A. JACOBSON ¹;
B. C. B. PRESTON ²;
C. V. A. BOETTNER ³ ;
and C. B. PEREIRA ⁴
 

¹ and ² - Department of Orthodontics, School of Dentistry, University of the Witwaterand Jan Smuts Avenue, Johannesburg 2001, S. Africa;
³ - Asunción, Paraguay
⁴ - Federal University of Santa Maria, Brazil

KEY WORDS Cephalometrics - Lengua Indians -  Reference - Norms
 
 
 

The purpose of the expedition to the Gran Chaco of Paraguay was to survey oral  health and study dental anthropology amongst the Lengua Indians.  The ethnography of the Chaco is described in great detail by Metraux ('46 ) while Crubb ('11) published a comprehensive monograph on a single Chaco tribe. The Indian tribes of the Chaco have remained culturally intact well into the twentieth century, long after most other Amerindian cultures have dissolved  (Brown, Gajducek. I.eyshon. Steinberg. Brown and Curtain '74).  A recent estimate of the Chaco tribal population is 27,000 of  which 3.000 to 4.000 are Lengua  (Brown et al. '74). The Lengua (fig. 1) have typical Mongoloid features as described  by Bjork  ('47, '50 ).  Their faces tend to  be flat, the tooth-bearing portions of the jaws give the appearance of prognathism, whereas the chin retrudes. The incisor teeth of the Mongoloid races are generally and characteristically  "shovel shaped"  (Jacobsorl, '68 ).
 

The Lengua Indians studied were born  at and live in the vicimtv of Makthlawaiya, a settlement approximately 160 statute miles north of Asuncion where there is a mission station run by the Sociedad Misionera en Sud America. The ages of all but a few of the Indians were obtained from the records of the mission station. The ages of subjects without recorded histories were assessed from their dental development. Dental ages were estimated from the number of teeth erupted as well as the degree of attrition of these teeth. The number of pregnancies in females was used as a guide to their ages. The degree of skin creasing also gave a rough indication of age but was not reliable in many instances. The age range in the present study is from 18 to 30 years with an average age of 25 years for both males and females.

Fig. 1 - Frontal and lateral facial   features of a female Lengua Indian

From 202 lateral cephalometric radiographs taken and developed on site we selected those of 30 males and 30 females for inclusion in the present study.
The selection was based on excellence of occlusion as well as the clarity and alignment of cephalometric landmarks. Selected traditional landmarks and  planes were traced onto acetate paper and the various measurements recorded as in figure 2. Additional measurements are separately defined. The findings were compared to similar observations made on young adult South African Caucasoids (Sadowsky and Jacobson, '73).
 
 

 The following additional measurements require definition.
 

RH  - Ramus height measured along a line which parses through gonion and is tangent to the posterior border of the condyle. The measured length extends from the intersection of this line with a plane perpendicular to the most superior point on the head of the condyle to gonion 5 CL   -  Linear corpus length from gonion to gnathion  Gonial angle   -  Angular reading between RH and CL  FC  -  Point of intersection between Frankfort Horizontal and the line RH.  FS  -   Point of intersection between Frankfort Horizontal and a perpendicular to it from  the center of Sella turcica (S).  FP  -   Point of intersection between Frankfort Horizontal and a perpendicular to it from  Pterygo-mandibular fissure.  FA  -  Point of intersection between Frankfort Horizontal and a line perpendicular to it from Subspinale (A).

Fig. 3  Tracing of lateral headfilms of a Caucasoid and Lengua whose measurements  approximate the mean measurements of the respective groups. Clearly evident are the  prognathic features and the large ANB angle of  the Lengua.

Fig. 4   Effect of anterior positioning of jaws relative to nation. A illustrates  the accepted normal with the angle ANB equal to 2°. In B the jaws are  retropositioned relative to nasion thus reducing the ANB angle to - 2°.  In C the jaws are positioned forward relative to nasion thus increasing the  ANB angle, in this instance to 5°. The relationship of the jaws to each other  remains unchanged.

Barrett et al. ('63) in studying Australian aborigines defined prognathism as the degree of prominence of the facial skeletal profile in relation to the braincase. The most obvious difference in the lateral cephalometric
radiographs of the Caucasoids and Lengua is the prevalence of prognathism in the latter. In figure 3 representative lateral headfilm tracings of a Caucasoid and Lengua are illustrated.
The mean ANB angle is 8.5° in males and 6.8° in females as opposed to 1.8° and 2.6° in Caucasoid males and females respectively (table 1). The angular difference in males is statistically less significant than in females and may be attributed to the large standard deviation (3.5) observed for this parameter in the Lengua males.
The shorter mean anterior cranial base measurement in the Lengua (SN) (table 1) as compared to those of Caucasoids may result in point Nasion being relatively retropositioned in the Lengua and this in turn may account for the large ANB angle of the group (fig. 4).
The inclination of the palatal, occlusal and mandibular planes relative to the anterior cranial base (SN) are significantly higher in the Lengua males. Although these planes are more inclined in the Lengua females, only the occlusal plane is significantly so (table 1).
Other findings are set out in table 1.
 
 

                                                 TABLE  1

Cephalometric measurements

"Z" scores of  the normal distribution to judge the significance of racial differences   by  are considered to be significant. The lower the values the greater the significance.

