dental microstructure
TRANSCRIPT
-
7/29/2019 Dental Microstructure
1/12
Max Planck Institute for Evolutionary Anthropology
DEPARTMENT OF HUMAN EVOLUTION
DENTAL HARD TISSUE LABORATORY
-
7/29/2019 Dental Microstructure
2/12
Table of Contents
Tooth Histology and Human Evolution 3Dental Microstructure 3
Principles of Incremental Development 3
Histological Facilities Available 6Significance 9
Contact Information 11
2
-
7/29/2019 Dental Microstructure
3/12
Tooth Histology and Human Evolution
The MPI-EVA Human Evolution Department has recently created
state of the art facilities for the study of dental development in fossil
hominids. Histological analysis of dental material facilitates understanding
of the final functional products of the processes of development and growth,
which may be understood in terms of enamel thickness (macrostructure) and
enamel microstructure. Recent studies have provided information on age at
death in hominids with developing dentitions, absolute and relative timing of
dental development, age at first molar emergence, and differences in the
developmental pathways of enamel formation. These studies have important
implications for our understanding of hominid evolution and the origin of
developmentally modern humans.
Dental Microstructure
Dental development in humans and great apes begins prior to birth
and continues throughout adolescence. Like many biological systems, hard
tissue formation is characterized by a circadian rhythm. Developmental rate
and time are permanently recorded by incremental lines in enamel and
dentine, which remain unchanged in these tissues for millions of years.
Given that dental remains are the most common, well-preserved type of
fossil evidence for extinct species of primates, examination of incremental
growth processes may shed new light on the evolutionary developmental
biology of early humans.
Principles of Incremental Development
Enamel is secreted by cells known as ameloblasts, which differentiate
at the enamel-dentine junction and migrate outward towards what becomes
the surface of the crown. The tracks left by these individual cells are known
as enamel prisms (Figure 1). The prisms show cross-striations that resultfrom the circadian rhythm of enamel secretion (Figures 1 & 2).
3
-
7/29/2019 Dental Microstructure
4/12
The successive positions of the advancing front of forming enamel are
preserved as long-period incremental structures termed Retzius lines
(Figures 1 & 3). These lines conform to the shape of the dentine horn in the
cuspal enamel. In the lateral and cervical enamel, Retzius lines contact the
enamel surface, forming circumferential rings known as perikymata
(Figures 4 & 5). This region is referred to as lateral or imbricational enamel.
The periodicity of Retzius lines may be determined in imbricational enamel
by counting the number of cross-striations between Retzius lines (shown in
the enlarged box in the upper right of Figure 1).
Figure 1. Schematic of enamel microstructure modified from Smith et al. (2003).
Dentine is produced by cells known as odontoblasts that generatedentine tubules (similar to enamel prisms), and show daily incremental lines
known as von Ebners lines (equivalent to cross-striations) and long-period
structures known as Andresens lines (equivalent to Retzius lines).
4
-
7/29/2019 Dental Microstructure
5/12
It has been demonstrated that both cross-striations and von Ebners lines
show a 24-hour frequency, and because they are easier to image than von
Ebners lines, cross-striations are used as a standard to determine the
periodicity of long-period features in both tissues. Long-period features
show a consistent periodicity within a single tooth and in all teeth belonging
to the same individual, although this may vary within a taxon. Counts and
measurements of these short- and long-period lines provide information on
the rate and duration of enamel and dentine secretion, which may be
combined to determine the total crown formation time and the rate and
duration of root extension.
Figure 2. High magnification polarized light image of a Paranthropus boisei molar showing
cross-striations. These light and dark bands run horizontally across the vertical enamel prisms,
and are spaced approximately 5.5 microns apart. Fifty to 55 lines can be counted from the bottom
to the top of the image, representing 50 - 55 days of tooth growth.
5
-
7/29/2019 Dental Microstructure
6/12
Histological Facilities Available
Hard tissue preparation and analysis laboratories are available for
examination of dental material. Molding, casting, and replicating techniques
may be used to study external features or naturally fractured surfaces.Standard refluxing and embedding techniques will be used to prepare
samples, which may be sectioned with the use of a diamond wafering blade,
ground, and polished to a fine sub-micron finish.
