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Introduction: Palatal rugae (rugae palatinae) are transverse folds on hard palate of most mammals, but their number and position is specific for each species. Palatal rugae are also known as plicae palatinae transversae. They are formed in the third month of intrauterine life from the covering connective tissue. Length of palatal rugae and space between them increase with development and growth of the anterior part of palate in early childhood. They are very wide-spread in mammals, but their biological significance is still unclear. When we talk about palatal rugae, we describe their shape, definition, length, distance between two folds, height and width.
Palatal rugae are irregular, asymmetrical elevations of the mucouse membrane made from the lateral membrane of the incisive papilla, directly along foramen incisivum and the anterior part of the medial palatal suture. The histological folds are a multi-layered, planocellular, mostly paraceratinized epithel on connective tissue of the base, similar to the adjacent palatal tissue.
For almost more than a hundred years, it has been attempted to categorize palatal rugae. Today, the most significant and the most wide-spread is the Lysell's classification from 1955. According to this classification, palatal rugae are divided into three categories and are measured in a straight line. The three categories are: primary (5 mm and more), secondary (3-5 mm) and fragmentary (2-3 mm). Lysell concludes that shape, length, width, prominence, number and orientation of palatal rugae vary greatly among patients. Besides Lysell's classification, another classification widely used in researches is the Lima's classification, which distinguishes among four main types: intermittent, straight, curvy and combined.
Generally, there is no symmetry in number, shape and position of rugae. Variations are also present, although in a smaller number, between left and right half of every person's palate. Growth of teeth or their loss does not affect the shape, appearance and characteristics of rugae.
A great number of researches agree that appearance and structure of rugae are unchangeable and do not alter under the influence of heath, chemicals, illness or trauma. If palatal rugae are destroyed, they are reproduced at the exact same place. This is why palatal rugae represent an ideal parameter in forensic identification.
Study of palatal rugae for the purpose of identification of people is called palatoscopy or palatal rugoscopy. In forensic researches in Bosnia and Herzegovina, palatal rugoscopy has not been used so far and researched in this area are quite modest. Therefore, the purpose of this research is to determine specificities of palatal rugae patterns based on a sample of Bosnian-Herzegovinian population of different age groups and different sex, so that the palatal rugoscopy could be used as an auxiliary method in identification in forensic researches in Bosnia and Herzegovina.
Examinees and research methods: The research includes 250 gypsum models of upper jaw of both sexes and different age groups from Sarajevo and the surrounding area. The sample did not include: patients with severe congenital anomalies, patients with severe systemic diseases and underage patients whose parents did not sign an approval for participation in the research. The gypsum models belong to 127 (50.8%) men and 123 (49.2%) women aged 10 to 60. Impressions were taken with commercial (factory) metal spoon of an appropriate size, depending on the state and size of jaw. The impression material used was alginate “Hydrogum“ produced by Zhermack Clinical.
On the gypsum models, counters of palatal rugae, median palatal suture and papillae incisiva were drawn with pencil HB 0.5 mm. Then, each model was placed on a flat surface and photographed with digital camera Olympus FE-130 placed vertically. Palatal rugae were then marked in computer program Paint with letter of the alphabet, starting from the anterior part of the right side of patient's palate and then clockwise. The measuring of palatal rugae on gypsum models was done in computer program VistaMetrix. Length of palatal rugae were measured with a straight line, regardless of eventual irregular shape of palatal rugae. Width of palatal rugae were taken on the widest part of rugae. Distance from the median palatal suture was taken with a straight line from the rugae to the closest point on median palatal suture. Distance from papillae incisiva was measured with a straight line, from the papillae incisiva to the same point from which the distance to the median palatal suture was measured. All measurements are in millimeters.
Results and discussion: Results of analysis of number, shape, size and position of palatal rugae in the sample of Bosnian-Herzegovinian population points to certain similarities, but also to differences from the populations researched so far. In the Bosnian-Herzegovinian sample, the number of palatal rugae is from 1 to 6 on the right side of palatal arch and 1 to 7 on the left side. The most frequent were examinees with 2 and 3 palatal rugae per each side of the gypsum model. Distribution of palatal rugae between right and left sides show great similarity, which leads to the conclusion that they are almost fully symmetrically distributed.
Distribution of palatal rugae classified according to length according to Lysell shows that, in Bosnian-Herzegovinian population, which was expected, each person has primary palatal rugae, secondary were present in only one third of examinees, while prevalence of fragmentary palatal rugae was insignificant.
Classification of palatal rugae according to their shape, i.e. according to Lima's classification, shows that in Bosnian-Herzegovinian population, the corrugated shape was predominant, being present in almost all examinees (94.8%). The curved shape was also very present (78%), and straight shapes were also very frequent (49.2%).
Analysis of sex- and age-related difference in number according to Lysell and Lima's classification of palatal rugae, especially according to their position in relation to the papillae incisiva, confirms to a great extent their independence from sex and age of examinees.
The research has shown almost no difference between sexes in the tested parameters, except in the number of secondary palatal rugae where, with the error of 7.6%, it can be concluded that women have more secondary palatal rugae. The 20-39 age group has, on average, a significantly higher total number of palatal rugae then a total number of primary palatal rugae according to Lysell, as well as a total number of corrugated shapes of palatal folds according to Lima than the other two age groups.
The literature used shows that most other authors have found statistically significant difference between men and women regarding different characteristics of palatal rugae (number, shape, length).
In an attempt to establish a person's sex based on palatal rugae characteristics, a great number of researchers has used the logistic regression analysis (LRA). In this research, LRA has not resulted in a statistically significant predictors, and is therefore insignificant in sex-based differentiation in Bosnian-Herzegovinian population.
Conclusion: Palatal rugae in humans are asymmetrical, which is unique for this species. Besides, in their shape, position and number, i.e. their pattern, palatal rugae are unique in each patient. Changes occur in bone structure, but palatal rugae pattern remains the same throughout life. In short, there are no two identical palatal rugae patterns, not even in identical twins.
The purpose of this research is to establish particularities of palatal rugae patterns in a sample taken from Bosnian-Herzegovinian population of various age groups and different sex, so that the palatal rugoscopy could be used as an auxiliary method in identification in forensic researches in Bosnia and Herzegovina.
Based on results of the research, it can be concluded that there are no statistically significant differences between palatal rugae on the right and those on the left side of palate regarding their dimensions, number and type. Unlike in case of sex, analysis of palatal rugae patterns of Bosnian-Herzegovinian population in different age groups has shown statistically significant differences.