Advances in Anthropology
2013. Vol.3, No.2, 71-77
Published Online May 2013 in SciRes (http://www.scirp.org/journal/aa) http://dx.doi.org/10.4236/aa.2013.32010
Study of P, Ca, Sr, Ba and Pb Levels in Enamel and Dentine
of Human Third Molars for Environmental and
Archaeological Research
Hwa-Yen Liu1*, Jiunn-Hsing Chao2, Chun-Yu Chuang1, Hung-Lin Chiu3,
Chung-Wei Yang1, Yuh-Chang Sun1
1Department of Biomedical Engineering and Environmental Sciences, National TsingHua University,
Hsinchu, Taiwan
2Nuclear Science and Technology Development Center, National TsingHua University,
Hsinchu, Taiwan
3Institute of Anthropology, College of Humanities and Social Science, National TsingHua University,
Hsinchu, Taiwan
Received January 7th, 2013; revised February 7th, 2013; accepted February 17th, 2013
Copyright © 2013 Hwa-Yen Liu et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited.
Elemental determination of 80 third molars, collected from local dental clinics in Hsinchu City, Taiwan
during 2009 to 2010, was conducted using inductively coupled plasma—mass spectrometry (ICP-MS).
Results show that the mean concentrations of P, Ca, Sr, Ba and Pb in enamel are respectively 14.63% ±
2.19%, 27.91% ± 4.03%, 108.31 ± 35.71 ppm, 1.96 ± 1.01 ppm, and 0.72 ± 0.49 ppm. The concentrations
of P, Ca and Sr are higher in enamel than in dentine, on the other hand, the concentrations of Ba and Pb
are higher in dentine than in enamel. In enamel and dentine the concentrations of P, Ca and Ca/P ratio are
kept constant. In enamelthe concentrations of Sr and Sr/Ca increase by age statistically but the concentra-
tions of Ba and Ba/Ca are not. Pb concentrations in both enamel and dentine increase by age and also in-
crease with significant differences among each birth era. This may indicate the dates of environmental
exposure. The levels of Pb in this study are lower than the previous published findings before 1979. The
concentrations and distribution of elements in enamel and dentine of third molars other than deciduous or
permanent teeth can provide reliable base references to past and future studies.
Keywords: Elemental Concentration; Third Molars; Enamel; Dentine; ICP-MS
Introduction
The Properties of Teeth
Humans usually have 20 primary (deciduous or “baby”) teeth
and 32 permanent (adult) teeth. Teeth are classified as incisors,
canines, premolars and molars. The development timeline is
very different among each type of tooth. Each tooth has its own
development stage time line. For example, for third molars, the
age of initial calcification, crown completion and root comple-
tion is from 7 to 10 years old, 12 to 16 years old and 18 to 25
years old respectively (Ash, 2002). Tooth eruption in humans is
a process in tooth development in which teeth enter the mouth
and become visible. Each tooth type has its own time of erup-
tion. For example, third molars erupt between 17 to 21 years
old (Ash, 2002). Therefore, a third molar’s root may be not com-
pleted but its crown may have completed development when it
erupts in the mouth.
Enamel, dentine, cementum and dental pulp are the four ma-
jor tissues which make up a tooth. The crown of a tooth is com-
posed of these major tissues and covered in enamel above the
neck of the tooth. The crown is visible after eruption. The root
of tooth is composed of dentine, cementum and dental pulp, but
without enamel. Although both enamel and dentine are essen-
tial components of teeth, they are derived from different sour-
ces, enamel from ectoderm and dentine from mesectoderm. In
addition, the maturation processes of these two components,
from initial calcification to completely maturity, occur at differ-
rent points in time. The enamel and dentine in third molars de-
monstrate the same phenomenon. Mineralization of enamel in
third molars is completed by the age of 12. After the time of
mineralization, the enamel remains closed and will no longer
perform a significant physiological exchange of elements. How-
ever, dentine is vital organ, and the odontoblast in pulp will ex-
tend its cell process into dentinal tubular to conduct dentine
inside and outside element exchange from blood circulation.
