Overlays
I Definition
This is a process that consists of superimposing two TLR tracings of a subject taken at a time interval: 1 initial shot, final shot and intermediate shot.
These superpositions make it possible to assess the modifications in space and time of the dental, skeletal and cutaneous structures of the same individual.
These superpositions are only possible on standardized shots taken on the same installation.
II Interests
Allow
• on the one hand: the study of growth and hereditary factors
• On the other hand, the control of the modifications observed during a treatment, and
• control of the growth mode of a patient before treatment.
• Analysis of the results of a treatment
III Technique
The different colors are used by the different tracings at the successive stages of the treatment
• During the treatment, we use blue
• End of active treatment, we use red
• End of containment, we use green
• After containment, we use brown
And to perform a superposition, we need to define a registration point “R” and a superposition plane (or line)
The registration point is the fixed reference point on which the tracings of the successive images are made to coincide exactly. The superposition
plane is determined from the registration point. Criteria for choosing a superposition plane: • It must be stable, far from the growth zone • It must be close to the area to be studied
IV The different superpositions
We generally proceed with overall superpositions from the cranial planes and local superpositions from the maxillary structures.
IV.A. Overall superpositions
At the level of the base of the skull, they objectify the differences in position of the structures of the face without
allowing to distinguish the part which is due to growth and that which is due to orthodontic treatment.
IV.AaBolton Plan
.From point BO to point Na used by Broadbent.
.From point S (center of the Turkish cell) we lower a perpendicular on the Bolton plane and the middle of this perpendicular, point R is recorded, it superimposes on the perpendicular while keeping the Bo-Na plane parallel to itself.
.The Bolton point (BO) is the most inclined point of the posterior concavity of the occipital condyle, it is halfway between the Basion (Ba) and Opisthion (Op)
. The Basion (Ba): it is the most inferior point of the anterior edge of the occipital hole.
.The Opisthion point (Op): it is the most posterior point of the occipital hole.
IV.AbDecoster Line
It is a line used since 1922, which follows the anterior region of the base of the skull (internal
frontal cortex, ethmoid, sphenoethmoidal suture and the anterior edge of the sella turcica)
Decoster considers that this line does not present modifications after the age of 7 years and in its length is a guarantee for superpositions.
IV.AcLine S-Na
Used by many authors such as Byork, Steiner, Brodie and this because of the ease of localization of the S and Na points which is located in a stable region after 7 and 8 years.
The superpositions on this line show changes in the anteroposterior and vertical direction
If we take as a recording point the subnasal point, we will have changes at the
level of the Na point (moves upwards and forwards)
The second modification is the inclination of the bispinal plane, changes in the ATM
And we will have an estimate of facial growth as a whole.
If the Na point is recorded, we will have information on the changes in the cutaneous plane, the facial plane and the bispinal plane (growth is rejected backwards)
IV.B. Local superpositions
IV.BaAt the level of the upper jaw
These local superpositions show the growth of the maxilla in length and its displacement relative to the base of the skull.
According to the authors, the superpositions can show either the modifications due to the treatment and the effect of growth.
The nasal spine line, post-anterior nasal spine (superposition plane)
• With the anterior nasal spine recorded, we can highlight the modifications at point A, displacement of the first upper incisor and the first molar in the anteroposterior and vertical directions.
• With the posterior nasal spine recorded, we will find at the level of the anterior edges of the maxilla, the combined effects of growth and treatment.
• With the anterior part of the pterygomaxillary cleft (recording point) this superposition shows the displacement of the first molar, the growth at the anterior level and the study of the occlusal plane.
IV.BbAt the mandibular level
These superpositions isolate the changes that occurred at this level and those that occurred in the rest of the face.
As in the maxilla and depending on the superposition method adopted, we can either obtain the sum of the changes in growth and orthodontic treatment or the effect of the growth of the isolated treatment.
On the posterior edge of the ascending branch with the top of the condyle recorded, we will find in the symphyseal region the results of the activity of the various fertile centers of growth in both vertical and horizontal directions.
2nd plane: at the level of the symphysis with point Me recorded, we will have modifications at the level of the teeth, we will find the results of the activity of the alveolar rim in the vertical direction, this displacement is objectified by the displacement of the occlusal plane in the vertical direction.
We will also have the increase in the length of the mandible in the horizontal direction, it is shown by the displacement of the posterior edge of the ascending branch at the level of which the bone apposition occurs.
The 3rd modification is the activity of the condylar center objectified by the displacement of the summit of the condyle in the vertical direction.
V Conclusion
Why superpositions?
Doing local superpositions is to have concrete results, it is not about comparing a series of angular and linear values recorded on the cephalometric charts and after treatment but especially to observe in the same glance different diagrams drawn with different colors of simple process and the different ones are visible without interpretation of numbers
Untreated cavities can damage the pulp.
Orthodontics aligns teeth and jaws.
Implants replace missing teeth permanently.
Dental floss removes debris between teeth.
A visit to the dentist every 6 months is recommended.
Fixed bridges replace one or more missing teeth.