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Congenital defects of the upper lateral incisors (ULI) and the morphology of other teeth in man.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 53:479-486 (19801
Congenital Defects of the Upper Lateral Incisors
(ULI) and the Morphology of Other Teeth in Man
PIERRE LE BOT, ALICE GUEGUEN, AND DENISE SALMON
FacultP de Chirurgie Dentaire, 1, rue Maurice Arnoux, 92120 Montrouge, France
(P.L.B.), and Groupe de Recherches INSERM U 88, 91, Bd de l’Hopita1, 75634 PARIS
cedex 13, France (A.G., D.S.)
KEY WORDS
Tooth Agenesis, Upper lateral incisors, Congenital defects,
Tooth morphology
ABSTRACT
A sample of 192 male propositi with a t least one ULI either
missing or reduced has been compared with 197 male controls in terms of the
morphology of the other teeth. Every class of propositi exhibits modifications in
the following characters: Significant differences between propositi and controls
were found for molar cusp number and groove pattern, particularly in the lower
first molar and in propositi with reduced ULI. Significant differences between
propositi and controls were also found with respect to caniniform pattern of the
lower first premolar. The Carabelli’s cusp is rarer in propositi. A hypothesis to account for these observations is proposed.
The congenital absence of particular teeth is
associated with quantitative and qualitative
modifications of other teeth. This phenomenon
was first observed in individuals missing the
third molars (Garn and Lewis, 1962, Keene,
1965, Baum and Cohen, 1971). More recently,
the number and size of teeth in individuals
with congenital defects of the upper lateral incisors (ULI) have been shown to be more
marked than they are in those with third
molar agenesis (Le Bot and Salmon, 1977). In
this study, we have analyzed morphological
characters of certain teeth in these same individuals and compared them with controls.
MATERIAL AND METHODS
Our sample was composed of 192 propositi
with a t least one maxillary lateral incisor
either missing or reduced in size. Controls
were 197 subjects selected at random from the
same population. All were males, aged 18 to 25
years, who were examined at the Selective
Service Center, Vincennes. Alginate impressions of both dental arches were obtained for
each subject and cast in plaster.
0002-9483/80/5304-0479501.70:C: 1980 ALAN R. LISS. INC.
Congenital absence of a tooth was verified
from dental history and radiographs. Reduction in size of a maxillary lateral incisor was
defined by one or more of the following
characteristics: conical (peg-shaped) crown
morphology; reduction in diameter from the
cervix to the incisal edge; asymmetry in
overall size between right and left incisors.
Previous studies disclosed morphological
differences in the dentition between individuals with size reduction of the maxillary
lateral incisor and those with agenesis of this
tooth (Le Bot and Salmon, 1977). Accordingly, the propositi were classified into three
main groups and four subgroups that were
determined by the morphology of the maxillary lateral incisor, as shown in Table 1. The
control subjects also were classified into three
subgroups according to the presence or
agenesis of third molars.
The morphological characters shown in
Table 2 were assessed for each subject and
scored according to the criteria listed. The
Received February 15. 1979; accepted April 21. 1980
P. LE BOT, A. GUEGUEN. AND D. SALMON
480
rating of cusp number-groove pattern, as
defined by Hellman (1928),was determined on
the right side of the mandible only. For the
other characters both sides of the dental arch
were examined. If asymmetry was present the
more “evolved score was used, that is, the
lesser cusp number, the X groove pattern, the
more extreme reduction of the Carabelli cusp,
and for the lower first premolar, the
caniniform pattern. In some instances, as
reflected in the number of observations, all
characters could not be scored. Furthermore,
the upper and lower third molars were excluded from the study, as their morphology could
not be determined with consistent reliability.
For each character the x2 test was used in
two types of comparisons: between the main
groups of controls and propositi (groups 1, 2,
3, and 4, and between subgroups l a , 2b, and
3b. In the latter comparison these subgroups
were representative of more extreme tooth
morphology; la-controls with complete dentition, 2b-propositi with two reduced incisors, and 3b-propositi with bilateral
agenesis of the incisor.
