الفهرس 
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Abstract
This study consisted of 45 patients submitted to the out patient clinic of The Faculty of Dentistry, Tanta University. The study was performed on 3 age groups and a control group. The prepubertal and rapidly progressive periodontitis groups were assessed using criteria described by Page et al. (1983 a,b), while juvenile periodontitis was assessed using criteria described by Baer (1971). The most affected teethwerechoosenfor-extraction and examined under light and scanning electron microscope. Detection of urinary PEA was measured using amino acid analyzer and serum ALP using Beckman Astra methods in the affected patients. The aim of this study was to evaluate the relationship between the odontohypophosphatasia and cementopathia as a possible etiological factor in the early onset periodontitis.
I -Regarding to the prepubertal periodontitis group examined, the results of the present study indicated that: a) By light microscopic examination of extracted tooth, it was found that: 1-Irregularity of the external root-resorption of cementum. 2-Cementum surface appear thin or area-devoid of cementum in many area of section examined. 3-Resorption bays are limited to cementum or extend into dentine in which remnants of periodontoUigament related to dentine. 4-III• defined calcified C.T layer covered some defects of dentine as an attempt for repair. 5-Collagen fibers of periodontol Iig~me~t approximate the underlying dentine but do not appear to connect with it. 6-Generally, normal dentine; in -some-area-hypo-calcified-interglobular dentine is abundant.