www.indiandentalacademy.com
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
www.indiandentalacademy.com
The dynamics of the growth of bones is a complex process. The growth pattern of the mandible has been assessed by the application of various methods described for the study of the growth of bones. The use of any one of these methods will reveal certain information. With the use of two or more of them - accurate information can be obtained. John Hunter's classical descriptions was more than 200 years ago, today refinement of older methods and the development of newer ones have come up. www.indiandentalacademy.com
To date, serial cephalometric roentgenography in concert with radiopaque implants, which serve as fixed reliable markers, is the most accurate method to determine the growth pattern of the mandible.
To this armamentarium, digital subtraction radiography, computerized tomography, and magnetic resonance imaging may be methods that will offer more detailed and accurate information.
Any study of growth of bones concerns itself with : What is the pattern of growth? What are the sites? What are the amounts? What are the rates? Do they vary? When? What are the directions? What are the changes in proportion? What factors are influential? www.indiandentalacademy.com
www.indiandentalacademy.com
www.indiandentalacademy.com
One approach might yield information about the sites of growth, another about the rate, and still another about direction. A combination of methods, however, potentially will yield more information, and in certain instances more accurately, than one alone Two types of bone growth occur in the following principal regions. One is continuous appositional/resorptive with differential bone remodeling at various periosteal and endosteal surfacess. In the ramus the posterior border is a particularly active site of bone apposition, whereas the anterior border is a particularly active site of bone resorption.
www.indiandentalacademy.com
The second type of mandibular bone growth is at the condyle, where cartilage is replaced by bone. Growth of the condyle and ramus, prolific sites, is generally in a superior and posterior direction. Because the condyle articulates with the mandibular fossa of the temporal bone, the final effect of growth there is a downward and forward displacement of the mandible.
www.indiandentalacademy.com
Two random age levels the mandibular outlines were superposed so that the surface fields of resorption and deposition are expressed. The mandible enlarges predominantly posteriorly and superiorly. www.indiandentalacademy.com
METHODS OF ASSESSING GROWTH OF BONES Direct measurements Anthropometry : can be performed on either the living or dried subject specimen. In spite of the accuracy of the anthropometric apparatus, exact measurements of growth are extremely difficult to obtain. When performed on the living, the measuring instruments must be placed on the soft tissues overlying the bony landmarks, thereby precluding minute www.indiandentalacademy.com accuracy of measurements.
Hunter was one of the first to apply anthropometry using the mandible In his study of four human mandibles, ranging from 5 years of age (with the complete primary dentition) to adulthood (with the complete secondary dentition), were aligned along the symphyseal and lower borders of the mandible.( No reason was noted for this choice of reference planes). Hunter described that (1) resorption was as characteristic of bone growth as deposition, (2) the body of the mandible gained in height principally by growth of alveolar bone, (3) the shedding of teeth was always accompanied by resorption of alveolar bone, whereas eruption of teeth was always accompanied by growth of alveolar bone, and (4) the deciduous second molar and permanent first, second, and third molars erupted in the same relation to the mandibular ramus. www.indiandentalacademy.com
Vital staining Madder feeding : Madder is a plant that possesses a deeply red colored root. Belchier in 1736 was one of the first to give an accurate account of the staining of bone of animals fed madder Duhamel (1742) demonstrated that only newly formed bone was stained by madder and from his studies described the manner of growth of bones. Hunter reported on the growth of the mandible in the pig. He also demonstrated the wide alternate red and white layers (corresponding to the prolonged periods when madder was fed and withheld) in longitudinal and transverse sections of long bones. www.indiandentalacademy.com
ALIZARIN RED INJECTIONS. Alizarin is one of the principal tinctorial agents found in madder and is available in synthetic form. sharp vital staining of calcifying substances may be obtained by a single intraperitoneal or intravenous injection of a 2% solution of alizarin red S Ground sections (25 to 50 Âľm thick) under higher magnification and strong transmitted illumination, the red lines (5 to 20 Âľm in width) are readily counted and the distance between them can be accurately measured with a micrometer eyepiece. They also have been used in studies of calcification in other conditions such as healing of fractures, kidney casts, calcified placques of an atheromatous aorta, and calcified scars. The egg shell, the shell of the turtle, and the dentin of teeth are also stained by alizarin red S. www.indiandentalacademy.com
Although growth of bones is greatest in the young, nevertheless bone tissue is in a state of continuous change throughout life as a result of an interplay of formation and destruction.
