Métodos de alarma

fifty-two years. Because both samples of Danish children entered school at the age of seven, permanent teeth that typically emerged earlier than seven years could not be included in Helm’s (1969) study. Helm (1969) eliminated the influences of observer error, race and clinical dental history, and considered the effect of residential conditions to have been small. While the physical development of the temporally later group was clearly advanced compared with the earlier group, dental development was often constant between the two samples (Helm 1969). Significant differences in emergence age only manifested themselves in certain teeth and at particular stages of development (Helm 1969). While Helm (1969) attributed the observed secular trend in tooth emergence to different relations between the timing of dental and physical development in the earlier and later groups of children, he could not account for why these differences had developed.

Although geographic and ethnic populations may vary, perhaps often significantly, in their schedules and patterns of dental growth, this may be less of an evolutionary phenomenon than perhaps expected. Garn, Lewis and Polachek (1959) concluded that variability of tooth formation (although only premolars and molars were studied) was approximately three times greater than what had been traditionally accepted. They found low variability in both tooth emergence and tooth mineralization, and that both were lower in their relative variabilities when compared with variability in skeletal development. Almost three decades later, Kieser and Groeneveld (1988a) supported Garn et a/.’s (1959) results with very similar profiles among South African Blacks, Native Americans, and Whites. No conclusive relationship between metric variability and occlusal complexity could be established (Kieser & Groeneveld 1988a). However, metric variability did correlate with length of developmental period.

1.2.3 Sexual dimorphism among the dentitions of modern human

populations

In a recent assessment of metric sexual dimorphism in the deciduous teeth of modern Pima, Alvrus (2000) showed absolutely low levels of

dimorphism. While these were exceeded by those of Australian Aboriginal youths (Margetts & Brown 1978, cited by Alvrus), they were greater than those of White children (Black 1978, cited by Alvrus). The deciduous teeth that exhibited the highest levels of sexual dimorphism were the mandibular first incisor and second molar, and the maxillary canine and second incisor (Alvrus 2000). Although sexual dimorphism was manifested in buccolingual and/or mesiodistal dimensions of many deciduous teeth, none of the measurements proved “significant at the p is ^ 0 .0 5 level” (Alvrus 2000). Previous work (Black 1978, Margetts & Brown 1978, Farmer & Townsend 1993) supported the finding that the degree of sexual dimorphism for this group was low (Alvrus 2000). Alvrus (2000) also found the amount of sexual dimorphism between the deciduous and the permanent teeth of the Pima studied was not significantly different. Tsai (2000) observed significant sexual differences in mean buccolingual crown dimensions of deciduous second molars, where boys' crowns were larger buccolingually. Tsai (2000) proposed sexual differences between the buccolingual and mesiodistal crown diameters of individual teeth were perhaps generated by distinct and different genes that independently controlled each of the two dimensions. Alvrus (2000) suggested that a prolonged period of amelogenesis in males might be responsible for sexual dimorphism in both deciduous and adult dentitions. This is supported by the earlier conclusions of Moss (1978) that duration of amelogenesis and enamel thickness contributed to morphological and metrical sexual dental differences. Additionally, somewhat earlier work showed negligible differences between both size and shape of the pulpal outline and dentine-enamel junction of boys and girls (Carlsen & Anderson 1966, Mjor & Hougen 1974, both in Moss 1978).

Sexual differences in tooth size have long been recognised in the permanent teeth, although the mechanisms through which this dimorphism derives have largely remained cryptic (Seipel 1946 & Moorrees 1959, in Kieser 1990, Ch.6, and Moss 1978). Moss (1978) surmised that gene loci such as

those on the X- or Y-chromosomes, or both, perhaps in combination with environmental factors, likely dictate sexual differences. While sexual dimorphism is most prominent in the canines (Kieser 1990, Ch.6, Thompson et

al. 1975), there are significant sexual differences in both anterior and postcanine tooth groups (Kieser et al. 1985e). Kieser and colleagues (1985e)

found the mesiodistal dimensions of upper and lower canines and upper second molars, and the buccolingual dimensions of upper and lower third premolars, to be the best dental discriminators of sex. Interestingly, Harris and Bailit (1988) noted sexual differences in dental size patterns, where females had better size- integrated adult teeth than males. A decade earlier. Moss (1978) had found evidence of sexual differences in dental development, and of dimensional dimorphism produced by differences in enamel thickness that resulted from differing durations of amelogenesis in boys and girls. Heilman (1936) found a higher incidence of congenitally absent MS’s in females: eighty-five percent of females sampled had one to two MS’s missing. However, a markedly greater proportion of males had a greater number of congenitally absent MS’s: two thirds of males sampled had between two and four MS’s missing (Heilman 19S6). Garn and Lewis (1970) found that hypodontia was more closely associated with crown-size reduction in females than males. In their study of Blacks and Whites, Merz et al. (1991) concluded that at least some level of sexual dimorphism (mesiodistal diameters) was completely unrelated to race. Garn and colleagues (1966, 1967, 1968a [Garn, Lewis & Kerewsky], and 1967 [Garn, Lewis, Swindler & Kerewsky]) found evidence of genetic control of the magnitude of sexual dimorphism among families.

