HISTORY OF ORTHODONTICS

BASIC CONCEPTS OF GROWTH & DEVELOPMENTPresented byDr. Sharmin SultanaBDS, FCPS Part II TraineeDept of Orthodontics and Dentofacial OrthopedicsDhaka Dental College and Hospital

A thorough background in craniofacial growth and development is necessary for every dentist. Scince dentists and orthodontists are heavily involved in the development of not just the dentition but the entire dentofacial complex, a conscientious practitioner may be able to manipulate facial growth for the benefit of the patient.

SOME DEFINITIONS RELATED TO GROWTH

As is the nature of growth, where in the concepts keep changing with new research findings, there has been no single definition associated with it. Different researchers have defined growth in various ways-

Growth refers to increase in size - ToddThe self multiplication of living substance -JX Huxley.Increase in size, change in proportion and progressive complexity-Krogman.Entire series of sequential anatomic and physiological changes taking place from the beginning of prenatal life to senility -Meredith.Growth is the quantitative aspect of biologic development and is measured in units of increase per units of time, for instance, inches per year or grams per day -Moyers.Growth usually refers to an increase in size and number ProffitChange in any morphological parameter which is measurable - Moss.

Some Definition Related to Development

Development refers to all the naturally occurring unidirectional changes in the life of an individual from its existence as a single cell to its elaboration as a multi functional unit terminating in death - MoyersDevelopment is a progress towards maturity ToddDevelopment connotes a maturational process involving progressive differentiation at the cellular and tissue levels Enlow

Some Definition

Differentiation:Differentiation is the change from generalized cells or tissues to more specialized kinds during development. Differentiation is change in quality or kind.

Translocation:Translocation is change in position. The chin point is translocated (moved) downward and forward far more than any growth at the chin itself. Indeed, most of the growth is taking place at the condyle and ramus while the entire mandible is translocated ventrally.

Maturation:The term maturation is sometimes used to express the qualitative changes which occur with ripening or aging. We speak, for example, of the ripening of the ovum and we think of pubescence as a period of rapid maturation as well as accelerated physical growth.

METHODS OF STUDYING PHYSICAL GROWTHThe data collection for the evaluation of physical growth is done in two ways:1. Measurement approach: It is based on the techniques for measuring living animals (including humans), with the implication that measurement itself will do not harm and that the animal will be available for additional measurements at another time.2. Experimental approach: This approach uses experiments in which growth is manipulated in some way. This implies that the subject will be available for some detailed study that may be destructive. For this reason, such experimental studies are restricted to non-human species.

Measurement Approaches:1. Craniometry2. Anthropometry3. Cephalometric radiography4. Three-Dimensional Imaging

1.Craniometry: The first of the measurement approaches for studying growth, with which the science of physical anthropology began, is craniometry, based on measurements of skulls found among human skeletal remains. Craniometry was originally used to study the Neanderthal and Cro-Magnon peoples whose skulls were found in European caves in the eighteenth and nineteenth centuries. Craniometry has the advantage that rather precise measurements can be made on dry skulls; it has the important disadvantage for growth studies that, by necessity, all these growth data must be cross-sectional. cross-sectional means that although different ages are represented in the population, the same individual can be measured at only one point in time.

2.Anthropometry : It is also possible to measure skeletal dimensions on living individuals. In this technique, called anthropometry, various landmarks established in studies of dry skulls are measured in living individuals simply by using soft tissue points overlying these bony landmarks. For example, it is possible to measure the length of the cranium from a point at the bridge of the nose to a point at the greatest convexity of the rear of the skull. This measurement can be made on either a dried skull or a living individual, but results would be different because of the soft tissue thickness overlying both landmarks. Although the soft tissue introduces variation, anthropometry does make it possible to follow the growth of an individual directly, making the same measurements repeatedly at different times. This produces longitudinal data- repeated measures of the same individual. In recent years, Farkas anthropometric studies have provided valuable new data for human facial proportions and their changes over time.

3.Cephalometric Radiology: The third measurement technique, cephalometric radiology, is of considerable importance not only in the study of growth but also in clinical evaluation of orthodontic patients. The technique depends on precisely orienting the head before making aradiograph, with equally precise control of magnification. This approach can combine the advantages of craniometry and anthropometry. The introduction of radiographic cephalometrics in 1934 by Hofrath in Germany and Broadbent in the United States provided both a research and a clinical tool for the study of malocclusion and underlying skeletal disproportions. It allows a direct measurement of bony skeletal dimensions, since the bone can be seen through the soft tissue covering in a radiograph, but it also allows the same individual to be followed over time. Growth studies are done by superimposing a tracing or digital model of a later cephalogram on an earlier one, so that the changes can be measure.The disadvantage of a standard cephalometric radiograph is that it produces a two-dimensional representation of a three-dimensional structure, and so, even with precise head positioning, not all measurements are possible.

4. Three-Dimensional Imaging : New information now is being obtained with the application of three-dimensional imaging techniques.Computed axial tomography (CAT or iust CT) allows 3-D reconstructions of the cranium and face, and this method has been applied for several years toplan surgical treatment for patients with facial deformities. Recently, cone beam rather than spiral CT has been applied to facial scans, signiflcantly reducing the radiation dose and allowing scans of patients with radiationexposuret hat is much closer to the dose from cephalograms. Superimposition of 3-D images is much more difficult than the superimpositions used with 2-D cephalometric radiographs, but methods developed recently are overcoming this difficulty. Magnetic resonance imaging (MRI) also provides 3-D images that can be useful in studies of growth, with the advantage that there is no radiation exposure with this technique. This method already has been applied to analysis of the growth changes produced by functional appliance.

Experimental approach:1. Vital staining2. Autoradiography3. Radioisotopes4. Implant radiography

1.Vital StainingVital staining, introduced first by John Hunter in the eighteenth century. Here growth is studied by observing the pattern of stained mineralized tissues after the injection of dyes into the animal. These dyes remain in the bones and the teeth, and can be detected later after sacrificing the animal. Alizarin was found to be the active agent and is still used for vital stainingstudies. Such studies are however not possible in the humans. With the development of radio isotropic tracers, it is now possible to replace alizarin. The gamma emitting isotope 99m Tc can be used to detect areas of rapid bone growth in humans but these images are more useful in diagnosis of localized growth problems than for studying growth patterns.

2. AutoradiographyAutoradiography is a technique in which a film emulsion is placed over a thin section of tissue containing radioactive isotope and then is exposed in the dark by radiation. After the film is developed, the location of radiation indicates where growth is occurring.

3. RadioisotopesThese elements when injected into tissues get incorporated in the developing bone and act as in vivo markers and can then be located by means of a Geiger counter, e.g. 99mTc,Ca-45 labeled component of protein, e.g. proline.

4. Implant RadiographyImplant radiography, used extensively by Arne Bjork and co-workers, is one of the techniques that can also be used in human subjects. Here in, inert metal pins (generally made of titanium) are inserted anywhere in the bony skeleton including face and jaws. These pins are biocompatible. Superimposing radiographs (cephalograms in case of face) on the implants allow precise observation of both changes in the position of one bone relative to another and changes in external contour of the individual bone.

Growth: Pattern, Variability, TimingIn studies of growth and development, the concept of pattern is an important one. Pattern in general terms indicates the proportionality of the given object in relation to its various sizes. However, in the concept of growth, it refers not only to the proportionality at a point of time but also to changes in this proportionality over a period of time. The fourth dimension "time" is of immense importance here. This can be clearly understood in the following illustration (Fig. 2.1), which depicts the change in overall body proportions over a period of time-from fetus to adulthood. The figure illustrates the changes in overall body proportions that occurs during normal growth and development. In fetal life, at about the third month of intrauterine development, the head takes up almost 50 percent of the total body length. At this stage, the cranium is large relative to the face and represents more than half the total head. In contrast, the limbs are still rudimentary and the trunk is underdeveloped. By the time of birth, the trunk and limbs have grown faster than the head and face, so that the proportion of the entire body devoted to the head has decreased to about 30 percent. The overall pattern of growth thereafter follows this course, with a progressive reduction of the relative size of the head to about 12 percent in the adult.

Growth: Pattern, Variability, Timing cont..

All of these changes, which are a part of the normal growth pattern, reflect the cephalocaudal gradient of growth (Table 2.1). This simply means that "there is anaxis of increased growth extending from the head toward the feet."Table 2.1 Cephalocaudal gradient of growthCephalocaudal gradient of growth-Scammons: There is an axis of increased growth extend ing from head towards the feet Tn fetal life, about the third month of intrauterine development (IUD), head occupies 50 percent of the total body length and within the head the cranium is large relative to tile face. The trunk and limbs are rudimentary At birth: head-39 percent of total body length , Legs-1/3rd of total body length ln adults: head-12 percent of total body length , Legs- 1/2 of the total body lengthTherefore, with growth, trunk and limbs grow faster than the head and face

Growth: Pattern, Variability, Timing cont..Another aspect of the normal growth pattern is that , not all the tissue systems of the body grow at the same rate (Figure 2-2) and Table 2.2 Scammons has classically described the growth of various tissues. Obviously, the muscular and skeletal elements grow faster than the brain and central nervous system, as reflected in the relative decrease of head size. The overall pattern of growth is a reflection of the growth of the various tissues making up the whole organism. To put it differently, one reason for gradients of growth is that different tissue systems that grow at different rates are concentrated in various parts of the body.Table 2.2 differential Growth( scammons growth curve)

Different tissues in the body grow at different times anddifferent rates. Therefore, the amount of growth accomplished at a particular age is variable. Scarnmon divided the tissues in the body into:a. Neural tissuesb. Lymphoid tissuesc. Somatic/general tissues (muscles, bone, viscera).d. Genital tissues Neural tissues complete 90 percent of their growth by 6 years and 96 percent by 10 years of age Lymphoid tissues reach 100 percent adult size by 7 years: proliferate far beyond the adult size in late childhood (200% by 14 years) and involute around the onset of puberty Somatic tissues show an S-shape curve with definite slowing of growth rate during childhood and acceleration at puberty going on till age 20 Growth of the genital tissues accelerate rapidly around the onset of puberty.

Even within the head and face, the cephalocaudal growth gradient strongly affects proportions and leads to changes in proportion with growth (Figure 2-3). When the skull of a newborn infant is compared proportionally with that of an adult, it is easy to see that the infant has a relatively much larger cranium and a much smaller face.This change in proportionality, with an emphasis on growth of the face relative to the cranium,is an important aspect of the pattern of facial growth. When the facial growth pattern is viewed against the perspective of the cephalocaudal gradient, it is not surprising that the mandible, being farther away from the brain, tends to grow more and later than the maxilla, which is closer.

Figure 2-3

The second important concept in the study of growth and development is variability. It indicates the degree of difference between two growing individuals in all four planes of space including the all-important time. Since everyone is not alike in the way they grow, it is clinically very difficult to decide and decipher the deviation of growth pattern of an individual from the normal. One way to do this is to compare the growth of a given child relative to person on a standard growth chart. Although charts of such nature are commonly used for height and weight, the growth of any part of the body can also be plotted this way. Such charts help us in two ways.To evaluate the present growth status of the individual, andTo follow the child's growth over a period of time using such charts.

A final major concept in physical growth and development is that of timing. All theindividuals do not grow at the same time or in other words possess a biologic clock that is set differently for all individuals. This can be most aptly demonstrated by the variation in timing of menarche (onset of menstruation) in girls. This also indicates the arrival of sexual maturity. Similarly, some children grow rapidly and mature early completing their growth quickly, thereby appearing on the high side of the developmental charts until their growth ceases and their peer group begins to catch up. Others grow and develop slowly and so appear to be behind even though in due course of time they might catch up or even overtake others.

RHYTHM AND GROWTH SPURTSHuman growth is not a steady and uniform process of accretion in which all body parts enlarge at the same rate and same increment per year. The rate of growthis most rapid at the beginning of cellular differentiation, increases until birth and decreases thereafter, e.g. in the prenatal period height increases 5000 timesfrom stage of ovum to birth whereas in the postnatal period increase is only 3 fold. Similarly weight increases 6.5 billion fold from stage of ovum to birth whereas in the postnatal period increase is only 20 fold. Postnatally growth does not occur in a steady manner. There are periods of sudden rapid increases, which are termed as growth spurts. Mainly 3 spurts are seen:

Name of spurt Female Male1. Infantile/childhood growth spurt 3 yrs 3 yrs2. Mixed dentition/Juvenile growth spurt 6-7 yrs 7-9 yrs3. Prepubertal/adolescent growth spurt 11-12 yrs 14-15 yrs

CLINICAL SIGNIFICANCE OF THE GROWTH SPURTS To differentiate whether growth changes are normal or abnormal. Treatment of skeletal discrepancies (e.g. Class Ii) is more advantageous if carried out in the mixed dentition period, especially during the growth spurt. Pubertal growth spurt offers the best time for majority of cases in terms of predictability, treatment direction, management and treatment time. Orthognathic surgery should be carried out after growth ceases. Arch expansion is carried out during the maximum growth period.

VARIABLES AFFECTING PHYSICAL GROWTHVariability may be seen in the rate, timing, or character of growth as well as the achieved or ultimate size.1. HeredityThere is genetic control of the size of parts to a great extent of the rate of growth, and of the onset of growth events, for example, menarche, dental classification, the eruption of teeth, ossification of bones, and the start of the adolescent growth spurt. Not all the genes are active at birth. Some only express themselves in the surroundings made possible by the physiologic growth of later years; such effects are called "age limited." An important point for orthodontics: there is a considerable degree of independence between growth before and growth during adolescence.

2. NutritionMalnutrition delays growth and may affect size of parts, body proportions, body chemistry, and the quality and texture of some tissues (e.g., teeth and bones). Malnutrition may also delay growth and the adolescent growth spurt, but children have fine recuperative powers provided the adverse conditions have not been too extreme. During rather short periods of malnutrition growth slows up and waits for better times. With the return of good nutrition growth takes place unusually fast until the genetically determined curve is neared once more and subsequently followed. Though "catchup growth" is seen in both sexes, girls seem to be better buffered against the effects of malnutrition and illness.

3. IllnessSystemic disease has an effect on child growth, but the plasticity of the human organism during growth is so great that the clinician must differentiate between minor illnesses and major illnesses. The usual minor childhood illnesses ordinarily cannot be shown to have much effect on physical growth. On the other hand, serious prolonged and debilitating illnesses have a marked effect on growth. The pediatrician is concerned not only with the diseases that may kill or maim the child but also with those that affect the growth process as well.4. RaceAnthropologists studying the racial aspects of growth have a problem in the definition of race. Some so-called racial differences are clearly due to climatic, nutritional, or socioeconomic differences. However, gene pool differences account for the fact that North American blacks are ahead of whites in skeletal maturity at birth and for at least the first 2 years of life. This progress is associated with advanced motor behavior and earlier ability to crawl and sit up. North American blacks also calcify and erupt their teeth about 1 year earlier than whites.

5. Climate and Seasonal Effects on GrowthThere is a general tendency for those living in cold climates to have a greater proportion of adipose tissue, and much has been made of the skeletal variations associated with variations in climate. There are seasonal variations in the growth rates of children and in the weights of newborn babies. Contrary to popular belief, climate has little direct effect on rate of growth.6. Adult PhysiqueThere are correlations between the adult physique and earlier development events. For example, tall women tend to mature later and there are variations in the rate of growth associated with differing somatotypes.7. Socioeconomic FactorsSocioeconomic aspects obviously include some growth factors mentioned previously (e.g., nutrition); yet, there are discrete differences. Children living in favorable socioeconomic conditions tend to be larger, display different types of growth (e. g., height weight ratios), and show variation in the timing of growth, when compared with disadvantaged children. Some of the causes of these differences are obvious and some of the implications are puzzling.

8. ExerciseA strong case for the effects of exercise on linear growth has not been made in a quantitative fashion. Although exercise may be useful for the development of motor skills, for increase in the muscle mass, for fitness, and for general well-being, those children who exercise strenuously and regularly have not been shown to grow more favorably.

9. Family Size and Birth OrderThere are differences in the sizes of individuals, in their maturational levels of achievement, and in their intelligence that can be correlated with the size of the family from which they came. First-born children tend to weigh less at birth and ultimately achieve less stature and a higher I.Q.

10. Secular TrendsSize and maturational changes in large populations can be shown to be occurring with time that, as yet, have not been well explained. Fifteen-year-old boys are approximately 5 inches taller than l5-year-old boys were 50 years ago. The average age at onset of menarche has steadily become earlier throughout the entire world. Both of these facts seem to be true when race, socioeconomic level, nutrition, climate, and other differences have been carefully controlled in the samples. Such changes are called secular trends in growth and, although thoroughly and meticulously studied, have yielded no really satisfactory and generally acceptedexplanation for such interesting findings.

11. Psychological DisturbanceIt has been shown that children experiencing stressful conditions display an inhibition of growth hormone. When the emotional stress is removed they begin again to secrete growth hormone normally, and "catch-up" growth is seen.Hypotheses of Craniofacial GrowthThrough the years, a number of hypotheses of craniofacial development have been formulated which are often encountered in textbooks and the periodical literature, where they are sometimes called "theories." Theory requires a basis of sound evidence; while hypothesis is thoughtful conjecture of the meaning of incomplete evidence.Genetic TheorySutural Dominance Theory (Sichers Hypothesis)Scott's Hypothesis (Nasal Septum)Moss' Hypothesis (Functional Matrix Hypothesis)Petrovic's Hypothesis (Servosystem)

Sicher's Hypothesis (Sutural Dominance)Sicher deduced from the many studies using vital dyes that the sutures were causing most of the growth; in fact, he said" the primary event in sutural growth is the proliferation of the connective tissue between the two bones. If the sutural connective tissue proliferates it creates the space for oppositional growth at the borders of the two bones." Replacement of the proliferating connective tissue was necessary for functional maintenance of the bones. He felt that the connective tissue in sutures of both the nasomaxillary complex and vault produced forces which separated the bones, just as the synchondroses expanded the cranial base and the epiphyseal plates lengthened long bones. Sicher viewed the cartilage of the mandible somewhat differently, stating that it grew both interstitially, as epiphyseal plates, and appositionally, as bone grows under periosteum. His ideas came to be called the "sutural dominance theory," but it would seem he held sutures, cartilage, and periosteum all responsible for facial growth and assumed all were under tight intrinsic genetic control.

Scott's Hypothesis (Nasal Septum)Scott,85-87noting the prenatal importance of cartilaginous portions of the head, nasal capsule, mandible, and cranial base, and feeling that this development was under intrinsic genetic control, held that they continued to dominate facial growth postnatally. He specifically emphasized how the cartilage of the nasal septum during its growth paced the growth of the maxilla. He claimed that growth in the sutures wassecondary and entirely dependent on the growth of the cartilage and adjacent soft tissues. Scotts hypothesis could explain the coordinated growth that had been observed within the skull, and between the skull and the soft tissues. He introduced the concept of cartilaginous 'growth centers'. The role of these growth centers was explained in a contemporary summary of craniofacial skeletal growth (Scott 1955). Several of Scott's basic tenets still hold credibility for researchers in the field of growth. Van Limborgh supported the view that synchondroses of craniaI base have some degree of intrinsic control. However, he felt that the periosteum should also be considered as a secondary growth site because of its similarity to the suture.

Functional Matrix Theory of GrowthMelvin Moss introduced the functional matrix hypothesis in 1960. His theory holds that neither the cartilage of the mandibular condyle nor the nasal septurn cartilage is a deterrninant of jaw growth. Instead, he theorizes that growth of the face occurs as a response to functional needs and neurotrophic influences and is mediated by the softt issue in which the jaws are embedded. In this conceptual view, the soft tissue grow, and both bone and cartilage react. Melvin moss was inspired by the ideas of Van der Klaauw (1952) that 'bones' were in reality, composed of several 'functional cranial components' the size, shape and position of which were relatively independent of each other.The original version of the functional matrix hypothesis held that: the head is a composite structure, operationally consisting of a number of relatively independent functions; digestion, respiration, vision, olfaction, audition, equilibrium, speech, neural integration, etc. Each function is carried out by a group of soft tissues which are supported and/ or protected by related skeletal elements. Taken together, the softtissues and skeletal elements related to a single function are termed a functional cranial component. The totality of all the skeletal elements associated with a single function is termed a skeletal unit. The totality of the soft tissues associated with a single function is termed as the functional matrix.

The growh of the cranium illustrates that, Pressure exerted by the growing brain separates the cranial bones at the sutures, and new bone passively fills in at these sites so that the brain case fits the brain. This phenomenon can be seen readily in humans in two experiments of nature. First, when the brain is very small, the cranium is also very small, and the condition of microcephaly results. In this case,the size of the head is an accurate representation of the size of the brain. A second natural experiment is the condition called hydrocephaly. In this case reabsorption of cerebrospinal fluid is impeded, the fluid accumulates ,and intracranial pressure builds up. The increased intracranial pressure impedes development of the brain, so the hydrocephalic may have a small brain and be mentally retarded; but this condition also leads to an enormous growth of the cranial vault. Uncontrolled hydrocephaly may lead to a cranium two or three times its normal size, with enormously enlarged frontal, parietal, and occipital bones. This is perhaps the clearest example of a "functional matrix" in operation. Another excellent example is the relationship between the size of the eye and the size of the orbit. An enlarged eye or a small eye will cause a corresponding change in the size of the orbital cavity.In this instance, the eye is the functional matrix.

Moss theorizes that the 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. The theory does not make it clear how functional needs are transmitted to the tissues around the mouth and nose, but it does predict that the cartilages of the nasal septum and mandibular condyles are not important determinants of growth, and that their loss would have little effect on growth if proper function could be obtained. From the view of this theory, however, absence of normal function would have wide-ranging effects.It has been known for many years that mandibular growth is greatly impaired byan ankylosis, defined as a fusion across the joint so that motion is prevented or extremely limited. Mandibular ankylosis can develop in a number of ways. For instance, one possible cause is a severe infection in the area of the temporomandibular joint, leading to destruction of tissues and ultimate scarring. Another cause, of course, is trauma, which can result in a growth deficiency if there is enough soft tissue injury to lead to severe scarring as the injury heals. It appears that the mechanical restriction caused by scar tissue in the vicinity of the temporomandibular joint impedes translation of the mandible as the adjacent soft tissues grow, and that this is the reason for growth deficiency in some children aftercondylar fractures.

It is interesting, and potentially quite significant clinically, that under some circumstances bone can be induced to grow at surgically created sites by the method called distraction osteogenesis.The Russian surgeon Alizarov discovered in the 1950s that if cuts were made through the cortex of a long bone of the limbs, the arm or leg then could be lengthened by tension to separate the bony segments. Current research shows that the best results are obtained if this type of distraction starts after a few days of initial healing and callus formation.In summary, it appears that 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 and its associated structures occurs from a combination ofgrowth at sutures and direct remodeling of the surfaces of the bone. The maxilla is translated downward and forward as the face grows, and new bone fills in at the sutures. 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 apposition and resorption of bone at surfaces. It seems clear that the mandible is translated in space by the growth of muscles and other adjacent soft tissues andthat addition of new bone at the condyle is in response to the soft tissue changes.

Q. Functional matrix theory of growth -july 2007, jan 2011,

Reference W.R.Proffit 27-58 pagr.Robert E. Moyers 6-16 page, 42-50 pages.Gurkeerat Singh 7-17 pages.

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