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Congenital defects of the upper lateral incisors (ULI) Condition and measurements of the other teeth measurements of the superior arch head and face.

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Congenital Defects of the Upper Lateral Incisors (ULI):
Condition and Measurements of the Other Teeth,
Measurements of the Superior
Arch, Head and Face
PIERRE L E BOT AND DENISE SALMON 2
Lnboratozre d’dnthropoloqze Bzologzque (Frofesseur Oliuier) Uniuersite
Parzs VII - 2 , Place Jusszeu 75005 Paris, France and 2 Group de
Recherche U88,Inserm, Mbthodologze lnformatzque e t
Statzshyue e n Mbdectne (Professeur F Greniy) 9 1 , bd
de I’HBpilnl, 75634 Parts Cvdrx 13, France
’
KEYWORDS
defects
Tooth agenesis . Upper lateral incisors . Congenital
ABSTRACT
We surveyed a French male population for the incidence of
missing or reduced upper lateral incisors (ULI). In 5,738 subjects, we observed
a n incidence of 1.59% with one or two reduced ULI (the other normal) and
1.90% with one or two missing ULI (the other normal or reduced), altogether,
3.49 % affected subjects. Furthermore, 250 random controls were observed.
Agenesis of other teeth is more frequent in propositi. Missing third molars were
12.4% in controls, 24.0% i n propositi with reduced ULI and 39.6% i n propositi
with two missing ULI. Furthermore, agenesis of incisors, canines and premolars
ranges from 0.4 % in controls to 1.3% i n propositi having reduced ULI and 5.0 %
in propositi with two missing ULI. So, propositi with reduced ULI are intermediate between the controls and the propositi with missing ULI with respect to
the frequency of agenesis of other teeth.
On the other hand, a different ranking is observed with respect to the teeth
measurements: reduction of tooth size is more marked in propositi with reduced
ULI than in propositi with missing ULI. The reduction mainly affects canines,
incisors and to a lesser degree, premolars. Arch length and interpremolar diameters are smaller in propositi with missing ULI, compared with controls.
acteristics: conoid (peg-shaped) ULI; ULI
reducing in diameter from the cervix to
the incisal edge; ULI with marked asymmetry in volume between the right and
left sides.
The control group consisted of normal
subjects examined after each propositus.
MATERIAL AND METHODS
Thus, 200 diagnosed propositi and 250
The subjects surveyed were 5,738 males, random controls were observed, and all
born in Paris, age 18 to 25, examined a t teeth of both groups examined by three
the Selective Service Center at Vincennes. types of X-rays: simple intra-alveolar films
This provided a large random sample with to check for the premolars or molars pregood dental health and permanent denti- sumed absent (most commonly, third motion and likely to remember any extraction. lars); occlusal films using the modified
Those with absent or reduced ULI consti- Simpson method, for all the cases where
tuted the experimental group. Congenital the incisors or the canines were missing;
absence was verified from past dental his- Panoramic films, using the Panorex proctory and from X-rays. Reduction was de- ess for cases of presumed multiple agenefined by one or more of the following char- sis. These films made it possible to have
Congenital absence of Upper Lateral Incisor teeth (ULI) has been associated with
other defects. We surveyed a French population for the incidence of missing or reduced ULI and compared their dentition
with controls.
AM. J. PnYs. ANTHROP.,46: 237-244.
231
232
PIERRE LE BOT AND DENISE SALMON
both complete arches on the same film,
obviously the ideal technique for this type
of study.
Each tooth was coded as following: 1 =
normal, erupted; 2 = reduced, erupted;
3 = congenitally absent; 4 = normal, not
erupted; 5 = normal impacted; 6 = reduced not erupted, not impacted (fig. 1).
Measurements
Dental impressions of the two arches for
all subjects were taken in alginate and
cast in plaster. Dental measurements of
maxillary teeth were carried out on the
casts, using the method elaborated by
Morrees et al. (‘57). Given the unavoidable
e
Fig. 1
Various possible combinations in congenital defects of ULI.
