Effects of two separation methods of crown and root on enamel thickness measurements

doi:10.16359/j.cnki.cn11-1963/q.2018.0028

Abstract

Abstract:

In computer-aided dental anthropology it is sometimes a regular process to separate the crown from the roots. In order to assess the methodological impact of sectioning crown and roots for the computation of enamel thickness, we compared two digital approaches(separating the crown from the root using the cervical line or a basal plane) for the 3D analysis of enamel thickness on a total number of 82 hominin lower postcanine teeth, including South African fossil hominins(n=26), Neanderthals(n=22), and modern humans(n=34). According to paired t-test, no significant difference is observed in the enamel thickness values between two methods, but subsequent inter-taxa comparisons reveal different results in average enamel thickness(AET) in premolars. Separation based on a basal plane is more operator-dependent, not practical to sinuous cervical margin and might mask between-group distinctions. Besides providing a set of raw data for further investigation, this study reports thinner premolar RET in Neanderthals compared with modern H. sapiens and therefore support the notion that Neanderthal has generally thinner relative enamel. Our results show that, for studies aimed at discriminating among different species, using the cervical margin to isolate the crown from the root is a practical option as it considers the anatomical nature of tooth, especially for those specimens(such as anterior dentition, or molars of Pan and Gorilla) with steep cervical line.

Key words: Taxonomic discrimination, Enamel thickness, Dental anthropology, 3D virtual measurements, Tooth crown, Tooth root

CLC Number:

Q983

PAN Lei. Effects of two separation methods of crown and root on enamel thickness measurements[J]. Acta Anthropologica Sinica, 2019, 38(03): 398-406.

