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The mandibular angle in the recent East African bantu population
Arclu oral Biol. Vol. 15, pp. 13734376,
1970. Fbqamon
THE MANDIBULAR EAST AFRICAN
Rws.
Printed in Great Britain.
ANGLE IN THE RECENT BANTU POPULATION S. ZIVANOVIC
Department of Anatomy, Medical College of St. Bartholomew’s Hospital, London, England Summary-Measurements were made of the mandibular angle in 335 mandibles, deriving from East African Bantu-speaking individuals, in order to ascertain the average value of the angle. The standard technique was used and measurements were confined to normal mandibles with intact alveolar edges and teeth, deriving from individuals of known sex and age and whose cause of death and tribal origin were also recorded. Variability and sexual differences of the angle were noted and the results obtained are discussed and compared with the data in the available literature. The average value of the mandibular angle was 120*14“ in male, and 127.96” in female E!astAfrican Bantu mandibles. Sexual differences were statistically sign&ant, and the average values of the mandibular angle for both sexes were characteristic for the Bantu population.
INTRODUCTION THE ANGLE of the mandible lies between a line running along the lower border of the
body of the mandible and a line along the posterior border of the ramus of the mandible. In children the angle is very obtuse and in adolescence it becomes almost a right angle. In old age, with the loss of the teeth, the angle of the mandible widens to between 130” and 140”. These changes in the angle are said to be dependent upon the influence of the masseter, internal pterygoid and temporal muscles (HUMPHRY, 1858). TALLGREN (1967), in a longitudinal study of denture-wearers covering a period of 7 yr, found no evidence of such change in the angle. Humphry stated that the mandibular angle during the first dentition varies between 150” and 130” and during the period of the second de&ion it is reduced to about 115”. In negroid and mongoloid populations the angle is rather wider than in the European. KEEN (1945) in his study of the mandibular angle in a mixed South African population (European and South African Bantu) showed that there was an increase in the angle in the edentulous mandible of all ages and that loss of the teeth, and not age, is responsible for changes in the mandibular angle. Prompt denture provision which arrests the absorption of the alveolar borders appears to preserve the angle. In some recent studies, some workers have disagreed with this and have shown that denture provision does not arrest the resorption of the alveolar borders (WICTOFUN, 1964; CARLSSON, BERGMAN, and HEDEGARD, 1967). AVIS (1961) has shown experimentally that in rats the size of the angular process is dependent on the integrity of the attached muscles. LOTRIC and JOVANOVK? (1965), however, observed that the mandibular angle of elderly
patients
with dystrophic
muscles
shows 1373
no change
provided
the teeth
are
1374
S.
ZIVAN~VIC
retained; the state of the dentition thus appears to be the most important factor determining the size of the human mandibular angle. Many authors (MARTIN, 1928; OLIVIER, 1969) state that the mandibular angle varies in different human populations and that the average values in adult males are 125” in Europeans, 120” in mongoloids and African Negroes, 115” in Melanesians and Australian aborigines, and 1lo” in neanderthals. Female mandibles were not usually measured, but most of the texts state that the mandibular angle is larger in females by 3”-5”. The majority of authors before KEEN (1945) disregarded the fact that the angle changes with the loss of the teeth, and for this reason the measurements for many populations may have to be revised. A recent examination of the mandibular angle in an African population was confined to the South African Bantu people (VILLIERS, 1968), and no comparable study has appeared for an East African population. The aim of the present investigation is to study the mandibular angle in normal, adult, non-edentulous East African Bantu mandibles of both sexes. It is desirable to have on record the normal average mandibular angle for every population so that changes can be assessed during eruption and loss of the teeth, and especially in certain diseases such as rickets (LOTRICand JOVANOVIC, 1965) when the angle is enlarged.