In areas where bone is being apposed, osteoblasts are found arranged in a continuous single layer like cuboidal epithelium on the surface of the bone. Osteoclasts are found in areas where bone is being destroyed or resorbed.
The osteoclasts are multinucleated giant cells of varying size and shape and are found in shallow hollows (Howship's lacunae) on the surface of the bone trabeculae. www.indiandentalacademy.com
Enlow, on the basis of extensive histologic studies, has reconstructed gross patterns of bone formation and destruction In response to the question of what reference points were used to superpose the two mandibular outlines, Enlow stated, "No actual points were utilized. Rather, registration was based on the 'typical' distribution of surface resorptive and depository fields, thus showing the endosteal and periosteal directions of cortical remodeling. Histochemical studies are also of value in obtaining further information about the nature of bone formation. By this method, for instance, the importance and the localization of various enzymes, particularly alkaline acid phosphatase and other substances such as glycogen and glycoproteins, have been determined. www.indiandentalacademy.com
Implants. Implants as reference markers have been used in the study of growth of bones as early as 1742 by Duhame
Hunter inserted two pellets along the length of the shaft of the tarsus of a young pig and measured the distance between the pellets. When the tarsus was fully grown, he found that the distance between the pellets had remained exactly the same and that the bone had increased in length at the ends. This experiment proved that there was no interstitial growth of bone www.indiandentalacademy.com
Implantation of gold, silver, dental silver amalgam, stainless steel, vitallium, and tantalum in the form of screws, pegs, pins, clips, or wires within a single bone can be used for the study of total amount of bone growth by measuring the increase in distance between the implants and the outer borders of the bone. Humphry, by placing wire loops around the ramus of the pig mandible, demonstrated that there was resorption on the anterior border and deposition of bone on the posterior border of the ramus.
www.indiandentalacademy.com
Impressions and casts. Duplication of various parts of the body (skull, face, orbit, maxillary sinus, teeth and dental arches, extremities) is possible by taking impressions with plaster of paris, hydrocolloid, Thiokol rubber, low fusing metal, stone, or other material. Individual or sectional impressions may be necessary, depending on the size, shape, and contour of the particular part that is to be duplicated. The impression serves as the negative and by filling it with a material such as plaster of paris, an accurate positive or duplication of the part can be obtained. www.indiandentalacademy.com
Photographs. The effects of disease on the face, jaws, teeth, and the human constitution have been shown by means of photographs. ď Ž
Photographs taken under controlled conditions with the subjects placed against a graduated grid have permitted a morphologic classification.
ď Ž
Sheldon, Stevens, and Tucker used such grids for establishing somatotypes. Although this method does not lend itself to accurate measurements of growth of individual bones, it does permit the study of growth of selected regions or the entire subject. www.indiandentalacademy.com
Radioautographs. A radioautograph is obtained by placing the tissues of an animal injected with a radioactive substance in close contact with a photographic emulsion for a suitable exposure period. Alpha or beta rays from the radioactive material affect the silver bromide crystals or a photographic emulsion in a manner similar to that of light. After development and fixation of the-film, darkened areas will be found that correspond to the distribution of the radioactive material. www.indiandentalacademy.com
Radioisotopes have already yielded considerable fundamental information previously unobtainable on the growth and development of animals. A radioactive isotope of an element will behave in exactly the same manner biologically and chemically as the stable isotopes of the same element as long as the radiations from the radioactive isotope are not sufficiently intense to produce pathologic changes. Radioactive phosphorus deposited in bone will behave like ordinary phosphorus Some other radioisotopes used are sodium, calcium, strontium, fluorine, chlorine, iodine, carbon, plutonium, uranium, americium, and gallium. www.indiandentalacademy.com
Roentgenographs. Roentgenography is a reliable indirect method of studying growth of bones.
In 1912, Tandler suggestd the use of x-ray films in anthropometry of the skull.
In 1931, Broadbent and Hofrath simultaneously but independently described a technique of cephalometric roentgenography.
In 1937, Broadbent reported his findings gained from studies of growing children.
