## 4 Discussion  
Based on the findings of the present study on an Iranian sub-population, in all the maxillary and mandibular anterior teeth, a significant negative correlation was observed between age and pulp-tooth volume ratio. In addition, pulp-tooth volume ratio of mandibular central incisors, maxillary lateral incisors, and maxillary canines in males and maxillary and mandibular central incisors, maxillary lateral incisors, and maxillary and mandibular canines in females can be used for age estimation. Age estimation was most accurate among females using maxillary central incisors and among males using mandibular central incisors and maxillary canines. Deposition of secondary dentin continues throughout an individual's life, reducing the size of the pulp cavity [11; 12]. In addition, studies have shown that root canal system configuration changes overtime [25; 26; 27]. The present study found that this trend can be used for age estimation of individuals over 16. In 1925, for the first time, [PERSON] noticed changes in the structure of teeth as age increases, and it was hypothesized that teeth could be used to estimate age. The first method of using teeth for estimating age was proposed by [PERSON] in 1950 [28]. Over time, various methods have been proposed for this purpose, including the method introduced by [PERSON] in 1995, in which the age of the tooth was estimated based on the amount of secondary dentin visible on radiography and the amount of pulp cavity. In this method, central incisors, lateral incisors, and second premolars of the maxilla and lateral incisors, canine, and first premolars of the mandible were examined in periapical intraoral radiography [29]. [PERSON] et al. developed a pilot study in 2006, which for the first time CBCT was used to compare pulp-tooth volume ratio in 28 single-rooted teeth. In this study, a special software was used for volumetric measurements and a formula was presented for estimating the age with a coefficient of determination of 29% [21]. CBCT imaging technique was also used in this study for providing the volumetric information. High-resolution images and the relatively low radiation dose of CBCT images make it an optimal three-dimensional modality for the craniofacial region. The deposition of secondary dentin on the walls of the pulp cavity is often non-uniform, making measurements on two-dimensional images inaccurate. [PERSON] et al. concluded that teeth in both jaws are reliable for estimating age. However, a stronger relationship was observed for maxillary teeth. According to the study of [PERSON] et al., the pulp-tooth volume ratio in all anterior teeth showed a significant relationship with age [24]. Nevertheless, canine teeth due to having large pulp cavities, less wear, and the possibility of remaining longer in the mouth are better options for age estimation [30]. In addition, [PERSON] et al. have also successfully used canine teeth for age estimation purposes [31]. Similar to our findings, in the study of [PERSON] et al., the correlation between age and pulp-tooth volume ratio in maxillary canines was higher than in mandibular canine [24]. Therefore, they are more reliable for predicting the age in adults. [PERSON] et al. reported that the degree of the relationship between the pulp-tooth volume ratio of canine teeth and age was higher in women than men, which is in line with the results of this study. Although, it should be noted that the study of [PERSON] et al. not only reported a weak relationship in women, but also men did not show any significant relationship between age and the pulp-tooth volume ratio of the maxillary canine [32]. This study showed that in some teeth, including the mandibular canine and maxillary central incisor, the intensity of the correlation was higher in women than men, which is consistent with the study of [PERSON] et al. [33]. One of the limitations of this study was its focus on one specific population in Iran.