# Estimation of Age in Humans Using Dental Translucency of Permanent Teeh: An Experimental Study
## 3 Results
The correlations between tooth measures and CA are reported in Table 4. The two sexes performed similarly for RH and RHT, but a higher coefficient of correlation is found in females for PH. As expected, RH correlated poorly with age; the strongest correlations were found between CA and RHT. Dividing age groups, RH did not result in significant correlations and PH only for the youngest age group. RHT was strongly correlated with CA in the youngest group, but no correlation resulted in the oldest one. As regards the differences between tooth types, for all three variables, the strongest correlations are found in the multi-rooted teeth. In Table 5, we have reported the prediction performance of the selected seven equations from the literature tested in our sample, and in Table S4, the results by age group. Considering the total sample, all the equations tend to underestimate age, with less bias found in the equations of [PERSON] and [PERSON] [19], [PERSON] and [PERSON] [8], and [PERSON] et al. [11]. The precision is low in all the formulas and ranges between 10.5 and 18 years, with the highest values in [PERSON] et al. [21] and the lowest in [PERSON] et al. [17] and [PERSON] et al. [6]. The inaccuracy is similar for all the equations, with values around 12 years; also, in this case, the equations of [PERSON] et al. [21] had the highest value. Dividing the sample into three age classes, heterogeneous results were obtained by the different formulas, but the equations that performed better seem those of [PERSON] and [PERSON] [19], [PERSON] et al. [6], [PERSON] et al. [17], and [PERSON] et al. [11]. Also, in this case, [PERSON]'s formula had the worst performance. All equations gave similar results for the 40-59 age group with a bias that never exceeds \(\pm\)5.5 years, except for [PERSON]'s formula. In general, all the equations performed poorly in the oldest age group, with [PERSON] and [PERSON] [19], [PERSON] and [PERSON] [8], and [PERSON] et al. [11] that had the best performance. As regard tooth type, the results from different formulas are heterogeneous, but generally, the application of the equations on multi-rooted teeth gave the best results, with lower bias, inaccuracy, and higher precision. Even if the results are quite different based on tooth type and age class, it can be concluded that, in general, the best formulas for our sample were those of [PERSON] and [PERSON] [19] and [PERSON] et al. [11]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**RH (mm)**} & \multicolumn{2}{c}{**PH (mm)**} & \multicolumn{2}{c}{**RHT (mm)**} \\ \hline  & **r** & _p_**-Value** & **r** & _p_**-Value** & **r** & _p_**-Value** \\ \hline Total sample & 0.31 & \textless{}0.001 & 0.35 & \textless{}0.001 & 0.80 & \textless{}0.001 \\ \hline Males & 0.31 & 0.014 & 0.47 & \textless{}0.001 & 0.77 & \textless{}0.001 \\ \hline Females & 0.28 & 0.007 & 0.30 & 0.004 & 0.82 & \textless{}0.001 \\ \hline
18–39 years & \(-0.12\) & 0.462 & 0.34 & 0.030 & 0.71 & \textless{}0.001 \\
40–59 years & 0.12 & 0.399 & \textless{}0.02 & 0.893 & 0.37 & 0.011 \\ \hline
60+ years & \(-0.07\) & 0.546 & \(-0.16\) & 0.222 & 0.08 & 0.553 \\ \hline Single rooted tooth & 0.04 & 0.791 & 0.26 & 0.108 & 0.42 & 0.005 \\ \hline Multi-rooted tooth & 0.34 & \textless{}0.001 & 0.40 & \textless{}0.001 & 0.86 & \textless{}0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Pearson correlation between variables and chronological age by sex, age classes, and tooth type. Subsequently, we randomly excluded from the total sample a holdout sample of 20 teeth (10 from each sex). From the remaining sample of 135 teeth, the regression analysis was performed. The non-linear quadratic regression gave the best fitting with the following equation:  
\[\text{Age}=23.2239+9.9108\text{x}+\left(-0.5366\text{x}^{2}\right)\]  
where x is RHT, the R\({}^{2}\) was 0.72, and the SEE was 10.9 years. The graphical representation is reported in Figure 1.