Articular Disc of a Human Temporomandibular Joint: Evaluation through Light Microscopy, Immunofluorescence and Scanning Electron Microscopy.

The extracellular matrix of the articular disc in a temporomandibular joint (TMJ) is composed mainly of collagen I and elastin. The collagen is important for resisting tensile forces, while the elastin is responsible to maintain the shape after deformation. We studied the orientation of collagen and elastin in a normal human temporomandibular joint disc by light microscopy, immunofluorescence and scanning electron microscopy. Our results demonstrated that collagen and elastin run parallel to each other in the intermediate zone with an anteroposterior orientation. From here, the orientation of two fibers groups changes into a disordered arrangement in the transition zone. Numerous elastic fibers cross with the collagen fibers, defining an interwoven knitted arrangement. The evaluation of the disc-condyle relationship shows that the medial margin of the articular disc is inserted directly at the superficial layer of the mandibular condylar cartilage. Therefore, the tensile properties of the TMJ disc are expressed in the directions corresponding to the orientation of the collagen fibers, and the complex orientation of elastin with the collagen determines the maintaining of the shape after the stresses by the joint movements. Moreover, the direct anatomical relationship between the articular disc and the mandibular condyle makes a decisive contribution to the understanding of TMJ movements.

Hemispheric prevalence during chewing in normal right-handed and left-handed subjects: a functional magnetic resonance imaging preliminary study.

This study evaluated the activation of different cortical areas during nondeliberate chewing of soft and hard boluses in five right-handed and five left-handed subjects with normal occlusion, to determine different hemispheric prevalences. The study was conducted with a functional Magnetic Resonance Imaging (1.5 T Magnetom Vision - Siemens Medical, Germany) using a head coil. The results showed that the most frequently activated areas were Brodmann's areas four and six in the primary motor and premotor cortex, the insula and Broca's area and, overall, showed greater activity of the cortical mastication area (CMA) in the right hemisphere for right-handed and in the left hemisphere for left-handed subjects.

An immunofluorescence study on VEGF and extracellular matrix proteins in human periodontal ligament during tooth movement.

The periodontal ligament (PDL) is a highly vascularized connective tissue surrounding the root of a tooth. In particular, the PDL is continuously exposed to mechanical stresses during the phases of mastication, and it provides physical, sensory, and trophic functions. It is known that the application of orthodontic force creates a change in periodontal structures. In fact, these forces generate a pressure on the ligament that closes the vessels. The aim of this study is to observe the modifications of vascular endothelial growth factor (VEGF) in the PDL and extracellular matrix proteins after application of a pre-calibrated and constant orthodontic force at different phases of treatment. We used a 50-g NiTi coiled spring and in vivo samples of PDL of maxillary and mandibular premolars of patients subjected to orthodontic treatment. These teeth were extracted at 1, 7, 14, 21, and 30 days, respectively, by application of force. The extraction of the PDL was effectuated by scarifying the radicular surface on the pressure and tension sides. The mechanical stress induced by the application of force caused an increase in the reactive type of metabolism of extracellular matrix proteins and modulation of neoangiogenesis until restoration.

An immunohistochemical, histological, and electron-microscopic study of the human periodontal ligament during orthodontic treatment.