MATERIAL AND METHODS Mandibles for the present study were selected from the Galloway skeletal collection of the Department of Anatomy of Makerere University College in Kampala, Uganda. The skeletons in this collection are representative of the East African population, and for all the skeletons sex, age, tribe and cause of death were recorded. Three hundred and thirty-five normal adult Bantu mandibles (284 male and 51 female), with all the teeth in situ or with preserved alveolar borders in those cases where some teeth had been lost post mortem, were available for study. The tribal differences between various East African Bantu tribes are negligible and are not statistically significant and it is therefore not necessary to give separate results for each tribe (GUDNARA and ~?IVANOVI~, 1968). The mandibles showed slight asymmetry (~IVANOVIC, 1969) but this does not affect the value of the mandibular angle when it is measured with the standard mandibulometer. The differences between the right and the left angles are statistically insignificant and fall within the range of the standard error of the mean (KEEN, 1945). MORANT(1923, 1936) introduced the standard technique for mandibular measurements; earlier studies are of doubtful comparability. In the present study, the mandibular angle was measured according to the accepted definition that the angle of the mandible is the angle between the standard horizontal and the standard ramal planes. The standard horizontal plane is the plane of the osteometric table (or mandibulometer) with the lower border of the body of the examined mandible placed on it. The ramal plane is represented by the ramal wing of the mandibulometer pressed against the posterior borders of both rami of the examined mandible. After obtaining the values of the angle for all the mandibles, the following statistical values were calculated for each sex separately: M (mean); range of variation (the range between the minimal and the maximal value of the angle); S.D. (standard deviation); S.E. (standard error of the mean); and CV (coefficient of variation). The significance of the sexual differences was tested by calculating the “t” test according to the following formula:
MI - Mz t = 1/S.E.12+ S.E.z2 in which Ml is the larger and MS is the smaller of the two means. The obtained values of the mandibular angle of the East African Bantu population were compared with the available values of the angle of the South African Bantu population (VILLIERS,1968) and the statistical difference between the means in the two populations was tested.
THE MANDIBULAR
ANGLEIN THERECENT EA.% AFRICANBANTTJ POPULATION RESULTS
AND
1375
DISCUSSION
The detailed results are given in Table 1. The mean values in both series show that there is a substantial sexual difference and that the mandibular angle is much larger in female mandibles. The “t” test demonstrates that this difference is statistically significant (t = 6.000). Standard deviations are almost the same in both series, and the range of variation is not large. Standard errors in both sexes are relatively small. Coefficient of variation appears to be greater in the female, as the number of mandibles in this series is much smaller. In general, the angle of the East African Bantu female is more open and obtuse than that of the male and the ramus of the male mandible is more vertical than in the female. The range of variation, and maximal and minimal values of the angle in both sexes, is similar and so the differences in the angle cannot be used in the diagnosis of sex of mandibles. In comparison with the average values of the mandibular angle given in the available literature, the average angle of the East African Bantu mandible is smaller than the average angle of the Negro population quoted by MARTIN (1928) who gives the following values: 125” in Negroes and 128” in Europeans; 110” in neanderthals; 119” in Chinese and Peruvians; and 124” in aboriginal Australians. The results of the present study correspond more to the values quoted by OLIVIER (1969) who gives an average value for xanthoderms and African Negroes of 120”. More interesting is the comparison between the values of the mandibular angle of the East African Bantu and the angle of the South African Bantu recently published (VILLIERS, 1968). The available values are given in the following comparative table (Table 2). The mean values, standard errors and range of variation of the mandibular angle of the East African Bantu mandible and the South African Bantu mandible are very similar. The “t” test shows that there is no significant difference between the mandibular angle of the two populations. TABLE1. MANDIBULAR ANGLEIN THEEASTAFRICAN
