Effects of fixation and demineralization on the intensity of autoradiographic labelling over the periodontal ligiment of the mouse incisor after administration of [3H]-proline

Synthesis of alveolar bone Sharpey's fibers during experimental tooth movement in the rat

There is little information concerning the effects of tooth movement on the relative synthesis of bone matrix and Sharpey's fiber collagenous proteins. The purpose of this study was to investigate this situation using radioautographic techniques. The maxillary first molar tooth in rats was tipped toward the midline using an appliance and the animals were injected with 3H-proline after 3 days and sacrificed 24 hr later. Maxillae were sectioned and silver grain proportional areas (grain density/5,000 microm2) evaluated over Sharpey's fibers and adjacent alveolar bone matrix using computerized densitometry and histomorphometric techniques. These data were compared to a group of untreated animals by Fisher's exact test. At depository surfaces of experimental tissues, the silver grain proportional area over bone matrix was significantly greater than over Sharpey's fibers (P<0.05) and control bone matrix (P<0.01). The silver grain proportional area over Sharpey's fibers was not different between the groups. At resorptive surfaces, the silver grain proportional area over both bone matrix and Sharpey's fibers was significantly greater in experimental tissues compared to controls (P<0.01). Thus, movements of adjacent teeth affect both the quantity and ratios of collagenous protein incorporation into Sharpey's fibers and adjacent alveolar bone, which is dependent on the intensity and characteristics of the force.

Regional differences in molecular cross-linking of periodontal ligament collagen of rat incisor, by polarizing microscopy

Collagen, a naturally birefringent biopolymer and key structural component of the periodontal ligament (PDL), is altered substantially with regard to its molecular cross-linked structure by the dietary lathyrogen, beta-amino-proprionitrile (beta-APN). Our purpose in studying beta-APN-fed animals was to learn if the strength of birefringence of periodontal collagen, measured microscopically by the Senarmont compensator method, correlates with the molecular changes known to occur in these lathyritic animals, and to explore this technique for the periodontal ligament. Five experimental animals were fed a diet containing 0.25% beta-APN for two weeks, and 3 control animals were fed normal rat chow. Tissues were decalcified and the mandibular incisors were cut in cross section at 4 microns and stained with eosin Y. The Senarmont compensator, an attachment for the polarizing microscope, was used to measure phase retardation. Ten measurements were taken from each of the three sides (mesial, lateral and lingual) of the triangularly shaped incisor sections. The collagen fibers of the beta-APN-fed rats had lower values of phase retardation than the controls (p < 0.001), indicating reduced molecular organization. In addition, minor but significant regional differences were revealed, supporting the method for structural studies on the periodontal collagen.

The effect of vinblastine on the incorporation of [3H]-glycine into proteins of the periodontal ligament of impeded and unimpeded mouse incisors

The effect of vinblastine on the protein metabolism of the periodontal ligament of impeded and unimpeded mouse incisors was studied by [3H]-glycine labelling and radioautography. The silver-grain concentration was determined in areas adjacent to the tooth, areas adjacent to bone and, as an internal control, in the dentine matrix. From 1 to 12 h there was no difference between treated and control animals; thus the drug did not alter protein biosynthesis. Later, the silver-grain concentration was significantly higher in areas adjacent to both bone and tooth in vinblastine-treated animals, suggesting a longer half-life of the labelled proteins. No significant differences between normal or unimpeded erupting incisors of both groups were detected. Dentine matrix showed a possibly higher re-utilization of the labelled amino acid in vinblastine-treated animals. The amount of labelled protein removed by collagenase was similar in both groups, while the concentration of grains due to collagenase-resistant proteins was significantly higher in treated animals, particularly at 96 h after the injection of labelled glycine. The relation between the increased amount of non-collagenous proteins in the periodontal ligament and the decrease in the rate of eruption caused by vinblastine was not established. However, among these proteins, fibronectin and proteoglycans are thought to be important factors in tooth eruption.

