Alimentary System

Tooth, Ameloblast - Metaplasia, Squamous

Narrative
Comment:
Squamous metaplasia can be seen following injury to the ameloblasts. While atrophy is characterized by decreased cytoplasm (shortening of individual ameloblasts), squamous metaplasia is characterized by loss of the columnar layer of ameloblasts and replacement by squamous epithelium (Figure 2 and Figure 4, arrows).
Recommendations:
Squamous metaplasia of the ameloblasts should be diagnosed and graded whenever present. Severity grading for squamous metaplasia is based on the extent of the lesion and the number of layers of squamous cells in the lesion.
References:

Brown HR, Hardisty JF. 1990. Oral cavity, esophagus and stomach. In: Pathology of the Fischer Rat (Boorman GA, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, CA, 9-30.

Abstract: https://www.ncbi.nlm.nih.gov/nlmcatalog/9002563

Fletcher AM, Bregman CL, Woicke J, Salcedo TW, Zidell RH, Janke HE, Fang H, Janusz WJ, Schlze GE, Mense MG. 2010. Incisor degeneration in rats induced by vascular endothelial growth factor/fibroblast growth factor receptor tyrosine kinase inhibition. Toxicol Pathol 38:267-279.

Abstract: https://www.ncbi.nlm.nih.gov/pubmed/20100840

National Toxicology Program. 1996. NTP TR-393. Toxicology and Carcinogenesis Studies of Sodium Fluoride (CAS No. 7681-49-4) in F344/N Rats and B6C3F1 Mice (Drinking Water Studies). NTP, Research Triangle Park, NC.

Abstract: https://ntp.niehs.nih.gov/go/12237
  • Image of normal ameloblast comparison to metaplasia, squamous in the tooth from a male B6C3F1 mouse in a chronic study

    Normal ameloblasts (arrow) in a male B6C3F1 mouse from a chronic study.

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Normal ameloblasts (arrow) in a male B6C3F1 mouse from a chronic study.
Normal ameloblasts (arrow) in a male B6C3F1 mouse from a chronic study.
Tooth, Ameloblast - Metaplasia, Squamous in a male F344/N rat from a chronic study. The ameloblasts (compare with Figure 1) have been replaced by squamous epithelium (arrow).
Tooth, Ameloblast - Metaplasia, Squamous in a male F344/N rat from a chronic study. The ameloblasts (compare with Figure 1) have been replaced by squamous epithelium (arrow).
Normal ameloblasts (arrow) in a male B6C3F1 mouse from a chronic study (higher magnification of Figure 1).
Normal ameloblasts (arrow) in a male B6C3F1 mouse from a chronic study (higher magnification of Figure 1).
Tooth, Ameloblast - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 2). The ameloblasts (compare with Figure 3) have been replaced by squamous epithelium (arrow).
Tooth, Ameloblast - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 2). The ameloblasts (compare with Figure 3) have been replaced by squamous epithelium (arrow).

Authors:

Linda H. Kooistra, DVM, PhD, DACVP
Pathologist
Charles River Laboratories, Inc.
Research Triangle Park, NC

Abraham Nyska, DVM, Diplomate ECVP, Fellow IATP
Expert in Toxicologic Pathology
Visiting Full Professor of Pathology
Sackler School of Medicine, Tel Aviv University Timrat Israel

Reviewers:

Joel R. Leininger, DVM, PhD
Senior Pathologist
MedImmune
Washington, DC

Amy Brix, DVM, PhD, DACVP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC