A New Approach to the Study of Tooth Wear M.F. TEAFORD and C.A. TYLENDA' Department of Cell Biology & Anatomy, The Johns Hopkins University School of Medicine, 725 N. Wolfe Street, Baltimore, Matyland 21205; and 'Center for Devices and Radiological Health, Food and Drug Administration, Rockville, Maryland 20850
Human tooth wear occurs so slowly that traditionally it has needed months or years to be measurable. This study showed that microscopic changes in wear patterns on human teeth could be detected in a matter of days and could be used as indicators of rates of wear. Thus, daily or weekly changes in rates of wear can be documented for specific locations on teeth. For instance, through this new approach, rates of wear of human teeth were shown to be significantly slower than rates of wear of the teeth of laboratory monkeys raised on hard or soft diets. Similar techniques may ultimately be used to monitor subtle changes in tooth use-including those associated with growth and development and those occurring in response to various dental clinical procedures. J Dent Res 70(3):204-207, March, 1991
than the months or years it takes to document changes in tooth shape. The purpose of this study was to determine whether a similar approach could be applied to the study of human teeth. If so, it would make possible a wide range of dental clinical research, including investigations of age-related changes in tooth use and objective evaluations of clinical procedures affecting tooth wear. For example, orthodontists and oral surgeons could monitor how tooth use changes as a result of their procedures rather than relying on indirect indicators (such as the number of occlusal contacts or the superimposition of cephalometric tracings) (Durbin and Sadowsky, 1986; Shaw et al., 1986; Ghafari and Efstratiadis, 1989) which tell nothing about how the teeth are actually used. Microscopic changes in wear might occur so fast that clinicians could even modify their procedures in response to changes in tooth use.
Introduction.
Longitudinal studies of human tooth wear are rare, largely because human tooth wear occurs so slowly. Annual decreases in molar cusp height rarely exceed 50 1Lm in most human groups (Xhonga et al., 1972; Roulet et al., 1980; Molnar et al., 1983b; Lambrechts et al., 1989). In light of these slow rates of wear, some workers (e.g., Davies and Pedersen, 1955; Barrett, 1958; Murphy, 1964; Molnar, 1971; Kieser et al., 1985) have chosen to forego longitudinal studies and have relied upon cross-sectional data. However, individual differences in tooth shape make intergroup comparisons in such cases difficult. As a result, only the most obvious differences in rates of tooth wear can be documented. Those investigators who have conducted longitudinal studies of human tooth wear have chosen between two alternatives: Either use relatively imprecise methods and wait long periods of time for large amounts of wear to occur (Beyron, 1954; Molnar et aL, 1983a, b; Carlsson et al., 1985), or use more precise methods and thus measure rates of wear more quickly (Roulet et al., 1980; Lambrechts et al., 1989). Changes in rates of wear cannot be documented in the long-term studies due to the extensive time between impressions (from six to 12 years). In the short-term studies, less time between impressions (from six to 18 months) allows certain changes in wear to be documented, but only if standard dental replication techniques are modified (Lambrechts et al., 1981). Neither type of study is capable of documenting the daily or weekly changes in tooth wear that may occur in response to various clinical procedures or as a result of the gradual incorporation of permanent or artificial teeth into the functional dentition. Recent work with laboratory monkeys has shown that changes in microscopic wear features on teeth can be used as indicators of rates of wear for specific teeth, or even specific locations on teeth (Teaford and Oyen, 1989b, c). These microscopic changes in wear can be documented in a matter of days rather Received for publication July 16, 1990 Accepted for publication November 30, 1990 This work was supported in part by NIH grant DE07182 and NSF grant 8904327. 204