Teeth are a composite of inorganic, organic and water frac-
tions in various amounts. Their inorganic phase consists of the
unit cell (Ca,X)10(P,C)6(O,OH)26. The microcations favor coor-
dination with oxygen and do not usually form complex ion spe-
cies. The common characteristics of these cations are a small
ionic radius and high charge/radius ratio. These cations can re-
place each other. The X in this chemical formula represents a
*Corresponding author.

H.-Y. LIU ET AL.
variety of possible substitutions for Ca, such as Sr, Ba and Pb
(McConnell, 1973). Gruner et al. suggested for enamel and
dentine the exact chemical formulas are enamel,
(OH)2Ca6[(P5.8C0.2)O24](Ca3.1Mg0.1C0.5), and dentine,
(OH)2Ca6[(P5.6C0.5)O24](Ca2.7Mg0.5C0.6). According to these for-
mulas, the Ca/P ratio is about 2.02 (Gruner, 1937).
Teeth Using for Study of Environmental and
Archaeological Purposes
In the 1930s, Dreal, Lowater and Murray reported that teeth
contain a variety of minor or trace elements (Dreal, 1936; Lo-
water, 1937). As more sensitive analytical instruments and
methods were developed, more information about trace ele-
ments and their functions in the different parts of teeth were
investigated. Teeth are believed to preserve great information
through a life span varying with environmental exposures. Ele-
mental analysis of deciduous and/or permanent teeth has been
frequently used for environmental and archaeological purposes
(Lowater, 1937; Reitznerová, 2000; Falla-Sotelo, 2005; Malara,
2006; Chao, 2009).
Most of the early dental elements data were obtained by
mixing various kinds of teeth or pooling samples. Nowadays
we know there are many differences in elemental composition
for various tooth types. Brown et al. suggested that in order to
use the elemental composition of human primary teeth as envi-
ronmental indicators, it is necessary to restrict to a single tooth
type (Brown, 2002). Thus, third molars are the unique type of
teeth selected to be analyzed in this study.
Reasons for Selecting Third Molars
The size of a third molar is larger than most of deciduous
teeth or permanent teeth. Also, its eruption timing is the latest
of all teeth and it is located in the last row of the alveolar ridge.
The degree of dental wear and dentine/enamel exposure of a third
molar is often less than other teeth in human adults. On the
other hand, the amount of material available for study is always
a factor affecting the results of trace elements analysis. Third
molars are extracted for two general reasons: either the tooth
has already become impacted, or the tooth could potentially
become problematic if not extracted. Preventive removal of the
third molars is a common practice in developed countries and is
usually recommended by dentists (Pinkham, 2005). Also, de-
ciduous teeth, specifically third molars, are more available than
permanent teeth for research purposes. Availability and quan-
tity are two of the most important reasons for selecting third
molars as the material for this study.
Most third molars are removed between the ages of 20 to 30
in recent clinical cases. Once a third molar is studied, it would
offer information of a definite time. For example, the trace ele-
ments in enamel of a third molar may reflect the subject’s diet
during the time they were 7 to 16 years old. This implication for
third molars is important in the study of environmental changes
and human mobility.
The incisal area of human third molars is always kept com-
plete because it is rarely used for grinding foods. Enamel in
third molar is rarely exposed to the oral environment. Addition-
ally, some third molars are embedded in bone. The un-erupted
third molars have less contamination from soil or water sources.
These are specific characteristics of third teeth which are dif-
ferent from other deciduous and permanent teeth for archaeo-
logical or paleologic studies.
As described above, third molars are a unique type of tooth
suggested as representative material for research. They may
provide definite information for supporting evidence for a his-
tory of events. Thus this study is devoted to elemental analysis
of enamel and dentine of unique third molars. We would like to
show the definite characteristics of a single type of tooth using
third molars to provide reliable base references for future stud-
ies.
Materials and Methods
Sample Collection
Samples of third molars were collected from a local dental
clinic in Hsinchu City, Taiwan, from 2009 to 2010.The donors
of the samples were 46 males and 34 females, with ages rang-
ing from 17 to 68 years old. The molars are grouped by ages in
10 years increments between 21 years to 40 years. Other groups
are included in samples ages 20 years or less and 41 years and
older. The molars in the age group of 21 to 30 years are further
divided in half to get a more balanced distribution. Distribution
of ages in all 5 age groups is shown in Tables 1 and 2.
