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Population contrasts based upon teeth with varying degrees of attrition
Journal of Dentistry, 7, No. 2, 1979, pp. 126-132.
Printed in Great Britain
Population contrasts based upon teeth with varying degrees of attrition C.L.B. Lavelle,
DSc,
MDS, FRCD (c)
Department of Oral Biology, Faculty of Dentistry, Winnipeg, Canada
ABSTRACT The permanent tooth mesiodistal and buccolingual diameters were measured for Negroid, Mongoloid, Australasian and Caucasian population samples. Multivariate analysis showed reduced discrimination between the samples when based upon the dimensions of teeth exhibiting attrition compared with analysis of teeth without attrition. The degree of attrition must therefore be considered in odontometric studies, particularly when using teeth as genetic distance markers between populations.
INTRODUCTION The preferential preservation of teeth, compared with other cranial or post-cranial skeletal remains, has led to their being the principal source of primate evolutionary data (DuBrul, 1974; Read, 1975). The majority of odontometric studies, however, either ignore attrition or are limited to teeth free from attrition, yet attrition is a natural dental phenomenon (Goose, 1963) arising from tooth function and is probably correlated with life style. Attrition is a complex process resulting from the interactions between the teeth, their supporting structures and the functioning of the masticatory apparatus as a whole. In many primitive human populations, attrition starts as soon as the deciduous dentition emerges and comes into occlusal contact, and continues progressively throughout life in the mixed and permanent dentitions. In spite of this, when teeth are used as genetic distance markers between populations, variation in attrition is frequently ignored. In addition to mastication, teeth are utilized for grasping, holding, exerting torsion and other manipulative functions (Campbell, 1925), e.g. gnawing (Dahlberg, 1963), tool-making (Brace, 1964), cutting and tearing(Brace, 1967) and manipulating objects(Bailit et al., 1968). Most of these functions affect the anterior rather than the posterior teeth (Brace, 1967), the latter being best adapted to withstand occlusal stress. In addition to the occlusal surface, attrition also affects the proximal surfaces so that the shape of the contact points continually changes. There is a progressive reduction in mesiodistal crown size which is compensated by changes in tooth position within the dental arcade in order to maintain proximal contact. This leads to a reduction in the dental arch perimeter. Progressive occlusal attrition with obliteration of cusp morphology tends to be associated with greater mandibular excursions and modified masticatory activity correlated with the development of an edge-to-edge incisor relationship. Approximal and occlusal attrition have therefore functional consequences on the gnathic apparatus in that contact between opposing dental arches increases, with cuspal interdigitation being replaced by broad occlusal surfaces articulating on a helicoidal plane in a reduced dental arch. Tooth attrition therefore affects all tooth surfaces and cannot be ignored in odontometric studies. Accordingly, this study was undertaken to analyse the contrasts between population samples when based upon teeth with and without attrition.