The periodontal ligament lies between the hard tissues of alveolar bone and cementum of teeth and serves to anchor the tooth to the alveolus and functions as a cushion between these hard tissues to migrate occlusal force during mastication. This tissue is always exposed to mechanical stress during mastication. When occlusal forces exceed the adaptive capacity of the periodontal ligament, the periodontal ligament tissue will be injured and then occlusal trauma will occur. The different modifications of periodontal ligament during load deformation can be monitored by analysis of the expression of different collagen types and fibronectin, with immunohistochemical techniques, and by morphological study of ligament, with light- and transmission electron-microscopic techniques. The use of continued and light orthodontic force generates a pressure of ligament with ejection of parodontal fluid externally and partial closing of vessels. On these basis we performed a study in order to evaluate periodontal ligament collagen types I and IV and the fibronectin modifications induced by application of a precalibrated orthodontic strength. We integrated these results, with light and transmission electron-microscopic observations, in order to evaluate the morphological modifications of periodontal tissue. Our observations showed that the type I collagen immunofluorescence staining is increased in the pressure side; in the tension side, it shows prior to treatment an increase, and after 72 h of treatment, a diminution of the staining pattern. Type IV collagen staining is reduced in both sides, but increased gradually after 7 days from treatment; finally, fibronectin staining pattern is gradually increased in the pressure side and reduced in the tension side. In light and transmission electron-microscopic observations it is possible to show a reduction of vessels at 72 h from treatment, and an increase of vessels after 7 days from treatment. The Malassez's epithelial residues are decreased at 72 h, while they are increased after 7 days from treatment. The modifications of immunofluorescence staining patterns of tested proteins revealed angiogenesis and reparative processes, and a thickening of fibrillar matrix as a defensive reply to mechanical stress. The modification of normal staining patterns of tested protein in our observations, could be determined by variation of scaffold geometry of periodontal ligament. The reduced movements of contraction and relaxation of periodontal ligament, due to orthodontic treatment, provoke a loss of mechanical stresses transmitted over ligament surface. Mechanical signals, therefore, could be integrated with other environmental signals and transduced into biochemical signals through force-dependent changes in scaffold geometry. Physical forces of gravity, hemodynamic stresses, and movement play a critical role in tissues, since the cells use tensegrity architecture for their structural organization.

Dentin Morphology of Root Canal Surface: A Quantitative Evaluation Based on a Scanning Electronic Microscopy Study.

Dentin is a vital, hydrated composite tissue with structural components and properties that vary in the different topographic portions of the teeth. These variations have a significant implication for biomechanical teeth properties and for the adhesive systems utilized in conservative dentistry. The aim of this study is to analyse the root canal dentin going from coronal to apical zone to find the ratio between the intertubular dentin area and the surface occupied by dentin tubules varies. Observations were conducted on 30 healthy premolar teeth extracted for orthodontic reasons in patients aged between 10 and 14. A SEM analysis of the data obtained in different canal portions showed that, in the coronal zone, dentinal tubules had a greater diameter (4.32 µm) than the middle zone (3.74 µm) and the apical zone (1.73 µm). The average number of dentinal tubules (in an area of 1 mm(2)) was similar in coronal zone (46,798 ± 10,644) and apical zone (45,192 ± 10,888), while in the middle zone they were lower in number (30,940 ± 7,651). However, intertubular dentin area was bigger going from apical to coronal portion. The differences between the analysed areas must be considered for the choice of the adhesive system.

Sarcoglycans and integrins in bisphosphonate treatment: immunohistochemical and scanning electron microscopy study.

Osteonecrosis of the jaw is an adverse outcome associated with bisphosphonate treatment. Bisphosphonates are used in conjunction with antineoplastic chemotherapy for the treatment of hypercalcaemia associated with malignancy, lytic bone metastasis and multiple myeloma. However, it is not known if the osteonecrosis of the jaw lesion originates in the bone or whether it initiates in the gingival epithelium. Two bisphosphonates are commonly used in cancer treatment. One of these is pamidronate disodium, a second-generation bisphosphonate that differs from the first-generation drug because it inhibits bone resorption at a dose that does not affect bone mineralization. The other widely used BP, zoledronate, is a third-generation drug that is the most potent bisphosphonate in clinical use, showing strong anti-osteoclastic activity, similar to pamidronate. The aim of the present study was to evaluate the modifications of human oral mucosa and underlying bone in patients after treatment with these nitrogen-containing bisphosphonates for 24 and 36 months. We analyzed the structural damage of the oral mucosa and damage of the perilesional mandibular bone observing possible correlations from them. Our results allow to express two hypotheses about the mechanism responsible for these results relating to mandible matrix necrosis; first, an increased skeletal microdamage associated with turnover suppression occurred early in treatment and progress with longer treatment duration, second, opening damage in osteonecrosis of the jaw modifies structural morphology of gingival epithelium.

