Sites and Types of Growth Dr Majid Heidarpour

Basic Concepts (1) The sites or location of growth, (2) The type of growth occurring at that location, and (3) The determinant or controlling factors in that growth.

Craniofacial Complex (1) Cranial vault (2) Cranial base (3) Nasomaxillary complex (4) Mandible.

Cranial Vault Formed directly by intramembranous bone formation, without cartilaginous precursors. Growth process is entirely the result of periosteal activity Remodeling and growth occur primarily at cranial sutures, but periosteal activity also changes both the inner and outer surfaces of bones Fontanelles, allow deformation of the skull at birth.

Cranial Base Formed initially in cartilage and are later transformed by endochondral ossification to bone. As one moves laterally, growth at sutures and surface remodeling become more important. Synchondroses: Growth centers Even within the cranial base, bone remodeling on surfaces is also important(e.g. sphenoid sinus)

Nasomaxillary Complex The maxilla develops postnatally entirely by intramembranous ossification. growth occurs in two ways:(1) by apposition of bone at the sutures and (2) by surface remodeling. It grows "out from under the cranium” in two ways: (1) by a push from behind created by cranial base growth(up to age 6 y/o), and (2) by growth at the sutures. Tuberosity

Remodeling and Translation

Mandible In contrast to the maxilla, both endochondral and periosteal activity are important in growth of the mandible, and displacement created by cranial base growth. The chin is almost inactive. The body of the mandible grows longer by periosteal apposition of bone on its posterior surface. The ramus grows higher by endochondral replacement at the condyle accompanied by surface remodeling.

Mandible As the mandible grows in length, bone at the tip of the condylar process at an early age can be found at the anterior surface of the ramus some years later. Direction of growth and translation Principal growth sites: Post border or ramus, Condyle, Coronoid

Growth of Lip

Growth of Nose

Theories of Growth Control Three major theories: 1-bone is the primary determinant of its own growth(genetic); 2-cartilage is the primary determinant of skeletal growth(genetic), while bone responds secondarily and passively(epigenetic); and 3- soft tissue matrix is the primary determinant of growth(genetic), and both bone and cartilage are secondary followers(epigenetic).

Sites Versus Centers of Growth A site of growth is merely a location at which growth occurs, whereas a center is a location at which independent (genetically controlled) growth occurs. All centers of growth also are sites, but the reverse is not true. The sutures between the membranous bones of the cranium and jaws are not growth centers: First, when an area of the suture between two facial bones is transplanted to another location the tissue does not continue to grow. Second, it can be seen that growth at sutures will respond to outside influences.

Cartilage As a Determinant Two kinds of experiments have been carried out : 1- transplanting cartilage. 2- removing cartilage.

Functional Matrix Neither the cartilage of the condyle nor the nasal septum cartilage is a determinant of jaw growth. Growth of the face occurs as a response to functional needs and neurotrophic influences and is mediated by the soft tissues. Major determinant of growth of the maxilla and mandible is the enlargement of the nasal and oral cavities, which grow in response to functional needs.

Distraction Osteogenesis under some circumstances, bone can be induced to grow at surgically created sites by the method called distraction Osteogenesis. The best results are obtained if distraction starts after a few days of initial healing and callus formation, and if the segments are separated at a rate of a millimeters per day.

Summary Growth of the cranium occurs almost entirely in response to growth of the brain. Growth of the cranial base is primarily the result of endochondral growth and bony replacement at the synchondroses, which have independent growth potential but perhaps are influenced by the growth of the brain. Growth of the maxilla occurs from a combination of growth at sutures and direct remodeling of the surfaces of the bone. The extent to which growth of cartilage of the nasal septum leads to translation of the maxilla remains unknown, but both the surrounding soft tissues and this cartilage probably contribute to the forward repositioning of the maxilla. Growth of the mandible occurs by both endochondral proliferation at the condyle and remodeling of bone at surfaces. Mandible is translated by the growth of muscles and other adjacent soft tissues, and that addition of new bone at the condyle is in response to the soft tissue changes

References  Contemporary Orthodontics, 4 th ed 2007:  Chapter 2, Pages: