INTRODUCTION

A review of the dental, anthropological, and forensic literature shows that research on dental morphology by observation, recording, and analysis of tooth crown morphological patterns (TCMP)-like biological markers-has focused, respectively, on the clinical role of morphological expressions as an etiological factor of caries by bacterial plaque retention; the anthropological study of past and present peoples to clarify their history, origin, training, contacts, travels, and isolations, and supporting the processes of forensic identification in reconstructing the odonto-biography of an individual.^1,4

Two of the TCMP’s most commonly studied are deflecting wrinkle and cusp pattern, whose expression contributes to the morphological configuration of the occlusal surface of deciduous and permanent lower molars. Due to their high taxonomic value, these traits have been used in the estimation of biological relationships among different human groups based on frequency, bilateralism, and sexual dimorphism. However, few studies have correlated the expression of TCMP’s with each other, focusing mainly on the correlation of the expression of a same morphological trait in different teeth, in order to understand the behavior of the morphogenetic fields during the odontogenesis of bifiodontia (dental system consisting of deciduous and permanent dentitions).^5-7

However, the correlation of the expression of two TCMP’s in a same tooth could explain the way the molar morphogenetic field sets the pattern of cusps and grooves from the centers of growth (enamel knots), and the way in which the main and secondary slopes of the primary grooves are phenotypically modeled. Therefore, the objective of this study was to correlate the expression of cusp pattern and deflecting wrinkle in six southwestern Colombian ethnic groups, participating in the debate on the phylogenetic mechanisms that shape the morphological variability of the tribosphenic quadritubercular molar.

MATERIALS AND METHODS

Descriptive observational study correlating the frequency and variability of cusp pattern and deflecting wrinkle in 480 plaster models of six ethnic groups from southwestern Colombia (Figure 1), corresponding to 100 Caucasoid mestizos from Cali (50 women and 50 men), 60 Afro-descendants from Cali (34 women and 26 men), 84 Afro-descendants from Puerto Tejada (42 women and 42 men), 116 Afro-descendants from Villa Rica (57 men and 59 women), 60 indigenous misak (37 women and 23 men) and 60 indigenous nasa (35 women and 25 men).

Figure 1 Geographical distribution of the six ethnic groups taken into account in this study. 1) mixed Caucasoid from Cali (Valle del Cauca), 2) Afro-descendants from Cali (Valle del Cauca), 3) Afro-descendants from Puerto Tejada (Cauca), 4) Afro-descendent from Villa Rica (Cauca), 5) indigenous misak from Silvia (Cauca), and 6) indigenous nasa from Morales (Cauca). 

The plaster models used in this study are part of the collection of the Research Line in Dental Anthropology and Forensic Dentistry (Línea de Investigación en Antropología Dental y Odontología Forense) of Universidad del Valle School of Dentistry, which were obtained for research projects previously endorsed by the Universidad del Valle’s Institutional Committee of Ethics in Human Studies, so that the sample complied with the assent and informed consent of participants, stating that the models could be used in future studies, in accordance with Resolution 008430 of the Ministry of Social Protection.¹⁷

The ASUDAS system for observation and analysis was used to observe the two TCMP’s using a 10 X magnifier and a thin tip probe, starting at the second deciduous lower molars (75 and 85), the first permanent lower molars (36 and 46) and the second permanent lower molars (37 and 47).¹⁰ As the models were observed, information about the two TCMP’s was recorded in an Excel® worksheet and was later processed in version 22.0 of the IBM SPSS® Statistics software, by means of descriptive statistic test for frequencies, univariate and bivariate analysis for sexual dimorphism (Mann-Whitney U), bilateralism (Wilcoxon) and correlation between traits (Spearman’s correlation coefficient). A value of p < 0.05 was considered statistically significant.

RESULTS

The two TCMP’s show diverse expressions in the six ethnic groups, which is possibly associated with the dental complex from which they have received influence (Table 2). The cusp pattern was characterized by a Y shape in the second deciduous lower molars of mestizos and Afro-descendants from Cali, as well as the two indigenous groups. This expression varied in the first permanent lower molar, where patterns + and X showed mid frequencies. In the case of permanent second lower molars, the most frequent pattern was +, and Y the less frequent. The deflecting wrinkle showed a more homogeneous behavior in the six ethnic groups, with significant presence in the second deciduous lower molars of mestizos from Cali and the indigenous nasa. The groups of mestizos from Cali, Afro-descendants from Villa Rica and indigenous misak had mid frequencies in the first permanent lower molars, as well as the second permanent lower molars of mestizos from Cali. None of the six ethnic groups showed sexual dimorphism and both TCMP’s were bilaterally expressed (Tables 3 and 4). Similarly, it was evident that there is correlation between expression Y of the cusp pattern and grades 2 and 3 of the expression of the deflecting wrinkle (Figure 2). In this way, the configuration of the Y cusp pattern would be determined-bilaterally and with no sexual dimorphism-by the morphological conformation of the main groove of the mesiolingual cusp as a deflecting wrinkle, being moderate in the second deciduous lower molars, high in the permanent lower first molars, and low in the second permanent lower molars (Table 5).

