The ‘oral fingerprint’

14 August, 2013 / infocus

Within forensic odontology, the use of the dental restorations, teeth and supporting bone to compare post-mortem findings with an ante-mortem record are the most commonly used and widely accepted methods of establishing identity.

The reasons for this have been described: “Under most conditions occurring in nature, the teeth are the least destructible part of the body and they may readily survive all of these changes… fire, putrefaction or prolonged immersion in water.”1 However, there may be circumstances where these tissues cannot be used – perhaps due to trauma, disease, absence of teeth, or significant change which has occurred within a dentition since the last record was made.

The term palatoscopy or palatal rugoscopy is the name given to the study of the palatal rugae in order to establish the identity of an individual. It was first proposed as an alternative method of human identification in 1889 by Dr Harrison Allen2. Since then, many have attempted to classify the palatal rugae with a view to employing rugoscopy techniques in those instances where primary, standalone methods of identification, such as DNA analysis, finger print analysis and conventional dental identification have failed or cannot be used.

The palatal rugae are irregular, asymmetrical ridges of mucous membrane found in the roof of the human mouth extending laterally from behind the incisive papilla and across the anterior part of the median palatal raphe3. The rugae form in the 12th to 14th week of intra-uterine life from the hard connective tissue covering the palatal bone and their formation is under genetic control 3-4.

Many researchers hypothesise that once formed, the palatal rugae pattern is distinct to an individual, and does not change throughout life, except for an increase in size due to normal growth. It follows that the palatal rugae, as a characteristic feature, could potentially be considered as a type of ‘oral fingerprint’ and used as a tool in forensic human identification.

However, very few studies using the palatal rugae as a means of forensic identification have been published and the perceived usefulness of the palatal rugae as an individualising marker within forensic odontology is controversial, throwing up numerous questions. Are the palatal rugae unique to the individual? Is the number of rugae stable throughout life? Does the palatal pattern change, other than due to normal growth? Can the palatal rugae pattern be classified and analysed? Is the interpretation of the analysis useful to an individual investigator, or on a universal basis? Are the palatal rugae of any relevance in human identification or in the field of forensic odontology?

To answer these questions fully would be beyond the scope of this article. In summary, published studies 5,8 concur that palatal rugae patterns are distinct to the individual. The sample sizes studied are generally small, but within each sample, distinctiveness to the individual is demonstrated. This concurs with the author’s own experimental research.

The effect of age on the mean number of palatal rugae does not appear to have, as yet, been fully addressed by the literature, there being a number of apparent contradictions. Various studies have reported rugae numbers increasing with age, decreasing with age, being stable from age 10 years until after death and rugae numbers increasing markedly from middle-age onwards9,13.

The palatal pattern has been shown to change in length, shape and orientation with growth and with orthodontic treatment. One study demonstrated that 32 per cent of rugae changed shape, while 26 per cent changed direction as subjects moved through their teens14,16. This does not promote the idea of a stable rugae pattern.

Numerous classification systems have been developed over the years, primarily descriptive in terms of the number and morphology of the rugae. Thomas and Kotze developed a comprehensive classification system for palatal rugae and claim to have had success identifying individuals using their method. Despite this, they consider a universal system of palatal rugae classification to be impossible, but suggest that standardising the analysis procedure would prove beneficial. They conclude that an individual operator, using his/her own classification method can “very successfully apply it in a comparative project” and that it is the “results of the comparisons and not the classification itself” which is important 2, 17, 18.

Which brings us to the key question: are the palatal rugae of any relevance in human identification or in the field of forensic odontology?

The position of the palate in the head means that rugae are often well protected from external trauma while being insulated from thermal insult by the tongue and the buccal fat pads. The rugae pattern has been shown to resist decomposition for up to seven days after death 19,20.

While much of this sounds promising, there are many issues and problems to be addressed before this method can, or should be embraced. One main issue surrounds the collection of the ante- mortem record to ensure that it is a true representation of the palatal rugae pattern.

The ante-mortem record will usually take the form of a dental cast or a clinical photograph of the dentition which has coincidentally captured the rugae pattern, which would be taken as part of the routine treatment for a particular patient and form part of the dental record belonging to that individual. While the dental cast is a direct replication of the dentition and surrounding oral tissues, intra-oral photographs present some difficulties, specifically concerning inherent distortion within the image.

