Growth and development l Orthodontics MCQs

PRENATAL & POSTNATAL GROWTH AND DEVELOPMENT  l Orthodontics & teeth alignment MCQs (multiple choice question) for dental students & orthodontists

CRANIOFACIAL BONE GROWTH

GENERALIZED SURFACE GROWTH FOLLOWING CESSATION OF GROWTH-CENTER ACTIVITY.

• The concept that generalized surface accretion of new bone occurs in a manner that simply conforms to existing contours is itself invalid, Summary of growth principles. The various bones of the craniofacial skeleton do not enlarge by a process of generalized surface accretion merely following existing contours.

• Facial growth is often regarded as a process occurring largely in facial sutures and by bone additions on the alveolar margin and maxillary tuberosity , this over simplification, however, does not take into account the extensive and fundamental process of remodeling growth that occurs in virtually all parts of all the bones.

• A bone may move by two means. It can grow (cortical drift) by selective deposition and resorption , or it can become displaced from one position to another. Relocation is shown by schematized segments.

Growth principles

• as mentioned above. However, this false notion is sometimes applied as an explanation for growth after sutures and other growth centers are presumed to become inactive. It is not possible for a bone to undergo any significant degree of surface accretion without corresponding additions at the various sutures. The sutural margin must also continue to grow proportionately as other bone surfaces receive continued deposits in order to maintain the proportionate configuration and dimensions of the whole bone and to retain its constant relative position.

•  It is noted that all periosteal and endosteal bone surfaces represent a series of local "growth sites" equal in significance to sutures, condyles, etc.

 

OVERALL GROWTH—SIZE INCREASE AND REMODELING.

• Two distinct but closely coordinated growth processes contribute to increasing size. One is the addition of new bone at sutures, condyles, synchondroses, alveolar margins, and other major growth sites. These centers are responsible for continued growth primarily in the particular parts of the bone directly associated with them—i.e., medullary bone in the neck and head of the condyle adjacent to the condylar growth center. All other parts of the bone, however, simultaneously and continuously undergo extensive processes of remodeling growth, which contributes two basic functions.

• It provides sequential adjustments in structure necessary as a companion process to overall growth. This serves to maintain the constant configuration of the growing bone. It further provides proportionate increases in the size of these areas and parts.

• Essentially, remodeling is a process of regional reshaping and resizing, and it functions as a response to relocation.

 

SURFACES FACING DIRECTIONS OF GROWTH.

• The particular surface that faces the actual growth direction is the surface that receives new bone deposits. Contralateral surfaces facing away from this growth direction are usually resorptive. The result is a drift movement of the entire cortical plate which follows the course of growth. Cortical movement produced by direct drift is to be distinguished from movements produced by displacement.

 

GROWTH MOVEMENTS—DRIFT AND DISPLACEMENT.

• A cortical plate can become moved by two means. It may grow from one position to another by addition and resorption of bone on selected surfaces, a process termed cortical drift; or it may move by being pushed or drawn as a consequence of growth displacement.

• Displacement is a result of two or more bones and contiguous soft tissues growing in relation to one another. In virtually all bones, various combinations of both kinds of movements occur at the same time, a factor which greatly complicates interpretations and analyses of the total growth process. The movements produced by displacement often appear to violate the principle stated above with regard to surfaces facing the irection of growth.

• For example, the premaxillary area faces the forward direction of overall enlargement. Yet this forward facing surface is actually regressive (resorptive) in nature. Facial growth, however, is a composite process involving actual growth in combination with displacement resulting from growth, so that a bone may undergo growth increases in one direction but become pushed or pulled in entirely different directions. Growth processes in each local area of a bone must be analyzed separately. The total growth of all the areas in each individual bone can then be visualized in an overall growth pattern. Finally, interrelated groups of bones may be viewed together in a composite picture that represents the cumulative sum of all these growth processes.

THE V PRINCIPLE.

• Many areas of the various craniofacial bones conform to a V configuration when viewed in section. These areas usually conform to a common growth plan which in most cases involves growth of the V toward its own wide end. Utilizing the principle stated above which deals with surfaces facing directions of growth, bone becomes added to the inner side of the V and removed from the outer. This serves to move the V and to reduce diameter progressively as wide parts become relocated into more narrow parts. The entire V enlarges in size at the same time.