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Dental wear scoring technique.

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Dental Wear Scoring Technique
E. C . SCOTT
Department ofdnthropology, Uniuersity of Kentucky, Lexington, Kentucky 40506
KEY WORDS Dental wear
Inter-observer reliability
. Dental attrition . Ordinal scales .
ABSTRACT
An ordinal dental attrition scoring technique for molar teeth
involving a quadrant system is applied t o three Amerind skeletal samples.
Molar teeth are visually divided into four sections and each section scored on a
1-10 scale. The score for the whole tooth is the sum of the quadrant scores and
ranges from 4-40.Scores are based on the amount of enamel in each quarter of
the tooth. The method’s reliability is demonstrated by a paired comparison type
of ANOVA, for both intra- and inter-observer repeated measurements. Because
the method is reliable, easy t o use, and produces data with lower variances than
a 1-8system (such as Molnar’s ”7111, it is recommended for use in the principal
axis technique for the analysis of wear data presented in the accompanying
paper.
The study of dental attrition and culture
has not progressed as far as it might largely
because (as Wilkinson pointed out in 1972)
the area lacks “formalized methodology”specifically, of data collection and data
analysis.
The biggest problem in the analysis of dental wear data is avoiding the correlation of age
and wear. This problem has been methopefully successfully -by shifting the focus
to rate of wear rather than degree of wear
(Smith, ’72, ’76; Walker, ’78; Scott, ’79). Scott
has discussed why the principal axis analysis
method is more satisfactory than others
(Scott, ’79). For the principal axis analysis to
perform most satisfactorily, however, the data
should be either interval level or the best approximation which an ordinal scale can give.
The present article presents an ordinal scoring procedure for data collection that is reliable and that better approximates interval
level data than other available methods.
THE TECHNIQUE
Molnar’s well known dental wear scoring
system involves a 1-8ordinal scale based upon the number of dentine patches and the
amount of secondary dentine present on the
occlusal surface of a tooth (Molnar, ’71). My
system is also ordinal, but involves a 4-40
scale based upon the amount of enamel present on the occlusal surface of the tooth.
AM. J. PHYS. ANTHROP. (1979)51: 213-218.
There are philosophical as well as practical
differences in the two methods. The variable
in which we are properly interested in the
study of occlusal attrition is the amount of
enamel left on the tooth, as the amount of
enamel is the best indicator of the functional
life of the tooth. Because secondary dentine
provides a “second enamel,” to some extent we
may be interested in the amount of secondary
dentine; however, not all individuals in a population exhibit secondary dentine. It is important to focus upon the amount of enamel present, rather than the amount of secondary dentine present.
I suggest the following procedure for recording occlusal attrition of molars:
Visually divide the occlusal surface of the
molar into four equal quadrants. Score each
quadrant according to the 1-10 scale found in
table 1. The sum of the four quadrants is the
score for that tooth.
The primary consideration in the scoring
procedure is the amount of enamel in the
quadrant. After the major occlusal features
have worn off (scores 1-41the amount of dentine exposure relative to the amount of
enamel present in the quadrant is considered.
Each quadrant is then scored according to the
following categories: Worn patch covers onefourth of quadrant or less (5); worn patch
greater than one-fourth of quadrant area but
still completely surrounded by enamel (6);
213
214
E.
C. SCOTT
TABLE 1
Attrition scoring technique
Description
Score
0
1
2
3
4
5
6
I
8
9
10
No information available (tooth not occluding, unerupted,
antemortem or postmortem loss, etc.)
Wear facets invisible or very small
Wear facets large, but large cusps still present and surface
features (crenulations, noncarious pits) very evident. It is
possible to have pinprick size dentine exposures or “dots”
which should be ignored. This is a quadrant with much enamel.
Any cusp in the quadrant area is rounded rather than being
clearly defined as in 2. The cusp is becoming obliterated but is
not yet worn flat.
Quadrant area is worn flat (horizontal) but there is no dentine
exposure other than a possible pinprick sized “dot.”