When photographing an object with the aim of minimising distortion, the object should be perpendicular to the digital sensor within the camera – in the case of the palatal rugae this is extremely difficult due to human anatomy. Intra-oral mirrors, held at appropriate angles, are used in an attempt to correct this inherent distortion. The image is usually being taken to assess the dentition, specifically the occlusal surfaces of the teeth.

In such images, there may be ‘zones’ where the palatal rugae are clearly focused, and therefore representative in shape and length. In other areas of the image, usually towards the periphery, distortion will have affected the appearance of the rugae, causing blurring and lack of distinction. Figure one illustrates inherent photographic distortion due to the vaulted anatomy of the human palate, with the central zone being focused and the peripheral rugae being out of focus.

Another issue surrounds the concept of ‘normal accepted growth’. It seems that the pattern changes over time are less well understood. Changes in orientation of the rugae and changes in the shape of the rugae are still changes, no matter how small they may be. While the distinctiveness of palatal rugae patterns to an individual may be accepted, it is more difficult to assess lifelong stability of the rugae pattern from the methodologies used in studies to date.

The hypothesis this technique bases itself on is that the palatal rugae pattern is distinct to the individual and does not change throughout life, except for an increase in length due to normal growth. If we consider the hypothesis differently, it is actually stating that there is a change in the rugae pattern and that it should be expected in accordance with normal growth.

The distinct pattern may appear ‘differently’ in the same individual at various phases within that individual’s chronological and dental development. But what is ‘normal’ growth? Is growth accurately predictable? Is growth uniform across age, ethnicity and the global population? If palatal rugae are to be relied upon as a supportive method of human identification, can we tolerate any change? Does it matter if it is only a small change? Isn’t any change a change?

Longitudinal studies may help resolve some of these questions, and are necessary if we are to accurately observe the behaviour and stability of the rugae pattern over a lifetime. Monitoring the palatal rugae patterns in a group of patients, starting from around age 14 when the dental arch width is considered fully developed and following the rugae pattern into late adulthood, is one way we can truly assess lifelong stability of the pattern, or otherwise. Even with necessary ethical approval in place for such a study, the logistics of acquiring and maintaining a suitable, consistent sample over a long number of years may prove challenging.

The current usefulness of rugoscopy as a supportive technique in human forensic identification may be improved by the development of practical and cost-effective three-dimensional intra-oral recording devices. Used along with complementary software, 3D images of the palate would help reduce the effects of distortion in current 2D clinical images, potentially elevating the usefulness of this technique.

The variation between the palatal patterns of individuals is often minor, and the inherent distortion when comparing what is in life a 3D structure as a flat, 2D image limits current usefulness of this technique. The development of palatal rugoscopy may only reach fruition when 3D technology becomes commonplace.

Interestingly, the Brazilian government insist upon 3D palatal scans of all pilots to ensure their speedy identification should they be involved in an accident2.

This article seems to raise more questions than it answers about the potential role of palatal rugae in human forensic identification, but the advancement of scientific techniques relies on such questions being asked, with those questions becoming the focus of future studies.

To summarise, there is, as yet, no reliable and consistent method of using the palatal rugae pattern successfully to aid human forensic identification. The potential changes in rugae patterns, whether growth-related, age-related or otherwise, need to be better understood as to whether these changes are tolerable and have a place in this technique. Reliability and repeatability will only be proven by continuing to research new knowledge and new methods which apply to lesser- known techniques. Just because a method is unconventional does not make it bad science. It should be as robust in its reasoning and testability as conventional methods.

Dental identification, conventional or otherwise, can bring immeasurable comfort and closure to a grieving family or loved one. On the rare occasion that conventional methods cannot be used, we owe it to the deceased, their family and to ourselves professionally to ensure we acknowledge the potential downfalls in alternative techniques, using them to support other forensic disciplines rather than as standalone methods.

About the author

Fiona Waddington graduated from Glasgow Dental School in 1998 and completed her Masters in Forensic Odontology in September 2012.
She works alongside her husband, Michael, at Corsehill Dental Care in Stewarton, Ayrshire.


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