Bovine periodontal ligament. An invesitation of the collagen, glycosaminoglycan and insoluble glycoprotein components at different stages of tissue development

Mechano-regulation of collagen biosynthesis in periodontal ligament

Periodontal ligament (PDL) plays critical roles in the development and maintenance of periodontium such as tooth eruption and dissipation of masticatory force. The mechanical properties of PDL are mainly derived from fibrillar type I collagen, the most abundant extracellular component. The biosynthesis of type I collagen is a long, complex process including a number of intra- and extracellular post-translational modifications. The final modification step is the formation of covalent intra- and intermolecular cross-links that provide collagen fibrils with stability and connectivity. It is now clear that collagen post-translational modifications are regulated by groups of specific enzymes and associated molecules in a tissue-specific manner; and these modifications appear to change in response to mechanical force. This review focuses on the effect of mechanical loading on collagen biosynthesis and fibrillogenesis in PDL with emphasis on the post-translational modifications of collagens, which is an important molecular aspect to understand in the field of prosthetic dentistry.

Polarized light microscopic analyses of collagen fibers in the rat incisor periodontal ligament in relation to areas, regions, and ages

We prepared decalcified sagittal sections (20 microm thick) from the incisal, middle, and basal regions of the mandibular incisor of male Wistar rats aged 2, 6, 12, and 24 months, and examined the sections using polarized light microscopy. Most of the birefringent fibers appeared to run obliquely across the periodontal ligament. Birefringent fibers running parallel to the long axis of the incisor were also found in the intermediate area of the ligament. Similar fiber architecture was observed in all four age groups. Quantitative analysis showed that the retardation values of collagen were higher in the bone- and tooth-related areas and lower in the intermediate area of the ligament. The values for the bone- and tooth-related areas increased from the basal toward the incisal regions in all four age groups. Age-related changes in the retardation values were found only in the incisal region of the incisor. In the incisal region, the values for the bone- and tooth-related areas increased markedly from 2-24 months of age, whereas those for the intermediate area increased slightly but significantly with age. Our findings indicate that the degrees of molecular organization and alignment of collagen fibers in the bone- and tooth-related areas of the ligament are higher than those in the intermediate area and increase near the incisal region and with age. It is also suggested that the collagen fibers in the intermediate area remain immature along the long axis of the incisor throughout the life span of the animal.

Mechanical characterization of bovine periodontal ligament

This study is part of a research program that aims to develop a constitutive three-dimensional model of the periodontal ligament (PDL) through the identification of pertinent material parameters. As part of this program, bovine PDL was utilized to establish stress-strain responses under tensile and compressive loading conditions. Fresh bovine molars were secured, frozen and prepared to appropriate dimensional specifications. Bar-shaped specimens that comprised portions of dentine, PDL and bone were produced. Push-pull tests were conducted using a specifically constructed loading machine. Full range monotonic stress-strain diagrams were generated. The effect of a rate increase on cyclic S-E diagrams was also determined. The influence of specimen thickness was expressed in terms of modulus of elasticity, strength, uniaxial maximizer strain, and strain energy density. The overall load-response was heavily hysteretic in compression. On the tensile side, after a steep rise, the curve tended to flatten out asymptotically. Variations in rate that spanned four orders of magnitude had no effect on reciprocal load responses. The E-modulus was in the 4-8 MPa range, the strength of the PDL was 1-2 MPa, the maximizer strain was at 45-60% and the strain energy density ranged between 0.3 and 0.4 MPa.

A mechanism of noncontinuous supraosseous tooth eruption

Numerous theories have been propounded to explain the various aspects of tooth eruption, but no general consensus exists about some of the underlying mechanisms that govern these aspects. An important unresolved issue is the source of the motive forces that displace teeth. We proposed that supraosseous eruptive forces are generated by tooth socket distortions caused by functional jaw deformations. Previous studies used basic equations of static equilibrium to demonstrate that the concomitant stretching of the oblique periodontal ligament (PDL) fibers give rise to forces that may cause supraosseous tooth eruption. For a more rigorous and expanded analysis, we applied the finite element method (FEM). Three functional loads were considered, but the FEM calculations strongly suggested that all jaw deformations contribute to tooth extrusion. It was also demonstrated that the PDL fiber disruptions that are likely to occur with increased stretching can provide a mechanism to stabilize the erupted position.