Sex
Nnmher
Male Female
259 51
Mean 120.14 127.96
Standard deviation 7.57 7.52
BANTUPOPULATION
Standard error 0.47 l-05
Range
Coefficient of variation
101-133 106-142
2.92 14.74
TABLE2. MANDIBULAR ANGLE IN EASTAFRICANAND SOIJTH AFRICANBANTIJ POPULATIONS Females
Males Population Number East African South African Natal Ngnni Cape Ngnni Sotho Shangana-Tonga
259 392 107 88 103 35
Mean&SE 120.14 120.6 120.9 119.5 121.5 120.3
f 0.47 f 0.31 f 0.62 + 0.71 f0.62 * 0.77
Range
Number
101-133 103-135 105-131 103-135 107-134 104131
51 104 30 19 53 -
Mean k SE 127.96 125.0 126.3 121.2 125.7 -
rt * f f f
1.05 0.55 1.05 1.23 0.70
Range 106-142 115-138 115-138 115-135 115-138 -
1376
s. ZlvANovIc
The values of the mandibular angle obtained for the East African Bantu mandible are characteristic for the African Negro population as a whole, but, because of the range of variation, this feature cannot be used for racial diagnosis. Acknowledgement-1 am indebted to Professor 0. J. LEWISfor help in preparation of this manuscript. R&stun&Des mesurages de l’angle mandibulaire de 335 mandibules derivant d’individus de 1’Afrique de l’Est, parlant le Bantu, ont ette faits atin de v&tier la valeur moyeme de l’angle. La technique standard a Ctt utili&e et les mesurages furent limited a des mandibules normales avec des bords alveolaires et des dents intactes, derivant d’individus de sexe et age connus; la cause de la mort et I’origine tribale ont et6 aussi enregistrees. La variabilite et les diff&ences sexuelles de l’angle ont ettc not&s et les msultats obtenus sont discutb et compares avec les dates de la littbature disponible. La valeur moyenne de l’angle mandibulaire est de 120,14” chez le mgle et de 127,96 chez les femelles, chez les Bantu de 1’Afrique de l’Est. Les differences sexuelles au point de vue statistique sont significatives et les valeurs moyennes de l’angle mandibulaire pour les deux sexes sont caracteristiques pour la population Bantu. Zusamnenfammg-Es wurden Messungen tiber den mandibularen Winkel bei 335 Unterkiefem von ostafrikanischen, Bantusprechenden Einwohhner gemacht, urn Man bediente sich der Standardmethode durchschnittliche Wiielwerte festzulegen. und die Messungen beschr%nkten sich auf normale Unterkiefer mit intakten alveolaren Randem und ziihnen von Einrelpersonen, deren Alter und Geschlecht bekannt war, und deren Todesmsache und Stammesursprung aufgezeichnet waren. Abwandhmgen und Verschiedenheiten der Wiiel je nach Geschlecht wurden festgestellt und die erzielten Resultate wurden besprochen und mit den Unterlagen von vorhandener Literatur verglichen. Der durchschnittliche Wert des Unterkieferwinkels ist 120,14’ bei mannlichen und 127,96’ bei weiblichen Unterkiefem von ostafrikanischen Bantus. Unterschiede je nach Geschlecht sind statistisch bedeutsam und die durchschnittlichen Werte der Unterkieferwinkel bei beiden Geschlechtem sind charakteristisch filr die Bantubeviilkerung. REFERENCES Avrs, V. 1961. The significance of the angle of the mandible: an experimental and comparative study. Am. J. phys. Anthrop. 19,55-61. CAIUSSON,G. E., BERGMAN,B. and Hamom, B. 1967. Changes in contour of the maxillary alveolar process under immediate dentures. Acta odont. stand. 25, 1, 45-75. GUDNARA,N. and ZIVANO~&, S. 1968. Asymmetry in East African skulls. Am. J. phys. Anthrop. 28, 331-336. HUMPHRY,G. M. 1858. A Treatise on the Human Skeleton. Macmillan & Co., Cambridge. KEEN, A. J. 1945. A study of the angle of the mandible. J. dent. Res. 24, 99-108. LOTRTC,N. and JOVANOMC,S. 1965. Deskriptivnu i topografska anatom+z Eoveka-osteologija. Zavod za izdavanje u&benika Srbije, Beograd. MARTIN, R. 1928. Lehrbuch der Anthropofogie. Bd. II. Gustav Fisher, Jena. MORANT,G. M. 1923. A 6rst study of the Tibetan skull. Biometrica 15, 193-260. MORANT,G. M. 1936. A biometric study of the human mandible. Biometricu 28, 84-112. OLMER, G. 1969. Practical Anthropology. Charles C. Thomas, Springtield, Ill. TALLGREN,A. 1967. The effect of denture wearing on facial morphology. Actu odont. scund. 25, 563-592. DE VILLIERS, H. 1968. The Skull of the South African Negro. Witwatersrand University Press, Johannesburg. WICTORIN,J. 1964. Bone resorption in cases with comolete uooer __ denture. Actu Rudiol. CStockholmj Supp. 228. ~ANOVIC, S. 1969. Bonwill’s triangle and asymmetry in East African human mandibles. Archs. oral Biol. 14, 1041-1044.