Materials and methods. Nine healthy adults volunteered to have two dental impressions taken for this study. Each volunteer kept a written record of all food consumed between baseline and follow-up impressions. The time between impressions never exceeded seven days. Before each impression, volunteers rinsed with a very dilute solution (0.15%) of sodium hypochlorite to minimize organic films on the tooth surface (Vossen et al., 1985; Teaford and Oyen, 1989a), after which the teeth were swabbed with gauze and air-dried for approximately 30 s. All impressions were taken with a polysiloxane, putty-wash system (Express, 3M, St. Paul, MN). Epoxy casts of the first and second mandibular molars were examined under a scanning electron microscope (Model 1810, AMRAY). Numerous studies (e.g., Scott, 1982; Rose, 1983; Beynon, 1987) have shown that these replication techniques will accurately resolve details smaller than one pLm. Thus, micrographs were taken at a magnification of 200x, and each micrograph represented an area of approximately 0.24 mm2 on the tooth surface. At least four micrographs were taken of each tooth: two each from contact areas on the buccal and lingual sides of the buccal cusps (i. e., shearing and crushing/ grinding facets, respectively) (Kay and Hiiemae, 1974; Kay,
1977). Baseline and follow-up micrographs of the same enamel areas were placed under an acetate transparency and examined under a 3x magnifying ring. A grid on the transparency effectively divided each micrograph into 20 smaller units to facilitate the recognition of identical microscopic wear features in each micrograph (see Fig. 1). All microscopic scratches and pits visible on the follow-up micrograph were counted. If a scratch or pit on the follow-up micrograph was not visible on the baseline micrograph, it was also recorded as a new feature (Fig. 1). The number of new features in the follow-up micrograph divided by the total number of features in the follow-up micrograph yielded the proportion of microscopic wear features created between baseline and follow-up. Since all volunteers were healthy adults and none was currently undergoing
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
A NEWAPPROACH TO THE STUDY OF TOOTH WEAR
Vol. 70 No. 3
205
Rates of Wear on Lower Ml Buccal Contacts 1.6
.w
1.4
F
1.2
F
1.0
F
-2 0 Mm
--1-
0.8 0.6 25 features
(1I
new)
27 features
28 features
(0 new)
(3 new)
I1r
0.4
0.2 0.0 NIDR patients
44..
soft diet hard diet Laboratory Monkeys
Rates ofWear on Lower Ml Occlusal Contacts 1.6 * v . . Yw
/// NEW
Fig. 1-Representative portions of baseline (top) and follow-up (bottom) micrographs. The overlying grid normally divides the micrographs into 20 cells. Three of those 20 cells are represented here. Eighty microwear features are visible in the follow-up cells, and of those, three are new features, yielding a proportion of new features of 0.0375. The time between baseline and follow-up impressions in this case was three days. Thus, if the remaining 17 cells (for this pair of baseline and follow-up micrographs) yielded similar results, the proportion of new features created in one week would be 0.0875. Another way to present these figures would be to say that, at this rate, it would take 80 days for all features to be replaced-i.e., to obtain a proportion of 1.0.
1.4
4-a
1.2
1.0
0.8 0.6 0.4 0.2
0.0
any clinical procedures that might affect rates of wear, all proportions were converted to proportions of features created in seven days. The same measurement, computed for the sample of laboratory monkeys (Teaford and Oyen, 1989b, c), correlated significantly with decreases in molar cusp height (r 0.71-0.82, p < between 0.02 and 0.005, depending on which facets were examined). Thus, the proportion of microscopic wear features created in one week was used as an indicator of the rate of tooth wear for each individual. The Mann-Whitney test was used to compare weekly rates of wear between the human sample and a previously-published sample of laboratory monkeys raised on a soft diet (Teaford and Oyen, 1989c). The Wilcoxon paired-sample test was used to test for differences in rates of wear between buccal and lingual contact areas and between homologous areas on M1 and M2. Because the data were collected as proportions, and proportions form a binomial (rather than normal) distribution, a variance stabilizing transformation (the arcsine transformation-i.e., X' = arcsine \/X was performed before the computation of the means and standard deviations used in the accompanying Figs. The transformation was unnecessary for data analysis, because both the Mann-Whitney test and the
NIDR patients
hard diet soft diet Laboratory Monkeys
Fig. 2-Rates of microscopic wear on the lower first molar in the present sample of dental patients (labeled NIDR patients) (Teaford and Oyen, 1989b, c) and previously published samples from laboratory monkeys raised on hard or soft diets. In all cases, figures from one week were extrapolated from data for three to six days. Top half of Fig. = wear on contact facets on buccal side of tooth. Bottom half of Fig. = wear on contact facets on occlusal surface of tooth.
Wilcoxon paired-sample test use ranks of measurements rather than actual measurements.