Quadrant is flat, with dentine exposure one-fourth of quadrant or
less. (Be careful not to confuse noncarious pits with dentine
exposure.)
Dentine exposure greater: more than one-fourth of quadrant area
is involved, but there is still much enamel present. If the
quadrant is visualized as having three “sides” (as in the
diagram) the dentine patch is still surrounded on all three
“sides” by a ring of enamel.
Enamel is found on only two “sides” of the quadrant.
Enamel on only one “side” (usually outer rim) but the enamel is
thick to medium on this edge.
Enamel on only one “side” as in 8, but the enamel is very thinjust a strip. Part of the “edge” may be worn through a t one or
more places.
No enamel on any part of quadrant-dentine exposure complete.
Wear is extended below the cervicoenamel junction into the
root.
enamel only partially surrounds worn patch,
being present on two “flanks” or “sides” of the
patch (7); enamel occurs on only one side of
the worn patch (usually on the outer rim) and
the enamel is thick to medium on this edge
(8);only a thin strip of enamel is present in
the quadrant, and it may be worn through at
one or more places (9) ; no enamel is left on any
part of the quadrant (10).
THE DATA
The scoring system was applied to three collections of American Indian skeletal material.
One collection, Indian Knoll (15 OH 2, Kentucky), has very heavy attrition. The other
collections showed considerably lower occlusal
attrition, and were from a Ft. Ancient culture
site in Kentucky (Hardin village site, 15 GP
22) and a Mississippian culture site in Mis
souri (Campbell site, 23 P M 5). The collections were chosen because of their relatively
large sizes and because they represented individuals from cultures following different subsistence strategies. Although there is the
possibility that the Indian Knoll site is multicomponent (Robbins, ’77), most of the prehistoric Indian Knoll individuals were likely
hunters and collectors with a concentration
upon riverine shell fish. The Ft. Ancient and
Mississippian sites represent a food producing,
horticultural strategy with complex social organization and stratification.
RELIABILITY TESTS
Both intra- and inter-observer reliability
tests were performed. I scored a series of 102
Indian Knoll molar teeth, waited a week, and
then rescored the same specimens (ECS-ECS).
Since Indian Knoll is a collection showing considerable attrition, this comparison tested the
reliability of the method in the upper ranges
of the scale. To test the reliability of the method in the lower ranges of the scale, I scored 93
Hardin site teeth, waited seven days, and rescored the same specimens. Inter-observer
reliability was tested by myself and a graduate student (ECS-RBT) whom I trained in the
scoring procedure. We practiced together for
two sessions, looking at a representative sample of teeth from all 10 wear categories. We
scored a new series of 88 teeth independently,
on different days and in one another’s absence.
Means, standard deviations, and correlation
coefficients on the pairs of data (ECS x ECS
215
DENTAL WEAR SCORING TECHNIQUE
TABLE 2
Reliability tests of methodtintra-obseruer tests (ECS-ECS)
Indian Knall
X
s.d.
N
r
Hardin Village
1st run
2nd run
1st run
2nd run
24.32
7.64
102
24.01
7.54
102
13.94
7.40
93
14.03
7.95
93
0.98
0.96
ANOVA tables
Source
ss
df
Measurements
Teeth
Remainder
Total
1
101
101
__
203
Measurements
Teeth
Remainder
Total
1
92
92
185
Indian Knoll
4.711
10,389.496
1,678.789
12,072.996
MS
F
4.711
102.866
16.621
0.283
6.1889**
Hardin Village
0.435
1,089.952
332.565
1,422.952
0.435
11.847
3.614
0.120
3.278*
TABLE 3
Reliability tests of method:inter-observer tests (ECS-RBTI
-
X
s.d.
N
r
RBT
ECS
19.19
7.52
88
19.10
8.37
88
0.98
ANOVA table
Source
’
Measurements
Teeth
Remainder
Total
df
ss
MS
F
1
87
87
175
0.09
10,889.75
259.410
11.149.25
0.09
125.1695
2.9817
0.0301
41.9792
for the intra-observer test and ECS X RBT for
the inter-observer test) were calculated. Because this sort of reliability test is a matched
pairs design, either a matched sample t-test or
paired comparison type of ANOVA could be
performed. As the two methods are equivalent, I present the more informative ANOVA
results (Sokal and Rohlf, ’69: p. 330).