Lavelle: Attrition
in population
studies
127
MATERIALS AND METHODS This study was based upon the maxillary and mandibular permanent teeth on the right side of the dental arch of male Caucasians (nineteenth century Londoners, St Brides), Negroes (West African natives), Mongoloids (North American Indians) and Australasians (Australian aborigines). The teeth were measured on skulls lodged in various museums in the United Kingdom, with the sexing depending upon written records and skull morphology. The teeth were selected on the basis that they were ‘morphologically normal’. The dentitions of each population sample were segregated into two groups: those with minimal or no occlusal and proximal enamel attrition and those with considerable occlusal and proximal enamel loss due to attrition, i.e. with exposed dentine on the cusp tips. Each population sample comprised 2.5 male dentitions with no attrition and 25 with attrition. Using dial callipers, the mesiodistal and buccolingual diameters were measured to the nearest 0.1 mm for each permanent tooth (excluding third molars). The mesiodistal crown diameter was defined as the minimum distance between the mesial and distal contact areas measured parallel to the occlusal plane. The buccolingual diameter was defined as the minimum distance between the most buccal and lingual crown convexities measured at right angles to the occlusal plane. All the teeth were measured by one observer. Based upon repeat measurements of samples selected at random, using analysis of variance, the component of variance introduced artificially as a result of inconsistency in measurement was not only statistically insignificant (F’X-2) compared with that existing within the corresponding population samples, but also of too small a scale to affect the overall results of this study. STATISTICAL ANALYSIS The data were analyzed by a computer program which enabled the mean dimensions and standard deviations of each tooth diameter with or without attrition to be printed out for each population sample. As previously described by Lavelle (1978), the program also subjected all the tooth dimensions to canonical analysis of discriminance. This technique maximally discriminated the population samples and provided an index in terms of squared generalized distances (D’), of the separation between all pairs of population samples based upon teeth with or without attrition. RESULTS The mean mesiodistal crown diameters of teeth with and without attrition for the four population samples included in this study are listed in Tables Z and ZZrespectively. Although the dimensions were all smaller for the teeth with attrition than without attrition, considerable variability was evident both within and between the samples. A similar feature was evident from comparison of the buccolingual crown diameters, although such dimensions were not so severely affected by attrition. Nevertheless, when comparing individual crown diameters, the degree of contrast between population samples varied depending upon the tooth compared and whether the sample was based upon teeth with or without attrition. Using univariate statistical techniques it was therefore not possible to obtain an overall picture of the contrasts between the population samples. When all the tooth diameters were combined together in the multivariate analysis, Caucasians were significantly separated from the other three population samples. These contrasts
128
Journal of Dentistry, Vol. ~/NO. 2
Table
1. Mesiodistal crown diameters of teeth without attrition of different population samples Australasian X
Negroid
Mongoloid x
d.
x
s. d.
o-57 O-61 0.58 041
9.27 7.61 8.35 7.79
O-46 0.52 O-63 0.48
8.96 6.84 8.11 7.21
s.
Caucasian s. d.
X
s.
d.
Maxillary I1 I2 C P’
9.34 7-64 8.32 7.74
$ M2
11.31 7-08 1O-49
0.42 o-50 o-77
Il.34 7.11 10.62
0.63 0.49 0.79
1045 6.95 1049
5.88 6-64 7.52 744 7.51 12.11 Il.49
0.41 0.44 o-41 O-52 o-49 0.64 O-67
5.89 6.67 7.74 7.48 7-60 12.22 11.51
O-52 O-63 0.41 0.54 O-47 0.71 O-52
5.52 6.12 7.11 7.29 7.69 11.26 11.18
0.52 0.62 044 0.34
8-76 6.65 7.84 7.11
0.44 0.62 0.41 9.49
O-37 0.47 O-61
10.82 6.85 10.34
9.39 6.54 0.66
0.35 o-41 O-38 0.36 0.42 O-58 O-67
546 586 6.91 7.11 7-28 11.11 10.77
o-41 0.33 0.31 0.37 0.50 0.49 0.47
Mandibular ‘1 ‘2
C PI p2
MI M2
x, Mean mesiodistal crown diameter (mm); s.d., standard deviation. Tab/e
II.
Mesiodistal crown diameters of teeth with attrition of different population samples.
X
Mongoloid
Negroid
Australasian sd.
X
s.
d.
X
Caucasian s.
d.
X
s.
d.
Maxillary
7.01 7.70 11.29 1o-45
0.69 0.76 0.68 0.83 O-85 0.86 0.74
9.24 7.58 8.31 7.68 6-94 11.29 10.58
O-63 0.84 O-88 0.79 0.74 0.79 0.82
8.91 6.82 8.05 7.14 6.91 1042 1047
0.52 0.69 O-85 0.89 o-94 0.69 0.75
8.75 6.60 7.80 7-06 6.81 IO.74 IO-31
0.49 0.52 O-65 0.47 0.73 0.79 0.65
5-82 6-61 7.50 7.41 7.48 12.09 1 l-36
0.71 0.68 0.69 0.65 O-72 0.79 O-68
5.81 6.63 7.71 7.41 7.54 12.19 Il.47
O-68 0.72 O-83 0.79 O-78 0.69 0.74
5.49 6-09 7.08 7.21 7.44 11.25 Il.14
049 048 O-82 0.63 O-68 0.75 o-79
540 5.85 6.87 7.08 7.21 11.04 IO-72
O-52 0.41 0.69 O-65 O-72 0.76 O-85
I’ I2 C
9.31 7.69 8.29
;: M’ M2
‘1
Mandibular ‘2
C Pl p2
Ml M2
x, Mean mesiodistal crown diameter; s.d. standard deviation.
