Basic mechanism of craniofacial growth /certified fixed orthodontic courses by Indian dental academy


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Basic mechanism of craniofacial growth /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. CONTENTS     Introduction Mechanisms of growth: - Bone growth - Growth processes - Growth fields - Enlow’s V- principle - Growth pattern - Growth movements Changing concepts and hypotheses of craniofacial growth. Conclusion.
  3. 3. INTRODUCTION The fully developed cranium represents the sum of its separate parts, in which growth is highly differentiated and occurs at different rates and in different directions, and is thus a complex concept. By birth the craniofacial skeleton has undergone between 30% and 60% of its total growth. Although this reflects the early development of the skull, the remaining increase in size is not equal in all parts of the cranium. Whereas the size of the neuro-cranium increases by about 50% after birth, the facial skeleton grows to more than twice the size, the increase in height being the greatest, that in depth somewhat smaller, and that in width smallest.
  4. 4. The old theory on facial growth, introduced by Brodie, that the skull increases in size by direct symmetric expansion of all surfaces and contours is an antiquated statement. It is now accepted that the fully grown skull is not simply a larger version of the infant form and that the adult skull differs not only in size but also in shape from that of the child, depending on a process of differential growth in various parts of the cranium.
  5. 5.     Craniofacial growth may be divided into four components: growth mechanism (how new bone is formed). growth pattern (change in size and shape of the bone). growth rate (speed at which bone is formed). the regulation mechanism, which initiates and directs those three factors.
  6. 6. MECHANISMS OF GROWTH All bone growth is a complicated mixture of two basic processes, deposition and resorption, which are carried out by growth fields comprised of the soft tissues investing the bone. Because the fields grow and function differently on different parts of the bone, the bone undergoes remodelling (i.e. shape change). When the amount of deposition is greater than the resorption, enlargement of the bone necessitates its displacement (i.e. the physical relocation) in concert with other bone displacement.
  7. 7. BONE GROWTH    Tissue growth generally connotes an increase in size. At the cellular level, there are three possibilities for growth: Increase in the size of individual cells hypertrophy. Increase in the number of cells hyperplasia. Secretion of extracellular material. Growth of soft tissues occurs by a combination of hyperplasia and hypertrophy. These processes go on everywhere within the tissues, resulting in interstitial growth, which means that it occurs at all points within the tissue.
  8. 8. Bone cannot enlarge by proliferation and/or hypertrophy of existing cells or intercellular material because of its calcified, rigid nature. Its cells, which are encased in a hard matrix, have no space to divide. Therefore, the calcification process which imparts to bone its unique and structural characteristics also compels bone to grow by specifically adapted growth mechanisms which do not involve interstitial expansion.
  9. 9. Two distinct growth methods exist: an intramembranous and an endochondral bone growth mechanism. Another unusual characteristic of bone growth is that the increase in size is accompanied by a remodelling of the existing structure to adjust the bone's shape and dimensions as it enlarges. The remodelling activity entails localized apposition and resorption of bone. Therefore, bone growth is not totally an additive procedure. In some areas, bone is lost.
  10. 10. Intramembranous bone formation Undifferentiated cells in a connective tissue membrane form a cluster. Primary center of ossification – small spicules of bone are formed. (Site of initial ossification) Osteoblasts – organic matrix which subsequently ossifies. Meshwork of delicate bony trabeculae. continued activity of osteoblasts Formation of osteoid which rapidly calcifies.
  11. 11. The inner surfaces of the bone are lined by the endosteal membrane, which has osteogenic and/or osteoclastic potential. Bone produced by this membrane is called endosteal bone tissue. When it is produced by apposition, the mechanism is intramembranous. Intramembranous bone tissue is widely distributed in the prenatal as well as the postnatal skeleton and is a particularly fast growth mechanism.
  12. 12. Endochondral bone formation Begins within cartilage tissue which is surrounded by its perichondrium. Within the primary ossification center, the chondrocytes hypertrophy. The matrix between these cells becomes calcified and small blood vessels from the perichondrium erode into this area.
