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10.5005/jp-journals-10021-1109
RESEARCH ARTICLE
Dental Arch Form Analysis in Gujarati Males and Females having Normal Occlusion
Dental Arch Form Analysis in Gujarati Males and
Females having Normal Occlusion
1
Vishnu Jagdishbhai Patel, 2Amarjitsingh F Bhatia, 3Sonali M Mahadevia, 4Shrey Italia, 5Malay Vaghamsi
ABSTRACT
Aim: To analyze and determine maxillary and mandibular arch form of Gujarati (Indian) adults with normal occlusions.
Materials and methods: Fifty seven study models of untreated individuals were examined. Six measurements of both the arches were taken,
and five independent ratios were determined. Character and shape of both the arches were studied and compared using various statistical analyses
for males and females between both the arches.
Results: As moving from anterior to posterior, both the arches diverge proportionally, except in second molar area where slight convergence toward
midline was noted. Females had proportionally narrower arch dimensions than those for males. Five arch forms were determined according to
relative deviations of various ratio combinations, and all subjects were classified for mandibular arch form by nonhierarchical stepwise method.
Keywords: Dental arch form, Occlusion, Mandibular arch, Maxillary arch, Arch form analysis.
How to cite this article: Patel VJ, Bhatia AF, Mahadevia SM, Italia S, Vaghamsi M. Dental Arch Form Analysis in Gujarati Males and Females
having Normal Occlusion. J Ind Orthod Soc 2012;46(4):295-299.
INTRODUCTION
In human dentition, ideal occlusion is a rarity due to variations
in dentition, which are exceedingly common. Even in normal
occlusion, variations are found at various levels in the dental
arches and one of the most commonly variable parts of the
dentition is the mandibular arch form. According to prior
literature,1 form and dimension of the mandibular dental arch
is a factor of stability of the therapeutic results. It is known
that the mandibular arch possesses different shapes in different
individuals though each one has normal occlusion. The factors
governing mandibular arch form are many and it is believed
that during orthodontic treatment procedures, one must not
attempt to alter the original arch form to have stable results.
Several studies had been performed associating a
geometric curve form with the mandibular dental arch form.
The concept of a circular arch form of the anterior part of the
arcade2 has been used by some authors in the straight wire
techniques3 as well as by the occlusodontists.4
1
Professor,
(3rd year)
2,3
Professor and Head, 4Reader, 5Postgraduate Student
1,3-5
Department of Orthodontics and Dentofacial Orthopedics
Ahmedabad Dental College, Ahmedabad, Gujarat, India
2
Department of Orthodontics and Dentofacial Orthopedics, KM Shah
Dental College and Hospital, Vadodara, Gujarat, India
Corresponding Author: Vishnu Jagdishbhai Patel, Professor, Department
of Orthodontics and Dentofacial Orthopedics, Ahmedabad Dental College
Ahmedabad, Gujarat, India, e-mail: [email protected]
In the present day orthodontic practice, with the introduction of new materials and new techniques,5 having greater
precision and for the convenience to the orthodontists, and
comfort of the patients; preformed archwires have gained
popularity. The shape of preformed archwires, especially
superelastic nitinol wires can not be altered easily. Hence,
the choice of the arch form of the mandibular dental arches
has become essential when using these elastic arches.
Some authors tend to individualize the arch form to respect
original mandibular intercanine width during treatment6-8 or
by a computer-assisted determination of an ideal dental arch
form9 for that particular individual.
To understand the shape and curvatures of mandibular arch,
Monique Raberin et al10 measured six arch dimensions,
calculated five ratios and suggested 6th degree polynomial
curves to describe five different arch forms.
Keeping all these facts in mind, the present study is carried
out with following aims and objectives:
1. To measure, correlate and compare the dimensions of
mandibular and maxillary arch at canines, first molars and
second molar levels in adult males and females having
normal occlusion and acceptable face.
2. To calculate and compare the different ratios in mandibular
and maxillary arch so, as to define and differentiate the arch
form between both the arches and in males and females.
3. To understand the probability of different types of
mandibular arch forms so, as to determine the most
frequent and rare types in Gujarati males and females.
4. To help the clinician to select proper shape of preformed
archwire for particular patient.
