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crowding and facial height and depth
Relationship between lower arch, spacinglcrowding and facial height and depth
‘3 Leighton
B. C. Leighton* and W. S. Hunter** London.
Englmd,
mnd London,
Onturio.
Canadtr
Previous research into the origins of lower incisor crowding have not yet established the part played by skeletal morphology in its development. Longitudinal cephalometric records of twelve cases with spaced lower teeth were compared with those of twelve moderately crowded cases and twelve severely crowded cases. Significant differences were found between the three groups. These suggested that crowded cases are more likely to have larger Frankfort-mandibular and occlusal plane angles and shorter posterior face height and mandibular body. Both lower incisors and mandibular symphysis were found to be less protrusive in the crowded cases. During the period of study, from 8 years to 14 years, mandibular prognathism increased more in the spaced cases, although labial inclination of lower incisors increased less in these subjects. Key words: Crowding,
face height, prognathism.
0
growth direction,
ne of the problems most commonly facing the orthodontist who treats patients of northwest European stock is that of crowding. Although the loss of teeth because of caries may alleviate some crowding, it is often the wrong teeth, such as first molars, which have to be removed. Increasing awareness of the value of preventive therapy, especially the use of fluoride, will in the future reduce the prevalence of caries. The decision whether or not to extract premolars will become more critical and require more precise knowledge of the amount of crowding or spacing to be expected when the dentition is complete. This is particularly true of the lower arch, as it is the foundation upon which occlusion is to be built. In order to study the changes which take place in the lower dental arch between the ages of 9 and 16 years, Fisk’ examined twenty male subjects whose occlusion had developed normally by the age of 16 years. He found that during normal development neither the future arch perimeter, tooth irregularity, nor spacing/ crowding (the leeway between arch perimeter and aggregated tooth size) at age 16 could be predicted with accuracy from dimensions measured at 9 years. He concluded that, to do so, it would be necessary to determine the relationship between skeletal growth, par-
*King’s England **Faculty Canada.
418
College
Hospital
of Dentistry.
Dental School, University
Denmark
of Western
Hill, Ontario,
London, London,
SE5 8RX, Ontario,
facial skeleton
titularly the degree and direction of mandibular growth, and changes in dental arch perimeter during the 9- to 16-year age period. Sanin and Savara,2 in a study of factors affecting mandibular incisor alignment in 150 subjects, noted that a vertical or lingual inclination of lower incisors in the mixed den&ion is associated with crowded incisors in the permanent dentition. The inclination and size of mandibular first permanent molars were also found to be related to subsequent incisor crowding. Lundstrom,:s in a study of twenty-five pairs of twins, examined the changes in incisor inclination between the ages of 12 to 15 years and 23 to 26 years and their relation to the growth direction of gnathion. He found an association between forward tilting of lower incisors and the vertical growth of gnathion. Backward incisor tilting was associated with growth of gnathion in a horizontal direction. However, he also found that age changes for lower arch spacing/crowding were correlated with neither change in incisor inclination nor growth direction of the mandible during this age period. Ronnerman and Thilander4 used records of 104 children to investigate the relationship between the craniofacial morphology and dental development after premature loss of deciduous teeth. Cases with and without crowding were compared. Linear measurements depicting the amount of prognathism were greater in cases with no crowding. However, the means of almost all linear dimensions except those of the teeth 0002.9416/82/110418+0X$OO.X0/0
0
1982 The C.V.
Mosby
Co.
Volume 82 Number 5
themselves were greater for the noncrowded cases, suggesting that those subjects had larger faces than did subjects with crowded teeth. Sakuda and associates” investigated the relationship between skeletal morphology and increased crowding between the ages of 12 and 17 years. They found some correlation between an increase in lower incisor crowding and high mandibular plane angles, short mandibular body lengths, great upper face height, and small vertical dimensions in upper posterior segments. In 1972, Hunter and Smith6 examined the prediction that spacing/crowding in the mixed-dentition stage was likely to obtain in the permanent dentition. Longitudinal records of fifty-two subjects from the Burlington Research Centre in Toronto were divided into three groups: (1) spaced, (2) moderately crowded, and (3) severely crowded. Each subject had to have all permanent teeth anterior to second molars present and erupted (unless impacted) at the time of the second recording. The sample selection was deliberately biased to include as many severely crowded cases as possible, since such cases are not abundant in most North American samples. The objective was to study the relationships of spacing/crowding with other factors, rather than to describe average populations. Comparison of spacing/crowding at 9 years and spacing/crowding at 15 years showed a moderately strong correlation of 0.78. In order to study this problem further, Hunter7 supplemented the Burlington sample with one from King’s College Hospital Dental School in London, England, where the correlation was found to be a little stronger (r = 0.88). He postulated the following as factors likely to influence the change in arch perimeter: (1) spacing/crowding of the teeth at 9 years, (2) molar relationship, (3) overbite and overjet relationship, (4) curvature of the mandibular curve of Spee, (5) tooth size, (6) inclination of mandibular incisors, (7) angular relationship of mandibular molars and incisors, (8) angular relationship of occlusal plane to the face, and (9) relative amounts of mandibular and maxillary growth. He observed an inverse relationship (r = -0.54) between the subsequent change in length of the arch perimeter and the degree of spacing/crowding at 9 years. However, very little correlation was found between the arch perimeter change and molar relationship, overbite, overjet, and extent of mandibular curve of Spee. Only about 6 percent of the variability in arch perimeter change could be accounted for by tooth size. On the other hand, the inclination of lower incisors to the mandibular plane was significantly greater in the spaced cases at 9 years, confirming the observation made by Sanin and Savara.’ Between 9 and 15 years
Lon
ET arch spacing/crowding
and facial heighr and depth
419
Table I. Distribution of male and female
subjects between the three groups of the King’s College and the Burlington samples Male
Female
Total
King’s College Hospital Spaced Moderately crowded Severely crowded Total
Sample-London 7 5 3 18
5 7 6 ii
12 12 12 36
Burlington Sample-Toronto Spaced Moderately crowded Severely crowded Total
16 10 9 35
6 8 3 17
22 18 12 52
the mean inclination increased for all three groups (spaced, moderately crowded, and crowded), but to a greater extent in the crowded cases. Although the molar inclination to the mandibular plane differed among the three groups it showed no change between 9 and 15 years. We therefore decided to investigate the relationship between spacing/crowding on the one hand and the face shape and growth direction of the face and the mandible on the other by testing the following hypotheses: (1) That there is a difference in skeletal morphology between cases with crowding and those with spacing. (2) That a relationship exists between the growth direction of the face and spacing/crowding. The investigation was based on cephalometric tracings of the same individuals used by Hunter from the Burlington and King’s College samples. Table I gives the distribution of individuals within each sample. Because the sex distribution for the samples showed little difference between the three groups, it was deemed justifiable to combine the sexes. There was, however, an age discrepancy between the three groups, allowance for which has been made when analyzing the results. It arose because of the need to record the severely crowded subjects before removal of permanent teeth. The average for that group was therefore 14 to 16 months younger than the other two at the second age of recording. The criteria for allocating cases to each group were as follows: Spaced cases were those with adequate or excessive space to accommodate the lower teeth mesial to the first permanent molars. The moderately crowded cases had a discrepancy of up to 4 mm. and the severely crowded cases had a discrepancy of more than 4 mm. The following parameters were used for the study: 1. The angle formed by the sella-nasion line and the mandibular plane (gonion-menton) (Fig. 1).