Patterns of deciduous tooth mineralization are generally similar between the sexes. If anything, Fanning’s (1961) results suggested these teeth may develop slightly earlier in girls, while Moorrees, Fanning and Hunt’s observations tended towards slightly advanced deciduous tooth growth in boys (196Sb). Leighton (1968) found deciduous tooth emergence tended to be slightly earlier in boys than in girls. In none of Leighton’s study cases did the reverse occur, and Leighton emphasised that no cases of advanced deciduous emergence in girls had been documented in previous work (Sandler 1944, and Robinow et al. 1942). However, only sexual differences in emergence ages associated with the upper deciduous canines proved statistically significant (Leighton 1968). Fanning (1961) found significant sex differences in deciduous tooth root resorption that increased with age; ages at which the lower central incisor, and the canine and second molars were shed were the least and the most sexually dimorphic, respectively. Eveleth and Tanner (1990) considered the persistent debates of whether and to what extent sexual differences were

manifest in the deciduous dentition. These workers tended towards the results found by Tanguay et al. (1984, 1986) that, at least by one postnatal year, there was no difference in deciduous tooth growth between boys and girls of equivalent body size.

While the deciduous teeth of males might typically emerge earlier than those of females, quite the reverse tends to be true of permanent tooth emergence. Both mineralization and emergence are generally advanced in females compared to males (Gleiser & Hunt 1955, Dahlberg & Menegaz-Bock 1958, Hotz et al. 1959, Nolla 1960, Demirjian & Levesque 1980, Thompson et al. 1975, and others). Thompson et al. (1975) observed sex-specific developmental patterns in crown mineralization and root formation in White preadolescent Canadians. Their study demonstrated that, with the exception of M3, permanent tooth development was delayed in males compared to females, with a maximum age delay of twenty percent in canine mineralization, followed successively by P3, 12, II and P4 (Thompson et al. 1975). In males, root formation was delayed in all teeth except M3; equivalent stages of root formation for this tooth were observed in females who were twenty-one percent older than the males sampled (Thompson et al. 1975). Nigerian females both initiated and completed third molar emergence about two years before males (Odusanya & Abayomi 1991). Debrot’s (1972) study of Black and White girls and boys demonstrated a maximum difference of 0.9 years for upper P4 emergence age, and the slightest difference, 0 .1 year, in emergence age for the

permanent canine between the sexes. Black children also emerged their permanent teeth significantly earlier than did the White children (Debrot 1972).

Kieser (1990, Ch.6) suggested two explanations for sexual dimorphism in

dental size. The first of these was that relative concentrations of hormones produced after the differentiation of male and female gonads influenced dental size. The second mechanism Kieser considered was the direct effect of genes on the sex chromosomes (originally discussed, for Kieser’s purposes, by Townsend and Alvesalo 1985). Certainly, some types of hormonal interference can affect the rate of tooth growth (Garn et al. 1965). Garn et al. (1965) confirmed that at least anabolic steroids, adrenally derived, “can and do spur tooth formation and movement". Although typical precocity in dental maturity is

but about one eighth that of skeletal advancement, females exposed to adrenally derived androgenic hormones prior to birth exhibited a twenty-nine percent (versus a seven percent) absolute and relative advance in dental development (Garn etal. 1965).

Years earlier, when Gleiser and Hunt (1955) studied permanent mandibular first molar development, they found that mediobuccal cusp mineralization was precocious in girls but not in boys, and occurred within the first three weeks after birth. These authors also noted that in girls, the average developmental span of M l, including both crown and root formation, was ninety- six percent that of boys, and that at approximately equivalent stages of permanent tooth development, girls were typically ninety-five percent as old as boys were. Gleiser and Hunt concluded that, as female first molars were smaller that their male counterparts’ by equivalent amounts in their linear dimensions, absolute velocities of M l “elongation” were similar between both sexes. A little later, Nolla (1960) summarised that although girls both began and completed their permanent tooth development before boys, both sexes developed their adult teeth at the same rate. Females in a population of Sinhalese schoolchildren emerged their permanent canines approximately nine months before males (Nanayakkara et al. 1993). Perhaps this was the result of growing absolutely smaller canines that were functionally ready sooner, and so emerged sooner, than the larger male canines. Although Nanayakkara and colleagues (1993) found no sexual differences in emergence sequence, they noted that tooth emergence in girls was typically ahead of the boys' by almost four and a half months. Sexual differences in the number of permanent teeth present in the children’s mouths peaked at eleven years, perhaps the age by which most children were well into puberty (Nanayakkara et al. 1993). Ultimately, girls completed their permanent tooth emergence about half a year before the boys (Nanayakkara et al. 1993). Blankenstein and colleagues (1990) found that, with the exception of h. South African (Soweto) Black girls emerged their permanent incisors between two and four months before the boys, typically at six and seven years compared to seven and eight years, respectively. The emergence time of M l, typically at six and seven years, was not statistically different between the sexes (Blankenstein et al. 1990). In their survey of Ugandan children, Krumholt et al. (1971) also observed earlier tooth emergence

in females, except for the first tooth, the permanent central incisor, which they noted emerged earlier in boys. This contrasted with White children, in whom “there is no doubt” that all the permanent teeth emerge first in the females (Krumholt et al. 1971). In addition, the permanent dentitions of the Ugandan Blacks sampled had fully emerged about one to one-and-a-half years before those of Whites (Krumholt at a/. 1971). For instance, while M l emerged between a mean range of 5.1 to 5.4 years in the Ugandan children (Krumholt at si. 1971), the same molar emerged between a mean range of 5.9 to 6.4 years in Whites (Hurme 1948, 1949).