Study of the noncollagenous components of the periodontium

A three-dimensional cell culture model to study the mechano-biological behavior in periodontal ligament regeneration

Periodontitis is a disease affecting the supporting structures of the teeth, which can eventually result in tooth loss. A three-dimensional (3D) tissue culture model was developed that may serve to grow a 3D construct that not only transplants into defective periodontal sites, but also allows to examine the effect of mechanical load in vitro. In the current in vitro study, green fluorescent protein labeled periodontal ligament (PDL) cells form rat incisors were embedded in a 3D matrix and exposed to mechanical loading alone, to a chemical stimulus (Emdogain; enamel matrix derivative [EMD]) alone, or a combination of both. Loading consisted of unilateral stretching (8%, 1 Hz) and was applied for 1, 3, or 5 days. Results showed that PDL cells were distributed and randomly oriented within the artificial PDL space in static culture. On mechanical loading, the cells showed higher cell numbers. Moreover, cells realigned perpendicular to the stretching force depending on time and position, with great analogy to natural PDL tissue. EMD application gave a significant effect on growth and upregulated bone sialoprotein (BSP) and collagen type-I (Col-I), whereas Runx-2 was downregulated. This implies that PDL cells under loading might tend to act similar to bone-like cells (BSP and Col-I) but at the same time, react tendon like (Runx-2). The combination of chemical and mechanical stimulation seems possible, but does not show synergistic effects. In this study, a new model was successfully introduced in the field of PDL-related regenerative research. Besides validating the 3D model to mimic an authentic PDL space, it also provided a useful and well-controlled approach to study cell response to mechanical loading and other stimuli.

Biomechanical behavior of oral soft tissues

BACKGROUND

Little attention has been given to understanding the variation in biomechanical behavior of oral soft tissues, and this represents an obstacle for the development of biomaterials that perform with appropriate biomechanical characteristics. With this as our motivation, a uniaxial mechanical analysis was performed on lingual and buccal aspects of the attached gingiva, alveolar mucosa, and buccal mucosa to gain insight into human tissue performance and site-specific mechanical variation.

METHODS

A discrete quantitative mechanical evaluation of each soft tissue region using tensile, dynamic compression, and stress relaxation analysis was conducted to correlate tissue structure with function as assessed histologically.

RESULTS

Results confirm the keratinized gingiva to have increased tensile strength (3.94 ± 1.19 MPa) and stiffness (Young modulus of 19.75 ± 6.20 MPa) relative to non-keratinized mucosal regions, where densely arranged elastin fibers contribute to a tissue with increased viscoelastic properties. Dynamic compression analysis indicated the instantaneous modulus (E(int)), steady modulus (E(s)), and peak stress increased with loading frequency and strain amplitude, with the highest values found in the buccal attached gingiva.

CONCLUSION

These investigations quantify the biomechanical properties of oral soft tissues and show region-to-region variation that details structure-function relationships and provides key parameters to aid development of biomaterials that perform with appropriate biomechanical properties.

Degradation of noncollagenous components by neutrophil elastase reduces the mechanical strength of rat periodontal ligament

BACKGROUND AND OBJECTIVE

We have previously shown that increases in neutrophil elastase in periodontal ligament with chronic periodontitis results in degradation of the noncollagenous components. The purpose of this study was to investigate whether the destruction of noncollagenous components by treatment with elastase in vitro causes changes in the mechanical properties of the periodontal ligament.

MATERIAL AND METHODS

The transverse sections of mandibular first molars, prepared from male Wistar rats at 6 wk of age, were digested with 0-50 microg/mL of neutrophil elastase at 37 degrees C for 4 h. Then, their mechanical properties and morphological features were examined.

RESULTS

Digestion with elastase dose-dependently decreased the maximum shear stress and failure strain energy density of the periodontal ligament (p < 0.05-0.01). The histological observations after digestion revealed marked degradation of oxytalan fibers, but no marked changes of the collagen fibers, which was confirmed by the detection of very low quantities of hydroxyproline in the digest. The light and scanning electron micrographs showed that the elastase degraded the interfibrillar substances in the periodontal ligament and exposed individual collagen fibrils.