were not so marked on analysis of either the maxillary or mandibular tooth diameters (Table IQ. In addition, such discrimination was greatest for the dimensions of teeth without attrition compared with the dimensions of teeth with attrition or combining the dimensions of teeth with and without attrition. In all the multivariate analyses a similar pattern of discrimination between the four population samples was apparent, although the degree of separation depended on the degree of tooth attrition. Discrimination between the samples was slightly greater from analysis of the maxillary tooth dimensions, compared with those of the mandibular arch, and from the
Lavelle: Attrition
Table /I/.
129
in population
studies
generalized
distances
Squared
based on analysis of mesiodistal
(0’)
between
and buccolingual
centroids
(means) of different
population
samples
tooth diameters Tooth dimensions
analysed
Maxillary
Mandibular
Maxillary and mandibular
2.95 3.04
2.88 2.91
4.69 3.85
Australasian
3.62
3.75
6.94
Teeth with attrition Negroid Mongoloid
2.01 2.14
1.86 2.05
2.96 3.14
Australasian
2.52
2.41
3.28
2.67 2-95 3.04
2.49 254 3.18
3.71 3.36 4.79
Population sample compared with Caucasian Teeth without Negroid Mongoloid
attrition
Teeth with and without Negroid Mongoloid Australasian All squared generalized
attrition
distances in standard deviation
Tab/e IV. Squared generalized distances (0’) on analysis of mesiodistal tooth diameters
between
units.
centroids
of different
Tooth dimensions Population samples compared with Caucasian
population
samples based
analysed
Maxillarv
Mandibular
Maxillary and mandibular
Teeth without attrition Negroid Mongoloid Australasian
l-19 1.04 l-36
1.13 O-98 I.27
2.47 2-12 3.43
Teeth with attrition Negroid Mongoloid Australasian
0.87 o-75 1.11
0.74 O-64 1.03
1.97 1.49 2-58
1.02 0.97 l-38
0.94 0.88 1.24
2.11 1.85 2.88
Teeth with and without Negroid Mongoloid Australasian All squared generalized
attrition
distances in standard deviation
units.
mesiodistal (Table W) then the buccolingual (Table v) crown diameters. In each analysis, however, the molar dimensions contributed most to the separation between the population samples compared with the premolar, canine and incisor tooth dimensions.
DISCUSSION The dentition was of importance
to individual survival in ancient times, although the increased use of mechanical methods in food preparation has gradually shifted food reduction from inside the mouth to outside (Campbell, 1939). Also the loss of jaw mass in primates was pro-
130
Table K Squared generalized distances (0’) on analysis of buccolingual crown diameters
Journal of Dentistry, Vol. ~/NO. 2
between centroids of different population samples based
Tooth dimensions analysed Population samples compared with Caucasian
Maxillary
Mandibular
Maxillary and mandibular
Teeth without attrition Negroid Mongoloid Australasian
099 O-85 1.01
0.83 o-72 o-94
l-86 1-44 2.05
Teeth with attrition Negroid Mongoloid Australasian
o-79 O-61 o-69
O-65 o-55 O-68
l-47 1.09 l-86
Teeth with and without attrition Negroid Mongoloid Australasian
O-78 o-59 0.96
O-67 o-51 O-88
1.58 l-21 1.96
All squared generalized distances in standard deviation units.
