The key difference between primary and secondary dentin is that primary dentin is a type of dentin formed before tooth eruption, while secondary dentin is a type of dentin formed after tooth eruption.
Dentin is a hard, bony tissue that makes up the main structure of a tooth. It is a mineralized connective tissue. Dentin is made up of highly specialized cells called odontoblasts and consists of inorganic components, organic matrix, and water. Dentin is of three types: primary (prominent one), secondary dentin (after tooth eruption), and tertiary dentin (forms reaction to stimulation).
CONTENTS
1. Overview and Key Difference
2. What is Primary Dentin
3. What is Secondary Dentin
4. Similarities – Primary and Secondary Dentin
5. Primary vs Secondary Dentin in Tabular Form
6. Summary – Primary vs Secondary Dentin
What is Primary Dentin?
Primary dentin is a type of dentin that forms before tooth eruption. Tooth eruption is the process of a tooth breaking through the gums and entering the mouth. Primary dentin is the most prominent dentin in the tooth. Primary dentin forms before the tooth are functional. It always lies between the enamel and the pulp chamber of the tooth, near the dentinoenamel junction. Primary dentin develops in early childhood. The outer layer of the primary dentin that is closest to enamel is known as the mantle dentin. This layer is very unique. Mantle dentin is formed by the newly differentiated odontoblasts. Mantle dentin forms a consistent layer 15 to 20 µm wide. Mantle dentin also lacks phosphorylation, has loosely packed collagen fibrils, and is less mineralized.
Below the mantle dentin lies the other part of the primary dentin called circumpulpal dentin. It is more mineralized and makes up most of the primary dentin layer. It is secreted after the mantle dentin by odontoblasts. The thickness of this layer is 6 to 8 mm. Furthermore, circumpulpal dentin is formed before the root formation is completed.
What is Secondary Dentin?
Secondary dentin is a type of dentin formed after tooth eruption and root formation. It is also formed after the tooth becomes functional and develops with age. Secondary dentin develops from odontoblasts lining the pulp cavity. It is laid down within the pulp cavity and is not uniformly formed. Typically, secondary dentin develops throughout life.
Secondary dentin grows much more slowly compared to primary dentin. Moreover, secondary dentin has a similar structure to primary dentin with only slight differences. Secondary dentin appears more on the roof and floor of the coronal pulp chamber. In these regions, secondary dentin protects the pulp from exposure to older teeth. Furthermore, both primary and secondary dentin do not form in response to any external stimuli as tertiary dentin.
What are the Similarities Between Primary and Secondary Dentin?
- Primary and secondary dentin are mineralized connective tissues.
- Both are made by odontoblasts.
- Both have a similar structure.
- They are not formed in response to any external stimuli as tertiary dentin.
- They support the structure of enamel.
What is the Difference Between Primary and Secondary Dentin?
Primary dentin occurs before tooth eruption, while secondary dentin occurs after tooth eruption. Thus, this is the key difference between primary and secondary dentin. Furthermore, primary dentin is developed before root formation. On the other hand, secondary dentin is developed after root formation. Thus, this is also a difference between primary and secondary dentin.
The below infographic presents the differences between primary and secondary dentin in tabular form for side-by-side comparison.
Summary – Primary vs Secondary Dentin
Dentin makes up the bulk of teeth. It is a mineralized connective tissue. Primary and secondary dentin are two different types of dentin. Primary dentin develops before the tooth eruption and root formation. In contrast, secondary dentin develops after the tooth eruption and root formation. So, this summarizes the difference between primary and secondary dentin.
Reference:
1. “8. Dentin.” Pocket Dentistry, 4 Jan. 2015.
2. Goldberg, Michel, et al. “Dentin: Structure, Composition and Mineralization.” Frontiers in Bioscience (Elite Edition), U.S. National Library of Medicine, 1 Jan. 2011.
Image Courtesy:
1. “1471-2350-8-52-2-l” By A novel DSPP mutation is associated with type II dentinogenesis Imperfecta in a Chinese family. BMC Med Genet. 2007 Aug 8;8:52 [1] (CC BY 2.0) via Commons Wikimedia
2. “Basic anatomy tooth” By w:user:Time3000 and w:user: Ian Furst (CC BY-SA 3.0) via Commons Wikimedia