Analysis of the immunoexpression of Ki-67 and Bcl-2 in the pericoronal tissues of impacted teeth, dentigerous cysts and gingiva using software image analysis

Abstract

Background: Pericoronal tissue is the soft tissue located between the bony crypt and the impacted tooth, which is histologically composed of fibrous connective tissue and is usually lined by the reduced enamel epithelium. Increased epithelial cell proliferation in the pericoronal tissue is associated with pathological changes such as development of an odontogenic cyst or an epithelial odontogenic tumor. This study is an attempt to evaluate and compare the proliferative index in the epithelium surrounding the impacted third molar teeth, dentigerous cysts, and gingiva.

Materials and methods: A case control study on pericoronal tissues and dentigerous cysts was carried out using immunomarkers. Forty pericoronal tissues were obtained from asymptomatic impacted third molars with pericoronal radiolucency less than 2.5 mm. Samples of 20 dentigerous cysts and normal gingiva were also included. Routine hematoxylin and eosin and immunostaining for Ki-67, a cell proliferation marker and Bcl-2, an anti apoptotic protein were performed on sections of pericoronal tissues, dentigerous cysts, and gingival tissues. The percentage of Ki-67-positive cells and Bcl-2 positive areas was found using the DigiPro™ version 4.0 Image analysis software. Bcl-2 immunopositivity and Ki-67-Li were analyzed using the Chi-square test and paired t-test. P- values of less than .05 were considered to indicate statistical significance.

Results: The immunohistochemical analysis revealed overexpression of Bcl-2 in the pericoronal tissues with squamous metaplasia, which was comparable to the dentigerous cyst. Ki-67 Li of the pericoronal tissue with squamous metaplasia was equal to the proliferative index of the dentigerous cyst. The expression of Ki-67 Li and inflammatory cells were highly significant (P < 0.0001).

Conclusions: The results of this study indicate that the pericoronal tissues of asymptomatic impacted third molars may be actively proliferating and normal pericoronal radiolucency cannot serve as an indicator for the differentiation potential.

Keywords: Apoptosis; Bcl-2; Ki-67 Li; dentigerous cyst; impacted third molar; pericoronal tissue.

Figure 1

Gross specimen of the pericoronal tissue (a) Photomicrographs showing reduced enamel epithelium (×10) (b) squamous metaplasia (×20) (c) squamous metaplasia (epithelium with proliferative rete processes) (d) (H and E original magnification ×40)

Figure 2

Immunohistochemical cytoplasmic staining of Bcl-2 in a dentigerous cyst (a) (×20) REE (b) (×10) squamous metaplasia (c) (X40) (d) (Immunostaining; original magnification ×10)

Figure 3

Immunohistochemical nuclear staining of Ki-67 in a dentigerous cyst (a) (×20) REE (b) (×10) squamous metaplasia of pericoronal tissue (c) (×40) (d) (×20)

Figure 4

Ki-67-Li in the pericoronal tissue in moderate-to-severe inflammation (a) and pericoronal tissue with slight inflammation (b) (Immunostaining; original magnification ×40)