Table 1.
Concentration of elements in enamel of various age groups.
Era of Birth Before 1969 1970-1979 1980-1984 1985-1989 After 1990
Age ≥41 (n = 11) 31 - 40 (n = 12) 26 - 30 (n = 21) 21 - 25 (n = 21) ≤20 (n = 15)
P (%) 14.70 ± 1.62 15.20 ± 1.85 14.44 ± 2.51 14.21 ± 2.47 15.00 ± 2.03
Ca (%) 28.47 ± 3.69 27.95 ± 3.74 27.81 ± 5.23 27.83 ± 3.70 27.74 ± 3.47
Sr (ppm) 32.22 ± 32.94 131.52 ± 45.44 94.33 ± 24.53 98.85 ± 30.19 105.00 ± 35.25
Ba (ppm) 1.87 ± 0.80 2.33 ± 1.40 1.99 ± 0.87 1.69 ± 0.52 2.07 ± 1.43
Pb (ppm) 1.17 ± 0.62 1.03 ± 0.66 0.77 ± 0.29 0.53 ± 0.31 0.35 ± 0.14
Ca/P 1.94 1.83 1.93 1.96 1.85
Sr/Ca (10−5) 46.97 46.97 34.04 35.46 38.0
Ba/Ca (10−5) 0.65 0.83 0.72 0.61 0.74
Pb/Ca (10−5) 0.42 0.38 0.29 0.20 0.13
72

H.-Y. LIU ET AL.
Table 2.
Concentration of elements in dentine of various age groups.
Era of Birth Before 1969 1970-1979 1980-1984 1985-1989 After 1990
Age ≥41 (n = 11) 31 - 40 (n = 2) 26 - 30 (n = 21) 21 - 25 (n = 21) ≤20 (n = 5)
P (%) 11.37 ± 1.32 12.05 ± 2.14 11.00 ± 1.49 11.00 ± 1.82 11.78 ± 2.27
Ca (%) 21.68 ± 2.93 21.48 ± 4.12 21.08 ± 3.79 21.05 ± 4.28 21.64 ± 3.15
Sr (ppm) 104.52 ± 34.75 98.29 ± 28.27 81.18 ± 17.97 82.70 ± 23.67 92.72 ± 31.12
Ba (ppm) 2.24 ± 1.06 3.42 ± 1.87 3.28 ± 1.82 2.28 ± 0.80 2.51 ± 1.17
Pb (ppm) 1.60 ± 0.84 1.25 ± 0.58 1.07 ± 0.46 0.7 ± 0.37 0.49 ± 0.28
Ca/P 1.91 1.78 1.92 1.91 1.84
Sr/Ca (10−5) 48.52 48.41 39.24 40.25 43,13
Ba/Ca (10−5) 1.05 1.87 1.57 1.11 1.17
Pb/Ca (10−5) 0.75 0.62 0.53 0.39 0.23
Sample Preparation
Each third molar was put in a clean tube after extraction and
then delivered to the laboratory. The bloodstains were rinsed
off with distilled water. The attached soft tissues were elimi-
nated with toothbrushes.
The third molar crown contains two parts: incisal and cervi-
cal areas. The incisal area is entirely enamel, and the cervical
area contains different quantities of coronal dentine. Using a
diamond-impregnated stainless-steel blade the enamel is cut
into a horizontal slice of 2-mm thickness from the crown near
the incisal and cervical areas of a third molar. If the thin slice
contains dentine, it must be fully removed. For example, circum
pulpal dentine found in the surroundings of pulp cavity of the
tooth must be removed.
Elemental Analyses
The enamel and dentine are separated with diamond blade
cuts. After weighing the samples, the enamel and dentine are
put into separate 15 ml test tubes (Labcon, green). Then, 5 ml
of ultrapure concentrated nitric acid is added to the tubes and
settled for a week until complete dissolution. Finally, deionized
water is added to dilute the sample to 15 ml.