Biomechanical and morphological studies on the periodontal ligament of the rat molar after treatment with alpha-amylase in vitro

Biomechanical properties and morphological features of the rat molar periodontal ligament were examined after treatment with alpha-amylase. Treatment with alpha-amylase induced dose-dependent decreases in the maximum shear stress, tangent modulus, and failure strain-energy density of the periodontal ligament; in addition, it weakened the alcian-blue staining of the periodontal ligament and exposed periodontal collagen fibrils as revealed by scanning electron microscopy. Azan staining and polarized microscopic observations of the periodontal collagen fibers were not markedly different between the control and alpha-amylase treated specimens. These results suggest that decreases in the strength of the periodontal ligament due to alpha-amylase digestion are largely due to removal of interfibrillar substances such as acid glycosaminoglycans and neutral polysaccharides from the periodontal ligament. It is also suggested that the interaction of the interfibrillar substances with collagen fibrils is involved the biomechanical properties of the periodontal ligament.

The structure of bovine periodontal ligament with special reference to the epithelial cell rests

The aim of this study was to determine the structure of the bovine periodontal ligament, with special reference to epithelial cell rests (ECR) and their cytokeratin content. Periodontal ligament was obtained from bovine molar teeth and studied at both the light microscopic and electron microscopic levels. Cytokeratin content was determined using immunohistochemistry against a number of cytokeratin antibodies and specificity tested against bovine and human oral mucosa. Collagen fibril diameters and the area of a fiber bundle occupied by collagen were determined using a digital planimeter with a digitizing tablet. The majority of periodontal fibroblasts possessed considerable quantities of roughened endoplasmic reticulum, indicating rapid synthesis and secretion of collagen, but no intracellular collagen profiles were present. Endothelial cells showed Weibel-Palade bodies. Collagen fibril diameters showed a unimodal distribution with a mean collagen fibril diameter of 55.3 nm. The mean percentage area of the extracellular matrix occupied by collagen was 42%. Structurally, ECR were unusual in exhibiting large numbers of microvilli and conspicuous amounts of cytokeratin filaments. Bovine ECR showed a positive reaction to the pancytokeratin MNF116 (which reacts with the cytokeratins 5, 6, 8, 17, and probably 19), to PCK-26 (which reacts with the type II cytokeratins 1, 5, 6, and 8) and to cytokeratin 13. There was no reaction for cytokeratins 1, 4, 10, 11 and 18. Structurally, bovine periodontal ligament showed features common to other species. However, ECR in terms of both structure and cytokeratin content showed features indicative of important species differences which may have relevance when considering the etiology of radicular cysts.

The effect of glycosylaminoglycans on the mineralization of sheep periodontal ligament in vitro

The effect of removal of glycosylaminoglycans on the mineralization of sheep periodontal ligament was determined using enzyme digests followed by incubation in solutions supersaturated with respect to hydroxyapatite at pH 7.4. TEM revealed that control periodontal ligament remained unmineralized. However, tissue from which glycosylaminoglycans had been removed contained plate-like crystals arranged parallel to and within the collagen fibrils. Electron probe and electron diffraction studies suggested that the crystals were apatitic with a similar order of crystallinity to dentine, and a Ca:P ratio of 1.61. In addition, the glycosylaminoglycan content of periodontal ligament, cementum and alveolar bone was compared using cellulose acetate electrophoresis. Periodontal ligament contained predominantly dermatan sulfate while cementum and alveolar bone contained mostly chondroitin sulfate. A role for glycosylaminoglycans in maintaining the unmineralized state of the periodontal ligament is suggested. Control of expression of specific proteoglycan species on a spatially restricted basis is presumably central to this role.

The effects of orthodontic tooth movement on the glycosaminoglycan components of gingival crevicular fluid

In this study, gingival crevicular fluid (GCF) was collected from around a canine tooth, in children, before and during orthodontic tooth movement. The aim was to identify and quantify the glycosaminoglycan (GAG) components of GCF and relate them to tooth movement, gingival inflammation, plaque accumulation, pocket probing depth and GCF volume recorded at the site of sampling. GAG in GCF samples, collected for a 15-min period into microcapillary tubes, were separated electrophoretically, stained with Alcian blue and quantified using a laser densitometer. 2 GAG components of hyaluronic acid (HA) and chondroitin sulphate (CS) were identified. The increase in GCF volume during orthodontic tooth movement was only partly due to increased gingival inflammation. GAG levels varied with different types of orthodontic tooth movement. In GCF, levels of CS, in particular, may reflect the changes in the deeper periodontal tissues which could be monitored during orthodontic tooth movements.

