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Quantitative and qualitative analysis of palatal rugae patterns in Gujarati population: A retrospective, cross-sectional study

Introduction: Palatal rugae are irregular and nonidentical mucosal elevations seen on the anterior third of palate. They are arranged in transverse direction on either side of the median palatine raphe (MPR) and are protected from high temperature and trauma because of their rational position in the oral cavity. Their number and patterns are not uniform in all the individuals, and they appear to vary in different population subsets. The study of palatal rugae is termed as “Rugoscopy” or “Palatoscopy”, and it finds its application in various fields such as anthropology, orthodontics, forensic sciences; including forensic odonto‐stomatology. Aim: The aim of this study was to evaluate the quantitative and qualitative parameters of palatal rugae using pre‐orthodontic study models of Gujarati samples. Objectives: (1) To identify the predominant palatal arch forms in the study samples. (2) To evaluate and correlate the rugae count in both male and female samples with the different palatal arch forms. (3) To assess the symmetry and/or asymmetry in rugae count between the right and left side. (4) To analyze and correlate the qualitative characters such as size, shape, direction, and unification in male and female study samples. Materials and Methods: One hundred pre‐orthodontic maxillary dental stone casts of patients with an age range of 17–25 years were selected. The outlines of the rugae were traced using microtip graphite pencil and examined using magnifying glass for different patterns. The quantity and quality of rugae patterns were recorded according to Thomas et al. classification and the data were statistically analyzed by the statistician using SPSS program. Results: Overall, 962 rugae were observed in the study sample. The mean rugae count was 9.86 in males and 9.38 in females. The left side rugae count was more than the right side in both the sexes and it was not statistically significant. Fifty‐six percent of the samples showed asymmetry in rugae count between the right and left. Class B palatal arch form was the most common type in the study samples. The number of primary rugae count was more in both the sexes. The distribution of straight (40.2%) and curved (40.4%) types of rugae were almost equal in males but in females, the straight rugae pattern (42.2%) was more than the curved (36.9%), followed by wavy and circular. Of 962 rugae, 36.4% were of horizontal type followed by forward (33.4%) and backward (29.2%). About 1 % of rugae showed ORiginAl ARticle


Introduction
"R ugae" are an anatomical term which refers to a series of ridges produced by folding of the wall of an organ. In the oral cavity, they are seen as irregular elevated ridges on the mucous membrane covering the anterior part of the hard palate. They radiate somewhat transversely from the incisive papilla and the anterior part of the palatine raphe on either side. [1] They are supported laterally by a submucosal cushion of adipose tissue, thus forming a fatty antero-lateral region. The lining epithelium is of stratified squamous type with an underlying dense collagenous connective tissue. [2] The study of palatine rugae is known as "Palatal Rugoscopy" or "Palatoscopy" and was first proposed by a Spanish investigator, Trobo Hermosa in 1932. [3] It is a well-established fact that the rugae patterns are stable, and unique oral topographical structures to an individual, like his or her finger prints [4] and this characteristic pattern remains stable from the time of development till the oral mucosa degenerates at death. Both the quantity and quality of rugae are found to be unchanged throughout life; however, some authors have reported changes in the mean rugae count with age. [5] The rugae are located at a more secured position in the oral cavity, well bounded by cheek, lip, tongue, teeth, and alveolar process. Hence, they are well protected from trauma, extreme finger sucking in infancy, and persistent pressure with orthodontic treatment and dentures. The uniqueness, stability and the resistance to damage, facilitate palatal rugae as one of the important anatomical landmarks in forensic investigations. [6] Similarly, racial, ethnic, and geographical variations in the patterns also influence the identification of individuals, especially during a mass disaster and in the field of forensic anthropology. [7][8][9] The palatal rugae are classified and studied qualitatively using their length, shape, direction, and unification parameters and quantitatively on the number of rugae present on either side of the mid-palatine raphe. Several classifications of palatine rugae were proposed by researchers in the past using the metric and non-metric characteristics. [6,10,11] On an average, 3-6 rugae are present on either side of the median palatine raphe, and the number may or may not be same on both the sides. The length of an individual ruga is usually measured from its starting point near the mid-palatine raphe to its end point transversely. The length parameter classifies rugae patterns into: • Primary rugae: 5-10 mm • Secondary rugae: 3-5 mm • Fragmentary rugae: <3 mm.
The shape of individual rugae usually fits in any of the following four major categories [Box 1].
The direction pattern of each ruga is determined in relation to the mid-palatal raphe (MPR). The angle between the line joining the origin and termination of a ruga determines the direction pattern of that particular ruga. The forward directed rugae (F) are associated with positive angles, and the angles are negative for backward directed rugae (B). If the angle is zero, then the ruga is considered a horizontal (H) and ruga running parallel to MPR are considered as perpendicular (P) [ Figure 1].
The term "Unification" is designated when two rugae are joined at their origin or insertion. Unifications in which two rugae begin from the same origin, but bifurcate transversely are considered as diverging (D) whereas rugae with different origins which are joined on their lateral positions are considered as converging (C) [ Figure 2].
Several studies were done in the past with the objective of investigating the pattern distribution, gender discrimination, and ethnic, or geographical variations as research parameters in the field of anthropology, anatomy, forensic odontology, orthodontics, and prosthodontics. [10][11][12][13][14] Here, we designed this study to explore the unique patterns of palatal rugae in Gujarati population using the quantitative and qualitative data, gathered through 100 pre-orthodontic dental casts. One of our objectives was also to compare the distribution of rugae patterns with palatal arch forms.

