Radiographic Determination of an Upcoming Aid in Forensic Radiology

The identification technique utilizing conventional radiography is of much importance in Forensic Odontology for age and gender determination. Various radiographic images that can be used in Forensic Odontology are intraoral periapical radiographs, lateral oblique radiographs, cephalometric radiographs, panoramic radiographs and advanced imaging techniques.

Recently Digital radiographs have also gained importance in comparison between ante-mortem images recorded in dental offices and centers with post-mortem radiographic images for individual identification. This along with the facility of internet has made Dentomaxillofacial radiographs, a useful tool in forensic science. This article aims for the evolvution in forensic radiology and to appraise their contribution in the field of forensic odontology.

Keywords: forensic odontology, personal identification, Age estimation, digital method, CBCT

Introduction

The word forensic, is derived from the Latin forensic, which means ‘before the forum’from ancient Rome the forum was where trials and debates took place and consequently served as a court of law. On the other hand odontology refers to the study of teeth or dentistry. 1 Keiser-Nielsen has defined forensic odontology as 'a branch of dentistry which deals with the proper handling and examination of dental evidence and with the proper evaluation and presentation of dental findings in the interest of the dentist. 'The identification of human remains is one of the most essential aspects of forensic science. As there is no humanitarian character to forensic medicine. Dr. Oscar Amoedo is considered as 'the father of Forensic Odontology. '

The application of radiology in forensic sciences was introduced in 1896, just 1 year after the discovery of the X-ray by Roentgen, to demonstrate the presence of lead bullets inside the head of a victim. Forensic Radiology usually comprises the performance, interpretation, and reportage of those radiological examinations and procedures that have to do with the courts and/or the law. Imaging techniques are a powerful tool in forensic science. The radiologist should be aware of the importance of storing radiographs over prolonged periods of time and of efficient record keeping methods, because various legal problems may require the radiograph for additional interpretation or for their presentation in court.

Dental radiographs constitute crucial information that plays an important role in the registration, detection, collection and preservation of forensic evidence. These records are of major significance during comparative dental identification, postmortem profiling and certain age estimations. Today, radiographs are a common diagnostic tool, widely used in dental practices, hospitals and health services throughout the world. Storage facilities exist in most health institutions which keep radiographs over long periods of time.

Radiographically assisted dental identification may be comparative or reconstructive in type. The former ‘‘compares’’ ante mortem radiographs with postmortem radiographs. Reconstructive identification may use radiographs as an aid in the generation of a biological profile of a person for whom the putative identity remains unknown.

Radiographic records provide objective evidence of the anatomical conditions and the dental treatment provided up to the point in time. Most cases of comparative identification use radiographic evidence of dental intervention (restorations, root fillings, crowns, extractions, etc. ) as common points of identification. Less commonly, anatomical features are used as concordant points. Dental interventions, especially restorative ones, in many cases provide unique identifiers that are common in ante mortem and post mortem examinations.

Radiography being a nondestructive method also plays a vital role in forensic dentistry to uncover the hidden facts, which cannot be seen by means of physical examination. The conventional radiographic methods allows the observation of anatomical characteristics such as coronal shape and size, pulp anatomy, positioning and shape of the alveolar bone crest, besides unique and individual characteristics resulting from dental treatments.

Personal identification

Identity, by definition, is the ensemble of characteristics that allow the individualization of a person or an object, distinguishing other subject from any other person or object. Identification is the act by which the identity of an individual is established, and is of unquestionable value, since social relations and/or civil, administrative, commercial and legal demands claim this form of recognition. The premortem and postmortem properties of a person inthe teeth are unique. They can be analyzed for the purpose offorensic identification.

Tooth has been used as quite reliable evidence in personal identification of living or dead persons using the specific features of the jaws and the teeth. Several researchers have advocated the uniqueness of tooth. Many scientists believe that tooth impression is more usable evidence than the bite marks, which are believed to be more specific than DNA. The genetic makeup may be same in both the twins but the dental impression may be different.

Dental and medical problems are ultimately concerned with the determination of each patient as a unique individual. Similarly, medico-legal identification is based on a set of characteristics which define the physical 'uniqueness' of each individual. It follows that a close relationship exists between human identification, individuality, and the biological sciences.

Age estimation

From the calcification of deciduous ones to the loss of permanent ones, the teeth, with their sequence of formation and eruption, have been used as indicators of age, mostly in the period from early childhood to adulthood. Radiology plays an indispensable role in human age determination. Radiological images are utilized in the process of age estimation, which is one of the essential tools of identification in forensic science. Saunders, a dentist, was the first to publish information regarding dental implications in age assessment by presenting a pamphlet entitled ‘‘Teeth A Test of Age’’ to the English parliament in 1837. While quoting the results from his study on 1000 children, he pointed out the value of dentition in age estimation.

