Supervisors info:
Κωνσταντίνος Ι. Τόσιος, Επίκουρος Καθηγητής Στοματολγίας ΕΚΠΑ,Νικόλαος Νικητάκης, Αναπληρωτής Καθηγητής Στοματολγίας ΕΚΠΑ, Παναγιώτης Χριστόπουλος, Επίκουρος Καθηγητής Στοματικής και Γναθοπροσωπικής Χειρουργικής ΕΚΠΑ
Summary:
Introduction: The term dental follicle has been used in the English literature
to describe two separate entities: the normal tissue of ectomesenchyme origin
surrounding the enamel organ and dental papilla of the developing tooth germ,
contributing to the coordination of tooth eruption and providing precursor
cells for the periodontium, as well as the tissue surrounding the crown of an
impacted tooth. The latter consists of connective tissue and odontogenic
epithelium. Certain odontogenic tumors have a predilection for anatomic
locations close to impacted teeth, suggesting a possible role of dental
follicles to their pathogenesis. Parathyroid hormone related peptide (PTHrP)
and its receptor (PTH1R) expression, which has been related to
osteoclastogenesis during normal tooth eruption and to cellular proliferation,
has been studied in odontogenic cysts (radicular and dentigerous cysts) and
tumors (keratocystic odontogenic tumors and ameloblastomas), but not in dental
follicles of impacted teeth.
The aim of this paper is to study the Immunohistochemical expression of PTHrP
and PTH1R in dental follicles of impacted third molars. To our knowledge, no
such study has ever been reported in the littearure.
Material and Methods: 16 cases of fully impacted third molars’ dental
follicles, in which odontogenic epithelium was noticed (islands, squamous
lining epithelium, epithelium resembling the enamel organ and/or combination of
the aforementioned) were retrieved from the archives of the Oral Pathology
Laboratory (School of Dentistry, University of Athens). 5μm-thick
formalin-fixed and paraffin embedded tissue sections were immunohistochemically
stained by standard Bond Polymer Refine Detection Kit in a fully automated
slide preparation system, using the following antibodies: PTHrP, rabbit
polyclonal, (H-137) sc-20728, Santa Cruz Biotechnology, Inc., in a dilution
1:20 and PTH1R, mouse monoclonal, (3D1.1) sc-12722, Santa Cruz Biotechnology,
Inc., in a dilution 1:20. Immunohistochemically stained sections were blindly
evaluated by two examiners using an optical microscope. A three-category scale
was used to determine the percentage of positive staining cells (PP) and a
four-category one to describe the staining intensity (SI) for each
subpopulation of cells (epithelial and stromal ones). Immunoreactivity score
(IRS) was estimated by multiplying PP*SI. Given the descriptive nature of this
paper and the limited size of the sample, statistical analysis was not
performed.
Results: In epithelial cells PTHrP expression followed both nuclear and
speckled cytoplasmic pattern. In all cases strong (IRS=6) PTHrP was noticed in
all types of epithelial cells (islands of odontogenic epithelium, squamous
epithelial lining, epithelium resembling the enaml organ). In stromal cells
PTHrP followed a nuclear pattern. In 15 out of 16 cases (93,75%) more than 50%
of stromal cells were positive for PTHrP and staining was intense in all cases.
PTH1R expression was strictly cytoplasmic and percentage of positive epithelial
cells exceeded 50% in all cases and in all types of epithelial cells. However,
only in two cases was the staining intense. In stromal cells PTH1R expression
was strong only in one case. In the majority of cases (75%) PTH1R intensity was
medium. As for the percentage of stained stromal cells, it exceeded 50% in 4
cases (25%) and in one out of the remaning 12 cases it was lower than 5%.
Conclusions: PTHrP and PTH1R are immunohistochemically expressed in odontogenic
epithelium and in stromal cells of impacted third molars’ dental follicles.
This expression is indicative of an active state of proliferation and a
differentiation potential. PTHrP expression was strong in almost all cases,
whereas PTH1R expression was different in each case. Covariance of PTH1R
expression was also noticed for epithelial and stromal cells, the former being
stronger than the latter. Differential expression of PTH1R could also reflect
diversity in differentiation potential. Dental follicles surrounding the crowns
of impacted third molars are not inert structures, but futher investigation in
this field is required. Given the PTHrP ability for intracrine action and the
effects of this action to the cell cycle, its pattern of immunohistochemical
expression should be described in detail in future research.
Keywords:
PTHrP, PTH1R, Dental follicle, Impated third molar