A refinement in the cross-sectional method was made by the use of roentgenography and the superpositioning of roentgenographic tracings over various supposedly stable bony landmarks to obtain the pattern of growth. www.indiandentalacademy.com
Symons, in studying the angular relationship of the occlusal plane of the lower teeth with the body proper of the human mandible, superposed tracings of roentgenographs of adult human mandibles on a line joining the center of the head of the condyle to the inferior dental foramen. Scott by this same method correlated tooth eruption with mandibular growth in superposed roentgenographs of pig mandibles of different ages. He observed little resorption at the anterior border of the ramus. The disadvantages of this method were 1. the same living animal was not studied, 2. the base line or points for superpositioning the roentgenographic tracings varied with different animals, and 3. the base changed with www.indiandentalacademy.com growth.
Brodie in 1941, was the first to apply Broadbent's method to a longitudinal growth study of human males from the third month to the eighth year of life. The accuracy of this method depends on standardization of technique. Selection of a stable anatomic base, however, for superposing the roentgenographic tracings is the key to reliable findings because any shift of the area used as a baseline distorts the true direction of growth. It permits a dynamic study of the growing child— that is, the increase in size and the change in proportion of the same growing bone (as the mandible) or group of bones forming a bone complex (as in the middle third of the face). It reveals the rate, the amount, and relative direction of bone growth. It does not, however, reveal either the sites or the www.indiandentalacademy.com mode of growth of bones.
Method of superposing in examining growth stages of the mandible. www.indiandentalacademy.com
In serial studies on the growth of the human mandible, Brodie, superposed tangents to the lower border of the mandible as a baseline for the serial roentgenographic tracings The angle formed by this line with a tangent to the posterior border was bisected to locate gonion, the point of superposition. However, this method was predicated on the fact that there was minimal growth or no growth at the lower border. Moyers and Bookstein, however, have reported that conventional cephalometrics fails to capture the curving of form and its changes and thus misrepresent growth.
www.indiandentalacademy.com
Serial cephalometric roentgenography and implantation. Use of a combination of serial roentgenography and radiopaque implants is a more accurate and reliable approach for a dynamic longitudinal study of the growth of bone a stable base for superpositioning the serial roentgenographic tracings is obtained by inserting two or more radiopaque implants into the mandible. Thus, the ensuing growth can be accurately determined and measured by superpositioning roentgenographic tracings over the images of the metallic implants. Measurements between implants and the outer borders of an individual bone are valid only after verification that with growth of the bone the implants remained within bone tissue and were not extruded into the surrounding soft tissues. To avoid foreshortening, implants must lie in a plane parallel to the x-ray www.indiandentalacademy.com film.
Another advantage of combined method is The ability to measure the amount of new bone formation and resorption that occurred from one period to another without killing or reoperation of the animal. There is also no interference with the normal diet such as occurs in madder-fed animals. A disadvantage is that the roentgenograph demonstrates the sum total of apposition and resorption at that particular time without the detailed intervening changes as shown with vital markers and histologic sections www.indiandentalacademy.com
In 1963, Bjรถrk reported on the growth pattern of the human mandible. This was a longitudinal roentgenographic study with tantalum implants initiated in 1951 on more than 100 children. He pointed out that the lower border of the mandible was unsuitable for a reference plane. In the analysis of lateral mandibular growth, the two profile roentgenographs to be compared were oriented so that the implants in the mandible were superposed. Examples were given of the individual differences in the development of the mandible
www.indiandentalacademy.com
For the most part, the anterior aspect of the chin underwent no visible remodeling. Beneath the chin there was some periosteal growth in many cases, accentuated during adolescence. The most pronounced remodeling occurred beneath the angulus region. Here resorption was usual, but periosteal apposition was also seen. The direction of growth at the condyles in the sagittal plane varied widely with an average direction slightly forward in relation to the posterior tangent to the ramus. www.indiandentalacademy.com
digital subtraction radiography, computerized tomography, and magnetic resonance imaging may be methods that will offer more detailed and accurate information.
SUMMARY The growth pattern of the mandible has been studied and described in this report in the pig, monkey, and human by use of anthropometry, vital stains, histology, serial roentgenography, and serial roentgenography combined with radiopaque implants. The last method gives the most accurate information about the gross growth pattern of the mandible. www.indiandentalacademy.com
www.indiandentalacademy.com