THE SUPERPOSITIONS
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 changes 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: they are used for
• On the one hand: research work.
– the study of growth and hereditary factors.
• On the other hand: Control of changes observed during treatment or growth mode before treatment
- Analysis of treatment results
- Growth simulation
III TECHNIQUE
The different colors are used by the different tracings at the successive stages of the treatment
• During treatment, we use blue
• End of active treatment: red
• End of containment: green
• After containment: 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.
Precise: easy to locate landmarks
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
a_ At the level of the base of the skull: they objectify the differences in position of the structures of the face without making it possible to distinguish the part which is due to growth and that which is due to orthodontic treatment.
Among the most used superposition lines and planes, we cite:
IV.Aa BOLTON PLANE (Bo-Na)
From point BO to point Na used by Broadbent.
From point S (center of the turcic 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.Ab DECOSTER LINE
This is a line used since 1922, which follows the anterior region of the base of the skull (internal cortex of the frontal, 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, it is therefore a guarantee for superpositions.
IV.Ac S-NA LINE
Used by many authors such as Bjork, Steiner, Brodie and this because of the ease of localization of the S and Na points which are located in a stable region after 7 and 8 years.
The superpositions on this line show modifications in the anteroposterior and vertical direction.
Superposition on S-Na with S recorded, shows the forward movement of Na, this direction is determined by the growth at the frontonasal suture, it allows an estimation of facial growth as a whole relative to the base of the skull.
Overlay on S-Na with recorded Na: the profile moves forward, which allows to highlight the modifications produced at the level of the profile, and of the facial plane.
IV.B. LOCAL SUPERPOSITIONS
IV.Ba AT THE LEVEL OF THE UPPER MAXILLA
These local superpositions show the growth of the maxilla in length and its displacement relative to the base of the skull.
Depending on the author, the superpositions can show either the modifications due to orthodontic treatment alone, or modifications due to the treatment and the effect of growth.
The nasal spine line, post-anterior nasal spine (superposition plane):
It represents the floor of the nasal fossae , SCHWARTS, SASSOUNI consider it to be one of the safest.
• With 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 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.Bb AT 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 growth and 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 the point Me recorded, we will have changes 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 top of the condyle in the vertical direction.
V CONCLUSION
Why superpositions?
Doing local superpositions is to have concrete results, it is not a question of comparing a series of angular and linear values recorded on the cephalometric charts and after treatment but above all of observing at a glance different diagrams drawn with different colors of simple process and the differences are visible without interpretation of numbers.
GROWTH FORECAST
I INTRODUCTION
The process of predicting the craniofacial skeleton consists, on the one hand, of lengthening certain axes of the face on the cephalometric tracing by a variable amount depending on the duration of the prediction and the growth rate of the subject, and on the other hand, of varying the orientation of these axes depending on the type of rotation (natural or therapeutic).
II DEFINITIONS
II.A. GROWTH
It is the progressive development of an organ or organism from birth to adulthood
II.B. GROWTH RATE
Growth goes through phases of acceleration and deceleration as shown by the growth curve targeting the increase in height per unit of time.
II.Ba Phase 1: From 0 to 6 months, very high growth rate.
II.Bb Phase 2: Infantile period, from 6 months to 2 years, growth decreases considerably.
II.Bc Phase 3: Juvenile period, from 2 years to the pre-pubertal period between 10 and 11 years for girls and 12~13 years for boys, the slope of the curve is very low.
II.Bd Phase 4: Growth rate gradually decreases until it is zero at 15~16 years for girls and 18 years for boys.
III EVALUATION OF THE GROWTH STAGE
It is evaluated according to Bjork based on 3 criteria:
III.A. STATURAL GROWTH RATE
By default, it is the amount of growth that has occurred in a given period of time.
An increase of 5 to 6mm per year corresponds to the pre-pubertal minimum.
An increase of 8cm for girls and 10cm for boys corresponds to the pubertal peak (growth peak)
Its interest was highlighted according to Bjork by its close relationship with facial growth.
Indeed, the condylar or sutural (sutures) statural growth curves of the face occur simultaneously, they are almost identical chronologically.
III.B. OSSIFICATION STAGE
- Phalangeal growth and maturation
Bone age is classically measured from a wrist X-ray. The stages of maturation of the phalangeal structures show very strong correlations between height and facial growth.
The appearance of a small round bone, the sesamoid, located on the inner side of the mecarpophalangeal joint of the thumb, signals the major pubertal growth spurt.
This bone is visible on average one year before the pubertal growth spurt, more precisely 9 months in women and 12 months in men. - Growth and vertebral age:
In 1972, Lamparski created cervical maturation standards for girls and boys, in relation to chronological age. The method analyzes the size and shape of the bodies of the five vertebrae from the 2nd to the 6th: the concavity of the lower edge, the inclination of the upper edge, the height of the anterior edge of the vertebral body, as well as the thickness of the intervertebral spaces. Lamparski thus establishes six stages: CVS1, CVS2, CVS3, CVS4, CVS5, CVS6.
