Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 12 5 2016 02 09 347 351 EN Mojgan Paknejad Associate Professor, Dental Research Center, Dentistry Research Institute, Department of Periodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Afshin Khorsand Associate Professor, Dental Research Center, Dentistry Research Institute, Department of Periodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Siamak Yaghobee Assistant Professor, Dental Research Center, Dentistry Research Institute, Department of Periodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Pooriya Motahhari Oral and Maxillofacial Pathologist, Private Practice, Tehran, Iran Arghavan Etebarian Postgraduate Student, Department of Oral and Maxillofacial Pathology, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Mojtaba Bayani Postgraduate Student, Department of Periodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ali Mehrfard Dental Student, Azad University of Medical Sciences, School of Dentistry, Tehran, Iran 2015 10 12 2015 10 12 Objectives: The aim of this study was to determine the cementum thickness in the first molars of patients with localized aggressive periodontitis (LAP) compared to healthy individuals. Materials and Methods: This case-control study compared eight first molar teeth af-fected by LAP with eight third molar teeth of healthy individuals. The teeth were dis- infected by immersion in 10% buffered formalin solution for three days and were then sectioned. External mesial root surfaces (middle one-third) were evaluated under a ste- reomicroscope by a blinded pathologist to determine the mean thickness of cementum. SPSS software (version 16.0) and t-test were used for statistical analysis. Results: Histological examination revealed a significant difference between the two groups in terms of the amount of cementogenesis (P<0.001) .The thickness of cemen- tum was higher in the control group (105.16±11.5 μm) than in LAP patients (86.44±7.3 μm). Conclusion: This study demonstrated the presence of cementum hypoplasia in mesial root surfaces of first molars affected by LAP. https://fid.tums.ac.ir/index.php/fid/article/view/308 https://fid.tums.ac.ir/index.php/fid/article/download/308/290