Characteristics Of Palatal Rugae Patterns Biology Essay

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Palatal rugae are the ridges present at the anterior part of palatal mucosa on either side of the median palatal raphe and behind incisive papilla. Various studies on different populations have reported unique rugal patterns within each population.

Aim: To study, analyse and report the significant palatal rugae patterns among West Godavari District population and compare with the patterns reported in the literature, which can aid as an additional method of identification in cases of crime or mass disasters.

Materials and Methods: Pre orthodontic casts of 100 samples (50 males and 50 females) were selected. The method of identification of the rugae pattern used was that of Thomas et al (1983) which includes the number, shape and unification patterns of rugae. The different types of rugae between males and females were statistically analyzed and compared with other population studies in the literature.

Results: A statistically insignificant (p>0.05) higher mean primary rugae scores was found in males (7.48±2.45) while secondary (3.38±2.02) and tertiary (2.56±1.84) rugae were more among females. Both genders showed predominance in wavy (males = 4.82±1.91 and females = 4.74±1.98) type of distribution. Commonly observed pattern in the mode of unification was converging (58%) in males and diverging pattern (62%) among females which was statistically significant (p=0.04).

Conclusions: The findings showed a specific rugae pattern in this group when compared to other populations reported in the literature. Palatal rugae patterns are definitely associated with regional variation and can aid as an additional tool in forensic identification procedures.

Key Words: forensic, mass disaster, palatal rugae, population characteristics, West Godavari.

INTRODUCTION

Human identification is one of the major fields of study and research in forensic science because it deals with the human remains and aims at establishing the identity. Importance of dental investigation in human identification is one of the most frequently applied and reliable method.by forensic odontologist, predominantly by the comparison of ante-mortem and post-mortem records. Forensic dental identification mainly involves determing gender, age, ethnic background, community etc of the individual.1 On predicting the ethnic background or community, it provides a clue in collection of other vital ante-mortem records and ultimately aids in building the biological profile of an unidentified corpse.

Palatal Rugoscopy i.e study of palatal rugae is one of the simple technique used by a forensic odontologist in human identification.2 Palatal rugae also called as rugae palatinae or plicae palatinae transversae are transverse ridges on the anterior part of palatal mucosa on either side of median palatal raphe and incisive papilla. In mice, palatal rugae develop prior to elevation of palatal shelves in the third month of intrauterine life as localised areas of epithelial proliferation.3 Beneath the epithelial thickening condensation of fibroblasts accumulate in the connective tissue tissue giving a distinctive rugal pattern4. The anatomic position of these transverse ridges aid in oral swallowing, suction in children, taste perception and participate in speech specially 's' and 'sh' phonemes.5

In clinical dentistry due to the stable nature of the palatal rugae it aids as a landmark during orthodontic treatment6, during cleft palate surgeries,7 palatal prosthesis8 and medicolegal identification.9 The rugae pattern in human is as unique as his or her fingerprints.10 It is one of the tool used by an forensic odontologist in human identification because of its internal position, stable in nature, perenity,11 uniqueness and low utilization costs. Rugal length and transverse palatal rugal region width increases with age in both genders and stops once the somatic growth stops.12 Also, authors have reported a significant correlation between the rugal pattern and ethnicity. In a forensic context, it is required to provide an evaluation of ethnic group as an aid in personal identification.

The purpose of this study was to assess the palatal rugae patterns and report the significant rugae patterns in West Godavari District population, which can aid as an additional method of identification in cases of crime or mass disasters.

MATERIALS AND METHODS

The material for this study consisted of 100 pre orthodontic dental casts of 50 male and 50 female of age group 15-30 years from the Department of Orthodontics, Vishnu Dental College, Bhimavaram, West Godavari District, Andhra Pradesh. All subjects were healthy individuals free of congenital abnormalities, inflammation, trauma or orthodontic treatment. All casts were free of air bubbles or voids specially at the anterior third of the palate.

The classification system of Thomas et al (1983) was followed for rugae identification.11 This includes the study of total number, length, shape, and unification pattern of rugae. Rugae patterns were outlined using sharp graphite pencil.