Some cell sizes were to small for x2 analysis,
and in these instances subjects were pooled to
increase the group size. For the mandibular
first molar (Table 3), subjects scored as five or
six cusps were pooled for the x2 analysis, as
were subjects with groove patterns + and X.
The same procedure was followed for the analysis of the maxillary second molar (Table 6),
where Carabelli scores two and three were
pooled, and for the analysis of the mandibular
second molar (Table 4), where scores for all
propositi were pooled. The xZ test was not applied to the cusp number-groove pattern
categories of Hellman (1928) or to the cusp
number ratings of the maxillary first molar.
RESULTS
Results are presented in Tables 3-7 according to tooth examined and morphological
categories. Each group and subgroup of propositi exhibited modifications of all dental
characters, which are sumarized as follows.
(Table 4) and the upper second molar (Table6),
but in these instances there were no marked
differences between the groups of propositi.
In the upper first molar only two propositi,
each with size reduction of the lateral incisor,
displayed a reduction in cusp number from the
usual pattern of four cusps displayed by all remaining subjects (Table 5 ) .
There were no significant differences between groups or subgroups with regard to cusp
number of the lower second premolar (Table7).
Groove pattern
I t is generally assumed that the order of
groove pattern, Y, +, and X, ranges from a
more archaic to a more evolved morphology.
Propositi exhibited significantly higher frequencies of the evolved pattern than did the
controls. This trend was evident in all groups
of propositi for both the mandibular first and
second molars (Tables 3 and 4).
Cusp number-groove pattern
Even greater differences between groups
were noted in the Hellman classification,
which associates cusp number and groove pattern. In the mandibular first molar, the Y5 pattern, which included Y6 ratings, diminished
in frequency from controls through group 3
propositi to group 2 propositi, who displayed
the lowest frequencies (Table 3). Similar
trends were observed in the mandibular second
molar, where the + 4 pattern was more frequent in all groups of propositi than in controls (Table 4). However, for this tooth the differences between groups of propositi were not
so clear-cut.
Carabelli complex
Although the Carabelli cusp occurred less
frequently in all groups of propositi, the differences between controls and propositi were
not significant for either the first molar or the
second (Tables 5 and 6).
Morphology of the lower first premolar
Propositi were more prone to caninification,
with differences in frequencies between conCusp number
trols and all groups or subgroups of propositi
In the lower first molar cusp number was highly significant (Table 7 ) .Propositi with size
significantly reduced in the propositi com- reduction or agenesis of the maxillary lateral
pared with controls, and, furthermore, the incisor were equally affected.
lowest cusp number was found in propositi
DISCUSSION
with size reduction of the maxillary lateral incisor (Table 3).
I t is generally assumed that a lowered cusp
A similar reduction in cusp number for pro- number in hominids corresponds to a more
positi was observed in the lower second molar evolved tooth morphology and, similarly, that
TOOTH MORPHOLOGY AND ULI ANOMALIES
481
TABLE 1. Classification of 197 control subjects and 192propositi according to dental criteria
Main
Group
Subgroup
Number
Criteria
Controls
1
197
134
46
17
la
lb
lc
Normal maxillary I2
Complete dentition
Agenesis of one or more M3
Radiographs unavailable to assess M3
Propositi
2
86
2a
2b
34
Size reduction of one or more maxillary I2
Unilateral size reduction of maxillary I2
Bilateral size reduction of maxillary I2
80
31
49
Agenesis of one or both maxillary I2
Unilateral agenesis of maxillary I2
Bilateral agenesis of maxillary I2
26
Agenesis of one and size reduction of the
other maxillary I2
52
3
3a
3b
4
TABLE 2. Morphological characters observed and scoring methods
Teeth
Max.
Man.
Man.
Man.
