Background: Counting the tooth cementum annulations (TCA) is a method for estimating the age at death of adults by sections of their tooth root. The objective of this study was to assess the precision of counting the cementum incremental lines and the congruence between known age and age estimates. Possible factors affecting the accuracy of the estimate were also analyzed. Methods: A sample of 67 permanent teeth extracted from individuals with known age (18–84 years) and sex was analyzed to calculate the dental age. Results: Results demonstrate an excellent inter- and intra-observer reliability of annuli counting, with dissimilarities within the limits of agreement. A moderate positive correlation was found between chronological age and TCA. Our results showed that age congruence rates differed across age groups (85% congruence in individuals \le30 years; 75% in individuals aged 31–60 years; 60% in the over 60s). Considering the bias, this method showed a clear tendency to underestimate age in specimens from old people. After age 43, the TCA estimate is highly inaccurate exceeding the underestimation of 10 years, on average, in comparison to the chronological age. Both chronological age and dental arch seem to influence the accuracy of estimates, unlike sex and the tooth root number. Conclusions: TCA analysis is characterized by high precision and low accuracy, decreasing with age. Therefore, its applicability is limited in elderly subjects. The choice of methods for age estimation in adult skeletal remains should take into account the particular age range of individuals. We recommend using different age estimation methods to verify the reliability of the performed assessments.