Measurement of length of the rugae

Rugae length was recorded from the starting point of rugae at mid palatine raphe to the end point of rugae transversely and in case of circular shape rugae the maximum diameter was taken into consideration. All measurements were made under magnification using a slide calliper to an accuracy of 0.05mm. There are three pattern determining the length of rugae:

1) Primary rugae (5-10mm)

2) Secondary rugae (3-5mm)

3) Fragmentary rugae (less than 3mm)

Measurement of shape of the rugae:

Shape of individual rugae were classified as follows: (Figure 1)

1. STRAIGHT- ran directly from the origin i.e mid-palatine raphe to termination 2. CURVY- gently curved with crescent shape. Cicular- with continuous ring formation

3. CIRCULAR- appears as ring formation 4. WAVY- in the form of serpentine. 5. UNIFICATION- when rugae has two arms which are joined either at their origin or termination which may be diverging and converging type. Diverging occurs when two arms of the rugae begin from the same origin and bifurcates transversely similarly converging occurs when two arms of rugae arise with different origins and converge transversely.

Figure 1

The readings were reported for each study cast and observations were tabulated.

Statistical Analysis

The recorded data was compiled and entered in a spreadsheet computer program (Microsoft Excel 2007) and then exported to data editor of SPSS version 15.0 (SPSS Inc., Chicago, Illinois, USA). Unpaired t test and Chi square tests were used for comparison of mean and relationship between the attributes. For all the tests, confidence interval and p-value were set at 95% and ≤0.05 respectively.

RESULTS

The total number of rugae in the study sample was 605 in males and 653 in females. Mean primary rugae was more in males (7.48±2.45) whereas secondary (3.38±2.02) and tertiary (2.56±1.84) rugae were more among females but the results were statistically insignificant (p>0.05). Based on the shape of palatal rugae both genders showed wavy type (males = 4.82±1.91 and females = 4.74±1.98) followed with straight (males = 3.9±2.35 and females = 3.76±1.91) type of distribution. However, these observations were statistically insignificant (p>0.05) [Table 1].

Based on unification pattern gender-wise distribution of the rugae showed predominant coverging pattern (58%) in males and diverging pattern (62%) among females with a p value of 0.04 which shows that difference is statistically significant [Table 2].

DISCUSSION

Forensic identification of human as alive or dead includes determination of various parameters like age, sex, race or geographical area. Palatal rugoscopy is one such tool employed successfully in identifying an individual based on the rugae pattern analysis as it is proved to be unique in shape, length, width, prominence, number and orientation considerably among individuals. Variation also exists in the right and left sides of the same person i.e no bilateral symmetry seen.13 Therefore, rugae patterns can be used in individual identification by comparing the postmortem rugae details with the antemortem records. Thomas and Van Wyk in 1987 reported identification of a severely charred edentulous body with the help of plaster casts made from the dentures in the victims mouth and compared with another set found in that individual's home.14 Use of palatal rugae in forensics is not only due to its uniqueness but also due to stability, post-mortem resistance and with low utilization cost, making it an ideal forensic identification parameter. Muthusubramanian et al in 2005 performed an analysis of rugae in burn victims and cadavers to simulate rugae identification in cases of incineration and decomposition. They reported that 93 percent of palatine rugae were normal and 77 percent of palatine rugae showed no colour change among subjects with third degree panfacial burns when examined after 72 hours stored in a mortuary at 5 degrees with 30 to 40 percent relative humidity.15

Pre-orthodontic stone casts were used in our study for the analysis of rugae patterns as these present an advantage of simulating the oral cavity in the forensic laboratory, easy to handle, simple analysis, reduced cost and easy fabrication. Sognnaes advocated that casts made from jaws give a reliable result than that of dentures 16 Various studies have shown the use of photographs taken by digital cameras, their transfer to the hard disk of the computer and later these images were analysed using a software programme.11,17 Neverthless, this process can conserve the physical space consumed in storing the stone casts, this process is complex as it involves specific photography skills in attaining the perfect photograph and includes complex data analysis and interpretation as the examiner must be well versed in photography and its software application and its execution.

