الفهرس 
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Abstract
The periodontal ligament is a fibrous connective tissue that is highly innervated and vascularized. Periodontal ligament connects the root of teeth with the alveolar bone. Aging, which we broadly define as the time-dependent functional decline that affects most living organisms, has attracted curiosity and excited imagination throughout the history of human kind. One of the few areas in which reasonable progress is being made in the age-related changes is connective tissue. Among aged connective tissues is periodontal ligament, The morphology of the Periodontal ligament changes as age increases.
Aim of the study: This Study aimed to assess the histological changes of periodontal ligament in different ages of albino rats and correlating these changes with corresponding human ages.
This was achieved by:
1-Light microscope:
a) Routine histological examination of specimens from rats stained by hematoxylin and eosin.
b) Special staining techniques of specimens from rats to examine ground substance and collagen by PAS and Masson’s trichrome respectively.
2-Radiographically:
Measurement of width of periodontal ligament space in sample of human Radiograph.
3-Histomorphometery:
Measurement of width of periodontal ligament in rats.
Material and method: We used 3 groups of 10 rats each, the animals were grouped in the following manner:
group 1: 6 months old group
group 2: 12 months old group
group 3: 24 months old group
Periapical x-ray films were used for measuring width of periodontal ligament in human, we used 3 groups of 10 periodontaly free humans each, group 1: ranges from 12 to 18 years old group 2: ranges from 30 to 36 years old and group 3: ranges from 68 to 72 years old.
Staining:
Hematoxylin and Eosin stain, Masson trichrome and Periodic acid Schiff.
Measurement of width of periodontal ligament:
Width of periodontal ligament in rats samples was measured by histomorphometry at faculty of dentistry Ain shams university using image J software. Width of periodontal ligament of human was measured by x-rays periapical films using digital sensor.
Width in both human and rat samples was analyzed in two histological thickness of root middle and apical.
Results:
1- Histological results:
First group: Examination revealed collagen fiber bundles of the periodontal ligament (PDL) which were dense and rich in fibers with little ground substance in between them. Furthermore, predominance of blue color on MT and intense magenta color of PAS.
Second group: Showed some collagen fiber bundles of Periodontal Ligament whose collagen component was not abundant. Some of the bundles showed thin, deficient fibers with spaces in between them. Furthermore, intermingling between blue and red color in MT and decrease in intensity of magenta color in PAS.
Third group: Examination revealed collagen fiber bundles of PDL whose collagen component was not abundant. The bundles showed obviously thin, deficient fibers with wide spaces in between them. Arrangement of the bundles was distorted, leading to loss of their normal wavy course from bone to cementum. Furthermore, predominance of the red color in MT stained sections and pale PAS reaction.
2-Statistical results: Histomorphometery statistical analysis for the measurement of periodontal ligament width in periapical films of human and H and E sections of rats revealed that width of periodontal ligament significantly increased by age.
Conclusions:
1- Periodontal ligament is a dense fibrous tissue supporting teeth and physiologically undergoes structural and functional age changes.
2-Well organized mature evenly distributed fiber bundles, normal cellularity with parallelism of cells between fibers and strongly attachment of Sharpey’s fibers to both bone surface and root surface are criteria of young aged periodontal ligament.
3- Disorganized thin irregular fiber bundles, decreased cellularity and severely attached Sharpey’s fibers to both bone surface and root surface are criteria of old aged periodontal ligament.
4- Periodontal ligament width was increased by age in rats and human, while there was no significant difference between oblique and apical fibers regarding width.