Evaluation of palatal rugae pattern in different sagittal skeletal relationship adolescent subjects.

The purpose of this study was to evaluate the morphological structure of palatal rugae in Turkish orthodontic subjects with different sagittal skeletal malocclusions. Orthodontic dental casts of 105 patients (Class I [23 females, 12 males]; 35, Class II [18 females, 17 males]; and 35, Class III [14 females, 21 males] 10-22 years old) were analyzed for rugae patterns. Palatal rugae pattern and number, direction of rugae alignment, shape of incisive papilla were analyzed. Modified Thomas and Kotze classification was performed to analyze palatal rugae characteristics. The data were analyzed using the Kruskal-Wallis test. Wavy and curved types were the most common types of rugae pattern in all groups (Class I, Class II, Class III). As regards to the number of primary and secondary rugae on the left and right sides, there was no statistically significant difference among subjects with different skeletal malocclusions. Droplet-shaped incisive papilla was the most common form of incisive papillae among different skeletal malocclusion groups. The most common palatal rugae were direction type arranged in the horizontal direction. All rugae patterns were unique for each individual. The use of antemortem or postmortem palatal rugae records may facilitate identification of the suspects in forensic investigations by enabling facial reconstruction through skeletal malocclusions.

Introduction

Palatal rugae are transverse ridges of the mucosa located at the upper jaw, on the anterior portion of the hard palate.[ The number, shape, width, height, and location of palatal rugae vary from the left side of the palate to the right side as well as from one person to another, and are unique to every individual.[ Recent studies have suggested that palatal rugae could be used in forensic identification.[ Palatal rugae remain stable throughout life and therefore they are commonly used by dental clinicians as a reference point to evaluate the extent of tooth movement.[

Palatal rugae are specific to individuals and remain unchanged, and thus, this area can be used to identify individuals where other methods have failed.[ The facts that palatal rugae remain unchanged even after death and they are easily analyzed, make this body area important in elucidating forensic cases.[ Having a unique structure and being protected by the cheek, tongue, and teeth in the oral cavity, palatal rugae have a particular importance in forensic dentistry.[ By their protected localization, palatal rugae are much less affected by burns, physical trauma, and other factors.[ In addition, number, shape, and localization of palatal rugae remain unchanged throughout life and studies have suggested that they could be used as a fingerprint in most forensic cases.[ Their applicability in cases of edentulous people highlights the superiority of forensic identification by palatal rugae.[

Although the literature has various studies that evaluated differences in morphological structure of palatal rugae in different populations,[ no study has been conducted on individuals with various sagittal skeletal malocclusion. The aim of the present study was to investigate morphological structure of palatal rugae in Turkish orthodontic subjects with various sagittal skeletal malocclusion.

Methods

Analyzing of the palatal rugae patterns

The study subjects comprised of 105 individuals aged 10 to 22 years who were admitted to the Department of Orthodontics at Ordu University Faculty of Dentistry for orthodontic treatment. The research was designed as a retrospective study and archive materials were used, therefore ethics approval was not required for this study. The subjects were grouped as Class I, Class II, and Class III according to the ANB angle measured on lateral cephalometric radiographs in order to perform skeletal classification of the study participants (Class I: ANB angle 0° to 4°; Class II: ANB angle > 4°; Class III: ANB angle < 0°). Of these subjects, 35 were classified into Class I (23 females, 12 males); 35, into Class II (18 females, 17 males); and 35, into Class III (14 females, 21 males). The subjects who previously underwent surgery in the palatal area and received orthodontic treatment were excluded from the study. The subjects whose palatal rugae were clearly visible on the cast models were included in the study. The number and pattern of palatal rugae were determined from maxillary cast models before orthodontic treatment in all groups. Maxillary dental cast models were produced using high-quality plaster. Digital photographs of the cast models were taken in a standard position focusing on the palatal rugae. The distance between the model and the camera lens was standardized. Each photo was assessed using the Adobe Photoshop CS3 software in its original size. The modified Thomas and Kotze classification system was used to determine the types of palatal rugae.[ The number and pattern of palatal rugae, shape of the incisive papillae, and direction of rugae pattern were evaluated on the cast models of maxilla (Figs. 1 and 2).

Figure 1

Modified Thomas and Kotze classification of the palatal rugae: (A) straight, (B) curve, (C) wavy, (D) unification, (E) annular pattern.

Palatal rugae anatomic landmarks: (A) incisive papilla, (B) primary palatal rugae, (C) secondary palatal rugae.

