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.

Histological and Immunofluorescence Study of Discal Ligaments in Human Temporomandibular Joint.

The temporomandibular joint (TMJ) is a bilateral synovial articulation stabilized by several anatomical structures such as ligaments. The existence of articular capsule reinforcement structures have been described in the lateral and medial sides of disc which have been defined as collateral ligaments, lateral and medial. Despite that, some macroscopic observations support that these collateral ligaments do not belong to the articular capsule but they belong to the disc. By that, the aim of the present work was to evaluate morphological aspects of TMJ from cadaveric frozen heads by histological and immunofluorescence techniques in order to verify the origin and insertion of lateral and medial collateral ligaments. Results show that both lateral and medial ligaments origin from the disc and insert directly to the articular cartilage of mandibula condyle. These data open a new approach in the study of human TMJ.

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.

The Effect of Different Cleaning Protocols on Post Space: A SEM Study.

Aim. Purpose of the present paper is to analyze the efficiency of different post-space irrigation protocols. Methods. 28 single rooted teeth were endodontically treated. After post-space preparation every sample was assigned to one of three experimental groups and to one control group. In each group different irrigation protocols were performed as follows: EDTA (Group A), 37% orthophosphoric acid (Group B), and EDTA + 37% orthophosphoric acid with ultrasounds activation (Group C). In the control group (Group D) the irrigate association was not activated by ultrasounds. Three zones (coronal, middle, and apical) of each sample were analyzed by using Scan Electron Microscopy (SEM) without any metallization procedures. The presence of smear layer on the canal surface was qualitatively evaluated by applying Serafino's score with values included between 0 and 2. Results. The results of the research showed how Group C recorded the better results (0.81 ± 0.72). Group A and Group B showed lower mean scores (1.06 ± 0.69 and 1.08 ± 0.77); Group D showed the lowest mean score of 1.30 ± 0.69. The SEM observation analysis demonstrated how the smear layer presence decreased in the crown-apical direction. Conclusions. The different post-space treatments statistically determine significant differences on the dentinal surfaces cleansing. The absence of ultrasonic activation lowers the cleansing efficacy of endocanalar irrigants, showing sensible differences among each post-space zone.

Effect of bisphosphonates on the mandibular bone and gingival epithelium of rats without tooth extraction.

Osteonecrosis of the jaw (ONJ) is an adverse effect of bisphosphonate treatment that has become the subject of increasing investigations, in particular due to its poorly understood pathogenesis. Several experimental studies on animal models have been conducted; however, the majority of these replicate human ONJ following tooth extraction, and describe alterations in the bone and gingival epithelium when necrosis is manifested. The aim of the present study was to analyze the rat mandibular bone and gingival epithelium during 45 days of zoledronate treatment (which is a bisphosphonate agent), without tooth extraction. Intraperitoneal injections of zoledronate acid (0.1 mg/kg) were performed three times a week in normal male Wistar rats (n=20), while a control group of rats (n=20) was treated with saline solution for 45 days. After 7, 15, 30 and 45 days of drug treatment, all rats were sacrificed and hematoxilin and eosin staining, immunofluorescence and scanning electron microscopy analyses were performed. The results of the analyses after 7 and 15 days of treatment were similar in the treatment and control group. After 30 and 45 days of treatment, structural alterations were observed in the bone. No structural alterations to the gingival epithelium were observed. Based on these results, it was hypothesized that low doses of zoledronate act directly on the bone tissues to induce morphological alterations from bone to necrotic tissue following surgical procedures, although no cytotoxic effects were detected in the gingival epithelium.

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.