Current concepts of the biology of tooth eruption

Tooth eruption is defined as the movement of a tooth from its site of development within the jaws to its position of function within the oral cavity. We present a critical review of evidence for the mechanisms and regulation of the intraosseous and supraosseous phases of eruption, with an emphasis upon the canine premolar model studied by the authors. Analyses at different stages of premolar eruption indicate that selective fragmentation of dental follicle protein DF-95 correlates with the presence of elevated levels of follicular collagenase and stromelysin, and with the onset of premolar movement. A dramatic decrease in these metalloproteinases followed initiation of movement. A biochemical and cell biological model for regulation of tooth eruption is proposed based upon these new and existing data.

Measurement of the force required to extract the mandibular first molar from its socket in the dissected jaw of growing young rats

Age-related changes in the mechanical strength of the periodontal ligament have been examined by measuring the force required to extract the mandibular first molar from its socket at an extension rate of 5 mm/min in the dissected jaws of growing young rats from 3 to 32 weeks of age. Almost linear increase in the ultimate loads was found from 3 to 8 weeks of age. However the values from 8 to 32 weeks of age did not show any significant differences. Close correlations were found between the ultimate loads and the weights of animals, mandibles and extracted teeth and between the load and length of the tooth from 3 to 8 weeks of age. It is supposed that a mechanical equilibrium has been established within the periodontal ligament in association with various external and internal factors such as root elongation, alveolar bone growth, turnover and maturation of periodontal ligament and occlusal activity, at about 8 weeks of age in the rat mandibular first molar.

Collagen remodelling in rat periodontal tissues: compensation for precursor reutilization confirms rapid turnover of collagen

Measurement of collagen turnover is complicated by the reutilization of isotopic precursors used to label the collagen. In an earlier study a novel approach was used to circumvent the problems of precursor recycling and unusually short half-lives were determined for collagen in adult rat periodontal tissues (Sodek, 1977). To verify these results we have used an alternate procedure devised by Poole (1971) in which the decay profile for the radiolabelled protein is corrected in accordance with the decay of the radiolabelled precursor. In this manner real half-lives for mature, neutral salt-insoluble collagen were determined as 3 days in the molar periodontal ligament, 6 days in the continuously erupting incisor ligament and approximately 10 days in the lamina propria of the gingiva, compared to apparent half-lives for these tissues of 6, 12 and approximately 20 days, respectively. The values calculated for actual half-lives are, therefore, approximately two-fold faster than values determined without compensating for reutilization, a difference that is in agreement with other protein turnover studies in which the effects of precursor reutilization have been measured. Although the real half-lives determined in this study indicate turnover rates for the periodontal tissues that are slightly slower than reported previously, the relative differences between the tissues in the rates of collagen turnover are similar. Moreover, the study confirms the existence of a remarkably high rate of collagen remodelling in these tissues.

Mechanisms of tooth eruption in a computer-generated analysis of functional jaw deformations in man

Two mechanisms that contribute to tooth eruption are proposed from analysis of the human jaws as elastic structures which are deformed intermittently under functional occlusal loads. One possible source of eruptive force is the transient pressure gradient established within each jaw as it is deformed. The second source, suggested by the computer model, is a consequence of the tension placed on periodontal-ligament fibres as individual tooth-sockets are distorted within the deformed jaws.

Intermolecular cross-linking and stereospecific molecular packing in type I collagen fibrils of the periodontal ligament

A trypsin digest of denatured NaB3H4-reduced native bovine periodontal ligament was prepared and fractionated by gel filtration and cellulose ion-exchange column chromatography. Prior to trypsin digestion, a complete acid hydrolysate was subjected to analyses for nonreducible stable and reducible intermolecular cross-links. Minute amounts of the former and significant amounts of the reduced cross-links dihydroxylysinonorleucine (1.1 mol/mol of collagen), hydroxylysinonorleucine (0.9 mol/mol of collagen), and histidinohydroxymerodesmosine (0.6 mol/mol of collagen) were found. The covalent intermolecular cross-linked two-chained peptides that were isolated were subjected to amino acid and sequence analyses. The structures for the different two-chained linked peptides were alpha 1CB4-5(76-90)[Hyl-87] X alpha 1CB6-(993-22c)[Lysald-16c], alpha 1CB4-5(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Hylald-16c], alpha 2CB4(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Lysald-16c], and alpha 2CB4(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Hylald-16c]. The cross-link in each peptide was glycosylated. This is the first characterization by sequence analysis of a cross-link involving Hyl-87 in an alpha 2 chain in collagen. A stoichiometric conversion of residue 16c aldehyde to an intermolecular cross-link in each of the COOH-terminal nonhelical peptide regions of both alpha 1 chains in a molecule of type I collagen was found. The ratio of alpha 1 to alpha 2 intermolecularly cross-linked chains involved was 3.3:1, indicating a stereospecific three-dimensional molecular packing of type I collagen molecules in bovine periodontal ligament.

