الفهرس 
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Abstract
In forensic investigations, age estimation is fundamental for the creation of the individual’s biological profile. The reduction in the dental pulp cavity associated with advancing age due to secondary dentin deposition was correlated with the chronological age. Dentin and cementum are the hard substances of the tooth, which are continuously synthesized and maintained throughout all stages of an individual’s adult life. The gradual and lifelong changes make dentin and cementum ideal tissues for the study of aging process. The present study was performed due to the relative deficiency of recent studies that compared the reliability of pulp to tooth volume ratio, root dentin translucency, and cementum annulation methods in adult age estimation.
Aim of the study:
The aim of the study was to compare the results obtained by three different parameters; pulp to tooth volume ratio, root dentin translucency, and incremental lines of cementum in chronological age estimation, and to improve the reliability of the results using (multiple linear regression model) through using the measurements obtained from pulp to tooth volume ratio and root dentin translucency.
Study methodology:
The present study was applied on a sample of 150 freshly extracted, sound maxillary first premolars with fully developed roots with age range 20-40 years old. The study was encompassing a heterogenous samples of both females and males.
A. Teeth Grouping:
The teeth samples were allocated into two groups based on the age; group (I) included age group 20 to 29 years old (45 females and 30 males), while group (II) included age group 30 to 39 years old (45 females and 30 males).
B. Cone Beam Computed Tomography Imaging & Mimics Software Application:
Teeth Coding and preparation: Each tooth sample was numbered using a permanent marker. Then the samples were arranged and mounted on modeling wax to be scanned using cone beam computed tomography.
Cone beam computed tomography images data processing and importing: cone beam computed tomography images were acquired. Images exporting was done in digital imaging and communications in medicine images format. Then Further steps of segmentation and calculation of pulp volume and tooth volume for further calculation of pulp to tooth volume ratio.
C. Histological Analysis:
1) Preparation of the ground sections: The teeth were prepared to be examined using both polarized light, and phase contrast microscopes. All the slides were coded with a unique identification number.
2) Measuring the Vertical Length of the Translucent Zone of Root Dentin Using Polarized Light Microscope:
Each prepared ground section was examined using the light microscope in the mode of Polarized light field for observation of the translucent root dentin under magnification 4X. A digital camera was used to take photographs of the root translucent zones. Image J program was used to measure the length of the vertical extension of the translucent zones on both sides of the midline independently, and the average of both sides was calculated. Under a constant source of light, the total vertical length of the root of each section was measured using a digital plastic vernier caliper. The vertical length of the root dentin translucent zone to the total root length ratio was subsequently calculated. The vertical length of the translucent zones of the root dentin to the total root length ratio was used in a statistical regression analysis to obtain an age estimation formula.
3) Cementum annulation Using Phase Contrast Microscope:
For counting the incremental lines of cementum, we selected the middle third of the root cementum. The prepared sections were examined and studied using microscope in phase contrast mode with (×200 magnification). Micrographs for each section were taken with the help of a digital camera mounted on the microscope. Photomicrographs were visualized using Image J image analysis software. Cementum width was measured in three different regions where the lines are approximately parallel, and calculations were made using the average of the three measurements as “X” i.e., the total width of cementum (from the cemento-dentinal junction to the outermost layer of cementum). The alternating light and dark bands were observed in photomicrographs, then, the width occupied by two successive bands (i.e., one dark and one light) was measured and designated as”Y”. The following formula was used to determine the total number of incremental lines in the total thickness of cementum: (n) = X/Y.
The individual`s estimated age was determined by the summation of the incremental lines of cementum and the average age of the eruption in years (t) as follow:
The estimated age (E) = Incremental lines of cementum total number (n) + average age of eruption (t).
Study Results:
• Cone beam computed tomography Results: The model was statistically nonsignificant (p=0.709) for the estimate age compared with the actual ages, indicating nonsignificant prediction of pulp to tooth volume ratio in estimating age for both age groups (I) and (II).
• Histological Analysis Results:
1) Polarized Light Microscope Results: The model showed that the vertical length of the translucent zones of the root dentin to the total root length ratio significantly predicted age (p<0.001) for both age groups (I) and (II).
2) Phase Contrast Microscope Result: The equation used showed that the cementum annulation significantly predicted age (p<0.001) for both age groups (I) and (II).
• Difference of results of all methods from the chronological age:
Reliability analysis showed a strong statistical significance agreement between the estimated and the actual age for the vertical length of the translucent zones of the root dentin to the total root length ratio and the cementum annulation (ICC>0.9, p<0.001), while for pulp to tooth volume ratio the statistical agreement was nonsignificant (p=0.443).
• (Multiple linear regression equation) using pulp to tooth volume ratio and root dentin translucency:
The model showed that the estimated age of the vertical length of the translucent zones of the root dentin to the total root length ratio is significant in correlation to the actual age (p<0.001).