bably made possible by the selective shifting of food collecting to the hands (DuBrul, 1962). Consequently, since the time of canine reduction and transference from the mouth to the hand of man of many of tool and defence devices, the teeth have assumed limited evolutionary significance (Dahlberg, 1963). During man’s evolution, therefore, dental selection pressures must have been reduced, although this does not entirely negate the evolutionary significance of the dentition in present-day man. Whilst the major influence of genetic factors on tooth form is apparent (Garn, Lewis and Walenga, 1968; Corruccini and Henderson, 1976), there is increasing realization that environmental factors also have significance (Biesenfeld, 1970). Tooth diameters are not isolated entities, however, since not only are the mesiodistal and buccolingual diameters associated one with another (Gam, Lewis and Kerewsky, 1968) but tooth size is correlated with cusp size (Biggerstaff, 1975). Furthermore, individual tooth size is related to that of the dentition as a whole (Garn and Lewis, 1969; Lombardi, 1975) and to other skeletal dimensions (Anderson et al., 1977; I.&elle, 1977). In non-human primates, tooth size probably has an association with occlusomandibular kinetics (Kay and Hiiemae, 1974; Every, 1975; Zingesser, 1976), although it is difficult to investigate this relationship in man. There is no doubt that tooth attrition affects both dental and skeletal relationships (Fishman, 1976), which in turn influence masticatory movements. Furthermore, the progression of tooth attrition is influenced by its location within the dental arch, and this is partially determined by the soft tissue environment of the tongue, cheeks and lips (Butler, 1972). Tooth size and tooth attrition are therefore more complex biological entities than traditionally accepted, so there is a limit to the biological data that can be abstracted from the examination of teeth within a dried skull. samples depending upon whether the dimensions of teeth with or without attrition are included in the analysis. Tooth attrition, however, is a continuous variable which is difficult to segregate objectively into different categories, so it was not possible to quantify precisely the effect of attrition on population separation. In addition, the mesiodistal and buccolingual
Lavelle: Attrition
in population
131
studies
crown diameters provide only a cursory metrical definition of tooth form. Attrition predominantly affects the occlusal surface, particularly cusp mophology, which is difficult to define by the mesiodistal and buccolingual tooth diameters. Thus, further data are required before the varying contrasts between population samples based upon teeth with or without attrition can be interpreted, especially relative to dietary habits. Nevertheless this study illustrates the necessity of considering dentitions as a whole rather than individual teeth in isolation in odontometric studies. REFERENCES
Anderson D. L., Thompson G. W. and Popovich F. (1977) Tooth, chin, bone and body size correlations. Am. J. Phys. Anrhropol. 46, 7-11. Bailit H. L., Dewitt S. J. and Leigh R. A. (1968) The size and morphology of the Wasioi dentition. Am. J. Phys. AnrhropoL 28, 271-288. Biggerstaff R. N. (1975) Cusp size, sexual dimorphism and heritability of cusp size in twins. Am. J. Phys. Anrhropol. 42, 127-239. Brace C. L. (1964) The probable mutation effect. Am. Naturalist. 97,453-455. Brace C. L. (1967) Experimental studies in human tooth wear. Am. J. Phys. Anrhropol. 27, 213-221.
Butler R. J. (1972) Age related variability
in occlusal wear planes. Am. J. Phys. Anrhropol
36, 38 l-390.
Campbell T. D. (1925) Denririon and Palate of the Australian Aboriginal. Adelaide, Hassell Press. Campbell T. D. (1939) Food and food habits of the Australian aborigines in relation to their dental conditions. Ausr. Dent. J. 43, l-15,45-55,73-87, 141-156, 177-198. Corruccini R. S. and Henderson A. M. (1976) Odontometric discriminant function analysis of American whites and blacks. J. Dent. Res. 55, 713. Dahlberg A. A. (1963) Dental evolution and culture. Hum. Biol. 35,237-249. DuBrul E. L. (1962) The Adaptive Chin. Springfield, Ill., Thomas. Dubrul E. L. (1974) Origin and evolution of the oral apparatus. Front. Oral Physiol. 1,2-30. Every R. G. (1975) Significance of tooth sharpness for mammalian, especially primate, evolution. Conrrib. PrimaroL 5, 293-325. Fishman L. S. (1976) Dental and skeletal relationships to attritional occlusion. Angle Orrhod. 46, 51-63.