Character
M1, M2
P2, M1, M2
M1, M2
M1, M2
Scoring method
Cusp number
Count of cusp number
Three categories: Y, + , X'
Four categories: Y5, +5, Y4, +42
Max. M1, M2
Groove pattern
Groove pattern,
cusp number
Carabelli complex
Man. PI
Cusp morphology
1 = no trace
2 = groove, pit, or slight elevation
3 = pronounced cusp
Molariform = well-developed lingual cusp
Caniniform = diminution of lingual cusp
-
' After Jorgensen 11955).
After Hellman 119281.
the order Y, + , X ranges from a more archaic
to a more highly evolved pattern (i.e., the
strongest distal drift of the buccal cusp).
Our results exhibit a significant decrease of
cusp number in propositi with agenesis of
ULI. This decrease affects the lower first
molar most and, to a lesser degree, the lower
second molar and the upper second molar. The
upper first molar is rarely affected, and the
lower second premolar also exhibits no difference between controls and propositi. I t may
be noticed that propositi with reduced ULI
seem more prone to these reductions in cusp
number in the lower first molar and are the
only class exhibiting three cusps in the upper
first molar.
As for groove pattern, a trend from a more
archaic to a more evolved pattern is observed
between controls and propositi. The Hellman
scheme, which combines these two morphological characters, reveals the same trend
towards the more highly evolved pattern in
propositi, especially in M1 and in propositi
class 2.
Similar studies have been carried out by
Keene (1965) and Davies (1968). who compared controls to subjects with agenesis of one
or more third molars. They found a significant
reduction of first and second molar cusp
number in the agenesis group. In this study
we treated controls with one or more missing
third molars as a separate class (class lb), but
except for the second upper molar, we did not
find differences between our third molar
agenesis group (class l b ) and controls with full
dentition (class la). This difference between
Keene's (1965) and Davies' (1968) results and
our own may be explained by several factors.
Keene, in fact, notes that in the class of subjects with M3 agenesis, 7.5% had other congenitally missing teeth, whereas our class of
control l b subjects with M3 agenesis pos-
48
33
75
29
46
22
2b
3
3a
3.b
4
~
54.5
57.6
65.5
52.2
36.4
50.0
44.4
71.1
71.2
68.9
Y5
22.7
29.3
31.0
28.3
33.3
29.2
30.9
19.6
19.7
20.0
+5
18.2
9.3
3.5
13.0
6.1
14.6
11.1
4.1
3.8
4.4
Y4
4.6
4.0
0.0
6.5
24.2
6.2
13.6
5.2
5.3
6.7
62.7
65.5
60.9
68.2
22
36.4
64.6
53.1
73.7
72.7
73.2
Y
75
29
46
33
48
81
194
132
45
+ 4 Number
27.3
32.0
27.6
34.8
57.6
33.3
43.2
24.7
25.8
24.5
+
% Subjects
4.5
5.3
6.9
4.3
6.0
2.1
3.7
1.6
1.5
2.2
X
Jorgensen classification’
________
22
75
29
46
33
51
84
194
132
45
Number
22.7
13.3
3.5
19.6
30.3
19.6
23.8
9.3
9.1
11.1
4
77.3
82.7
86.2
80.4
69.7
78.4
75.0
85.0
86.4
80.0
5
0.0
4.0
10.3
0.0
0.0
2.0
1.2
5.7
4.5
8.9
6
Cusp number’
YO Subjects
4.8
4.9
5.1
4.8
4.1
4.8
4.8
5.1
5.0
5.0
number
Mean
CUSP
= 15.571.
’Cusp number Differences between main f l u u p s 1. 2. 3, and 4 significant a t p < 0.01 If
Ix’
=
11,631: differences between subgroups l a , 2h. and 3b significant a t p
< 0.01 (x’ = 10.59)
‘Groove pattern (Jorgensen 19561. Differences hctween main groups I , 2 . 3 , and 4 significant a t p < 0.01 (s2= 11.62);differences between suhgroups l a , 2h, and 3h significant a t p < 0.001
81
2
194
132
45
Number
~-
2a
Propositi
1
la
lb
Controls
Group
% Subjects
Hellman classification
______
TABLE -3. Analysis of the mandibular first molar shoioing percentages of controls and propositi
according to classification of grooue pattern and cusp number
p
?