  13. 13. Spontaneous resorption occurs in the old calcified matrix and the lacuna spaces are created in this zone. Connective tissue accompanying the blood vessels is osteogenic – cells differentiate into osteoblasts and produce osteoid tissue directly on the cartilage spicules. A thin crust of bone is formed when the matrix becomes calcified.
  14. 14. Endochondral bone tissue, therefore, is formed within cartilage by a process involving partial calcification of a cartilaginous matrix, partial removal of calcified cartilage and its replacement by bone which has formed according to the conventional appositional (intramembranous) pattern. The bone increases in thickness by deposition on its growing surfaces, and the lumina of the original resorptive spaces are progressively reduced by the continuing process of bone formation.
  15. 15. In the skull, some bones form by the process of endochondral ossification. These are parts of the sphenoid and occipital bones which partly form as a result of activity in the sphenooccipital synchondrosis. In addition, the endochondral growth process occurs in the mandibular condyle.
  16. 16. The intramembranous and endochondral processes represent the main growth mechanisms of bone. For this reason, bones are characteristically classified as either membranous or endochondral. Some bones such as the mandible contain both mechanisms. Since most of the endochondral bone is ultimately resorbed and replaced by endosteal bone which forms according to the intramembranous pattern, few scattered remnants of endochondral bone survive in the adult skeleton.
  17. 17. GROWTH PROCESSES Deposition & Resorption. Bones grow by adding new bone tissue on one side of a bony cortex and taking it away from the other side. The surface facing toward the direction of progressive growth receives new bone deposition (+). The surface facing away undergoes resorption(-). This composite process is termed "drift." It produces a direct growth movement of any given area of a bone.
  18. 18.
  19. 19. GROWTH FIELDS The outside and inside surfaces of a bone are completely blanketed by a mosaic-like pattern of "growth fields." About half of the periosteal surface of a whole bone has an arrangement of resorptive fields and the other half is covered by depository fields. If a given periosteal area has a resorptive type of field, the opposite inside (endosteal) surface of that same area has a depository field, and vice versa. These combinations produce the drift of all parts of an entire bone.
  20. 20. Darkly stippled areas Lightly stippled areas Resorptive fields Depository fields
  21. 21.
  22. 22. The operation of the growth fields covering and lining the surfaces of a bone is carried out by the membranes and other surrounding tissues rather than by the hard part of the bone. Thus, growth is produced by the soft tissue matrix that encloses each whole bone. The genetic and functional determinants of bone growth reside in the soft tissues such as the muscles, tongue, lips, cheeks, integument, mucosae, connective tissues, nerves, blood vessels, airway, pharynx, the brain as an organ mass, tonsils, adenoids, and so forth.
  23. 23. All the various resorptive and depository growth fields throughout a bone do not have the same rate of growth activity. Some depository (or resorptive) fields grow much more rapidly or to a much greater extent than others. Fields that have some significant role in the growth process are often termed growth sites.
  24. 24. Some growth sites are called “growth centers ”. They are considered to be areas that somehow control the overall growth of the bone. This term also implies that the “force”, “energy” or “motor” for a bone resides primarily or solely within its growth center. The concept of growth centers finds support in relation to the growth of the epiphyseal plates of the long bones, but is no longer considered important in the growth of the craniofacial region.
  25. 25.    Thus, bone growth is now considered to be controlled by growth sites, not active growth centers as believed earlier. The following basic phenomena are involved in the growth mechanisms: conversion of cartilage (synchondroses, nasal septal cartilage, condylar cartilage). sutural deposition. periosteal remodeling.
  26. 26. SYNCHONDROSES     Displacement growth in the cranial base is made possible mainly by the synchondroses. Only a few persist postnatally in the region of the cranial mid base, the spheno-occipital synchondrosis being the most important one. The synchondroses of the cranial base may be regarded as special joints enabling growth to take place at younger ages. They contribute to the growth of the skull in all three dimensions. It is considered that this cartilage plays a relatively greater role in the adjustment changes in cranial base flexure than in its linear growth (Bjork, 1955 ; Scott, 1962).
