|Year : 2014 | Volume
| Issue : 4 | Page : 264-268
Ameloglyphics: An adjunctive aid in individual identification
Ravindrakumar Bharanidharan, Raghavendhar Karthik, A Rameshkumar, P Rajashree, K Rajkumar
Department of Oral Pathology, SRM Dental College, Ramapuram, Chennai, Tamil Nadu, India
|Date of Web Publication||20-Nov-2014|
Department of Oral Pathology, SRM Dental College, Ramapuram, Chennai - 600 089, Tamil Nadu
Human identification in homicides and mass disasters has been largely possible with skeletal remains, especially teeth, when soft tissue cannot provide reliable information or has been lost. From the point of forensic dental identification especially in identifying victims of man-made disasters such as in military conflicts and wars involving multiple fatalities, there is urgent need for new and reliable methods of identification and corroboration. Various methods currently employed in forensic odontology for personal identification include comparing with ante mortem dental charts, rugoscopy, denture labelling, DNA analysis from dental pulp, bite mark analysis, etc. Recently there is growing interest in the study of enamel rod end patterns. These enamel rod end patterns are termed as tooth prints and the study of these prints is known as Ameloglyphics (amelo: Enamel, glyphics: Carvings). The tooth prints are unique, exhibiting dissimilarity both between teeth of different individuals and of the same individual. This uniqueness of the tooth print could be used as a valuable tool in forensic science for personal identification. This review highlights about the basis of using enamel rod end patterns, methods of obtaining the patterns, and delineating its sub-patterns.
Keywords: Biometric analysis, peel technique, rod end pattern, tooth prints
|How to cite this article:|
Bharanidharan R, Karthik R, Rameshkumar A, Rajashree P, Rajkumar K. Ameloglyphics: An adjunctive aid in individual identification. SRM J Res Dent Sci 2014;5:264-8
|How to cite this URL:|
Bharanidharan R, Karthik R, Rameshkumar A, Rajashree P, Rajkumar K. Ameloglyphics: An adjunctive aid in individual identification. SRM J Res Dent Sci [serial online] 2014 [cited 2019 Aug 18];5:264-8. Available from: http://www.srmjrds.in/text.asp?2014/5/4/264/145147
| Introduction|| |
In forensic science, finger prints, dental patterns and more recently DNA analyses are used for personal identification, but these identification methods may not be efficient when bodies are decomposed, burnt, or in cases where only small fragments of calcified tissues are available for identification. In such situations, dental hard tissues gain importance for identification based on the condition of the deceased. Teeth can withstand extreme temperatures and are resistant to postmortem decomposition. Therefore, the use of dental evidence is the method of choice in establishing an identity from badly burned, traumatized, decomposed and skeletonized remains. ,
Odontogenesis is genetically modulated. The formation of enamel is a highly organized dynamic process, in which the ameloblast lay down enamel rods in an undulating and intertwining path. This is reflected on the outer surface of the enamel as a series of enamel rod end patterns. The term "Ameloglyphics" means the study of enamel rod end patterns (amelo: Enamel, glyphics: Carvings).  Tooth print is the word used to describe these enamel rod end patterns.
| Enamel Rods/Prisms|| |
Enamel is a product of ectoderm derived cells called ameloblasts.  The basic structural unit of enamel is the enamel rods (enamel prisms). Enamel does not remodel nor does it remain in close contact with the cells which synthesize it, rather the ameloblasts retract away from the enamel surface once it has matured and the tooth has erupted. Enamel prisms morphology reflects the morphology of ameloblasts in a species-specific manner. Alterations to the matrix are reflected as defects in the structural organization of enamel. 
Macroscopically, incremental pattern of enamel rods is exhibited on tooth surface as perikymata,  but microscopically, groups of enamel rods run in unique direction, which differ from adjacent group of enamel rods and results in forming different patterns of enamel rod endings on tooth surface. ,
It has been estimated that each tooth has millions of enamel rods and that the number varies from tooth to tooth. The length of the rods is greater than the thickness of the enamel as a result of the oblique direction and wavy arrangement of the rods. It varies in different portions of the crown of the tooth, being long in the thicker portions (cuspal area) and short in the thinner portions (cervical area) [Figure 1].
The size and diameter of the enamel rods increase as they reach the outer surface. Although it is observed that the average diameter of the enamel rod is 4-5 μm, there is considerable variation along its course. It has been suggested that the diameter of the enamel rods increases in the ratio of 1:2 while passing from the dentinoenamel junction to the outer surface.
shape of the enamel prisms approximates to one of the three main patterns [Figure 2]:
- Pattern I: Prisms are circular.