Fig. 1. The angles which were measured for this research: a, That formed by the sella-nasion line and the mandibular plane. b, That formed by the sella-nasion line and the functional occlusal plane. c, That formed by the sella-nasion line and a line joining the center of sella to the most lingual point of the internal contour of the mandibular symphysis (endognathion).
Fig. 3. Linear distances which were measured for this researoh: e, Distance from the center of setla to the projection on the SN line of endognathion. f, Distance from the center of sella to the projection on the S-N line of the most labiatly placed lower incisor tip. g, Anterior face height as measured from nasion to menton. h, Posterior face height as measured from seffa to gonion i, Mandibular length as measured from gonion to the projection of endognathion on the mandibular ptane.
II. Errors of measurement for parameters used, calculated from double determinations carried out on twelve cases of -the series using the formula
Table
Si=
Fig. 2. The angle (d) formed by the change of inclination of the selia-nasion line when Biork’s “structural method” is used for superimposing the silhouettes of the mandible at 8 years and at 14 years.
2. The angle formed by the sella-nasion line and the functional occlusal plane (lower molar cusps to premolar or first deciduous molar cusps) (Fig. 1). 3. The angle formed at the center of sella by the S-N line and a line connecting sella to the most lingual point on the internal aspect of the bone of the mandibular symphysis. The name endognathion is given to this point (Fig. 1). 4. The angle formed by the change in inclination of the S-N line, when the mandibular silhouettes at 8 years and 15 years are superimposed on the internal contour of the symphysis and the mandibular canal in the “structural manner” described by Bjiirl? (Fig. 2).
J
$
Angles: N-S - symphysis S-N plane/mandibular
plane
-tO.38”
20.27
ltl.05”
-ro.73
t I .48”
21.47 t1.10”
S-N plane/occlusal plane Lower incisor/mandibular
plane
Lower incisor/S-N plane Change in S-N inclination
kO.98 tl.lo”
(Bjiirk)
lrO.81”
Linear
t1.20”
dimensions:
Projection symphysis on S-N plane Projection lower incisor on S-N plane Anterior face height (N-Me)
20.52 20.43 20.35
mm. mm. mm.
CO.71 +0.43 to.39
mm. mm. mm.
Posterior face height (S-Go) Mandibular length (Go-symphysis)
a0.91 mm. + 1.08 mm.
t0.60 kO.80
mm. mm.
5. The distance from sella along S-N to the projection perpendicular to the S-N plane of the most lingual point of the internal contour of the mandibular symphysis-endognathion (Fig. 3). This point was used in preference to pogonion in order to avoid confusion caused by variable growth of the mental -process.
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Lower
arch
spacing/crowding
and facial
height
421
and depth
Number
Table III. Comparison between three groups, from both samples, of the angle formed by the S-N line and the mandibular plane 14 years
8 years n Spaced group Moderately crowded group Severely crowded group
Mean
S.D.
33.60 36.20 37.21
34 30 24
“x” indicates significant difference level. Differences between severely
(degrees)
(degrees)
24.21 23.94 24.59
xy x y
at the 5 percent level, and “ y ” indicates crowded cases were not significant.
between groups and moderately
Mean
(degrees)
S.D.
k-5.49 24.35 25.63
31.57 34.53 35.38 differences
which
(degrees)
are significant
xx x x
at the 1 percent
Table IV. Comparison between three groups from both samples of the angle formed by the S-N line
and the occlusal plane 8 years n Spaced group Moderately crowded group Severely crowded group “xl’ indicates significant difference level. Differences were significant cases at 14 years.
Mean
(degrees)
14 years S.D.
19.69 21.28 20.81
34 30 24
(degrees) k2.28 ?3.85 23.23
Mean
x x
(degrees)
S.D.
14.96 18.07 18.50
(degrees)
23.92 k4.68 k4.20
xy x y
between groups at the 5 percent level, and “y” indicates differences which are significant at the 1 percent only between spaced and moderately crowded cases at both ages and between spaced and severely crowded
Table V. Comparison between three groups of both samples of the angle N-S-endognathion 14 years
8 years n Spaced Moderately crowded Severely crowded
34 30 24
Mean
(degrees) 68.34 69.53 70.69
“x” indicates significant differences between groups at the 5 percent Differences were significant only between spaced and severely crowded at 14 years.
6. The distance from sella along S-N to the perpendicular projection of the most labially placed lower incisal edge (Fig. 3). 7. The anterior face height as measured from nasion to menton (Fig. 3). 8. The posterior face height measured from sella to gonion (Fig. 3). 9. The mandibular length as measured from gonion along the mandibular plane to the perpendicular projection on it of the most lingual point on the internal aspect of the mandibular symphysis (endognathion) (Fig. 3). Because two different cephalostats had been used in recording the King’s College sample, it was necessary to make calculations of the amount of enlargement. Correction factors were computed, using the size of the image of the head holder, which was constant. Those
S.D.
(degrees) k3.04 23.18 k3.15
x x
Mean
(degrees) 67.25 69.31 10.44
S.D.
(degrees)
a3.51 23.61 23.21
xy x y
level, and “y” indicates significant differences at the 1 percent cases at both ages and between spaced and moderately crowded
level. cases
factors were confirmed by comparison with values obtained using a leaded millimeter scale in a series of test films. A random sample of these films was used to calculate the error involved. Using the formula Si =
d2 where d is the difference between the d- 2n measured and calculated enlargement and n is the number of subjects, the error of enlargement was found to be * 0.24 percent, which is considered to be small enough for the purpose of this article. ERROR OF MEASUREMENT OF RADIOGRAPHS
Double determinations were used to calculate the d2 error of measurement. For this, the formula Si = 2n dwas used and the results are shown in Table II. As these were considerably less than such differences as are
VI. Comparison between the three groups, from both King’s College and Burlington samples, the distance from sella to the perpendicular projection of endognathion on the S-N line ~..-.-___..-_---_x yeam 14ywr, ---- -. ----.-__-.-_ .~---_-__- N Meun (mm.) S.D. (mm.) .Mrun imtn.) S.D. (mm.)
