Enlarged occlusal surfaces on first molars due to severe attrition and hypercementosis Examples from prehistoric coastal populations of Texas.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 78:9-15 (1989) Enlarged Occlusal Surfaces on First Molars Due to Severe Attrition and Hypercementosis: Examples From Prehistoric Coastal Populations of Texas ANTHONY G. COMUZZIE AND D. GENTRY STEELE Department ofdnthropology, Texas A&M University, College Station, Texas 77843 ABSTRACT During a n examination of prehistoric samples from the Texas coast, individuals consistently exhibited a suite of traits on the first molars that included severe wear, hypercementosis, and resorption of the buccal margin of the alveolus. The occlusal surface of the tooth was worn below the cervical margin, with the subsequent incorporation of the buccal surface of the buccal roots into the occlusal plane. This expanded occlusal surface, which extends the buccal surface beyond the normal edge of the tooth, is composed of a combination of original enamel, secondary dentin, and cementum. There is a marked rounding of the buccal aspect of the occlusal surface. These conditions were noted in both maxillary and mandibular first molars. The resorption of alveolar bone surrounding the buccal roots resembles resorption associated with periodontal infection and is thought to be the result of severe levels of stress being applied to this portion of the dentition. The dentition, like the skeleton, is a dynamic system responding to the forces to which it is subjected. One of the most common forms of dental response is attrition. Attrition is produced principally by the normal processing of foods andor the use of teeth in technological applications (Dahlberg, 1963; Molnar, 1970, 1971, 1972; Roydhouse and Simonsen, 1975; Sicher, 1960). Lavelle (1970) described attrition as a “complex polymorphism” resulting from an interactive combination of external forces and the physical composition and morphological structure of the dentition. Since work done by Leigh (19251, attrition has increasingly come to be viewed as a natural and often desirable process, functioning in the maintenance of proper occlusion as well as contributing to the prevention of caries and periodontal infection (Hall and German, 1975; Patterson, 1984; St. Hoyme and Koritzer, 1976; Smith, 1986). In extreme cases, however, the reductive effects of attrition can be pathogenic (Cawson, 1968; Kraus et al., 1969; Ross, 1970; Spouge, 1973) and can dramatically alter the shape of a single tooth or the entire dental arcade. Regardless of its causes or final effects, attrition is, in principle, a destructive process, evidenced by the wearing away of the occlusal surface of a tooth. @ 1989 ALAN R. LISS, INC Since duration of occlusion plays a significant role in the level of attrition seen in a tooth, typically the first molars exhibit the greatest wear in a normal dental arcade (Gordon, 1982; Lavelle, 1970; Marks et al., 1985; Miles, 1963; Reinhardt, 1983; Schmucker, 1985). Authors describing the wear of first molars have noted the invariable loss of enamel and exposure of the dentin, and often a shift in the orientation of the occlusal surface as well (Hall, 1976; Hall and German, 1975; Murphy, 1959; Smith, 1986; Reinhardt, 1983). Three other less often noted, but highly important, characteristics seen in severely worn molars are exposure of the pulp cavity, erosion of the buccal alveolar border (Linn et al., 1987; Tal, 1983), and exaggerated lingual tilting of upper and lower molars (Reinhardt, 1983; Taylor, 1963). Reinhardt (1983) presented a detailed review of lingual tilting and erosion of the buccal margin in severely worn teeth. Lingual tilting of the teeth, particularly the first molars, was described a s the physical displacement of the tooth from its normal orientation to one with a pronounced buccal to lingual slope. This tilting of the tooth often resulted in extension of the occlusal surface onto the buccal margin and abandonment of part or all of the original occlusal surface (Rein- 10 A.G. COMUZZIE AND D.G. STEELE TABLE 1. Number of individuals from Texas coastal sites who possessed first molars (N) and the number of these in.dividuals exhibiting hypercementosis and expansion. o f the occlusal surface Site name Blue Bayou Palm Harbor Oso Creek Cay0 Del Oso Tot.nl Site number 41 VT 94 41 AS 80 41 NU 37 41 NU 2 N 19 4 3 28 54 Individuals with hypercementosis 3 1 2 4 10 Individuals with expanded occlussal surface -I 1 2 1 4 ‘Although heavily worn, these teeth do not yet sh ow evidence of expansion hardt, 1983; Taylor, 1963). Based on observations of lingual tilting of molars in selected California populations, Reinhardt (1983) believed that lingual tilting, and its associated characteristics, could be attributed to a “severe attrition syndrome” created by the normal process of mastication and bruxism. Alternatively, Taylor (1963), Buck (19251, and Campbell (19251, suggested that the buccally oriented slope of the severely worn occlusal surface on maxillary and mandibular molars, the extension of occlusal wear onto the buccal roots, and the lingual tilting of both upper and lower molars observed in samples of Australian Aborigines and of Maoris were created by a specific type of mastication associated with the processing of fern rhizomes. In fern root processing, the buccal extension of the occlusal surface results from a functional expansion of the occlusal surface created by a n expanded use of the tooth. It did not represent a n occlusal adjustment as the tooth tilted in its socket. Other researchers, notably Anderson (1965) and Saunders (1972),thought that the use as a tool of the region around the first molar at least exacerbated the development of some of these traits, particularly the lingual tilting of the teeth. This study documents additional features associated with severe attrition in a sample of hunter-gatherers from the Texas coast: hypercementosis and expansion of the occlusal surface by incorporating cementum in the surface. This study further documents that a n extension of the occlusal surface onto the buccal margin can OCCUT without significant tilting of the tooth and abandonment of the original occlusal surface. MATERIALS AND METHODS Material from four prehistoric sites from the Texas coast were examined for evidence of severe attrition (Table 1).All samples represent Archaic and/or Late Prehistoric hunter-gatherer societies utilizing a coastal environment. Several studies have suggested some degree of biological affinity between these populations (Wilkinson, 1977; Comuzzie, 1987; Comuzzie et al., 1986). From a sample of 54 individuals with associated first molars, 10 individuals exhibited two distinct features resulting from severe attrition: 1) hypercementosis associated with dehiscence and 2) the incorporation ofthe buccal surface of the root and cementum into the occlusal plane. Whereas all individuals in this sample displayed high levels of attrition in the entire dentition, only the first molars exhibited the inclusion of the buccal roots as part of the occlusal surface and hypercementosis associated with dehiscence or abscesses. Unfortunately, because of poor preservation of the remains recovered, none of the affected individuals is represented by a complete dental arcade. Therefore, it was not possible to compare the pattern of wear on a n affected tooth’s antagonist in the opposing dental arcade. However, four individuals possessed left and right first molars in the arch, which permitted comparison of measurements and wear patterns from the same individual for both affected and nonaffected molars. In a n effort to describe the changes in the teeth exhibiting the two distinctive features, measurements were made of those that exhibited occlusal expansion and those that did not. Two authors have developed techniques 11 PREHISTORIC MOLAR OCCLUSAL SURFACES TABLE 2. Surface area (mm2)of both affected and nonaffected first molars for the same individual Site Palm Harbor Tooth tvDe Mi Oso Creek M1 Cayo Del Oso Mi MI for quantifying the degree of lingual tilting of teeth. Reinhardt (1983) measured lingual tilt by use of a protractor and a straight edge, recording the amount of angulation in increments of 5". This was done by first placing the 90" mark of the protractor even with, and approximately parallel to, the alveolar buccal margin. Next, a straight edge was placed along the buccal roots of the tooth, and the degree of tilting was read from the protractor. Molnar (1971) presented a qualitative method for scoring the tilting of the occlusal surface of severely worn teeth. Although this method has been suggested to be quick and reliable (Schmucker, 1985; Hall, 1976; Butler, 1972),it did not offer a complete description of the form of the occlusal surface. The technique presented by Reinhardt (1983) also was attempted, but we were unable to measure the tilt of the molars for the individuals in this study with the precision we desired. The maximum buccolingual and mesiodistal widths of the occlusal surface of the tooth were measured by use of dental sliding calipers and recorded to 0.1 mm. The occlusal surface was identified on the basis of tooth orientation and polishing of the dentin and cementum. These measurements were used to estimate the area of the effective occlusal surface of the tooth. Epoxy casts of two specimens, produced following Rose's (1983)guidelines, were further examined with the electron microscope. Micrographs were produced with a Jeol JSM 25SII scanning electron microscope, using a n accelerating voltage of 15 kV and magnifications of x15 to ~ 7 0 Electron . micrographs were also taken of a nonaffected third molar from this same sample for comparative purposes. Surface area nonaffected molar Surface area affected molar 109.8 83.7 94.1 106.1 118.7 116.6 111.6 110.9 RESULTS AND DISCUSSION The attrition in these ten first molars was extreme, with the complete loss of enamel from all tooth surfaces (Fig. 1A). Along with the extreme attrition, there was a marked reduction in crown height. Whereas the original occlusal surface of these molars is still relatively flat, it does curve onto the buccal margin, with pronounced wear continuing onto the buccal surfaces of the buccal roots in four instances (Fig. lB,C). In these cases, there is a deposition of adventitious dentin, usually of a clear, glassy variety (Taylor, 1963), surrounding the outer margin of the molar. The roots of these extremely worn molars were enlarged as a result of hypercementosis (Spouge, 1973) (Fig. lB,C). These affected molars exhibited evidence of dehiscence or abscessing of the buccal alveolar border in conjunction with the inclusion of the buccal surface of the buccal roots into the functioning occlusal surface (Fig. lB,C). There did, however, appear to be some variation in the degree of expression of the hypercementosis between individuals. A visual examination of the affected molars failed to reveal marked tilting of the tooth in its socket and abandonment of portions of the original occlusal surface as Reinhardt (1983)suggested. However, the increase in the effective occlusal surface of these molars could be documented (Table 2). The average increase in surface area, in the four individuals for whom affected and nonaffected teeth could be compared, was 15.5 mm2 over first molars