Distribution of 3H-proline within transseptal fibers of the rat following release of orthodontic forces

Maxillary right first molar teeth of rats were tipped mesially with an orthodontic appliance for 2 weeks (experimental group), 3H-proline was injected, and orthodontic forces were removed 6 hr later (time 0). The contralateral molar teeth of treated (internal control group) and age- and weight-matched untreated animals (external control group) were also studied. Diastemata were created between the molar teeth by the orthodontic appliance, and transseptal fibers between first and second (P less than 0.001) and second and third molars (P less than 0.005) were significantly lengthened as compared to external and internal controls at time 0. Diastemata between molar teeth were closed 5 days after removal of orthodontic force. Transseptal fibers adjacent to the source of the orthodontic force (mesial region) had the highest mean number of 3H-proline-labeled proteins at time 0 and at all times following removal of the force (P less than 0.001), and had the highest rate of labeled protein removal (P less than 0.001). Half-lives for removal of 3H-proline-labeled transseptal fiber proteins were significantly greater in mesial and distal regions and significantly less in middle regions of experimentals than in corresponding regions of external controls (P less than 0.001). These data suggest the following: 1) transseptal fibers adjust their length by rapid remodeling in regions experiencing a tensile force; 2) collagenous protein turnover within the middle third of the transseptal fibers is more rapid subsequent to release of orthodontic force than during normal physiologic drift, suggesting that this region adapts rapidly to changes in adjacent tooth position and that these fibers do not play a significant role in relapse of orthodontically relocated teeth; and 3) significant differences in turnover rates of 3H-proline-labeled transseptal ligament proteins of external and internal control quadrants suggest that tooth movement produces both local and systemic effects on collagenous protein metabolism.

Effect of altered occlusal function on transseptal ligament and new bone thicknesses in the periodontium of the rat

Alteration of tooth function is assumed to change stress/strain on the adjacent alveolar bone and its mucoperiosteum, producing changes in morphology similar to those described for other load-bearing bones. The present study suggested that crestal alveolar bone and its mucoperiosteum respond differently to stress/strain than load-bearing bones in other locations, possibly due to differences in the mechanism of bone loading by muscles and teeth. Occlusal hypofunction was initiated by extraction of agonist teeth; the contralateral teeth were placed in hyperfunction by the surgery. Untreated animals were also studied. 3H-proline was injected, animals were killed 1-5 weeks later, and the thicknesses of new bone and transseptal ligament were measured. After 5 weeks of altered function, total thickness (new bone + transseptal ligament) was similar in untreated and in hypofunctional and hyperfunctional situations; however, a new ratio between transseptal ligament and new bone thicknesses was established. Occlusal force was negatively correlated with new bone and positively correlated with transseptal ligament thickness; both thicknesses were statistically correlated in each functional situation (P less than 0.001). Hyperfunction resulted in increased transseptal ligament thickness, but decreased new bone thickness as compared to untreated controls (P less than 0.001). In contrast, hypofunction resulted in an increased new bone thickness, but a decreased transseptal ligament thickness (P less than 0.001). Tissue responses assure appropriate support for the teeth in each functional situation.

Effects of hypofunction on the distribution of 3H-proline in the transseptal fibers of the periodontium of the rat

There is little information concerning the effect of altered occlusal forces on the turnover of collagenous proteins of transseptal fibers of the periodontium. In the present study, hypofunction was induced in rats by extraction of the maxillary teeth, allowing the mandibular teeth to supererupt (hypofunctional side, herein). The contralateral side served as an internal control, although it was likely experiencing occlusal hyperfunction (hyperfunctional side, herein). Untreated animals were also studied (external controls, herein). Animals were injected with 3H-proline and silver grains were counted on radioautographic preparations. The study demonstrated significant differences in the synthesis and degradation of collagenous proteins coincident to altered occlusal function; 3H-proline was most heavily incorporated into the transseptal fibers of hyperfunctional and least rapidly into the external control tissues (P less than .001). Significant differences in grain counts were evident during the first 3 weeks after injections. Collagenous proteins were degraded most rapidly in transseptal fibers of the hyperfunctional and least rapidly in hypofunctional tissues (P less than .001). The study also demonstrated regional variability in the turnover of labeled collagenous proteins, that is, proteins were synthesized and degraded most rapidly in the middle third and least rapidly in the mesial third of the ligament (P less than .001). "Whole" counts (mean of counts over middle, mesial, and distal thirds) were not similar to those of any specific region and could provide erroneous information concerning remodeling of collagenous proteins of transseptal fibers. Transseptal fibers, labeled by the 3H-proline pulse, migrated occlusally with the teeth; new transseptal fibers and bone were formed at the crest of the interdental septum.