Table of
Spaced group Moderately crowded group Severely crowded group
34 30 24
35.28 32.90 30.83
k4.68 15.76 24.93
y
ih.65 ‘7.23 +-(>.()I
41.99 37.46 34.96
y
sy x y
“x” indicates differences between groups which are statistically significant at the 5 percent level, and “y” indicates differences which nificant at the 1 percent level. Differences were significant only between spaced and severely crowded cases at both ages and between and moderately crowded cases at I4 years.
are sigspaced
VII. Comparison between the three groups, from both King’s College and Burlington samples, of the distance from sella to the perpendicular projection of the lower central incisor tip on the S-N line
Table
8 years ” Spaced group Moderately crowded group Severely crowded group “y” indicates differences and moderately crowded subjects.
34 30 24
Mean
(mtn.)
14 years S.D.
54.30 50.64 48.915
(mm.)
14.41 k4.77 r5.11
yy y y
Mean
(mm.)
S.D.
60.96 55.42 54.52
t5.92 es.43 k5.96
(mm.)
yy y y
between groups which are statistically significant at the I percent level. Differences were significant between spaced and between spaced and severely crowded cases, at both ages, but not between moderately and severely crowded
VIII. Comparison between the three groups from both King’s College and Burlington samples of the posterior face height (sella-gonion)
Table
14 year.7
8 years
n Spaced group Moderately crowded group Severely crowded group
34 30 24
Mean
(mm.)
64.14 62.49 61.90
“x” indicates differences between groups which are statistically significant significant at the I percent level. Differences were significant only between moderately crowded cases at 14 years.
claimed to be statistically significant, they are considered acceptable. STATISTICAL
ANALYSIS
The means, standard deviations, and standard errors were calculated for each parameter. The significance of difference between mean values was assessed by Student’s t test. MORPHOLOGIC COMPARISON OF SPACED CROWDED CASES AT 8 AND 14 YEARS
AND
Tables III, IV, and V summarize the findings for the angles between the S-N line and the mandibular plane, the occlusal plane, and the sella-endognathion
S.D.
(mm.)
23.51 23.18 k3.51
x x
Mean
(mm.)
74.93 71.99 70.34
S.D.
25.63 24.70 k5.11
indicates differences at the 5 percent level, and “y” spaced and crowded groups at both ages and between
(mm.)
xy x y which spaced
are and
plane. Each of the angles was found to be larger for the crowded cases at both mixed- and permanent-dentition stages, and the differences were statistically significant. As the differences were similar in both the Burlington and the King’s College samples, it would seem highly probable that a real difference exists between the crowded and spaced cases for these variables. It implies that the anterior part of the mandible is situated either farther forward or less downward in the spaced cases. In other words, the difference may lie in the anteroposterior direction, the vertical direction, or both. Further clarification required the use of linear measurements. In Tables VI to IX the three groups are compared with respect to five linear dimensions. Al-
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urch
spacing/crowding
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423
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5
Table IX. Comparison between the three groups from both King’s College and Burlington samples of the mandibular length (gonion to the projection of endognathion on the mandibular plane) 8 years n
Mean
34 30 24
Spaced group Moderately crowded group Severely crowded group
(mm.)
S.D.
53.16 51.07 50.46
“x” indicates differences which are significant at the 5 percent level, Differences were significant between spaced and moderately crowded not between moderately and severely crowded cases.
14 years
23.26 22.93 k3.00
(mm.)
Mean
xy x y
(mm.)
S.D.
(mm.)
24.26 23.91 k4.06
61.83 5-l 87 58.10
yy y y
and “y” indicates differences which are significant at the 1 percent level. cases and between spaced and severely crowded cases at both ages, but
Table X. Comparison between the age, height, weight, and length of S-N at the mixed and permanent dentition stages between three groups of the King’s College sample
I Parameter
Spaced
group
Mean
n = 12
Moderate
I
S.D.
group
n = 12
Mean
I
Crowded
group
Mean
S.D.
n = 12 S.D.
Age First Second Height 8 yr. 14 yr. Weight 8 yr. 14 yr. S-N 8 yr. 14 yr. “x” indicates a difference severely crowded groups
8.475 14.400 144.455 165.455
20.492 kO.706 k5.871 k 8.092
30.190 58.770
25.546 k15.237
63.919 67.072
22.913 23.574
which is significant at 14 years of age.
x
at the 5 percent
level.
though the projections of the symphysis (endognathion) and lower incisor were farther from sella in the spaced cases, the anterior face height showed very little difference. The posterior height, however, was a little larger in the spaced group, and the difference was statistically significant (Table VIII). It is perhaps not surprising to find that the mandibular length was smaller in the crowded cases (Table IX). The findings of Lundstrom and of Ronnerman and Thilander4 that crowding occurs more frequently in less prognathous persons are thus confirmed. Because all dimensions were larger in the spaced group, it might be suggested that these are merely larger individuals, a fact which would fit very conveniently the finding of more space for the teeth. Heights and weights were available for the King’s College sample (Table X). The subjects in the spaced groups were both the tallest and the heaviest of the three groups; this cannot be entirely due to an age difference because they were, in fact, the youngest group at the first visit. On the other hand, they were the oldest at the second visit.
kO.702 “0.710
8.983 14.242
k-o.651 20.989
8.883 13.633
145.583 163.333
a7.255 29.948
141.000 158.750
+ 10.287 2 11.022
29.733 50.967
k4.397 kg.351
28.333 41.692
25.756 k3.084
62.741 65.300
22.821 k3.857
62.853 65.032
“2.439 52.733
This level of difference
was found only between
the weights
x
of spaced
and
In spite of that, the length of S-N shows only a small difference between the three groups (Table X). It was decided, therefore, to express the distance from sella to the projection of endognathion and from sella to the projection of the lower incisor as a proportion of the length S-N. These ratios will show significant differences between the groups, and they support the thesis that mandibular prognathism is more marked in spaced cases than in crowded cases. Examination of the ratio of height to weight for the King’s College sample revealed a small difference in stature between the groups. Although not large enough to be statistically significant, there is a consistent gradation from spaced to severely crowded cases, which might suggest that an underlying difference in stature exists between the groups. It would appear, therefore, that there are morphologic differences between spaced and crowded cases, especially in the anteroposterior dimensions. The small difference in posterior face height might be related to lower incisor inclination, which Hunter has
Table Xl. Comparison between the three groups from both samples of the annual rate of both angular and linear parameters in the 8- to I&year age period -. Spucwi .ModeruIely crowded n = .<4
Parumeter Angle
S-N/mandibular
Angle
S-N/occlusal
plane plane
Angle N-S-endognathion Mandibular rotation Projection endognathion Projection Anterior Posterior Mandibular “x”
indicates
Meun
on S-N from
“S”
S.D.