For the preparation lab, we offer the use of two Buehler Isomet
precision saws, a Buehler Ecomet Grinder-Polisher, and a large-diameter
Logitech automated annular saw (APD1). Several forms of microscopy are
available to study casts and histological sections, including transmitted and
polarized light microscopy. We use the automated Olympus SZX9 Stereo
microscope with the 12.5 mega-pixel DP 70 camera and SIS Imaging
software for stereo microscopy, and the Olympus BX51 upright lightmicroscope for transmitted and polarized light imaging, which can be
coupled with the DP 70 and SIS software for a range of measurements, or
used to capture images to 35 mm film. The microscopes are coupled to a
high-speed computer with a 21-inch monitor and sufficient space to archive
images to DVDs or for storage on our department server.
A range of printing options is available, including local poster-sized
image generation and high quality photo printing. Additional forms of
analysis include scanning electron microscopy (SEM) and tandem scanning
reflected light microscopy (confocal) available though collaborativearrangements with Stony Brook University and the University of Leipzig
(Figures 6 & 7).
6
-
7/29/2019 Dental Microstructure
7/12
Figure 3. Polarized light photo montage of the lateral and cervical enamel of a Paranthropus
boisei molar showing prominent accentuated growth lines and structural features known as
Hunter-Schreger bands running from the lower border towards the tooth surface. The vibrant
colors are partially due to post-mortem mineralization that is characteristic of fossil material.
7
-
7/29/2019 Dental Microstructure
8/12
Figures 4. (above) and 5. (below) illustrating perikymata (growth lines) on hominid teeth. These
high-resolution replicas have been sputter coated with a metallic source to enhance the
appearance of horizontally oriented long-period lines.
8
-
7/29/2019 Dental Microstructure
9/12
Significance
Early studies of fossil dentitions concentrated on aspects of crown size
and morphology, root morphology, and the mechanics of occlusal wear.
Additional studies have looked at the age of emergence and developmentalchronology in fossil and extant taxa in an attempt to understand aspects of
life history and phylogeny. Phylogenetic and functional importance has also
been attached to tooth enamel thickness in analyses of Miocene hominoid
fossils and interpretations of hominid origins. Examination of hard tissue
development from a histological perspective is a relatively new field of
odontological inquiry, particularly in relation to answering phylogenetic
questions. Recently, there has been a dramatic increase in the number of
studies on incremental dental development in hominoids. Studies on Plio-
Pleistocene hominids and Neanderthals have indicated that the relatively
slow developmental rate and prolonged duration of modern human crownformation is a fairly recent and unique development.
Figures 6. (above) and 7. (following page) illustrating prisms and incremental features on
Moroccan hominid teeth. Figure 6 is a scanning electron micrograph of naturally fractured
enamel (scale bar = 20 microns), and Figure 7 is a confocal micrograph of sub-surface enamel
from the same tooth.
9
-
7/29/2019 Dental Microstructure
10/12
Members of the Department of Human Evolution are currently
utilizing incremental structures preserved on the surface of teeth to study the
growth processes of early humans (Figures 4 & 5). Current projects include
a study of the development of Moroccan hominid dental material, as well as
on-going work on Neanderthal growth processes. Additional projects includea study of fossil and extant Asian hominoid dental development, including a
study of temporal and geographic developmental variation in Pongo, which
may provide insight into the evolutionary developmental biology of the
genusHomo.
Over the next few years, we aim to build a substantial reference
collection of histological sections of hominid material. This will yield
additional developmental information that is not available from external
surfaces or naturally fractured teeth, including developmental rate and total
formation time. These types of data are illustrated here with images from
histological sections ofParanthropus boisei (Figures 2 & 3). Fossil sections
will be considered in the context of a large comparative collection of
histological sections of extant hominoid material. We are open to
considering proposals for collaborative work within all of these broad
themes. Please do not hesitate to contact us for more information.
10
-
7/29/2019 Dental Microstructure
11/12
Contact Information
Tanya M. Smith
Max Planck Institute for Evolutionary Anthropology
Department of Human EvolutionDeutscher Platz 6
D-04103 Leipzig
Germany
Tel: + 49 (0) 341 - 35 50 362
Fax: + 49 (0) 341 - 35 50 399
E-mail: [email protected]
11
-
7/29/2019 Dental Microstructure
12/12
2005
Department of Human Evolution
Max Planck Institute for Evolutionary Anthropology
12