Trobo Hermosa, a Spanish investigator first proposed palatal rugoscopy in 1932.18 Since then various classifications were proposed by many researchers like Silva in 1938,19 Carrea in 1955,20 Lysell in 1955,21 Basauri in 1961,22 Lima in 1968,23 Caruso in 1969,24 Tzatscheva and Jordanov in 1970,25 Thomas in 1983,26 Kotze in 198327 and many more. Each classification had its own merits and demerits in practical application. Thomas and Kotze26-28 in all their articles emphasised the necessity for standardizing the procedure in observing, classifying and interpreting the variations of palatal rugae patterns. They also suggested that "a single operator alone (eliminating inter-observer error), using his own classification can very successfully apply it in a comparative project and that the results of the comparisons and not the classification itself are important." In our study Thomas et al26-28 classification was used in observing and interpreting the palatal rugae patterns. This classification was chosen because it is simple as no complex instrumentation is required, practically easy to apply and covers most of variables like total number, length, shape and unification patterns of the palatal rugae.

On deriving the association of palatal rugae and ethnicity various classifications were employed and each author claiming their classification method employed was most accepted. Whatever may be the classification system employed in various population studies, a definite significant variation among population and among ethnic group exists (Table 2).

Dohke and osato reported that males have greater number of rugae than that of females among the Japanese.29 Kapali et al in 1997 through their longitudinal and cross-sectional approaches aimed to investigate changes of rugae patterns with age in Australian Aborigines and compared the patterns between Australian Aborigines and Caucasians. They employed classification described by Lysell21 and Thomas and Kotze.26-28 Authors analysed the number, length, shape, direction and unification of rugae and concluded that The mean number of primary rugae was lesser in Caucasians than that of Australian aborigines.30 Fahmi et al in 2001 studied the rugae patterns in Saudi males and females. Authors employed classification of Thomas et al 26-28 and reported that females showed a significant difference in the converge type and males had a significant difference in the circular type and concluded that the rugae patterns can be an additional method of differentiation between Saudi males and females in conjunction with the other methods such as visual, fingerprints and dental characteristics in forensic sciences.31

Nayak et al in 2007 examined the possible difference in rugae shape between Southern Indians and Western Indians and also the effectiveness of rugae shape in identfying the populations using discriminant function analysis. According to the classification given by kapali et al the authors reported low incidence of unifications and absence of circular rugae indicating that these two Indian populations were characterised by fewer types of rugae shape and also significant difference between two populations were observed in straight and curved rugae as they were seen in more number among Southern and Western Indians respectively. On discriminant function analysis moderate differentiation of the populations were possible with an attributed accuracy of 70% and concluded that discrete variables such as rugae shape are better suited for the purpose of discrimination than continuous variables like rugae length.32

Paliwal et al in 2010 determined the number and pattern of palatal rugae among Madhya Pradesh and Kerala populations of India and reported that straight rugae pattern on the right side of the palate among males were significantly predominant when compared to Madhya Pradesh population.33 Kashima et al compared shape of hard palate and palatine rugae among Japanese and Indians children and reported that Japanese children had more primary rugae than Indian children and the palatal raphe of Japanese children was wider when compared to those of the Indian children.34 In a comparative study between Indians and Tibetan population by Shetty et al, it was reported that Indian males had more primary rugae on the left side as compared to females and vice versa for the Tibetan population. 35

In our study of Palatal rugae pattern of West Godavari District population we observed unique features. There was a significant difference in the average number of rugae, females showing increased number of rugae when compared to males. Unification pattern among males and females showed increased converging pattern in males and increased diverging pattern in females. No significant difference was found in gender-wise comparison of length and shape of palatal rugae of study sample.

Further research should be indicated with a larger sample size in order to validate our findings. Comparison with other geographical populations would give better understanding of population variations. Databank for storing the palatal rugae pattern must be established as these patterns may serve as ante-mortem record, which could be utilized in identification procedures of forensic odontology.

CONCLUSIONS

We observed the existence of a specific rugae pattern in West Godavari population when compared to other populations reported in the literature. Thus, this study highlights that palatal rugae pattern could be used as one of the adjunct in comparative identification process of forensic odontology. Due to the regional variation of rugae pattern in different populations, rugae databank needs to be established which will serve as a forensic reference centre.

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