Assessment of palatal rugae in a multiethnic population

Introduction: Palatogenesis is an important component of facial development that leads to the formation of an intact palate via the fusion of three palatal components—the two lateral palatal shelves and the anterior primary palate. On the soft tissue side, the union of the two lateral palatal shelves forms the median palatal raphe. Problems in any of the steps of palatogenesis can lead to the development of a cleft palate (CP). Palatal rugae development takes place during palatogenesis. These folds of tissue on the hard palate can be seen even before palatal shelf elevation and fusion. There is some evidence that palatal rugae development and palatal shelf elevation share some common molecular mechanisms. The exact function of the palatal rugae is not known, but proposed roles include assisting in infant suckling, enhancing taste perception, and adding in speech and phonation, among others. Different classification schemes exist to characterize rugae patterns, which tend to vary among different demographics. Moreover, another structure that can be present on the palate is a palatal torus, a benign bony protuberance in the middle of the palate. These do not tend to develop until adolescence or beyond. They are more frequently seen in older patients and in women. This study aims to characterize palatal rugae patterns (including right and left differences in rugae patterns), median palatal raphe patterns, and palatal tori patterns in subjects of different ages, biological sex, and races. Evaluation of palatal rugae patterns included a classification scheme in the transverse dimension, which has not been previously undertaken. Methods: A total 1020 maxillary digital casts were evaluated by three raters for the patterns of palatal rugae, median palatal raphe, and palatal tori. The study population consisted of subjects with a family history of cleft lip and/or palate (CL/P) (case relatives) and subjects without a family history of CL/P (controls). The classification scheme for palatal rugae patterns was designed and revised by teams at the University of Pittsburgh and the University of Iowa. Three calibration attempts were done to ensure rater precision. Further, one internal control set was evaluated separately by each rater. Only those variables with moderate or greater intra- and inter-rater agreement (kappa values at or above 0.4) in both the calibration Set 3 and the set of internal controls were included in the analysis. A total of 51 statistical tests were run, including Chi-Square Test of Independence, Fisher’s Exact Test, the Wilcoxon Rank Sum Test, the Wilcoxon Sign Rank Test, and the Kruskal-Wallis Rank Sum Test. Results: The relationships between age and 4 of the 9 rugae patterns (Category 1 L, Category 3 R, Complex L, Granular Rugae) were significant. Older subjects tended to have less rugae counts in all four categories. Women had a significantly higher prevalence of palatal tori than men (34.71% v. 15.52%). The relationships between race and 5 of the 9 rugae patterns (Category 1 R, Simple L, Complex R, Complex L, and Granular Rugae) and between race and Torus Palatinus were also significant. Asians had the highest prevalence of Torus Palatinus (46.99%), followed by Whites (26.51%), Other/Unknown races (25.76%), and lastly by Blacks (15.65%). The relationships between palatal tori and the rugae variables observed were not statistically significant. Right to left differences were significant for Category 1, Category 3, and Complex rugae. For both case relatives and controls, counts of all four rugae patterns examined for asymmetry occurred more often in the right side of the palate. These differences were statistically significant for Category 1 rugae in controls, Category 3 rugae in both cases and controls, Simple rugae in controls, and Complex rugae in case relatives. There was no evidence that differences in the right-left counts between the case relative and controls were statistically significant. Conclusion: Certain rugae patterns are significantly associated with age and race. Neither palatal tori nor biologic sex are associated with any of the rugae patterns examined. Palatal tori were significantly associated with biologic sex and with race. Women have a higher prevalence of palatal tori than men. Asians have the highest prevalence of palatal tori compared to the other three race groups examined. Right to left differences were significant for Category 1, Category 3, and Complex rugae, indicating that rugae patterns are asymmetric. Certain right-left differences continue to be significant when stratified by case relatives and controls.