Results. The human subjects showed tooth wear significantly slower than that of the laboratory monkeys raised on a soft diet (Fig. 2). For both M1 and M2, contact areas near the central fossa of the tooth (the crushing/grinding facets) showed significantly faster rates of wear than areas on the buccal side of the tooth
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
J Dent Res March 1991
TEAFORD & TYLENDA
206
Differences in Rates of Wear between Contact Areas on Lower Ml 30
It
E
20
la
F
L 1
0) rA
W
10
et
0 -M=TI
C8
C18
C21 NIDR
C22
C23
Clinic
C24
C25
C28
C30
Volunteers
Differences in Rates of Wear between Contact Areas on Lower M2
M2 (C24 in Fig. 3) was also the only individual to eat mainly salads and fresh vegetables throughout the study-i.e., food items requiring finer cutting and shearing in chewing. The lack of significant differences in rates of wear between M1 and M2 does not rule out the possibility of such differences in larger samples of different age groups. Overall, the results of this study show that daily or weekly changes in enamel surfaces can be detected on human teeth. These changes are readily detectable in comparisons of otherwise similar micrographs. Thus, this work might be particularly suited for image analysis (Kay, 1987; Grine and Kay, 1988). It may also be possible (through stereology and SEM stereophotogrammetrics) to convert these measures into estimates of the amount of dental material lost per unit of time. However, as noted above, significant correlations exist between the proportion of microwear features created in one week and annual decreases in cusp height. This shows that changes in microscopic wear features may also be used as indicators of rates of wear. Admittedly, the creation of new wear features on a surface may only be a good indicator of certain types of wear (e.g., abrasion) and not others (e.g., erosion). The key point is that these microscopic changes occur quickly, and thus the relative effects of different types of wear can be easily tested. Through the new approach, changes in tooth use or denture use may be quickly and objectively established, and relative wear rates for dental materials may be easily documented in vivo.
5._
as
Acknowledgments.
-
We thank Beverly Handelman for her help in taking the dental impressions and Rose Keller for her help in preparing and cataloging casts and in taking SEM micrographs. We also thank Ralph Bunge, Stanford Hamburger, Mickie Kivel, Phyllis Silverman, Alan Walker, and two anonymous reviewers for their comments on the manuscript.
v Cs
I..3
C8
C18
C23 C24 C28 C21 NIDR Clinic Volunteers
C30
Fig. 3-Differences in rates of wear between areas on the same teeth in the present sample. Top half of Fig. = data for lower first molar. Bottom half of Fig. = data for lower second molar.
(the shearing facets) (Fig. 3). There were no significant differences in rates of wear between M1 and M2.
Discussion. The slower tooth wear in humans, as compared with laboratory monkeys, is probably a reflection of differences in the abrasive content of their foods, since even the soft laboratory monkey food is fairly abrasive (Teaford and Oyen, 1989b). These results also show that the new approach can yield results similar to those documented by traditional means, since wearrelated changes in tooth shape for the laboratory monkeys also occurred at a much faster rate than in any modern human sample (Teaford and Oyen, 1989b). The fact that contact areas near the central fossa of the tooth (the crushing/grinding facets) showed significantly faster rates of wear than contact areas on the buccal side of the tooth (the shearing facets) should come as no surprise, since the prepared foods that make up most of our diet probably require our teeth to do more crushing and grinding than cutting and shearing (Lucas, 1979). Interestingly, the only individual to show faster wear on the shearing (as opposed to crushing) areas of Ml and