Synthesis and secretion of sulphated glycosaminoglycans by bovine peridontal ligament fibroblast cultures

The cultures were allowed to incorporate 35SO2-4 for various periods of time. 35S-labelled macromolecules were isolated from the medium, a trypsin digest of the cells and the cell residue. Ion-exchange chromatography separated the radioactive polysaccharides into heparan sulphate and a galactosaminoglycan population. Most heparan sulphate was in the trypsin digest and cell residue fractions. The galactosaminoglycan fractions were investigated by differential degradations with chondroitinase ABC and AC and ethanol fractionation. The medium galactosaminoglycans contained both glucuronic and iduronic acid residues and existed in copolymeric structures as chondroitin sulphate/dermatan sulphate hybrid molecules. Dermatan sulphate was also detected. In contrast, the trypsin-digest fraction contained mainly chondroitin sulphate-like molecules.

Effects of cells of epithelial rests of Malassez and endothelial cells on synthesis of glycosaminoglycans by periodontal ligament fibroblasts in vitro

Cultures of fibroblast-like cells (PLF) and epithelial rest cells (PLE) prepared from explants of porcine periodontal ligament synthesized and secreted four glycosaminoglycans (GAG) in differing proportions. The PLF produced predominantly chondroitin sulfate (greater than 60%) with smaller amounts of hyaluronic acid (HA) (17%), dermatan sulfate (13%), and heparan sulfate (7%), whereas PLE produced predominantly HA (greater than 80%). In coculture and under conditions of reciprocal transfer of conditioned media neither cell type affected the other's GAG synthesis. Endothelial cells (EC), however, or their conditioned growth media, were able to stimulate increased GAG synthesis, especially HA, in PLF. A similar result was obtained with smooth muscles cells (SMC) cultured in EC growth media but here again PLE were unable to stimulate GAG synthesis by SMC. These findings suggest that the spectrum of GAG found in whole ligament results both from independent production by, and from interaction between, the different cell types within the ligament. The results also provide support for a general hypothesis that loose connective tissues, which are rich in HA, are formed and maintained under the influence of epithelial, including endothelial, cells.

Age-related changes in reducible crosslinks of human dental pulp collagen

Coronal pulp of human third molars from patients ranging in age from 16 to 40 yr was analysed for collagen, protein, calcium and reducible crosslink content. Dihydroxylsinonorleucine (DHLNL) was the major crosslink; it decreased with age. Hydroxylsinonorleucine (HLNL) and lysinonorleucine (LNL) appeared in insignificant amounts. Calcium content increased with age. Based on the premise that collagen synthesis is characterized by the presence of reducible crosslinks, the study showed that coronal pulp collagen synthesis decreases with age; this is accompanied by a decrease in collagen concentration in terms of dry weight and total protein between 16 and 30 hr of age.

Transplantation of enzyme-treated teeth in the monkey Macaca fascicularis

Homologous tooth transplants evoke immunogenic rejection against antigens within donor periodontal ligaments cells and ground substance. Eight maxillary incisors of 6 juvenile animals were extracted, crowns and pulps removed by gutta percha; the roots were incubated serially in enzyme solutions and glutaraldehyde at 37 degrees C for 5 h to destroy cells, glycoproteins and proteoglycans. Seven control teeth from the same 6 animals were incubated in saline at 37 degrees C for 15 min. All teeth were then speedily transplanted to other animals which were killed at 6 wk or 3 months. Radiographs and histologic sections revealed extensive resorption and inflammation of all control teeth. Enzyme-treated teeth showed less inflammation with resorption mostly on the surface of the cut coronal dentine. A loose fibrous attachment usually formed on most aspects of the root surface with deposition of new cellular cementum within the donor ligament. Inflammation, where present, may have resulted from incomplete removal of periodontal ligament cells, ground substance, or from salivary bacterial contamination.

