Growth of the Maxilla, Growth of the Maxilla, Mandible, Soft Tissue and BodyMandible, Soft Tissue and Body

Heekyoung Jo, D.D.S., M.S.Heekyoung Jo, D.D.S., M.S.

ORTD 323

Summer 2002

•General concepts of Growth•Growth Assessment•Bone formation and growth control•Growth of cranial complex

•General concepts of GrowthGeneral concepts of Growth•Growth Assessment•Bone formation and growth control•Growth of cranial complex

Growth and Development

• Terminology– Growth

– Development

• Pattern, Variability, and Timing

Pattern vs.. Variability• Normal growth patternex) Changes in overall body proportions

Cephalocaudal gradient of growth

Pattern vs. Variability

Scammon’s Curve

Pattern vs. VariabilityBoys GirlsGrowth Curves

Variability

• Racial and ethnic differences

• Gender

• Sickness

• nutrition

• Timing factor -Late/early maturers

• Problems with growth (hormones or genetics)

Timing Variation

• Early, average, and late matuerers

• Chronological age vs. Developmental age

•General concepts of Growth•Growth AssessmentGrowth Assessment•Bone formation and growth control•Growth of cranial complex

Why do we assess growth?

• To determine optimum time for treatment (growth modification and surgery)

• to determine the amount of growth left

• to determine type of growth

How to assess growth clinically

• Hand wrist x-ray

• sexual maturity: onset of menarche in girls, voice changes and facial hair in boys

• lateral cephalogram tracings: superimpositions

• Ask parents how much the child grew last year (height and shoe size)

• look at parent’s phenotype: tall or short

The Human Head ShapeBrachycephalic Dolichocephalic

•“Brachy” tends to grow horizontally; “Dolicho” tends to grow vertically.•Knowing the general pattern of growth and the expected direction can be helpful in orthodontic diagnosis and treatment planning.

Growth - cellular level

• Hypertrophy

• Hyperplasia

• Increased production of extracellular matrix

Hard Tissue Soft Tissue• Bone, teeth,

sometimes cartilage• Hyperplasia

hypertrophy mineralized ECM

• Interstitial growth, remodeling, endochondral

• Everything including some cartilage except bone and teeth

• Hyperplasia hypertrophy

• Interstitial growth

Soft Tissue Profile

convex straight concave

retrognathic orthognathic prognathic

Soft Tissue Changes with Growth

Boy growing normallyBlack - 10 yoRed - 14 yo

• Soft tissue profile tends to flatten with growth

• Nose and chin button growth at teenage years may change facial appearance

•General concepts of Growth•Growth Assessment•Bone formation and growth controlBone formation and growth control•Growth of cranial complex

Types of Bone formation

• Intramembranous– by secretion of bone matrix directly within C.T.

without any intermediate formation of cartilage– Through the activity of cells in the periosteum– Cranial vault, Mx & body of Md

• Endochondral – Cartilage is replaced by bone– Cranial base, Md condyle

Theories of Growth Control

• Determinants of the growth control– Bone– Cartilage– The soft tissue matrix in which the skeletal

elements are embedded - 60’s “Functional Matrix Theory” by Moss

• Level of control: Sites vs. Centers

Principles of Growth - Remodeling

• Resorption• Apposition

• Surface remodeling of a bone in the opposite direction to that in which it is being translated by growth of adjacent structures

•General concepts of Growth•Growth Assessment•Bone formation and growth control•Growth of cranial complexGrowth of cranial complex

Growth of the Craniofacial Complex

• Cranial Vault

• Cranial Base

• Maxilla (Nasomaxillary Complex)

• Mandible

Cranial Vault

• Intramembranous bone formation without cartilaginous precursor

• Apposition of new bones at the cranial sutures, periosteal activity(remodeling) due to the pressure from the growing brain

Cranial Base

• Mostly formed by endochondral ossification.• Bands of cartilage are formed between centers of

ossification called synchondrosis:– Spheno-occipital synchondrosis

– Inter-sphenoid synchondrosis

– Spheno-ethmoid synchondrosis

Cranial Base

• Cranial base grows by endochondral ossification that occurs at both margins of the synchondrosis.

Cranial Base

• Cranial base grows by endochondral ossification that occurs at both margins of the synchondrosis.

• Maxilla ( Nasomaxillary Complex)– Intramembranous ossification

• by apposition of bone at the sutures that connect the Mx to the cranium and cranial base

• by surface remodeling

• Mandible– Intramembranous and endochonral ossification

• The body grows longer by periosteal appposition of bone on its posterior surface

• The ramus grows higher by endochondral replacement at the condyle accompanied by surface remodeling

Maxilla • Remodeling of the palatal vault moves it in the same direction as it is being translated

• bone is removed from the floor of the nose and added to the roof of the mouth

•On the anterior surface, bone is removed, partially cancelling the forward translation. As the vault moves downward, the same process of bone remodeling also widens it.

Maxilla

• Growth of the surrounding soft tissues translates the maxilla downward and forward, opening spaces in the sutures where bone is added.

Maxilla

• Midpalatal suture is opened until teenage years.• Apposition of bone in the molar area accounts for

space for the third molars.

Mandible

• Remodeling is done by resorption in the anterior part of the ramus and deposition in the posterior part of the ramus

Mandible

• Overall growth direction results in a downward and forward displacement with most of growth occurring in the ramus.

Mandible

• Mandibular symphysis is closed by age of 1 year.• Late mandibular growth can occur in the late

teenage years or adulthood - most often seen in asians and males

When things go wrong

• Congenital craniofacial malformations: cleft lip/palate, syndromes (Apert, Crouzon, etc..), craniosynostosis

• Non-syndromic craniosynostosis

• Trauma

• Ankylosis

• Juvenile rheumatoid arthritis

When things go wrong

Trauma• Blow to one side of

the mandible may fracture the condylar process on the opposite side

• pull of the lateral pterygoid muscle distracts the condylar fragment including all the cartilage = resorption occurs