Struys et al. Journal of Medical Case Reports 2010, 4:328 http://www.jmedicalcasereports.com/content/4/1/328 that proliferation of ERM occurs during experimental tooth movement [6], the aim of this study was to investi- gate whether an auto-transplantation could also act as a trigger for this epithelial proliferation. Case presentation A 21-year-old Caucasian woman presented to our clinic with multiple caries and inflammatory paradental cysts (IPCs). One of the IPCs was located in the lower jaw near molar 37. A histopathological examination revealed that the cyst was predominantly surrounded by granulation tissue although the local presence of Malpighian epithe- lium could be found. On the periphery it was surrounded by an inflammatory infiltrate which consisted mainly of lymphocytes, plasmocytes and neutrophilic polymorpho- nuclear cells. The outermost lining consisted of a dense compact connective tissue and no signs of malignant degeneration could be detected. Two weeks later, the IPCs were enucleated after inci- sion and trepanation of the bone. We decided to extract teeth 15, 37, 45 and 47 because of multiple and severe carious lesions. As the patient had a substantial loss of molars, the intra-osseous teeth 18 and 48 were extracted carefully and transplanted into position 36 and 47, respectively. The procedure was done as atraumatically as possible with no visible damage to the periodontal ligament of the extracted teeth. No problems were encountered during surgery and the auto-transplantation was a success. After four months, an X-ray was taken of the upper and lower jaw (Figure 1) with a Siemens Orthoceph 10E operated at 70 kV and 15 s of irradiation. Two years later, the patient requested a partial extrac- tion of the lower jaw teeth because of recurrent infec- tions. As a result of renewed progressive caries of the two auto-transplanted teeth, she agreed with the removal of the auto-transplanted elements. The teeth were collected Figure 1 X-ray of the upper and lower jaw four months after surgery. Teeth 18 and 48 were extracted carefully and transplanted into position 36 and 47, respectively (marked by circles and arrows). Page 2 of 5 with her informed consent and the approval of the ethical board. The extracted auto-transplanted teeth were immedi- ately immersed and conserved in formol. The tissue of interest was collected by removing the PDL from the mid-cervical part of the teeth and it was fixed a second time in 2% glutaraldehyde in 0.05 M cacodylate buffer (pH 7.3). The fixative was gently aspirated with a glass pipette and the specimens were post-fixed in 2% osmium tetroxide, put through a dehydrating series of graded concentrations of acetone and embedded in araldite according to the conventional method. Semi-thin sec- tions (0.5 μm) were stained with a solution of thionin and methylene blue (0.1 aqueous solution) for light microscopy. Ultra-thin sections (0.06μm) were mounted on 0.7% formvar-coated grids, stained with uranyl acetate and lead citrate and examined in a Philips EM 208 trans- mission electron microscope operated at 80 kV. From a light microscopic examination of the semi-thin sections, we concluded that the ERM of the transplanted teeth were slightly larger than in normal PDL. A mean value of 20 cells was counted in the transplanted tissue in contrast to a mean value of 10 cells in normal/control PDL (Figure 2). We also noted compartmentalization of collagen bundles in the PDL (arrows in Figure 3). From transmission electron microscope (TEM) analysis we concluded that the auto-transplantation was success- ful because fully developed blood vessels appeared in the PDL (Figure 4a). The lumen was surrounded by mature endothelial cells which were firmly connected to each other with tight junctions (arrows in Figure 4a). In the periphery, the blood vessels were supported by smooth muscle cells (asterisks in Figure 4a). The enlargement of the ERM seen with the light microscope was confirmed by the TEM images (Figure 4b). The epithelial cells formed typical clusters which were separated by bundles of collagen fibres. The epithelial nuclei were large, predo- minantly euchromatic and irregular in shape. The ERM were lined by a basal lamina (arrow in Figure 4b). Another interesting feature was the innervation of the ERM. Some fine neurites made contact with the ERM (Figure 5). These were characterized by the presence of neurofilaments in the cytoplasm (asterisks in Figure 5). Apart from these neurites, fully matured myelinated nerve fibres (arrow in Figure 5) accompanied by their Schwann cells were another feature of the successful regeneration of the PDL. Discussion The specific morphological features which could be detected on the ultrastructural level can be regarded as typical for ERM and are confirmed in the recent literature [7-9]. ERM cells produce prostaglandin E2 [10] and prostaglandin E2 is capable of activating