Oclusivon and Attrition of the Primitive Yanomami Indians of Brazil
Cleber Bldegain Pereira, C.D.*
Harry Evans, D.M.D **
*Director and Coordinator, Inter-Brazilian Argentinian Studies, Research in the Federal Territorio of Roraima - Federal University of Santa Maria, Brazil

** Associate Director, Abe Stark Philantrophies Orthodontic Clinic, Brooklyn, New York; Visiting Professor, University of Buenos Aires Dental School, Argentina


In an attempt to understand the normal physlology of our dental structures, a number of studies of more primitive peoples have been undertaken. 1,2.6,7 The Yanomami Indians of northern Brazil were chosen for this study because they are racially pure and have not been subjected to cultural adaptation. According to Ribeiro's 9 "External Controls Category" the Yanomamis are classified as "lsolated." Consequently, they live in an authentic environment and have the habits and customs characteristic of their culture. Further they are of the same morphologic evolution as Modern Man. Dentally, the periodontium, tooth attrition, cervical abrasion, caries, missing teeth, gonial angle, and jaw relationships were studied. Generally, the Yanomamis exhibit a high prevalence of malocclusion (71 per cent), marked occlusal attrition, 83 per cent incidence of periodontal disease, and a total absence of cervical abrasion. The maxillomandibular relationship ln the adult tends to be prognathic and displays little or no vertical overlap, and the anterior teeth are usually edge to edge. The Yanomami according to lexical and structural evidence form a Family from the Karib or Protokarib, group and originated from the Macho-Chibcha phylum. They belong to the South Atlantic subrace of the American Indian and to the mongolian racial group. They are thus in a similar stage of morphologic evolution as modern man, as opposed to the Australian aborigines studied by Begg who belong to a more primitive racial group, and thus have a less advanced morphologic evolution.


The Yanomamjs speak one language and do not have any written language. Their drawings are limited to simple figures painted on their bodies on festival days (Fig. 1). Their only contact with civilization is through a religious mission and the Brazilian National Foundation of Indians, who have been careful to respect their culture. The mission is supplied by a small airplane, the only means of access to the outside world. These Indians live ln the northern part of Brazil borderilig on Venezuela and the contiguous part of Venezuela.

Racial Characteristics

The Yanomamis are short, well built, and muscular. Their shoulders are sliglitly wider than their hips. Their skin tone is brownish yellow, while their hair is black, straight, and thick. On their bodies they exhibit scant hair; beards are almost nonexistent. The "mongolian spot" frequently appears before the age of three. 'l'heir faces show typical but somewhat attenuated mongolian characteristics. The eyes are almond-shaped and have slanted eyelid openings whose external cleft ls higher than the lnternal (Fig. 2), and among some clildren the mongolian plica can be found. Their head structure is either brachiocephalic or mesiocephalic; dolichocephalons are rare. They exhibit wide noses with thick lips and prominent cheek bones. The gonial angle is constant in most cases, with frequent dentoalveolar bimaxillary protrusions (Fig. 3).
                                                                    Click in the image for look major

Yanomami with almond shaped slanting eyers which denote mongolian ancestry

Female adult Yanomami with normal profile ------ Young male with bimaxilary prominence
Food Sources

Land is cleared wlth stone axes and by burning. lt is then plowed with a hook shaped stick. Sweet cassava, manioc, bananas, tobacco, cotton, and sugar cane (a very recent cultural adaptation) are planted. Plants that yield medicinal and hallucinogenic drugs are also grown. The area is rich in game and fish with the exception of the Surucucu Mountain region. Consequently the tribes of that area have less meat and their diet and dental findings are different, which will be discussed later. Bows and arrows are used for larger game; the arrows are poisoned with curare. The natives are able to imitate the sounds of the birds and animais to a remarkable degree and utilize these skills ili hunting. Fishing was a secondary food source but with gifts of hooks and fishing lines (cultural adaptation), it is now increasing. Previous to the possession of hooks and lines, the fish were shot with arrows in the rapids, and poisoned in the still ponds then caught by liand. For cutting and preparing their food, the Yanomami use stone axes, animal jaws, and their own teeth. They also peel frults, nuts, and roots such as manioc with their teeth. The diet of the Yanomami from the Surucucu Mountaln region consists mainly of carbohydrates from the forest and fields. The other Yanomamis eat mostly meat. The grains stich as manioc are ground with stones that leave a grit in the "flour."