Figure 2 Variations in cusp pattern and deflecting wrinkle (*) of the first permanent lower molar. A. dryopithecine Y cusp pattern and grade 3 deflecting wrinkle (constriction with L-shape); B. X cusp pattern and grade 1 deflecting wrinkle (shallow constriction). 

DISCUSSION

The cusp pattern and the deflecting wrinkle, as stated in this study, have experienced great variability in their expression, associated with the behavior of global dental complexes since the second half of the last century. In this way, Hanihara included the Y cusp pattern and the deflecting wrinkle in the Mongoloid dental complex to group different populations of East Asia that had a complex dental morphology in common. Later, Turner II divided the Mongoloid dental complex into Northeastern Asian populations, or sinodonts, characterized by the Y cusp pattern and the intensification of expression of the deflecting wrinkle (grades 2-3), and Southeastern Asian populations, or sundadonts, who retained the ancestral Y condition but simplified the deflecting wrinkle (grade 1). Similarly, Zoubov divided the global populations into the Eastern dental complex (the same Mongoloid dental complex of Hanihara) and the Western dental complex, consisting of northern Caucasoid and Negroid or southern Caucasoid populations, whose dental features include the high frequency of the + and X cusp pattern, and a low expression of deflecting wrinkle. Subsequently, Irish classified the southern Negroid populations of Africa (the same western dental complex of Zoubov) into the sub-Saharan dental complex and the North African dental complex, with significant expressions of pattern + and low expression of deflecting wrinkle.^{18,19,20,21,22} Concerning the populations of the Americas, there is still some debate on the inclusion of the Paleo-Indian and contemporary peoples (indigenous groups, Afro-descendants and Caucasoid mestizos) in an americanoide dental complex, with morphological variations and frequencies very similar to the sinodont Mongoloid dental complex.²³

In the case of the cusp pattern, Gregory described pattern Y with the presence of five cusps, a combination that is recognized as the classic or dryopithecine pattern of lower permanent molars.⁸ Thus, a series of phylogenetic variations derived from this more primitive cusp pattern, including a first stage corresponding to the Y5 dryopithecine pattern as such, a second stage Y4 which reduces the number of cusps to four, a third stage + 5 or cross-shaped stage that changes the expression of the pattern, and a much more variable fourth stage including patterns + and X. In this way, it has been determined that expression Y is considered present, while patterns + and X are considered reductions.^9,24 Studies in modern human populations have shown that one characteristic of the ethnic groups of Mongoloid and Negroid origins is that the first permanent lower molars have retained the ancestral condition Y, while the groups of Caucasoid origin have more frequent expressions + and X. In the case of the second permanent lower molars, the Negroid and Mongoloid show the same trend, but the number of cusps reduces from five to four with respect to the first molar.^25,27

In this study, the permanent first lower molars maintained the same trend in the group of Afro-descendants from Cali, while the other five ethnic groups showed greater variability, as patterns + and X had mid frequencies, much more variable than the group of indigenous misak. In the case of the Caucasoid mestizos from Cali, there is a significant frequency of pattern +, agreeing with the literature reports. Regarding the cusp pattern of permanent second lower molars, the behavior was similar to what has been reported, with patterns + and Y being the most frequent. Finally, the second deciduous lower molars presented significant frequencies of pattern Y in the two groups from Cali and the two indigenous groups.

On the other hand, since it was first described in the first hominids from the Miocene, the deflecting wrinkle has been a TCMP frequently used to differentiate the Mongoloid populations from the Negroid and Caucasoid peoples, with a higher expression (grades 2-3) in the first permanent lower molars, and lower expression (grades 1-2) in the second permanent lower molars. Also, the higher frequencies of deflecting wrinkle have been observed in sinodont populations.¹⁶

In this study, the expression of this TCMP showed low frequency in the second deciduous lower molars (except in indigenous nasa) and mid frequencies in the first permanent lower molars (in Afro-descendants from Villa Rica and indigenous misak) and in the second permanent lower molar (mixed Caucasoid). Thus, the behavior of these two TCMP´s was associated with miscegenation of the contemporary Colombian population as a result of various ethnohistorical processes that have been traced back to the initial peopling of the Americas by groups derived from the sinodonts (Mongoloid dental complex) that formed the Paleo-Indian characterized by Y cusp pattern and grade 3 deflecting wrinkle; the arrival of different Northern Caucasoid human groups from Western Europe (Western dental complex) who populated the American territory during the discovery, conquest, and colony, which were characterized by an X cusp pattern and deflecting wrinkle in grades 0 and 1; the arrival of Negroid people groups (southern Caucasoid of the Western dental complex) brought into slavery, whose lower molars showed cusp pattern + and X, as well as low frequencies of deflecting wrinkle; and the numerous and constant microevolutionary processes (migrations, displacements, contacts, and isolations) that have occurred due to different social, religious, political, economic and demographic phenomena that have occurred in the territory, and that finally have influenced the establishment of the multi-ethnic, multicultural, and polygenic nature of the Colombian population, represented in the average tri-ethnic genetic composition of Colombians from the 62% Caucasoid, 26% Mongoloid and 12% Negroid genes.^28,29