In children and young adults, age estimation is done by clinical methods such as eruption sequence, radiographic methods such as Schoulr and Masslers method, Moorer, Fanning and Hunt method, Demirijian, Goldstein and Taners method and Nolla's technique.

According to recent research, tooth cementum angulation may be used more reliably than other methods for age estimation. Analysis of these various radiographic features in the dentition of an individual corresponding to the phase of human development aids in age determination. These can be grouped into three phases:

1. Pre-natal, neonatal and post-natal
2. Children and adolescents and
3. Adults

For age determination, two methods are commonly used: the “Atlas method” in which radiographic dental development (mineralization) is compared with published standards and the “Scoring method” in which dental development is divided into various stages that are then assigned the scores that are evaluated through statistical analysis. Acharya A. B has been credited to utilize Demirjian's criteria to assess the third molar development by analysing the OPGs of Indian subjects belonging to the age group of 1521 years. He came to the conclusion that a significant one fourth population of India has been wrongly analyzed for age estimation and havebeen placed in wrong age group.

Sex determination through dental radiographs

Sex determination is an important step for identification of human remains and for medico-legal investigations in forensic odontology. There are various methods for sex determination in forensic dentistry, but by assessing the symmetry, morphology, border outline and presence of septa and cells of the frontal sinus in dental radiographs has gained much attention. The frontal sinuses are two, in the posterior part of the supercilliary arcs, and lies between the external and internal faces of the frontal bone.

They are seldom symmetrical; generally, there is a septum between both, which usually deviates from the midline. They point upwards beyond the middle part of the supercilious and backwards to the medial part of the orbital roof. Frontal sinus radiographs may be used because it is commonly exposed in sinus series investigations. Camargo JR et al. , studied morphology of frontal sinus in radiographs of Brazilian population and found accuracy rate of 79. 7% by using logistic regression model in sex determination.

Various studies have been conducted in the past to evaluate the forensic importance of frontal sinus radiograph. Studies report that, statistically, the frontal sinuses are larger in men than in women, and in women the upper borders of the frontal sinuses are deeper. Also, other factors may affect the regular anatomy of the frontal sinuses in adult individuals, as follows: fractures, traumas, surgeries, diseases, mucoceles and some enlargement in elder individuals, all of them of rare incidence. .

Digital method

Digital radiography, used for a decade or more by radiologists has become the solution of choice in mass casualty situations where the number of victims overwhelms the ability of forensic medical examiners to quickly and accurately identify descendents.

“Digital radiography dramatically increases the quality and timeless associated with the use of dental x-rays in forensic dental victim identifications, particularly when combined with computer based dental chart matching software”.

The process of identification based on conventional radiography became more difficult because of the dissemination of prophylactic dental treatments and the consequential, significant reduction in the incidence of cavities, particularly in developed countries. At the same time, the spectacular development of microelectronics and information technology in association with the decrease in costs of computational equipment has allowed the development of more powerful and reliable techniques for comparison of radiological images with application in forensic dentistry.

Innumerable variations of digital radiology techniques can be found in the literature, but, essentially, the method comprises the following steps: 1) radiographic image digitization with the aid of a scanner, video camera or, yet with images acquisition directly from a x-ray system coupled with a computer with monitor, printer and CD-ROM recorder; 2) image processing through an appropriate software, allowing comparisons based either on image superimposition, interposition or subtraction.

These modern techniques allow an accurate analysis of the spatial relations of teeth roots and supporting structures on ante- and post-mortem images. There are softwares with resources for images rotation, translation and scaling, facilitating the correct alignment between ante- and postmortem radiographs without the necessity of new exposures. It is important to observe that differences in the geometry between radiographs represent the main factor of error in this type of technique, and the above mentioned correction is essential to reduce the noise resulting from the process of image subtraction.

Conventional, two-dimensional or three-dimensional computed tomography (CT) is a useful imaging method in the process of human identification, and presents innumerable advantages in this field as compared with the traditional radiographic projection. Firstly, because this method is free from the problem of structures superimposition beyond the plane of interest, and also for allowing the visualization of small differences of density.

Anthropologically, CT has been utilized in the study of skulls and also, in the forensic context, as an additional resource in processes of identification. Additionally, studies have demonstrated the applicability of facial reconstruction by means of 3D CT for the purposes of individual identification

Secondary dentine apposition is a significant morphological dental age predictor. It is defined as the formation of dentine after the completion of the primary dentine and starts at the moment the related tooth root is completed. The formation of secondary dentine may be caused by attrition, abrasion, erosion, caries, changes in osmotic pressure throughout the pulp chamber, or aging and decreases the volume of the dental pulp chamber. Therefore, the volume changes of the pulp chamber in intact teeth are considered as a dental age predictor. Although the apposition of secondary dentine is not homogenously spread over all the walls of the pulp cavity and even differs in relation to the examined tooth type, bucco-lingual and mesio-distal pulp width as well as the pulp cavity height decreases with aging. These variables can be measured on the involved tooth after extracting and sectioning it or on its two-dimensional (2D) dental radiographs.