Food Preparation

Grilling. Large game is cut up whereas monkeys, birds, and small game are grilled whole. This type of food requires a strong masticatory effort. Boiling. Small game, fish, tapioca cake, etc., are boiled in clay pots. The grain derived from cassava and manioc is coarse and gritty and therefore has a marked abrasive effect on the teeth. Roasting. This process ls used mostly when the Indians are on a march. The fowl or small game is thrown into a fire to burn off the feathers or fur. It is then thrown on the ground to extinguish the flames. The outer layers of meat that are eaten are sandy and gritty. When the outer layers have been consumed the process is repeated. This method of food preparation has a considerable abrasive effect on the teeth.

Oral Habits

Noxious oral habits as such were not observed. Children breast feed until the age of three, at which time a new child is usually born. (Children are intentionally spaced every three years by the use of anticonceptional herbs.) Unwanted pregnancies, and defective and deformed infants are aborted or eliminated at birth. Mouth hygiene is unknowni. Adults often place a roll of tobacco between the lower lip and teeth producing a lingual pressure and movement of the lower anteriors. As previously mentioned, the teeth are used to portion out food and assist in handicrafts such as spinning cotton, and making nets and sleeping bags. They also weave baskets and fashion bows and arrows with the aid of their teeth. As a cosmetic consideration, women perforate their lips and cheeks, then place sticks in these perforations (Fig. 4).

Decorative sticks in lip an cheek perforation --- Yanomami with festive drawing face

Age Determination

The Yanomami count only one, two, or many. Therefore ages have to be calculated as they can relate their age to others chronologically. A girl reaches puberty at about twelve years (when the second molars erupt) and this is marked by a public ceremony. She marries shortly thercafter and has a child. Every three years she has another child. In this way serial deductions of ages can be estimated. It ls interesting to note that the difference in the abrasion of the first and second molars gives us the best clue as to age determination.

Age Criteria

One hundred fifty subjects were examined and classified as follows (1) ) 56 adolescents, 13 to 18 years old; (2) 38 adults, 19 to 29 years old; (3) 33 mature, 30 to 49 years old; and (4) 23 senile, 50 years or more.

Masticatory Activity

Two groups can be differentiated according to masticatory efforts. The Tototobl and Catrimani who llve in an arca where game is plentiful have teeth which are badly abraded but without stains or plaque due to vigorous mastication. Yet the senile group who chew less vigorously exhibit some staln and plaque. The group living in the Surucucu Mountains where game is scarce feed mostly on bananas alld some birds. Here there is less wear on the teeth, and tobacco stalns and plaque are abundant. Even the children exhlbit staining. However, the gingiva and supporting structures in both groups were in good health due to vigorous mastication.

Masticatory Activity

Two groups can be differentiated according to masticatory efforts. The Tototobi and Catrimani who live in an area where game is plentiful have teeth which are badly abraded but without stains or plaque due to vigorous mastication. Yet the senile group who chew less vigorously exhibit some stain and plaque. The group living in the Surucucu Mountains where game is scarce feed mostly on bananas and some birds. Here there is less wear on the teeth, and tobacco satins and plaque are abundant. Even the children exhibit staining. However, the gingival and supporting structures in both groups were in good health due to vigorous mastication.