The studies of Baccetti, Franchi and Mc Namana conclude that there is a strong increase in mandibular growth at the time of stages CVS3 and CVS4 of maturation of the cervical vertebrae, stages where the peak of height growth occurs.
THE SUPERPOSITIONS
III.C. SEXUAL MATURATION
In girls, the first monstrous periods always appear after the peak, generally 17 months later.
In men, muscle development, the appearance of facial and trunk hair as well, the change in the timbre of the voice, appear just after the peak.
IV. EVALUATION OF THE TYPE OF GROWTH
(For the mandible only)
It can be an anterior or posterior rotation.
This evaluation is done using the 1st teleradiography, the beginning of the treatment which allows us to predict what the mandibular behavior will be, because the type of growth leads to particular morphologies and Bjork in 1969 looked for morphological criteria to predict the probable rotation of the mandible for this, he determined 6 elements.
| Anterior rotation | Posterior rotation |
| -condyle Vertical orientation and its shape is thick. -Curvature of the lower dental canal Very curved -Inclination of the symphysis Center -Shape of the lower edge of the mandible -Absence of the pregonial notch -Inter-incisal angle Very open Very closed -Height of the lower floor Decreased and the lips are pressed against each other | -Orientation and shape of the posteriorly directed and fine-Practically rectilinear -the symphysis directed posteriorly Directed forward.–Presence of the pregonial notch -Increased and the lips are in occlusion. |
V INTEREST OF ASSESSING THE TYPE OF MANDIBULAR GROWTH
Its therapeutic interest lies in the fact that extreme types of rotation are difficult to treat, and will tend to relapse.
The treatment of malocclusion in this case must be either late at the time of puberty or it must be hyper-corrected with a long retention.
VI – FORECASTING SHORT AND LONG TERM GROWTH
VI.A. PREDICTION TECHNIQUE
It consists of taking a tracing of the TLR image which must include:
• The skin profile
• The sella turcica
• Na
• Ba
• CAE
• The lower edge of the orbit
• The outline of the mandible
• XI
• Upper and lower maxilla, center of the condyle
Before starting the prediction tracing, it is necessary to set the period over which the prediction relates which can be short term (18 to 35 months) or long term (6 to 10 years)
We must also evaluate the types of growth and the type of mandibular rotation.
Afterwards, we will trace on the first tracing with a different color and we reconstruct the tracing by zones or structures.
THE SUPERPOSITIONS
VI.Aa THE CRANIO-FACIAL SKELETON
1 At the level of the base of the skull
• The sella turcica-Na line lengthens on average by 0.9 to plus or minus 3mm per year
• The S-Basion segment lengthens by 0.7mm per year
• The Ba-Na segment lengthens by 1mm per year.
2 at the level of the mandible:
The ascending branch: the central segment of the condyle, XI (at the level of the center of the ascending branch) increases in length and on average by 1.5mm per year, the orientation of this segment varies with the type of rotation (anterior or posterior), the neuromuscular behavior (the muscles) and the incidences of the treatment such as:
• Extractions cause anterior rotation.
• Class II elastics cause a posterior rotation of 1 to 2mm per year.
• The horizontal branch: from XI towards the pogonion, lengthens by 2mm per year.
3 at the level of the maxilla :
• The upper level of the face: Na-ENA, increases by approximately 1/3 of the total increase in the face
• The palatal plane, ENA-ENP, remains constant compared to the S-Na without treatment, but it tilts down and a little forward under the effect of extra-oral forces with cervical support.
• Dawn’s point A, does not vary compared to the Nasion in the vertical direction but in the sagittal direction, we can have a recoil of this point under the effect of extraoral forces which can be 1 to 2mm per year.
VI.Ab THE DENTURE
The two reference planes by the installation of the dentition are the occlusal plane and the A-Pog plane
• The occlusal plane, its inclination does not vary naturally, class II elastics cause a downward and backward movement of 2° per year, class III elastics cause an upward and forward movement.
• The A-Pog plane: it is a function of the movements of point A and the pog point
The lower incisor: the optimal position is a function of the distance from A-Pog, Ricketts advises placing the free edge of the lower incisor between -2 and 2mm from the A-Pog plane, its position is a function of the lips, E lines and the labio-lingual muscular balance.
The upper incisor placed in a suitable position and orientation in relation to the lower incisor (take into account the OJ and the OB)
The upper molars must be in class I occlusion, but we can finish our treatment with a class II or therapeutic class II.
VI.Ac THE SOFT COVERING TISSUES
1 The nose:
The nose grows by 1mm per year on average, 1.5 and even 2mm at the time of puberty, this growth varies according to sex and age, especially in boys: it is more important during puberty and after, it does not change.
2 Upper lip:
Its profile varies according to certain elements
Its own growth which makes it advance by 1mm per year
The displacement of the upper incisor on which it rests, the thickness of the upper lip and a third of what the lower incisor moves back
3 Lower lip:
The part of point B faithfully follows the variations of the anterior edge of the mandible, the lower lip does not thicken in the event of a retreat of the lower incisor.
4 The chin:
Its soft tissues are slightly affected by skeletal growth.
Bjork’s height growth chart
