Effects of irradiation in the mandibular bone loaded with dental implants. An experimental study with a canine model.

Radiation therapy may compromise the quality of bone around dental implants, and its ability to regenerate, remodel, and revascularize. This study aimed to describe the irradiation effect on the bone microstructure of the mandible using dental implants in a canine model. Five beagle dogs were exposed to 40 Gy fractionated radiation. In total, 20 dental implants were inserted, two in the irradiated and two in the non-irradiated side. The mandible bone blocks were subjected to 3D micro-computed tomography (µCT) imaging, later evaluated histomorphometrically by light microscopy and scanning electron microscopy. Alterations in irradiated bone were observed under µCT imaging showing an increased anisotropy, porosity, and pore volume. Bone surface-to-bone volume decreased. The bone to implant contact index was significantly reduced in the irradiated bone (75.6% ± 5.8%) as compared to the non-irradiated bone (85.1% ± 6.8%). In the irradiated mandible, osteocytes with their filopodial processes, the bone beneath the periosteum, and subperiosteal veins showed structural differences but were not significant, whereas the diameter of Haversian canals were smaller statistical significant as compared to the control side. The study highlights that radiation dosage of fractioned 40 Gy causes alterations in the alveolar bone microstructure with compatible osseointegration and clinically stable dental implants.

Alveolar bone remodeling after tooth extraction in irradiated mandible: An experimental study with canine model.

OBJECTIVES: The aim of the present study is to investigate the morphological and cellular changes in dental extraction socket that has been irradiated after the tooth extraction and to describe morphological characteristics of the osteocytes and osteocyte-lacunar-canalicular network (LCN) by scanning electron microscopy (SEM). MATERIAL AND METHODS: Five beagle dogs aged 1-2 years were used in this study. One side of each mandible was irradiated in two sessions and the other side of mandible (non-irradiated) served as a control. The mandible bone blocks were processed by bulk staining en bloc in basic fuchsin and the specimens were embedded routinely in polymethyl methacrylate resin without preliminary decalcification. All blocks were subjected to micro-CT imaging, after that the specimens were prepared for light microscopy and SEM. RESULTS: Alterations in bone macrostructure are minimal in irradiated bone, but the changes in LCN are clear. In the area of the tooth extraction socket, the connections of osteocytes to the vessels and to neighboring osteocytes were not observed both in irradiated and nonirradiated bone. However, osteoclasts were located in the bone surface entering inside to the bone between osteons. In the lamellar bone of lateral sides, a decrease in canalicular connections between osteocytes and periosteum was found in irradiated bone as compared to the non-irradiated side. CONCLUSIONS: The novelty of the present study is that radiation disrupts osteocytes and their dendrites.

Radiation-induced changes in the microstructure of epithelial cells of the oral mucosa: A comparative light and electron microscopic study.

OBJECTIVES: The microplicae is a typical structure of the epithelial cell surface of the oral mucosa. The cell surface is potentially of great significance, as it provides the underlying basis for the protective function of the salivary pellicle. The aim of this study was to investigate whether radiation therapy affects the surface morphology of the superficial cells of the human oral mucosa in patients who have received radiotherapy for oral cancer. MATERIAL AND METHODS: Oral mucosal tissue samples from 91 patients were collected during dental implant surgery or ablative surgery. Study group 1 consisted of 28 patients who underwent dental implant surgery after radiotherapy. Group 2 consisted of five patients who developed osteoradionecrosis. Group 3 consisted of eight oral cancer patients without radiotherapy. Group 4 consisted of 50 clinically healthy subjects as controls. The samples were studied with scanning electron microscopy and compared with both light and transmission electron micrographs. RESULTS: Radiation therapy (RT) induces breakage and destruction in the microplicae morphology and declines the density of the microplicae surface structures. In some of the irradiated cells, the microplicae were completely vanished, especially in patients who developed osteoradionecrosis. In non-irradiated tissue, the microplicae of the superficial epithelial cells were intact in all cases. CONCLUSION: Scanning electron microscopy, in contrast to light microscopy, appears to be a useful tool to reveal the condition of superficial oral mucosal cells. In respect of the possible pathogenesis of osteoradionecrosis, the radiation-induced damage of the microplicae and its influence on the mucosal salivary pellicle is discussed.