in which the roots were not incorporated into the occlusal surface. In all cases, the expanded portion of the tooth was along the buccal margin. Electron micrographs documented buccolingually oriented striations on all first 12 A.G. COMUZZIE AND D.G. STEELE PREHISTORIC MOLAR OCCLUSAL SURFACES molars. Although all molars displayed buccolingually oriented striations to some degree, those first molars displaying a n increase in area of their occlusal surface revealed a greater predominance of well defined buccolingual striations than those occurring in the nonaffected molars (Fig. 2AC). Striations were as long as one-half the width of the tooth. Some began on the original occlusal plane and extended onto the buccally curved extension of the occlusal surface. This suggests that the original occlusal surface plus the sloped surface on the lingual border functioned as a n expanded occlusal surface. A nonaffected third molar (Fig. 2D) exhibited fewer and shorter striations, which were more varied in their orientation. Gordon (1982) documented the decreased number of striations in posterior teeth in Pan, proposing that these differences were a result of changing amounts of shear and compression, and differences in the length of transverse movement of the occluding partners from the first to the third molars. The unusual characteristics of these severely worn molars are the presence of hypercementosis and the incorporation of the cementum into the occlusal surface. The roots of these molars are markedly enlarged, with secondary deposition of cementum present. In these teeth, the roots were commonly exposed either by abscesses or dehiscence of the buccal alveolar border, causing the hypercementosis to be readily apparent. In all these cases, the occlusal surface of the tooth incorporated this cementum layer. It is believed that both dehiscence of the alveolar border and hypercementosis are often symptomatic of traumatic occlusion or severe wear (Spouge, 1973; Linn et al., 1987; Tal, 1983). Consequently, it has been suggested that the deposition of secondary cementum functions to strengthen the anchoring of a tooth in the face of extreme occlusal stress (Spouge, 1973). Although this increase in tooth size is generally confined below the gum line, and within the alveolar margin, it has little effect on the occlusal function of the affected tooth. However, in the molars from this sample, the buccal roots were exposed antemortem by dehiscence or abscessing, and the enlarged -~ ~ ~ ~~ Fig. 1. Maxillary dentition of individual from Palm Harbour Site (41 AS 80), Texas. A Occlusal view. B: Distal view of first molar illustrating hypercementosis of roots and rounded occlusal surface on buccal margin of crown. C: Buccal view of first molar illustrating antemortem exposure of roots and extentsion of occlusal surface onto buccal margin. 13 surfaces of the buccal roots were incorporated into the functioning occlusal surface. As a result, the secondary effect of hypercementosis was to increase the occlusal surface of the afYected molar even in the face of extreme attrition. In this respect, it may appear to function analogously to the buccal or lingual cingula seen in some of the non-human primates. Furthermore, this lateral expansion and rounded buccal margin superficially resembles lingual tilting as described by Reinhardt (1983) and Taylor (1963). Normally, in a worn dental arcade, the occlusal surface of the first mandibular molar slopes buccally, and its maxillary antagonist slopes lingually. To account for a buccally sloped maxillary molar, Reinhardt (1983) proposed that the maxillary tooth shifted from a buccally oriented tooth to a tooth that tilted lingually. More specifically, he proposed that the loss of intercuspation in worn teeth allowed greater lateral mandibular excursion, which increased incursive lateral force. This, in turn, traumatized buccal aspects of the alveolus, allowing the tooth to begin to tilt lingually. As the tooth tilted lingually, the buccal side of the tooth was incorporated in the occlusal surface as the lingual side was abandoned. With this model, wear extending onto buccal surface of the tooth, and incorporating the buccal roots, occurred if the tooth became tilted. The Texas coastal samples document that expansion of the occlusal surface onto the buccal surface can occur without significant tilting and can result in the expansion of the functional occlusal surface. SUMMARY In summary, hypercementosis can be affiliated with severe attrition, and, if the tooth wears to the point where the roots become included within the occlusal surface, the occlusal surface may become larger than the original. Furthermore, incorporation of the roots into the occlusal surface on the buccal margin of the tooth can occur without appreciable lingual tilting or loss of the effectiveness of the original occlusal surface. This condition has been documented only on first molars, and only in Texas coastal populations. ACKNOWLEDGMENTS The authors thank E. Miller for technical assistance and Virginia K. Massey for preparing the electron micrographs. Fig. 2. Electron micrographs of selected molars of individuals from Palm Harbour Site (41 AS 801, Texas. A buccal margin of mesiobuccal cusp of left first maxillary molar. B: Lingual aspect of occlusal surface of left first maxillary molar. C: Close-up view of buccal margin of mesiobuccal cusp. D: Distolingual cusp of lower third molar. Electron micrographs A-C are of left first molar illustrated in Figure 1. PREHISTORIC MOLAR OCCLUSAL SURFACES LITERATURE CITED Anderson JE (1965) Human skeletons of Tehuacan. Science 148:46-497. 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