Figures/Tables 6

References 36

[1]	Kay R. The nut-crackers—A new theory of the adaptations of the Ramapithecinae[J]. American Journal of Physical Anthropology, 1981,55:141-151
[2]	Kay R. Dental evidence for the diet of Australopithecus[J]. Annual Review of Anthropology, 1985,14:315-341
[3]	Martin L. Significance of enamel thickness in hominoid evolution[J]. Nature, 1985,314:260-263 URL pmid: 3920525
[4]	Ungar PS, Grine FE, Teaford MF, et al. Dental microwear and diets of African early Homo[J]. Journal of Human Evolution, 2006,50:78-95
[5]	Kono R, Suwa G. Enamel distribution patterns of extant human and hominoid molars: occlusal versus lateral enamel thickness[J]. Bulletin of the National Museum of Nature and Science, 2008,34:1-9
[6]	Olejniczak A, Tafforeau P, Feeney RNM, et al. Three-dimensional primate molar enamel thickness[J]. Journal of Human Evolution, 2008,54:187-195 URL pmid: 18045652
[7]	Smith TM, Olejniczak AJ, Reh S, et al. Brief communication: Enamel thickness trends in the dental arcade of humans and chimpanzees[J]. American Journal of Physical Anthropology, 2008,136:237-241 doi: 10.1002/ajpa.20796 URL pmid: 18324634
[8]	Beynon A, Wood B. Variations in enamel thickness and structure in east African hominids[J]. American Journal of Physical Anthropology, 1986,70:177-193 URL pmid: 3090891
[9]	White TD, Suwa G, Asfaw B. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia[J]. Nature, 1994,371:306-312 doi: 10.1038/371306a0 URL pmid: 8090200
[10]	Molnar S, Hildebolt C, Molnar IM, et al. Hominid enamel thickness: I. The Krapina neandertals[J]. American Journal of Physical Anthropology, 1993,92:131-138 doi: 10.1002/ajpa.1330920202 URL pmid: 8273825
[11]	Smith TM, Olejniczak AJ, Zermeno JP, et al. Variation in enamel thickness within the genus Homo[J]. Journal of Human Evolution, 2012,62:395-411 doi: 10.1016/j.jhevol.2011.12.004 URL pmid: 22361504
[12]	Skinner MM, Alemseged Z, Gaunitz C, et al. Enamel thickness trends in Plio-Pleistocene hominin mandibular molars[J]. Journal of Human Evolution, 2015,85:35-45 URL pmid: 26024565
[13]	Schwartz GT. Taxonomic and functional aspects of enamel cap structure in South African plio-pleistocene hominids: a high resolution computed tomographic study[D]. Ph. D. Dissertation, Washington University, 1997, 1-22
[14]	Zhang LZ, Zhao LX. Enamel thickness of Gigantopithecus blacki and its significance for dietary adaptation and phylogeny[J]. Acta Anthropologica Sinica, 2013,32:365-376
[15]	Tafforeau P. Phylogenetic and functional aspects of tooth enamel microstructure and three-dimensional structure of modern and fossil primate molars[D]. Ph.D. Dissertation, Université de Montpellier II, 2004, 1-133
[16]	Olejniczak A. Micro-computed tomography of primate molars[D]. Ph. D. Dissertation, Stony Brook University, 2006, 1-194
[17]	Feeney RNM, Zermeno JP, Reid DJ, et al. Enamel thickness in Asian human canines and premolars[J]. Anthropological Science, 2010,118:191-198
[18]	Benazzi S, Panetta D, Fornai C, et al. Technical Note: Guidelines for the digital computation of 2D and 3D enamel thickness in hominoid teeth[J]. American Journal of Physical Anthropology, 2014,153:305-313 doi: 10.1002/ajpa.22421 URL pmid: 24242830
[19]	Benazzi S, Fornai C, Bayle P, et al. Comparison of dental measurement systems for taxonomic assignment of Neanderthal and modern human lower second deciduous molars[J]. Journal of Human Evolution, 2011,61:320-326 doi: 10.1016/j.jhevol.2011.04.008 URL pmid: 21624638
[20]	Fiorenza L, Benazzi S, Tausch J, et al. Molar macrowear reveals Neanderthal eco-geographic dietary variation[J]. PLOS ONE, 2011,6:e14769 doi: 10.1371/journal.pone.0014769 URL pmid: 21445243
[21]	Beaudet A, Dumoncel J, Thackeray F, et al. Upper third molar internal structural organization and semicircular canal morphology in Plio-Pleistocene South African cercopithecoids[J]. Journal of Human Evolution, 2016,95:104-120 doi: 10.1016/j.jhevol.2016.04.004 URL pmid: 27260177
[22]	Olejniczak A, Smith TM, Feeney RNM, et al. Dental tissue proportions and enamel thickness in Neandertal and modern human molars[J]. Journal of Human Evolution, 2008,55:12-23 URL pmid: 18321561
[23]	Zanolli C. Brief communication: molar crown inner structural organization in Javanese Homo erectus[J]. American Journal of Physical Anthropology, 2015,156:148-157 doi: 10.1002/ajpa.22611 URL pmid: 25209431
[24]	Kuman K, Clarke R. Stratigraphy, artefacts, industries and hominid associations for Sterkfontein, Member 5[J]. Journal of Human Evolution, 2000,38:827-847 URL pmid: 10835264
[25]	Balter V, Blichert-Toftv J, Braga J, et al. U-Pb dating of fossil enamel from the Swartkrans Pleistocene hominid site, South Africa[J]. Earth and Planetary Science Letters, 2008,267:236-246
[26]	Rink WJ, Schwarcz HP, Smith FH, et al. ESR dates for Krapina hominids[J]. Nature, 1995,378:24 doi: 10.1038/378024a0 URL pmid: 7477281
[27]	Girard M. La brèche à “Machairodus” de Montmaurin(Pyrénées centrales)[J]. Bulletin de l’Association Française pour l’étude du Quaternaire, 1973,3:193-207
[28]	Macchiarelli R, Bondioli L, Debénath A, et al. How Neanderthal molar teeth grew[J]. Nature, 2006,444:748-751 doi: 10.1038/nature05314 URL pmid: 17122777
[29]	Pan L, Dumoncel J, de Beer F, et al. Further morphological evidence on South African earliest Homo lower postcanine dentition: enamel thickness and enamel dentine junction[J]. Journal of Human Evolution, 2016,96:82-96 URL pmid: 27343773
[30]	Molnar S. Human tooth wear, tooth function and cultural variability[J]. American Journal of Physical Anthropology, 1971,34:175-189 doi: 10.1002/ajpa.1330340204 URL pmid: 5572602
[31]	Kono R. Molar enamel thickness and distribution patterns in extant great apes and humans, new insights based on a 3-dimensional whole crown perspective[J]. Anthropological Science, 2004,112:121-146
[32]	Buti L, Le Cabec A, Panetta D, et al. 3D enamel thickness in Neandertal and modern human permanent canines[J]. Journal of Human Evolution, 2017,113:162-172 doi: 10.1016/j.jhevol.2017.08.009 URL pmid: 29054166
[33]	Benazzi S, Slon V, Talamo S, et al. The makers of the Protoaurignacian and implications for Neandertal extinction[J]. Science, 2015,348:793-796 doi: 10.1126/science.aaa2773 URL pmid: 25908660
[34]	Kono R, Suwa G, Tanijiri T. A three-dimensional analysis of enamel distribution patterns in human permanent first molars[J]. Archives of Oral Biology, 2002,47:867-875 doi: 10.1016/s0003-9969(02)00151-6 URL pmid: 12450518
[35]	Kono RT, Zhang Y, Jin C, et al. A 3-dimensional assessment of molar enamel thickness and distribution pattern in Gigantopithecus blacki[J]. Quaternary International, 2014,354:46-51
[36]	Zanolli C, Pan L, Dumoncel J, et al. Inner tooth morphology of Homo erectus from Zhoukoudian. New evidence from an old collection housed at Uppsala University, Sweden[J]. Journal of Human Evolution, 2018,116:1-13 doi: 10.1016/j.jhevol.2017.11.002 URL pmid: 29477178

