Morphological analysis of various rugae patterns among Dravidian population.

AIM: The aim of this study was to analyze and identify differences in the palatal rugae patterns and genderwise distributions in three different populations (Kerala, Mahe and Puducherry).
MATERIALS AND METHODS: Ninety maxillary study models (30 from each group including males and females) were examined in the age group ranging from 18 to 25 years. The palatal rugae pattern was analyzed for shape.
RESULTS: After analyzing the rugae patterns among the groups, the most common pattern was the wavy pattern (53.57%) followed by curved (18.22%) and straight (13.66%). The least was circular (1.3%). When compared between sex, the most common pattern was found to be wavy (male - 54.3% and female - 53.09%), while the curved pattern was more common among the females (21.09%) than males (13.97%). The straight pattern was more common among the males (18.8%) than females (10.18%). The least common pattern was found to be the circular in both sexes which accounted for around 1%.
CONCLUSION: This study shows no two palates are identical in terms of their rugae pattern. Palatal rugae possess unique characteristics as they are absolutely individualistic. Study also confirms that the "wavy" type of palatal rugae pattern was the most predominant among these three populations.

INTRODUCTION

In forensic dentistry, the oral cavity plays an important role because of its unique anatomy of the teeth. Teeth are more durable than other parts of the body. However, in certain situations, if teeth are lost, the use of palatal rugae has been suggested as an alternative method for identification.[1] Palatal rugae or transverse palatine folds are irregular mucosal elevations present in the anterior third of the palate. Rugae are well protected by the lip, the buccal pad of fat and teeth. Hence, they survive postmortem insults. It is asymmetrical and arranged in the transverse direction from palatine raphe located in midsagittal plane.[2] Palatal rugae are known to be stable and unique to an individual and are well protected from trauma and insulated from heat and thus survive postmortem insults.[3] Once formed, they do not undergo any changes except in length (due to normal growth) and remain in the same position throughout a person's entire life.[1]

They are not only unique to humans but also specific to ethnic groups, facilitating population identification which is essential in mass disasters and hence useful in population identification in forensic dentistry.[45] In fact, differences in rugae patterns have been found in relatively similar population groups.

The present study was aimed at analyzing the rugae pattern between three different populations of Kerala, Puducherry (bound by the state of Tamil Nadu) and Mayyazhi/Mahe U.T of Puducherry (which is surrounded by the state of Kerala) subpopulation.

MATERIALS AND METHODS

The sample comprised of three population groups, namely Mahe, Puducherry and Kerala. A total of 90 participants were selected using random sampling with 30 participants in each group. An age group ranging from 18 to 25 years was included. Individuals with full erupted permanent teeth with the exception of the third molar were included in the study. The individuals with a history of facial trauma, maxillofacial surgery, orthodontic treatment, craniofacial abnormalities and endocrine disease were excluded from the study. Before the study, the details of the procedure were explained to the study participants, and written informed consent was obtained.

Each study sample was examined clinically, and appropriate maxillary impression tray was selected and impressions were recorded using irreversible hydrocolloid material. The impressions were then poured with dental stone [Figure 1]. These casts were numbered accordingly belonging to individual states and gender.

Figure 1

Photograph showing palatal rugae

The rugae were demarcated using a sharp graphite pencil under adequate light and magnification and recorded according to the classification given by Kapali et al.[6] Rugae were categorized as “straight,” “wavy,” “curved” and “circular.” In addition, if rugae had two arms, it was categorized as “unification.” Thomas and Kotze[7] have categorized two-armed rugae as “branches” or “unification” depending on the length of their origin; unifications have further been classified as converging or diverging, depending on the type of origin.[6] The present study has, however, categorized all forms of unified and branched rugae – irrespective of length and origin – as “unification.” Moreover, all rugae were considered for the study, irrespective of their length. All the identification and measurements were done by two independent observers. Association between rugae shape and ethnicity as well as rugae shape and sex were tested using statistical analysis and a stepwise discriminant function developed using the IBM SPSS Statistics for Window, version 22.0 (Armonk, NY, US).

RESULTS

The present study was carried out among three different groups, to analyze if there was any significant difference in rugae patterns. The total number of participants was 90 with 30 (male – 10 and female – 20) in each region. The total number of patterns examined was 461 (male – 186 and female – 275) [Table 1]. The most common pattern was a wavy pattern (53.57%) followed by curved (18.22%) and straight (13.66%) [Table 1]. The least was circular (1.3%). When compared between sex, the most common patterns were found to be wavy (male – 54.3% and female – 53.09%), while the curved pattern showed more common among the females (21.09%) than males (13.97%). The straight pattern was more common among the males (18.8%) than females (10.18). The least common was found to be the circular pattern in both sexes which accounted for around 1% [Table 1].

Table 1

Mean and percentage palatal rugae shape in Puducherry, Mahe and Kerala sample population

RUGAE SHAPE	PUDUCHERRY		MAHE		KERALA		Total n (%)
Total (30)	Incidence n (%)	Mean	Incidence n (%)	Mean	Incidence n (%)	Mean
WAVY	97 (61)	3.2	84 (57.9)	2.8	66 (42.03)	2.2	247 (53.57)
Curved	22 (13.8)	0.73	25 (17.2)	0.83	37 (23.6)	1.2	84 (18.22)
Straight	17 (10.7)	0.56	19 (13.1)	0.63	27 (17.2)	0.9	63 (13.66)
Unification	14 (8.8)	0.46	11 (7.58)	0.36	15 (9.6)	0.5	40 (8.67)
Circular	3 (1.9)	0.1	1 (0.68)	0.03	2 (1.2)	0.06	6 (1.3)
Nonspecific	6 (3.8)	0.2	5 (3.4)	0.16	10 (6.3)	0.33	21 (4.55)
Total	159		145		157		461
Male (10)
Wavy	39 (60)	3.9	27 (58.7)	2.7	35 (46.6)	3.5	101 (54.3)
Curved	7 (10.8)	0.7	6 (13.04)	0.6	13 (17.3)	1.3	26 (13.97)
Straight	9 (13.8)	0.9	8 (17.39)	0.8	18 (24)	1.8	35 (18.8)
Unification	7 (10.8)	0.7	3 (6.5)	0.3	6 (8)	0.6	16 (8.6)
Circular	1 (1.5)	0.1	1 (2.17)	0.1	0	0	2 (1)
Nonspecific	2 (3.1)	0.2	1 (2.17)	0.1	3 (4)	0.3	6 (3.2)
Total	65		46		75		186
Female (20)
Wavy	58 (61.7)	2.9	57 (57.57)	2.85	31 (37.8)	1.55	146 (53.09)
Curved	15 (15.95)	0.75	19 (19.19)	0.95	24 (29.26)	1.2	58 (21.09)
Straight	8 (8.5)	0.4	11 (11.11)	0.55	9 (10.97)	0.45	28 (10.18)
Unification	7 (7.4)	0.35	8 (8.08)	0.4	9 (10.97)	0.45	24 (8.72)
Circular	2 (2.1)	0.1	0	0	2 (2.4)	0.1	4 (1.45)
Nonspecific	4 (4.3)	0.2	4 (4.04)	0.2	7 (8.5)	0.35	15 (5.45)
Total	94		99		82		275

Percentage distribution of different rugae patterns among Mahe, Kerala and Puducherry showed that wavy pattern was the highest followed by curvy and straight. A wavy pattern in the Kerala individuals was lower than the Puducherry and Mahe. While, Curved (23.6%), and straight (17.2%) pattern were more among Kerala than Puducherry and Mahe individual's [Table 1]. To further investigate the difference between various rugae pattern Tukey pairwise comparison has been used. It shows that there is significant difference among the rugae pattern [Table 2]. Three-way ANOVA was done to test if there was any significant difference between pattern, gender and region [Table 3].

Table 2

To further investigate the difference between various rugae pattern Tukey pairwise comparison has been used

Difference of levels	Difference of means	t	P
Curved- wavy	-1.811	-14.89	0.000
Straight- wavy	-2.044	-16.81	0.000
Unification-wavy	-2.300	-18.91	0.000
Circular-wavy	-2.678	-22.01	0.000
Nonspecific-wavy	-2.511	-20.64	0.000
Straight-curved	-0.233	-1.92	0.391
Unification-curved	-0.489	-4.02	0.001
Circular-curved	-0/867	-7.12	0.000
Nonspecific-curved	-0.700	-5.75	0.000
Unification-straight	-0.256	-2.10	0.287
Circular-straight	-0.633	-5.21	0.000
Nonspecific-straight	-0.467	-3.84	0.002
Circular-unification	-0.378	-3.11	0.023
Nonspecific-unification	-0.211	-1.74	0.508
Nonspecific-circular	0.167	1.37	0.745

Table 3

The interrelation between the three character i.e., pattern, gender and region

Character	F	P
Pattern	48.46	0.000*
Region	0.18	0.838
Gender	8.27	0.017*
Interaction between
Pattern - region	1.26	0.36
Pattern - gender	2.41	0.11
Region - gender	1.66	0.239

R2=96.54%. *P value shows significant at 5% level

Test result shows the following:

The significant difference between pattern and gender

No significant difference in pattern and region

No interrelation between the three characters (pattern, region and gender).

