General principles of growth and development l Orthodontics MCQs

GENERAL PRINCIPLES OF GROWTH AND DEVELOPMENT l Orthodontics & teeth alignment MCQs (multiple choice question) for dental students  & orthodontists

 

Growth and development 

Scammon’s curve of growth

•  Lymphoid tissue grows by 200% in late childhood then decreases
•  Neural tissue grows rapidly until the age of 6-7 then stops
•  Genitals negligible growth until puberty
•  Somatic tissue [ 2-3 years and 18-20 years = rapid growth]

 

• In jaw bones: Deposition occurs on the side of growth + Resorption occurs on the opposite side of growth → cortical drift

 

Bone displacement

 Primary bone displacement : 

• bone is displaced because of it’s own growth / enlargement – displacement occurs in the opposite side but parallel to the direction of growth and amount of displacement depends on amount of bone deposited

 Secondary bone displacement : 

• the displacement is not related to the growth of the bone itself.

 

Mandibular cartilage

1.            Primary cartilage : Meckel’s cartilage → forms the body of the mandible
2.            Secondary cartilage : condylar and coronoid cartilage [ coronoid cartilage completely ossifies after birth]

• Condylar cartilage is the major site of mandible growth after birth
• During mandible growth the posterior border of the ramus undergoes deposition and the anterior border undergoes resorption + mental protuberance is accentuated by bone resorption above it

 

Growth spurt:

Boys

1. 12.5 – 15 years old [ avg 14 year]
2. Max velocity is 10 cm / year
3. Results in height increase of 20 cm and weight increase of 20 kg
4. principal hormone is testosterone but some estradiol may be converted from testosterone.

Girls

1. 10.5 -13 years old [ avg 12 years]
2. Max velocity 8 cm / year
3. Results in height increase of 20 cm and weight increase of 16 kg
4. The principal hormone is estradiol but some testosterone may be converted from androstenedione

Q: how can you determine the child’s age?

•          Skeletal age = based on ossification of bones [ mostly assessed by radiographs of the hands and wrists compared to an atlas of radiographs that covers the entire developmental period ]
•          Dental age = based on tooth formation + eruption [ degree of cusp/ root calcification , development of the roots, closure of the apical foramen, emergence ( penetration of the gingiva) , eruption ( contacting the opposing tooth ) is assessed]
•          Simplest way to determine age is look for number of teeth erupted and the sequence of eruption

            Morphological age = based on height

              Sexual = based on development of sexual features

 

 

Face development

• With growth the profile will straighten

 

Nose growth 

length and depth changes continue after skeletal growth stops

A. At puberty :

•                         frontal bone to nasal bone angulation changes and the genetically determined dorsal hump is expressed
•                         • female growth changes are greatest between 10 to 13 years
•                         • male growth changes are greatest between 13 to 16 years                         

B. between 13 and 18 years:

• nasal bone angulation can change by 30%
• the dorsum can lengthen by 1mm/year
• the columella depth may change by 0.5mm/year
• nose and chin size can be inversely correlated
• a well balanced profile before puberty may deteriorate

 

lip growth

• the lower lip grows faster than the upper lip
• the combined growth of the lips exceeds the growth of the lower anterior face height
• lip incompetency decreases with age
• with age lips lose their tone and the lip line drops
• Growth of the lips trail behind the growth of the facial skeleton until puberty , then catches up and exceeds the skeletal growth thereafter
• Lips grow earlier in girls than in boys
  
• Lip thickness increases during childhood and adolescence and reaches maximum at the end of puberty (14 in girls and 16 in boys) and then decreases in late teens
• Girls have more lip thickness than boys at all ages

 

Chin growth

•  the symphysis shape is genetically determined
•  males usually have greater chin change than females
•  changes are accentuated at puberty
•  most change in the chin form and position is due to growth rotations

1.       chin prominence increases with upward and forward growth rotation patterns [short face]
2.       chin prominence decreases with downward and backward growth rotation patterns [ long face]

 

GENERALIZED SURFACE GROWTH.

• The growth of facial bones does not occur by a process of uniform, overall surface accretion that simply follows the surface contours already present Note that it is impossible to derive an adult bone, such as the mandible or maxilla, from its neonatal form by such a growth process . Surface contours would become progressively more disproportionate, and the configuration of the bone would be lost.

CENTERS OF GROWTH.

• A given craniofacial bone usually has two or three major growth sites (sutures, condyles, synchondroses, etc.). However, it is a common misconception to assume that these "centers" are responsible for virtually all increases in the growing bone. The many other inner and outer surfaces of the bone are not passive, and virtually all parts in each individual bone are active during the growth period. The entire bone is directly involved in the complex remodeling changes that occur throughout its regional areas.