Materials and Methods
This study was aimed at the analysis of a sample which is representative of Gujarati Population. Therefore, individuals whose mother tongue is not Gujarati and who are not of Gujarati origin were excluded to get a homogeneous study sample. The individuals, whose casts were selected for this study, were of different social classes and from various geographical regions of Gujarat. All these individuals underwent orthodontic treatment, and their pre-orthodontic dental casts were utilized for this study. Casts of cleft palate and maxillary expansion cases were excluded from this study. Pre-orthodontic maxillary casts of 50 males and 50 females whose age ranged from 17 to 25 years were selected, and the rugae were delineated using 0.1 µ tip HB pencil to enhance their visualization [ Figure 3]. The mid-palatal raphe was identified, and the number of rugae on the right and left of it was noted down. Each ruga, on the right and left of MPR, was assigned a number (such as 1, 2, 3… 6) from the anterior to posterior [ Figure 4]. The metric and non-metric characteristics of palatal rugae were noted down in the prescribed performa. As the degree of development of rugae is dependent on the growth of palatal arch, we for the first time, tried to compare the rugae patterns with the form of the palatal vault.
Accordingly three types of palatal forms were identified.     statistician. Student's t-test was utilized to compare the mean values of two samples, and Chi-square test was done to analyze the significant difference between two groups of data.

Results
After a thorough analysis of 100 study models, the following observations were noted.

Palatal arch forms
The Class B form of the palate (52%) was the most predominant type, followed by Class A (26%) and Class C (22%) [ Table 1]. In male samples, Class C was the least prevalent (14%) whereas in females it was Class A (26%). The distribution of the palatal arch forms however was not statistically significant (P = 0.126).

Number of rugae
Overall, 962 rugae with a mean value of 9.62 were observed in this study sample. The mean rugae count in the right side was 4.73 (standard deviation [SD] = 0.88) and in the left side was 4.89 (SD = 1). There was no statistical significance between the mean rugae count between right and left side [ Table 2]. The mean rugae count in male was 9.86, whereas for female it was 9.38. The difference in the mean rugae count between male and female was also not statistically significant [ Table 3]. The quantitative analysis on the number of rugae in the right and left of MPR revealed a total count ranging from 6 to 12 rugae. Maximum of 12 rugae was observed in 18% of male and 16% of females. The least number of rugae count in male was 7, and it was present in 4 (8%) of male samples. In female, the lease count of 6 rugae was seen in only one sample (2%). A maximum of 8 rugae count was observed in 19 female samples (24%) [ Table 4]. In this study, 52% of males and 56% of females showed differences in the number of rugae between the right and left of MPR. The number of rugae was same on both the sides in 48% of male samples and in 44% of female samples. Overall, only 46% of the study sample showed symmetry in the number of rugae on the right and left sides. [ Figure 5] When the palatal arch forms were compare for the quantitative distribution of rugae in both the genders, it was observed that the mean rugae count (right and left) was 10.23 for both males and females in Class A palatal form, 9.42 for Class B palate, and 9.36 for Class 3 palate form. The mean rugae count was more on the left side for Class A palate form, whereas, for Class B, and C palatal forms, it was more on the right side [ Table 5]. Figure  6 shows the graphical representation of the difference in the mean rugae count between the right and left and in male and female samples and in all the three palatal arch forms are compared. There is greater difference in the mean rugae count between male and female samples; whereas the least difference in count is there between the right and left counts in female samples [ Figure 6].