The methods of tabulation used to classify characteristics of the dental structures of the Yanomami Indians are listed in Table I and discussed in detail below,


The findings presented in Table 2 were based on an examination of 94 adolescents and young adults. The prevalence of malocclusion is very close to that of civilised societies. Though the overall pattern is similar, the problems are generally of less severity than in civilise man. Overjets with lips interposed were absent. As for crowding, few had a discrepancy larger than the width of a lower incisor because of the habit of placing a wad of tobacco between the lower lip and teeth; some crowding is caused by this custom. No congenital defects such as cleft palate or harelip were found owing to the practice of eliminating abnormal or defective infants at birth. Begg's study of the Australian aborigines showed a lower incidence of crowding (l4 per cent) probably because they belong to a more primitive racial group with primitive morphologic features. The fossils of the hominids and prehominids who were man's ancestors seem to indicate the absence of malocclusions.

Table 1. Methods of Tabulation in Study of Dental Structures of Yanomami Indians of Northern Brazil

Survey of Malocclusion Index 1. Canadian index 3 2. Occlusion feature index (National Institute of Dental Research)' Gonial Angle Measurement Profile Cervical Abrasion Caries and Missing Teeth Proximal Abrasion Attrition Asymmetry Occlusal Wear

1. Pedersen index

Frontal plane 2. Occlusal surfaces Spherical - anterior posterior 3. Permanence of cusps

Table 2. Survey of Malocclusion Index in the Yanomami Indians of Northern Brazil


Malocclusion Per Cent Malocclusion Per- Cent

Class I (Angle) 77.7 Crowding 48.0 Class 11 (Angle) 22.3 Distal Occlusion 21.7 Class 111 (Angle) 0.0 Overbite 19.0 Crowding 52.7 Overjet 36.0 Overjet 20.9 Overbite 17.6 Edge-to-edge 12.8 Openbite 0 Crossbite 23.6 Mandibular shift 2.7 Diastemas 7.4 Inclined teeth 10.0 Impacted teeth 1.3 Atrophic teeth 2.0 Supernumeraries 2.0 Nondental congenital defects 0

Gonial Angle

The posterior border, body, and ramus of the mandible were palpated and marked with soft pencil or crayon on the skin (Fig. 5). By means of a protractor the angle was measured. Obviously, these were gross measurements however- a consistency of arigulation was observed. Note that the gonial angle of 78 per cent of the cases fall within 123 to 133 degrees. As in other primitive peoples little variation of the gonial angle results because the Yanomami belong to a definite racial group without mixture. Consequently the type of Class 11 malocclusion usually identified with a reduced gonial angle and with lip interposition is not likely to be found. The same holds true for the absence of large gonial angles and their concomitant open bites.

Gonial angle determination markings on face and measurements


The soft tissue profile was observed visually and recorded the Canadian Index (Table 2). When it appeared normal it was designated as Class I; when the mandible was retrognathic it was designated as Class II; and when prognathic, Class III. Of the sampling shown in the Canadian Index, 94 apparently presented a good profile. Even in CIass II malocclusions, the majority of those examined seemed to be purely dental; no micrognathia or macrognathia was seen. lt. was observed that there, was good lip posture and competence with no apparent mouth breathing or deviate swallow (tongue thrust). lt. would appear that because the children are breast fed until the age of three, the likelihood of perverse swallowing habits with concomitant orofacial muscle imbalance do not develop.

Cervical Abrasion

The total absence of cervical abrasion In the Yanomamis suggests that this phenomenon so common in our civilisation is caused by toothbrushing. The Yanomami Indians have no brushing habits and no oral hygiene.

Caries and Missing Teeth

On visual examination 4.5 per cent had one carious lesion, 10 per cent had two carious lesions, and 2.5 per cent had three carious lesions or more. The lesions are usually found in the older age group. Eight per cent had lost one tooth, 6.5 per cent had two teeth missing, and 8 per cent had three or more teeth missing. Sixty per cent of the missing teeth were lost by injury or because of their use in craft activities, whereas 40 per cent were lost due to caries. These findings are less than those of modern society but still significant since the Yanomamis do not have sweets (sugar cane was introduced very recently) or refined foods and have to chew vigorously. The marked abrasion of the teeth results in less sulci and fissures where lesions can develop.

