Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 8 2 2021 10 02 51 59 Izzati Ismail Department of Oral and Maxillofacial Surgery and Diagnosis, Kulliyyah of Dentistry, International Islamic University Malaysia. Mohammad Abu Bakar Kulliyyah of Dentistry, International Islamic University Malaysia. Khairul Hairul Anuar Kulliyyah of Dentistry, International Islamic University Malaysia. Mohamad Ramlee Dental and Maxillofacial Surgery, Sultan Ahmad Shah Medical Center, International Islamic University Malaysia. 2021 04 30 2021 06 28 Objectives: This study is aimed at analysing the accuracy and reliability of the cone beam CT (CBCT) measurements and direct physical measurements of the posterior mandible. Materials and Methods: Eighteen cadaveric hemi-mandibles were dissected from the soft tissues and the CBCT images of the mandibles were taken. Direct physical and cone beam CT measurements of six landmarks which includes height of ramus (R), distance of lingula to sigmoid notch (LS), distance of lingula to inferior border (LI), position of lingula in relation to occlusal plane (L-OP), ramus thickness at crestal level (RT-C), and ramus thickness at midway between sigmoid notch and lingula (RT-M) were determined. Accuracy and reliability of the measurements were tested. Results: Four landmarks showed high accuracy when measuring the posterior mandible, while two landmarks, LI and RT-M, showed statistically significant weaker accuracy (p<0.05). Inter-reliability were good for all landmarks when measured directly physically on mandibles (ICC>0.7 and p>0.05), but were low on two landmarks, LI and RT-C, on CBCT measurement (ICC<0.5 and p<0.05). Conclusion: A generally strong accuracy between direct physical and CBCT measurements for most landmarks on posterior mandible were found. Reliability between two researchers were high on direct physical measurements. Meanwhile, two landmarks on CBCT which include LI and RT-C showed low inter-reliability. Hence, CBCT measurements proved to be a good tool for pre-operative assessment, since high inter-reliability and strong accuracy corresponding to direct physical were recorded. Keywords: CBCT accuracy; CBCT measurements; CBCT reliability; Physical measurements; Posterior mandible. https://jcr.tums.ac.ir/index.php/jcr/article/view/370 https://jcr.tums.ac.ir/index.php/jcr/article/download/370/323