DYNAMICS OF GROWTH .
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An in new depth understanding of facial morphogenesis is
essential so that clinician can grasp. a) Differences between normal and range of abnormal. b) Biologic reasons for these variations and differences. c) Reasons for rationales utilized in diagnosis, treatment planning and selection of appropriate clinical process. d) Biologic reasons underlying the problems of retention, rebound andwww.indiandentalacademy.com relapse after treatment.
Concepts to be discussed in dynamics of growth are:-
Pattern of growth
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Variability
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Timing
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Differential growth
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Remodeling www.indiandentalacademy.com
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Drift
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Displacement
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Relocation
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Basicranial flexure
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Growth field boundaries www.indiandentalacademy.com
Pattern: In general sense, the pattern reflects proportionality. Pattern in growth represents not just a set of proportional relationship at a point in a time, but the change in these proportional relationships over time. Pattern of growth refers to the changes in these spatial proportions over time. www.indiandentalacademy.com
The facial growth pattern also shows the cephalocaudal gradient. Mandible being further away from the brain, tend to grow more and later than the maxilla, which is closer. An important aspect of pattern is predictability. The proportional relationship within a pattern can be specified mathematically. A change in growth pattern would indicate an alteration in the expected and predictable sequence of changes in proportions expected for that individual. www.indiandentalacademy.com
VARIABILITY: -
Variability is the law of nature. Because of infinite number of genetic possibilities, no to individuals are ever exactly alike.
Variations in response to environment cause increasing difference among similar individuals with time. Variability may be demonstrated in many ways. In physical growth, variability is demonstrated by the use of statistics, which express quantitatively the range of differences found in a large population of individuals of similar age, sex, www.indiandentalacademy.com socioeconomic background and race
It can be difficult, but clinically very important to
decide weather an individual is merely at the extreme of the normal variation of changes in proportions expected for that individual. Rather than categorizing people as normal or abnormal, it is more useful to think in terms of deviations from the usual pattern and to express variability quantitatively. One way to do this is to evaluate a given child relative to peers on a standard growth chart. www.indiandentalacademy.com
TIMING: -
A final major concept in physical growth and development is timing.
Variation in growth and development because of timing are particularly evident in human adolescence. Some children grow rapidly and mature early, completing their growth quickly and thereby appearing on the high side of developmental charts until their growth ceases and their contemporaries begin to catchwww.indiandentalacademy.com up.
Differential Growth -
The human body does not grow at some rate throughout the life. Different organs grow at different rates to a different amount and at a different times. This a termed differential growth. -
The concept of differential growth can be explained on the basis of scammons curve of growth www.indiandentalacademy.com
The body tissue can be broadly classified into four types i.e. Lymphoid tissue Neural tissue General tissue Genital tissue -
Each of these grow at different times and different rates. www.indiandentalacademy.com
A bone
does not grow by generalized, uniform deposition of new bone (+) on all outside surfaces, with corresponding resorption (-) from all inside surfaces. Because of the topographically complex nature of each bone's shape, the bone must have a differential mode of enlargement, in which some of its parts and areas grow much faster and to a much greater extent than others www.indiandentalacademy.com
Two basic kinds of growth movement occur during the enlargement of each bone in the facial and cranial skeleton: (1) remodeling, which produces the size, shape, and fitting of a bone, and (2) displacement. Displacement is a movement of whole bones away from one another, creating the space within which growth enlargement of each of the separate bones takes place. Cortical drift is the process that carries out the remodeling functions, and it is a direct growth movement produced by deposition of new bone on one side of a cortical plate, with resorption from the opposite side. www.indiandentalacademy.com
THE BONE REMODELING PROCESS The surface that faces toward the direction of movement is depository (+). the opposite surface, facing away from the growth direction, is resorptive (-). If the rates of deposition and resorption are equal, the thickness of the cortex remains constant. If deposition exceeds resorption, overall size and cortical thickness gradually increase. Different combination of resorption and deposition (drift) in a variety of regional directions and amounts throughout the entire bone provide for the remodeling enlargement of the bone as a whole. www.indiandentalacademy.com
DIFFERENTIAL GROWTH
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DIFFERENTIAL GROWTH
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CORTICAL DRIFT
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RELOCATION
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V PRINCIPLE AND REMODELING PATTERN
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DISPLACEMENT
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DISPLACEMENT
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SECONDARY DISPLACEMENT
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POST NATAL GROWTH OF MAXILLA
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POST NATAL GROWTH OF MANDIBLE
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BRAIN ENLARGEMENT, BASICRANIAL FLEXURE, AND FACIAL ROTATIONS The enormous human cerebrum similarly expands around a much smaller enlarging midventral segment (the medulla, pons, hypothalamus, optic chiasma).This causes a bending of the whole underside of the brain. The flexure of the cranial base results. The foramen magnum in the typical mammalian skull is located at the posterior aspect of the cranium. In man, it is in the midventral part of the expanded cranial floor at an approximate balance point for www.indiandentalacademy.com upright head support on a vertical spine.