-0.31”
‘to.40
-0.73
10.54
-0.16 0.92”
-eO.33O -0.49
Mean
S.D.
Mean
S.D.
-m0.28” -0.58
kO.34”
-- 0.3 1”
LO.45
kO.70
-0.35
x
-0.02 0.76”
kO.21’ kO.31
t 1.02 -to.32
x
xx
0.84
mm.
20.70
x
to.56 to.49 20.47
x
0.84 mm. 2.21 mm. I .69 mm.
20.40 20.75 20.58
x
face height face height
1.08 mm. I .99 mm. I .74 mm.
length
1.32 mm.
to.30
x
1.13
to.40
x
differences
on S-N from
between
“S”
groups
which
are statistically
significant
shown to differ between the three groups, through the medium of the tongue. It might be profitable, therefore, to investigate the size and position of the tongue in spaced and crowded cases. CHANGES IN THE PARAMETERS WHICH EXPRESS THE GROWTH DIRECTION OF THE FACE Table X1 summarizes the differences found between spaced, moderately crowded, and crowded groups for the change in each of the parameters already discussed. Each of these changes was expressed as the annual rate, calculated by dividing the total change by the number of years that the cases was studied. This was done because the average period of observation was a little different between the three groups (6.65 years for the spaced cases and 5.7 1 years for the crowded cases). The angle between the S-N line and the mandibular plane diminished with age, but the reduction was similar in all three groups. The change in the angle between S-N and the occlusal plane, however, was found to be smaller for the spaced group of cases, a difference that was significant and set them apart from the other two groups. Because there was considerable variation in the change in angle N-S-endognathion, the greater mean reduction in the spaced cases fell short of statistical significance. Bjork’s method of measuring the change in inclination of the S-N line was used to estimate the amount of mandibular rotation between the two ages by superimposing the mandible itself on the outline of the most lingual and inferior aspect of the internal border of the symphysis and the mandibular canal. Although the spaced cases in both the King’s College and Burlington samples showed a greater amount of forward rotation,
Severelyimwded II = 174 ..--.
to.67
central
of
n = so
I .08 mm.
lower
change
at the 5 percent
mm.
- 0.04” 0.72” 0.71 mm.
50.38 ‘0.64
x
kO.62
I .03 mm. 2.06 mm. 1.53 mm.
20.72 20.43
1.32 mm.
20.43
level.
it was not sufficiently large to be statistically significant. When the linear dimensions of anteroposterior growth were examined, the spaced cases were found to increase to a greater extent than the crowded cases (Table XI). This was reflected in the mandibular length and in the distances from sella to projections on the S-N line of endognathion and of the lower incisai edges. However, the difference was greatest and most significant in the case of endognathion. It appears, therefore, that the mandibular symphysis is carried forward to a greater extent in the faces of the spaced cases, a change that may be associated with a slightly more forward mandibular rotation. Although Lundstrom reported similar relationships between change in incisor inclination and growth direction, he could not establish a correlation between change in spacing/crowding and growth direction, perhaps because his sample did not include a large number of spaced or severely crowded cases. Since the subjects of the present investigation were selected for intact permanent dentitions at the age of 13 to 14, there is no assurance that the severely crowded cases represent those severely crowded subjects whose premolars were removed earlier as part of a serial extraction programme. Both the studies by Ronnerman and Thilandel”’ and by Sakuda and associates,; in which similar findings are reported, also involved only children with intact dentitions. Hence, the findings can be applied at this time only to subjects with intact dentitions. The data of this study suggest that downward and deficient growth of the mandible is associated with both upright or “reclined ” mandibular incisors and with crowding in the mandibular dentition. Although not surprising in the light of the findings
Volume 82 Number 5
of Sakuda and colleagues5 and of Ronnerman and Thilander,4 it is apparent that severe crowding of the mandibular dentition tends to occur in faces that have steep mandibular plane and occlusal plane angles. Compared with subjects who have spaced mandibular dentitions, the mandibular corpus of subjects with severely crowded dentitions is shorter, the mandibular symphysis is more posterior, their mandibles grow less from 9 to 14 years of age, and the direction of growth is more downward. SUMMARY
The facial skeletal characteristics associated with spacing or crowding of the mandibular dentition were studied in the mixed and permanent dentitions of a longitudinal sample of eighty-eight subjects grouped as follows: (1) thirty-four with spaced mandibular dentitions, (2) thirty with moderately crowded mandibular dentitions, and (3) twenty-four with severely crowded mandibular dentitions. The study revealed that the severely crowded subjects had larger mandibular plane and occlusal plane angles to S-N than the others. A metric evaluation disclosed that although the anterior face heights were similar for all three groups, the severely crowded subjects had shorter posterior face heights than did the other groups. They also had shorter mandibular corpora, with both symphyses and dentitions more posteriorly positioned than in the moderately crowded or spaced subjects. During the period studied, the mandibles of the severely crowded and moderately crowded subjects grew
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425
forward less than did those of the subjects spaced with spaced dentitions and their mandibles rotated forward less (though not significantly so). Hence, the evidence from this selected sample is that crowded mandibular dentitions exist in a morphologically distinct supporting structure, which has a downward growth direction and a relatively deficient amount of growth. REFERENCES 1. Fisk,
2.
3.
4.
5.
6.
I.
8.
R. 0.: Normal mandibular arch changes between ages 9- 16, 1. Can. Dent. Assoc. 32: 652-658, 1966. Sanin, C., and Savara, B. S.: Factors that affect the alignment of the mandibular incisors: A longitudinal study, AM. J. ORTHOD. 64: 248-257, 1973. Lundstriim, A.: A study of the correlation between mandibular growth direction and changes in incisor inclination, overjet, overbite and crowding, Trans. Eur. Orthod. Sot., pp. 131-140, 1975. Ronnerman, A., and Thilander, B.: Facial and dental arch morphology in children with and without early loss of deciduous molars, AM. J. ORTHOD. 73: 47-58, 1978. Sakuda, M., Kuroda, Y., Wada, K., and Matsumoto, M.: Changes in crowding of teeth during adolescence and their relation to the growth of the facial skeleton, Trans. Eur. Orthod. Sot., pp. 93-104, 1976. Hunter, W. S., and Smith, B. R. W.: Development of mandibular spacing-crowding from 9 to 16 years of age, J. Can. Dent. Assoc. 38: 178-185, 1972. Hunter, W. S.: The dynamics of mandibular arch perimeter changes from mixed to permanent dentitions. In McNamara, J. A., Jr., et al.: The biology of occlusal development, Ann Arbor, 1977, Center for Human Growth and Development, University of Michigan, pp. 169-178. Bjiirk, A., and Skieller, V.: Facial development and tooth eruption: An implant study at the age of puberty, AM. J. ORTHOD. 62: 339-383, 1972.