In the particular case of Southwestern Colombia, all the described processes occurred more intensely than in other regions of the country-hence this region is considered an “ethnographic melting pot”-, so the study of morphological variations of contemporary mestizo Caucasoid, Afro-descendant and indigenous groups has shown that the phenotypic expressions of the TCMP’s go hand in hand with the historical miscegenation.³⁰

Between the 17th and 19th centuries, the demographic development (geographic and ethnic distribution) of the territory between south of the Department of Valle del Cauca and north of the Department of Cauca arose from the haciendas as a socio-economic model represented in the cultivation of land, mining, and livestock estates; and from there, several municipalities in the South of the Department of Valle del Cauca (Southeast of Cali and Jamundi) and North of the Department of Cauca (Robles, Puerto Tejada, Villa Rica and Santander de Quilichao), among others, arose from the settlement of freedmen, maroons and slaves of African descent in the territories of three large estates of field. With the abolition of slavery since 1852, the big landowners developed the terraje system, in which free people of African descent were allowed to settle on marginal lands of the estates and grow their own crops, in exchange for work. Given this new mechanism of disguised slavery, many black families preferred to occupy idle lands along the Cauca River, where they founded settlements.

At the beginning of the 20th century, with the emergence of sugar mills and the industrialization of plantations, the descendants of African slaves who failed to keep any plot of land entered the proletariat which was responsible for cutting the sugar cane, worked in other types of crops (cocoa, coffee, banana, tobacco), or emigrated to the city of Cali, where they occupied wasteland. Later, in the second half of the 20th century, there was an important demographic concentration of Afro-descendants in what is today known as the Aguablanca District, due to the migratory flows from the Pacific coast (caused by the tsunami that hit the Pacific coast), to the numerous migration waves mestizo peasants from the coffee belt (and on a lesser extent indigenous nasa, yanacona, and misak from the departments of Cauca, Huila and Nariño due to the public order situation of the region), and the job possibilities that still offer the sugar cane plantations.^31,32 This is why the mestizos and Afro-descendants from the city of Cali taken into account in this study, inhabiting the Southeast area of the town, have retained the Y cusp pattern in the deciduous molars and have expressed patterns + and X in permanent molars, as well as mid frequencies of grades 1 and 2 of the deflecting wrinkle, as expressions that relate them to the sundadont Mongoloid complex of Hanihara, the Caucasoid dental complex of Turner II, the Western dental complex of Zoubov, the sub-Saharan dental complex of Irish and the Saharan Africa dental complex of Edgar.

In the case of indigenous groups, the nasa occupy the Musse Ukwe reservation of the municipality of Morales, and historically they have been exposed to a greater contact with settlers and mestizo peasants, hence the mean expression of both TCMP’s suggest the ancestral influence of the Mongoloid sinodont dental complex and the modern miscegenation with groups of the Caucasoid dental complex. Otherwise has occurred with the nasa who occupy the territory of the Guambía reservation within the urban area of the municipality of Silvia, where they have remained relatively isolated from other populations, hence the expressions of the Y cusp pattern in deciduous and permanent molars (although they showed mid frequencies of the + pattern) and grades 2 and 3 of the deflecting wrinkle, approaching them to the Mongoloid sinodont dental complex. Finally, the Afro-descendent groups from Villa Rica and Puerto Tejada are characterized by mid frequencies of the Y cusp pattern, mainly in the deciduous molars, and significant frequencies of +, in addition to a low expression of the deflecting wrinkle (grades 1-2), suggesting the maintenance of the dental morphology of the Caucasoid dental complex and influences of the Mongoloid sinodont dental complex, due to contacts with indigenous groups.

CONCLUSIONS

Due to the miscegenation of the population in Southwestern Colombia (South of Valle del Cauca and North of Department of Cauca) from mixed Caucasoid, indigenous and Afro-descendant ethnic groups, the frequencies of cusp pattern and deflecting wrinkle show a wide variability according to the ASUDAS criteria; therefore, the expression of both TCMP’s helped differentiate the mixed Caucasoid and African-descendant groups (with a tendency towards the Caucasoid dental complex) from indigenous groups (with a tendency towards the Mongoloid dental complex). We can then conclude that, in the six ethnic groups taken into account in this study, the cusp pattern configuration may vary according to the degree of expression of the deflecting wrinkle, in such a way that the expression of the Y cusp pattern prevails when the deflecting wrinkle is expressed in grades 2 and 3-a special trait of contemporary Colombian populations who have received influences from Mongoloid sinodont groups as evidenced by the Spearman’s rank correlation coefficient.

Finally, in the dental context, it is essential to recognize the way the occlusal surface-from the expression, variability, bilateral symmetry, and sexual dimorphism in morphological traits-of the lower molars is set up during procedures of morphofunctional restoration of the tooth structure altered through operation and oral rehabilitation. Hence the importance for dentists to address morphology from different areas of knowledge, including dental anthropology.