  27. 27. NASAL SEPTAL CARTILAGE    The nasal septum is thought to play an important part in the prenatal and very early postnatal growth of the middle face. According to Scott, the septal cartilage occupies a unique location for pushing the whole maxilla forward and downward. The opposing view, commonly termed the functional matrix by Moss, suggests that the nasal septal cartilage is a locus of secondary, compensatory, and mechanical growth. Growth of the nasal septal cartilage is secondary to and compensatory for a prior passive displacement of the midfacial bones but plays a significant biomechanical role in maintaining normal midfacial form.
  28. 28. CONDYLAR CARTILAGE    This is a secondary type of cartilage. It participates in growth early in human life and absorbs pressure forces later in life. The condyle and its cartilage participate in regional adaptive growth and are thus not a major growth center for the whole mandible, as was believed earlier. The condyle has a great capacity to adapt to mandibular displacement during growth. As the condyle is also part of the ramus the fibrous layers of condylar cartilage are continuous with the periosteum of the ramus, and remodeling processes are seen in all components of the joint.
  29. 29. SUTURES Displacement growth is made possible by the cranio­facial sutures, which have a dual function of permitting growth movement and uniting the bones of the cranium. When cranial growth ceases, most sutures ossify. 1. 2. 3. The main biologic function of the sutural tissue, besides being an articulation, includes: To unite bones, while allowing minor movement. To act as areas of growth; and To absorb mechanical stress, thus protecting the osteogenic tissues of the bone.
  30. 30. 1. 2. The movements that takes place between bones at suture sites are of two types: The first type is the displacement of bones, which together with an intrinsic deformation of the bones enables a 'molding' of the skull when the head is passing through the birth canal. The second type of movement occurring at suture sites is displacement of bones relative to each other as a part of skull growth.
  31. 31. PERIOSTEUM   A periosteal cell layer is established with the initiation of the intramembranous ossification of the bone, and the surrounding mesenchymal cells aquire the character of osteoblasts. Bone growth involves a continuous replacement of the matrix- producing cells via cell division in the cambium layer. Owing to their location, both matrix-producing and proliferating cells are subject to mechanical influence.
  32. 32.    If the pressure exceeds a certain threshold level, so that the blood supply to these cells is reduced, osteogenesis ceases and osteoclasts appear leading to resorption, until a biochemical equilibrium is restored. If, on the other hand, the periosteum is exposed to tension, it responds with bone deposition. The periosteum continues to function as an osteogenic zone throughout life, but its regenerative capacity is extremely high in the young child. The influence of the periosteum is of greatest significance for the change in size and shape of the bones.
  33. 33. GROWTH PATTERN Growth pattern refers to the change in the size and shape of the bone. Bone grows by two fundamental physiologic processes - modeling and remodeling. MODELING. Modeling is a surface-specific activity (apposition and resorption) that produces a change in the size and shape of the bone.
  34. 34. REMODELING. Remodeling is a basic part of the growth process. A bone remodels during growth because its regional parts become moved ("drift“) from one location to another as the whole bone enlarges. This requires sequential remodeling changes in the shape and size of each region.
  35. 35.
  36. 36. For example, the ramus moves progressively posteriorly by a combination of deposition and resorption. As it does so, the anterior part of the ramus becomes remodeled into a new addition for the mandibular corpus. This produces a growth elongation of the corpus. This progressive, sequential movement of component parts as a bone enlarges is termed relocation . Relocation is the basis for remodeling. The whole ramus is thus relocated posteriorly, and the posterior part of the lengthening corpus becomes relocated into the area previously occupied by the ramus.
  37. 37.
  38. 38. In the maxilla, the palate grows downward by periosteal resorption on the nasal side and periosteal deposition on the oral side. This growth and remodeling process enlarges the nasal chambers. The bony maxillary arch and palate of early childhood are thus remodeled into the nasal chambers of the adult.