‘3 Leighton
B. C. Leighton* and W. S. Hunter** London.
Englmd,
mnd London,
Onturio.
Canadtr
Previous research into the origins of lower incisor crowding have not yet established the part played by skeletal morphology in its development. Longitudinal cephalometric records of twelve cases with spaced lower teeth were compared with those of twelve moderately crowded cases and twelve severely crowded cases. Significant differences were found between the three groups. These suggested that crowded cases are more likely to have larger Frankfort-mandibular and occlusal plane angles and shorter posterior face height and mandibular body. Both lower incisors and mandibular symphysis were found to be less protrusive in the crowded cases. During the period of study, from 8 years to 14 years, mandibular prognathism increased more in the spaced cases, although labial inclination of lower incisors increased less in these subjects. Key words: Crowding,
face height, prognathism.
0
growth direction,
ne of the problems most commonly facing the orthodontist who treats patients of northwest European stock is that of crowding. Although the loss of teeth because of caries may alleviate some crowding, it is often the wrong teeth, such as first molars, which have to be removed. Increasing awareness of the value of preventive therapy, especially the use of fluoride, will in the future reduce the prevalence of caries. The decision whether or not to extract premolars will become more critical and require more precise knowledge of the amount of crowding or spacing to be expected when the dentition is complete. This is particularly true of the lower arch, as it is the foundation upon which occlusion is to be built. In order to study the changes which take place in the lower dental arch between the ages of 9 and 16 years, Fisk’ examined twenty male subjects whose occlusion had developed normally by the age of 16 years. He found that during normal development neither the future arch perimeter, tooth irregularity, nor spacing/ crowding (the leeway between arch perimeter and aggregated tooth size) at age 16 could be predicted with accuracy from dimensions measured at 9 years. He concluded that, to do so, it would be necessary to determine the relationship between skeletal growth, par-
*King’s England **Faculty Canada.
418
College
Hospital
of Dentistry.
Dental School, University
Denmark
of Western
Hill, Ontario,
London, London,
SE5 8RX, Ontario,
facial skeleton
titularly the degree and direction of mandibular growth, and changes in dental arch perimeter during the 9- to 16-year age period. Sanin and Savara,2 in a study of factors affecting mandibular incisor alignment in 150 subjects, noted that a vertical or lingual inclination of lower incisors in the mixed den&ion is associated with crowded incisors in the permanent dentition. The inclination and size of mandibular first permanent molars were also found to be related to subsequent incisor crowding. Lundstrom,:s in a study of twenty-five pairs of twins, examined the changes in incisor inclination between the ages of 12 to 15 years and 23 to 26 years and their relation to the growth direction of gnathion. He found an association between forward tilting of lower incisors and the vertical growth of gnathion. Backward incisor tilting was associated with growth of gnathion in a horizontal direction. However, he also found that age changes for lower arch spacing/crowding were correlated with neither change in incisor inclination nor growth direction of the mandible during this age period. Ronnerman and Thilander4 used records of 104 children to investigate the relationship between the craniofacial morphology and dental development after premature loss of deciduous teeth. Cases with and without crowding were compared. Linear measurements depicting the amount of prognathism were greater in cases with no crowding. However, the means of almost all linear dimensions except those of the teeth 0002.9416/82/110418+0X$OO.X0/0
0
1982 The C.V.
Mosby
Co.
Volume 82 Number 5
themselves were greater for the noncrowded cases, suggesting that those subjects had larger faces than did subjects with crowded teeth. Sakuda and associates” investigated the relationship between skeletal morphology and increased crowding between the ages of 12 and 17 years. They found some correlation between an increase in lower incisor crowding and high mandibular plane angles, short mandibular body lengths, great upper face height, and small vertical dimensions in upper posterior segments. In 1972, Hunter and Smith6 examined the prediction that spacing/crowding in the mixed-dentition stage was likely to obtain in the permanent dentition. Longitudinal records of fifty-two subjects from the Burlington Research Centre in Toronto were divided into three groups: (1) spaced, (2) moderately crowded, and (3) severely crowded. Each subject had to have all permanent teeth anterior to second molars present and erupted (unless impacted) at the time of the second recording. The sample selection was deliberately biased to include as many severely crowded cases as possible, since such cases are not abundant in most North American samples. The objective was to study the relationships of spacing/crowding with other factors, rather than to describe average populations. Comparison of spacing/crowding at 9 years and spacing/crowding at 15 years showed a moderately strong correlation of 0.78. In order to study this problem further, Hunter7 supplemented the Burlington sample with one from King’s College Hospital Dental School in London, England, where the correlation was found to be a little stronger (r = 0.88). He postulated the following as factors likely to influence the change in arch perimeter: (1) spacing/crowding of the teeth at 9 years, (2) molar relationship, (3) overbite and overjet relationship, (4) curvature of the mandibular curve of Spee, (5) tooth size, (6) inclination of mandibular incisors, (7) angular relationship of mandibular molars and incisors, (8) angular relationship of occlusal plane to the face, and (9) relative amounts of mandibular and maxillary growth. He observed an inverse relationship (r = -0.54) between the subsequent change in length of the arch perimeter and the degree of spacing/crowding at 9 years. However, very little correlation was found between the arch perimeter change and molar relationship, overbite, overjet, and extent of mandibular curve of Spee. Only about 6 percent of the variability in arch perimeter change could be accounted for by tooth size. On the other hand, the inclination of lower incisors to the mandibular plane was significantly greater in the spaced cases at 9 years, confirming the observation made by Sanin and Savara.’ Between 9 and 15 years
Lon
ET arch spacing/crowding
and facial heighr and depth
419
Table I. Distribution of male and female
subjects between the three groups of the King’s College and the Burlington samples Male
Female
Total
King’s College Hospital Spaced Moderately crowded Severely crowded Total
Sample-London 7 5 3 18
5 7 6 ii
12 12 12 36
Burlington Sample-Toronto Spaced Moderately crowded Severely crowded Total
16 10 9 35
6 8 3 17
22 18 12 52
the mean inclination increased for all three groups (spaced, moderately crowded, and crowded), but to a greater extent in the crowded cases. Although the molar inclination to the mandibular plane differed among the three groups it showed no change between 9 and 15 years. We therefore decided to investigate the relationship between spacing/crowding on the one hand and the face shape and growth direction of the face and the mandible on the other by testing the following hypotheses: (1) That there is a difference in skeletal morphology between cases with crowding and those with spacing. (2) That a relationship exists between the growth direction of the face and spacing/crowding. The investigation was based on cephalometric tracings of the same individuals used by Hunter from the Burlington and King’s College samples. Table I gives the distribution of individuals within each sample. Because the sex distribution for the samples showed little difference between the three groups, it was deemed justifiable to combine the sexes. There was, however, an age discrepancy between the three groups, allowance for which has been made when analyzing the results. It arose because of the need to record the severely crowded subjects before removal of permanent teeth. The average for that group was therefore 14 to 16 months younger than the other two at the second age of recording. The criteria for allocating cases to each group were as follows: Spaced cases were those with adequate or excessive space to accommodate the lower teeth mesial to the first permanent molars. The moderately crowded cases had a discrepancy of up to 4 mm. and the severely crowded cases had a discrepancy of more than 4 mm. The following parameters were used for the study: 1. The angle formed by the sella-nasion line and the mandibular plane (gonion-menton) (Fig. 1).
