RHYTHM AND DIRECTION OF FACIAL GROWTH
Plan
Introduction
- General / Definitions
- Means of studying growth
2-1 Teleradiography
2-2 Histo-anatomical techniques
2-3 Animal testing
2-4 The study of pathological cases
2-5 Statistical methods
- Estimation of growth stage
3-1 Civil age
3-2 Dental age
3-3 The rate of height growth
3-4 Bone age
3-4-1 Wrist X-ray
3-4-2 Hand X-ray
3-4-3 Profile teleradiography (vertebral age)
3-5 Secondary sexual characteristics
- Growth Directions
4-1 Growth direction at the face level
4-2 General directions of mandibular growth
Conclusion
- General:
Definitions:
Growth: is defined by Meredith as a series of anatomical and physiological changes from prenatal life until the end of growth.
According to Bassigny, it is the progressive development of an organism or organ, from birth to adult size.
According to Delaire : the face reaches approximately eighty percent of its adult dimensions by the age of five.
This growth is linked to genetic, hormonal and environmental determinants.
Growth rate:
Growth is not a regular phenomenon; it goes through phases of acceleration and deceleration from birth to adulthood, these variations are uniform for the entire skeleton including also the maxilla and the mandible.
Growth has two peaks: one at birth and one at puberty.
The growth rate:
Growth rate is the amount of growth that occurs in a given time period, the increase in height per unit time is visualized by the Bjork growth curve or height growth rate curve (Figure 1).
- Interpretation of Bjork’s height growth curve:
The growth rate is very high from birth to 6 months, then it decreases significantly from 6 months to 2 years, that is to say during the infantile period, during the juvenile period, from 2 years until the pre-pubertal period (10 ~ 11 years in girls and 12 ~ 13 years in boys), the slope of the curve is very low, stable but low growth.
The growth rate then increases considerably until the pubertal peak (on average 12 years in girls and 14 years in boys). Girls therefore have their growth peak two years earlier than boys and finally around 14 years in girls and 16~18 years in boys the growth rate gradually decreases until it stops completely. When growth stops only the ears and nose continue to grow.
Figure 1: Bjork’s height growth curve
- The means of study:
2-1 Teleradiography:
Teleradiography has made it possible to study craniofacial growth by superposition procedures (Broadbent and Brodie) and also by the tantalum implant method (Bjork), in the maxilla or mandible in living animals. This procedure has made it possible to follow the movement of bone structures using X-rays.
Figure 2: Profile teleradiography
2-2 Histo-anatomical techniques :
These studies are carried out on cadavers of varying ages where the authors study the bone pieces from an anatomical point of view (shape, position and relationship of the bone with the surrounding structures) and histological point of view (the study of the microscopic structure of the tissues and bone cells).
2-3 Animal experimentation:
These studies are carried out on laboratory animals such as guinea pigs, mice, monkeys, etc.
2-4 Study of pathological cases:
It is the study of pathological cases observed in human clinic, study of craniofacial malformations.
- Figure 3: Apert syndrome Figure 4: Crouzon syndrome
2-5 Statistical methods:
Epidemiological and statistical tests have become almost obligatory companions of researchers.
- Estimation of growth stage:
It is necessary to establish an orthodontic treatment plan to specify the subject’s growth stage and its location on the Byork growth curve; this is in order to be able to take advantage of a strong growth spurt or to avoid its effects; for this we take into account:
3-1 Civil age:
We cannot base ourselves on the civil age because there are very significant variations in bone development from one individual to another at the same civil age.
3-2 Dental age: There does not appear to be any significant correlation between facial growth and dental age (stage of dentition reached by a subject at a given time in their development).
Figure 5: Dental age 8 years
3-3 The rate of height growth:
Knowledge of the rate of height growth is of great interest to the orthodontist because the face in general, and the maxilla and mandible in particular, grow at the same rate as height.
Knowing that the peak of height growth precedes the peak of facial growth by approximately 3 months.
• Growth of 5 to 6 cm per year corresponds to the pubertal minimum.
• A growth of 8cm in girls and 10cm in boys corresponds to the growth peak.
Figure 6: Stature and maxillomandibular growth curves
- It can be seen from the curves that the rate of height growth shows a certain parallelism with the growth of the maxilla and the mandible.
- The mandible continues to grow after the end of maxillary growth and the end of statural growth.
- Mandibular growth continues on average 2 years after that of the upper jaw , but individual variations are very significant.
- – Condylar growth continues beyond height growth.
- – In girls, the mandibular length increases again later, around 17-18 years old, whereas in boys the length is greater and its growth lasts until 20 years old.
- The study of height growth allows us to monitor facial growth.
However, we cannot reliably locate a subject on the Bjork curve since the latter only takes into account civil age.
3-4 Bone age:
Bone age is the stage of maturation of a subject’s bones at a given time, reading bone age is done from an X-ray of the wrist, hand or a profile teleradiography (vertebral age).
