The measures of maturity are as under:
- Skeletal age
- Dental age
- Morphological age or shape age
- Secondary sex character age
1. SKELETAL AGE
The most commonly used indicator of physiological maturity is the skeletal age (Baldwin et al., 1928; Cattelll934; Flory, 1936; Kelly, 1937; Todd, 1937; Greulich and Pyle, 1950, Speijer 1<)50; Falkner, 1958), Each bone begins as a primary centre of ossification, passes through the stage of enlargement and shaping of the ossified area, acquires, perhaps, one or more epiphyses and finally reaches its adult form with epiphyseal fusion. Skeletal maturity is judged both on the number of centres present and the stage of development of each. At birth, some babies have more primary centres developed than others, or have the same number but with larger areas ossified; they are said to have a greater skeletal age. Though area was used as an indication of maturity in the earlier studies, shape change is now considered. of much greater importance. This is because the area depends too much on the size of the individual, irrespective of his maturity (Tanner, 1962).
The skeletal maturity assessment is made by comparing the given X-ray with a set of standards. There are two ways in which this may be done, In the older ‘atlas’ method one matches the given X-ray successfully with standards representing age 5, age 6, age 7, and so on, and compares it with the standard to observe perfect matching. The X-ray is then assigned a skeletal age equal to that of the nearest age standard, or, if it is intermediate between two standards, a skeletal age is assessed correspondingly intermediate. Another method (Acheson, 1954, 1957; Tanner and Whitehouse 1959; Tanner et al., 1961) is to establish a series of standard stages through which each bone passes, and to match each bone of the given X-ray with these stages. Each stage of each bone has a numerical score associated with it. The scores have been determined mathematically so that at any given age most weight is given to those bones that are developing fastest and thus most precisely defining the overall stage reached. The whole X-ray thus scores a total of so many maturity points. A percentile status is then given to the child in skeletal maturity just as it is for height or weight, by reference to the distribution of maturity scores of a standard group at each age.
The atlas standards are constructed by X-raying a group of healthy children all of chronological age equal to the skeletal age of the required standard. The X-rays are arranged in order of maturity and the average one is taken as the standard. Thus, to make the skeletal age 4 standard a group of children all chronologically aged 4.0 years is taken, as the standard. The same is done at each age, so that the child who is exactly average relative to the standardizing group has throughout growth a skeletal age equal to his chronological age.
In theory any or all parts of the body could be used for assessment, but in practice the hand and wrist is the most convenient at least after the age of one year, because so many bones and epiphyses are present; there in such a small and easily X-rayed area. During the first year an X-ray of the knee and ankle together in lateral view probably gives the best assessment and has been used for estimating the degree of prematurity or post maturity at birth (Hartley, 1957) though this has not been put on a very quantitative basis.
The atlas-type standards are published in the form of radiographs. Comparisons of given radiograph with a set of age standards involves a good deal of subjective judgment. Standards based on skeletal maturity indicators, had their origin in the 1950 edition of Greulich and Pyle’s atlas where drawings were given of the individual stages distinguishable in the development of each hand and wrist bone. These drawings were considerably improved and revised for the 1959 edition. Acheson (1954), Acheson et al.(1955) used the essentially simpler and more direct approach of assigning scores achieved by each stage illustrated, adding together the scores achieved by each bone, with or without differential weighting. Acheson thus reached a sum total maturity score for the whole wrist for comparison with the mean score of the standard series. This approach has much to recommend it over the age-standard method, and form the basis of the new Tanner-Whitehouse-Healy standards (1961).
The skeletal maturity standards are given separately for boys and girls since girls are more mature at birth, before it, and throughout the whole period of growth. At birth girls are ahead by about a matter of weeks, at mid growth by months and at adolescence by the two years which separate the sexes in their growth spurts.
Various factors like physique, socio-economic condition, nutritional status, etc. affect advancement and retardation in skeletal maturity
2. DENTAL AGE
Dental age can be used as a measure of biological age. The commonly used method is simply to record emergence of the teeth above the level of the gum by oral examination.
The deciduous dentition erupts from about six months to two years and can be used as a measure of physiological maturity during the short period, or for a little longer if the full growth to occlusion and the root development are also considered. The order of emergence of the twenty deciduous teeth is practically fixed and only occasional individual variations occur. The importance of genetic control in the age of emergence of teeth is evident from various twin studies (Hatton, 1955; Gam et e1., 1965; Baily and Gam, 1986). While most aspects of growth can be slowed up with relative impunity under poor conditions, non-eruption of teeth could result in increased malnutrition. Probably infants with severe malnutrition do suffer some small delay, but the effect is certainly much less than the effect on weight, height or skeletal development (Cifuentes and Alvarado 1973; Meredith, 1973; Neil et al., 1973 and Truswell and Hansen, 1973). There are evidences to show that the boys are ahead of the girls in the laying down of teeth during fetal life, and in the early stages of deciduous eruption. In later stages girls catch up or go ahead (Infante, 1974). The result above seems probably to give the definitive answer-no difference at the same body size-at least by 12 months.
The permanent teeth begin to erupt at the age of 6 years of age and conclude with the emergence of the wisdom teeth till about 25 years (Harris, 2000). Unlike deciduous dentition, the permanent dentition is subject to some postnatal environmental influences. Nutrition, social class and urban living have been reported to affect emergence of the teeth.
Eruption of the incisors, canines and upper first molar of the children of Japanese immigrants in Brazil was found to be significantly earlier than that of the Japanese in Japan (Eveleth and Freitas, 1969). In Poland, children in poor rural villages were delayed compared with city children (Charzewski, 1963; Polanski and Jarosz, 1969). There are also differences, on average, between ethnic groups. In all the groups, girls on average are ahead of boys.