CONCLUSION

These results suggest that the increased neutrophil elastase observed in periodontal disease degrades the oxytalan fibers and interfibrillar substances in the periodontal ligament to decrease its mechanical strength.

Neutrophil elastase is involved in the initial destruction of human periodontal ligament

BACKGROUND AND OBJECTIVE

It has been reported that noncollagenous proteins may provide mechanical strength to the periodontal ligament. Several proteolytic activities, including that of neutrophil elastase, are reported to increase significantly in periodontal disease. The aim of this study was to investigate the function of neutrophil elastase in the initial destruction of periodontal ligament at early stages of periodontal disease.

MATERIAL AND METHODS

The detection and identification of proteinases in chronic periodontitis and healthy periodontal ligament were examined by zymographic and zymo-Western analysis. The morphological changes of periodontal ligament, digested with or without authentic proteinases, were observed using scanning electron microscopy.

RESULTS

Increases in neutrophil elastase, plasminogen, and matrix metalloproteinase-9 were detected in periodontal ligament from chronic periodontitis, compared with healthy periodontal ligament. Among these proteinases, only neutrophil elastase digested the intact noncollagenous proteins of periodontium. When human healthy periodontal ligament was directly digested by neutrophil elastase in an in vitro system, the morphological features were quite similar to that of the periodontal ligament in chronic periodontitis . In healthy periodontal ligament, the collagen fibrils are covered with noncollagenous proteins containing 110 kDa acidic glycoprotein, which was degraded initially by the neutrophil elastase.

CONCLUSION

It was concluded that neutrophil elastase is involved in the degradation of noncollagenous protein-covered collagen fibrils in the early destructive stages of periodontal disease.

Site-specific variations in the biochemical composition of healthy sheep periodontium

A topographical biochemical analysis of the periodontal soft tissues was carried out. The protein distribution in the tooth-supporting structures was determined from site by amino acid analysis and was compared with the collagen distribution in tissue protein, based upon hydroxyproline content. The biochemical composition of the periodontal ligament was heterogeneous but some specific patterns of protein and collagen distribution emerged. Protein concentration was highest at the gingival epithelium and adjacent to the cementum. Collagen concentrations were highest at the alveolar bone and below the junctional epithelium adjacent to the tooth. Such patterns may influence the way in which periodontal disease is propagated through the tissue.

3H-mannose utilization by fibroblasts of the periodontal ligament

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.

Biochemistry of glycosaminoglycans in the skin and oral mucosa of the rat

Glycosaminoglycans (GAG) were extracted by digestion with papain followed by ultrafiltration and separated by cellulose-acetate electrophoresis and by chromatography of their cetyl-pyridinium complexes on cellulose microcolumns. The uronic-acid content of the tissues ranged from 0.8 to 2.4 mg/g of dry defatted tissue. Hyaluronic acid and dermatan sulphate were found in all tissues with chondroitin-4-sulphate also in skin, palatal mucosa and gingiva. There was 3-fold more hyaluronic acid in palatal mucosa than in any other tissue; it was concentrated in the antemolar rugae. A substance of presumptive salivary origin staining with alcian blue was found in cheek and floor of mouth mucosa. It migrated differently from reference GAG by electrophoresis and was not degraded by testicular hyaluronidase.

The autoradiographic utilization and distribution of [1-3H]-galactose by the dental tissues of ageing mice

The uptake, turnover and distribution of [1-3H]-galactose by periodontal tissues associated with maxillary first molars of mice 5, 26 and 78 weeks of age showed that galactose was utilized by all oral tissues studied throughout the life-span. Uptake and turnover of the tracer revealed pulsed events. Synchrony of the pulsed events was noted. With increasing age, diminished utilization of galactose was evident, as well as a change in peak-time of the curves characteristic of ageing. The complex plots represent several metabolic events occurring simultaneously. The uptake of galactose by fibrogenic, osteogenic and cementogenic cells was low. Matrical output, on the other hand, remained high. Cementogenic cell output was the highest of all the tissues over the 30-day period. Despite decreased physiological activity with age and superimposed age changes, galactose utilization remained high throughout the study.