- 3-4-1 Wrist X-ray :
This region contains many small bones whose appearance is progressive. The average age of calcification follows a progression whose average is known. However, the variability of this estimate is significant, which makes this process quite imprecise.
- 3-4-2 Hand X-ray :
It should be noted that the appearance of a small bone; the sesamoid, opposite the internal face of the diaphysis of the first phalanx of the thumb signals the onset of the major pubertal growth spurt. This bone is visible on average 1 year before the growth spurt, more precisely 9 months before in girls and 12 months before in boys.
Figure 7: The sesamoid bone
Phalangeal maturation goes through three stages and correlates with statural and facial growth.
• Lenticular stage (=): corresponds to an epiphysis with a thin edge as wide as the diaphysis
• Capsular stage (“cap” stage): epiphysis with a thick and wide edge extending beyond the diaphysis
• Union stage (“U” stage): fusion of the epiphyses to the corresponding diaphyses, which indicates bone maturation
Bone age
Each finger of the hand has three (03) phalanges:
– PP: first phalanx.
– MP: middle phalanx.
– DP: distal phalanx.
The fingers are numbered from 1 to 5 from the thumb to the little finger.
- The PP1CAP stage corresponds to the growth peak :
the epiphysis of the first phalanx of the thumb exceeds the diaphysis at the time of peak growth.
| Phalangeal maturation stage PP2 = MP3 = S PP1 cap. MP3 cap. DP3 U. PP3 U. MP3 U. RU | Correlation of facial growth stage -3 – 1 – 1 0 (within 1 year before peak) – 1 0 (1 year before peak) 0 pubertal peak 0 + 1 (within 1 year after peak) + 2 2 + 3 Complete union of the epiphysis with the radius. |
- 3-4-3 Profile teleradiography: vertebral age
Cervical vertebrae visible on lateral teleradiographs can be used to interpret signs of facial and especially mandibular maturation. The method was discovered in 1972 by Lamparski, later taken up by Baccetti, Franchi and MacNamara.
The CVMS (cervical vertebrae maturation stage) method is a reliable procedure for establishing skeletal maturation in order to determine the best time to perform orthopedic-functional treatment.
The advantage of CVMS is that the necessary information is available on the lateral teleradiography, which is routinely used to establish orthodontic diagnosis.
This involves assessing the size and shape of the vertebrae from the 2nd to the 6th:
Vertebral age
_ Concavity of the lower border : a gradual development of a concavity at the base of the vertebrae is noted during growth.
_ The inclination of the upper edge: we note a modification of the inclination of the upper edges of the cervical vertebrae, at the first stages of growth the upper edges of the vertebrae are inclined from top to bottom while at the last stages (CVS 5 and CVS 6) the upper edges are straight.
_ Height of the anterior edge of the vertebral body : an increase in the height of the cervical vertebrae with skeletal maturity is present. These vertebrae become, at the end of growth, taller than they are wide.
_ The thickness of the intervertebral spaces.
_ The shape of the vertebrae: the shape of the cervical vertebrae passes through different stages during growth, from the initial trapezoidal shape, it passes at the time of the pubertal peak to the horizontal rectangular shape, then to the square shape, until reaching the vertical rectangular shape at the end of growth.
Six stages have been established: CVS 1, CVS 2, CVS 3, CVS 4, CVS 5, CVS 6.
3-5 Secondary sexual characteristics:
Very strong correlations were found between the appearance of sexual characteristics and the date of peak growth.
The first period occurs approximately seventeen (17) months after the peak of growth, as does the growth of hair and the change of voice in boys.
- Growth directions:
4-1 Growth direction at the face level :
Bjork, using the technique of implants inserted under the periosteum in areas not subject to remodeling, found that the average growth direction of the face follows a vector with an angulation of 51° relative to the subnasal plane. This displacement is more sagittal during the juvenile period and more vertical during adolescence.
BJORK implant method
On a profile TLR, a line drawn connecting an anterior implant with a posterior implant on the same side, allows us to know the direction of rotation of the maxilla in the different age periods.
According to Broadbent ‘s work , there is a radiating expansion of the face from a point slightly below the sella turcica . The face therefore moves downward and forward along a line from point S (center of the sella turcica) to the gnathion.
4-2 General directions of mandibular growth:
In 1969, using implants and the method of cephalometric superpositions , BJORK highlighted different types of facial rotations.
BJORK differentiates three types of growth direction, according to the mandibular shapes observable on lateral teleradiography.
- A type of anterior mandibular rotation: the direction of growth being rather horizontal.
- A type of average mandibular rotation.
- A type of posterior mandibular rotation: the growth direction being rather vertical.
Conclusion
A good part of orthodontic treatments are aimed at subjects in a period of growth presenting a certain disharmony between the different elements of the face.
The growth rate, the amount of residual growth, and the direction of growth specific to each individual are essential elements in establishing an accurate diagnosis and developing an individualized treatment plan.
RHYTHM AND DIRECTION OF FACIAL GROWTH
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