6.2 ANÁLISIS DEL RIESGO PARA CADA ZONA DEPORTIVA
6.2.8 Caso: Zonas de entrenamiento al aire libre
In their study of the chronology, sequence, and pattern of great ape dental development. Dean and Wood (1981) set guideline assumptions of zero temporal overlap between developing adjacent molar crowns, and equal time intervals of 2.5 years for sequential molar crown mineralization, beginning at birth with M l. Contrary to Dean and Wood (1981), Anemone and colleagues (1991) later recorded significantly different molar crown mineralization periods and degrees of overlap in the developing adjacent molars of chimpanzees {Pan troglodytes). These workers (Anemone et al. 1991) found significant differences in timing of molar crown initiation between apes and humans, and thus argued that chimpanzees exhibited marked overlap of mineralizing adjacent molar crowns while humans did not. Using radiographs. Anemone et al. (1991) noted molar crown initiation times at and up to three weeks after birth.
at eighteen months, and at forty-eight months for M1, M2, and M3, respectively. Crown completion for the same teeth was logged at twenty-four months, forty- eight months, and about ninety-six months, respectively, where M1 crown formed in 2 years, M2 crown in 2.5 years, and M3 crown in little over 3.5 years (Anemone et al. 1991). However, while these results demonstrated that periods of M l and M2 crown mineralization overlapped by about six months, periods of M2 and M3 crown formation barely coincided.
Anemone and colleagues (1991) found that durations of both crown and root development appeared to increase from M l to M3. Dean and Wood (1981) had also assumed that the roots of similar teeth required the same time to form. However, Anemone et ai. (1991) recorded molar root development over 3-4 years for M l and 4-5 years for M2 and M3. While root mineralization times may have varied in molar teeth, they appeared consistent in premolars (Anemone et al. 1991). Anemone et al. (1991) found that initial premolar development occurred at a slightly earlier age than the little more than two years assessed by Dean and Wood (1981) with mineralization starting at eighteen months. The premolars were crown complete between 5 and 6 years of age, and achieved
apical root closure between 9 and 10 years of age (Anemone et al. 1991). While Anemone et al. (1991) documented initial mineralization of the incisors at 6-10 months, and Dean and Wood (1981) at 2-4 months, the consensus was a significantly earlier onset of mineralization of the incisors relative to onset of the premolars, and crown completion of the premolars around 5 years.
While chimpanzees, gorillas and orang-utans demonstrate at least some degree of overlap in the sequential development of their adjacent molars, in humans the sequential development of adjacent molars is typically punctuated by substantial temporal gaps (Anemone et al. 1991, Anemone 1995, Anemone et al. 1996, Beynon et al. 1991, and Winkler et al. 1996). However, the existence of a temporal gap in crown mineralization between at least human M is and M2s is questionable (Reid et al. 1998) as these workers found an overlap of 0.27 years in crown formation periods of these two teeth. Anemone et al. (1991) observed an increase in duration of crown and root development from first to last molar teeth in chimpanzees. In orang-utans, when M l crowns were approximately one-half complete, M2 crowns and all or most antemolar
tooth crowns were mineralizing (Winkler et al. 1991). In a later study, Winkler at al. (1996) found M2 to be less advanced relative to M l in a male orang-utan. In this ape, at the stage at which mVi had not yet emerged but root development had begun, M% crowns were about % complete. M% had not yet begun to mineralize (Winkler at al. 1996). This relative rate of M2 development also appeared to be the case in chimpanzees (Anemone at al. 1996), but not in gorillas, where M2 initiation was slightly retarded relative to the other teeth, occurring in the last quarter of M l crown growth (Beynon at al. 1991a). While both Beynon at al. (1991a) and Winkler at al. (1991) observed M2 developing
after M^ in orang-utans, Winkler at al. (1991) marked M2 development at least
as young as twelve months of age, about one year earlier than estimated by Beynon at al. (1991a). These workers (Beynon at al. 1991a) suggested that the fourth premolars began their development both in coincidence with (P4), and slightly before (P"^), the development of the second molars. In contrast, Winkler at al. (1991) found instances where M2 began to mineralize before the fourth
premolars.
Whether a pattern of developmental molar overlap is diagnostic of great apes remains uncertain. Simpson at a/.’s (1991) study found no developmental hiatus between human MTs and M2’s. In both great apes and humans, not only did the first molar develop before the second molar tooth, it also achieved full apical root closure before M2 root growth was complete (Simpson at al. 1991). According to Simpson at al. (1991), apes and humans shared similar relative rates of growth, as well as onset times of mineralization, for M l and M2. However, other investigations have noted some degree of overlap in sequential developing molar patterns between humans and chimps (Simpson 1993, and Conroy & Mahoney 1991 in Winkler at al. 1996). In a study of chimpanzees and orang-utans Winkler (1995) concluded that, while considerable developmental temporal overlap of the lower first and second molars was common, it “may not always occur”. More recently, Kuykendall (1996) determined that while timing of molar tooth mineralization stages was both relatively and absolutely distinct, it remained sufficiently similar so as to fail to diagnose modern humans from chimpanzees {Pan troglodytes). Rather, the canine was the most diagnostic tooth between these two taxa (Kuykendall 1996). Alternatively, in the same year. Anemone at al. (1996) proffered that chimps {Pan troglodytes)
demonstrated advanced molar development relative to anterior tooth development compared to humans, in whom anterior teeth were more developed relative to molars at the same given developmental stage.
Simpson et al. (1991) had stated that developmental patterns of ape and human postcanine teeth were also fundamentally similar, with no hiatus between human M l and M2 development. They had also asserted that patterns of dental development between gorillas and chimpanzees were indistinguishable (Simpson et al. 1991). However, Anemone and Watts (1992) disputed this finding based upon work published the previous year (Anemone et al. 1991). Beynon et al. (1991a) histologically examined the teeth of a gorilla and an orang-utan, and reported that these apes shared a similar pattern of dental formation, although completion of the orang-utan teeth took longer. Both the gorilla and orang-utan had molars that mineralized in overlapping series. M l crown complete by three years of age, and early emergence and apical root closure of M l prior to canine and premolar crown completion (Beynon et al. 1991a). Both apes had upper and lower incisors mineralized at approximately the same time, with 12 crowns taking only slightly longer to form than II crowns (Beynon et al. 1991a). Interestingly, in both taxa, development of the incisor and canine crowns took about 5 years and 7.75-8.5 years, respectively, and was substantially prolonged by more than two years longer than previously thought (Beynon et al. 1991a). This emphasised the absolutely longer developmental period of ape anterior teeth compared to the same teeth in humans. Yet, overall dental development in apes was completed within 10-12 years, whereas humans required an average 18 years to complete their permanent dentition (Beynon etal. 1991a).