REFERENCES BARRETT, M.J. (1958): Dental Observations on Australian Aborigines, Aust Dent J 3:39-52. BEYNON, A.D. (1987): Replication Technique for Studying Microstructure, Scanning Microsc 1:663-669. BEYRON, H.L. (1954): Occlusal Changes in Adult Dentition, JAm Dent Assoc 48:674-686. CARLSSON, G.E.; JOHANSSON, A.; and LUNDQVIST, S. (1985): Occlusal Wear. A Follow-up Study of 18 Subjects with Extensively Worn Dentitions, Acta Odontol Scand 43:83-90. DAVIES, T.G.H. and PEDERSEN, P.O. (1955): The Degree of Attrition of the Deciduous Teeth and First Permanent Molars of Primitive and Urbanised Greenland Natives, Br Dent J 99:35-43. DURBIN, D.S. and SADOWSKY, C. (1986): Changes in Tooth Contacts Following Orthodontic Treatment, Am J Orthod Dentofac Orthop 90:375-382. GHAFARI, J. and EFSTRATIADIS, S. (1989): Mandibular Displacement and Dentitional Changes during Orthodontic Treatment and Growth, Am J Orthod Dentofac Orthop 95:12-19. GRINE, F.E. and KAY, R.F. (1988): Early Hominid Diets from Quantitative Image Analysis of Dental Microwear, Nature 333:765768. KAY, R.F. (1977): The Evolution of Molar Occlusion in the Cercopithecidae and Early Catarrhines, Am J Phys Anthropol 46:327352. KAY, R.F. (1987): Analysis of Primate Dental Microwear using Image Processing Techniques, Scanning Microsc 1:657-662. KAY, R.F. and HIIEMAE, K.M. (1974): Jaw Movement and Tooth Use in Recent and Fossil Primates, Am J Phys Anthropol 40:227256. KIESER, J.A.; GROENEVELD, H.T.; and PRESTON, C.B. (1985):
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
Vol. 70 No. 3
A NEWAPPROACH TO THE STUDY OF TOOTH WEAR
Patterns of Dental Wear in the Lengua Indians of Paraguay, Am J Phys Anthropol 66:21-29. LAMBRECHTS, P.; BRAEM, M.; VUYLSTEKE-WAUTERS, M; and VANHERLE, G. (1989): Quantitative in vivo Wear of Human Enamel, J Dent Res 68:1752-1759. LAMBRECHTS, P.; VANHERLE, G.; and DAVIDSON, C. (1981): A Universal and Accurate Replica Technique for Scanning Electron Microscope Study in Clinical Dentistry, Microsc Acta 85:4558. LUCAS, P.W. (1979): The Dental-Dietary Adaptations of Mammals, N Jb Geol Palaont Mh 8:486-512. MOLNAR, S. (1971): Sex, Age, and Tooth Position as Factors in the Production of Tooth Wear, Am Antiq 36:182-188. MOLNAR, S.; McKEE, J.K.; and MOLNAR, I. (1983a): Measurements of Tooth Wear among Australian Aborigines: I. Serial Loss of the Enamel Crown, Am J Phys Anthropol 61:51-66. MOLNAR, S.; McKEE, J.K.; MOLNAR, I.M.; and PRZYBECK, T.R. (1983b): Tooth Wear Rates among Contemporary Australian Aborigines, J Dent Res 62:562-565. MURPHY, T. (1964): The Relationship between Attritional Facets and the Occlusal Plane in Aboriginal Australians, Arch Oral Biol 9:269-280. ROSE, J.J. (1983): A Replication Technique for Scanning Electron Microscopy: Applications for Anthropologists, Am JPhys Anthropol 62:255-261.
207
ROULET, V.J.F.; METTLER, P.; and FRIEDRICH, U. (1980): Studie uber die abrasion von komposits im seitenzahnbereich-resultate nach 3 jahren, Dtsch Zahndrztl Z 35:493-497. SCOTT, E.C. (1982): Replica Production for Scanning Electron Microscopy: A Test of Materials Suitable for Use in Field Settings, J Microsc 125:337-341. SHAW, W.C.; ADDY, M.; DUMMER, P.M.H.; RAY, C.; and FRUDE, N. (1986): Dental and Social Effects of Malocclusion and Effectiveness of Orthodontic Treatment: A Strategy for Investigation, Community Dent Oral Epidemiol 14:60-64. TEAFORD, M.F. and OYEN, O.J. (1989a): Live Primates and Dental Replication: New Problems and New Techniques, Am J Phys Anthropol 80:73-81. TEAFORD, M.F. and OYEN, O.J. (1989b): Differences in the Rate of Molar Wear between Monkeys Raised on Different Diets, J Dent Res 68:1513-1518. TEAFORD, M.F. and OYEN, O.J. (1989c): In vivo and in vitro Turnover in Dental Microwear, Am J Phys Anthropol 80:447-460. VOSSEN, M.E.M.H.; LETZEL, H.; STADHOUDERS, A.M.; HERTEL, R.; and HENDRIKS, F.H.J. (1985): A Rapid Scanning Electron Microscopic Replication Technique for Clinical Studies of Dental Restorations, Dent Mater 1:158-163. XHONGA, F.A.; WOLCOTT, R.B.; and SOGNNAES, R.F. (1972): Dental Erosion. II. Clinical Measurements of Dental Erosion Progress, J Am Dent Assoc 84:577-582.