100.0
0.0
0.0
0.0
23
4
~
94.9
90.0
98.0
3.8
6.7
2.0
1.3
3.3
0.0
0.0
23
79
30
49
0.0
1.3
0.0
2.0
6.1
5.9
6.0
6.7
6.8
6.5
Y
60.9
51.9
56.7
49.0
45.4
51.0
48.8
69.7
71.2
69.6
i
39.1
46.8
43.3
49.0
48.5
43.1
45.2
23.6
22.0
23.9
X
25
80
31
49
33
52
85
196
133
46
Number
~
Cusp number'
100.0
98.7
96.8
100.0
94.0
98.1
96.5
88.3
89.0
89.1
4
0.0
1.3
3.2
0.0
6.0
1.9
3.5
11.7
11.0
10.9
5
% Subjects
Mean
4.0
4.0
4.0
4.0
4.1
4.0
4.0
4.1
4.1
4.1
cusp number
(x'=
'Groove pattern (Jorgensen 1955).Differences between main groups 1. 2. 3, and 4 significant at p < 0.001 lx2 = 20.38);differences between subgroups l a , Zh, and 3h significant at p < 0.001
16.73).
'Cusp number. Differences between main groups 1. 2.3, and 4 sibmificant at p < 0.001 (x2 = 13.751; differences between subgroups la, 2b. and 3b significant at p < 0.05 (xz= 5.14).
0.0
0.0
79
30
49
3
33
87.8
3a
3b
6.1
6.1
0.0
33
2b
84
51
8.0
195
132
46
Number
70Subjects
Jorgensen classification'
92.0
7.2
2.4
0.0
0.0
90.4
75.4
76.5
73.9
+4
0.0
13.3
12.9
15.2
Y4
50
10.3
9.8
8.7
-
+5
83
1.0
0.8
2.2
Y5
2
195
132
46
Number
2a
Propositi
1
la
lb
Controls
Group
% Subjects
Hellman classification
TABLE 4. Analysis of the mandibular second molar showing percentages of controls and propositi
according to classification of groove pattern and cusp number
P
E
P. LE BOT, A. GUEGUEN, AND D. SALMON
484
TABLE 5. Analysis of the maxillary first molar showing percentages of controls and propositi
according to classification of the Carabelli complex and cusp number
Carabelli complex'
% Subjects
Group
Number
1
Cusp Number
% Subjects
2
3
Number
Mean
4
3
cusp number
Controls
196
134
46
33.2
32.8
37.0
48.5
47.8
50.0
18.3
19.4
13.0
197
134
46
0.0
0.0
2a
2b
85
51
34
36.5
29.4
47.1
55.3
62.8
44.1
8.2
7.8
8.8
3
3a
3b
4
78
30
48
26
41.0
43.3
39.6
38.4
46.2
40.0
50.0
30.8
1
la
lb
0.0
100.0
100.0
100.0
4.0
4.0
4.0
86
52
34
2.3
1.9
2.9
97.7
98.1
97.1
4.0
4.0
4.0
12.8
16.7
10.4
79
31
48
0.0
0.0
0.0
100.0
100.0
100.0
4.0
4.0
4.0
30.8
26
0.0
100.0
4.0
Propositi
2
'Carabelli complex. Differences between main groups 1, 2 . 3 , and 4 non-significant (x' = 11.63): difterences between subgroups l a . 2h. and 3h
nonsignificant If = 4.841.