Code 1 - 2
A - Right normal, left reduced
Code 2 - 1
B - Right reduced, left normal
Code 2 - 2
C - Right reduced, left reduced
Code 1 - 3
D - Right normal, left missing
Code 3 - 1
E - Right missing, left normal
Code 2 - 3
F - Right reduced, left missing
Code 3 - 2
G - Right missing, left reduced
Code 3 - 3
H - Right missing, left missing
CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS
TABLE 1
Upper lateral incisos (ULI) defects, by type
in 5,738 subjects
ULI dfects
Code
Right
ULI
Left
90 in
POPU-
R
L
No.
lation
1
2
2
Reduced
2 Normal
Normal
1 Reduced
2 Reduced
Reduced
1 or 2 reduced ULI
(the other normal)
28
37
0.49
0.45
0.64
91
1.59
Missing
3 Normal
Normal
1 Missing
Missing
3 Reduced
Reduced
2 Missing
Missing
3 Missing
1 or 2 missing ULI
(the other normal
or reduced)
16
14
18
12
49
0.28
109
1.90
200
3.49
1
3
2
3
3
All propositi
ULI
26
0.24
0.31
0.21
0.85
R, right; L, left; 1, normal, erupted tooth; 2, reduced,
erupted tooth; 3, missing tooth: No., number of observed
propositi.
233
molars have been excluded from these comparisons because of the inherent uncertainty regarding the cause of absence.
After regrouping the eight categories of
propositi, we obtained three large classes
and six subclasses:
Class 1: Controls having both ULI normal (class l a : controls with four third molars present; class l b : controls lacking at
least one third molar).
Class 2: Propositi having one (class 2a)
or both (class 2b) ULI reduced.
Class 3: Propositi lacking one (class 3a)
or both (class 3b) ULI; in the former case,
the other ULI may be either normal or
reduced.
Only in the case of the third molars
(tables 2, 3) did the data fall into the predicted states, i.e. code 1 to 6.
For the other teeth (table 4), only their
presence or absence was taken into consideration.
1. Relationship between agenesis of the
ULI and agenesis of the
inaccuracy of dental measurements the
third molars
use of very precise measuring instruments
is pointless. A specially adapted sliding
The grouped results (table 3) show that,
caliper with ground tips accurate to 0.01 for the controls, 12.4% of the third molars
mm was used in this study.
were lacking, while for the propositi having
We also measured the following: trans- absence of both ULI (class 3b), 39.6% of
verse diameters of the upper arch between the third molars were absent. This differthe first premolars (grooves), between the ence is highly significant (X2 = 87.8, 3
first molars (grooves), and between the d.f.,p < 0.001).
second molars (buccal surface); length:
A more detailed analysis (table 2) shows
between the distal surface of the second that the position of the affected ULI (left
molars and the central incisors; head: or right), has no influence whatsoever on
maximum length (glabella opisthocranion), the third molar. This is important because
maximum width; face: height (gnathion- it shows that the malformation is not spenasion) and bizygomatic width.
cific to a particular side. Symmetry is thus
almost perfect between the two sides of the
RESULTS
arch. Third molars are absent more freThe condition of ULI in the 200 propositi quently in the lower arch than in the upis shown in table 1. Thus 109 (or 1.90% of per for all classes of subjects (table 3).
the population) had one or both ULI missThe situation “tooth not erupted and
ing and the other normal or reduced, while impacted” (code 5, i.e., that it is mechanthe remaining 91 (or 1.59% of the popula- ically impossible for the third molar to astion) had one or both ULI reduced and the sume its normal position in the arch) is
other normal. No impacted ULI were found. almost always observed in the mandible,
We found no difference between the left these teeth being most often impacted in
and the right sides; the slightly higher a horizontal position. We note (table 2)
incidence of the malformation on the left that this anomaly is equally frequent in
side is not statistically significant.
class 1 (controls, 5.2% of examined teeth)
class 2 (4.4%) and class 3 (4.5%).