                                               DISCUSSION

The Lengua Indians have relatively large ANB angles (table 1) as compared to the South African Caucasoid group. The generally shorter anterior cranial base of the Lengua (table 1) contributes to the higher mean SNA angle of this group. The position of Point B relative to the anterior cranial base is however not  significantly different in the two population groups, as indicated by their SNB angles (table 1). A high ANB angle in normal occlusions may also be attributed to a clockwise rotation of the jaws relative to the anterior cranial base (Jacobson, '75).
The facial plane angle is used to assess antero-posterior relationship of the mandible relative to the cranial base. The facial plane angles are not greatly different in the two  groups (table 1). This is due to the fact that clockwise rotation of the jaws tends to retroposition pogonion. The steeply inclined Frankfort Horizontal plane evident in the divergent type skeletal pattern (Sassouni, '69) of the Lengua reduces the facial angle.
An indication of the relative antero-posterior position and length of the maxilla (fig. 2) is obtained by measuring the distances along the Frankfort Horizontal plane between perpendiculars drawn to this line from sella (FS), the pterygo-maxillary fissure (FP), and Point A (FA). The distance FS to FP provides na indication of the relative antero-posterior relationship of the posterior part of the maxilla since this portion of the maxilla abuts against the lateral pterygoid plate of the pterygomaxillary fissure on either side.
The mean antero-posterior length of the maxilla (FP-FA) in the Lengua is not greatly different from the means observed in the Caucasoids (table 1). The male Indians do however, appear to have slightly longer maxillae than their Caucasoid counterparts.
The maxillae of the two groups are also similarly positioned relative to their craniofacial complexes. The values FS to FP in the Lengua are not significantly different from those of the Caucasoids (table 1).
Mean ramus height (RH) (fig. 2) in the Lengua males is 65.4 mm and in females 57.6 mm whereas in the Caucasoids the respective values are 65.2 mm and 58 mm. These differences are not significant.
The mean corpus lengths (CL) of the Lengua are slightly shorter in females (78.4 mm) but significantly shorter in males (81.9 mm) than those of the Caucasoid (females, 81 mm and males 88 mm). The genial angles of the two population groups show no significant difference on average (table 1).
The relative antero-posterior position of the mandible in the craniofacial complex is indicated by the distance between the points of intersection of perpendiculars to Frankfort Horizontal from the posterior border of the condyle (FC) and sella (FS). The mean distances in Lengua males and females is significantly shorter than those of Caucasoids (table 1) indicating that on average the mandibles in the Lengua are positioned further forward in their skulls. In effect this tends to protrude the chin of the Lengua which is offset to some degree by the relatively shorter mandibular bodies of this group (table 1).
The axial inclination of the incisor teeth were measured according to the Steiner analysis ('53, '59, '60). In spite of the prognathic appearance of the Lengua jaws the upper teeth in this group are less labially proclined than those of Caucasoids (table 1).
The lower incisors in the Lengua on average are significantly more labially inclined in both sexes than those of the Caucasoids (table 1). The interincisal angles between the two groups are not significantly different from each other.
 
 

                           SUMMARY AND CONCLUSION

On comparing lateral headfilms with South African Caucasoids the most striking feature of the Lengua is the prognathic appearance of the jaws. The average position and size of the maxillae in both groups are, however, much the same. The larger mean SNA angle observed in the Lengua may be attributed to a relatively shorter anterior cranial base in this population group.
The significantly larger mean ANB angle observed in the Lengua may likewise be
attributed to the short anterior cranial base. Contributing to the large ANB angle in this group is a clockwise rotation of the jaws relative to the anterior cranial base.
The larger ANB angle observed in both sexes in the Lengua is in no way indicative of Angle Class II disharmony. On the contrary, the selected samples all possessed normal occlusion with Class I dental relationships. In fact the Lengua revealed a mild tendency towards mandibular protrusion which in this group may result from the occlusal attrition. Occlusal wear results in the mandible moving forward relative to the maxilla. The chinpoint of the mandible relative to the anterior cranial base is much the same in both population groups in spite of the generally forward location of the condyle in the Lengua. This forward positioning of the condyle which tends to position the chinpoint more anteriorly is offset by the shorter body of the mandible in the Lengua.
Although the upper jaws in the Lengua display a degree of prognathism the axial
inclination of the incisor teeth in these jaws are no different on average from those observed in Caucasoids. In the mandibular arch, however, the Lengua generally possess more labially inclined incisors than those of Caucasoids.

                                   ACKNOWLEDGMENTS

Our sincere thanks and appreciation are extended to His Excellency President Alfredo Stroessner of Paraguay who made available to us air transport, much needed equipment and food for the duration of our stay in the Chaco.
To the staff of the Mission Anglicana our grateful thanks for their invaluable assistance.
We wish to thank Professor Luck of the Department of Physiology, School of Dentistry, University of the Witwatersrand, for constructing our cephalometer in his workshop.
We gratefully acknowledge financial assistance received from the Research Education and Development Fund of the Dental Association of South Africa.
Our sincere thanks are extended to Mr. L.Veres for his valuable contribution to the success of the project in acting as our technician.

Prof. Dr. Alex Jacobson e        Dr. Cléber Bidegain Pereira,        na chegada  no Paraguai.	O saudoso Dr. Victor Boettner, tomando uma impressão    sendo auxiliado pelo Dr. Cléber e observado pelos índios    que pacientemente esperavam a sua vez.

                                  Trabalho publicado - Atrição e Apinhamento   

                                    Fotografias no Chaco Paraguaio