MATERIALS AND METHODS
Received on: 1/1/12
Accepted after Revision: 31/3/12
The sample for the present study consists of 57 Gujarati
students (30 females and 27 males) of Government Dental
The Journal of Indian Orthodontic Society, October-December 2012;46(4):295-299
295
Vishnu Jagdishbhai Patel et al
College and Hospital, Ahmedabad within the age range of 17
to 25 years. As there are significant changes to arch form in
accordance with aging process11,12 this age range was selected.
The reason for selecting only those subjects who have Class I
normal occlusion is to eliminate variations that are likely to
occur due to change in dentoalveolar skeletal pattern of Class II
and III malocclusions.13,14
The criteria for sample selection are:
1. A person belonging to Gujarati community for at least two
prior generations was selected.
2. An individual must show an acceptable face and normal
occlusion with complete intact permanent dentition without
proximal restorations or prosthesis.
3. The dental arches must have coinciding midline.
4. The dental arches must apparently show bilateral symmetry.
The impressions of upper and lower dental arches were
taken in alginate impression material and casts were prepared in
dental stone. Routine trimming, shaping and finishing of the
casts was done.
Three sagittal and three transverse arch dimensions of both
the arches were measured at following reproducible reference
points as shown in Figure 1.
A. Mid-incisal edge (labial side midline)
B. Canine tip (right and left)
C. Mesiobuccal cusp tip of first molar (right and left)
D. Distobuccal cusp tip of second molar (right and left).
Dimensions were obtained by measuring the maximum linear
distance between the reference points.
Mandibular
arch
Maxillary
arch
A.
1.
2.
3.
Transverse
Intercanine width
LL33
Mean intermolar width
LL66
Posterior intermolar width LL77
UL33
UL66
UL77
B.
1.
2.
3.
Sagittal
Canine depth
Mean arch length
Total arch length
UL31
UL61
UL71
LL31
LL61
LL71
These six factors determine both the form and dimensions
of dental arch. From these dimensions, five ratios for both
the arches (31/33, 61/66, 71/77, 33/66 and 61/71) were
estimated for arch form analysis.
Percentage relative deviations of each ratio from its overall
mean value were calculated for mandibular arch and the cases
were classified into five categories of arch form according to
these percentage relative deviations. This is a nonhierarchical
stepwise method, which each time it is repeated, questions
the subject’s membership of one group or another.
All the measured and estimated parameters were
statistically analyzed for various comparison and correlations.
296
Fig. 1: Reference points and associated measurements
RESULTS
On correlation comparison, there is high correlation at each
level when transverse parameters were compared with one
another in both the arches. Same is true when sagittal parameters
were compared with one another. However, when the correlation
is examined between the transverse and sagittal parameters,
strong correlation is found between different parameters except
for the dimension of the arch measured at the level of second
permanent molar.
Comparison of the five calculated ratios between males and
females (Tables 1 to 4) suggests that the values for the ratios
61/66 and 71/77 differ significantly with higher values in
females for both the arches indicating relatively narrower
arches in females than in males. Values for the ratios 31/33,
33/66 and 61/71 do not differ significantly between males
and females and for both the arches.
DISCUSSION
Previous literatures and studies on dental arch shape used
conventional anatomical points on the incisal edges and molar
cusp tips, etc. in order to classify dental arch forms by means of
various mathematical forms,15 such as spline curves,16 and the
beta function. 17 Despite their biological significance,
conventional anatomic points do not provide clinical evidence
of appropriate archwire blank forms. On the contrary, landmarks
taken on the vestibular surface of the teeth [facial axis points
(FA points)] give direct representation of clinical archwire
shape18 as these correspond fairly well to the position of the
brackets for straight wire therapy.