I. The frequency of congenital defects of
In the same way, the case “impacted
other teeth in propositi and controls
tooth capable of normal evolution” (code
The first and second upper and lower 4, table 2) has nearly the same frequency
L
ULI
2
1
2
3
1
3
2
3
6
6
1 4
2
5
7
2
10
98
52
L
3
7
1 4
4
4
7
3
16
98
58
Up
7
8
1 0
5
7
6
4
12
1
1
0
2
0
0
1
2
1
7
113 103
51 59
4
7
1 0
5
5
7
2
11
R
Up
L
Lo
R
Lo
L
1
0
0
2
0
2
0
1
3
6
Up
(2 )
0
0
0
0
0
0
0
0
9
5
4
0
2
3
2
0 18
0
0
0
0
0
0
0
5
4
4
0
4
2
4
18
31
41
0 29
0 43
1
0
R
L
Up
L
LoUp
6
6
4
4
9 1 1
1
0
3
3
3
5
6
5
19 21
29
55
35
51
L
Lo
Lo
R
Congenitally
absent
(3)
La
R
Reduced
erupted
R
L
Up
R
Lo
8
8
11
7
6
5
7
17
4
6
4
5
12
15
9
11
1
5
9
4
4
3
3
1
117 116 77
69 66 52
Up
(4)
L
3
6
8
5
2
3
3
87
47
Lo
1
non-erupted
Normal
R ULI, right ULI; L ULI, left ULI; R Up, right upper; L Up, left upper; R Lo, right lower; L Lo, left lower.
ULI
1
2
2
1
3
2
3
3
R
Controls
Propositi
R
Up
erupted
(1)
Normal
Third molor status
TABLE 2
9
1
R
0
0
0
0
0
0
2
0
Up
0
0
0
0
0
0
1
0
0
1
0
Up
L
0
4
2
1
2
2
1
0
2
2
1
1
2
1
0
5
28
12
21
19
L
Lo
Lo
R
impacted
(5)
Normal
2
R
3
0
1
0
1
0
0
3
3
0
Up
1
0
0
0
0
0
0
0
1
0
0
1
1
0
0
0
1
1
3
3
R
Lo
1
L
Up
Reduced
not erupted
not impacted
(6)
0
0
0
0
0
0
0
1
3
1
L
Lo
Total
15
12
48
14
24
20
30
11
250
174
subject
W
0
+I
235
CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS
TABLE 3
Distribution of missing third molars
Missing third molars
Total of
examined
subjects
Total of
examined
third
molars
R Up
L Up
R Lo
LLO
9%
250
1,000
29
31
29
35
12.4
74
296
18
13
21
19
24.0
52
208
7
10
13
13
20.7
48
192
18
18
21
19
39.6
~
~~~~
Number
~
Controls
class 1
Propositi with 1 or
2 reduced ULI
class 2
Propositi with 1
missing ULI
class 3a
F'ropositi with 2
missing ULI
class 3b
R ULI, right ULI; L ULI, left ULI; R Up, right upper; L Up, left upper; R Lo, right lower; L Lo, left
lower.
in the three classes: class 1 , 40.8% of examined teeth; class 2, 38.2% and class 3,
32.25 % .
2 . Relationship between agenesis of ULI
and agenesis of the incisors,
canines and premolars
In table 4, we regrouped the findings
for absence of all these teeth, except the
ULI and molars.
The differences in frequency of agenesis
of these teeth between the classes of subjects appear to be even more striking than
for the third molars, since agenesis varies
from 0.4% for controls (class 1) to 5 % for
propositi, with two teeth absent (class 3b).
Nevertheless, the increase could be due
to the presence of a few cases having multiple agenesis. Thus, in effect, subjects
have substantial multiple agenesis, among
them an individual who lacked 14 teeth,
These individuals always lacked the ULI;
they were all propositi. On the other hand,
if we only take into consideration the iiumber of affected subjects, the differences
between the groups remain highly significant ( 4 % , class 1 and 26.5%, class 3b).
There is thus both a qualitative and quantitative effect.
As a result of these findings, we can
thus rank teeth according to the frequency
of agenesis. In 250 controls, we observed
12.8% oflower third molars absent, 12.0%
of upper third molars absent, 2.0% of lower second premolars absent. In 5,738 subjects sampled, we noted 1.6% with ULI
missing. In the 250 controls, we found less
than 1% with other teeth absent in decreasing order (lower central incisors, upper second premolars, upper canine, lower
lateral incisor, upper first premolar, lower
canine and lower first premolar).
11. Measurements of other teeth, head
and face in propositi and controls
Reduction of most of the dental measurements is in the following order: controls
l a , controls l b , propositi of classes 3a, 3b,
2a and 2b (tables 5, 6).
The reduction studied tooth by tooth is
not always significantly different. Nevertheless, the sum of the buccolingual diameters ( S B.L. diameters) of the teeth in the
upper arch is significantly smaller (p <
0.01) in the propositi. This is also true for
the sum of the mesiodistal diameters
(2 M.D. diameters).
