Skeletal Age Versus Dental

Conservatively, skeletal age in Nariokotome was more than 2.5 years greater than his mean dental age (SA - DA = 13 - 10.2 = 2.8 years); the discrepancy only rises if strictly African standards

Table 10.2 Dental age of KNM-WT 15000 by human standards compared to ages of children in similar developmental stages in other samples

Tooth

Stage

Mean

KNM-WT 15000 (Smith, 1993)

UI1 Ac

UM3 Cr 3/4

LI2 Ac

LM2 R 1/2 Dental age (mandibular teeth) Dental age (all)

Worldwide sample-boys (Liversidge et al., 2006)

>10.60 10.10 12.30 >9.90 10.20 10.00 10.50 10.50 10.30 10.60

LI2

G

688

8.76

8.83

12.98

1.100

LC

F

1,069

7.05

9.78

14.88

1.220

LP3

F

930

8.56

10.29

14.38

1.240

LP4

F

958

5.56

10.98

15.98

1.430

LM2

F

575

5.56

11.34

14.99

1.180

Age in stage

10.24

Modern Africans-boys (Liversidge, H., pers. comm., 2008)

UI1

Rc

24

7.10

8.54

10.50

0.902

UI2

R 3/4

41

5.74

8.74

11.50

1.299

UM3

C 3/4

15

6.5

11.09

13.50

2.056

LI2

Rc

16

5.74

7.81

10.00

0.994

LC

R 3/4

76

7.50

10.16

13.92

1.276

LP3

R 3/4

66

7.50

10.67

13.50

1.260

LP4

R 3/4

85

8.50

11.17

14.20

1.260

LM2

R 3/4

48

9.66

11.92

14.20

1.139

Age in stage

10.01

Boston (Gron, 1962)

LI1

Gingival emergence

41

4.85

6.45

7.81

0.450

LI2

"

52

5.89

7.37

9.21

0.320

LC

"

50

8.33

10.91

13.90

1.180

LP3

"

51

8.18

10.60

14.45

1.140

LP4

"

50

8.49

11.04

13.36

1.130

LM1

"

30

4.68

6.35

7.40

0.690

LM2

"

58

8.89

11.96

15.09

1.160

are applied (14.0 - 10.1 = 3.9 years). It is firmly established that skeletal and dental development are separate processes with only moderate correlations (see Lewis, 1991), yet, when children are assessed by experts, there is a characteristic degree of difference between the two. Fairly extensive data exist on the contrast between dental and skeletal ages for normal American children (Lewis, 1991; S.L. Smith, 2004) and there is a growing data base on children with endocrine disorders (Garn et al., 1965; Vallejo-Bolanos et al., 1999) and disease (Holderbaum et al., 2005).

The most comprehensive study of skeletal versus dental age comes from Lewis (1991), who described 694 Ohio children presenting (but not yet treated) as orthodontic patients. In two thirds of cases, skeletal age and dental ages differed by 1 year or less; 95% of cases differed by ±2 years or less. Extremes extended to as much as 3 years, but a lag of skeletal age was more common than the reverse. Lewis presented a detailed distribution broken down in months, reproduced here in Table 10.3 for the 320 boys. Only one of 320 boys nears Nariokotome in advancement of skeletal age.

Shelly Smith (2004) also explored variation in dental, skeletal and chronological age using data from Demirjian's well known study of growth of Canadian children, and her data are shown for further comparison. Matched for sex and grossly similar tooth formation stages to Nariokotome, discrepancy between skeletal and dental maturation ran from -1.8 to +1.6 years (-21.6 to +19.6 months) in 13 normal boys. The resulting distribution of SA - DA (skeletal age minus dental age) largely mirrors that of Lewis, although it is less extreme. Enlarging her search, Smith tracked all 40 boys in the study from ages 10-15, looking for a skeletal age advanced more than 2 years over dental age. Of 221 records over the 6 years, only four records (1.8%) showed >2 year

Table 10.3 Distribution of discrepancy between skeletal age (SA) and dental age (DA) in North American boys, children with endocrine disorders, and the Nariokotome Homo erectusyouth KNM-WT 15000

Percent of cases (nearest whole %)

SA - DA mos

American boysa

Canadian boysb Hypopituitaryc

Sexual precocityc KNM-WT 15000 Direction

-36 or more

3

20

-30 to -35.9

0

20

-24 to -24.9

5

-18 to -23.9

8

15 40

-12 to -17.9

15

15 20

-6 to -11.9

17

8

0 to -5.9

19

23

Skeleton lags T

0-5.9

16

15

Skeleton advances 1

6-11.9

6

15

12-17.9

6

20

18-23.9

2

8

20

24-29.9

1

30 or more

1

60 X

N

320

13 5

51

Chronological age range (year)

6-15

10-13 ~8-13

~7-10

a Ohio boys presenting for orthodontic treatment (Lewis, 1991).