1970. Fbqamon
THE MANDIBULAR EAST AFRICAN
Rws.
Printed in Great Britain.
ANGLE IN THE RECENT BANTU POPULATION S. ZIVANOVIC
Department of Anatomy, Medical College of St. Bartholomew’s Hospital, London, England Summary-Measurements were made of the mandibular angle in 335 mandibles, deriving from East African Bantu-speaking individuals, in order to ascertain the average value of the angle. The standard technique was used and measurements were confined to normal mandibles with intact alveolar edges and teeth, deriving from individuals of known sex and age and whose cause of death and tribal origin were also recorded. Variability and sexual differences of the angle were noted and the results obtained are discussed and compared with the data in the available literature. The average value of the mandibular angle was 120*14“ in male, and 127.96” in female E!astAfrican Bantu mandibles. Sexual differences were statistically sign&ant, and the average values of the mandibular angle for both sexes were characteristic for the Bantu population.
INTRODUCTION THE ANGLE of the mandible lies between a line running along the lower border of the
body of the mandible and a line along the posterior border of the ramus of the mandible. In children the angle is very obtuse and in adolescence it becomes almost a right angle. In old age, with the loss of the teeth, the angle of the mandible widens to between 130” and 140”. These changes in the angle are said to be dependent upon the influence of the masseter, internal pterygoid and temporal muscles (HUMPHRY, 1858). TALLGREN (1967), in a longitudinal study of denture-wearers covering a period of 7 yr, found no evidence of such change in the angle. Humphry stated that the mandibular angle during the first dentition varies between 150” and 130” and during the period of the second de&ion it is reduced to about 115”. In negroid and mongoloid populations the angle is rather wider than in the European. KEEN (1945) in his study of the mandibular angle in a mixed South African population (European and South African Bantu) showed that there was an increase in the angle in the edentulous mandible of all ages and that loss of the teeth, and not age, is responsible for changes in the mandibular angle. Prompt denture provision which arrests the absorption of the alveolar borders appears to preserve the angle. In some recent studies, some workers have disagreed with this and have shown that denture provision does not arrest the resorption of the alveolar borders (WICTOFUN, 1964; CARLSSON, BERGMAN, and HEDEGARD, 1967). AVIS (1961) has shown experimentally that in rats the size of the angular process is dependent on the integrity of the attached muscles. LOTRIC and JOVANOVK? (1965), however, observed that the mandibular angle of elderly
patients
with dystrophic
muscles
shows 1373
no change
provided
the teeth
are
1374
S.
ZIVAN~VIC
retained; the state of the dentition thus appears to be the most important factor determining the size of the human mandibular angle. Many authors (MARTIN, 1928; OLIVIER, 1969) state that the mandibular angle varies in different human populations and that the average values in adult males are 125” in Europeans, 120” in mongoloids and African Negroes, 115” in Melanesians and Australian aborigines, and 1lo” in neanderthals. Female mandibles were not usually measured, but most of the texts state that the mandibular angle is larger in females by 3”-5”. The majority of authors before KEEN (1945) disregarded the fact that the angle changes with the loss of the teeth, and for this reason the measurements for many populations may have to be revised. A recent examination of the mandibular angle in an African population was confined to the South African Bantu people (VILLIERS, 1968), and no comparable study has appeared for an East African population. The aim of the present investigation is to study the mandibular angle in normal, adult, non-edentulous East African Bantu mandibles of both sexes. It is desirable to have on record the normal average mandibular angle for every population so that changes can be assessed during eruption and loss of the teeth, and especially in certain diseases such as rickets (LOTRICand JOVANOVIC, 1965) when the angle is enlarged.
