AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 88:105-107 (1992)
Brief Communication: Interproximal Tooth Wear: A New Observation JOHN A. KAIDONIS, GRANT C. TOWNSEND, AND LINDSAY C. RICHARDS Department of Dentistry, The University of Adelaide, Adelaide, South Atistralia 5000, Australia
ABSTRACT Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which verticle or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to “interdigitate”with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation. o 1992 Wiley-Liss, Inc. KEY WORDS
Microwear, Humans, Dental wear
Interproximal wear of dental crowns has been observed and described in various extinct and extant mammalian species (Jolly, 1967, 1970; Wolpoff, 1971; Daws, 1986). Among human populations, interproximal and occlusal wear tends to be more extensive among nonindustrial groups living in harsh environments requiring vigorous masticatory activity than among modern societies consuming processed foods (Campbell, 1925; Molnar, 19721, although some individuals who grind (brux) their teeth excessively may exhibit considerable interproximal and occlusal wear as well. Quantitative analyses of the extent and rate of interproximal tooth wear among Australian Aboriginals, studied cross sectionally in museum material, have demonstrated significant reductions in dental arch length throughout life, and it has been proposed that this process may provide space into which developing third molars can emerge (Begg, 1954). It has generally been accepted that interproximal wear is related to two separate forces operating on the dentition, a mesial vector that tends to maintain the teeth in proximal contact and a buccolingual compo0 1992 WILEY-LISS, INC
nent of force resulting from lateral masticatory movements. Though many opinions exist on how the mesial force vector arises, it has generally been thought that occlusal forces, acting along the long axes of teeth with distally tilted roots, are responsible (Wolpoff, 1971). As interproximal wear progresses, the contact points of newly erupted teeth enlarge into contact areas. In severe cases, the proximal surfaces of affected teeth are worn flat, with a sharply defined boundary running in a buccolingual direction between them. Commonly this boundary becomes concave on the mesial surfaces of teeth, with the distal surfaces of the adjacent anterior teeth remaining convex (Fig. 1).Only rarely is the reverse situation seen. Occasionally the contact area assumes a n S-shaped appearance when viewed from the occlusal aspect. OBSERVATIONS As part of a n ongoing study of tooth wear, over 200 skeletal specimens of Australian
Received January 24,1991; accepted October 30,1991
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J.A. KAIDONIS ET AL
Fig. 1. Mandibular specimen of an Aboriginal juvenile showing the primary right first molar (dm,), the primary right second molar (dm,), and the permanent first molar (MI). Two separate wear configurations are evident, one being the concavity of the mesial surface of the lower permanent first molar (A) and the other being the flat interproximal surfaces between the primary first and second molars (B).
Fig. 2. Example of furrowing on the interproximal surface of a premolar tooth. Arrows indicate wear facet border, and one of the vertical furrows is labeled f. x25.
Aboriginals housed in the South Australian Museum have been examined as well a s over 100 teeth from whites. Observations of proximal surfaces of dental crowns have been made both in situ and on isolated teeth. Microscopic assessment of interproximally worn tooth surfaces has also been made using a Wild Heerbrugg stereomicroscope with mounted camera. Figure 2 shows a typical
Fig. 3. Mandibular specimen from a n Australian Aboriginal showing the left permanent molars. Note how the interproximal surfaces of M1 and M2 fit together like “lock and key” (indicated by arrow).