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
Human tooth wear occurs so slowly that traditionally it has needed months or years to be measurable. This study showed that microscopic changes in wear patterns on human teeth could be detected in a matter of days and could be used as indicators of rates of wear. Thus, daily or weekly changes in rates of wear can be documented for specific locations on teeth. For instance, through this new approach, rates of wear of human teeth were shown to be significantly slower than rates of wear of the teeth of laboratory monkeys raised on hard or soft diets. Similar techniques may ultimately be used to monitor subtle changes in tooth use-including those associated with growth and development and those occurring in response to various dental clinical procedures. J Dent Res 70(3):204-207, March, 1991
than the months or years it takes to document changes in tooth shape. The purpose of this study was to determine whether a similar approach could be applied to the study of human teeth. If so, it would make possible a wide range of dental clinical research, including investigations of age-related changes in tooth use and objective evaluations of clinical procedures affecting tooth wear. For example, orthodontists and oral surgeons could monitor how tooth use changes as a result of their procedures rather than relying on indirect indicators (such as the number of occlusal contacts or the superimposition of cephalometric tracings) (Durbin and Sadowsky, 1986; Shaw et al., 1986; Ghafari and Efstratiadis, 1989) which tell nothing about how the teeth are actually used. Microscopic changes in wear might occur so fast that clinicians could even modify their procedures in response to changes in tooth use.
Introduction.
Longitudinal studies of human tooth wear are rare, largely because human tooth wear occurs so slowly. Annual decreases in molar cusp height rarely exceed 50 1Lm in most human groups (Xhonga et al., 1972; Roulet et al., 1980; Molnar et al., 1983b; Lambrechts et al., 1989). In light of these slow rates of wear, some workers (e.g., Davies and Pedersen, 1955; Barrett, 1958; Murphy, 1964; Molnar, 1971; Kieser et al., 1985) have chosen to forego longitudinal studies and have relied upon cross-sectional data. However, individual differences in tooth shape make intergroup comparisons in such cases difficult. As a result, only the most obvious differences in rates of tooth wear can be documented. Those investigators who have conducted longitudinal studies of human tooth wear have chosen between two alternatives: Either use relatively imprecise methods and wait long periods of time for large amounts of wear to occur (Beyron, 1954; Molnar et aL, 1983a, b; Carlsson et al., 1985), or use more precise methods and thus measure rates of wear more quickly (Roulet et al., 1980; Lambrechts et al., 1989). Changes in rates of wear cannot be documented in the long-term studies due to the extensive time between impressions (from six to 12 years). In the short-term studies, less time between impressions (from six to 18 months) allows certain changes in wear to be documented, but only if standard dental replication techniques are modified (Lambrechts et al., 1981). Neither type of study is capable of documenting the daily or weekly changes in tooth wear that may occur in response to various clinical procedures or as a result of the gradual incorporation of permanent or artificial teeth into the functional dentition. Recent work with laboratory monkeys has shown that changes in microscopic wear features on teeth can be used as indicators of rates of wear for specific teeth, or even specific locations on teeth (Teaford and Oyen, 1989b, c). These microscopic changes in wear can be documented in a matter of days rather Received for publication July 16, 1990 Accepted for publication November 30, 1990 This work was supported in part by NIH grant DE07182 and NSF grant 8904327. 204
