The issue of age estimation in living adults is getting more important along with increased numbers of illegal immigrants entering e.g. European Union without valid identity documents and/or verifiable birth certificate (1,11,13). Since taking radiographs solely for forensic purposes is ethically questionable due to potential burden of ionizing radiation, methods basing on existing X-ray images are highly desired. OPGs provide images of both anterior and posterior teeth registered during a single, relatively short, X-ray exposure what makes it an ideal tool for dental evaluation. No further radiographic examinations need to be performed (7).
Indeed, age estimation by pulp/tooth ratio can be done also on the basis of intraoral periapical radiographs (16). For this purpose taking mesial and vestibular periapical X-rays was proposed, but this approach is not feasible in living adults as technically it is impossible to take radiographs in mesial projections of teeth present in dental arches (17). Well-established techniques of taking periapical X-rays in labio-vestibular projections like paralleling technique and bisected angle technique are prone to technical errors, especially the latter one. Moreover these radiographs are not always easy to obtain in clinical settings e.g. in case of gagging reflex, only canine present in dental arch which may result in unstable position of image sensor during exposure, in patients with lockjaw etc. Therefore OPGs remain an alternative to intraoral periapical radiographs, especially when they are taken due to clinical indications, and not for the purpose of forensic investigations.
Recently Cone-Beam Computed Tomography (CBCT), cross-sectional imaging technique applied among others in dentomaxillofacial radiology, has been tested for dental age estimation using the pulp/tooth ratio. The study based on Korean adults involved the largest buccolingual and horizontal dimensions of canines, while in Malaysian population volumetric changes in pulp cavity occurring with age were registered (18,19). On the other hand, in a group of 91 subjects examined by CBCT in the material of De Angelis et al. (14) the rate of pulp chamber volume and total volume of an upper canine was estimated. CBCT seems promising in forensic applications as it is characterized by a much lower image distortion than OPGs. However, potential drawbacks of CBCT in dental age estimation in comparison with two-dimensional radiographs (intraoral periapical and OPG), are lower image resolution, still lower availability of equipment as well as usually higher X-ray dose than in case of OPGs and definitely higher than that of periapical radiographs (20). One more advantage of OPG over periapical radiographs is demonstration of all 4 permanent canines in one radiograph, instead of taking 4 separate periapical views which yields four exposures to ionizing radiation. However, this was not the case in the current study due to reasons mentioned below as limitations.
Both digitized and digital (direct or indirect) radiographs as well as different methods of AR tracing were proposed in research studies (16,21). For example, Saxena (21) measured lengths of tooth, pulp and root at 3 levels – cemento-enamel junction, middle of the root and halfway between these two points. In the present study lasso tool of the commercially available image processing software was used to manually trace the outlines of each tooth and its pulp.
Estimation of dental age by means of the AR is not restricted only to canines, nonetheless these teeth appear to be the foremost suitable for the method. Not only their anatomy is simple, but they also are preserved in the oral cavity longer than other teeth groups (12,14). Moreover, maxillary canines have been shown to be more predictive than lower canines (standard error of estimate 2.37 years vs. 2.55 years) (22). Hence we decided to base on the image of upper maxillary canine only for the purpose of this study.
Ex vivo research demonstrating validity of AR method included age at death estimation in a sample of 20th -century Mexican prisoners as well as individual age estimation in adult Neolithic skeletons in Italy, Middle-Ages skeletons in Italy, collections of skulls from Bologna, Italy, and canines from Coimbra, Portugal (22–26). In all these studies AR provided estimates which were significant in terms of forensic dentistry and archeology, respectively. The research on Portuguese sample yielded a much lower error of age estimation, i.e. 2.5 years, than the one derived from anthropological methods reaching 5 years (22).
The samples from the following populations have already been tested for application of the pulp/tooth area ration in dental age estimation of living subjects: Italian (23), Indian (12,21), Brazilian (27) and Iranian (28).
In the material of 100 digitized OPGs of Italian white Caucasians the pulp/tooth area ratio of right upper canine was highly correlated with calendar age of studied individuals (23). Standard error of estimate reached 5.35 years, while the absolute value of residual error was lower than 4 years.
The next population sample to be found in literature was the Indian one (21). In 120 OPGs of patients of both genders aged from 21 to 60 years, there were no statistically significant differences between chronological and estimated dental ages, both in males and females. Another Indian sample was evaluated basing on digital periapical radiographs and consisted of 228 subjects aged from 16 to 62 years (12). It confirmed that gender did not influence the AR of canines in a significant way, and this observation proved true also for the studied Polish population sample.
Brazilian sample used for dental age estimation using pulp/tooth ratio consisted of individuals aged from 20 to 87 years, assigned to 5 groups consisting of 80 subjects, apart from the oldest age group over 70 years of age, in which there were not enough X-rays of individuals meeting the inclusion criteria. In this population the mean error of estimate was higher as in previously quoted studies and reached from 7.96 to 9.68 years. It is worth underlining that the largest errors affected extreme age groups, i.e. 20–29 years and over 60 years. Once a formula for DA estimation dedicated to the studied population was elaborated, the mean error decreased to 7.99–8.56 years (27). Following this observation, we decided to propose separate formulas for the Polish sample, which proved useful.
Three hundred OPGs were submitted for DA estimations using pulp/tooth area ratio in an Iranian study by Dehghani et al. (28). A total of 542 upper and lower canines of patients aged from 16 to 64 were included in the analysis following rejection of OPGs not meeting the selection criteria. The quoted results confirmed usefulness of AR in estimation of chronological age of living adult individuals.
To the best Authors’ knowledge, this is the first study validating the pulp/tooth area ratio in the Polish population. It seems that age estimation by means of AR is a relatively simple, rapid, convenient and inexpensive method for forensic purposes. Preliminary results of this study prove that even if only one canine is present, dental age estimation can still be performed.
Limitations of the study include restriction of the evaluation only to the maxillary right canine. This is due to high caries prevalence in the Polish population and edentulism rate in older age groups. An average number of teeth for a person living in a big Polish city over the age of 65 is only 14.3, however people from small cities have two teeth less according to the survey from 2013 (29). The situation in a younger group of patients appears to be better since the average count of teeth in the age group 35–44 years is between 24.5 and 25 teeth. It also influenced the number of OPGs included in the study as all consecutive radiographs fulfilling selection criteria taken during 4 years in our Department were gathered in the study, and it yielded 521 radiographs out of 3316 that had been done.
Another limitation might be the use of panoramic radiography instead of periapical X-rays, but in our opinion the most up-to-date direct digital panoramic machines, like the one used in our study, provide very clear images when compared to digitalized analogue OPGs obtained by means of earlier generations of equipment. Potential image distortion as an inherent feature of OPG is greatly reduced by application of area ratio in contrast to linear measurements which are prone to error.