More specifically, the last two variables can be applied for radiological age estimation on living individuals without tooth extraction. Similarly researchers have tried to relate the ratio of the surface area of the pulp and the surface area of the tooth measured on clinically obtained 2D dental radiographs to chronological age. Three-dimensional (3D) radiographs of extracted teeth generated by a desktop X-ray micro-computed tomography (CT) scanner or a cone beam computed tomography (CBCT) allow for the calculation of the volume of each tooth and corresponding pulp chamber. To reduce the variation in tooth sizes, the ratio of both obtained volumes is related to the chronological age of the subjects. In a pilot setup, the same procedure is plied on CBCT images of unextracted monoradicular teeth. 19 N. Jagannathan et al conducted a study and assessed the suitability of pulp/tooth volume ratio of mandibular canines for age prediction in an Indian population.

Volumetric reconstruction of scanned images of mandibular canines from 140 individuals (aged ten - 70 years), using computed tomography was used to measure pulp and tooth volumes.

Cone Beam Computed Tomography (CBCT)

At the present time, three-dimensional digital tooth images can be acquired from living individuals using Cone-Beam Computed Tomography (CBCT).

Yang et al reported that, using their three dimensional images, the ratio of pulp/tooth volume could be calculated for living individuals. They selected 28 sets of CBCT tooth images (15 incisors, 12 canines and 1 premolar) from 19 different individuals ranging in age from 23 to 70 years. The selection was restricted to upper and lower single-rooted teeth that revealed neither deep carious lesions nor restorations and showed normal dental anatomy. Thus, Yang et al. describe a first approach to age estimation. 23 CBCT was used to calculate the pulp/tooth volume ratio in our study, for two reasons:

(1) The analysis of the volumes of the pulp chamber and tooth is more reliable than calculation of area ratios, possibly because secondary dentine formation may not be uniform along all pulp surfaces and, hence, measurements of projected areas could give an incorrect impression of the extent of this process;

(2) CBCT is an accurate technique for studying the anatomy of the pulp chamber and root canal system which provides three-dimensional volumetric information of the teeth of living individuals by a single scan and can be operated non-destructively. The newest CBCT operating modes and optimization of the ratio measurement software, together with increased numbers of samples, could bring the technique to maturity in forensic odontology research. We also believe that investigations employing larger sample sizes may also demonstrate that CBCT data can be helpful to study other aspects of dental morphology in greater depth, especially dental growth. CBCT data could be helpful in defining new parameters for the rating of dental development, for a quantitative description of the fractions of crown and root formed during tooth growth.

Data obtained by X-ray transmission are restricted to two dimensional information at a low resolution. Improvement of the X-ray transmission technique might be obtained by using X-ray microfocus computed tomography (μCT), a high resolution imaging modality, which allows non-destructive testing. In μCT the same scanning principle as in medical computed tomography (CT) is utilized; however, the spatial resolution is orders of magnitude higher. During the last 20 years, μCT has shown its potential in various fields. In dental research, the technique has been used to analyze the three dimensional structure of root canal systems of extracted teeth before and after endodontic instrumentation. μCT could develop a potential in forensic research as well. The advantages of the technique together with the use of appropriate software may lead to more precise formulas for age estimation based on the quantitative measurements of volumes.

It is foreseen by some people that CT will replace other modalities in forensic radiology and potentially some autopsies, mainly those on trauma patients. Much research is still needed in this area and groups from around the world are working towards proving the validity of CT in forensic work.

Similarly, MRI (magnetic resonance imaging) has been used in forensic cases but has a limited role to play. The strong magnetic currents required limits the potential for use and most cases would need a MDCT prior to an MRI scan. Obviously the associated costs involved constrain the use of MRI but this is a further avenue for research.

Conclusion

Data obtained by X-ray transmission are restricted to two dimensional information at a low resolution. Improvement of the X-ray transmission technique might be obtained by using X-ray microfocus computed tomography (μCT), a high resolution imaging modality, which allows non-destructive testing. In μCT the same scanning principle as in medical computed tomography (CT) is utilized; however, the spatial resolution is orders of magnitude higher. During the last 20 years, μCT has shown its potential in various fields.

In dental research, the technique has been used to analyze the three dimensional structure of root canal systems of extracted teeth before and after endodontic instrumentation. μCT could develop a potential in forensic research as well. The advantages of the technique together with the use of appropriate software may lead to more precise formulas for age estimation based on the quantitative measurements of volumes.