Materials and methods. Nine healthy adults volunteered to have two dental impressions taken for this study. Each volunteer kept a written record of all food consumed between baseline and follow-up impressions. The time between impressions never exceeded seven days. Before each impression, volunteers rinsed with a very dilute solution (0.15%) of sodium hypochlorite to minimize organic films on the tooth surface (Vossen et al., 1985; Teaford and Oyen, 1989a), after which the teeth were swabbed with gauze and air-dried for approximately 30 s. All impressions were taken with a polysiloxane, putty-wash system (Express, 3M, St. Paul, MN). Epoxy casts of the first and second mandibular molars were examined under a scanning electron microscope (Model 1810, AMRAY). Numerous studies (e.g., Scott, 1982; Rose, 1983; Beynon, 1987) have shown that these replication techniques will accurately resolve details smaller than one pLm. Thus, micrographs were taken at a magnification of 200x, and each micrograph represented an area of approximately 0.24 mm2 on the tooth surface. At least four micrographs were taken of each tooth: two each from contact areas on the buccal and lingual sides of the buccal cusps (i. e., shearing and crushing/ grinding facets, respectively) (Kay and Hiiemae, 1974; Kay,
1977). Baseline and follow-up micrographs of the same enamel areas were placed under an acetate transparency and examined under a 3x magnifying ring. A grid on the transparency effectively divided each micrograph into 20 smaller units to facilitate the recognition of identical microscopic wear features in each micrograph (see Fig. 1). All microscopic scratches and pits visible on the follow-up micrograph were counted. If a scratch or pit on the follow-up micrograph was not visible on the baseline micrograph, it was also recorded as a new feature (Fig. 1). The number of new features in the follow-up micrograph divided by the total number of features in the follow-up micrograph yielded the proportion of microscopic wear features created between baseline and follow-up. Since all volunteers were healthy adults and none was currently undergoing
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
A NEWAPPROACH TO THE STUDY OF TOOTH WEAR
Vol. 70 No. 3
205
Rates of Wear on Lower Ml Buccal Contacts 1.6
.w
1.4
F
1.2
F
1.0
F
-2 0 Mm
--1-
0.8 0.6 25 features
(1I
new)
27 features
28 features
(0 new)
(3 new)
I1r
0.4
0.2 0.0 NIDR patients
44..
soft diet hard diet Laboratory Monkeys
Rates ofWear on Lower Ml Occlusal Contacts 1.6 * v . . Yw
/// NEW
Fig. 1-Representative portions of baseline (top) and follow-up (bottom) micrographs. The overlying grid normally divides the micrographs into 20 cells. Three of those 20 cells are represented here. Eighty microwear features are visible in the follow-up cells, and of those, three are new features, yielding a proportion of new features of 0.0375. The time between baseline and follow-up impressions in this case was three days. Thus, if the remaining 17 cells (for this pair of baseline and follow-up micrographs) yielded similar results, the proportion of new features created in one week would be 0.0875. Another way to present these figures would be to say that, at this rate, it would take 80 days for all features to be replaced-i.e., to obtain a proportion of 1.0.
1.4
4-a
1.2
1.0
0.8 0.6 0.4 0.2
0.0
any clinical procedures that might affect rates of wear, all proportions were converted to proportions of features created in seven days. The same measurement, computed for the sample of laboratory monkeys (Teaford and Oyen, 1989b, c), correlated significantly with decreases in molar cusp height (r 0.71-0.82, p < between 0.02 and 0.005, depending on which facets were examined). Thus, the proportion of microscopic wear features created in one week was used as an indicator of the rate of tooth wear for each individual. The Mann-Whitney test was used to compare weekly rates of wear between the human sample and a previously-published sample of laboratory monkeys raised on a soft diet (Teaford and Oyen, 1989c). The Wilcoxon paired-sample test was used to test for differences in rates of wear between buccal and lingual contact areas and between homologous areas on M1 and M2. Because the data were collected as proportions, and proportions form a binomial (rather than normal) distribution, a variance stabilizing transformation (the arcsine transformation-i.e., X' = arcsine \/X was performed before the computation of the means and standard deviations used in the accompanying Figs. The transformation was unnecessary for data analysis, because both the Mann-Whitney test and the
NIDR patients
hard diet soft diet Laboratory Monkeys
Fig. 2-Rates of microscopic wear on the lower first molar in the present sample of dental patients (labeled NIDR patients) (Teaford and Oyen, 1989b, c) and previously published samples from laboratory monkeys raised on hard or soft diets. In all cases, figures from one week were extrapolated from data for three to six days. Top half of Fig. = wear on contact facets on buccal side of tooth. Bottom half of Fig. = wear on contact facets on occlusal surface of tooth.
Wilcoxon paired-sample test use ranks of measurements rather than actual measurements.