These results confirm that reduction affects all the teeth.
The question to be raised now is the following: does this reduction affect all the
measurements? Is the entire dentition
smaller but in the same proportion, or are
the relative values of each tooth modified?
A. Mesiodistal diameters
Figure 2, where the measurements are
given in absolute values, immediately provides an answer to our question. It is evident that all of the teeth are not equally
affected, neither in absolute values, nor
still less, in proportion.
We found no statistically significant difference between the measurements of the
1,376
896
784
56
49
4,000
Number of
examined
teeth
86
250
Number of
examined
subjects
3
1
0
0
3
5
0
0
R
Lo
1
1
2
Lo
Lo
0
L
R
No missing upper central incisor was observed.
2 reduced
ULI
class 2
Prop0 siti
with 1
missing
ULI
class 3a
Propositi
with 2
missing
ULI
class 3b
Controls
class 1
Propositi
with 1 or
Classes
2
2
4
0
0
0
2
3
0
L
Up
1
0
0
0
R
Lo
Missing
canine
0
0
Up
Lo
0
R
L
Missing
Missing
central
lateral
incisor
incisor
0
1
0
0
Lo
I,
0
1
1
1
Up
R
0
~
1
1
1
L
Up
0
0
1
0
Lo
R
Missing
first
premolar
Number of missing teeth (excluding molars)
TABLE 4
0
0
1
0
2
4
0
0
R
Up
L
Lo
1
3
4
3
5
4
R
Lo
1
1
L
Up
4
Missing
second
premolar
L
5
3
6
Lo
1
13
10
1
10
Number
4
%
1.4
5.0
26.5
1.3
0.4
5%
Missing
teeth
17.9
12.8
Affected
subjects
z
z
0
vl
M
vl
+9
2
M
tr
3
>
W
0
ri
m
r
m
zM
CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS
237
11
10
I
I
I
I
1
9
I
i
F
F
A
I
I
I
I
I
7
I
I
I
I
I
6
I
Lentrill
Zncisor
1
I
I
I
\:
!
P>
I
I
I
I
I
i
I
Canine
'\
?--
I
I
I
I
1
2
I
I
A.
J
I
I
1
First
rrenciar
Fig. 2
I
I
Iecond
PPemolar
I
I
I
I
L
I
I
irst
Mrllar
Second
molar
Mesiodistal diameters of the upper maxilla.
left and right side or a trend in this differ- controls 1 a, controls 1b, propositi of classes
ence. This thus allows us to restrict our 3a, 2a, 3b and 2b. Analysis of variance beattention to the teeth situated on the right tween the three classes: controls, propositi
side of the maxilla.
2 and propositi 3 showed that the reduction
If we classify these teeth in decreasing gradient is, in decreasing order: PI, P2, MI,
order of the absolute difference in tooth M2, both in absolute values, and also prosize between the three classes of controls portionally. So,premolars are clearly more
and propositi, we obtain: C, Pl, I], M2, P2, reduced (F = 27 and 22 for 2 and 389 df,
MI.
p < 0.001) than are molars (F = 7.5 and
Nevertheless, this difference is not sig- 3.3 for 2 and 385 df, p < 0.01 and p <
nificant for M1 (F = 1.26, 2 and 362 df) 0.05). Furthermore, we note that the bucand the significant differences observed colingual diameters are proportionally more
between the three classes for the five others reduced than the mesiodistal ones.
We also note that M1 is more reduced
MD diameters may be ranked in the following decreasing order: C, P1, P2, 11, M2 (F than M2 in contrast with our findings for
from 28 to 7.2, 2 and 383 to 411 df) point- the mesiodistal diameters.
