BACKGROUND: Dental age of adults can be estimated by the analysis of the progressive physiological and degenerative phenomena which affect dental tissues. The pulp-dentinal complex is one of the dental structures that show modifications related to age, mainly resulting in the reduction of the pulp chamber volume due to the continual deposition of secondary dentin. The study aims to evaluate the accuracy of a simple and conservative method for estimating the age of adults based on CBCT (Cone Beam Computed Tomography) analysis of the narrowing of the pulp chamber caused by secondary dentin deposition. MATERIALS AND METHODS: Two operators have randomly analyzed 148 CBCT (Scanora 3D - Soredex) and considered the upper left central incisor. The sample consists of 57 male individuals and 91 females aged between 10 and 80 years. This research was designed to simplify dental volume measurement through geometric approximation of the different parts of the tooth. The root and the pulp were assimilated to elliptical based cones and the crown to an elliptical based truncated cone and these volumes were calculated through measurements using Osirix(®) software (OnDemand 3D software CyberMed Inc.). The ratio between the pulp volume and the hard tissues volume (PHr) was assumed as a variable according to the following formula: PHr = V pulp/V ht. The proposed method based on geometric approximation of dental volumes was validated comparing volumes calculated using CBCT with physical measurements of real volumes of 3 teeth. RESULTS: The physical measurements revealed that the measurement procedures using CBCT produce a regular underestimation of real volumes, that ranges from 53% to 70%. Since the error occurs quite regularly both for pulp and for hard tissue volume, it tends to be eliminated when their ratio is considered. The PHr was statistically significant (p-value < 0.001) as a predictor for age estimation. The gender variable was not significantly correlated with age (p = 0.7694) and it was, therefore, excluded from the linear regression formula for age estimation: Age = -64.14 - 32.00*Ln PHr. The age cohorts between 30 to 59 years showed the highest accuracy in age prediction (residual errors 0.71, 2.88, and -5.86 years), whilst for other age cohorts the estimation error is similarly reported by applying other dental methods. CONCLUSION: The outcomes of this pilot study show that the narrowing of the pulp chamber is a reliable parameter for estimating the age of adults, and that CBCT is an easy and conservative approach that allows accurate calculation of tooth volumes. The proposed approach based on geometric approximation of upper central incisor volumes measured by CBCT remarkably reduced the operating time in comparison to other more complex and expensive techniques. The validation procedure in which real volumes are compared with those calculated using CBCT supports the accuracy of the experimented approach and the good inter-examiner agreement (ICC 0.99) demonstrates that the method is highly reproducible.