Results. The human subjects showed tooth wear significantly slower than that of the laboratory monkeys raised on a soft diet (Fig. 2). For both M1 and M2, contact areas near the central fossa of the tooth (the crushing/grinding facets) showed significantly faster rates of wear than areas on the buccal side of the tooth
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
J Dent Res March 1991
TEAFORD & TYLENDA
206
Differences in Rates of Wear between Contact Areas on Lower Ml 30
It
E
20
la
F
L 1
0) rA
W
10
et
0 -M=TI
C8
C18
C21 NIDR
C22
C23
Clinic
C24
C25
C28
C30
Volunteers
Differences in Rates of Wear between Contact Areas on Lower M2
M2 (C24 in Fig. 3) was also the only individual to eat mainly salads and fresh vegetables throughout the study-i.e., food items requiring finer cutting and shearing in chewing. The lack of significant differences in rates of wear between M1 and M2 does not rule out the possibility of such differences in larger samples of different age groups. Overall, the results of this study show that daily or weekly changes in enamel surfaces can be detected on human teeth. These changes are readily detectable in comparisons of otherwise similar micrographs. Thus, this work might be particularly suited for image analysis (Kay, 1987; Grine and Kay, 1988). It may also be possible (through stereology and SEM stereophotogrammetrics) to convert these measures into estimates of the amount of dental material lost per unit of time. However, as noted above, significant correlations exist between the proportion of microwear features created in one week and annual decreases in cusp height. This shows that changes in microscopic wear features may also be used as indicators of rates of wear. Admittedly, the creation of new wear features on a surface may only be a good indicator of certain types of wear (e.g., abrasion) and not others (e.g., erosion). The key point is that these microscopic changes occur quickly, and thus the relative effects of different types of wear can be easily tested. Through the new approach, changes in tooth use or denture use may be quickly and objectively established, and relative wear rates for dental materials may be easily documented in vivo.
5._
as
Acknowledgments.
-
We thank Beverly Handelman for her help in taking the dental impressions and Rose Keller for her help in preparing and cataloging casts and in taking SEM micrographs. We also thank Ralph Bunge, Stanford Hamburger, Mickie Kivel, Phyllis Silverman, Alan Walker, and two anonymous reviewers for their comments on the manuscript.
v Cs
I..3
C8
C18
C23 C24 C28 C21 NIDR Clinic Volunteers
C30
Fig. 3-Differences in rates of wear between areas on the same teeth in the present sample. Top half of Fig. = data for lower first molar. Bottom half of Fig. = data for lower second molar.
(the shearing facets) (Fig. 3). There were no significant differences in rates of wear between M1 and M2.
Discussion. The slower tooth wear in humans, as compared with laboratory monkeys, is probably a reflection of differences in the abrasive content of their foods, since even the soft laboratory monkey food is fairly abrasive (Teaford and Oyen, 1989b). These results also show that the new approach can yield results similar to those documented by traditional means, since wearrelated changes in tooth shape for the laboratory monkeys also occurred at a much faster rate than in any modern human sample (Teaford and Oyen, 1989b). The fact that contact areas near the central fossa of the tooth (the crushing/grinding facets) showed significantly faster rates of wear than contact areas on the buccal side of the tooth (the shearing facets) should come as no surprise, since the prepared foods that make up most of our diet probably require our teeth to do more crushing and grinding than cutting and shearing (Lucas, 1979). Interestingly, the only individual to show faster wear on the shearing (as opposed to crushing) areas of Ml and