It appears further that in the domain
ing out that the ordering of the proportional reductions of these diameters is dif- of dental measurements the propositi of
ferent from the ordering of absolute dif- class 2 (i.e., those having a reduction of
ferences. So there is a strong constraint the ULI) have a more extreme phenotype
with respect to canines, incisors and pre- than the propositi of class 3 (i,e., those
molars; the molars, on the other hand, are having an absence of the ULI). In contrast
to the results involving agenesis of the
less affected.
other teeth, class 2 does not represent an
B. Buccolingual diameters
intermediary between the controls and the
As for the mesiodistal diameters, we propositi that carry the phenotype for abfound a reduction in size, but in a slightly sence. In particular, we observe that the
different ranking, i.e. by decreasing order: teeth most often affected by reduction are
N
81.63
(6.28)
22
84.44
(6.33)
81
85.02
(6.58)
35
85.80
(6.41)
109
87.66
(5.85)
30
87.95
(5.57)
135
74.95
(4.79)
22
76.96
(4.57)
78
76.97
(4.90)
35
77.74
(5.33)
110
80.76
(4.65)
30
81.45
(4.48)
139
MD
MD
65.00
(4.81)
22
67.58
(4.96)
79
67.00
(4.65)
35
68.50
(4.97)
102
71.27
(4.68)
29
72.07
(4.61)
132
MD
P'
82.31
(5.13)
22
86.83
(6.28)
81
85.60
(7.13)
35
87.43
(7.11)
106
89.72
(6.79)
29
92.60
(6.07)
133
BL
Each cell gives, from first to third lines, the average
teeth (N).
Propositi
class 2b
Propositi
class 2a
Propositi
class 3b
Propositi
class 3a
Controls
Ib
Controlsla
X
S.D.
C
I'
86.81
(5.32)
22
88.81
(6.20)
77
88.40
(7.28)
35
90.52
(7.23)
101
92.28
(7.75)
28
94.63
(6.10)
128
BL
103.90
(6.39)
22
104.59
(5.92)
72
105.57
(6.78)
35
104.87
(6.65)
95
106.07
(6.13)
28
105.93
(5.97)
113
MD
MI
111.27
(5.40)
22
113.05
(5.91)
75
112.65
(7.23)
35
113.23
(7.42)
99
114.10
(6.43)
28
116.18
(6.32)
122
BL
95.77
(6.36)
22
96.67
(5.74)
76
97.48
(6.62)
35
98.24
(7.40)
98
100.73
(6.54)
30
100.28
(6.81)
132
MD
M2
112.18
(6.86)
22
113.75
(7.44)
74
113.48
(8.86)
35
114.64
(9.17)
102
113.48
(7.14)
29
116.68
(8.44)
131
BL
969.63
(48.92)
22
991.32
(48.30)
61
994.05
(52.26)
35
1,001.12
(53.55)
75
1,035.50
(47.47)
24
1.026.49
(43.84)
100
ZMD
785.54
(40.54)
22
803.78
(44.95)
61
800.05
(50.75)
35
810.58
(52.52)
75
824.26
(51.10)
23
838.26
(42.99)
100
ZBL
(within 0.1 mm), the standard deviation (S.D.) (within 0 . 1 mm), and the number of examined
63.04
(4.44)
22
65.30
(4.89)
73
65.08
(4.13)
35
66.47
(4.90)
100
68.41
(5.32)
29
68.66
(4.96)
127
MD
P2
Dental measurements
TABLE S
CONGENITAL DEFECTS OF ULI: OTHER
239
TEETH OBSERVATIONS
TABLE 6
Arch head arid fnce m e a s u r e m e n t s
Upper arch
He ad
~
Controls
ff
la
S.D.
N
Face
First
width
Second
width
Third
width
Length
Length
Width
Length
Width
364.34
(24.13)
135
481.76
(29.89)
105
626.07
(31.28)
130
474.16
(25.76)
130
195.71
(7.13)
100
155.72
(5.57)
100
139.99
(4.78)
100
121.32
(7.08)
100
363.41
(22.30)
29
481.07
(32.67)
28
622.10
(25.05)
30
473.26
(27.20)
30
191.67
(6.83)
31
153.74
(5.84)
31
138.58
(4.73)
31
119.67
(5.99)
31
351.37
(28.67)
110
472.30
(31.03)
104
617.23
(34.99)
110
453.54
(28.13)
108
93.82
(6.82)
75
155.05
(5.81)
75
138.72
(4.74)
75
119.72
(5.88)
75
344.14
(30.25)
35
471.14
610.54
(29.48)
449.05
(26.44)
94.48
(7.42)
35
154.62
(5.66)
35
139.22
(4.86)
35
120.57
(6.14)
35
365.35
(23.57)
81
485.93
(28.02)
72
620.89
(33.37)
79
483.12
(28.44)
81
194.37
(5.90)
61
155.21
(5.02)
61
139.72
(4.11)
61
119.19
(4.80)
61
365.86
(24.68)
22
486.38
(28.13)
21
625.04
(22.87)
22
455.77
(33.40)
22
194.22
(4.65)
22
154.54
(4.55)
22
140.50
(2.80)
22
118.50
(4.86)
22
~
Controls
lb
Propositi
class 3a
Propositi
class 3b
(30.38)
35
35
35
Propositi
class 2a
h p o sit i
class 2b
Each cell gives from first to third lines, the average ( g ) (within 0.1 mm for arch measurements, within mm for
head and face measurements) the standard deviation (S.D.)