Taxa	P₃(n)	P₄(n)	M₁(n)	M₂(n)	M₃(n)	Provenance	Enamel thickness data
P. robustus	2	2	2	6	7	Swartkrans Members 1, 2; Kromdraai B	Pan et al^[29]
Au. africanus		1		1	1	Sterkfontein Member 4	Pan et al^[29]
Early Homo	1	1	1		1	Swartkrans Members 1, 2	Pan et al^[29]
Neanderthals	5	4	5	3	5	Montmaurin; La Chaise Abri Suard; Krapina Level 8	Pan et al^[29] ; original data
Modern humans	7	7	9	6	5	Central Europe; East Asia	Pan et al^[29]; original data

Taxa	P₃(n)	P₄(n)	M₁(n)	M₂(n)	M₃(n)	Provenance	Enamel thickness data
P. robustus	2	2	2	6	7	Swartkrans Members 1, 2; Kromdraai B	Pan et al^[29]
Au. africanus		1		1	1	Sterkfontein Member 4	Pan et al^[29]
Early Homo	1	1	1		1	Swartkrans Members 1, 2	Pan et al^[29]
Neanderthals	5	4	5	3	5	Montmaurin; La Chaise Abri Suard; Krapina Level 8	Pan et al^[29] ; original data
Modern humans	7	7	9	6	5	Central Europe; East Asia	Pan et al^[29]; original data

		AET-b(mm)		AET-c(mm)		RET-b		RET-c
		Mean	Range	Mean	Range	Mean	Range	Mean	Range
Au. africanus	Premolars	1.35	-	1.53	-	22.38	-	24.67	-
	Molars	1.82	1.81-1.83	1.94	1.88-1.99	26.91	25.74-28.08	29.50	28.00-31.00
P. robustus	Premolars	1.83	1.70-2.06	1.95	1.83-2.17	29.87	23.38-35.46	32.84	27.09-41.17
	Molars	2.06	1.66-2.70	2.18	1.64-2.78	24.83	19.32-38.00	27.51	19.44-48.56
Early Homo	Premolars	1.64	1.48-1.79	1.65	1.46-1.85	31.00	29.03-32.97	32.46	28.45-36.48
	Molars	1.57	1.38-1.77	1.58	1.37-1.79	23.78	20.05-27.52	26.31	20.23-32.39
Neanderthals	Premolars	0.73	0.59-1.10	0.80	0.60-1.11	12.80	9.96-19.03	13.92	10.27-19.07
	Molars	1.31	1.10-1.54	1.30	1.04-1.61	19.08	16.05-23.73	18.84	15.06-24.77
H. sapiens	Premolars	1.13	0.81-1.61	1.14	0.85-1.65	25.31	18.19-31.72	24.73	19.84-32.75
	Molars	1.36	1.06-1.69	1.37	1.12-1.60	22.53	17.56-28.39	23.06	19.04-27.26

		AET-b(mm)		AET-c(mm)		RET-b		RET-c
		Mean	Range	Mean	Range	Mean	Range	Mean	Range
Au. africanus	Premolars	1.35	-	1.53	-	22.38	-	24.67	-
	Molars	1.82	1.81-1.83	1.94	1.88-1.99	26.91	25.74-28.08	29.50	28.00-31.00
P. robustus	Premolars	1.83	1.70-2.06	1.95	1.83-2.17	29.87	23.38-35.46	32.84	27.09-41.17
	Molars	2.06	1.66-2.70	2.18	1.64-2.78	24.83	19.32-38.00	27.51	19.44-48.56
Early Homo	Premolars	1.64	1.48-1.79	1.65	1.46-1.85	31.00	29.03-32.97	32.46	28.45-36.48
	Molars	1.57	1.38-1.77	1.58	1.37-1.79	23.78	20.05-27.52	26.31	20.23-32.39
Neanderthals	Premolars	0.73	0.59-1.10	0.80	0.60-1.11	12.80	9.96-19.03	13.92	10.27-19.07
	Molars	1.31	1.10-1.54	1.30	1.04-1.61	19.08	16.05-23.73	18.84	15.06-24.77
H. sapiens	Premolars	1.13	0.81-1.61	1.14	0.85-1.65	25.31	18.19-31.72	24.73	19.84-32.75
	Molars	1.36	1.06-1.69	1.37	1.12-1.60	22.53	17.56-28.39	23.06	19.04-27.26

Tooth position	Group 1	Group 2	AET-b	AET-c	RET-b	RET-c
Premolars	Neanderthals	P. robustus	<	<
	Neanderthals	Early Homo	<
	Neanderthals	H. sapiens			<	<
	Neanderthals	P. robustus			<	<
	Neanderthals	Au. africanus			<	<
Molars	Au. africanus	Neanderthals			>	>
	P. robustus	H. sapiens	>	>
	P. robustus	Neanderthals	>	>	>	>
	Early Homo	Neanderthals
	H. sapiens	Neanderthals			>	>