Download Inter-Arch Tooth Size Discrepancies: Validity of Bolton Analysis

Inter-Arch Tooth Size Discrepancies: Validity of Bolton
Analysis
Edoardo Sicurezza1, Giuseppe Palazzo2
Research Assistant, Department of Orthodontics, University of Catania, Italy. 2Professor, Department of Orthodontics, University
of Catania, Italy.
1
Abstract
Study background: Bolton Index is one of the most commonly used analysis in order to evaluate tooth-size discrepancy. Even if this
measure could represent an important tool in clinical practice, many Authors questioned its widespread applicability.
The aim of this study was to compare the anterior and total tooth width ratios of an orthodontic population with the Bolton standards
and analyse differences in Bolton Index among genders and three malocclusion groups.
Methods: A sample of 647 dental casts form the Department of Orthodontics, University of Catania (312 male and 335 female
patients between 12 and 21 years old, mean age 16.9 ± 3.1 years) were considered in this study between January 2012 and June
2013. Mesiodistal tooth diameters were evaluated from its mesial contact point to its distal contact point at its greatest interproximal
diameter by using a digital calibre and then Bolton indexes were obtained on each model.
A one-way ANOVA test was conducted to compare tooth size discrepancies among different malocclusion groups and a Dunn’s
Multiple Comparison post hoc test was performed to test which means were different.
Results: Mean values and standard deviations for maxillary to mandibular anterior tooth-width ratios were 78.8% ± 3.75% and
91.8% ± 2.50%. The discrepancies outside the ± 1 SD and ± 2 SD ranges from the Bolton means were also calculated the results
were 16.9% and 61.5% respectively for BA and 21.5% and 33.8%, respectively for BO.
Conclusion: No statistically significant differences have been found concerning tooth-size disharmony among the three malocclusion
groups. Furthermore our population showed clearly a higher incidence of tooth-size discrepancies.
Key Words: Orthodontics, Bolton analysis
Introduction
clinically significant ratio as 2 SD outside Bolton’s mean [9].
Subsequent researches about Bolton indexes, conducted
in different populations, reported that tooth size discrepancies
may be influenced by several factors, including ethnical
[3,10-13], gender [14,15] and malocclusion group differences
[11,16-18].
Since Bolton’s ratio represent a useful tool for the
orthodontic treatment, clinicians should be conscious of its
intrinsic limitation due to different factors as it is based on
studies carried out on a unrepresentative sample and therefore
could result in a lack of widespread applicability.
Accordingly, the aim of this study was to compare the
anterior and total tooth width ratios of an orthodontic sample
with the Bolton standards, evaluating the differences between
the different classes of malocclusion and its applicability in
our population.
Inter-arch tooth-size relationship is an important factor in
orthodontic diagnosis and treatment planning [1,2]. In this
respect, a primary role is played by the evaluation of mesiodistal
tooth size. In fact, it is widely accepted in literature that many
malocclusions can occur as a result of abnormalities in tooth
size [1] and that a normal condition of occlusion is based on a
specific relation among teeth [3-5].
Several authors evaluated different methods of
investigation of inter-arch tooth size discrepancies during
orthodontic treatment.
Seipel [6] studied random 365 patients and concluded that
the amount of mesiodistal size of superior and inferior teeth
had a specific ratio for each type of tooth.
Neff defined a mathematic relation between tooth size and
overbite analysing 200 dental cast of orthodontic patients [7].
Nevertheless, Bolton analysis of tooth size discrepancies
is the most popular and widely used model in clinical
practice [8]. It expresses the ideal centesimal relationship
between superior and inferior arch volumes. He developed
two ratios between inferior and superior mesiodistal width,
an overall ratio (BO, Bolton Overall) of 91.3 ± 0.2 per cent,
which involves all permanent teeth except the second and
third molars, and the anterior ratio (BA, Bolton Anterior) of
77.2 ± 0.2 per cent, which considers only the sixth anterior
maxillary and mandibular teeth. The original analysis was
carried out in 1958 on 55 patients with normal occlusion,
including 44 orthodontically treated and 11 untreated subjects.
Bolton suggested that a discrepancy higher than 1 SD may be
responsible of clinical affections even if most authors defined
Materials and Methods
The study was carried out in the Department of Orthodontics,
University of Catania, Catania, Italy, between January 2012
and June 2013. A sample of 790 dental casts of patients
from the Department of Orthodontics, University of Catania
was considered in this study but only 647 met the following
selection criteria:
Good condition of dental casts.
No previous orthodontic treatment.
No absent permanent teeth (except the second and third
molars).
No severe tooth abrasion or tooth restorations.
No tooth anomalies.
Corresponding author: Giuseppe Palazzo, Department of Orthodontics, University of Catania, Italy Via Santa Sofia 78, Policlinico,
Catania 95123, Italy; e-mail: [email protected]
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OHDM - Vol. 13 - No. 3 - September, 2014
Coincidence between dental and skeletal classes.
The sample comprised 312 male and 335 female between
12 and 21 years old (mean age 16.9 ± 3.1 years). Class I
occlusion was diagnosed on a Class I molar and canine
relationship and on an ANB angle between 0 and 4 degrees;
the diagnosis of Class II occlusion was based on a Class II
molar and canine relationship as well as an ANB angle greater
than Class I; A Class III molar and canine relationship and an
ANB angle less than 0 degrees identified Class III patients.
The ethical approval for the study was obtained from the
Ethical Committee of the University of Catania.
Mesiodistal tooth diameters were evaluated from its
mesial contact point to its distal contact point at its greatest
interproximal diameter (Figure 1) by using a digital calibre as
described in literature [2,19,20].
In order to compare our sample with the Bolton’s one,
data were classified in Normal for BA and BO values < ± 1
SD, Discrepant for BA and BO values < ± 1 SD and Clinically
Significant Discrepant for values < ± 2 SD.