Proteoglycans of bovine periodontal ligament and skin. Occurrence of different hybrid-sulphated galactosaminoglycans in distinct proteoglycans

A proteoglycan purified from 4 M-guanidinium chloride extracts of bovine periodontal ligament closely resembled that of bovine skin, except for a rather lower protein content and a higher molecular weight (120 000 compared with about 90 000) by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The latter difference was explained by the molecular weights (29 000 and 16 000) of the respective dermatan sulphate components, each of which was rich in L-iduronate (about 75% of the total hexuronate). Significant amounts of other glycosaminoglycans did not occur in these proteoglycans, which were homogenous on gel chromatography and agarose/polyacrylamide-gel electrophoresis. Polydispersity was observed in sedimentation equilibrium experiments, but proteolysis or self-association of the proteodermatan sulphates may have affected these results. Ligament proteoglycans that were almost completely extracted with 0.1 M-NaCl contained less protein of a completely different amino acid composition than the proteodermatan sulphates. They were heterogeneous in size but generally smaller than cartilage proteoglycans and L-iduronate was a component, comprising about 7% of the total hexuronate of the sulphated galactosaminoglycan chains. The latter consisted of two fractions differing in molecular weight, but a dermatan sulphate with a high L-iduronate content was not present. These proteoglycans had some resemblance to D-glucuronate-rich proteoglycans of other non-cartilaginous tissues. Such compounds, however, are difficult to categorize at present.

Sulfated galactosaminoglycans of bovine periodontal ligament. Evidence for the presence of two major types of hybrids but no chondroitin sulfate

Sulfated galactosaminoglycans of mature bovine periodontal ligament were separated into four fractions by ethanol precipitation. Fractions I and II were dermatan sulfates with high contents of L-iduronate, but only small amounts of this hexuronic acid were present in fractions III and IV. Effects of digestion with testicular hyaluronidase or a periodate-alkali treatment showed that most if not all of the glycans in fractions I, II and III were hybrid chains containing both L-iduronate and D-glucuronate. The composition of fraction IV was less certain, but the chains strongly resembled fraction III hybrids in electrophoretic characteristics, not chondroitin sulfate. The total amount of the D-glucuronate-rich fractions III and IV in the ligament was similar to that of I plus II. In contrast, almost all of the sulfated galactosaminoglycans of mature skin were rich in L-iduronate. The more varied composition of the ligament glycosaminoglycans may be related to the mixed population of cells in this tissue.

Crosslink analysis as an indicator of collagen turnover in periodontal ligament from functioning and non-functioning teeth in the dog

The assay of transiently-occurring reducible collagen crosslinks was used as an indication of collagen turnover in the periodontium from individual teeth. A tooth was removed on one side of the jaw to relieve the antagonist tooth of all occlusal forces. This did not influence the very high rate of collagen turnover observed in periodontal ligaments. It is concluded that this high rate of turnover is an intrinsic property of the tissue and is uninfluenced by occlusal or eruptive forces.

Leaching of glycosaminoglycan from cow uterus and vagina into fixative solution

Samples from the genital tract of two cows in metoestrus and two in dioestrus were fixed with formalin-cetyltrimethylammonium bromide and the amount of glycosaminoglycan leached into this histological fixative was estimated using an Alcian Blue method. Uronic acid content was estimated by a carbazole method. Total glycosaminoglycan was estimated after digestion with papain. No more than 10% of the glycosaminoglycan was soluble in the fixative and in comsequence 90% is potentially stainable by Alcian Blue in tissue sections. Total glycosaminoglycan in uterus and vagina is higher in metoestrus than in dioestrus. Estimation of uronic acid in the leached material confirmed the results and indicated that little of it consisted of mucin or keratan sulphate.

The determination of small amounts of collagen hydroxylysyl glycosides

Glucosylgalactosylhydroxylysine (GlcGalHyl) and galactosylhydroxylysine (GalHyl) in alkaline hydrolysates of insoluble collagens were separated on 130 x 0.6 cm and 45 x 0.6 cm columns of Chromobeads A resin (Technicon) and simultaneous analyses with ninhydrin and orcinol-H2SO4 were performed. Ninhydrin, which is the standard reagent in existing methods, gave erroneously high results with both columns due to overlapping, resistant peptides. A rapid and more accurate procedure employing the smaller column, the orcinol-H2SO4 reagent and a new internal standard was developed. The losses of the glycosides in alkaline hydrolysis, especially in the presence of collagen peptides, were much larger than had been reported previously. A shorter alkaline hydrolysis following digestion of the collagen with papain was effective and allowed more reliable corrections to be made. Purging with nitrogen reduced the losses further. Mature bovine skin collagen contained less GlcGalHyl than embryonic skin collagen whereas the differences in GalHyl were insignificant.