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Photographic essay of chronic fluorosis in horses
Addendum to
Part 1: first four adult horses,
Histopathology report on Case 4
Larry H. Kelly, DVM
Lomita, California
USA
email: hossdox@sbcglobal.net
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Copyright © 2022 Larry H. Kelly. All rights reserved. All data and images are the property of
Larry H. Kelly, DVM. For reprint permission, please email hossdox@sbcglobal.net.
Histopathology Report
The following report was provided for the horse identified in Part 1 of this series as Case 4, an aged (20+
year-old) gelding who had been living for years in the Twentynine Palms region of southern California
and consuming the local well water (3–22 ppm F-).
The tissues examined were Triadan tooth 403 (mandibular right corner or third permanent incisor) and the
adjacent mandibular bone.
Below are gross-anatomical images, taken postmortem, of tooth 403 in situ, from various angles: left,
vestibular/labial surface; center, distal and occlusal surfaces ; right, distal, lingual, and occlusal surfaces.
Descriptive histopathology
One longitudinal section through the tooth and alveolar bone was examined. In addition, four sections
taken at different levels through the tooth, alveolar bone, and mandible, were examined. One cross section
of the mandible just proximal to the root of the tooth was also examined.
The tooth was characterized by moderate hypercementosis with regions of irregular cementum along the
surface. The hypercementosis was mostly present near the gingival attachment and beneath the crown
along the root.
There was also a locally extensive region of lysis in the root of the tooth in the longitudinal section. This
region of lysis was characterized by a loss of dentin and cementum with central amorphous necrotic
cellular debris and empty space and an irregular scalloped outer surface. There was no evidence of
globular dentin or excessive predentin in any of the tooth sections examined. There were no significant
findings within the pulp cavity in the sections examined.
Within the gingiva and periodontal ligament in all sections that contained these tissues, there was
multifocal lymphoplasmacytic inflammation with multifocal aggregates of Mott cells. The cemental
surface of the tooth was occasionally irregular in regions of periodontal ligament inflammation.
In two of the cross sections through the tooth there was squamous epithelium present segmentally along
the cemental surface, which may represent a downgrowth of epithelium in this region. Occasionally,
mulitifocal lysis was noted along the cemental surface beneath this epithelium.
403
403
403
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Copyright © 2022 Larry H. Kelly. All rights reserved. All data and images are the property of
Larry H. Kelly, DVM. For reprint permission, please email hossdox@sbcglobal.net.
There were small numbers of islands and trabeculae of woven to mostly lamellar bone within the
periodontal ligament. In the cross section taken proximal to the root of the tooth there was a focal, fairly
well-demarcated, roughly round, proliferation of fibrous connective tissue surrounded by normal
appearing trabeculae of lamellar bone. This fibrous connective tissue was thought to most likely represent
the periodontal ligament at the base of the root of the tooth.
The alveolar bone appeared normal histologically in all of the sections examined with no evidence of
significant lysis or periosteal reactive bone formation. In the most proximal sections taken through the
mandible, the medullary cavity multifocally contained either fibrous connective tissue or poorly cellular
adipose tissue. The trabecular bone that surrounded the regions of fibrous connective tissue appeared to
be normal. In regions of medullary adipose tissue, the trabeculae may have been a little thin and sparse;
however, an age-matched control sample from the same region would be needed to interpret this finding
as it may simply represent a function of cut.
Diagnosis(es)
Locally extensive lysis of the tooth and regional hypercementosis with irregular cementum proliferation;
multifocal lymphoplasmacytic gingivitis and inflammation of the periodontal ligament.
Comments
The primary findings were regional lysis of the tooth and hypercementosis with gingival and periodontal
ligament lymphoplasmacytic inflammation. These findings are consistent with those reported in cases of
equine odontoclastic tooth resorption and hypercementosis syndrome (EOTRH).
Specific features of fluorosis, such as either osteosclerosis or osteopenia with reactive periosteal new
bone formation, excessive predentin, globular dentin, and pulp cavity fibrosis were not noted in the
sections examined. It was not possible to examine enamel as the specimen was decalcified. In some
regions, the mandibular trabecular bone may be slightly thin with increased amounts of adipose tissue in
the medullary cavity, but an age-matched control sample from the same region would be needed to
interpret this finding.