  39. 39.
  40. 40. In summary, the process of growth remodeling is paced by the composite of soft tissues housing the bones, and the functions are to: (1) progressively enlarge each whole bone; (2) sequentially relocate each of the component parts of the whole bone to allow for overall enlargement; (3) shape the bone to accommodate its various functions in accordance with the physiologic actions exerted on that bone; and (4) carry out regional structural adjustments so that a functional fitting of all the separate bones to each other and to their soft tissues is achieved.
  41. 41. Four different kinds of remodeling occur in bone tissues:  Biochemical remodeling , taking place at the molecular level. This involves the constant deposition and removal of ions to maintain blood calcium levels and carry out other mineral homeostasis functions.  Secondary reconstruction of bone by haversian systems and also the rebuilding of cancellous trabeculae.  Regeneration and reconstruction of bone during or following pathology and trauma.  Growth remodeling – remodeling process in facial growth.
  42. 42. ENLOW’S V - PRINCIPLE One of the basic concepts in facial growth is the "V" principle. Many facial and cranial bones, or parts of bones, have a V-shaped configuration. Bone deposition occurs on the inner side of the "V“ and resorption takes place on the outside surface. The "V" thereby moves from position A to B and simultaneously increases in overall dimensions. The direction of movement is toward the wide end of the "V."
  43. 43. Thus, a simultaneous growth movement and enlargement occurs by additions of bone on the inside with removal from the outside.
  44. 44. The diameter at A is reduced because the broad part of the bone is relocated to position B. This is a remodeling change that converts a wider part into a more narrow part, as both become sequentially relocated. Periosteal resorption and endosteal deposition of bone tissue carry this out.
  45. 45.  A transverse histologic section of the bone at A shows that the periosteal surface is resorptive; bone-removing osteoclasts blanket this surface during the active period of bone growth. The depository endosteal surface is lined with bone-producing osteoblasts.  A transverse section at B shows new endosteal bone added onto the inner surface of the cortex.  A transverse section made at C shows an endosteal layer that was produced during the inward growth phase. This is covered by a periosteal layer of bone following outward reversal, as this part of the bone now increases in diameter.
  46. 46.  A transverse section at D shows a cortex composed entirely of periosteal bone. The outer surface is depository, and the endosteal surface is resorptive.
  47. 47. GROWTH MOVEMENTS Two kinds of growth movements are seen during the enlargement of craniofacial bones: - Cortical drift. Displacement.
  48. 48. Cortical Drift. Drift encompasses both relocation and shifting of an enlarging portion of the bone by the remodeling action of its osteogenic tissues. The continuous remodeling maintains the shape and proportions of the bone throughout the growth period. As bone deposition occurs during a simultaneous breakdown of opposing bone surfaces, the bone will migrate in relation to a fixed structure. This migration through remodeling is known as drift .
  49. 49. As a general rule, the surface towards which growth occurs is appositional, whereas the surface facing away from the direction of growth is resorptive. The two processes do not always occur with the same intensity. Rather, appositional activity normally exceeds resorption during the growth period.
  50. 50. Due to new bone deposition on one surface, all other parts of the structure will undergo shifts in relative position, a movement that is termed relocation . As a result of this process, further adaptive bone remodeling has to take place, to adjust shape and size of the bone to its new position. An example of such passive drift in the facial region is the hard palate, which subsides in relation to the overlying structures, due to resorption of the nasal floor and concomitant deposition on the roof of the palate. Relocation and structural remodeling thus are closely related to each other.
  51. 51.
  52. 52. Displacement. Displacement is the movement of the whole bone as a unit. It is of two types – primary and secondary displacement. Primary displacement. As a bone enlarges, it is simultaneously carried away from other bones in direct contact with it. This creates the "space" within which bony enlargement takes place. The process is termed primary displacement (sometimes also called "translation").
  53. 53. It is a physical movement of a whole bone and occurs while the bone grows and remodels by resorption and deposition. As the bone grows by surface deposition in a given direction, it is simultaneously displaced in the opposite direction.
  54. 54. Thus, primary displacement is associated with a bone's own enlargement, and it always takes place in the direction opposite to the vector of bone growth. The process of new bone deposition does not cause displacement by pushing against the articular contact surface of another bone. Rather, the bone is carried away by the expansive force of all the growing soft tissues surrounding it. As this takes place, new bone is added immediately onto the contact surface, and the two separate bones thereby remain in constant articular junction.
  55. 55. For example, the nasomaxillary complex is in contact with the floor of the cranium. The whole maxillary region is displaced downward and forward away from the cranium by the expansive growth of the soft tissues in the midfacial region. This then triggers new bone growth at the various sutural contact surfaces between the nasomaxillary complex and the cranial floor. Displacement thus proceeds downward and forward as growth by bone deposition simultaneously takes place in an opposite upward and backward direction (that is, toward its contact with the cranial floor).
  56. 56.
  57. 57. Similarly, the whole mandible is displaced "away" from its articulation in each glenoid fossa by the growth enlargement of the composite of soft tissues in the growing face. As this occurs, the condyle and ramus grow upward and backward into the "space" created by the displacement process. The ramus also remodels as it relocates posterosuperiorly. It also becomes longer and wider to accommodate: (1) the increasing mass of masticatory muscles inserted onto it; (2) the enlarged breadth of the pharyngeal space; and (3) the vertical lengthening of the nasomaxillary part of the growing face.
  58. 58.
  59. 59. Secondary displacement. Secondary displacement is the movement of a whole bone caused by the separate enlargement of other bones, which may be nearby or quite distant. The secondary displacement is not associated with growth of the bone itself but initiated by enlargement of adjacent bones and soft structures and transferred to adjacent bones.
  60. 60. For example, increases in size of the bones that compose the middle cranial fossa (in conjunction with growth of the brain) result in a marked displacement movement of the whole maxillary complex anteriorly and inferiorly. This is independent of the growth and enlargement of the maxilla itself.
  61. 61.
  62. 62. (1) (2) In summary, the overall skeletal growth process (displacement and remodeling) carries out two general functions: It positions each bone, and It designs and constructs each bone and all of its regional parts to carry out that bone's multifunctional role. The functional input to the membranes of the bone from the aggregate of soft tissues causes a bone to develop into its definitive morphologic structure and to occupy the location it does.
  63. 63. CHANGING CONCEPTS AND HYPOTHESIS OF CRANIOFACIAL GROWTH Craniofacial morphology is now considered to be multifactorial; that is, facial development is influenced by several genes together with various environmental factors.  Sicher’s hypothesis (Sutural Dominance). Sicher (1940) claimed that craniofacial growth as a whole was the result of innate genetic formation in the skeletal tissues. The importance of environmental factors, such as pressure from adjacent organs, was reduced to a certain influence on the shape of the bone during development.
  64. 64.  Scott’s hypothesis (Nasal septum) Scott limited the heredity and expansive growth of the osteogenic tissues to the periosteum and chondral structures. In contrast to Sicher, he considered suture growth to be a response to growth in adjacent structures, which carried the genetic information (epigenetic regulation). He considered the displacement of the bones of the cranium to be secondary to the morphogenetic requirements of the brain mass, while the growth of the middle face was mainly the result of growth of the chondrocranium - above all the nasal septum - which pushed the bones away from the structures in the cranial base. Similarly, the growth of the mandible was considered to be the result of the autonomic expansive growth of the condylar cartilage.
  65. 65.  Moss’ hypothesis (Functional Matrix). He hypothesised that the osteogenic tissue is deprived of all innate genetic control (bone has no genes). The craniofacial complex is regarded as a structure with certain functions, classified as functional cranial components. These consist of a functional matrix, comprising the tissues and cavities that carry out the function as such, and a skeletal unit, consisting of bone, cartilage, and tendons, which protects and supports this matrix.
