its bracket is not edgewise, but it's called "Ribbon arch-type brackets" and depends more on the auxiliaries.
Stages of treatment:
Alignment ,correction of overbite, overjet and molar relation (It wasn’t the first stage in Edgewise)
Space closure and to maintain stage I correction.
Corrects inclination of teeth (Torque) and maintains stage I and II corrections
Its philosophy is "a lighter force and less anchorage"
Friction is less(no bodily movment)
Emphasis on extraction
Anchorage demand is less (because we're doing a tipping movement and there is no friction).
Lack of precision (control is much more in edgewise system and that’s why finishing of edgewise is better).
Reliance on elastics.
Depends on Oral hygiene because of the auxiliaries.
So it takes some advantages of Begg technique and some of Edgewise .We're not required to know about it in details, but you need to know that it has a less friction, the stages of treatment are the same as Begg's and it also relies on elastics like Begg technique.
Friction is less.
Reliance on elastics.
Less anchorage demand (It depends more on tipping movement and less on bodily movement )
Narrow brackets .
Good finishing because we can use a rectangular wires like Edgewise.
The doctor didn’t explain it.
If we have a single rotated tooth we can use this bracket which is called Whip spring appliance .
-It is not very common.
Sometimes in patients with an impacted tooth we can use an attachment and a removable appliance to extrude it. However, the advantage of using removable appliance for extrusion that we are here use the whole palate for extrusion as an anchorage. Whereas fixed appliance uses the teeth,but again here it uses the palate (better anchorage).
Good finishing and detailing.
Possible Decalcification, bone resorption and bone loss