Garn S. M. and Lewis A. B. (1969) Effect of agenesis on the crown-size profile pattern.
J.
Dent. Res. 48, 1314.
Garn S. M., Lewis A. B. and Kerewsky R. S. (1968) Relationship between buccolingual and mesiodistal tooth diameters. J. Dent. Res. 47, 495. Garn S. M., Lewis A. B. and Walenga A. J. (1968) Crown size profile pattern comparisons of 14 human populations. Arch. Oral. Biol. 13, 1325-1242. Goose D. H. (1963) Dental measurement: an assessment of its value in anthropological studies. In: Brothwell D. R. (ed.) Dental Anthropology. New York, Pergamon, pp. 125-148. Kay R. F. and Hiiemae K. M. (1974) Jaw movement and tooth use in recent and fossil primates. Am. J. Phys. Anrhropol. 49, 227-256. Lavelle C. L. B. (1977) Relationship between tooth and long bone size. Am. J. Phys. Anrhropol.
46,423-425.
Lavelle C. L. B. (1978) An analysis of molar tooth form. Acra Anar. 100,282-288. Lombardi A. V. (1975) A faster analysis of morphogenetic fields in the human dentition. Am. J. Phys. AnrhropoL
42,99-104.
Journal of Dentistry,
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Read D. W. (1975) Phys. Anthropol.
Hominid
teeth and their relatlonship
to hominid
Vol. ~/NO. 2
phylogeny.
Am. J.
42, 105-125.
Riesenfeld A. (1970) The effect of environmental factors on tooth development: an experimental investigation. Acta Anat. 77, 188-215. Zingesser M. R. (1976) Arch form, tooth size and occlusomandibular kinesis in the Ceboidea. Am. J. Phys. Anthropol.
45, 317-320.
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Population contrasts based upon teeth with varying degrees of attrition C.L.B. Lavelle,
DSc,
MDS, FRCD (c)
Department of Oral Biology, Faculty of Dentistry, Winnipeg, Canada
ABSTRACT The permanent tooth mesiodistal and buccolingual diameters were measured for Negroid, Mongoloid, Australasian and Caucasian population samples. Multivariate analysis showed reduced discrimination between the samples when based upon the dimensions of teeth exhibiting attrition compared with analysis of teeth without attrition. The degree of attrition must therefore be considered in odontometric studies, particularly when using teeth as genetic distance markers between populations.
INTRODUCTION The preferential preservation of teeth, compared with other cranial or post-cranial skeletal remains, has led to their being the principal source of primate evolutionary data (DuBrul, 1974; Read, 1975). The majority of odontometric studies, however, either ignore attrition or are limited to teeth free from attrition, yet attrition is a natural dental phenomenon (Goose, 1963) arising from tooth function and is probably correlated with life style. Attrition is a complex process resulting from the interactions between the teeth, their supporting structures and the functioning of the masticatory apparatus as a whole. In many primitive human populations, attrition starts as soon as the deciduous dentition emerges and comes into occlusal contact, and continues progressively throughout life in the mixed and permanent dentitions. In spite of this, when teeth are used as genetic distance markers between populations, variation in attrition is frequently ignored. In addition to mastication, teeth are utilized for grasping, holding, exerting torsion and other manipulative functions (Campbell, 1925), e.g. gnawing (Dahlberg, 1963), tool-making (Brace, 1964), cutting and tearing(Brace, 1967) and manipulating objects(Bailit et al., 1968). Most of these functions affect the anterior rather than the posterior teeth (Brace, 1967), the latter being best adapted to withstand occlusal stress. In addition to the occlusal surface, attrition also affects the proximal surfaces so that the shape of the contact points continually changes. There is a progressive reduction in mesiodistal crown size which is compensated by changes in tooth position within the dental arcade in order to maintain proximal contact. This leads to a reduction in the dental arch perimeter. Progressive occlusal attrition with obliteration of cusp morphology tends to be associated with greater mandibular excursions and modified masticatory activity correlated with the development of an edge-to-edge incisor relationship. Approximal and occlusal attrition have therefore functional consequences on the gnathic apparatus in that contact between opposing dental arches increases, with cuspal interdigitation being replaced by broad occlusal surfaces articulating on a helicoidal plane in a reduced dental arch. Tooth attrition therefore affects all tooth surfaces and cannot be ignored in odontometric studies. Accordingly, this study was undertaken to analyse the contrasts between population samples when based upon teeth with and without attrition.