REFERENCES BARRETT, M.J. (1958): Dental Observations on Australian Aborigines, Aust Dent J 3:39-52. BEYNON, A.D. (1987): Replication Technique for Studying Microstructure, Scanning Microsc 1:663-669. BEYRON, H.L. (1954): Occlusal Changes in Adult Dentition, JAm Dent Assoc 48:674-686. CARLSSON, G.E.; JOHANSSON, A.; and LUNDQVIST, S. (1985): Occlusal Wear. A Follow-up Study of 18 Subjects with Extensively Worn Dentitions, Acta Odontol Scand 43:83-90. DAVIES, T.G.H. and PEDERSEN, P.O. (1955): The Degree of Attrition of the Deciduous Teeth and First Permanent Molars of Primitive and Urbanised Greenland Natives, Br Dent J 99:35-43. DURBIN, D.S. and SADOWSKY, C. (1986): Changes in Tooth Contacts Following Orthodontic Treatment, Am J Orthod Dentofac Orthop 90:375-382. GHAFARI, J. and EFSTRATIADIS, S. (1989): Mandibular Displacement and Dentitional Changes during Orthodontic Treatment and Growth, Am J Orthod Dentofac Orthop 95:12-19. GRINE, F.E. and KAY, R.F. (1988): Early Hominid Diets from Quantitative Image Analysis of Dental Microwear, Nature 333:765768. KAY, R.F. (1977): The Evolution of Molar Occlusion in the Cercopithecidae and Early Catarrhines, Am J Phys Anthropol 46:327352. KAY, R.F. (1987): Analysis of Primate Dental Microwear using Image Processing Techniques, Scanning Microsc 1:657-662. KAY, R.F. and HIIEMAE, K.M. (1974): Jaw Movement and Tooth Use in Recent and Fossil Primates, Am J Phys Anthropol 40:227256. KIESER, J.A.; GROENEVELD, H.T.; and PRESTON, C.B. (1985):
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
Vol. 70 No. 3
A NEWAPPROACH TO THE STUDY OF TOOTH WEAR
Patterns of Dental Wear in the Lengua Indians of Paraguay, Am J Phys Anthropol 66:21-29. LAMBRECHTS, P.; BRAEM, M.; VUYLSTEKE-WAUTERS, M; and VANHERLE, G. (1989): Quantitative in vivo Wear of Human Enamel, J Dent Res 68:1752-1759. LAMBRECHTS, P.; VANHERLE, G.; and DAVIDSON, C. (1981): A Universal and Accurate Replica Technique for Scanning Electron Microscope Study in Clinical Dentistry, Microsc Acta 85:4558. LUCAS, P.W. (1979): The Dental-Dietary Adaptations of Mammals, N Jb Geol Palaont Mh 8:486-512. MOLNAR, S. (1971): Sex, Age, and Tooth Position as Factors in the Production of Tooth Wear, Am Antiq 36:182-188. MOLNAR, S.; McKEE, J.K.; and MOLNAR, I. (1983a): Measurements of Tooth Wear among Australian Aborigines: I. Serial Loss of the Enamel Crown, Am J Phys Anthropol 61:51-66. MOLNAR, S.; McKEE, J.K.; MOLNAR, I.M.; and PRZYBECK, T.R. (1983b): Tooth Wear Rates among Contemporary Australian Aborigines, J Dent Res 62:562-565. MURPHY, T. (1964): The Relationship between Attritional Facets and the Occlusal Plane in Aboriginal Australians, Arch Oral Biol 9:269-280. ROSE, J.J. (1983): A Replication Technique for Scanning Electron Microscopy: Applications for Anthropologists, Am JPhys Anthropol 62:255-261.
207
ROULET, V.J.F.; METTLER, P.; and FRIEDRICH, U. (1980): Studie uber die abrasion von komposits im seitenzahnbereich-resultate nach 3 jahren, Dtsch Zahndrztl Z 35:493-497. SCOTT, E.C. (1982): Replica Production for Scanning Electron Microscopy: A Test of Materials Suitable for Use in Field Settings, J Microsc 125:337-341. SHAW, W.C.; ADDY, M.; DUMMER, P.M.H.; RAY, C.; and FRUDE, N. (1986): Dental and Social Effects of Malocclusion and Effectiveness of Orthodontic Treatment: A Strategy for Investigation, Community Dent Oral Epidemiol 14:60-64. TEAFORD, M.F. and OYEN, O.J. (1989a): Live Primates and Dental Replication: New Problems and New Techniques, Am J Phys Anthropol 80:73-81. TEAFORD, M.F. and OYEN, O.J. (1989b): Differences in the Rate of Molar Wear between Monkeys Raised on Different Diets, J Dent Res 68:1513-1518. TEAFORD, M.F. and OYEN, O.J. (1989c): In vivo and in vitro Turnover in Dental Microwear, Am J Phys Anthropol 80:447-460. VOSSEN, M.E.M.H.; LETZEL, H.; STADHOUDERS, A.M.; HERTEL, R.; and HENDRIKS, F.H.J. (1985): A Rapid Scanning Electron Microscopic Replication Technique for Clinical Studies of Dental Restorations, Dent Mater 1:158-163. XHONGA, F.A.; WOLCOTT, R.B.; and SOGNNAES, R.F. (1972): Dental Erosion. II. Clinical Measurements of Dental Erosion Progress, J Am Dent Assoc 84:577-582.
Downloaded from jdr.sagepub.com at University of Sussex Library on March 26, 2015 For personal use only. No other uses without permission.