MATERIAL AND METHODS Mandibles for the present study were selected from the Galloway skeletal collection of the Department of Anatomy of Makerere University College in Kampala, Uganda. The skeletons in this collection are representative of the East African population, and for all the skeletons sex, age, tribe and cause of death were recorded. Three hundred and thirty-five normal adult Bantu mandibles (284 male and 51 female), with all the teeth in situ or with preserved alveolar borders in those cases where some teeth had been lost post mortem, were available for study. The tribal differences between various East African Bantu tribes are negligible and are not statistically significant and it is therefore not necessary to give separate results for each tribe (GUDNARA and ~?IVANOVI~, 1968). The mandibles showed slight asymmetry (~IVANOVIC, 1969) but this does not affect the value of the mandibular angle when it is measured with the standard mandibulometer. The differences between the right and the left angles are statistically insignificant and fall within the range of the standard error of the mean (KEEN, 1945). MORANT(1923, 1936) introduced the standard technique for mandibular measurements; earlier studies are of doubtful comparability. In the present study, the mandibular angle was measured according to the accepted definition that the angle of the mandible is the angle between the standard horizontal and the standard ramal planes. The standard horizontal plane is the plane of the osteometric table (or mandibulometer) with the lower border of the body of the examined mandible placed on it. The ramal plane is represented by the ramal wing of the mandibulometer pressed against the posterior borders of both rami of the examined mandible. After obtaining the values of the angle for all the mandibles, the following statistical values were calculated for each sex separately: M (mean); range of variation (the range between the minimal and the maximal value of the angle); S.D. (standard deviation); S.E. (standard error of the mean); and CV (coefficient of variation). The significance of the sexual differences was tested by calculating the “t” test according to the following formula:
MI - Mz t = 1/S.E.12+ S.E.z2 in which Ml is the larger and MS is the smaller of the two means. The obtained values of the mandibular angle of the East African Bantu population were compared with the available values of the angle of the South African Bantu population (VILLIERS,1968) and the statistical difference between the means in the two populations was tested.
THE MANDIBULAR
ANGLEIN THERECENT EA.% AFRICANBANTTJ POPULATION RESULTS
AND
1375
DISCUSSION
The detailed results are given in Table 1. The mean values in both series show that there is a substantial sexual difference and that the mandibular angle is much larger in female mandibles. The “t” test demonstrates that this difference is statistically significant (t = 6.000). Standard deviations are almost the same in both series, and the range of variation is not large. Standard errors in both sexes are relatively small. Coefficient of variation appears to be greater in the female, as the number of mandibles in this series is much smaller. In general, the angle of the East African Bantu female is more open and obtuse than that of the male and the ramus of the male mandible is more vertical than in the female. The range of variation, and maximal and minimal values of the angle in both sexes, is similar and so the differences in the angle cannot be used in the diagnosis of sex of mandibles. In comparison with the average values of the mandibular angle given in the available literature, the average angle of the East African Bantu mandible is smaller than the average angle of the Negro population quoted by MARTIN (1928) who gives the following values: 125” in Negroes and 128” in Europeans; 110” in neanderthals; 119” in Chinese and Peruvians; and 124” in aboriginal Australians. The results of the present study correspond more to the values quoted by OLIVIER (1969) who gives an average value for xanthoderms and African Negroes of 120”. More interesting is the comparison between the values of the mandibular angle of the East African Bantu and the angle of the South African Bantu recently published (VILLIERS, 1968). The available values are given in the following comparative table (Table 2). The mean values, standard errors and range of variation of the mandibular angle of the East African Bantu mandible and the South African Bantu mandible are very similar. The “t” test shows that there is no significant difference between the mandibular angle of the two populations. TABLE1. MANDIBULAR ANGLEIN THEEASTAFRICAN