To assess whether there is any difference between various characteristics, one-way ANOVA has been performed. It is clear from Table 4 that there is a significant difference between the various characteristics (F = 129.13, P = 0.000) [Table 4].

Table 4

To assess whether there is any difference between various characteristics, one-way ANOVA has been performed

Factor	Mean	F	P
Wavy	2.744	129.13	0.0000
Curved	0.933
Straight	0.700
Unification	0.4444
Circular	0.0667
Nonspecific	0.2333

It is clear from the table that there is significant difference between the various characteristics. (F=129.13, P=0.000)

DISCUSSION

The practice of palatal rugae pattern for personal identification was suggested by numerous authors.[1467] Palatal rugoscopy was first proposed in 1932, by a Spanish investigator named Trobo Hermosa.[8] It was around 1955 that a proper classification of palatal rugae was put forward by Lysell.[9] Later, this classification was modified by Thomas and Kotze in 1983, and it was considered to be the most acceptable one.[710] Although there is numerous classification of palatal rugae based on length and shape,[11] there are difficulties in distinguishing, categorizing and concluding the minute variations in palatal rugae.[12] Therefore, the classification based on the shape was used for the present study.

The use of palatal rugoscopy in forensic identification has benefits because the rugae in the mouth remains unchanged in its position throughout life and are protected from trauma and high temperatures due to its unique location in the oral cavity i.e. surrounded and protected by lips, cheeks, tongue, teeth and bone.[1314]

The present study was an attempt to determine the predominant pattern of rugae if any in the sample population of South Indian state. An attempt was also made to determine the differences in rugae pattern among two genders in the selected groups. The present study revealed that wavy pattern appears to be the most predominant pattern in males and females followed by curved, straight and circular patterns. This finding was in accordance with the study done by Sumathi et al.[15] on the Puducherry population where they found the most predominant pattern was wavy followed by straight, curved, branched and circular pattern. Shanmugam et al.[2] had done a study on population from Tamil Nadu and found wavy pattern as the predominant pattern followed by curved, straight, unification and nonspecific, and the least was circular, which is comparable with our findings for the Puducherry population.

Surekha et al.[1] had done a study on the Manipuri and Kerala population where they found wavy as the predominant pattern among Kerala population followed by curved, straight and circular, which is in accordance with the findings of the present study, while a study done by Shetty et al.[12] on Kodava and Malayalee population found that wavy and straight patterns were the highest among the Kerala population. In the present study, we found a curved pattern followed by straight, while Shetty et al.[12] found a straight pattern followed by curved, unification and nonspecific. Circular pattern was totally absent in Shetty et al.'s study[12] while the present study and Surekha et al.[1] found a circular pattern among the Kerala population.

Kotrashetti et al.[16] found that the more prevalent forms in Maharashtra and Karnataka were straight and wavy, followed by curved. Few circular and nonspecific rugae forms were also recorded. The straight type was more in number among Maharashtra, and the wavy type was more in number among Karnataka.

Nayak et al.[4] had done a study on Western and South Indian population and showed that wavy and curved patterns were the most prevalent rugae shapes followed by straight rugae. Unification was few in number, while the circular pattern was found to be absent.

Shanmugam et al.[2] had done a study on North and South Indian population and concluded that wavy, curved and straight rugae pattern were predominant.

The above studies[12461216] suggest that wavy pattern is the most predominant pattern among South Indians followed by curved and straight patterns. When compared to other parts of India, Nayak et al.[4] found curved pattern as the predominant followed by wavy and straight rugae pattern among Western Indians. Shanmugam et al.[2] found that curved and wavy patterns showed equal predominance in North Indians followed by a straight rugae pattern.

When compared between both sex, in the present study, we found that the most common pattern was wavy (male – 54.3% and female – 53.09%), while curved pattern was more common among the female (21.09%) than male (13.97%), which is consistent with findings of Kotrashetti et al.[16] In the present study also confirms the straight pattern was more common among the male with mean value of 1.8 and in female about 0.45 which is similar to the findings of Shetty et al.[12] Where the Kerala males showed mean of (2.26) and female (1.2). The least common was found to be the circular pattern in both sexes which accounted for around 1%.

CONCLUSION

The present study did not show statistical significance between pattern and region as well as there was no interrelation between the three characters (pattern, region and gender). It could be due to the fact that the study populations were of the same geographical region and shared ancestry, which probably reduced these discrepancies to moderate levels. As the sample size was limited, variation in the above interpretations should be considered as a preliminary study and should be examined with a large sample to further validate the study findings.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.