Lavelle: Attrition
in population
studies
127
MATERIALS AND METHODS This study was based upon the maxillary and mandibular permanent teeth on the right side of the dental arch of male Caucasians (nineteenth century Londoners, St Brides), Negroes (West African natives), Mongoloids (North American Indians) and Australasians (Australian aborigines). The teeth were measured on skulls lodged in various museums in the United Kingdom, with the sexing depending upon written records and skull morphology. The teeth were selected on the basis that they were ‘morphologically normal’. The dentitions of each population sample were segregated into two groups: those with minimal or no occlusal and proximal enamel attrition and those with considerable occlusal and proximal enamel loss due to attrition, i.e. with exposed dentine on the cusp tips. Each population sample comprised 2.5 male dentitions with no attrition and 25 with attrition. Using dial callipers, the mesiodistal and buccolingual diameters were measured to the nearest 0.1 mm for each permanent tooth (excluding third molars). The mesiodistal crown diameter was defined as the minimum distance between the mesial and distal contact areas measured parallel to the occlusal plane. The buccolingual diameter was defined as the minimum distance between the most buccal and lingual crown convexities measured at right angles to the occlusal plane. All the teeth were measured by one observer. Based upon repeat measurements of samples selected at random, using analysis of variance, the component of variance introduced artificially as a result of inconsistency in measurement was not only statistically insignificant (F’X-2) compared with that existing within the corresponding population samples, but also of too small a scale to affect the overall results of this study. STATISTICAL ANALYSIS The data were analyzed by a computer program which enabled the mean dimensions and standard deviations of each tooth diameter with or without attrition to be printed out for each population sample. As previously described by Lavelle (1978), the program also subjected all the tooth dimensions to canonical analysis of discriminance. This technique maximally discriminated the population samples and provided an index in terms of squared generalized distances (D’), of the separation between all pairs of population samples based upon teeth with or without attrition. RESULTS The mean mesiodistal crown diameters of teeth with and without attrition for the four population samples included in this study are listed in Tables Z and ZZrespectively. Although the dimensions were all smaller for the teeth with attrition than without attrition, considerable variability was evident both within and between the samples. A similar feature was evident from comparison of the buccolingual crown diameters, although such dimensions were not so severely affected by attrition. Nevertheless, when comparing individual crown diameters, the degree of contrast between population samples varied depending upon the tooth compared and whether the sample was based upon teeth with or without attrition. Using univariate statistical techniques it was therefore not possible to obtain an overall picture of the contrasts between the population samples. When all the tooth diameters were combined together in the multivariate analysis, Caucasians were significantly separated from the other three population samples. These contrasts
128
Journal of Dentistry, Vol. ~/NO. 2
Table
1. Mesiodistal crown diameters of teeth without attrition of different population samples Australasian X
Negroid
Mongoloid x
d.
x
s. d.
o-57 O-61 0.58 041
9.27 7.61 8.35 7.79
O-46 0.52 O-63 0.48
8.96 6.84 8.11 7.21
s.
Caucasian s. d.
X
s.
d.