According to Brader6 and Proffit WR19 dental arch form
consists of dental units arranged in unique positions along a
compound curve which represents a steady state of equilibrium
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Dental Arch Form Analysis in Gujarati Males and Females having Normal Occlusion
Table 1: Comparison of arch dimensions at various levels of both the arches between male and female (n = 57)
Dimension
Mandibular
arch
Maxillary
arch
Male (n = 27)
Female (n = 30)
Significance
Mean
SD
Mean
SD
Transverse
LL33
LL66
LL77
26.06
45.18
54.46
1.76
2.19
2.62
25.68
43.25
51.72
1.32
1.74
2.49
NS
p < 0.0005
p < 0.0005
Sagittal
LL31
LL61
LL71
5.89
24.27
39.81
0.87
1.68
2.19
6.00
24.43
39.80
1.31
1.98
2.44
NS
NS
NS
Transverse
UL33
UL66
UL77
35.15
53.35
59.02
2.00
1.98
2.40
34.10
50.67
56.35
1.67
2.71
2.63
p < 0.05
p < 0.0005
p < 0.0005
Sagittal
UL31
UL61
UL71
9.17
28.24
43.63
0.95
1.68
2.13
9.05
28.35
43.77
1.65
2.37
2.85
NS
NS
NS
NS: Not significant
Table 2: Comparison of the five calculated ratios between maxillary and mandibular arch (n = 57)
Ratio
Maxillary arch
31/33
61/66
71/77
33/66
61/71
Mandibular arch
Significance
Mean
SD
Mean
SD
0.26
0.55
0.76
0.67
0.65
0.037
0.043
0.057
0.037
0.019
0.23
0.55
0.75
0.59
0.61
0.046
0.043
0.057
0.036
0.017
p < 0.0005
NS
NS
p < 0.0005
p < 0.0005
NS: Not significant
Table 3: Relative deviation of each ratio from its overall mean value to
determine the shape of the mandibular arch in males and females (n = 57)
Ratio
LL31/33
LL61/66
LL71/77
LL33/66
LL61/71
Male (n = 27)
Female (n = 30)
Mean
SD
Mean
SD
–1.26
–2.17
–2.36
–2.17
–0.25
16.66
7.50
6.29
6.32
2.47
1.72
2.72
2.82
0.76
0.55
23.14
7.45
7.81
5.72
2.96
delimited by the counter balancing force fields of the tongue
and of the circumoral tissues. Preformed archwires have
tendency to alter the arch form, if they are left longer than 6 to
7 weeks. Our findings from this study confirm that the ideal
dental arch has not a single and unique form, even in untreated
adults with normal occlusion.
Valerie Ronay et al20 in their study concluded that both
reference points (1. FA, the most prominent part of the central
lobe on each crown’s facial surface, and 2. WALA, a point at
the height of the mucogingival junction) derived arch forms
were individual and, therefore, could not be defined by a
generalized shape. They also pointed out that WALA points
proved to be a useful representation of the apical base and
helpful in the predetermination of an individualized dental arch
form.
In the present study, when each parameter was compared
with similar parameter of opposite sex (Table 1), it was found
that no significant difference was found for any sagittal
parameter in both the arches. The arch width of mandibular
arch at the level of canine is similar for males and females but
significant difference is found in the arch width at the level of
canine in maxillary arch. Highly significant differences were
also noted for arch width at the level of first and second
permanent molars in both the arches between males and
females. Males showed greater values for these parameters.
High correlation at each level between transverse
parameters and similar correlation between sagittal parameters
suggest that as we move from anterior to posterior, there is
Table 4: Distribution of the five forms of mandibular arch according to sex
No.
1
2
3
4
5
Form name
Narrow
Wide
Mid
Pointed
Flat
Male row (%)
30.00
66.70
46.20
44.40
40.00
Female raw (%)
70.00
33.30
53.80
55.60
60.00
The Journal of Indian Orthodontic Society, October-December 2012;46(4):295-299
Total
10
15
13
9
10
Total percentage
17.50
26.40
22.80
15.80
17.50
297
Vishnu Jagdishbhai Patel et al
well-proportioned increase in the arch width in both the arches
as well as the length of the arch is also increasing in proportion.
Results of correlation comparison between the transverse and
sagittal parameters suggests that the arch width is in proportion
to arch length from incisor to first permanent molar while
position of the second molar does not follow the similar arch
curve as followed by rest of the teeth.
To understand, determine and classify the dental arches
into various arch forms, various ratios were estimated from
the recorded arch parameters. The values of ratios 31/33, 61/
66 and 71/77 suggest whether arch is narrow or wide. Their
higher values than their respective means suggest narrow arch
form. Ratio 31/33 describes anterior arch form. If their values
are excessively high than their mean, it suggests pointed
anterior segment and if their values are excessively lower than
their mean, it suggests flat anterior segment. Values of ratios
33/66 and 61/71 suggest posterior divergence tendency of
the arches distal to canines.