The distribution of 3H-proline in alveolar bone of the mouse as seen by radioautography

Previous studies of the turnover of alveolar bone collagenous proteins have devoted little attention to the variable patterns in this process caused by bone remodeling. The present study seeks to document changes resulting from physiologic tooth movements in the incorporation and removal of the 3H-proline label within the interdental septum of alveolar bone. One week following 3H-proline injection, three zones could be distinguished: the appositional band, new bone, and old bone. Radioautography demonstrated that formation of new bone on the distal wall of the septum entrapped fibers of the periodontal ligament to create Sharpey's fibers. At the alveolar crest, new bone entrapped transseptal fibers to form transalveolar Sharpey's fibers. Grain counts were made within each area and over the total septum and were compared statistically. The data strongly suggested regional variations in protein remodeling. Counts from old and new bone were significantly different from the total septum or the appositional band (P less than .001). Regression lines were drawn to represent incorporation and removal of the isotope; slopes were calculated and compared statistically. The rate of incorporation and removal was significantly greater in the appositional band and in the total septum in comparison to old bone (P less than .001). The rates of incorporation and removal in the appositional band, old bone, and total septum were significantly different (P less than .001). Half-life of the labeled protein of old bone was 16.78 weeks; in the appositional band, 7.66 weeks; and in the total septum, 7.64 weeks. These data suggest that regional variations in collagen remodeling must be considered in a study of interdental bone and that the total septal grain counts are not indicative of the remodeling in the component zones.

Autoradiography of protein turnover in subcrestal versus supracrestal fibre tracts of the developing mouse periodontium

Eighteen-day-old C57Bl mice were injected with 5 muCi/g body weight [3H]-proline and killed at intervals of 4 h to 7 wk later. Grain counts in three fibre tracts revealed that (1) half-lives of labelled protein in the developing periodontium were much shorter than those found previously for the mature periodontium , and (2) the half-life of labelled protein in the dento-gingival region was longer than the half-lives in the trans-septal and dento-alveolar fibre tracts (half-lives: dento-alveolar = 2.5 days, trans-septal = 3.8 days; dento-gingival = 7.9 days). Eight mice were given injections of [3H]-proline on days 11, 13, 15 and 17, which encompasses the formation of the three fibre tracts, and killed 4 h, 2.5, 5 and 8 wk after the last injection. All label incorporated during the formation of the periodontium had been lost by 5 wk post-injection, showing that a stable core fibre (i.e. one which is not metabolized) was not present.

The site of remodeling of collagen in the periodontal ligament of the mouse incisor

In an attempt to localize the site of remodelling of collagen in the periodontal ligament of the continuously erupting mouse incisor a radioautographic and stereologic investigation was undertaken. Grain distributions in radioautographs for light microscopy were studied at various time intervals after administration of [3H]-proline. The distribution of rough endoplasmic reticulum cisternae in fibroblasts and the incidence of collagen phagocytosis across the ligament were studied by means of stereologic methods at the electron microscopic level. No significant differences were found in half lives of [3H]-labelled substances among the various regions across the ligament. Rough endoplasmic reticulum cisternae within fibroblasts were distributed more or less uniformly throughout the entire width of the ligament. Analysis of the distribution of collagen phagocytosis, however, revealed that in the midregion of the ligament the amount of phagocytosed collagen was approximately four times as high as in the area adjacent to the tooth and about nine times as high as in the alveolar compartment. It is concluded that synthesis and turnover of total protein occurs throughout the periodontal ligament but that remodelling of collagen predominantly takes place in an intermediate area of the ligament.