Maxillary I1 I2 C P’
9.34 7-64 8.32 7.74
$ M2
11.31 7-08 1O-49
0.42 o-50 o-77
Il.34 7.11 10.62
0.63 0.49 0.79
1045 6.95 1049
5.88 6-64 7.52 744 7.51 12.11 Il.49
0.41 0.44 o-41 O-52 o-49 0.64 O-67
5.89 6.67 7.74 7.48 7-60 12.22 11.51
O-52 O-63 0.41 0.54 O-47 0.71 O-52
5.52 6.12 7.11 7.29 7.69 11.26 11.18
0.52 0.62 044 0.34
8-76 6.65 7.84 7.11
0.44 0.62 0.41 9.49
O-37 0.47 O-61
10.82 6.85 10.34
9.39 6.54 0.66
0.35 o-41 O-38 0.36 0.42 O-58 O-67
546 586 6.91 7.11 7-28 11.11 10.77
o-41 0.33 0.31 0.37 0.50 0.49 0.47
Mandibular ‘1 ‘2
C PI p2
MI M2
x, Mean mesiodistal crown diameter (mm); s.d., standard deviation. Tab/e
II.
Mesiodistal crown diameters of teeth with attrition of different population samples.
X
Mongoloid
Negroid
Australasian sd.
X
s.
d.
X
Caucasian s.
d.
X
s.
d.
Maxillary
7.01 7.70 11.29 1o-45
0.69 0.76 0.68 0.83 O-85 0.86 0.74
9.24 7.58 8.31 7.68 6-94 11.29 10.58
O-63 0.84 O-88 0.79 0.74 0.79 0.82
8.91 6.82 8.05 7.14 6.91 1042 1047
0.52 0.69 O-85 0.89 o-94 0.69 0.75
8.75 6.60 7.80 7-06 6.81 IO.74 IO-31
0.49 0.52 O-65 0.47 0.73 0.79 0.65
5-82 6-61 7.50 7.41 7.48 12.09 1 l-36
0.71 0.68 0.69 0.65 O-72 0.79 O-68
5.81 6.63 7.71 7.41 7.54 12.19 Il.47
O-68 0.72 O-83 0.79 O-78 0.69 0.74
5.49 6-09 7.08 7.21 7.44 11.25 Il.14
049 048 O-82 0.63 O-68 0.75 o-79
540 5.85 6.87 7.08 7.21 11.04 IO-72
O-52 0.41 0.69 O-65 O-72 0.76 O-85
I’ I2 C
9.31 7.69 8.29
;: M’ M2
‘1
Mandibular ‘2
C Pl p2
Ml M2
x, Mean mesiodistal crown diameter; s.d. standard deviation.
were not so marked on analysis of either the maxillary or mandibular tooth diameters (Table IQ. In addition, such discrimination was greatest for the dimensions of teeth without attrition compared with the dimensions of teeth with attrition or combining the dimensions of teeth with and without attrition. In all the multivariate analyses a similar pattern of discrimination between the four population samples was apparent, although the degree of separation depended on the degree of tooth attrition. Discrimination between the samples was slightly greater from analysis of the maxillary tooth dimensions, compared with those of the mandibular arch, and from the
Lavelle: Attrition
Table /I/.
129
in population
studies
generalized
distances
Squared
based on analysis of mesiodistal
(0’)
between
and buccolingual
centroids
(means) of different
population
samples
tooth diameters Tooth dimensions
analysed
Maxillary
Mandibular
Maxillary and mandibular
2.95 3.04
2.88 2.91
4.69 3.85
Australasian
3.62
3.75
6.94
Teeth with attrition Negroid Mongoloid
2.01 2.14
1.86 2.05
2.96 3.14
Australasian
2.52
2.41
3.28
2.67 2-95 3.04
2.49 254 3.18
3.71 3.36 4.79
Population sample compared with Caucasian Teeth without Negroid Mongoloid
attrition
Teeth with and without Negroid Mongoloid Australasian All squared generalized
attrition
distances in standard deviation
Tab/e IV. Squared generalized distances (0’) on analysis of mesiodistal tooth diameters
between
units.
centroids
of different
Tooth dimensions Population samples compared with Caucasian
population
samples based
analysed
Maxillarv
Mandibular
Maxillary and mandibular
Teeth without attrition Negroid Mongoloid Australasian
l-19 1.04 l-36
1.13 O-98 I.27
2.47 2-12 3.43
Teeth with attrition Negroid Mongoloid Australasian
0.87 o-75 1.11
0.74 O-64 1.03
1.97 1.49 2-58
1.02 0.97 l-38
0.94 0.88 1.24
2.11 1.85 2.88
Teeth with and without Negroid Mongoloid Australasian All squared generalized
attrition
distances in standard deviation
units.
mesiodistal (Table W) then the buccolingual (Table v) crown diameters. In each analysis, however, the molar dimensions contributed most to the separation between the population samples compared with the premolar, canine and incisor tooth dimensions.