- Pattern II: Prisms are aligned in parallel rows.
- Pattern III: Prisms are arranged in staggered rows such that the tail of prism lies between two heads in the next row, giving a key hole appearance. 
Studies with the electron microscope reveal that the enamel rods have a keyhole or paddle-shaped pattern with a rounded head and a narrow tail region. The rounded head of each rod fits closely into the concavities between the heads and tails of the rods on either side. The region between the two enamel rods in one row, thought to be the interrod substance, actually represents the tail portion of the enamel rod in the previous row. The rods measure about 4-5 μm in breadth and 9 μm in length. Many patterns are observed regarding the arrangement of rods, but usually they are arranged with their head portion near the occlusal or the incisal surface and their tail portion pointing cervically. 
| Orientation of enamel rods|| |
The general orientation of the enamel rods is perpendicular to the dentin surface. In deciduous teeth, the enamel rods lie in a horizontal plane in the cervical and middle third. They gradually become more oblique in the incisal and occlusal third and are almost vertical in the incisal edge or the cusp tip.
In permanent teeth, the arrangement is similar to deciduous teeth in the occlusal and middle third; in the cervical third, the enamel rods show a rootward inclination or pass outward. 
| Materials used in recording enamel rod patterns on tooth surface|| |
In Ameloglyphics, recording of enamel rod endings on tooth surface is proceeded by using acid etchant, acetate peel technique, and automated biometrics as sequential steps for reproducing complete and accurate enamel rod end patterns for personal identification.
The acid etching on the surface enamel results in the removal of the surface mineral component in the rod and rod sheath. As the rods and rod sheaths have a different mineral density, the etching results in an uneven dissolution of the surface enamel along with the removal of the smear layer.
The effect of acid etching on enamel depends on:
- Kind of acid used.
- Acid concentration.
- Etching time.
- Form of etchant.
- Rinse time.
- Whether enamel is instrumented before etching.
- Chemical composition and condition of enamel. 
About 10% orthophosphoric acid in gel form is the most commonly used acid to condition the enamel for in vivo studies.
Three types of etch patterns can be obtained:
- Predominant dissolution of prism cores.
- Predominant dissolution of prism peripheries.
- No prism structure is evident. 
A peel is a replica of an acid-etched mineral surface, made on acetate film. Peeling is a simple, inexpensive, and rapid way of making replicas of dental hard tissue surfaces. The peel-making technique was first developed by palaeobotanists to study the cellular structures of fossil plants and later taken up by palaeobotanists, carbonate petrologists, and palaeontologists to study both the texture and structure of carbonate rocks and fossils. Further modifications were done to study dental hard structures due to its unique mineralogical composition.  The peel can be examined under microscope with incident or transmitted light or with combinations of both and can be stored for posterity.
The term "biometrics" refers to identification techniques which are based on specific physical characteristics. It is a technology of identification or authentication of a person which transforms a biological, morphological or behavioral characteristic in a digital value.
When the patterns studied are consistently recognized and provide greater confidence, they are referred to as "positive identification". Biometric-based identification and verification methodologies such as fingerprint verification, iris scanning and facial recognition have been steadily improved and refined in automated systems and softwares, which have the capacity to distinguish individuals reliably.
Unique identification of an individual based on biometric information, should have certain desirable prerequisite characteristics: Highly unique to each individual, easily transmittable, able to be acquired as un-intrusively as possible and distinguishable by humans without much special training. 
| Review of methods|| |
The enamel rod end patterns could be duplicated by various methods such as using cellulose acetate paper, rubber base impression materials, and cellophane tape. 
Gupta et al. recorded enamel rod end patterns on tooth surface using cellophane tape and revealed that enamel rod end patterns seem to be unique to an individual; however, they not only found dissimilarities between different individuals, but also within the same individual. 
Manjunath et al. analyzed the efficacy of cellulose acetate film, cellophane tape, and light body rubber base impression material in recording enamel rod endings on tooth surface for personal identification and concluded that, the cellulose acetate film reproduced the complete and accurate enamel rod end patterns compared with cellophane tape and light body rubber-base impression material. 
Customary literature search on studies conducted on various pathological alteration of enamel surface (rod end) morphology such as in amelogenesis imperfecta, environmental enamel hypoplasia, etc., revealed limited results, with the exception of few studies on enamel caries.