interproximal wear facet displaying the following features. 1) The affected area displays a well-defined border. 2) Within the border, deep vertical or near vertical furrows ranging from about 0.1 to 0.5 mm in width have been observed. These grooves are not exactly parallel to each other and vary in depth. 3) The enamel surface in the facet appears pitted, not polished smooth. 4) The furrows on the proximal surface of one tooth seem to “interdigitate” with the furrows on the proximal surface on the adjacent tooth. Furrowing has been observed with varying degrees of expression in approximately 60% of the Aboriginal teeth and about 30% of the teeth from whites that show interproximal wear. Teeth from whites have shown furrowing less often because interproximal wear has not been as advanced and therefore has been harder to distinguish than that in Aboriginals. At times, the vertically directed furrows in both samples have been distinguished only when light has been directed from a buccal or lingual direction. INTERPRETATION The observations reported in this brief communication are not consistent with the commonly held view that interproximal wear of dental crowns results from a buccolingual movement of adjacent teeth that maintain contact through a tendency to migrate mesially. Vertical or near vertical movement of teeth must be a n important
INTERPROXIMAL TOOTH WEAR
factor, although the precise cause of the vertical furrows remains unclear at present. The observation that opposing interproxima1 surfaces tend to interdigitate further supports the idea of vertical movement (Fig. 3). That the furrows vary in depth and width and are not exactly parallel to each other could imply that each furrow is produced at different times. The force vectors related to interproximal wear are undoubtedly complex, and the resultant patterns observed reflect a variety of factors, including tooth alignment, occlusal forces, cusp height and form, alveolar support, proximal morphology of adjacent teeth, and width of the masticatory stroke. We postulate that movement of posterior teeth resulting in interproximal wear is principally vertical in direction with simultaneous tipping of the teeth, although further research is required to substantiate this hypothesis. ACKNOWLEDGMENTS We thank Mr. Graeme Pretty, Senior Curator, South Australian Museum, for his as-
107
sistance and for permission to examine the Aboriginal material; Mrs. S. Hastings for manuscript preparation; and The University of Adelaide for making the project possible. LITERATURE CITED Begg PR (1954) Stone age man’s dentition. Am. J. Orthod. 40t298-312,373-383,462-475. Campbell TD (1925)Dentition and palate of the Australian Aboriginal. Thesis presented for the degree of Doctor of Dental Science, University of Adelaide, The Hassel Press, Adelaide. Daws BE (1986) Dental arch crowding in prehistoric man, and in indigenous racial groups of North America and Australia. Thesis presented for the degree of Master of Dental Surgery, University of Sydney. Jolly CJ (1967) The evolution of the baboons. In H Vagtborg (ed): The Baboon in Medical Research, Vol. 2. Austin; University of Texas, pp. 23-50. Jolly CJ (1970)The seed eaters: A new model of hominid differentiation based on a baboon analogy. Man 5t126. Molnar S (1972) Tooth wear and culture: A survey of tooth functions among some prehistoric populations. Curr. Anthropol. 13:511-526. Wolpoff MH (1971) Interstitial wear. Am. J. Phys. Anthropol. 34:205-228.
Brief Communication: Interproximal Tooth Wear: A New Observation JOHN A. KAIDONIS, GRANT C. TOWNSEND, AND LINDSAY C. RICHARDS Department of Dentistry, The University of Adelaide, Adelaide, South Atistralia 5000, Australia
ABSTRACT Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which verticle or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to “interdigitate”with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation. o 1992 Wiley-Liss, Inc. KEY WORDS
Microwear, Humans, Dental wear
Interproximal wear of dental crowns has been observed and described in various extinct and extant mammalian species (Jolly, 1967, 1970; Wolpoff, 1971; Daws, 1986). Among human populations, interproximal and occlusal wear tends to be more extensive among nonindustrial groups living in harsh environments requiring vigorous masticatory activity than among modern societies consuming processed foods (Campbell, 1925; Molnar, 19721, although some individuals who grind (brux) their teeth excessively may exhibit considerable interproximal and occlusal wear as well. Quantitative analyses of the extent and rate of interproximal tooth wear among Australian Aboriginals, studied cross sectionally in museum material, have demonstrated significant reductions in dental arch length throughout life, and it has been proposed that this process may provide space into which developing third molars can emerge (Begg, 1954). It has generally been accepted that interproximal wear is related to two separate forces operating on the dentition, a mesial vector that tends to maintain the teeth in proximal contact and a buccolingual compo0 1992 WILEY-LISS, INC
nent of force resulting from lateral masticatory movements. Though many opinions exist on how the mesial force vector arises, it has generally been thought that occlusal forces, acting along the long axes of teeth with distally tilted roots, are responsible (Wolpoff, 1971). As interproximal wear progresses, the contact points of newly erupted teeth enlarge into contact areas. In severe cases, the proximal surfaces of affected teeth are worn flat, with a sharply defined boundary running in a buccolingual direction between them. Commonly this boundary becomes concave on the mesial surfaces of teeth, with the distal surfaces of the adjacent anterior teeth remaining convex (Fig. 1).Only rarely is the reverse situation seen. Occasionally the contact area assumes a n S-shaped appearance when viewed from the occlusal aspect. OBSERVATIONS As part of a n ongoing study of tooth wear, over 200 skeletal specimens of Australian
Received January 24,1991; accepted October 30,1991
106
J.A. KAIDONIS ET AL
Fig. 1. Mandibular specimen of an Aboriginal juvenile showing the primary right first molar (dm,), the primary right second molar (dm,), and the permanent first molar (MI). Two separate wear configurations are evident, one being the concavity of the mesial surface of the lower permanent first molar (A) and the other being the flat interproximal surfaces between the primary first and second molars (B).