TABLE 6. Analysis of the maxillary second molar showing percentages of controls and propositi
according to classification of the Carabelli complex and cusp number
-
Carabelli complex'
% Subjects
Group
Number
1
Cusp Number'
% Subjects
2
3
Number
3
Mean
4
CUSD
number
Controls
197
134
46
32.5
31.3
41.3
67.5
68.7
58.7
3.7
3.7
3.6
0.0
86
52
34
41.9
36.5
50.0
58.1
63.5
50.0
3.6
3.6
3.5
7.7
6.7
8.3
1.3
0.0
2.1
79
31
48
43.0
35.5
47.9
57.0
64.5
52.1
3.6
3.7
3.5
20.0
0.0
25
40.0
60.0
3.6
la
lb
197
134
46
88.3
91.0
87.0
11.7
9.0
13.0
0.0
0.0
Propositi
2
2a
2b
85
51
34
87.1
82.4
94.1
12.9
17.6
5.9
0.0
0.0
3
3a
3b
78
30
48
91.0
93.3
89.6
4
25
80.0
1
0.0
'Carabelli complex. Differences hetween main groups 1. 2. :i. and 4 non-significant I\' = 2.291: differences hrtween subgroups l a , 2h. and 3h
nonmgnificant ( \ * = 0.521.
'Cusp number. Differences between suhgroups 1. 2. :iand
. 4 non significant 11' = 3.911: differences hetwpen YuhLToupn la. 2h. and 3h signifi< o.ns I \ ' = 6.601
cant
sessed all their other teeth. Moreover, Keene
(1965) considered separately subjects whose
M3 agenesis was located in the maxilla and
those whose M3 agenesis occurred in the mandible. Onthe other hand, Davies (19681,who set
M3 agenesis apart from agenesis of other teeth,
obtained results more consistent with ours. In
the first lower molar he found 25.3%of subjects
missing the fifth cusp (hypoconulid)in the class
with agenesis of one or more teeth other than
third molars, versus 8% in the class of subjects
possessing the full dental complement.We find
19.6%of these subjects missing the fifth cusp in
class 3b propositi versus 9.1% in full dentition
controls.
Because of the assignment of his propositi,
485
TOOTH MORPHOLOGY AND ULI ANOMALIES
T A B L E 7. Analysis of the mandibular premolars showing percentages of controls and propositi
according to classification of morphology and cusp number
First premolar-morphology'
_____
Group
Number
B Subjects
Caniniform
Molariform
Second premolar-cusp number'
% Subjects
Mean
Number
2
3
cusp number
Controls
1
196
133
46
13.8
I 0.5
13.0
86.2
89.5
87.0
194
132
45
54.6
54.5
55.6
45.4
45.5
44.4
2.5
2.5
2.4
2
2a
2b
85
51
34
38.8
33.3
47.1
61.2
66.7
52.9
83
49
34
48.2
49.11
47.1
51.8
51.0
52.9
2.5
2.5
2.5
3
3a
3b
80
31
49
37.5
22.6
46.9
62.5
77.4
53.1
78
31
47
57.7
58.1
57.5
42.3
41.9
42.5
2.4
2.4
2.4
4
23
26.1
71.9
23
47.8
52.2
2.5
la
lb
Propositi
____.
'Man. PI morphology. Differences between main groups 1. 2. 3, and 4 significant a t p < 0.001 (x2 = 28.511: ditferences
between subgroups l a . Zb, and 3b significant a t p < 0.001 lx* = 36.691.
'Man P2 cusp number. Differences between main groups I. 2, 3. and 4 non-significant lx2 = 1.891; differences between
subgroups l a , 2b. and 3b non-significant (x' = 0.90).
Keene (1965) found significant differences between his classes of subjects with regard to
Carabelli's trait, whereas we did not find any
difference in our l b controls. In subjects with
the same agenesis of M3, Garn et al. (1966)
could not find any marked difference with
respect to his controls and suggested that further exploration in cases of hypodontia be
u n d e r t a k e n . Conversely, our r e s u l t s
demonstrate that a relationship exists between ULI congenital defects and Carabelli's
trait. Carabelli's trait is less marked in propositi 2b (2 ULI reduced) than in controls with
full dentition.