Size of rugae
Primary rugae (>5 mm) constituted 84.9% of the total rugae count in our study samples. The mean value of primary rugae count in male samples was 34.14 for the right and 36.17 for the left side. Similarly, for females, it was 32.17 and 33.67 for the right and left, respectively. Furthermore, it was found that the primary rugae were more concentrated on the anterior       rugae, i.e., rugae number 1, 2, and 3 in both the genders. The secondary rugae count was more on the right side for male, whereas the count was more on the left side for female samples. The fragmentary rugae count was more on the left side for male and reverse in case of females [Tables 6 and 7]. The quantity of secondary rugae was more in females than males, but the fragmentary rugae were slightly more in males than females, and they were seen more on the right side.

Shape of rugae
Of the 962 rugae in both male and female, 41.2% were straight (S) type, 38.7% were curved type (Cu), 19.2% were wavy (W) type, and 0.9% were of circular (Ci) type [ Figure 7]. About 40.2% of rugae in males and 42.2% of rugae in females were of straight type. The table is showing the distribution of shape pattern in male and female samples in right and left side is given below: S>Cu>W>Ci Cu>S>W>Ci Tables 8 and 9 shows the distribution of each and every ruga according to the direction on both sides in male and female samples, respectively. When the direction of rugae was compared on either side, it was found that forward (F) direction rugae were more on the left side in both the genders. The backward (B) direction rugae were more concentrated on the right side in both the genders. Of 962 total rugae count, 350 rugae (36.4%) were of horizontal (H) type, followed by forward, backward, and perpendicular types [ Figure 8]. The distribution of direction pattern of rugae in male and female samples on the right and left side is given below:

Unification of rugae
Only 8% of the rugae in males and 9.60% of rugae in females showed unification pattern [ Figure 9]. In males, the left side    showed more unification than the right side, whereas in females, the right side showed more unification than the left side. About 76.4% of rugae unification was of divergent (D) type while the remaining 23.6% showed converging (C) pattern.