(same remarks) and the number of examined subjects (N)
not the same as those affected by agenesis.
The average measurements of each subgroup of subjects (tables 5 , 6; fig. 2) show
the following results: the dental measurements of the controls of class 1b fall between those of the controls of class l a and
those of the propositi except for the first
and second molars, the measurements of
which are slightly greater for the controls
l b than for the controls la. On the other
hand, propositi class 3b have clearly smaller tooth measurements than propositi class
3a. Similarly, propositi of class 2b have
smaller teeth than propositi of class 2a.
Moreover, their measurements are far inferior to those of the other classes, so that
they have the smallest teeth in the sample.
We find at the level of these subgroups
the same process as in principal classes,
and with the same hierarchy. Thus, clearly, the phenomenon “agenesis” is distinct
from the phenomenon “reduction”.
C . Measurements of arch head and face
As for the dimensions of the arches, the
comparison of each group of propositi with
the controls gives the following results:
the differences between propositi and controls, with respect to the average length of
the arch, are all highly significant; the
differences between controls and propositi
class 3 (with ULI absent) are always significant, in decreasing order from the first
to the third diameters; the differences between controls and propositi class 2 (with
reduction of the ULI) are not significant
with respect to the transverse diameters.
Analysis of variance between the three
groups confirms these results: p < 0.001
for the arch length and bipremolar diameter, p < 0.05 for the inter first molar
diameter, no significant difference for the
inter second molar diameter.
As for the head and face measurements,
the differences are far less clear; average
measurements in the propositi are smaller
than those of the controls particularly for
facial height, and to a lesser degree for
head length. Analysis of variance between
the three groups did not show any significant difference. We should note, however,
240
PIERRE LE BOT AND DENISE SALMON
TABLE 7
Percentage of agenesis and reduction of upper lateral incisors from the Literature
Authors
Rose, '06
Rose, '06
Rose, '06
HrdliEka, '21
HrdliEka, '21
Campbell, '34
Dolder, '36
Montagu, '40
Brekhus et al..'44
Rantenen, '53
Grahnen, '56
Grahnen, '56
Clayton, '56
Brown, '57
Meskin and
Gorlin, '63
Davies, '67
Number of subjects examined
10,238 European males
8,618 European females
12,250 European militaries
500 White male Americans
500 White female Americans
2,000 Americans of both sexes
10,000 Swiss of both sexes
528 American males
11,487 Americans of both sexes
2,200 Finnish students
531 Scandinavian males
Group A
475 Scandinavian females
547 Scandinavian males
Group
475 Scandinavian females
3,557 Americans of both sexes
5,276 Americans of both sexes
5,165 American male students
3,124 American female students
1,220 Australian males
950 Australian females
}
}
(non-aborigene)
Le Bot, present study
Percent of
agenesis
Percent of
reduction
1.1
1.9
1.7
1.4
3.0
1.75
0.54
2.6
0.96
1.0
1.5
2.3
1.8
3.4
2.8
1.0
0.87
2.5
0.52
1.0
1.6
1.7
1.7
1.3
2.6
0.94
0.76
1.28
1.55
0.83
0.96
1.0
2.1
1.3
1.91
1.58
5,738 Parisian recruited males
(non-selected)
14-years-old, the minimum age for proper
study of third molars. Aside from the fact
that their sample was composed of orthoDISCUSSION
dontic patients, which could have biased
Of several studies relating to congenital the results, their methods are comparable
dental abnormalities, that most similar to to ours.