Immunohistochemical analysis of TGF-ß1 and VEGF in gingival and periodontal tissues: a role of these biomarkers in the pathogenesis of scleroderma and periodontal disease.

Periodontal disease is characterized by inflammation and bone loss. The balance between inflammatory mediators and their counter-regulatory molecules may be fundamental for determining the outcome of the immune pathology of periodontal disease. Transforming growth factor-ß (TGF-ß) and vascular endothelial growth factor (VEGF) represent a family of polypeptide proteins involved in the inflammation and regulation of immune responses, especially in rheumatic disease. The relationship between these growth factors and periodontitis has resulted in a new field of osteoimmunology and provides a context for better understanding the pathogenesis of periodontal disease. Therefore, the aim of this study was to compare the protein expression profile of these inflammatory mediators in 90 patients divided in three groups: healthy control, chronic periodontitis and in rheumatic disease, scleroderma. The findings presented here highlight that biomarkers, such as TGF-ß1 and VEGF, play a key role in the evolution of the immune response, which in turn influences the outcome of disease establishment.

Expression of muscle-specific integrins in masseter muscle fibers during malocclusion disease.

Integrins are heterodimeric cell surface membrane proteins linking the extracellular matrix to actin. α7B integrin is detected in proliferating and adult myofibers, whereas α7A plays a role in regenerating muscle fibers with a minor function in mature muscle fibers. The expression levels of ß1A appear to be very low, whereas ß1D appears to be the predominant integrin form in mature muscle. Considering the important features of masseter muscle we have studied integrin expression in masseter muscle specimens of surgical patients with posterior right crossbite and comparing them to left side masseter muscle specimens. Our results showed that the expression of integrins was significantly lower in the crossbite side muscle. Furthermore, the most important finding is that ß1A is clearly detectable in adult masseter muscle. This behavior could be due to the particular composition of masseter, since it contains hybrid fibers showing the capacity to modify the contractile properties to optimize the energy efficiency or the action of the muscle during contraction. Moreover, masseter is characterized by a high turnover of muscle fibers producing a regeneration process. This may indicate a longer time to heal, justifying the loss of ß1D and the consequential increase of ß1A. Thus, our data provide the first suggestion that integrins in masseter muscle play a key role regulating the functional activity of muscle and allowing the optimization of contractile forces.

Immunohistochemial evaluation of sarcoglycans and integrins in gingival epithelium of multiple myeloma patients with bisphosphonate-induced osteonecrosis of the jaw.

Osteonecrosis of the jaw (ONJ) is an adverse outcome associated to bisphosphonate treatment. However, it is not known whether the ONJ lesion originates in the bone, or whether it may initiate in the oral mucosa. The aim of our study was to evaluate the pattern of basal lamina of oral mucosa after bisphosphonate administration and to analyze the structural damage of the mucosa in ONJ patients, and in subjects treated with bisphosphonates without osteonecrosis. By immunohistochemistry, we evaluated changes in basement membrane by expression of signalling proteins, laminin, and type IV collagen. All tested proteins were almost absent in basal lamina and mucosa of subjects treated with bisphosphonates without osteonecrosis, whereas in mucosa of patients with ONJ, they showed a clearly detectable pattern of the same proteins, specifically in basal lamina, but less in comparison to control samples. Moreover, in pathological mucosa, the clearly detectable staining pattern for VEGF indicated a massive neoangiogenesis. Bisphosphonates induce changes in expression of proteins also in oral mucosa. The increase of these proteins in basal lamina, and the neo-angiogenesis, concomitant with formation of the lesion, could indicate a compensative behaviour in the remodelling of the gingival mucosa in order to restore the epithelial architecture.