The results of the intra- and inter-observer
tests are presented in tables 2 and 3. Following Jamison and Zegura (‘741, correlation
coefficients are presented, although they are
not sufficient in themselves to indicate high
reliability (in t h e sense of measurement precision). Because the correlation coefficient reflects how closely the two sets of measurements are varying, “a high positive correla-
tion between the results of two investigators
who measured the same group of subjects
could mean either t h a t they obtained essentially the same results or t h a t the values
covaried in a systematic fashion” (Jamison
and Zegura, ’74: p. 200). I suggest the high
correlations shown in t h e intra-observer
reliability tests (ECS-ECS) support a conclusion of high precision of measurement. Examination of the close means and variances of the
two sets of measurements supports this, as did
an examination of the differences between the
first week’s scores minus the second week’s
scores. All differences (and there were few)
appeared random. The F ratios of t h e
ANOVAS were likewise insignificant, adding
to the confidence that the scoring procedure
2 16
E. C. SCO'IT
could be performed with precision by one individual a t two different times.
Similarly close means and variances were
found in the inter-observer comparisons, but
the matched sample t-test and the paired comparisons analyses of variance both rejected
the null hypothesis of no difference between
the ECS and RBT scores (data not presented).
Upon examining the sets of data it became
clear that one of the observers (RBT) consistently scored teeth slightly lower than the
other observer. The combination of the difference in means of the two observers along
with the large sample sizes of these comparisons almost insured findings of significant differences with even small differences
between the sets of scores. A correction factor
of 1unitkooth (i.e., 1 out of a possible 40) was
subsequently added to all of RBT's scores. This
constant did not affect the variance, of course,
but did affect the mean. This corrected RBTECS ANOVA demonstrated (as did the ECSECS comparisons) no significant differences
between the paired observations (table 31.'
DISCUSSION
Because different parts of the tooth (buccal,
lingual, mesial, distal) wear differently, scoring by quadrants allows a more accurate reflection of the amount of enamel present on
the occlusal surface than do procedures where
the whole tooth is viewed. The variability in
the data is thus better reflected with this
technique.
My experience in scoring teeth leads me to
believe that the amount of enamel lost in
each successive class is approximately equal,
though I would be reluctant to declare an
amount or percent of enamel lost. The 4-40
scale presented here approximates an interval
scale, in my view, better than other published
scales. The principal axis method of analysis,
mentioned in the beginning of the article and
the topic of the accompanying paper, works
best when the scale approximates an interval
level. That alone makes the 4-40scale preferable for data collection if one is analyzing the
data by the principal axis technique, but there
are other advantages as well.
The principal axis technique, like other
least squares techniques, is sensitive to variance. Confidence intervals are larger when
the data exhibit higher variances. Tied ranks
(duplicate scores) can inflate the variance and
therefore extend the confidence regions of the
principal axis slope if such ties occur a t a distance from (rather than close to) the mean.
TABLE 4
Comparison of numbers of MlM2pairs in tied ranks
scored on 1-40 and 1-8s v s t e m
Maxillae
No.
pairs
Mandibles
No. pairs
i n tied
ranks
No.
pairs
No. pairs
i n tied
ranks
Indian Knoll
Scott
system
29
2
27
3
30
21
26
16
Molnar
system
Campbell Site
Scott
system
34
6
36
10
system
34
22
36
21
Molnar
Hardin Site
Scott
system
30
7
18
6
27
21
18
12
Molnar
system
To test whether the 4-40scale produces data
with fewer tied ranks than Molnar's 1-8scale,
the same specimens were scored with both
methods. Data is presented in table 4. The
Scott system clearly produces fewer duplicate
scores than the Molnar system, as would be expected. Confidence regions for the data scored
with the 4-40scale are narrower than those
for data scored with the 1-8scale, as discussed
in the accompanying paper.