Statistical analysis

All data were analyzed using SPSS (version 20.0, SPSS Inc., Chicago, IL) software. The Kolmogorov–Smirnov test was used to test if the data were normally distributed. The Kruskal–Wallis test was used to compare the number of primary palatal rugae (PPR) and secondary palatal rugae (SPR) among the groups. In order to determine intra-observer reliability, 20 cast models were reassessed by the same observer 4 weeks after the first assessment. Kappa statistics were used to evaluate intra-observer correlation. P values of less than 0.05 were considered statistically significant.

Results

The direction of palatal rugae, shape of the incisive papillae, and the shapes of PPR and SPR secondary rugae were reassessed on 20 cast models 1 month after the initial assessment. More than 80% concordance was achieved between the 2 measurements in all assessments. Morphological distribution of PPR and SPR in subjects with different sagittal skeletal malocclusion is presented in Table 1. Wavy and curved types were the most common types of rugae pattern in all groups (Class I, Class II, Class III). As regards to the number of PPR and SPR on the left and right sides, there was no statistically significant difference among subjects with different skeletal malocclusions (Table 2). Droplet-shaped incisive papilla was the most common form of incisive papillae among different skeletal malocclusion groups (Fig. 3). In all groups, most of the palatal rugae were arranged in the horizontal direction (Fig. 4).

Table 1

Distribution of number of primary rugae in different sagittal relationships.

Table 2

Distribution of primary and secondary rugae palatina number in different sagittal skeletal relationships.

Figure 3

Shape of incisive papilla in different sagittal skeletal malocclusions.

Figure 4

Direction of palatal rugae alignment in different sagittal skeletal malocclusions.

Discussion

Forensic identification through palatal rugae becomes important in cases where fingerprints are unavailable.[ Palatal rugae are composed of collagen fibers that are resistant to stretching and abrasion, allowing postmortem examination of this area.[ In addition, studies have reported that palatal rugae are unique to every individual.[ Similarly, in this present study, each subject's palatal rugae were found to be unique. Some authors suggest that palatal rugae remain unchanged as of 12th weeks of intrauterine life,[ whereas other authors suggest that palatal rugae may change in number with increasing age but retain their general configuration.[ The present study did not investigate the changed in palatal rugae in different period time, but evaluated the number and shape of the palatal rugae among different skeletal malocclusion groups.

Due to their unique and stable structure, palatal rugae can be used in forensic identification.[ Several authors analyzed palatal rugae and proposed various classifications to evaluate them.[ Lysell has been the first to define their shapes.[ Subsequently, other classification systems were proposed by other researchers.[ The method described by Thomas and Kotze, which is the most commonly used and simplest method, was used in the present study to define the types of rugae pattern.[

The number of PPR ranged from 2 to 6 in the subjects examined in the present study. In addition, there was no significant difference among different sagittal skeletal malocclusion groups in terms of the number of PPR and SPR on either sides of the palate. These findings are consistent with those reported by Suhartono et al.[ As a result, PPR and SPR showed symmetric distribution in terms of their numbers on either sides of the palate among different skeletal malocclusion groups.

Some studies have provided evidence that the structure of palatal rugae remained unchanged even in postmortem period, and that an individual could be reliably identified based on the structure of palatal rugae.[ The number and shape of palatal rugae on the right and left sides of the palate differ between males and females in different populations checked in various studies.[ However, to the best of our knowledge, this is the first study that compared morphological structure of palatal rugae in different sagittal skeletal malocclusion groups. In this study, which is the first study in the literature to evaluate the shape and number of palatal rugae in different sagittal skeletal malocclusion groups, no significant difference was detected among the groups.

Distribution of the shape of palatal rugae in a population shows racial differences.[ In the present study, wavy type of rugae was the most common pattern in different sagittal skeletal malocclusion groups of Turkish background. The studies by Azab et al[ and Kapali et al[ also reported wavy type of rugae as the most commonly observed rugae pattern. Consistent with these studies, the wavy type of rugae was the most common rugae pattern in the present study.

Conclusion

Further studies on a larger number of subjects are required in order to confirm the relationship between the pattern of palatal rugae and sagittal skeletal malocclusion. This may allow identification of potential suspects through skeletal malocclusions and palatal rugae and lead the path in forensic dentistry. Moreover, the use of antemortem or postmortem palatal rugae records may facilitate identification of the suspects in forensic investigations by enabling facial reconstruction through skeletal malocclusions.