人类牙齿齿冠和齿根分离两种技术方法对牙釉质厚度测量的影响

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

人类学学报 ›› 2019, Vol. 38 ›› Issue (03): 398-406.doi: 10.16359/j.cnki.cn11-1963/q.2018.0028

人类牙齿齿冠和齿根分离两种技术方法对牙釉质厚度测量的影响

潘雷¹^,²^,³()

1. 中国科学院古脊椎动物与古人类研究所,中国科学院脊椎动物演化与人类起源重点实验室,北京 100044
2. 中国科学院生物演化与环境卓越创新中心,北京 100044
3. 中国科学院南京地质古生物研究所,现代古生物学和地层学国家重点实验室,南京 210008

收稿日期:2017-05-05 修回日期:2018-03-27 出版日期:2019-08-15 发布日期:2020-09-10
作者简介:潘雷,中国科学院古脊椎动物与古人类研究所助理研究员,主要从事体质人类学、早期人类起源与演化研究。Email: panlei@ivpp.ac.cn
基金资助:
中国科学院战略性先导科技专项B类(XDB26000000);国家自然科学基金(41672020);国家自然科学基金青年基金项目(41702026);现代古生物学和地层学国家重点实验室开放基金项目(中国科学院南京地质古生物研究所)(173119)

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

PAN Lei¹^,²^,³()

1. Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, CAS, Beijing 100044, China
2. CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044,China
3. Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing 210008, China

Received:2017-05-05 Revised:2018-03-27 Online:2019-08-15 Published:2020-09-10

摘要/Abstract

摘要：

在基于计算机断层扫描技术（CT）和虚拟图像处理技术的灵长类牙齿测量学研究中,经常需要分离三维虚拟模型的齿冠和齿根,再进行后续测量工作,如计算机辅助的生物力学分析、釉质厚度测量等。而分离齿冠和齿根这一步骤,目前有多种方法,如,1)根据齿颈线切分齿冠,或2)人工建立基底平面切分齿冠。为了评估这两种不同的处理方式对后续的牙齿测量学上的影响,本文使用三维方法测量了82例化石和现代人类下颌后部牙齿的釉质厚度,包括南方古猿、早期人属、尼安德特人和现代人。使用配对t检验对比发现,两种方法得到的釉质厚度数值上没有显著差别,但随后进行的种间比较发现,使用基底平面切分齿冠的方法比较费时,更依赖于测量者的人工操作,并且可能弱化了物种间前臼齿绝对釉质厚度的差异,造成系统误差。其原因是对于前臼齿和前部牙齿等齿颈线形状不规则的标本,基底平面难以建立或误差较大。在未来对釉质厚度的种间差异的研究中,特别对齿颈线形状不规则的标本（如人类前部牙齿及猩猩、黑猩猩的牙齿等）,本文推荐使用齿颈线分离齿冠和齿根,测量和计算齿颈线之上的釉质厚度。釉质厚度有一定的分类学、功能形态学和系统发育学意义。本文积累了一批可供未来对比研究的原始数据,并且发现尼安德特人前臼齿的相对釉质厚度显著小于现代人,这与前人利用臼齿、犬齿所做的对比研究结果相同,支持了尼安德特人拥有较薄的相对釉质厚度这一观点。

关键词: 分类学差异, 釉质厚度, 牙齿人类学, 三维虚拟测量, 齿冠, 齿根

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

中图分类号:

Q983

潘雷. 人类牙齿齿冠和齿根分离两种技术方法对牙釉质厚度测量的影响[J]. 人类学学报, 2019, 38(03): 398-406.

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

图/表 6

图1 两种测量方法示意图（修改自Benazzi等[18]） A. 3D-b方法根据齿颈线（橙色）分离齿冠,随后软件自动根据齿颈线的形状差值生成成一光滑曲面覆盖齿冠底部,计算其上的釉质体积、齿质体积等。B. 3D-c方法建立一个与平面A和平面B（橙色）距离相等的平面（红色）,以它作为基底平面切分齿冠和齿根。平面A和B的建立方法见"引言"

Fig.1 A sketch of two protocols(modified from Benazzi et al[18]) A. Method 3D-b digitally isolates the crown using the cervical line(orange), the bottom of the crown was sealed by a smooth surface interpolating the cervical line. B. Method 3D-c sections the teeth using a basal plane(red), which is halfway between Plane A and Plane B(orange). See Introduction for the explanation of Planes A and B

表1 本文使用的牙齿标本

Tab.1 Composition of the study sample

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

表2 两种方法所得牙齿釉质厚度的平均值和区间

Tab.2 Average and range of enamel thickness values using 3D-b and 3D-c methods

		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

表3 Kruskal-Wallis非参数检验后的成对比较结果,仅显示釉质厚度存在显著性差异的类群

Tab.3 Conover’s post hoc pairwise comparisons after the Kruskal-Wallis test are reported below(significant results only)

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			>	>

图2 分别使用3D-b和3D-c测得各类群的平均厚度(mm)和相对釉质厚度 A, B.平均釉质厚度;C, D.相对釉质厚度。标准箱线图显示了50% 的样本数据、样本数据的中位数和上、下四分位数。对于极个别超出了理论上、下限的数据（极端异常数据）,则以圆圈或星标表示。缩写：ROB：粗壮傍人;AFR：南方古猿非洲种;EH：现代人;NEA：尼安德特人

Fig.2 Average and relative enamel thickness(AET and RET) values in each taxon, provided by 3D-b and 3D-c methods A, B. AET; C, D. RET. Standard box and whisker plot revealing the interquartile range(25th-75th percentiles: boxes), 1.5 interquartile ranges(whiskers) and the median values(black line). Outliers more than 1.5 interquartile ranges from the box are signi?ed with circles, extremes more than 3 interquartile ranges from the box are signified with asterisks. AFR: Au. africanus; ROB: P. robustus; NEA: Neanderthals; EH: Extant human

表4 两种测量方法所得牙齿釉质厚度的配对t检验结果(Alpha=0.05)

Tab.4 Paired t-test for differences in the enamel thickness values between 3D-b and 3D-c methods

Dental classes	Premolar AET	Premolar RET	Molar AET	Molar RET
Sig.(p)	0.06	0.27	0.15	0.1

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人类牙齿齿冠和齿根分离两种技术方法对牙釉质厚度测量的影响

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

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