Fig. 1. The angles which were measured for this research: a, That formed by the sella-nasion line and the mandibular plane. b, That formed by the sella-nasion line and the functional occlusal plane. c, That formed by the sella-nasion line and a line joining the center of sella to the most lingual point of the internal contour of the mandibular symphysis (endognathion).
Fig. 3. Linear distances which were measured for this researoh: e, Distance from the center of setla to the projection on the SN line of endognathion. f, Distance from the center of sella to the projection on the S-N line of the most labiatly placed lower incisor tip. g, Anterior face height as measured from nasion to menton. h, Posterior face height as measured from seffa to gonion i, Mandibular length as measured from gonion to the projection of endognathion on the mandibular ptane.
II. Errors of measurement for parameters used, calculated from double determinations carried out on twelve cases of -the series using the formula
Table
Si=
Fig. 2. The angle (d) formed by the change of inclination of the selia-nasion line when Biork’s “structural method” is used for superimposing the silhouettes of the mandible at 8 years and at 14 years.
2. The angle formed by the sella-nasion line and the functional occlusal plane (lower molar cusps to premolar or first deciduous molar cusps) (Fig. 1). 3. The angle formed at the center of sella by the S-N line and a line connecting sella to the most lingual point on the internal aspect of the bone of the mandibular symphysis. The name endognathion is given to this point (Fig. 1). 4. The angle formed by the change in inclination of the S-N line, when the mandibular silhouettes at 8 years and 15 years are superimposed on the internal contour of the symphysis and the mandibular canal in the “structural manner” described by Bjiirl? (Fig. 2).
J
$
Angles: N-S - symphysis S-N plane/mandibular
plane
-tO.38”
20.27
ltl.05”
-ro.73
t I .48”
21.47 t1.10”
S-N plane/occlusal plane Lower incisor/mandibular
plane
Lower incisor/S-N plane Change in S-N inclination
kO.98 tl.lo”
(Bjiirk)
lrO.81”
Linear
t1.20”
dimensions:
Projection symphysis on S-N plane Projection lower incisor on S-N plane Anterior face height (N-Me)
20.52 20.43 20.35
mm. mm. mm.
CO.71 +0.43 to.39
mm. mm. mm.
Posterior face height (S-Go) Mandibular length (Go-symphysis)
a0.91 mm. + 1.08 mm.
t0.60 kO.80
mm. mm.
5. The distance from sella along S-N to the projection perpendicular to the S-N plane of the most lingual point of the internal contour of the mandibular symphysis-endognathion (Fig. 3). This point was used in preference to pogonion in order to avoid confusion caused by variable growth of the mental -process.
Volume 82 S
Lower
arch
spacing/crowding
and facial
height
421
and depth
Number
Table III. Comparison between three groups, from both samples, of the angle formed by the S-N line and the mandibular plane 14 years
8 years n Spaced group Moderately crowded group Severely crowded group
Mean
S.D.
33.60 36.20 37.21
34 30 24
“x” indicates significant difference level. Differences between severely
(degrees)
(degrees)
24.21 23.94 24.59
xy x y
at the 5 percent level, and “ y ” indicates crowded cases were not significant.
between groups and moderately
Mean
(degrees)
S.D.
k-5.49 24.35 25.63
31.57 34.53 35.38 differences
which
(degrees)
are significant
xx x x
at the 1 percent
Table IV. Comparison between three groups from both samples of the angle formed by the S-N line
and the occlusal plane 8 years n Spaced group Moderately crowded group Severely crowded group “xl’ indicates significant difference level. Differences were significant cases at 14 years.
Mean
(degrees)
14 years S.D.
19.69 21.28 20.81
34 30 24
(degrees) k2.28 ?3.85 23.23
Mean
x x
(degrees)
S.D.
14.96 18.07 18.50
(degrees)
23.92 k4.68 k4.20
xy x y
between groups at the 5 percent level, and “y” indicates differences which are significant at the 1 percent only between spaced and moderately crowded cases at both ages and between spaced and severely crowded
Table V. Comparison between three groups of both samples of the angle N-S-endognathion 14 years
8 years n Spaced Moderately crowded Severely crowded
34 30 24
Mean
(degrees) 68.34 69.53 70.69
“x” indicates significant differences between groups at the 5 percent Differences were significant only between spaced and severely crowded at 14 years.
6. The distance from sella along S-N to the perpendicular projection of the most labially placed lower incisal edge (Fig. 3). 7. The anterior face height as measured from nasion to menton (Fig. 3). 8. The posterior face height measured from sella to gonion (Fig. 3). 9. The mandibular length as measured from gonion along the mandibular plane to the perpendicular projection on it of the most lingual point on the internal aspect of the mandibular symphysis (endognathion) (Fig. 3). Because two different cephalostats had been used in recording the King’s College sample, it was necessary to make calculations of the amount of enlargement. Correction factors were computed, using the size of the image of the head holder, which was constant. Those
S.D.
(degrees) k3.04 23.18 k3.15
x x
Mean
(degrees) 67.25 69.31 10.44
S.D.
(degrees)
a3.51 23.61 23.21
xy x y
level, and “y” indicates significant differences at the 1 percent cases at both ages and between spaced and moderately crowded
level. cases
factors were confirmed by comparison with values obtained using a leaded millimeter scale in a series of test films. A random sample of these films was used to calculate the error involved. Using the formula Si =
d2 where d is the difference between the d- 2n measured and calculated enlargement and n is the number of subjects, the error of enlargement was found to be * 0.24 percent, which is considered to be small enough for the purpose of this article. ERROR OF MEASUREMENT OF RADIOGRAPHS
Double determinations were used to calculate the d2 error of measurement. For this, the formula Si = 2n dwas used and the results are shown in Table II. As these were considerably less than such differences as are
VI. Comparison between the three groups, from both King’s College and Burlington samples, the distance from sella to the perpendicular projection of endognathion on the S-N line ~..-.-___..-_---_x yeam 14ywr, ---- -. ----.-__-.-_ .~---_-__- N Meun (mm.) S.D. (mm.) .Mrun imtn.) S.D. (mm.)