They found, as we do, that agenesis of
ours is that of Meskin and Gorlin ('63),
carried out at the University of Minnesota third molars is more frequent in the manat Minneapolis. Their study included both dible than in the maxilla. They also obmale and female students but we restrict served symmetry between the left and the
the comparison between their study and right side. On the other hand, these auour exclusively male sample. The differ- thors noted that the propositi with no third
ences are marked in all of the categories. molar had, with respect to the other teeth,
On the other hand, Rose's ('06) percent- 13 times more agenesis than did the conages (table 7) for Europeans are very close trols who had third molars. In our study
to ours.
the propositi with absent or reduced ULI
Until this type of study is normalized, had, with respect to the other teeth (not
comparisons are not valid. Nevertheless, including the third molar), 32 times more
Meskin and Gorlin appear to have followed agenesis than the controls with normal
the same protocol as ours and we are of ULI.
the opinion that the divergence in the reMoreover, the controls observed by Garn
sults are worthy of note, although not ex- ('62) had agenesis that usually involved
plicable at this time.
the ULI and the second premolars. SimilarIt is also very interesting to compare our ly in our study the controls most often preresults with those of a similar study car- sented agenesis of the third lower molars
ried out by Garn et d. ('62) on the third and second lower premolars. But, with remolar. They compared a group of 100 sub- spect to the date of eruption of the teeth,
jects that lacked at least one third molar our findings were not consistent with Garn's
with a group of 398 controls that had all conclusions. He observed indeed, a delay
third molars present as verified by X-rays. in the dental development of the subjects
The subjects were young, but were at least having third molar agenesis, a maximum
that variability is clearly smaller for the
propositi affected with reduction.
24 1
CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS
TABLE 8
Other teeth modifications in propositi w i t h absent ULI and propositi with reduced ULI
(3) Propositi
with absent
ULI
(2) Propositi
with reduced
ULI
Proportional reduction
of the sum of mesiodistal diameters of
propositi relative to
controls’ diameters
Proportional reduction
of the sum of buccolingual diameters of
propositi relative to
controls’ diameters
Percentage of
agenesia of
third molars
2.4%
3.3%
30 %
3%
3.4%
4.1%
24 %
1.3%
delay for the posterior teeth particularly
with respect to the last of the series. According to these data, we should have seen
a large number of affected third molars.
But such was not the case in our study
where the average age of the subjects was
19; there is a striking similarity in the
eruption dates of the third molars in the
propositi and in the controls.
Moreover, Bailit et al. (‘68) in a study
on the relationship between hypodontia and
the age of dental eruption also showed no
relationship between the two phenomena.
Our goal was to study the ULI and to
compare our propositi with the controls.
However, combinations of agenesis in the
controls are of a general nature.
In agenesis in decreasing order of fi-equency, other workers found some different results. All of them found the third
molars in first place as we did. Second
place is occupied by ULI for Brekhus et al.
(‘44), Cohen and Anderson (‘31), Goldman
(‘62), Mosmann (‘63), Poulton and Pruzanski (‘58), Rosenweig and Garbarski (‘65),
and by the second lower premolars for
Grahhen (‘56), Sabres and Bartholdi (‘62),
Volk (‘631, Gysel (‘57), Monteil (‘68) and
the present work.
Our results show, as do those of Garn,
that the third molars, the ULI and the second lower premolars can be absent independently of one another. On the other
hand, the absence of at least one of these
three teeth appears to be necessary for
agenesis affecting the rest of the dentition.
Thus, according to our data, agenesis
of a particular tooth is not an isolated phenomenon. The dentition as a whole is affected by a process that has a tendency to
reduce the number of elements and acts
selectively on the most vulnerable points
of the dentition. The reduction of a tooth
Percentage of
ageneda of
11 C PI p2
thus appears to be intermediate between
presence and absence. On the other hand,
comparisons of dental measurements show
that for each group of propositi these measurements were reduced compared with
all controls. The results do not conform to
the classic notion that the most distal of
each type of tooth is the least stable. In
fact, P1is clearly more reduced than P2.
Thus, where ULI are involved, we found
a new dental profile characterized by a
differential reduction in all of the dental
measurements, greatest by far, with the
premolars and canines. In the premolars
and molars, to this reduction in size is
added a modification in shape in the direction of a greater proportional reduction in
the buccolingual diameters.