In almost all populations the emergence of the first molars are the teeth with the lowest average ages. In all populations the last tooth of the first phase is 12. The start of the second active phase is typically signaled by the emergence of PMl in the upper jaw and C in the lower; hence the values are mostly the averages of’ these two ages. In few populations, however, the average time of emergence was lower for the upper canine and / or the lower premolar, and where this occurred these lower values have been used. However, there are, on the average, some ethnic differences. Africans begin the first phase a little earlier than Europeans, with Asiatics intermediate. Africans end the first phase slightly earlier than Europeans, but Asiatics end as the last of the three groups. Asiatics, however, start the second phase earliest, so the quiescent period for them is on average 2.0 years in boys compared with 2.5 years in Africans and Europeans, and 1.8 years in girls compared with 2.2 to 2.3 years in Africans and Europeans. Australian Aborigines end the first phase late, but start the second phase early, having a much shorter period of quiescence than other groups. The inhabitants of New Guinea, in contrast, ‘are the earliest in all aspects of permanent tooth emergence (Eveleth and Tanner, 1990).
Kaul and Pathak (1988) tried to .estimate the age on the basis of the total number of emerged teeth against the chronological age of the Punjabi children. The errors were found to be large; between 11% and 35% in the average case, depending on age and sex. In Hong Kong, skeletally advanced children had more permanent teeth erupted than skeletally retarded children (Lee et al., 1965). Dental maturation is only slightly, though positively, correlated with the age peak height velocity (Hagg and Taranger, 1982) and percentage of final height attained, for taller and heavier children tend to have more teeth erupted than smaller children of the same age (Gam et al., 1965, Billewicz et al., 1973). However, dental age is not as highly correlated with chronological age, height and weight as skeletal age (Green, 1961; Filipsson and Hall, 1976).
3. MORPHOLOGICAL AGE: SIZE AND SHAPE AGE
It is obvious that morphological age is applied to size. A child having above average height for his age may be in advance-of the others in his journey to maturity. But he may .instead be merely a tall child, then and later. Thus, though a ‘height developmental age’ can be easily obtained by finding the age at which the given child’s actual stature equals the height of the average child, the measure has limited usefulness, asit confounds maturity with size (Tanner, 1962).-
The ‘shape age’ is a concept more subtle and rewarding one. The body proportions change gradually into those of the adult, and if it could be measured how far this change of proportion had progressed that could be a measure of maturity. Here again the same problem arises as in size age. The differences in proportion due to growing from differences in proportion that distinguish adults are to be distinguished. But chances of finding growth changes independent of adult differences seem greater with shape than with size. However, there is difficulty in measuring change in shape (Tanner, 1962).
It is necessary to define the gradients of maturity in man. The head grows first, and reaches to near its adult status much earlier than the chest. The chest, in its turn, grows earlier than the legs (Meredith, 1939). In man head is advanced over the trunk and the trunk as a whole over the limbs. The arms are in their upper two segments advanced over the corresponding segments of the legs. Within the limbs the distal segments are ahead of the proximal ones (Davenport, 1932; Maresh, 1955; Anderson et al., 1956}.This gradient is independent of sex difference in maturity. In addition the second phalanges are ahead of the third, fourth and fifth, which follow in that order. All these gradients should be taken into account when constructing a composite measure of shape age..
4 SECONDARY SEX CHARACTER AGE
The deepening of voice, penis and testes development and growth of beard and moustache in boys; the onset of menstruation and breast development in girls and pubic and axillary hair growth in both the sexes are some of the key events of maturity that occur around puberty.
Menarche
The most commonly used indicator has been the age at menarche: onset of menstruation. Bergsten-Brucefors (1976) in a longitudinal study compared the known ages at menarche with the ages recalled some four years after the event. Only 68% of the girls recalled the date correctly to within three months. The, second problem with the retrospective method concerns the sample taken. In the sample there may be girls who have not yet menstruated. Also there may be some who are permanently sterile. If they are excluded the resulting mean is of course biased downwards. Bias also results from common practice of stating one’s age as that the preceding birthday: For example, a girl who experienced menarche at the age of 12.75 years may say that she experienced it when she was 12. In a large sample this kind of error would lead to the mean being underestimated by just 0.5 years but, in a smaller sample, the bias is less consistent. “
There is small range’ of variation in the age at menarche of North West Europe from 13.0 years in Sweden through 13.4 years in Holland, Switzerland, Northern UK to 13.5 years in Irish Republic. In Mediterranean countries it is clearly earlier, ranging from 12.2 to 12.8 years. Girls of European ancestry living in the United States (12.8 years), Canada (13.1), Australia (13.0) and New Zealand (13.0) tend to be fractionally earlier than their parent populations; those in South America are the same as or fractionaily earlier than their parent populations. Japanese (12.5) and well-off Chinese (Hong Kong-12.4, Singapore-12.4) are as early as or earlier than the majority of Mediterranean populations. Well-off Indians in Punjab (12.5) and Madras (12.9) are not unlike Mediterranean populations, though in poor rural populations in India the average age is around 14.0 years, as it is in Egypt and Iraq and Meso-America, The age at menarche is clearly delayed in the populations of Nepal (16.2), New Guinea (15.6 to 18.0) and the poorer areas of Sub-Saharan Africa (15.0 to 17.0) (Eveleth and Tanner, 1990).
Menarche is delayed by chronic undernutrition. Improvement in environmental conditions, more particularly nutritional and infective is a principal cause of earlier maturation. Amongst almost all populations the well-off girls attain menarche earlier than the poor and urban girls earlier than rural. Of course there are some exceptions.