Girish et al. aimed at ascertaining the possibility of a correlation between enamel rod end patterns and occurrence of dental caries, which might help in identifying predisposition to dental caries. He found out that, no particular rod end pattern was found in teeth affected by dental caries. Also, no particular pattern was found to be unique to teeth not affected by dental caries. 
| Method to be followed|| |
- Step 1: The selected teeth should to be scaled and polished.
- Step 2: In order to avoid error in positioning the acetate film over recording area during serial recordings, a circle of 5-mm diameter should be marked on the comparatively flat area (middle thirds) on the labial surface of the tooth.
- Step 3: The marked area should be conditioned with 10% orthophosphoric acid for 20 seconds.
- Step 4: Rinse with water and dry the conditioned surface.
- Step 5: A drop of acetone to be applied on to the tooth surface and should be covered by a small piece of cellulose acetate film and left undisturbed for 20 min.
- Step 6: The acetone dissolves a layer of cellulose acetate and the dissolute settles down along the irregularities on the enamel surface.
- Step 7: The film should be gently peeled after 20 min and observed under light microscope.
- Step 8: A photomicrograph of the acetate peel should be obtained at 40X magnification and then subjected to biometric analysis  using Verifinger standard SDK version 5.0 software (NEUROtechnology) [Figure 3].
- Step 9: The software recognizes the patterns of enamel rod endings as series of lines running in varying directions.
- Step 10: The software uses certain points called minutiae for identification of each pattern. These minutiae will be used by the software to compare the similarity/variability of two patterns.
|Figure 3: Photomicrograph of acetate peel and biometric generation with minutiae using verifinger standard SDK version 5|
Click here to view
| Enamel rod end patterns|| |
Each tooth print obtained will be composed of series of lines representing series of adjacent enamel rod ends. These lines are seen running in varying directions creating distinct sub-patterns. Manjunath et al. analyzed 30 tooth prints which yielded eight distinct sub-patterns namely wavy-branched, wavy-unbranched, linear-branched, linear-unbranched, whorl-open, whorl-closed, loop, and stem-like. Each tooth print was a combination of these sub-patterns. 
These tooth prints, are unique, exhibiting dissimilarity both between teeth of different individuals and of the same individual. This uniqueness of the tooth print could be used as a valuable tool in forensic science for personal identification. 
| Uses|| |
Enamel rod end patterns are unique for each tooth in an individual and may be used as an adjunct with other methods for personal identification. This technique is simple, inexpensive, and rapid method which can be performed by even a dental auxiliary staff. Usually, this method of personal identification can be included as adjunct ante-mortem dental records of fire fighters, soldiers, jet pilots, divers, and people who live or travel to politically unstable areas. And this record must be updated periodically to overcome the enamel loss due to wear and tear. 
| Conclusion|| |
Even though enamel is the hardest substance in the body, the enamel surface is always subject to both micro and macro-wearing. Processes such as routine tooth brushing, abrasion, erosion, exposure to acidic occupational hazards, wears the outermost layer of enamel rod ends, and exposes the underneath layer. The effect of these processes on the pattern of enamel rod ends needs to be determined.
It is common observation that teeth surfaces which are usually spared from any significant wear and tear, such as in routine tooth brushing, are maxillary and mandibular premolars (especially the middle third of buccal surface). Future studies can be done taking these teeth surfaces for standard recording of ante-mortem documentation.
Secondly, the enamel rods do not traverse the whole length of enamel in a straight path. Instead, they traverse in undulating and inter-twining path which has been attributed to provide high tensile strength to enamel. So, the course of enamel rods is not the same throughout the thickness of enamel. Hence, theoretically the enamel rod end pattern should vary at varying depths of enamel. This needs to be verified by further in vitro studies.
Also, the process of acid etching needs to be studied in detail with respect to varying concentrations of the etchant and time of exposure that in turn determines the depth of penetration and exposure of the enamel rod end pattern. Standardization of this step is of paramount importance for consistency of recording the data for periodic updating of ante-mortem records.
It must be remembered that adequate protection has to be provided for early remineralization of the etched surface after recording the rod end pattern, without causing alteration of the surface morphology. Rather than using prophylactic polishing and remineralization agents that may rub off the exposed rod ends it may be prudent to avoid any brushing but use remineralizing mouth rinses for a specific period of time.
Even though tooth prints are unique to an individual tooth, the value of it as a tool in forensic science for personal identification lies in its reproduction and permanency. These two attributes of tooth prints needs to be evaluated by prospectively studying a larger cohort.
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[Figure 1], [Figure 2], [Figure 3]