Table of
Spaced group Moderately crowded group Severely crowded group
34 30 24
35.28 32.90 30.83
k4.68 15.76 24.93
y
ih.65 ‘7.23 +-(>.()I
41.99 37.46 34.96
y
sy x y
“x” indicates differences between groups which are statistically significant at the 5 percent level, and “y” indicates differences which nificant at the 1 percent level. Differences were significant only between spaced and severely crowded cases at both ages and between and moderately crowded cases at I4 years.
are sigspaced
VII. Comparison between the three groups, from both King’s College and Burlington samples, of the distance from sella to the perpendicular projection of the lower central incisor tip on the S-N line
Table
8 years ” Spaced group Moderately crowded group Severely crowded group “y” indicates differences and moderately crowded subjects.
34 30 24
Mean
(mtn.)
14 years S.D.
54.30 50.64 48.915
(mm.)
14.41 k4.77 r5.11
yy y y
Mean
(mm.)
S.D.
60.96 55.42 54.52
t5.92 es.43 k5.96
(mm.)
yy y y
between groups which are statistically significant at the I percent level. Differences were significant between spaced and between spaced and severely crowded cases, at both ages, but not between moderately and severely crowded
VIII. Comparison between the three groups from both King’s College and Burlington samples of the posterior face height (sella-gonion)
Table
14 year.7
8 years
n Spaced group Moderately crowded group Severely crowded group
34 30 24
Mean
(mm.)
64.14 62.49 61.90
“x” indicates differences between groups which are statistically significant significant at the I percent level. Differences were significant only between moderately crowded cases at 14 years.
claimed to be statistically significant, they are considered acceptable. STATISTICAL
ANALYSIS
The means, standard deviations, and standard errors were calculated for each parameter. The significance of difference between mean values was assessed by Student’s t test. MORPHOLOGIC COMPARISON OF SPACED CROWDED CASES AT 8 AND 14 YEARS
AND
Tables III, IV, and V summarize the findings for the angles between the S-N line and the mandibular plane, the occlusal plane, and the sella-endognathion
S.D.
(mm.)
23.51 23.18 k3.51
x x
Mean
(mm.)
74.93 71.99 70.34
S.D.
25.63 24.70 k5.11
indicates differences at the 5 percent level, and “y” spaced and crowded groups at both ages and between
(mm.)
xy x y which spaced
are and
plane. Each of the angles was found to be larger for the crowded cases at both mixed- and permanent-dentition stages, and the differences were statistically significant. As the differences were similar in both the Burlington and the King’s College samples, it would seem highly probable that a real difference exists between the crowded and spaced cases for these variables. It implies that the anterior part of the mandible is situated either farther forward or less downward in the spaced cases. In other words, the difference may lie in the anteroposterior direction, the vertical direction, or both. Further clarification required the use of linear measurements. In Tables VI to IX the three groups are compared with respect to five linear dimensions. Al-
Volume 82 Number
Lower
urch
spacing/crowding
and facial
height
and
423
depth
5
Table IX. Comparison between the three groups from both King’s College and Burlington samples of the mandibular length (gonion to the projection of endognathion on the mandibular plane) 8 years n
Mean
34 30 24
Spaced group Moderately crowded group Severely crowded group
(mm.)
S.D.
53.16 51.07 50.46
“x” indicates differences which are significant at the 5 percent level, Differences were significant between spaced and moderately crowded not between moderately and severely crowded cases.
14 years
23.26 22.93 k3.00
(mm.)
Mean
xy x y
(mm.)
S.D.
(mm.)
24.26 23.91 k4.06
61.83 5-l 87 58.10
yy y y
and “y” indicates differences which are significant at the 1 percent level. cases and between spaced and severely crowded cases at both ages, but
Table X. Comparison between the age, height, weight, and length of S-N at the mixed and permanent dentition stages between three groups of the King’s College sample
I Parameter
Spaced
group
Mean
n = 12
Moderate
I
S.D.
group
n = 12
Mean
I
Crowded
group
Mean
S.D.
n = 12 S.D.
Age First Second Height 8 yr. 14 yr. Weight 8 yr. 14 yr. S-N 8 yr. 14 yr. “x” indicates a difference severely crowded groups
8.475 14.400 144.455 165.455
20.492 kO.706 k5.871 k 8.092
30.190 58.770
25.546 k15.237
63.919 67.072
22.913 23.574
which is significant at 14 years of age.
x
at the 5 percent
level.
though the projections of the symphysis (endognathion) and lower incisor were farther from sella in the spaced cases, the anterior face height showed very little difference. The posterior height, however, was a little larger in the spaced group, and the difference was statistically significant (Table VIII). It is perhaps not surprising to find that the mandibular length was smaller in the crowded cases (Table IX). The findings of Lundstrom and of Ronnerman and Thilander4 that crowding occurs more frequently in less prognathous persons are thus confirmed. Because all dimensions were larger in the spaced group, it might be suggested that these are merely larger individuals, a fact which would fit very conveniently the finding of more space for the teeth. Heights and weights were available for the King’s College sample (Table X). The subjects in the spaced groups were both the tallest and the heaviest of the three groups; this cannot be entirely due to an age difference because they were, in fact, the youngest group at the first visit. On the other hand, they were the oldest at the second visit.
kO.702 “0.710
8.983 14.242
k-o.651 20.989
8.883 13.633
145.583 163.333
a7.255 29.948
141.000 158.750
+ 10.287 2 11.022
29.733 50.967
k4.397 kg.351
28.333 41.692
25.756 k3.084
62.741 65.300
22.821 k3.857
62.853 65.032
“2.439 52.733
This level of difference
was found only between
the weights
x
of spaced
and
In spite of that, the length of S-N shows only a small difference between the three groups (Table X). It was decided, therefore, to express the distance from sella to the projection of endognathion and from sella to the projection of the lower incisor as a proportion of the length S-N. These ratios will show significant differences between the groups, and they support the thesis that mandibular prognathism is more marked in spaced cases than in crowded cases. Examination of the ratio of height to weight for the King’s College sample revealed a small difference in stature between the groups. Although not large enough to be statistically significant, there is a consistent gradation from spaced to severely crowded cases, which might suggest that an underlying difference in stature exists between the groups. It would appear, therefore, that there are morphologic differences between spaced and crowded cases, especially in the anteroposterior dimensions. The small difference in posterior face height might be related to lower incisor inclination, which Hunter has
Table Xl. Comparison between the three groups from both samples of the annual rate of both angular and linear parameters in the 8- to I&year age period -. Spucwi .ModeruIely crowded n = .<4
Parumeter Angle
S-N/mandibular
Angle
S-N/occlusal
plane plane
Angle N-S-endognathion Mandibular rotation Projection endognathion Projection Anterior Posterior Mandibular “x”
indicates
Meun
on S-N from
“S”
S.D.
-0.31”
‘to.40
-0.73
10.54
-0.16 0.92”
-eO.33O -0.49
Mean
S.D.