Sex
Nnmher
Male Female
259 51
Mean 120.14 127.96
Standard deviation 7.57 7.52
BANTUPOPULATION
Standard error 0.47 l-05
Range
Coefficient of variation
101-133 106-142
2.92 14.74
TABLE2. MANDIBULAR ANGLE IN EASTAFRICANAND SOIJTH AFRICANBANTIJ POPULATIONS Females
Males Population Number East African South African Natal Ngnni Cape Ngnni Sotho Shangana-Tonga
259 392 107 88 103 35
Mean&SE 120.14 120.6 120.9 119.5 121.5 120.3
f 0.47 f 0.31 f 0.62 + 0.71 f0.62 * 0.77
Range
Number
101-133 103-135 105-131 103-135 107-134 104131
51 104 30 19 53 -
Mean k SE 127.96 125.0 126.3 121.2 125.7 -
rt * f f f
1.05 0.55 1.05 1.23 0.70
Range 106-142 115-138 115-138 115-135 115-138 -
1376
s. ZlvANovIc
The values of the mandibular angle obtained for the East African Bantu mandible are characteristic for the African Negro population as a whole, but, because of the range of variation, this feature cannot be used for racial diagnosis. Acknowledgement-1 am indebted to Professor 0. J. LEWISfor help in preparation of this manuscript. R&stun&Des mesurages de l’angle mandibulaire de 335 mandibules derivant d’individus de 1’Afrique de l’Est, parlant le Bantu, ont ette faits atin de v&tier la valeur moyeme de l’angle. La technique standard a Ctt utili&e et les mesurages furent limited a des mandibules normales avec des bords alveolaires et des dents intactes, derivant d’individus de sexe et age connus; la cause de la mort et I’origine tribale ont et6 aussi enregistrees. La variabilite et les diff&ences sexuelles de l’angle ont ettc not&s et les msultats obtenus sont discutb et compares avec les dates de la littbature disponible. La valeur moyenne de l’angle mandibulaire est de 120,14” chez le mgle et de 127,96 chez les femelles, chez les Bantu de 1’Afrique de l’Est. Les differences sexuelles au point de vue statistique sont significatives et les valeurs moyennes de l’angle mandibulaire pour les deux sexes sont caracteristiques pour la population Bantu. Zusamnenfammg-Es wurden Messungen tiber den mandibularen Winkel bei 335 Unterkiefem von ostafrikanischen, Bantusprechenden Einwohhner gemacht, urn Man bediente sich der Standardmethode durchschnittliche Wiielwerte festzulegen. und die Messungen beschr%nkten sich auf normale Unterkiefer mit intakten alveolaren Randem und ziihnen von Einrelpersonen, deren Alter und Geschlecht bekannt war, und deren Todesmsache und Stammesursprung aufgezeichnet waren. Abwandhmgen und Verschiedenheiten der Wiiel je nach Geschlecht wurden festgestellt und die erzielten Resultate wurden besprochen und mit den Unterlagen von vorhandener Literatur verglichen. Der durchschnittliche Wert des Unterkieferwinkels ist 120,14’ bei mannlichen und 127,96’ bei weiblichen Unterkiefem von ostafrikanischen Bantus. Unterschiede je nach Geschlecht sind statistisch bedeutsam und die durchschnittlichen Werte der Unterkieferwinkel bei beiden Geschlechtem sind charakteristisch filr die Bantubeviilkerung. REFERENCES Avrs, V. 1961. The significance of the angle of the mandible: an experimental and comparative study. Am. J. phys. Anthrop. 19,55-61. CAIUSSON,G. E., BERGMAN,B. and Hamom, B. 1967. Changes in contour of the maxillary alveolar process under immediate dentures. Acta odont. stand. 25, 1, 45-75. GUDNARA,N. and ZIVANO~&, S. 1968. Asymmetry in East African skulls. Am. J. phys. Anthrop. 28, 331-336. HUMPHRY,G. M. 1858. A Treatise on the Human Skeleton. Macmillan & Co., Cambridge. KEEN, A. J. 1945. A study of the angle of the mandible. J. dent. Res. 24, 99-108. LOTRTC,N. and JOVANOMC,S. 1965. Deskriptivnu i topografska anatom+z Eoveka-osteologija. Zavod za izdavanje u&benika Srbije, Beograd. MARTIN, R. 1928. Lehrbuch der Anthropofogie. Bd. II. Gustav Fisher, Jena. MORANT,G. M. 1923. A 6rst study of the Tibetan skull. Biometrica 15, 193-260. MORANT,G. M. 1936. A biometric study of the human mandible. Biometricu 28, 84-112. OLMER, G. 1969. Practical Anthropology. Charles C. Thomas, Springtield, Ill. TALLGREN,A. 1967. The effect of denture wearing on facial morphology. Actu odont. scund. 25, 563-592. DE VILLIERS, H. 1968. The Skull of the South African Negro. Witwatersrand University Press, Johannesburg. WICTORIN,J. 1964. Bone resorption in cases with comolete uooer __ denture. Actu Rudiol. CStockholmj Supp. 228. ~ANOVIC, S. 1969. Bonwill’s triangle and asymmetry in East African human mandibles. Archs. oral Biol. 14, 1041-1044.