b Canadian boys from Demirjian's study of normal growth; this subset was matched for tooth formation grossly similar to Nariokotome by Shelley Smith (2004).

c Male and female patients with endocrine disorders affecting growth (Garn et al., 1965).

a Ohio boys presenting for orthodontic treatment (Lewis, 1991).

b Canadian boys from Demirjian's study of normal growth; this subset was matched for tooth formation grossly similar to Nariokotome by Shelley Smith (2004).

c Male and female patients with endocrine disorders affecting growth (Garn et al., 1965).

advance of skeletal age, and all four were 14 or 15 years old, where dental age prediction begins to tail off in accuracy as most teeth reach maturity. Although Smith interpreted her study as a cautionary one about variation, she also clearly recognized that Nariokotome was atypical.

We do know that truly eye-catching discrepancies between SA and DA can occur in endocrine disorders. Classic data from patients with endocrine disorders presented by Garn et al. (1965) are reproduced in Table 10.3 for children of comparable age range. In hypopituitary patients, Garn et al. showed that the skeletal development lags behind dental development; these cases make up a distribution at one end of the extremes of Table 10.3. The discrete pile up of 3% of Lewis's cases in the extreme skeletal delay category also suggests some of these orthodontic patients had an underlying growth deficiency. The opposite condition characterizes children with sexual precocity, when sex hormones are released years too early. In this case, skeletal maturation is accelerated - in 60% of the patients beyond 30 months in advance of dental development. The most extreme case was a 9 year old who had nearly closed all epiphyses (SA - DA = 7.3 years!). Comparing the data sets in Table 10.3, it is clear that for a child like Nariokotome, with skeletal age advanced by 34+ months over the dentition, a pediatrician would be justified in sending the case to an endocrinologist.

As is typical when experts gather the data, all the studies in Table 10.3 (see also Vallejo-Bolanos et al., 1999) found that dental age was the more accurate predictor of chronological age. Although both skeletal and dental development can be delayed by undernutrition or advanced by supernutrition, the dentition is much more resistant to environmental effects than is the skeleton (see Smith, 1991). Thus, chronic undernutrition, disease, or growth hormone deficiencies hit the skeleton harder, producing a lag of skeletal to dental age (SA - DA = a negative value in Table 10.3). Undernutrition likely contributes to the repeated finding that skeletal age in African children is delayed with respect to European children, quite markedly so in children under 10 years of age (Mackay and Martin, 1952; Clegg et al., 1972). When we turn to prehistory and cemetery samples, a lag of skeletal age behind dental age should be much more common than the reverse, judging from other evidence of growth faltering (e.g., Humphrey, 2003). Nariokotome, of course, shows just the opposite: his skeletal age is greater than his dental age, something more commonly found in obese or sexually precocious children today (Garn et al., 1967), a direction of difference which is particularly unexpected.

The hundreds of cases described in Table 10.3 show Nariokotome outside 99% limits for normal children and well into the distribution of growth disorders. One study, however, gives results at odds with the literature: Clegg and Aiello (1999) presented data from historical burials at Spitalfields for ten children they claimed had widely disparate dental and skeletal ages (ranging between -3.3 to + 3.5 years at least), a study sometimes cited as evidence that Nariokotome is not so unusual (Anton and Leigh, 2003; S.L. Smith, 2004; Ruff, 2007). Several aspects of the data, however, isolate this study: skeletal age was a better predictor of chronological age than dental age and 80% of cases were graded as advanced in skeletal age, as in obese children or sexual precocity, despite the fact that the Spitalfields mortuary is famous for small body size and late growth (Molleson and Cox, 1993). Certainly, most of the Clegg and Aiello subjects were too old for the problem at hand: indeed six of the ten were ages 14-18, with nearly every tooth mature except third molars, a poor comparison to Nariokotome, a much younger adolescent with ten immature teeth. For all these teenagers, systematic undergrading of mature teeth by Clegg and Aiello built up large apparent errors. But in any case, fatal errors corrupt the data set: broken roots of fully mature P4 teeth were graded as immature in two cases (giving dental ages below 13 to the 14 and 17 year olds. The 10 year old, a boy of normal size and dental development, was assigned a dental age of 8.4 even though the Clegg and Aiello data actually average to 9.9; their assignment of a skeletal age of 6 years to him is equally questionable. Thus, comparisons of dental versus skeletal age by Clegg and Aiello (1999) are founded on faulty or irrelevant data.

Once again, there is no point in claiming that extremes cannot happen; the point is, simply, that Nariokotome's fit into human growth and development standards is uneasy at best, overlapping less than 1% of the well fed boys in Western growth studies; cemetery samples or the living malnourished should drift even further from Nariokotome because disease and malnutrition delay skeletal maturation disproportionately. As Smith (1993) concluded, while Nariokotome's size and maturation might be matched in some aspects at some human percentile, he cannot be made ordinary.

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