Microstructure of oral epithelial cells as an underlying basis for salivary mucosal pellicle.

BACKGROUND: Salivary mucosal pellicle forms the structural basis of the local innate immune defense mechanism of the oral mucosa. At the surface of the oral mucosa, the apical cell membrane adjacent to the saliva interface contains short membrane folds, termed microplicae (MPL). This MPL structure of oral epithelial cells and its function as a basis to the salivary mucosal pellicle is unclear. In this preliminary study, we describe the ultrastructural morphology of cell membrane of superficial cells of the oral mucosa and study the membrane-associated mucins (MAMs), MUC1 and MUC4, with immunohistological methods. MATERIALS AND METHODS: Oral mucosal specimens were obtained from six healthy patients. Half of each specimen was prepared routinely for light microscopy, and the other part for scanning and transmission electron microscopy. The presence of MUC1 and MUC4 were studied by immunohistochemical methods in oral mucosal specimens. RESULTS: Morphologically, the cell membrane of MPL is partly discontinuous and membrane-associated molecules extrude from the cell membrane. MUC1 expression was detected in the superficial part of the buccal epithelium, while MUC4 had no expression in the oral squamous epithelium. CONCLUSIONS: The novel of this study is that the membrane-tethered molecules seem to occur onto the cell membrane of the superficial epithelial cells of the oral mucosa. Furthermore, the stratified squamous epithelium of the buccal mucosa produces MUC1 for the surface-saliva pellicle interface. The interaction between MPL structure, MUC1 mucin, and salivary mucosal pellicle is discussed.

Surface morphology of superficial cells in irradiated oral mucosa: an experimental study in beagle dog.

OBJECTIVES: The aim of the present study is to investigate if radiation induces changes in the superficial cells of the oral mucosa and secondly to describe morphological characteristics of the cell surface structure by scanning electron microscopy (SEM). MATERIALS AND METHODS: Ten beagle dogs aged 1-2 years were used in this study. One side of each mandible was irradiated in two sessions, each lasting 1 week. The total dosage was 40 Gy (Group A; 5 dogs) and 50 Gy (Group B; 5 dogs), in five fractions of 4 Gy. The other side of mandible (non-irradiated) served as a control. The specimen was harvested with a scalpel from the alveolar mucosa of the irradiated area 1 year after irradiation and studied with SEM. RESULTS: In the control side, the surface structure of the cell contains straight parallel or branched microplicae (MPL), which were equally spaced over the cell surfaces. Discontinuous and short MPL were typical cell structure of irradiated mucosa. In 50 Gy group, the surface structure of epithelial cell was pitted and the cell boundaries were thick. CONCLUSIONS: The novelty of the present study is that radiation disrupts superficial cells of the oral mucosa. The role of the MPL structure of the superficial cells in mucositis development is discussed.

Microstructure of the superficial epithelial cells of the human oral mucosa.

BACKGROUND: The apical cell membrane of the oral mucosa adjacent to the saliva interface is thrown into membrane folds, termed microplicae (MPL) with variation in morphology. The present study classifies morphological changes undergone by MPL into qualitative and quantitative categories. MATERIAL AND METHODS: Oral mucosal specimens were obtained from 32 healthy patients. Half of each specimen was prepared routinely for light microscopy, and the other part for scanning and transmission electron microscopy. Different measurements of cell structure were presented: the density of MPL, the width and height of MPL, the width of furrows between two adjacent MPL and the distance of the centre of MPL. Morphometric measurements were obtained using a semiautomatic ImageJ analysis software (W Rasband, National Institutes of Health, Bethesda, MD). RESULTS: Parallel and branching MPL was common observation in the area of lining mucosa and in the tongue between the filiform papillae. The density of MPL was higher in the cells of the buccal mucosa than in the cells of the tongue, 43.69 + 11.43% and 31.68 + 10.32%, respectively. The difference was significant (p < 0.001). The width of MPL was 0.16 µm in cells of the buccal mucosa and 0.12 µm in cells of the tongue. CONCLUSIONS: Our findings support the idea that MPL structure is a determining factor for the functionality of the oral epithelium since the values of the MPL were kept relatively stable. The role of MPL structure of the oral mucosal cells is discussed.