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Year : 2020  |  Volume : 31  |  Issue : 2  |  Page : 241-246
Morphology of the palatal rugae before and after orthodontic treatment with and without rapid maxillary expansion and dental extractions

1 Department of Dentistry, Meridional Faculty (IMED), Passo Fundo, Russia
2 Department of Therapeutic Dentistry, Institute of Dentistry, Sechenov University, Moscow, Russia
3 Department of Preventive and Community Dentistry, School of Dentistry, Federal University of Uberlândia, Uberlândia, Brazil

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Date of Submission07-Jan-2019
Date of Acceptance07-Jun-2019
Date of Web Publication19-May-2020


Background: The palatal rugae contribute to oral swallowing, taste perception, and speech. From a forensic point of view, the distinctive morphology of these structures can be used to support human identification. However, the morphology of the rugae may be altered by trauma or therapeutic interventions in the palate. Objective: This study aimed to analyze the morphology of the palatal rugae before and after orthodontic treatment performed with and without maxillary expansion and dental extractions. Materials and Methods: The sample consisted of 60 dental casts taken before (n = 30) and after (n = 30) orthodontic treatment from patients aged >18 years. The patients were treated with rapid maxillary expansion by using Haas appliance (n = 10), by extracting the maxillary first premolars (n = 10) and by using only conventional fixed orthodontic appliances (n = 10). All the dental casts were analyzed twice by two independent examiners that were blind for the type of treatment. Results: All the differences between groups were statistically significant (P < 0.05). More alterations in the morphology of the palatal rugae were observed in patients treated with rapid maxillary expansion, whereas few alterations were performed in patients treated with no maxillary expansion or dental extractions. Conclusion: The use of palatal rugae for forensic purposes must be avoided in patients that underwent invasive orthodontic treatments, such as those founded on maxillary expansion and dental extractions.

Keywords: Anatomy, forensic dentistry, human identification, orthodontics, palatal rugae

How to cite this article:
Bavaresco D, Von Meusel LD, Franco A, Makeeva I, Paranhos LR, Cericato GO. Morphology of the palatal rugae before and after orthodontic treatment with and without rapid maxillary expansion and dental extractions. Indian J Dent Res 2020;31:241-6

How to cite this URL:
Bavaresco D, Von Meusel LD, Franco A, Makeeva I, Paranhos LR, Cericato GO. Morphology of the palatal rugae before and after orthodontic treatment with and without rapid maxillary expansion and dental extractions. Indian J Dent Res [serial online] 2020 [cited 2023 Mar 20];31:241-6. Available from:

   Introduction Top

The human palatal rugae manifest in the oral cavity around the 12th week of intrauterine life as an expression of the connective tissue that transversally folds in the anterior region of the hard palate.[1] From childhood to adulthood, the palatal rugae play an important part in oral swallowing, taste perception, and speech.[2] In forensic dentistry, the study of the palatal rugae – known as palatal rugoscopy – may be used to support criminal investigations.[3] More specifically, the scientific literature shows that the palatal rugae may contribute to the human identification process as an individualizing marker[4] that relies on the potentially distinctive shape and pattern of the rugae among different persons.[5] Other studies in the field refer to these rugae as tools for possible sexual dimorphism[6] and ethnic differentiation.[7]

During the human development process, the palatal rugae may change in size but not considerably in shape and pattern.[4] External factors that could trigger alterations in the shape and pattern of the palatal rugae include trauma or therapeutic interventions in the inherent soft tissue and the underlying bone structure of the palate.[8],[9] Orthodontic treatment of malocclusions and orthopedic management of atrophic maxillae with rapid maxillary expansion are commonly performed in the routine of dentistry. These therapeutic interventions are founded on systematically induced tooth and bone movements, respectively, and figure as potential factors that may influence on the morphology of the palatal rugae.

Based on the hypothesis that the morphology of the human palatal rugae changes after orthodontic treatment, this study aimed to assess and compare the shape and pattern of palatal rugae from dental casts of orthodontic patients before and after treatment.

   Materials and Methods Top

The study was conducted in accordance with Helsinki Declaration of 1975, as revised in 2000, and was approved by the local committee of ethics in human research (protocol number: 1.813.507/2016). A quantitative, observational, and cross-sectional study was designed. The methodological information of this study is presented according to the standards of The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE statement).[10]

A nonprobabilistic sampling strategy for performed. The sample consisted of patients that underwent dental treatment in the local dentistry center. The inclusion criteria for the selection of participants consisted of male and female patients that had complete dental records in the archives of the local dental center, patients that underwent orthodontic treatment, patients that had initial and final orthodontic dental casts, and patients older than 18 years of age. The exclusion criteria consisted of orthodontic dental casts in poor condition, orthodontic dental casts in which the palatal rugae were not properly visible, patients with history of trauma in the maxillofacial region, patients with visible diseases in the soft and hard tissue of the palate, and patients with history of systemic diseases. At the end of the sampling approach, 30 patients were eligible for the study. All the patients were requested to sign an informed consent that allowed the use of their dental casts and records in this study.

The eligible patients were divided into three groups according to the type of orthodontic treatment that they underwent. Group 1 (n = 10) consisted of patients that underwent rapid maxillary expansion with Hass orthopedic appliance followed by fixed orthodontic treatment with no dental extractions. Group 2 consisted of patients that underwent fixed orthodontic treatment with the extraction of the maxillary first premolars followed by space closure via anterior retraction. Group 3 included patients that underwent fixed orthodontic treatment with no maxillary expansion and dental extractions [Table 1]. All the patients were treated under straight-wire technique. The mean treatment time in the total sample was 30 months (±5.4 months).
Table 1: Sample distribution based on the type of therapeutic approach and treatment phase

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Photographs of the orthodontic dental casts were standardly taken in occlusal view by using a Canon EOS Rebel T3® camera and 18-55 mm lenses (Canon Inc.®, Tokyo, Japan). The photographs were stored in.jpeg format and were imported in PhotoScape 3.7® software package (Mooii Tech Co. Ltd.®, Cheonan-si, Korea) for visualization and eventual adjustments of brightness and contrast.

The morphological analysis of the palatal rugae was performed according to a technique previously described in the scientific literature [Figure 1].[11] According to the technique the rugae are coded based on their shape and position in the palate [Table 2]. The combination of codes individually provided to each fold results in a pattern of palatal rugae that may be distinctive for each person. Two examiners blind for the sample group separately performed the analysis of the palatal rugae in pair of casts before and after orthodontic treatment for each patient. After the initial classification of palatal rugae morphology, they clustered the dental casts that present or not alterations in shape. This process was repeated by both examiners within an interval of 15 days to enable inter- and intraexaminer agreement tests.
Figure 1: Illustration of the orthodontic dental cast in occlusal view and the respective palatal rugae. The palatal rugae were classified according to a system previously proposed in the scientific literature.[11] According to the system, the palatal rugae on the right of the observer (left side of the dental cast) are described as “initial” ( first fold) and “complementary” (remaining folds). Similarly, the contralateral rugae are described as “subinitial” ( first fold) and “subcomplementary” (remaining folds). Based on their shape, the initial and subinitial rugae are coded with a capital letter, whereas the complementary and subcomplementary rugae are coded with a number from 0 to 9 [Table 2]. The combination of letters and numbers culminate in individual palatal rugae patterns coded for each person

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Table 2: Types of shapes and the inherent codes used for the classification of the palatal rugae based on their position, according to Martin-dos-Santos described by Vanrell (2009)[11]

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The reproducibility and agreement intra- and interexaminer was assessed by means of Kappa statistics. The interpretation of the outcomes was performed according to the classification of Landis and Koch (1977).[12] Fisher's exact test was used to compare the outcomes between groups. The statistical analysis was performed by using Stata® 12 software package (StataCorp.® LP, College Station, TX, USA) and considering a significance level of 5% and confidence interval of 95%.