The ICP mass spectrometer used in the study is an Agilent
7500ce system (Agilent, CA, USA). A Micromist nebulizer
(AR35-1-EM04EX, Glass Expansion, Victoria, Australia) is
fitted to a Scott-type quartz double-pass spray chamber. Based
on the experimental results, the method detection limit obtained
for P, Ca, Sr, Ba and Pb are 0.584 ppm, 2.933 ppm, 0.005 ppm,
0.003 ppm and 0.016 ppm, respectively.
Statistical Analysis
The data was analyzed using SPSS for Windows version
13.0. Non-parametric Spearman correlation is used to analyze
the correlation of age with the concentrations of P, Ca, Sr, Ba
and Pb in enamel and dentine of the third molars. A two-tailed
p-value < 0.05 is considered significant.
Results
In Table 3, the mean concentrations of P, Ca, Sr, Ba and Pb
respectively in enamel are 14.63% ± 2.19%, 27.91% ± 4.03%,
108.31 ± 35.71 ppm, 1.96 ± 1.01 ppm and 0.72 ± 0.49 ppm, and
in dentine are 11.35% ± 1.01%, 21.32% ± 3.68%, 89.52 ±
27.11 ppm, 2.75 ± 1.46 ppm and 0.96 ± 0.61 ppm. The levels of
P, Ca and Sr are higher in enamel than in dentine, and Ba and
Pb concentrations are higher in dentine than in enamel.
Additionally, correlation coefficients between age and con-
centration individually in enamel and dentine of third molars
are shown in Table 3. There are remarked positive correlations
between age and dentine Pb, enamel Pb or enamel Sr. There is
no correlation between age and concentration in enamel or
dentine for P, Ca and Ba. The P and Ca concentrations are kept
constant by age.
In this study, Sr, Ba and Pb concentrations in various age
groups are shown in Tables 1 and 2. Concentrations of Pb pre-
sent in enamel and dentine increased in all age groups. In re-
gards to Post Hoc tests, there are significant differences for Pb
in enamel between the ages of ≤20 and 31 - 40 (p = 0.002), ≤20
and ≥41 (p > 0.001), 21 - 25 and 31 - 40 (p = 0.029), 21 - 25
and ≥41 (p = 0.003). And there are significant differences for
Pb in dentine between the ages of ≤20 and 26 - 30 (p = 0.024),
≤20 and 31 - 40 (p = 0.006), ≤20 and ≥41 (p < 0.001), 21 - 25
and ≥41 (p < 0.001).
Sr concentrations increased from the 26 - 30 age group to the
≥41 age group, but higher concentrations in enamel and dentine
were noted in the ≤20 age group. Concentrations of Ba in
enamel and dentine increased from the 21 - 25 age group to the
31 - 40 age group. Then the drop of Ba concentration is noted
in the ≥41 age group. However, there are no significant dif-
ferences among them.
There are significant differences for Sr/Ca in enamel between
the ages 26 - 30 and 31 - 40 (p = 0.037), 26 - 30 and ≥41 (p =
0.046).
Discussion
Ca and P Concentrations and Ca/P Ratio in Third
Molars
Ca and P are the two main elements in teeth. In this study,
the average P and Ca concentration and Ca/P ratio in the den-
tine and enamel of third molars, shown as Table 3, are very
closely related to the previous study by Arora et al., which

H.-Y. LIU ET AL.
Table 3.
Mean concentration, correlation coefficients with age, and enamel/den-
tine ratio of the elements in third molars.
Element/
concentration
(n = 80)
Enamel conc.
(range)
correl. coeff.
(p value)
Dentine conc.
(range)
correl. coeff.