The classes of subjects fall into the following order in diameters of the other
teeth: controls class la, controls class l b ,
propositi class 3 (with absence of the ULI)
and propositi class 2 (with reduction of the
ULI). Indeed, propositi class 2 are intermediate between the controls and propositi
class 3 in the frequency of agenesis of the
other teeth. But dental measurements of
the propositi class 2 have a phenotype more
extreme than the propositi class 3.
The classic hypothesis that the reduction
of a tooth is an intermediate phenomenon
between its presence or its absence is thus
subject to question. These observations can
be summarized as follows: agenesis of the
ULI is associated with agenesis of other
teeth and with a reduction in their measurements. On the other hand, reduction
of the ULI is associated above all with a
reduction in the measurements of all of
the other teeth and even an absence of certain of these. Table 8 summarizes this situation by giving for each group of propositi
the characteristics of agenesis of the other
242
PIERRE LE BOT AND DENISE SALMON
teeth as well as the reduction on the sum
of the mesiodistal and buccolingual diameters of the other teeth. It is as though
missing one tooth diminishes the impact
of reduction of the other teeth. We thus
have a clear but localized effect in the measurements in the case of absence and a
constraint less spectacular, but more general, in the case of reduction.
The conoid ULI represents an extreme
of reduction. A simple asymmetry between
the two teeth with diastema, often minor,
may represent the beginning of the phenomenon. Thus the actual frequency of reduced ULI is very much higher than our
minimum figures.
We took the measurements of the upper
arch at the level of the teeth. The arch
system permits an equilibrium between
muscular forces, on the condition that dental points of contact exist. The absence or
reduction of the ULI alters this equilibrium
by diastema; and thus allows the facial
muscles to exert pressure towards the interior to the extent that the lower arch
permits it. Thus, the mechanical explanation alone suffice to justify the differences
observed at the level of the dental arch.
How bone and tooth dimensions are related is presented in a companion paper
(Salmon and Le Bot, ’77). Where mechanical constraints do not come into play, the
related arch measurements are independent
of dental measurements.
Other studies to be compared with our
results are those of Baum and &hen
(‘7la,b), Garn and Lewis (‘70), Hanihara
(‘70), Keene (‘65), and Sofaer et al. (‘71).
Garn and Lewis (‘70), on a sample of
658 subjects of both sexes from Southwestern, Ohio, found, as we did, that the mesiodistal diameters are reduced in the following order: controls, propositi with missing
third molars, propositi with multiple agenesis.
In both the studies the molars are the
least affected. Garn even found that the
molars were larger in his sample of multiple agenesis than in controls. We also observed that among our controls who had
an agenesis of the third molar, diameters
of the first and second molars increased
when compared with the controls having
all their third molars. Garn and Lewis (‘70)
concluded that those affected by congenital
agenesis show a regularly decreasing gra-
dient from central incisors to molars. Any
gradient in our sample from front to back
is not apparent. Indeed, in our subjects,
the canines and the premolars are reduced
most.
On both studies, the reduction in the
size of the teeth is not related to the immediate vicinity of the missing teeth. The
scheme remains roughly the same whether
the third molar or an ULI is absent.
According to Garn et al. (‘61) dental development of the propositi is delayed with
posterior-anterior gradient especially affecting the third molar, second premolar
and the ULI. In particular, the frequency
of the sequences of P2M2 should be considerably higher among the propositi. According to Garn’s hypothesis, the third molars
should be affected most since they are at
the end of the series, and the last teeth in
the arch. Our results completely invalidate
this prediction since we found, on the contrary, a remarkable identity in the age of
eruption of this tooth in both our propositi
and our controls.
Hanihara (’70) isolated 60 Pima Indians
with normal ULI, and 23 with reduced ULI,
and showed for the propositi both a reduction in the measurements of the central
incisors, canines and premolars and an
increase in the measurements of the molars. Once again homogeneity of these findings underscore the particularity of these
molars.
Baum and Cohen (‘71a) also compared
dental measurements of two samples of
European ancestry from northeastern
U.S.A.: controls and propositi affected by
agenesis of any tooth. They found as we
did, a strong reduction of canines in propositi. However, contrary to our results,
they observed a strong reduction in mesiodistal diameters in first molars and only
a slight reduction for buccolingual diameters in other teeth.
Sofaer et al. (’71) proposed an interesting hypothesis concerning interaction between developing human teeth, especially
incisors. Our present results don’t permit
us to verify this hypothesis.
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