Assessment of tooth cementum annulations (TCA) is acknowledged for its potential as a more accurate method for estimating age-at-death than conventional macroscopic methods typically employed. Thermal alteration of remains in a forensic context is not uncommon; however, the use of TCA in heat-treated remains has hitherto received no quantitative assessment of accuracy. This study applies TCA to a sample of modern teeth of known demographics after experimental heat treatment at 600, 800 and 1000°C. Cementum annulations do survive thermal alteration; however, their visibility is dependent on exposure temperature. Physical and chemical changes resulted in TCA being applicable to only 63.3% of samples. An overall correlation to known age of r = 0.522 (p < 0.05) was found, while correlations of r = 0.868 (p < 0.01), r = 0.249, and r = −0.185, were found for 600, 800, and 1000°C subsets, respectively. These results indicate that in teeth exposed to temperatures >600°C, TCA no longer yields accurate enough results to be of use in forensic investigations.