(p value)
Enamel/
Dentine ratio
P (%)
14.63 ± 2.19
7.59 - 18.94
r = 0.011
(p = 0.922)
11.35 ± 1.83
6.23 - 16.53
r = 0.015
(p = 0.895)
1.29
Ca (%)
27.91 ± 4.03
13.72 - 36.25
r = 0.067
(p = 0.554)
21.32 ± 3.68
23.06 - 31.88
r = −0.031
(p = 0.785)
1.31
Sr (ppm)
108.30 ± 35.71
51.26 - 199.74
r = 0.301*
(p = 0.007)
89.52 ± 27.11
47.73 - 179.0
r = 0.199
(p = 0.077)
1.20
Ba (ppm)
1.96 ± 1.01
0.68 - 6.70
r = 0.116
(p = 0.307)
2.75 ± 1.46
0.33 - 8.12
r = 0.082
(p = 0.471)
0.69
Pb (ppm)
0.72 ± 0.49
0.12 - 2.55
r = 0.719*
(p < 0.001)
0.96 ± 0.61
0.1 - 2.77
r = 0.654*
(p < 0.001)
0.70
Sr/Ca (10−5)
38.87 ± 11.86
r = 0.300*
(p = 0.007)
42.88 ± 14.40
r = 0.139
(p < 0.220)
Ba/Ca (10−5)
0.70 ± 0.32
r = 0.135
(p = 0.231)
13.47 ± 9.47
r = 0.082
(p = 0.468)
Pb/Ca (10−5)
0.27 ± 0.19
r = 0.678*
(p < 0.001)
0.47 ± 0.31
r = 0.625*
(p < 0.001)
conc.: element concentration. correl. coeff.: Spearman correlation coefficient bet-
ween element concentration and donator’s age. Enamel/dentine ratio: the ratio of
element concentration in enamel to that in dentine.
reported Ca and P concentrations in cervical region of 24.35%
and 12.41% respectively, with a Ca/P ratio of 1.96 (Arora,
2004).
The enamel itself is an entirely calcified tissue, and is re-
garded as a non-vital organ. Conversely, dentine is viewed as
vital organ because many dentinal tubules exist within it. Ca
and P in enamel might participate in body calcium turnover
activity for only the first few years of life, and would be iso-
lated from it after tooth eruption. So it is reasonable for con-
stant Ca or P concentrations in enamel of third molars in vari-
ous age groups (Manea-Krichten, 1991). In Table 2, the con-
centrations of Ca and P in dentine are also constant (with no
significant differences) in various age groups. That might mean
only minor parts of Ca or P in dentine participating in turnover
activity (e.g. dentine eburnation), which does not seem to affect
their whole concentration.
Murray reported the Ca/P ratio for human teeth varied from
1.92 (lowest in dentine) to 2.15 (highest in enamel) (Murray,
1936). He suggested the deposition process of calcification is
an active and specific cell process, and not merely a precipita-
tion from saturated or supersaturated solutions of a salt of con-
stant composition dependent on the ionic composition of the
blood plasma. Hillson discovered biogenic Ca/P ratio ranges
from 1.91 to 2.17 for enamel, and 2.1 to 2.2 for dentine. Dif-
ferent Ca/P ratios mean different nature in enamel and dentine
(Hillson, 1996). Arnold and Gaengler reported differences be-
tween the Ca/P ratio in predentin and dentin indicating that
different calcium phosphate minerals occur during dentino-
genesis. They also showed the Ca and P content in enamel of
permanent teeth was even higher than in the enamel of devel-
oping teeth (Arnold, 2007).
Sr, Ba and Pb Concentrations in Third Molars
Sr
Sr is one of constituent elements of teeth. Steadman et al.
(1959) reported Sr concentrations ranging from 80 to 620 ppm
in human teeth from different geographic areas (Steadman,
1959). The Sr content of teeth seems to parallel the level of
intake by the individual. There are various studies of Sr deter-
mination which are summarized in Tables 4 and 5 (Brown,
2002; Brown, 2004; Soares, 2008). The Sr concentrations de-
termined in this study are close to the Brown’s data from den-
tine of deciduous teeth.
In this study, no significant differences were found in the
higher concentration present in the ≤20 age group for enamel
and dentine. One possible explanation for this phenomenon is
that Sr is one of the component elements of teeth and the Sr2+
ion would strongly and rapidly substitute for Ca2+ in the ordered
apatite lattice during the third molars’ growing period.