DISCUSSION The dentition was of importance
to individual survival in ancient times, although the increased use of mechanical methods in food preparation has gradually shifted food reduction from inside the mouth to outside (Campbell, 1939). Also the loss of jaw mass in primates was pro-
130
Table K Squared generalized distances (0’) on analysis of buccolingual crown diameters
Journal of Dentistry, Vol. ~/NO. 2
between centroids of different population samples based
Tooth dimensions analysed Population samples compared with Caucasian
Maxillary
Mandibular
Maxillary and mandibular
Teeth without attrition Negroid Mongoloid Australasian
099 O-85 1.01
0.83 o-72 o-94
l-86 1-44 2.05
Teeth with attrition Negroid Mongoloid Australasian
o-79 O-61 o-69
O-65 o-55 O-68
l-47 1.09 l-86
Teeth with and without attrition Negroid Mongoloid Australasian
O-78 o-59 0.96
O-67 o-51 O-88
1.58 l-21 1.96
All squared generalized distances in standard deviation units.
bably made possible by the selective shifting of food collecting to the hands (DuBrul, 1962). Consequently, since the time of canine reduction and transference from the mouth to the hand of man of many of tool and defence devices, the teeth have assumed limited evolutionary significance (Dahlberg, 1963). During man’s evolution, therefore, dental selection pressures must have been reduced, although this does not entirely negate the evolutionary significance of the dentition in present-day man. Whilst the major influence of genetic factors on tooth form is apparent (Garn, Lewis and Walenga, 1968; Corruccini and Henderson, 1976), there is increasing realization that environmental factors also have significance (Biesenfeld, 1970). Tooth diameters are not isolated entities, however, since not only are the mesiodistal and buccolingual diameters associated one with another (Gam, Lewis and Kerewsky, 1968) but tooth size is correlated with cusp size (Biggerstaff, 1975). Furthermore, individual tooth size is related to that of the dentition as a whole (Garn and Lewis, 1969; Lombardi, 1975) and to other skeletal dimensions (Anderson et al., 1977; I.&elle, 1977). In non-human primates, tooth size probably has an association with occlusomandibular kinetics (Kay and Hiiemae, 1974; Every, 1975; Zingesser, 1976), although it is difficult to investigate this relationship in man. There is no doubt that tooth attrition affects both dental and skeletal relationships (Fishman, 1976), which in turn influence masticatory movements. Furthermore, the progression of tooth attrition is influenced by its location within the dental arch, and this is partially determined by the soft tissue environment of the tongue, cheeks and lips (Butler, 1972). Tooth size and tooth attrition are therefore more complex biological entities than traditionally accepted, so there is a limit to the biological data that can be abstracted from the examination of teeth within a dried skull. samples depending upon whether the dimensions of teeth with or without attrition are included in the analysis. Tooth attrition, however, is a continuous variable which is difficult to segregate objectively into different categories, so it was not possible to quantify precisely the effect of attrition on population separation. In addition, the mesiodistal and buccolingual
Lavelle: Attrition
in population
131
studies
crown diameters provide only a cursory metrical definition of tooth form. Attrition predominantly affects the occlusal surface, particularly cusp mophology, which is difficult to define by the mesiodistal and buccolingual tooth diameters. Thus, further data are required before the varying contrasts between population samples based upon teeth with or without attrition can be interpreted, especially relative to dietary habits. Nevertheless this study illustrates the necessity of considering dentitions as a whole rather than individual teeth in isolation in odontometric studies. REFERENCES
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