Figure 0.1: This home-made record player stand is used as a metaphor. Bonus points if you can name the two records visible.

Why study histology and embryology?

This home-built stand for a record player is going to serve as a metaphor. Measurements were made to ensure there would be enough space for records. It is built out of wooden dowels, and used some floor tiles to create a smooth surface. Why use those materials? Actually, those building materials were re-used, they were left over from previous projects. Sure, a trip to the hardware store could have yielded more appropriate materials, but would the hassle have been worth it? No. This is why you should study embryology, many instructions and materials are re-used during human development. As a result, while some organs or tissues have a shape that matches their function, others do not. For example, why is enamel made by epithelial cells, when it looks like bone tissue? Why can a piece of pig heart be used to surgically repair gingival tissue? What is the function of the philtrum? These are questions that can be better answered by studying where things come from (embryology) rather than studying what they look like (anatomy). Imagine not knowing that flies develop from maggots, you might believe in spontaneous generation after observing the appearance of maggots on rotting food.

Then why study histology? The answer to that is simple: embryos are tiny, you need a microscope to see what is going on. But with a basic understanding of oral histology you will understand why a pocket depth over 3 mm is considered unhealthy. You can conceptualize what makes the linea alba appear white in some patients. You can explain what causes perikymata. You are on your own, however, on how to pronounce perikymata.

Because it is no possible to take tissue samples from human embryos, we occasionally look at the development of other species. These include rats, frogs (in space!), sea urchins and tunicate worms. We can learn a lot from distant relatives because humans re-use developmental processes for different purposes. Hopefully, you will gain an appreciation for the link between evolution and development. What can a headless, toothless sea creature teach you about dental hygiene?

Author bios:

Laird C. Sheldahl, Ph.D.

Open educational resources: OER Commons


Laird Sheldahl is the lead author and illustrator of this textbook. He has a Ph.D. in physiology and pharmacology. He currently teaches at Mt. Hood Community College in Gresham, OR. His Ph.D. thesis studied a morphogen (Wnt) involved in the formation of the head and neural crest cells. This morphogen is re-used during development of the teeth. To study this process in frogs (their embryos are not inside uteruses, which makes them easier to study) he did a lot of microscopy. He does not have a background in dental hygiene, and is therefore very happy to have expert collaborators.

Raye Ann Yapp

bio to be written


Babiy, Ilya, RDH, MS, EPP

Student editors

Amen Mohammed

Choose your own adventure

Some links in the book take you to an external website, such as Wikipedia. These links should be a  monospace font, such as this: external link. We don’t have control over how they appear on your eReader. External links are for further reading or watching if you are interested, but are not required to understand the material we present. If your eReader or computer is not connected to the internet, these links will not work.

Definitions, such as , allow you to click on a word and read a short description. Their behavior may be missing in some eReaders. Definitions appear once per paragraph, and the description is limited to human biology. We do at times cover the development of sea urchins, mice, fish and frogs (in space, no less). Humans share aspects with all of these critters, for reasons that should become clear.

For important words and phrases defined in another chapter, such as , you can read the definition by clicking on the word, or follow the icon to jump forward or back to the section where it is described in detail. Use the “back” button on your web browser to return to your spot. Some eReaders may not have a way for you to return to your spot easily (try testing it now). Unlike external links, definitions should work regardless of your internet connection, assuming your eReader supports them. We encourage you to use icons to pick your own non-linear path through this textbook.

The basic format of each chapter is as follows:

Table 0.1: Basic format of this textbook
Chapter outline Content:
Overview Where we try to provide a road-map for what we will be covering, and why we are covering it.
Physiology Where we cover histology and embryology.
Clinical significance Where we cover why the histology or embryology is relevant to your practice.

histology and animation of areolar CT
Figure 0.2: Example of an animated image.

Animated images

The image in Fig. 0.2 is an animated .gif file, it should be cycling through a series of changes. The authors wish to take advantage of things that can be done in an eBook, but not a print book. Unfortunately, animated gifs do no work in pdfs or on the Amazon Kindle (.mobi format). They cannot be slowed down or paused. Also, .gif is pronounced like gift without the t.

Figure 0.3 : Example of an image created by someone else. Image credit: “Fluorescent cells” by NIH image is in the Public Domain CC0

Other images

Images that we have not created have their sources listed in the figure legend, such as Fig. 0.3. This is to keep in line with the Creative Commons rules for using other people’s work the way they have asked. This may be of use to teachers, but students can ignore this information.

Broken image
Fig. X: This image link is broken on purpose to show you what that looks like.

If you see something that looks like Fig. X, an image has failed to load. Try hitting the reload button if you are in a web browser (often located up in the menu bar, it probably  looks like a circular arrow).

Course objectives

Table 0.2: Course objective (for instructor use)
Course objective Textbook chapter(s)
1. Identify core concepts of cell biology and general histology related to the face and oral cavity 1,2
2. Demonstrate an understanding of the role of epithelial tissues, underlying connective tissues and neural crest cells in the face and oral cavity 3,4,5
3. Identify the basic patterns of early human developmental biology related to formation of the face and oral cavity 6,7
4. Describe the major steps of amelogenesis and enamel structure 8
5. Describe the major steps of odontogenesis and formation of the dentin-pulp complex 9
6. Describe the major steps of development of tooth roots and the periodontium 10
7. Identify mesenchymal-epithelial relationships in tooth development and tooth eruption. 8, 9, 11

Copyright information

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Histology and Embryology for Dental Hygiene is published under the Creative Commons Attribution-NonCommercial-ShareAlike license. This license states that:

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When attributing derivatives of Histology and Embryology for Dental Hygiene, please use the following attribution:

Sheldahl, Laird C. and Yapp, Raye Ann. Histology and Embryology for Dental Hygiene. Retrieved from . ISBN: 978-0-578-76350-7 Licensed under a Creative Commons Attribution NonCommercial ShareAlike (BY-NC-SA) license.

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