CONCLUSIONS
The dental wear scoring method presented
here is designed to supplement Molnar's procedure. Whether a researcher would use my
method or Molnar's would depend upon the
objectives of the research; as the accompany' In addition to demonstrating the high reliability of the technique, the reliability comparisons illustrate some interesting facts
about the use of t h e correlation coefficient as a n indicator of
reliability. In t h e inter-observer comparisons, t h e high correlation
coefficient reflected precision of measurement (both sets of ohaervations were internally reliable) hut a consistent (if correctable)
source of error. The correlation coefficient as t h e sole indicator in
inter-observer reliability is therefore ambiguous, a9 Jamison and
Zegura ('74) pointed out. Nonetheless, it is probably a g d intra-observer reliability measure.
The reason for this statement is something of a prohabdity statement itself. If a n observer were making observations consistently,
using t h e same criteria on each specimen ("reliably") a high positive
correlation coefficient would occur between observations in t h e
same set of data measured a t two times. It is not likely if the ohserver is truly consistent i n hidher choice of landmarks or characteristics that a systematic bias would inflate the correlation coefficient; random errors would not. Thus a high positive correlation
coefficient is a goad indicator of intra.ohserver comparisons. In
either intra- or inter-observation comparisons, a perusal of the data
for systematic biases would add confidence to t h e decision.
DENTAL WEAR SCORING TECHNIQUE
ing article illustrates, my procedure for expressing degree of wear is preferable t o
Molnar’s if the objective is a principal axis
analysis of dental wear, or by extension, any
analysis dealing with rate of wear rather than
central tendency expressions of degree.
Molnar’s scoring system includes direction of
wear and type (shape) of wear as well as
degree of wear. Someone interested in these
other characteristics of wear could simply
substitute the 4-40 system for Molnar’s 1-8
degree of wear variable category.
It must be pointed out that this procedure is
useful for molars (though possibly modifiable
for premolars) and anyone interested in degree of wear studies in which different parts
of the dentition are compared would be
advised t o utilize the same scale throughout
all tooth groups.
The wear score categories are quickly
learned, and even a relatively inexperienced
observer can score a complete dentition in
three t o five minutes. Experienced observers
can score a dozen or so complete dentitions in
about a half hour.
ACKNOWLEDGMENTS
I thank the Museum of Anthropology of the
University of Kentucky and the Anthropology
217
Museum of the University of Missouri for
kindly allowing me access to their skeletal collections. A great deal of thanks goes t o Mr.
Robert B. Tincher, graduate student in the
Anthropology Department at the University
of Kentucky, for assistance in the inter-observer reliability analysis. Useful comments
by B. R. DeWalt are greatfully acknowledged.
LITERATURE CITED
Jamison, P. L., and S . L. Zegura 1974 A univariate and
multivariate examination of measurement error in anthropometry. Am. J. Phys. Anthrop., 40: 197-204.
Molnar, S. 1971 Human tooth wear, tooth function and
cultural variability. Am. J. Phys. Anthrop., 34: 175-189.
Robbing, L. M. 1977 The Story of Life Revealed by the
Dead. In: Biocultural Adaptation in Prehistoric America.
Southern Anthropological Society Proceedings, No. 11.R.
L. Blakely, ed. University of Georgia Press, Athens.
Scott, E. C. 1979 Principal axis analysis of dental attrition data. Am. J. Phys. Anthrop., 51: 203-212.
Smith, P. 1972 Diet and attrition in the Natufians. Am.
J. Phys. Anthrop., 37: 233-238.
1976 Dental pathology in fossil hominids: What
did Neanderthals do with their teeth? Curr. Anthro., 17:
149-151.
Sokal, R. R., and R. J. Rohlf 1969 Biometry. Freeman, San
Francisco.
Walker, P. L. 1978 A quantitative analysis of dental a t trition rates in t h e Santa Barbara Channel Area. Am. J.
Phys. Anthrop., 48: 101-106.
Wilkinson, R. G. 1972 Comment on Molnar’s “Tooth
Wear and Culture.” Curr. Anthro., 13: 521.
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