Comparison of the five calculated ratios between maxillary
and mandibular arches (by paired t-test) is shown in Table 2.
The value for ratio 31/33 differ significantly indicating
significant difference in anterior curve or intercanine arc
shape. Values for ratios 33/66 and 61/71 differ significantly
indicating significant divergence of the mandibular arch distal
to canines than the maxillary arch. Ferrario VF et al21 also
studied maxillary and mandibular arch forms and dimensions
in human permanent dentition assessed by Euclidean distance
matrix analysis and concluded that the maxillary arch was larger
than the mandibular arch and arch shape was also significantly
different between both the arches.
Trivino T (2008) et al22 in their study concluded that the
mandibular dental arch is represented by 23 forms; thus, a
normal dental arch cannot be represented by only one simple
arch form.
Now to determine the arch forms of mandibular arch of an
individual case, percentage relative deviations of each ratio
from its overall mean value (Table 3) are estimated and
depending upon relative positivity and negativity of each ratio,
the arch form of that particular case is decided by a
nonhierarchical stepwise method as follows:
1. If all three sagittal/transverse ratios were positive, then
the arch form is considered to be narrow.
2. If all three sagittal/transverse ratios were negative, then
the arch form is considered to be wide.
3. If none of the ratios significantly deviates from the average,
the arch form is considered to be mid.
4. If the sagittal/transverse ratio at the level of canine is too
high as compared with others, then the arch form is
considered to be pointed.
5. If the sagittal/transverse ratio at the level of canine is too
low as compared with others then the arch form is
considered to be flat.
All the cases are thus, classified into one of the arch-form
out of five different types. The distribution of subjects
298
Fig. 2: Relative deviation for each form, of each ratio from its
overall mean value
Fig. 3: Arch guide of mandibular dental arch
(according to mean arch dimensions of each form)
according to these five forms (Table 4) is more or less
balanced with a frequency of each group varying between 15.8
and 26.40% showing predominance of wide arch form and
fewer tendencies for pointed arch form. Narrow arch form is
more common (70%) in females whereas wide arch form is
more common (66.70) in males. Mid and pointed arch forms
are relatively equally distributed between both the sexes. Flat
arch form is somewhat more common (60%) in females.
Figures 2 and 3 show the various types of arch forms
derived from the mean values of various parameters of
different type for Gujarati population. This may help us to
correlate the arch form of an individual and accordingly we
may select the preformed archwire of proper shape and
dimension for the better and efficient diagnosis and treatment
of an individual. Another mode to identify patient’s arch form
is to find out the five ratios as shown in Table 3 and Figure 2
and calculate their percentage relative deviation from the
overall mean as shown in the Table 3 and matching the closest
JAYPEE
JIOS
Dental Arch Form Analysis in Gujarati Males and Females having Normal Occlusion
readings of percentage relative deviation with the finding shown
down in the Figure 2; individual’s membership to one of the
five arch form group can be determined.
CONCLUSION
Correlation comparison between sagittal and transverse
measurements suggest that there is a uniformity and proportion
in arch dimensions from mid incisor area to first permanent
molar, however, the placement of second molar does not follow
the same uniformity and proportion. Transverse arch dimensions
are significantly larger in males than in females at all levels
from canine to second permanent molar in both arches.
Comparison of various ratios suggests proportionally
narrow intercanine width in maxillary arch as compared with
mandibular arch. Mandibular arches have greater divergence
as moving from canine to molars.
The idea of a single, standard arch form could not be
expected in this sample of untreated adults having normal
occlusion, but, arch form distribution in at least five different
groups by special combination of the five calculated ratio
values can be helpful in this regard. Arch form distribution in
five different groups by special combination of the five
calculated ratio values indicates greater tendency for wider
arch and least for the pointed arch form. Females showed
greater tendency for narrow arch form while males showed
greater tendency for wider arch form.
The mean value of various ratio for particular arch form can
be utilized to determine subject’s (belonging to same race)
membership to one of the five arch form.
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