Fig. 2. Example of furrowing on the interproximal surface of a premolar tooth. Arrows indicate wear facet border, and one of the vertical furrows is labeled f. x25.
Aboriginals housed in the South Australian Museum have been examined as well a s over 100 teeth from whites. Observations of proximal surfaces of dental crowns have been made both in situ and on isolated teeth. Microscopic assessment of interproximally worn tooth surfaces has also been made using a Wild Heerbrugg stereomicroscope with mounted camera. Figure 2 shows a typical
Fig. 3. Mandibular specimen from a n Australian Aboriginal showing the left permanent molars. Note how the interproximal surfaces of M1 and M2 fit together like “lock and key” (indicated by arrow).
interproximal wear facet displaying the following features. 1) The affected area displays a well-defined border. 2) Within the border, deep vertical or near vertical furrows ranging from about 0.1 to 0.5 mm in width have been observed. These grooves are not exactly parallel to each other and vary in depth. 3) The enamel surface in the facet appears pitted, not polished smooth. 4) The furrows on the proximal surface of one tooth seem to “interdigitate” with the furrows on the proximal surface on the adjacent tooth. Furrowing has been observed with varying degrees of expression in approximately 60% of the Aboriginal teeth and about 30% of the teeth from whites that show interproximal wear. Teeth from whites have shown furrowing less often because interproximal wear has not been as advanced and therefore has been harder to distinguish than that in Aboriginals. At times, the vertically directed furrows in both samples have been distinguished only when light has been directed from a buccal or lingual direction. INTERPRETATION The observations reported in this brief communication are not consistent with the commonly held view that interproximal wear of dental crowns results from a buccolingual movement of adjacent teeth that maintain contact through a tendency to migrate mesially. Vertical or near vertical movement of teeth must be a n important
INTERPROXIMAL TOOTH WEAR
factor, although the precise cause of the vertical furrows remains unclear at present. The observation that opposing interproxima1 surfaces tend to interdigitate further supports the idea of vertical movement (Fig. 3). That the furrows vary in depth and width and are not exactly parallel to each other could imply that each furrow is produced at different times. The force vectors related to interproximal wear are undoubtedly complex, and the resultant patterns observed reflect a variety of factors, including tooth alignment, occlusal forces, cusp height and form, alveolar support, proximal morphology of adjacent teeth, and width of the masticatory stroke. We postulate that movement of posterior teeth resulting in interproximal wear is principally vertical in direction with simultaneous tipping of the teeth, although further research is required to substantiate this hypothesis. ACKNOWLEDGMENTS We thank Mr. Graeme Pretty, Senior Curator, South Australian Museum, for his as-
107
sistance and for permission to examine the Aboriginal material; Mrs. S. Hastings for manuscript preparation; and The University of Adelaide for making the project possible. LITERATURE CITED Begg PR (1954) Stone age man’s dentition. Am. J. Orthod. 40t298-312,373-383,462-475. Campbell TD (1925)Dentition and palate of the Australian Aboriginal. Thesis presented for the degree of Doctor of Dental Science, University of Adelaide, The Hassel Press, Adelaide. Daws BE (1986) Dental arch crowding in prehistoric man, and in indigenous racial groups of North America and Australia. Thesis presented for the degree of Master of Dental Surgery, University of Sydney. Jolly CJ (1967) The evolution of the baboons. In H Vagtborg (ed): The Baboon in Medical Research, Vol. 2. Austin; University of Texas, pp. 23-50. Jolly CJ (1970)The seed eaters: A new model of hominid differentiation based on a baboon analogy. Man 5t126. Molnar S (1972) Tooth wear and culture: A survey of tooth functions among some prehistoric populations. Curr. Anthropol. 13:511-526. Wolpoff MH (1971) Interstitial wear. Am. J. Phys. Anthropol. 34:205-228.