Ba
Manea-Krichten et al.determined the Ba concentrations in
enamel to be 6.4 ppm in dry weight (Manea-Krichten, 1991).
Ba may diffuse from a blood-dentine source into enamel, where
it replaces Ca and accumulates with age. The distribution does
characterize a natural situation for biological occurrences of Ba
in humans. There is little research on Ba concentrations in third
molars, but more research exists for deciduous and a mixture of
permanent teeth. Brown et al. showed Ba concentrations of
deciduous and permanent teeth are 6.41 and 4.4 ppm respec-
tively (Brown, 2002; Brown, 2004). Brown’s results are higher
than this study as shown in Tables 4 and 5. In this study, both
Ba and Pb are several ppm in concentration, and Ba concentra-
tions are higher than Pb in enamel and dentine. Pb concentra-
tion would be much higher than that of Ba if Pb exposure exists
(Manea-Krichten, 1991). This indicates the subjects in this
study have no exposure to Pb.
Pb
Pb is a naturally occurring element that is also a ubiquitous
environmental pollutant due to its widespread uses. It is well-
known that leaded gasoline was a major source of lead expo-
sure in the population. Brudevold and Steadman reported an
increased Pb level with age. They found the concentration of Pb
in enamel is about 30 ppm in teeth from young adults and about
90 ppm in teeth over 50 years of age (Brudevold, 1956). Derise
and Ritchey found the concentration of Pb in enamel and den-
tine are from 38.9 to 51.5 ppm (Derise, 1974). Thomas et al.
showed that reducing lead from gasoline significantly de-
creased population blood lead from 1978 to 1996 on six conti-
nents (Thomas, 1999). Thus, there are no more high levels of
Pb in teeth reported in literature within the last ten years (Ma-
lara, 2006; Brown, 2002; Brown, 2004; Arora, 2004; Zaichick,
1997). There are few studies about the Pb concentration in third
74

H.-Y. LIU ET AL.
Table 4.
Concentration of elements in dentine of human teeth reported in previous studies.
Authors Method Teeth types No P (%) Ca (%) Sr (ppm) Ba (ppm) Pb (ppm)
this work ICP-MS third molar n = 90 11.37 ± 1.91 21.26 ± 3.74 89.27 ± 28.42 2.78 ± 1.58 1.09 ± 0.91
Soares INAA
permanent
deciuous
10
8 21.40 ± 1.79 25.0 ± 2.2
174.2 ± 118.7
92.1 ± 25.4
Shi EMPA deciduous I 37 34.33 ± 1.33
Liang EMPA deciduous 38 17.42 ± 0.59
Arnold EDX third molar 3 17.2 ± 2.2 37.7 ± 5.9
Zenóbio ICP/AES third molar 30 10.98 ± 0.5 23.10 ± 0.5
Soremark INAA 13.5 ± 2.8 28.2 ± 1.2
Arora ICP-MS
deciduous
molar
canine
incisor
5
4
7
Cervical
12.41 ± 0.53
12.56 ± 0.33
11.86 ± 0.22
Cervical
24.35 ± 1.29
23.84 ± 1.14
22.56 ± 0.43
Cervical
1.11 ± 0.30
0.87 ± 0.41
1.23 ± 0.39
Arora ICP-MS
deciduous
molar
canine
Incisor
5
4
7
Apical
11.97 ± 0.54
12.52 ± 0.32
11.28 ± 0.20
Apical
24.21 ± 1.38
24.22 ± 0.68
22.45 ± 0.31
Apical
2.95 ± 2.06
2.17 ± 0.70
3.32 ± 1.56
Malara AAS
permanent
incisor
canine
pre-molar
molar
33
38
43
41
root
55.27 ± 8.52
58.11 ± 10.84
56.90 ± 8.12
57.03 ± 9.73
root
14.08 ± 2.74
9.97 ± 3.57
10.39 ± 2.85
10.11 ± 2.14
Brown ICP-MS
deciduous
whole teeth
UK 27
UG 21 31.4 ± 19.6 31.5 ± 13.7
118 ± 37.8
175 ± 38.0
6.41 ± 2.92
9.87 ± 4.43
1.33 ± 0.89
1.21 ± 0.44
AAS: atomic absorption spectrometer. EDX: energy-dispersive X-ray analysis. EDXRF: energy dispersive X-ray fluorescent analysis. EMPA: electron microprobe X-ray
mMicroanalyzer. ICP/AES: ductively coupled plasma spectrometer. ICP-MS: inductively coupled plasma mass spectrometer. INAA: instrument neutron activation analy-
sis.
