The structure of the periodontal ligament: an update.
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Collagen↗
Biomedical subjects
B K Berkovitz
Publications and source records attributed to B K Berkovitz.
How teeth erupt.
The cause of delayed eruption is usually obvious and treatable (as with lack of space or impeding supernumerary teeth). However, in some cases there is no obvious cause. Treatment of these cases might be easier if we fully understood the mechanism of eruption itself. Unfortunately, the precise process of generating the eruptive force for teeth has not yet been fully elucidated. Various hypotheses have been put forward. In this article the author reviews current theories, and describes some of the experimental difficulties in testing them.
Humans↗
The development of the periodontal ligament with special reference to collagen fibre ontogeny.
The development of the periodontal ligament was investigated from serial sections of the mandibles of ferrets ranging in age from 42 days to 66 days post partum. Both succedaneous and non-succedaneous teeth were studied and similarities were seen in both types of tooth. No significant amounts of alveolar bone were observed being deposited beneath the erupting root apices and periodontal collagen fibres were seen attached to the walls of the sockets just prior to emergence of the crown into the oral cavity. Compared with the condition a few days after eruption, the collagen fibres on, and just prior to, emergence were thinner, had a more limited area of attachment, and were more randomly orientated. The results indicate that alveolar bone deposition and collagen traction do not generate the eruptive force and that there are species differences in these structural features during the eruptive process.
Aging↗
Effects of inflammatory periodontal disease ('broken mouth') on the mobility of the sheep incisor.
Loads directed linguolabially and between 0.01 N and 0.2 N were applied to a mandibular central incisor in each of 12 four-year-old ewes with evidence of inflammatory periodontal disease ('broken mouth'). For every incisor, tooth position was monitored continuously with an ultrasonic displacement transducer. Each load chosen was suddenly applied and then maintained for five minutes, producing a biphasic, viscoelastic-like response (a phase of rapid displacement being followed by a more gradual phase of creep). A similar biphasic recovery response was seen on suddenly removing the load. Comparing the findings with those obtained in a previous study for incisors in healthy dentitions, there was a considerable increase in mobility with inflammatory periodontal disease. Surprisingly, however, the patterns of the responses did not differ. The reason for the change in the amount of mobility may be related simply to the quantity of the tooth supporting tissues which is lost, although there is some evidence that qualitative changes occurring in these tissues may also be important.
Animals↗
A comparison of the biomechanical properties of the periodontal ligaments of erupting and erupted teeth of non-continuous growth (ferret mandibular canines).
Extrusive loads of 0.01-0.2 N were applied to the permanent mandibular canine teeth of two groups of ferrets. In one group, aged approx. 7 weeks, the tooth had only recently emerged into the mouth. In the second group, comprising adult animals, the tooth had fully erupted and had been in function for a considerable time. Biphasic, viscoelastic-like responses followed both the application and removal of the load in both groups. However, there was significantly more mobility for all phases of the loading and recovery cycles in the erupting teeth. The data were compared with previous findings for continuously growing teeth. They highlight the marked periodontal changes which take place when tooth erupts into the mouth, provide some evidence against the generation of a tractional eruptive force, and show some differences in response between teeth of limited or continuous growth.
Animals↗
Effects of inflammatory periodontal disease ('broken mouth') on the ultrastructure of collagen fibrils in the sheep incisor periodontium.
The ultrastructure of the matrix of the sheep central incisor periodontium showing clinical signs of severe periodontitis was analysed quantitatively. The distribution of collagen fibril diameters in the lower dental pad changed from a bimodal distribution seen in healthy periodontia to a unimodal distribution. Collagen fibrils with an abnormal morphology were seen in the connective tissue adjacent to the crest of the alveolar bone. These results suggest that the deepening periodontal pocket resulting from inflammation removes the major area of support for the tooth and abnormal loads are applied to fibres deeper within the tissue.
Animals↗
Continuous monitoring of the movements of erupting and newly erupted teeth of limited growth (ferret mandibular canines) and their responses to hexamethonium.
