Human deciduous mandibular molar incremental enamel development

Abstract

Quantitative studies of incremental markings retained within human enamel have reconstructed the duration and rate (crown and cusp formation times, initiation and completion, daily enamel secretion rates) of permanent tooth development. This approach has provided one way of estimating human age-at-death, and facilitated comparative dental studies of primate evolution. Similar applications from deciduous enamel are inhibited because developmental reconstructions from incremental markings for these teeth are less frequently reported in the literature. This study quantified the duration and rate of enamel development for mesial (protoconid, metaconid) and distal cusps (hypoconid, entoconid) for first (dm1) and second (dm2) deciduous mandibular molars from an archaeological sample of modern human juveniles. Crown formation time can be calculated from the dm1 protoconid because growth initiates and completes in this cusp, and from the dm2 protoconid combined with the final period of hypoconid growth. The dm1 postnatal crown formation time included the time taken for the tubercle of Zuckerkandl to develop, and differed slightly compared to radiographic methods. The majority of dm1 protoconid cuspal (occlusal region) enamel formed before birth. The dm2 entoconid enamel formed mainly after birth. Birth reduced daily enamel secretion rates, changed the visibility of incremental markings, and disrupted enamel growth for 3 to 8 days. Findings presented here can contribute to age-at-death estimates for human infants aged 13-postnatal months or less, and should facilitate comparisons of primate deciduous incremental enamel development in an evolutionary context. Regression equations are included so that cuspal formation time can be estimated from enamel thickness. Human deciduous molar enamel development (crown and cusp formation times, initiation and completion, growth rates) has been documented from studies of radiographs, measurements of tooth length, and direct observation of the developing fetal dentition (e.g., Logan and Kronfeld, 1933;Schour and Massler, 1941;Kraus, 1959;Fanning, 1961;Moorrees et al., 1963;Gilster et al., 1964;Kraus and Jordan, 1965;Fanning and Brown, 1971;Demirjian et al., 1973;Liversidge et al., 1993;Liversidge and Molleson, 2004). Standards of formation time have been developed from some of these studies, which are routinely used to estimate age-at-death for human skeletons recovered from bioarchaeological and forensic contexts (e.g., Demirjian et al., 1973). Others have used a different methodology and calculated formation times from histological studies of incremental markings retained within enamel (Boyde, 1963). Though these histologically-derived formation times are well reported for permanent teeth in the literature (e.g., Reid and Dean, 2006), they are scarcely reported for deciduous teeth (FitzGerald et al., 1999;Katzenberg et al., 2005; also see Shellis 1984, and comments by Smith et al., 2006). This lack of data is mainly due to the poor preservation of these markings in deciduous...

Incremental enamel development in modern human deciduous anterior teeth

“…Since deciduous incisor enamel develops in advance of molars, birth is recorded at different times in these different tooth types (e.g., Kraus and Jordan, 1965). Birth is an influence on DSRs in deciduous enamel, temporarily reducing postnatal rates (e.g., Macchiarelli et al, 2006;Birch and Dean, 2009;Mahoney, 2011). Thus, it would seem likely that DSRs from deciduous incisors might differ when compared with equivalent regions in deciduous molars.…”

“…One would expect similar findings in human deciduous teeth, thought this is not clear from the very few studies that have reported such values. Mahoney (2011) reported one value of 9 days for one deciduous second molar. As part of their study, Bowman (1994, 1995) reported a range of values from 4 or 5 days (depending on the observer) to 8 days for one canine and two deciduous molars, but this included variation within a tooth.…”

“…Although some previous researchers have described human deciduous incremental enamel development along the tooth row (e.g., FitzGerald et al, 1999;Birch and Dean, 2009;FitzGerald and Hillson, 2009;Mahoney, 2011), the topic has generally received limited attention. Nevertheless, there are clear differences in the environment in which human deciduous and permanent teeth grow which could influence incremental enamel development.…”

Nejsou čáry jako čáry: inkrementální linie v mikrostruktuře zubů a jejich využití při analýze kosterních nálezů

“…Věk v čase iniciace růstu korunky, délka formování korunky a věk v čase ukončení růstu korunky jsou shrnuty v tabulce 1. Délka formování korunky druhé dolní dočasné stoličky (mesiolinguální hrbolek/ metaconid) odpovídá publikovaným hodnotám (Mahoney 2011) jak z hlediska formování v prenatálním období (54 dní), tak i v postnatálním období (300 dní). Vývoj druhé horní dočasné stoličky začal dříve a při narození byla zformována větší část jak hrbolku mesiobukálního/ protoconid (114 dní), tak i mesiolinguálního/ metaconid (105 dní).…”

“…FitzGerald et al 2006;Thomas 2003;Mahoney 2011Mahoney , 2012Birch -Dean 2014), které však vyžadují přípravu histologického prepará-tu a tudíž destrukci zubu. Díky rozvíjejícímu se oboru virtuální histologie je v poslední době možná i nedestruktivní analýza mikrostruktury zubů v 3D zobrazení pomocí rentgenové mikrotomografie (µCT) se synchrotronem jakožto zdrojem rentgenového záření a s využitím fázo-vého kontrastu (Smith -Tafforeau 2008).…”