Table 5.
Concentration of elements in enamel of human teeth from various studies.
Authors Method Teeth No P (%) Ca (%) Sr (ppm) Ba (ppm) Pb (ppm)
this work ICP-mass third molar n = 90 14.63 ± 2.21 27.87 ± 4.08 107.57 ± 37.31 1.91 ± 1.01 0.76 ± 0.54
Soares INAA
permanent
deciduous
10
8 31.20 ± 4.76 29.0 ± 5.2
285.8 ± 181.7
84.8 ± 16.7
Shi EMPA deciduous 38.74 ± 1.31
Liang EMPA deciduous 38 18.29 ± 0.44
Arnold EDX third molar 3 19.9 ± 1.8 42.7 ± 5.1
Zenóbio ICP-AES third molar 30 17.5 ± 0.5 36 ± 0.5
Lakomaa INAA 18.6 ± 0 34 ± 2.0
Zaichick EDXRF permanent 35 36.3 ± 0.8 240 ± 40 ≤3
Brown ICP-MS permanent 8 78% ± 5% 4.4% ± 6% 6.0% ± 5%
AAS: atomic absorption spectrometer. EDX: energy-dispersive X-ray analysis. EDXRF: energy dispersive X-ray fluorescent analysis. EMPA: Electron microprobe X-ray
mMicroanalyzer. ICP/AES: ductively coupled plasma spectrometer. ICP-MS: inductively coupled plasma mass spectrometer. INAA: instrument neutron activation analy-
sis.
molars. The present results of third molars compare with other
studies of permanent teeth are shown in Tables 4 and 5.
Pb Concentrations in Various Age Groups Indicate
Eras of Exposure
There are significant positive correlations between age and
Pb in enamel and dentine. Pb is believed to have a cumulative
effect. This study shows the Pb concentration in teeth increases
from younger groups to older groups. This means that Pb is
deposited in teeth year by year.
The various age groups may be looked upon as eras of birth
groups. Eras of birth indicate the eras of environmental expo-
sure. Initial calcification of human third molars occurs between

H.-Y. LIU ET AL.
the ages of 7 to 10. That means if more Pb exists in one’s third
molars, he may have been exposed to Pb before 7 to 10 years
ago. The eras are defined by birth year of the donor as follows:
≤20 age group is 1990 and later, 21 - 25 age group is 1985-
1989, 26 - 30 age group is 1980-1984, 31 - 40 age group is
1970-1979, and ≥41 age group is before 1969.
Figure 1 shows Sr, Ba and Pb concentrations in various eras
of birth. Pb concentrations are seen to increase by age group.
More importantly, this shows Pb concentration increases by
eras of birth. In Taiwan, unleaded gasoline was supplied start-
ing in 1986, which decreased the extent of cord blood lead level
decline in the Taipei area from 1985 to 2002 (Hwang, 2004). It
is reasonable that donors born before 1979 will have higher
concentrations of Pb in their teeth.
Sr/Ca and Ba/Ca
The ratio of Sr to Ca concentration is an indicator for bio-
puri- fication of calcium. The Sr/Ca ratio in teeth is an interest-
ing issue (Chao, 2009; Arora, 2004; Webb, 2005). Data for
Sr/Ca and Ba/Ca in teeth enamel may offer much information
for researchers in many fields of study, such as environmental
sci- ence, ecology, biology, paleontology and archaeology
(Wang, 2010).