  66. 66. Parts of the functional matrix can be shown to have direct influence on the bone through the periosteum - for example, muscle function in muscle insertions and the teeth in the alveolar process - and are therefore referred to as the periosteal matrix. This control of osteogenesis is a local process comprising remodeling and drift and is limited to changes in the size and shape of small skeletal units. A broader effect is achieved by the tissues and functional cavities surrounded by capsules, summarized by the term capsular matrix - for example, the brain mass and respiratory function - which produce the movement of the whole bone classified as displacement.
  67. 67.  van Limborgh’s theory. Postnatal facial growth is controlled by a multifactorial system that is influenced by intrinsic, genetic, and local factors. According to van Limborgh, craniofacial morphogenesis is controlled by five different factors: Intrinsic genetic factors, local and general epigenetic factors and local and general environmental factors. According to this theory, both local and general factors can cause anomalies.
  68. 68. The intrinsic genetic factors exert their influence within the cells in which they are contained and determine the characteristics of cells and tissues (cranial differentiation). Epigenetic factors are those that are determined genetically but are effective outside the cells and tissues in which they are produced. According to van Limborgh, these factors can have an effect on the adjacent structures such as local epigenetic factors (for example, embryonic induction influences), or have a distant influence such as general epigenetic factors (for example, sex and growth hormones). The local environmental factors (such as muscular force) are of much greater relevance to the postnatal craniofacial growth control than the general factors (for example, food, oxygen supply).
  69. 69.  Petrovic’s hypothesis (Servosystem) Petrovic et al. (1990) developed a cybernetic model (direction and control of a course of events), illustrating the complexities of multifactorial relationships involved in the growth process. In sum, the physiologic effect of factors controlling the facial growth is not limited to simple commands but includes relays, implying interactions and feedback loops as follows: 1)All of them form a structured system, a servosystem, in which the position of occlusal adjustment plays the role of the peripheral 'comparator';
  70. 70. 2)The sagittal position of the upper dental, arch is the 'constant changing reference input', controlled by somatotrophin and somatomedin and by septal cartilage growth and by tongue growth; 3)The sagittal position of the lower dental arch is cybernetically, the controlled variable; and 4)Signals originating from the 'peripheral comparator' of the servosystem produce an increased postural activity of the lateral pterygoid muscle and of some other masticatory muscles, enabling the lower dental arch to adjust to the optimal occlusal position. The increased muscle activity hence induces a posterior growth rotation of the mandible and, secondly, a supplementary growth rate of the condyle.
  71. 71. CONCLUSION Malocclusion and craniofacial deformity arise through variations in the normal developmental process, and so must be evaluated against a perspective of normal development. Because orthodontic treatment often involves manipulation of skeletal growth, clinical orthodontics requires an understanding of the growth of the craniofacial skeleton. Planned changes of bone growth and morphology are a fundamental basis of orthodontic treatment.
  72. 72. The vectors of growth can be modified and manipulated for treatment during the growing years. Thus, a knowledge of the basic concepts of craniofacial growth is an essential for sound treatment planning, and goes a long way in achieving the desired treatment outcome.
  73. 73. REFERENCES    Gianelly A., Goldman H.: Biologic basis of orthodontics. 2nd Edition, 1971. Enlow D.H.: Handbook of facial growth. 2nd Edition. Proffit W.R.: Contemporary orthodontics. 3rd Edition, 2000.
  74. 74.    Moyers R.E.: Handbook of orthodontics. 4th Edition. Enlow D.H., Harris D.B.: A study of the postnatal growth of the human mandible. Am J Orthod. 1964; 50: 25-50. Thilander B.: Basic mechanisms in craniofacial growth. Acta Odontol Scand 1995; 53: 144-151.
  75. 75.   Persson M.: The role of sutures in normal and abnormal craniofacial growth. Acta Odontol Scand 1995; 53: 152-161. Ronning O.: Basicranial synchondroses and the mandibular condyle in craniofacial growth. Acta Odontol Scand 1995; 53: 162-166.
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