These results lead to the following conclusion: Congenital defects of ULI are associated
with morphological changes in other parts of
the dentition, and the effects appear to be
greater than those observed in cases of third
molar agenesis.
I t is of some interest to note the marked
morphological defect of the first lower
premolar in ULI propositi, whereas the second
lower premolar remains more stable. In our
preceding study (Le Bot and Salmon, 1977)we
have already observed that the first upper
premolar was more variable in size than the
second. These facts are in agreement with
Butler's model (1939),which associates molars
and premolars in a single morphogenetic field
in mammals. According to this hypothesis,
the first molar is the most stable tooth, the
key-tooth, neighbouring teeth becoming more
variable the farther away they are from this
key-tooth. However, the high frequency of
second lower premolar agenesis in hominids is
not explained by this theory. In contrast,
Dahlberg (1945) distinguishes between the
molar field and the premolar field in man, considering the fact that in both fields the most
distal tooth is the least stable. Our results
disagree with this hypothesis.
Another striking fact in our results is that
ULI reduction is associated with modifications of size and morphology that are more
pronounced than the corresponding modifications observed in ULI agenesis. We can explain this difference with the hypothesis of
Sofaer et al. (1971). According to this, the
agenesis of a tooth may give an increased
growth potential to other teeth belonging to
the same morphogenetic field. A compensatory effect may occur. This hypothesis tallies
well with the otherwise paradoxical fact
observed by ourselves and others: M 1
measurements are greater in subjects with M3
agenesis than in controls (Garn and Lewis
1970, Hanihara 1970).
In the present study and in our previous one
(Le Bot and Salmon, 1977),we observed an increasing alteration of dentition in the following order: controls with full dentition, controls
486
P. LE BOT, A. GUEGUEN, AND D. SALMON
with one or more missing third molars, propositi with one ULI missing, propositi with
two ULI missing, propositi with one ULI
reduced, propositi with two ULI reduced, This
was observed on most mesiodistal and buccolingual diameters and also on morphological
characters. This trend is statistically significant.
CONCLUSIONS
We propose the following model for the morphological simplification of man’s dentition
observed in our propositi sample. This
modification may be described in the following
sequence: Initially, a change in developmental
timing resulting in delayed tooth eruption
may lead to progressive simplification of dental morphology.
The second step, in the lower molars, is a
modification of the groove pattern tending
from Y through
to X. Concomitantly, the
cusp number decreases. By associating the
two characters, we may observe successively
Y5 + 5 , Y4 + 4 . This phenomenon may be
described as a distal drift of buccal cusps with
groove reorganisation. The distal drift leads to
hypoconulid reduction and secondly to
hypoconulid loss. I t is associated with a
mesial drift of lingual cusps, and then the
groove pattern modification is accelerated.
In the maxilla, we will observe the reduction
and, later on, the disappearance of the hypocone. A reduction then appears and accompanies this second step. I t is a differential
reduction of mesiodistal and buccolingual
diameters, the latter being the more affected.
Some teeth will be more affected, following a
gradient that we have previously described. A
stronger constraint will determine dwarfism
firstly of the third molar and secondly of the
ULI. The bilateral reduction of this latter
tooth marks the end of the reduction of dentition.
The next step will be the disappearance of
some teeth, according to the following order:
third molar, second lower premolar, ULI. But
the paradox is that this last step will be
associated with quantitative and qualitative
modifications less marked than in the
preceding step. We previously mentioned that
+
Sofaer et al.’s (1971) hypothesis may explain
this phenomenon. So the trend will continue
from presence to reduction and, later on, the
loss of some teeth (particularly third molars
and the upper lateral incisor), even if certain
crown components do not follow this progression.
This evolutionary scheme attempts to explain the different studies on agenesis. Further investigations will be necessary to settle
some points, in particular with respect to
eruption timing. However, Firschs (1965)conclusions concerning phylogenesis seem to corroborate our hypotheses.
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