Proximal Abrasion

This was determined by measuring the wear on the proximal surfaces between the first and second lower molars on the side of the greatest wear. Adolescents and young adults generally show little or no perceptible wear, whereas the mature adults had .5 to I.5 mm wear, and the senile group had more than I.5 mm of wear. These findings show less degree of abrasion than Begg found in the Australian aborigines.

Attritional Asymmetry

This was seen only in cases of crossbite, where a tooth was lost, or owing to a craft activity.

Occlusal Wear

Pedersen Index. This index is used to show occlusal wear: O denotes normal outline without facets; I denotes marked enamel facets; 11 denotes marked enamel facets with dentine exposed; and 111 denotes advanced dentine exposure. The progression of war with age is shown in Figure 7.

Occlusal Surfaces

In a Class I jaw relationship the maxillary teeth usually overlap the mandibular teeth. This overlap is greatest in the incisor region and decreases posteriorly. Ninety-three per- cent of the young Yanomamis exhibit this overlap which is similar to the Class I adolescent of modern man. With continued wear of the teeth, an edge-to-edge bite develops. This was found in almost all of the mature and senile groups . The frontal plane plane exhibits a curve of the incisors as shown in Figure . The incidence of an edge-to-edge incisor relationship is low in adolescence. in the mature it is higher and with continued occlusal wear it increases to maximum in old age. This progression is shown in Figure . With further attrition in the senile group the lower incisors may protrude beyond the maxillary incisors to produce a typical Class 111 relationship. A distinct change is seen on the extremely worn occlusal surfaces of the mature adult between the anterior and posterior portions of the occlusal plane, which occurs distal to the first molar. The spherical plane refers to the hypothetical eight inch sphere of Monson, with its center in the region of the glabella and its lower tangent serving to form the occlusal table (Monson's curve). 'This curve or sphere is divided into an anterior and posterior portion; the anterior is first molar to first molar and the posterior is the second and third molars of both sides. The normal dentition of a young adult exhibits Monson's curve (Fig. 11 A). Marked attrition changes the shape of the occlusal plane to an inverse of the Monson curve which is called the Villain curve. Fish in 1952 4 credited Villain with being the first to describe this reverse curve (Fig. 11 B ). interestingly the reverse curve ends at the first molar (anterior portion). The second and third molars retain Monson's curve (posterior portion). Most of the adults and older Yanomamis exhibit a Villain curve. To date no satisfactory explanation for its formation has been found.

 Frontal Plane showing curve with wear

Monson curve - positive and negative

Permanence of Cusps

Adults generally had all cusp heights eliminated by abrasion with only the chief prominences or peaks , of the occlusal anatomy remaining. In senility there was a tendency to total flattening. Cusp elimination by physiologic abrasion does not seem to impair masticatory efficiency.

Summary and Conclusion

A study of the dentitions of the Yanomami Indians of northern Brazil was undertaken because they are racially pure and in their isolated state have not been subject to a large degree of cultural adaptation. The diet of the Yanomamis consisting of cultivated cassava, manioc, and other vegetation as well as small game and fish is generally prepared in a manner that requires great masticatory effort. The prepared food retains a large amount of abrasive grit which results in marked occlusal and proximal attrition and elimination of tooth cuspation in the mature adult. Malocclusions long the adolescents are prevalent in comparable proportion to civilized man, but generally of less severity. The dentition of the mature and senile groups are characterised by marked attritional wear, anterior edge-to-edge occlusion, and a Class 111 dental relationship. These findings are similar to those found by Begg his investigation of the Australian aborigines and Van Reenan study of the Kalahari Bushman of Africa. It appears that severe e attrition of the dentition results in an anterior edge-to-edge occlusion and a Class 111 molar relationship in most cases where this phenomenon is seen.

Dentition of adolescent
Senile dentition



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