The rates of these eruption-like movements were high and were consistent with reports that eruption is fastest at the time of emergence into the mouth. Once the tooth had attained its initial functional position, there was a significant reduction in the rates. Following administration of the hypotensive agent, hexamethonium, the emerging tooth showed a significant decrease in eruption rates. However, no change was observed for the tooth which had attained its initial functional position. These findings support the view that there are physiological differences at the eruptive and initial functional stages of eruption. The effects of hexamethonium on the erupting ferret canine differ from those reported for the erupting rabbit incisor. This may reflect differences in the eruptive processes for teeth of limited and continuous growth, although other evidence suggests similarities between these.
Animals↗
A quantitative ultrastructural study of the extracellular matrix of the sheep incisor periodontium.
The ultrastructure of the matrix of the sheep central incisor periodontium was quantitatively analysed. Ewes with healthy mouths were selected. The distribution of collagen fibril diameters was bimodal in the lower dental pad with a population standard deviation significantly larger than the unimodal distribution of fibril diameters found in the periodontal ligament. The lower dental pad connective tissue also contained significantly more oxytalan fibres, some of which resembled mature elastin. These results are consistent with the view that the sheep central incisor is supported primarily by tension within the fibres of the lower dental pad.
Animals↗
Fenestrated capillaries in the periodontal ligaments of the erupting and erupted rat molar.
Quantitative ultrastructural studies were conducted on eight rats (four aged 21 days and four aged 8 weeks) using the periodontal tissues around the mesial root of the mandibular first molar. The periodontal ligament of the erupting tooth contained significantly more capillary fenestrations than the erupted tooth, both in terms of the number per unit area of endothelium (2.2/microns2) and in terms of total number per cubic millimetre of tissue (30.5 X 10(6)/mm3). Differences were also discerned with respect to the percentage of capillaries in the tissue. Thus, the periodontal vasculature demonstrates marked morphological changes which may be related to the eruptive phase of the tooth.
Animals↗
A laboratory method for studying tooth mobility of the mandibular central incisor of the sheep.
Linguolabially directed loads of 0.01 to 1.0 N were applied to a mandibular central incisor in each of 12 four-year-old ewes with healthy mouths. For each incisor, tooth position was monitored continuously with an ultrasonic displacement transducer. On suddenly applying a load and maintaining it for five minutes, a biphasic pattern of displacement was recorded, a phase of rapid displacement being followed by a more gradual one. A similar biphasic recovery response was seen on suddenly removing the load. These patterns are viscoelastic-like. The group mean displacements showed that for all phases the responses were force-dependent, though not linearly graded. For a given load, the group mean displacements were considerably larger than those reported previously for the teeth of other animals, supporting the impression that the sheep incisor is extremely mobile. These data will provide a baseline for studies on the mobility of the teeth of sheep with inflammatory periodontal disease ('broken mouth').
Animals↗
Computer-controlled force transducer and ultrasonic displacement transducer to continuously record movement of a tooth during loading.
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Humans↗
The effects of preventing movement of the rat incisor on the structure of its periodontal ligament.
A quantitative, ultrastructural study was made on the periodontal ligaments of rat mandibular incisors immobilized for 18 days. Fibroblasts and their organelles (i.e. endoplasmic reticulum, mitochondria, microtubules, microfilament bundles, lysosomes, intracellular collagen profiles and intercellular contacts), oxytalan fibres, collagen fibrils and ground substance were quantified. There was re-orientation of tissue at the lateral borders of the ligament and an apparent increase in size of epithelial cell rests. Within the matrix, the mean collagen-fibril diameter decreased and the amount of ground substance increased. No change occurred in oxytalan fibres. Within the cells, effects were seen only in cell contacts and in the relative volume of intracellular collagen, lending no support to the view that fibroblast activity generates the force responsible for tooth eruption.
Animals↗
Fenestrated capillaries in the connective tissues of the periodontal ligament.