   Results Top

Kappa statistics outcomes revealed agreement values that ranged between substantial (0.60) to nearly perfect (0.86) [Table 3]. The reproducibility within and between examiners increased gradually from the first to the second analysis of the orthodontic dental casts.
Table 3: Outcomes of the intra- and interexaminer agreement test for the reproducibility in classifying the morphology of the palatal rugae in orthodontic dental casts before and after treatment

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According to the first and second analyses of the first and second examiners, a higher number of dental casts with morphological alterations of the palatal rugae was observed in group 1, in which the patient were treated with rapid maxillary expansion. A slightly lower number of occurrences of morphological alterations of the palatal rugae were observed in group 2, in which the patients were treated with dental extractions and without maxillary expansion. Only two orthodontic dental casts presented morphological alterations of the palatal rugae in group 3, in which the orthodontic treatment was conducted with no maxillary expansion or extractions. The differences between groups were statistically significant (P < 0.05) for all the four analyses (n = 2 for the first examiner and 2 for the second examiner) performed in this study [Table 4].
Table 4: Outcomes of Fisher's exact test for the comparison of palatal rugae morphology before and after orthodontic treatment within the three different groups

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   Discussion Top

The human palatal rugae play an important role in physiological processes – especially in the early childhood as an essential support in the biomechanics of suction and speech.[13] Throughout life, the palatal rugae also participate in taste perception and oral swallowing.[14] In a forensic scope, the palatal rugae may be tool for human identification.[15] More specifically, the human identification process relies on distinctive evidences that are detected antemortem and postmortem that can indicate a potential association between an unknown cadaver and an alleged victim.[16] In practice, ridgeology (the analysis of friction ridges, e.g. fingerprints), forensic odontology, and genetics figure as the primary means for human identification.[17] However, other morphological structures of the human body may be used to support the investigations, such as the paranasal sinuses,[18],[19],[20] lingual mandibular canals,[21] and the palatal rugae.[22] The most eminent contribution of the palatal rugae for human identification consists of its distinctive morphology and pattern. However, the local influence of extrinsic factors, such as therapeutic procedures in the palate[8] or even finger sucking habits,[23] may modify the morphology of the rugae and consequently limit their use for forensic purposes. This study tested in the potential influence of orthodontic treatment on promoting morphological alterations of the palatal rugae.

Dental casts were used in this study because they are usually taken for treatment plan (initial) and follow-up (final) of orthodontic patients. The photographic analysis of this material was justified by the fact that imaging navigation software packages could be used to ameliorate the visualization of the palatal rugae by using adjustments of brightness and contrast. Additional methodological settings consisted of performing the analysis of the palatal rugae by two independent examiners. This approach was designed to quantify the bias inherent to the qualitative assessment of the morphology of the palatal rugae. The double analysis performed by each of the examiners also figured as a quality control procedure to assure that the bias related to the morphological analysis could be addressed and explored by statistical analyses. The analyses of the total sample were maintained and reported in this study because the examiner agreement tests reached substantial and nearly perfect reproduction. Opposite results from these tests would make necessary new training and calibration of the examiners for the analysis of the total sample.