The expansion of the frontal lobes displaces the frontal bone upward and outward. This results in the distinctive, bulbous, upright "forehead" of the human face, although it is really part of the neurocranium and not the face proper. The frontal lobes also relate to a rotation of the human orbits into new positions. As the forehead is rotated into a vertical plane by the brain behind it, the superior orbital rim is carried with it. The eyes now point at a right angle to the spinal cord. The spine is vertical, and the orbital axis is horizontal. Vision is directed toward forward body movement. www.indiandentalacademy.com
The expansion of the frontal and, particularly, the temporal lobes of the cerebrum relates to a rotation of the orbits towards the midline and the eyes come closer together. The enlarged human cerebrum has caused a downward rotational displacement of the olfactory bulbs. the olfactory bulbs relate directly to the alignment and the direction of growth of the adjacent nasal region. The plane of the nasomaxillary region is thereby approximatelywww.indiandentalacademy.com perpendicular to the plane of the olfactory bulbs.
As the bulbs become rotated progressively from a vertical position to horizontal one because of increase in brain size or because of its shape, the whole face is similarly rotated from a horizontal to a vertical plane. Or, stated another way, the face is rotated down by the expanded anterior cranial floor as it rotates downward as a result of the enlargement of the frontal lobes. .
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NASOMAXILLARY CONFIGURATION The maxilla of most mammals has a triangular configuration .In man, it is uniquely rectangular. This is caused by a rotation of the occlusion into a horizontal plane to adapt to the vertical rotation of the whole midface. In the human maxilla, the design change that allows for this resulted in the creation of a new archpositioning facial region, the suborbital compartment. Most of this phylogenetically expanded area is occupied by the otherwise nonfucntional maxillary sinus (uses such as air warming, nasal drip, and voice resonance are secondary. An orbital floor was also newly created in www.indiandentalacademy.com conjunction with this added facial region.
The characteristic vertical human facial profile is a composite result of (1) a bulbous forehead, (2) rotation of the nasal region into a vertical plane, (3) reduction of snout protrusion in conjunction with medial orbital convergence, (4) rotation of the orbits into upright positions, (5) rotation of the maxillary arch downward and backward, and (6) bimaxillary reduction
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Reduction of the nasal region associated with orbital convergence and olfactory-anterior cranial fossa rotation must necessarily also be accompanied by a more or less equal reduction in maxillary arch length, because the floor of the nasal chamber is also the roof of the mouth. The protrusion of the cartilaginous and soft tissue portion of the nasal complex provides for downward-directed external nares. This aims the inflow of air obliquely upward into the vertically disposed nasal chambers towards the vertically aligned sensory nerves of the olfactory bulbs located on the ceiling of the chambers. www.indiandentalacademy.com
GROWTH FIELD BOUNDARIES The growth of each of the face involves two basic considerations. The first is the amount of growth, and the second is the direction of growth. These two factors constitute the growth "vector." The floor of the cranium, in turn, is the template upon which the face is built. The junctional part of the face cannot be significantly wider, for example, than the maximal width of the cranium The length of specific parts of the cranial floor are expressed as equivalent dimensions for the face. www.indiandentalacademy.com
The forward boundary of the brain is shared by the forward border of the nasomaxillary complex. The direction of growth by the nasal part of the face is established by the olfactory bulbs and the sensory olfactory nerves. These two factors underlie the "vector" of midfacial growth, that is, the amount and the direction. The nasomaxillary complex grows as far forward as the edge of the brain in a direction approximately perpendicular to the olfactory bulbs. www.indiandentalacademy.com
The posterior boundary of this fossa establishes the corresponding posterior boundary for the midface. This is essentially a nonvariable anatomic relationship. The direction of growth in this region is established by the particular special sense located in this part of the face, which is the visual sense. the posterior plane of the midface extends from the junction between the anterior and middle cranial fossae (and the inferior junction between the frontal and temporal lobes) downward in a direction perpendicular to the neutral line of the orbit. This plane passes almost exactly along the posterior surface of the maxillary tuberosity. www.indiandentalacademy.com
The inferior boundary of the nasomaxillary complex is established by the bottom-most surface of the brain and cranial. A line from the floor of the posterior cranial fossa passes through , or very nearly so, both the inferior corner of the posterior maxillary tuberosity and the inferior corner of the front part of the bony maxillary arch (prosthion). This relationship is achieved only after facial development is complete, because neurocranial growth precedes facial growth. www.indiandentalacademy.com
Any variation in the alignment of the nerve is usually accompanied by a corresponding upward or downward rotational alignment of the palate. In its neutral position. If the palate has undergone a severe clockwise or counterclockwise rotation during development, the palatal plane will project well above or below, respectively, the occipital point. www.indiandentalacademy.com
The growth in each region of the face involves two basic factors: (1) the amount of growth by any given part and (2) the direction of growth by that part. The brain establishes (or at lest shares) the various boundaries that determine the amount of facial growth. this is because the floor of the cranium is the template upon which the face is constructed. The directions of regional growth among the different parts of the face are inseparably associated with the special sense organs housed within the face. These two factors establish a prescribed growth perimeter that defines the borders of the growth compartment occupied by the nasomaxillary complex www.indiandentalacademy.com
CONCLUSION The conventional method used to show facial growth is superimposition of serial head film tracings. Sella is usually used as a registration point for the superimposition. Superimposing on the cranial base demonstrates the downward and forward expansion of the whole face relative to cranial base. www.indiandentalacademy.com
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