A quantitative ultrastructural study was undertaken to assess the number and distribution of fenestrated capillaries in the periodontal ligaments of the rat dentition. Experiments were conducted on four animals using the right mandibular incisors and first molars. For the incisor, analysis was performed in three sites along the length of the periodontal ligament. Regardless of site, there was 0.1 fenestration per micron2 of endothelium. In the basal region, the incisor periodontal ligament contained 3.5 X 10(6) fenestrations per mm3 of tissue whereas more occlusally it contained 1 X 10(6) fenestrations per mm3 of tissue. For the molar, the capillaries showed more fenestrations, 0.4 fenestration per micron2 of endothelium. There were also more per unit volume of tissue, 12 X 10(6) fenestrations per mm3. Thus, the vasculatures of the rat incisor and molar periodontal ligaments exhibit significant numbers of fenestrations which, in the case of the incisor, are not distributed uniformly along its length.
Animals↗
The mobility of the lathyritic rabbit mandibular incisor in response to axially-directed extrusive loads.
Axially-directed extrusive loads of 0.01-0.1 N were applied to the lathyritic mandibular incisors of 12 rabbits. Tooth position was monitored continuously with a variable capacitance displacement transducer. Compared with pair-fed controls, lathyritic teeth showed markedly reduced resistance to extrusive loading, indicating that the periodontal collagen has a role in supporting the tooth. The pattern of tooth mobility, however, was little affected. The results may have implications for the eruptive mechanism. That eruption rates can appear unchanged by lathyrogens might not preclude an effect of the drug upon the eruptive force, assuming that there is a concomitant decrease in the resistance of the periodontal tissues to eruption. The teeth of rabbits in the pair-fed control group showed increased resistance to extrusive loading compared with animals fed ad libitum, indicating that changes in food and water intake may also influence the mechanical properties of the periodontium.
Aminoacetonitrile↗
Histological study, including ultrastructural quantification, of the periodontal ligament in the lathyritic rat mandibular dentition.
A 0.15 per cent solution of aminoacetonitrile was added to the drinking water of young adult male Wistar rats for 18 days. Their right mandibular incisors were maintained unimpeded by frequent trimming. After 18 days, the periodontal ligaments of the right mandibular incisors and first molars were prepared for light and electron microscopy. For control purposes, similar material was obtained from animals fed on a normal diet ad libitum or pair-fed. With light microscopy, lathyritic incisor periodontal ligaments showed areas of normal connective tissue appearance interspersed with areas of degeneration. In the lathyritic molars, cell-free areas were observed. With electron microscopy, quantification of features in the connective tissue regions of the lathyritic ligament showed little change. In cell-free areas, many collagen fibrils had smaller fibril diameters than normal.
Aminoacetonitrile↗
Changes in collagen fibril diameters in a lathyritic connective tissue.
Collagen fibril diameters were measured in molar and incisor periodontal ligaments of adult rats given aminoacetonitrile (0.15% in their drinking water). Fibrils were also measured in the periodontal ligaments of pair-fed control animals and animals fed ad libitum. The lathyrogen produced a significant change in the distribution of fibril diameters in both molars and incisors and an increase in mean fibril diameter in incisors relative to pair-fed controls. The reduced food intake of the pair-fed control group produced a significant decrease in mean fibril diameter in incisors relative to the ad libitum control group. These results that lathyrogens may affect collagen fibril diameters in an adult connective tissue in a manner similar to that previously shown for a fetal tissue.
Aminoacetonitrile↗
The occurrence of a lamellated nerve terminal in the periodontal ligament of the rat incisor.
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Animals↗
An analytical ultrastructural study of the iron-rich surface layer in rat-incisor enamel.
Electron-dense particles, approximately 4 nm (40 A) in diameter were present. Evidence is offered that these particles represent iron probably in the form of amorphous hydrous ferric hydroxide. From X-ray probe analytical data, it is suggested that this iron component is accommodated through the process of adsorption rather than by direct substitution of calcium and phosphorus. The iron-rich surface layer was more resistant to acid etching than subsurface enamel. Reported areas of reduced mineral density of enamel at the enamel-dentine junction appear to be preparation artifacts.
Animals↗