Once the morphological analyses were performed, the sample was invested based on the different therapeutic groups. In this study, the groups were systematically organized and distributed from the most invasive type of treatment (group 1 – with rapid maxillary expansion) to the less invasive (group 2 – no maxillary expansion and no dental extractions). In group 1, more evident alterations of the morphology of the palatal rugae were expected, because the rapid maxillary expansion performed with orthopedic device has a direct impact in the palatal bones underlying the palatal rugae.[24] Statistically significant differences were observed between patients that presented or not morphological alterations of the palatal rugae (P < 0.05). The combination of both the analyses of examiner 1 reached a prevalence of patients with alterations of 70%, whereas the analyses of examiner 2 reached 80%. This outcome, corroborate the previous scientific literature that does not support the use of palatal rugae for forensic purposes in patients that underwent rapid maxillary expansion.[25],[26] In specific, the palatal rugae appear to remain stable in number after rapid maxillary expansion, but not in position and shape. Because the rapid maxillary expansion promotes the lateral enlargement along the palatine raphe, the distance between the medial ends of contralateral rugae increases[26] – consequently, the rugae are positioned differently after treatment.

Group 2 consisted of patients that were treated with the extraction of maxillary first premolars and figured as a group in which mild impact in the morphology of the palatal rugae was expected. During the orthodontic treatment, the extraction of first premolars may be necessary in the treatment of crowding or dental/skeletal protrusion.[27] The hypothesis of not having more evident alterations in the morphology of the palatal rugae is justified by the fact that the first premolars are less related to the palatal rugae than the underlying palatal bones previously discussed in face of the rapid maxillary expansion. In short, these teeth are only adjacent to the rugae but not necessarily inherent to them. Even though, the analysis of examiners 1 and 2 showed a prevalence of patients with morphological alterations of the palatal rugae of 55% and 65%, respectively. In the forensic practice, these outcomes raise a flag to highlight caution in the use of the palatal rugae from orthodontic patients treated with premolar extractions. The scientific literature is controversial whether or not premolar extractions play an essential modification in the palatal rugae.[28] However, some authors clarify that the extractions promote morphological alterations in the lateral edges of the rugae, whereas the medial edges remain more stable.[29] This phenomenon may be explained by the fact premolars are laterally positioned in relation to the palatal rugae. In this context, premolar extraction followed by the orthodontic movement of the adjacent teeth into the empty space promotes morphological alterations in the edges of the palatal rugae that are closer to the extraction site.

In the last group, the patients were solely treated with conventional fixed orthodontic appliances. Differently from the outcomes obtained in groups 1 and 2, visible morphological alterations were not expected in the palatal rugae, especially because the induced tooth movement in these patients was gradual and noninvasive. Accordingly, the first analysis of examiner 1 was to only that resulted in occurrences of morphological alterations before and after treatment (20%). All the other analyses resulted in 100% of lack of morphological alterations of the palatal rugae. The outcomes found in this group were significantly different to the other two groups (P < 0.05). Despite the promising use of the palatal rugae for forensic purposes in patients that underwent noninvasive orthodontic treatment, attention must be given to previous studies that showed prevalence rates of morphological alterations up to 62% in similar patients.[30] The reason behind the evident difference between studies may be founded on the different sampled populations, the different methods used for the classification of the palatal rugae and also the applied orthodontic techniques.

Future studies in the field should focus on improving the limitations found in the current scientific literature. In this context, intraoral scanning units could be used instead of manually taking dental impressions and making casts. This approach would reduce the bias of making two different casts from the same patient. Additional improvements include the implementation of a unified system for the classification of palatal rugae. This methodological setting would benefit comparative studies in the field. Moreover, it enables meta-analyses between outcomes in order to generate more evidence-based science between anatomy and forensics.

Based on the exposed in this study, the use of palatal rugae for human identification in persons with history of orthodontic treatment with rapid maxillary expansion or bilateral first premolar extractions should be avoided. In these patients, evident morphological differences in the palatal rugae were observed before and after treatment. Oppositely, morphological alterations of the palatal rugae barely occurred in patients that underwent orthodontic treatment with no rapid maxillary expansion or bilateral first premolar extractions.

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Correspondence Address:
Prof. Ademir Franco
Department of Therapeutic Dentistry, Institute of Dentistry, Sechenov University, Trubetskaya 8, Moscow - 119991
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijdr.IJDR_12_19

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]

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