In this study, the Sr/Ca ratio is 3.86 × 10−6 and 4.20 × 10−6 in
enamel and dentine of third molars, respectively. In Tables 1
and 2, Sr/Ca ratios increase with age except in the under the
Period of time
after 19901985-19891980- 19841970-1979befor e 1969
Concentration (ppm)
0
1
2
3
4
5
6
7
8
9
10
80
100
120
140
160
180
Enamel Sr
Dentine Sr
Enamel Ba
Dentine Ba
Enamel Pb
Dentine Pb
*** ** **
#
#
Figure 1.
Sr, Ba and Pb concentration in in enamel or dentine of third molars at
various eras of birth year. #: p value, 0.05 < p < 0.1. *: p value, p < 0.05.
Sr concentrations are higher in enamel than that in dentine. Ba and Pb
concentrations are higher in dentine than that in enamel. Sr concentra-
tions in enamel or dentine are higher in after 1990, and increased grad-
ually from 1985-1989 to before 1969. However there are no significant
differences among each group. Pb concentrations increased gradually
by age in both enamel and dentine. For enamel there are significant dif-
ferences between after 1990 and 1970-1979 (p = 0.002), after 1990 and
before 1969 (p < 0.001), 1985-1989 and 1970-1979 (p = 0.029), 1985-
1989 and before 1969 (p = 0.003). For dentine there are significant
differences between after 1990 and 1980-1984 (p = 0.024), after 1990
and 1970-1979 (p = 0.006), after 1990and before 1969 (p < 0.001),
1985-1989 and before 1969 (p < 0.001). Ba concentrations decay in
older age groups in both enamel and dentine. There are no significant
differences among each group.
20-year-old age group. Chao et al. also indicated that Sr/Ca
ratios in teeth are dependent on age (Chao, 2009). The informa-
tion for third molars in this study provides a reference for the
diet of modern adults.
Element Concentration Rati o of Enamel to Dentine
In Table 3, elements with enamel/dentine ratio >1 means
that the element concentration in enamel is higher than that in
dentine. Enamel is the hardest tissue in the human body. P and
Ca are major component elements in teeth. Enamel is closed
construction where no more elemental exchange since P and Ca
are deposited at about the age of 16. It is reasonable that their
concentrations are higher in enamel than those in dentine. In
this study, both of P and Ca concentrations are always higher in
enamel than those in dentine (Table 3). These results of third
molars are compared with other studies of different teeth types
in spite of fewer references in the past (Tables 4 and 5).
Cate also showed that the composition of enamel is 96 wt%
inorganic material and 4 wt% organic material and water, while
70% of dentin consists of the mineral hydroxylapatite, 20% is
organic material and 10% is water (Cate, 1998). Therefore, P
and Ca elements are more concentrated in enamel than in den-
tine.
However, for trace elements in teeth the concentrations of Pb
and Ba are higher in dentine than those in enamel as shown in
Table 3. The reasonable explanation is that dentine is a vital
organ where trace elements, like Ba and Pb, could enter dentine
from blood circulation, resulting in an increasing in concentra-
tion year after year.
In this study, the level of Sr is higher in enamel than in den-
tine. This may be due to the fact that Sr, as well as Ca and P,
are essential elements for tooth structure, which deposits during
the enamel formation process. These observations in Tables 4
and 5 are consistent with the results reported by Soares et al.
(Soares, 2008).
Conclusions
Enamel and dentine of 80 third molars were analyzed by
ICP-MS in this study. The concentrations of P, Ca and Sr are
higher in enamel than in dentine of third molars, and the con-
centrations of Ba and Pb are higher in dentine than in enamel.
In enamel and dentine, the concentrations of P, Ca and Ca/P
ratio are stable and persist. In enamel the concentrations of Sr
and Sr/Ca increase by age statistically but the concentrations of
Ba and Ba/Ca do not. In spite of increasing with age, the con-
centration of Sr is higher in the under 20-year-old age group. Pb
concentrations in enamel and dentine are increased by birth eras,
which may indicate the years of environmental exposure. The
levels of Pb in this study are lower than the previous published
findings before 1979.
Teeth are believed to be a particularly rich source of infor-
mation on life history and environmental exposures. A single
type of teeth such, as third molars, may be suitable for demon-
strating the definite characteristics of teeth. These results show
some basic data that may offer information for supplemental
evidence to the history of events.
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