Discussion
Palatal rugae patterns, from a forensic point of view, are used primarily to establish a person's identity and to know his/her ethnic origin. This study was designed after a thorough literature review on palatal rugae. Regional variations in the palatal rugae patterns in male and females were reported by several investigators in the past, but there was a scarcity of articles comparing the rugae count on the right and left of the MPR and also its significance with the palatal arch forms. Our study like many other earlier studies [ Table 10] revealed that rugae pattern did not comprise one type  Male Rugae 1 49  50  1  0  0  0  100  Rugae 2 47  43  3  3  0  4  100  Rugae 3 40  40  7  6  3  4  100  Rugae 4 36  38  10  6  1  3  94  Rugae 5 26  30  3  6  4  1  70  Rugae 6 7  16  3  3  0  0      alone, but a mixture of various patterns. The mean rugae count in our study was 9.86 and 9.38 in males and females, respectively. A similar study [13] done in Meerut population revealed a mean rugae count of 7.04 and 6.8 in males and females, respectively. Similar to our study, there was no statistical difference between the rugae count in male and female sample in their study. In a Lucknow population study, [14] the mean rugae count in males was 8.86 and in females was 8.53, and there was no statistical significance in rugae count between males and females and between right and left sides in that study too. Similarly, in an Andhra population study, there was no statistical significance in the number of rugae between males and females. [19] A comparative analysis of rugae patterns between Indian (Mysore population) and Tibetan population by Shetty et al. [9] revealed that Indian males had more primary rugae on the left side than females, and the reverse was seen in Tibetan population. They also reported that Indian males had more number of curved rugae on both right and left side than Tibetan males, whereas Tibetan females had greater number of wavy rugae on both sides than Indian females. Kallianpur et al. [24] compared the patterns in Indian and Nepalese population and reported that the mean rugae count was greater in Indians, and the wavy rugae were predominant in both races followed by curved type in Indian samples and straight type in Nepalese samples. A statistically significant difference in total number of rugae between the two sexes in the West Indian Population was reported by Gondivkar et al.; [17] whereas in our study and also from the studies done by Kapali et al., [25] Fahmi et al., [26] Jibi et al., [18] Saraf et al., [27] and Kamala et al., [14] there was no such significance. Kapali et al. in Aboriginal samples also showed insignificant differences in rugae count between right and left in both the sexes. Hence, we can assume that the quantitative parameter does not contribute much for the sexual dimorphism in rugae. Furthermore, the discriminant function analysis of palatal rugae using length and shape parameters for gender determination yielded an accuracy of only 73.08% in a Coastal Andhra population study. [19] Nayak et al., [10] in their Indian sample study, also showed more number of rugae on the right side, whereas in our study, the number of rugae was more on the left side. The wavy and curved rugae were more predominant in their study while curved and straight patterns dominated in our study. The mean rugae count as observed in samples from Chile was 12.27, and the most prevalent rugae shapes were sinuous and curved types. This finding was similar to the study by Nayak et al. A comparative study of palatal rugae in populations of 5 different states in India by Byatnal et al. [23] showed predominant wavy pattern followed by straight in Andhra, Karnataka, Madhya Pradesh, and Maharashtra population. In Tamil Nadu population, the wavy pattern was followed by curved type of rugae. In our sample (Gujarati Population), we found the predominance of straight rugae followed by curved one. The mean value of number of rugae in females was slightly higher than that of the males in a Nigerian population study, [28] which was reversed in our findings. Indian studies by Sharma et al. [29] and Nayak et al. [10] showed wavy and curved rugae forms as predominant patterns in their study samples. However, a study by Rai and Anand [30] showed that North Indian population had a predominance of straight pattern. Their findings were similar to our study but were contrary to the study by Shanmugam et al. [21] Although the palatal rugae patterns do not possess any gender-based differences, the discriminatory ability in population differentiation showed an accuracy of 93.5% [31] and 70% [10] in Indian Population studies. According to Saraf et al., [27] the quantity of rugae did not show any gender variation; however, the logistic regression analysis of rugae shape (one of the qualitative parameters) enabled high accuracy in gender predilections (>99%). A study [16] comparing the rugae of Madhya Pradesh and Kerala populations showed a significant predominance of straight type on the right side in the former population samples while in the latter the wavy pattern was common. In their study, there was no significance in the rugae shape in female subjects. A West Godavari population study [22] revealed insignificant result in the distribution of shapes of rugae while the distribution of unification pattern showed significant difference among gender. In our study, there was no significance in the gender distribution of the unification patterns. Shetty et al. [32] showed a significant difference between Malayalees and Kodavas population for wavy and unification patterns. They reported 100% distribution of wavy patterns in Kodavas, whereas in our Gujarati population, the curved and straight patterns dominated over wavy types. The Malayalees population in their study showed significant differences between sexes for straight rugae which were insignificant in our study. About 56.7% of Malayalees and 43.3% of Kodavas showed unification pattern while in our study, unification was observed in only 9.27%. A significant difference in unification pattern among genders was also observed in Coastal Andhra population. [19] Similar Indian study [15] between Karnataka and Manipur populations also showed significant differences in the rugae patterns. Another Indian study, [20] comparing the rugae shape of Manipuri and Kerala populations showed statistically significant association which was lacking in our study. In contrast to our study, their female samples showed more rugae than the males; however, the quantitative predominance on the left side was similar to our finding. Thus from the majority of the studies, it is observed that palatal rugae patterns vary between different population groups, and there is no significant sexual dimorphism in relation to the quantitative and qualitative parameters of palatal rugae.

Conclusion
Palatal rugae are anatomical structures with clinical, forensic, and anthropological significances. Through literature analysis, it is evident that there is no quantitative significance among genders. Based on the rugae patterns alone, population identification also becomes difficult as similar patterns are seen in different population groups.
Further studies on larger sample size are required to validate the role of palatal rugae in forensic identification and gender discrimination. However, with the availability of ante-mortem records of the palatal rugae, the forensic investigators might face fewer challenges in identification of burn victims or a person in case of mass disasters.