Mean
S.D.
-m0.28” -0.58
kO.34”
-- 0.3 1”
LO.45
kO.70
-0.35
x
-0.02 0.76”
kO.21’ kO.31
t 1.02 -to.32
x
xx
0.84
mm.
20.70
x
to.56 to.49 20.47
x
0.84 mm. 2.21 mm. I .69 mm.
20.40 20.75 20.58
x
face height face height
1.08 mm. I .99 mm. I .74 mm.
length
1.32 mm.
to.30
x
1.13
to.40
x
differences
on S-N from
between
“S”
groups
which
are statistically
significant
shown to differ between the three groups, through the medium of the tongue. It might be profitable, therefore, to investigate the size and position of the tongue in spaced and crowded cases. CHANGES IN THE PARAMETERS WHICH EXPRESS THE GROWTH DIRECTION OF THE FACE Table X1 summarizes the differences found between spaced, moderately crowded, and crowded groups for the change in each of the parameters already discussed. Each of these changes was expressed as the annual rate, calculated by dividing the total change by the number of years that the cases was studied. This was done because the average period of observation was a little different between the three groups (6.65 years for the spaced cases and 5.7 1 years for the crowded cases). The angle between the S-N line and the mandibular plane diminished with age, but the reduction was similar in all three groups. The change in the angle between S-N and the occlusal plane, however, was found to be smaller for the spaced group of cases, a difference that was significant and set them apart from the other two groups. Because there was considerable variation in the change in angle N-S-endognathion, the greater mean reduction in the spaced cases fell short of statistical significance. Bjork’s method of measuring the change in inclination of the S-N line was used to estimate the amount of mandibular rotation between the two ages by superimposing the mandible itself on the outline of the most lingual and inferior aspect of the internal border of the symphysis and the mandibular canal. Although the spaced cases in both the King’s College and Burlington samples showed a greater amount of forward rotation,
Severelyimwded II = 174 ..--.
to.67
central
of
n = so
I .08 mm.
lower
change
at the 5 percent
mm.
- 0.04” 0.72” 0.71 mm.
50.38 ‘0.64
x
kO.62
I .03 mm. 2.06 mm. 1.53 mm.
20.72 20.43
1.32 mm.
20.43
level.
it was not sufficiently large to be statistically significant. When the linear dimensions of anteroposterior growth were examined, the spaced cases were found to increase to a greater extent than the crowded cases (Table XI). This was reflected in the mandibular length and in the distances from sella to projections on the S-N line of endognathion and of the lower incisai edges. However, the difference was greatest and most significant in the case of endognathion. It appears, therefore, that the mandibular symphysis is carried forward to a greater extent in the faces of the spaced cases, a change that may be associated with a slightly more forward mandibular rotation. Although Lundstrom reported similar relationships between change in incisor inclination and growth direction, he could not establish a correlation between change in spacing/crowding and growth direction, perhaps because his sample did not include a large number of spaced or severely crowded cases. Since the subjects of the present investigation were selected for intact permanent dentitions at the age of 13 to 14, there is no assurance that the severely crowded cases represent those severely crowded subjects whose premolars were removed earlier as part of a serial extraction programme. Both the studies by Ronnerman and Thilandel”’ and by Sakuda and associates,; in which similar findings are reported, also involved only children with intact dentitions. Hence, the findings can be applied at this time only to subjects with intact dentitions. The data of this study suggest that downward and deficient growth of the mandible is associated with both upright or “reclined ” mandibular incisors and with crowding in the mandibular dentition. Although not surprising in the light of the findings
Volume 82 Number 5
of Sakuda and colleagues5 and of Ronnerman and Thilander,4 it is apparent that severe crowding of the mandibular dentition tends to occur in faces that have steep mandibular plane and occlusal plane angles. Compared with subjects who have spaced mandibular dentitions, the mandibular corpus of subjects with severely crowded dentitions is shorter, the mandibular symphysis is more posterior, their mandibles grow less from 9 to 14 years of age, and the direction of growth is more downward. SUMMARY
The facial skeletal characteristics associated with spacing or crowding of the mandibular dentition were studied in the mixed and permanent dentitions of a longitudinal sample of eighty-eight subjects grouped as follows: (1) thirty-four with spaced mandibular dentitions, (2) thirty with moderately crowded mandibular dentitions, and (3) twenty-four with severely crowded mandibular dentitions. The study revealed that the severely crowded subjects had larger mandibular plane and occlusal plane angles to S-N than the others. A metric evaluation disclosed that although the anterior face heights were similar for all three groups, the severely crowded subjects had shorter posterior face heights than did the other groups. They also had shorter mandibular corpora, with both symphyses and dentitions more posteriorly positioned than in the moderately crowded or spaced subjects. During the period studied, the mandibles of the severely crowded and moderately crowded subjects grew
Lower
urch
spacing/crowding
and fucial
height
and
depth
425
forward less than did those of the subjects spaced with spaced dentitions and their mandibles rotated forward less (though not significantly so). Hence, the evidence from this selected sample is that crowded mandibular dentitions exist in a morphologically distinct supporting structure, which has a downward growth direction and a relatively deficient amount of growth. REFERENCES 1. Fisk,
2.
3.
4.
5.
6.
I.
8.
R. 0.: Normal mandibular arch changes between ages 9- 16, 1. Can. Dent. Assoc. 32: 652-658, 1966. Sanin, C., and Savara, B. S.: Factors that affect the alignment of the mandibular incisors: A longitudinal study, AM. J. ORTHOD. 64: 248-257, 1973. Lundstriim, A.: A study of the correlation between mandibular growth direction and changes in incisor inclination, overjet, overbite and crowding, Trans. Eur. Orthod. Sot., pp. 131-140, 1975. Ronnerman, A., and Thilander, B.: Facial and dental arch morphology in children with and without early loss of deciduous molars, AM. J. ORTHOD. 73: 47-58, 1978. Sakuda, M., Kuroda, Y., Wada, K., and Matsumoto, M.: Changes in crowding of teeth during adolescence and their relation to the growth of the facial skeleton, Trans. Eur. Orthod. Sot., pp. 93-104, 1976. Hunter, W. S., and Smith, B. R. W.: Development of mandibular spacing-crowding from 9 to 16 years of age, J. Can. Dent. Assoc. 38: 178-185, 1972. Hunter, W. S.: The dynamics of mandibular arch perimeter changes from mixed to permanent dentitions. In McNamara, J. A., Jr., et al.: The biology of occlusal development, Ann Arbor, 1977, Center for Human Growth and Development, University of Michigan, pp. 169-178. Bjiirk, A., and Skieller, V.: Facial development and tooth eruption: An implant study at the age of puberty, AM. J. ORTHOD. 62: 339-383, 1972.