All measurements were expressed in millimetres and
performed by the same operator (E.S.).
Bolton indexes were obtained on each model as following:
Bolton overall ratio (%): [summed width of mandibular
twelve (6-6)/ [summed width of maxillary twelve (6-6)] x
100%
Bolton anterior ratio (%): [summed width of mandibular
anterior six (3-3)/ [summed width of maxillary anterior six
(3-3) x 100%.
Measurement error
Measurements were conducted twice by the same operator
with a distance of one month. Method error has been calculated
by using Dahlberg’s equation for repeating measurements.
Statistical analysis
The subjects were divided by gender and malocclusion
Class. Statistical computation was performed by using Prism
4.0 for Macintosh (Graphpad Software Inc, USA, 2007).
A Shapiro-Wilk test was performed to test normality. To
determine whether there was gender disphormism in tooth
size discrepancies, a Student’s t-test was performed with a
P level of significance of 0.05. A one-way ANOVA test was
conducted to compare tooth size discrepancies among different
malocclusion groups and a Dunn’s Multiple Comparison Post
hoc test was performed to test which means were different.
Figure 1. Determination of the mesio-distal widths on models.
Furthermore, frequency of discrepancies ± 1 and ± 2 SD in
each group were calculated.
Results
The results are summarized in Table 1. The Shapiro-Wilk test
showed a normal distribution for both the anterior and the
total tooth widths ratios, so we could use parametric statistical
tests.
Mean values and standard deviations for maxillary to
mandibular anterior tooth-width ratios were 79.5% ± 3.24%
and 77.86% ± 4.21% for males and females, respectively,
with a P value of 0.12; mean values and standards deviations
for the overall tooth-width ratios were 91.33 ± 2.5% and
92.11% ± 2.49% for females and males, respectively, with a
P value= 0.57.
No significant differences were found in anterior and total
tooth-width ratios according to sex (P = 0.12 and P = 0.57,
respectively), so the groups were combined, and new anterior
and total ratios were calculated: 78.8% ± 3.75% and 91.8% ±
2.50%, respectively (Table 1).
As reported in Table 2, the anterior and total tooth-size
discrepancies outside the ± 1 SD and ± 2 SD ranges from the
Bolton means were also calculated for the sample; the results
were 16.92% and 61.54% respectively for BA and 21.54% and
33.85%, respectively for BO. Analyzing BA and BO results
among the various malocclusion groups we found that there
was a high prevalence of patients with > 2DS for BA values
in each Angle’s class group. Considering BO results, Angle I
class and Angle II class showed more normal values (45.83%
and 55.56% respectively) than Angle III class patients that
belonged mainly to the > 1 SD group (Tables 3-5).
Discussion
Tooth-size discrepancy evaluation has been widely accepted
in clinical practice during orthodontic treatment plan by
several authors [2,20-23] because it plays a fundamental role
for the success of therapy [9,10,18,24,25]. The best-known
study of tooth-size disharmony in relation to treatment of
malocclusion was done by Bolton in 1958b [8] and his
standards have been proposed as a model by many studies in
literature [3,15,21,24,26,27].
Comparison with Bolton’s sample
The descriptive statistics for anterior and overall ratios among
various malocclusions groups are shown in Table 3 and 4. In
our study the means and the standard deviations of the total and
anterior ratios were slightly larger than in Bolton’s one. The
reason for this finding might be the different population of the
sample and the ethnic group. Table 5 compares anterior and
overall ratios for various populations (white and Dominican
Americans, blacks, Spanish, Peruvians, etc.) as reported by
several authors [1,3,11-13, 16,17,21,25,26].
Both the anterior and the overall ratios values were larger
than the Bolton standards in all of them, even if total ratios
were closer to Bolton’s standards. Our results are more
similar to those obtained by Paredes [2], Struiić [20], Santoro
[25] and Al-Omari [3].
If means of our samples were near Bolton’s results, more
interesting is the analysis of data when they are divided into
three groups according to the standard deviation values from
2
OHDM - Vol. 13 - No. 3 - September, 2014
Table 1. Comparison of male and female mean values of tooth size discrepancies.
Male mean ± SD (%) Female mean ± SD (%)
P value
Total mean ± SD (%)
79.50 ± 3.24
77.86 ± 4.21
0.12
78.8 ± 3.75
92.11 ± 2.49
91.33 ± 2.50
0.57
91.8 ± 2.50
Tooth ratios
BA
BO
Bolton Index
77.2
91.3
Table 2. Anterior Bolton ratios and Total (whole arch) Bolton ratios: The distribution of subjects in this study categorized by the standard
deviations of Bolton’s original study.
BA
Total
BO
Total
Normal
21.54 %
Normal
44.62%
> ± 1 SD
16.92%
> ± 1 SD
21.54%
> ± 2 SD
61.54%
> ± 2 SD
33.85%
BA
Normal
> ± 1 SD
> ± 2 SD
Table 3. Percentage of subjects with anterior tooth size ratios compared with Bolton’s standard.
Angle I Class
Angle II Class
Angle III Class
16.67 %
18.52%
28.57%
16.67 %
11.11%
28.57%
66.67%
70.37%
42.86%
BA
Normal
> ± 1 SD
> ± 2 SD
Table 4. Percentage of subjects with overall tooth size ratios compared with Bolton’s standard.
Angle I Class
Angle II Class
Angle III Class
45.83%
55.56%
21.43%
12.50%
14.81%
42.86%
41.67%
29.63%
35.71%
Table 5. Dunn’s multiple comparison post hoc test for the different malocclusion classes.
Class
N
Mean ± SD (%)
ANOVA
I
24
79.4 ± 2.7
II
27
78.6 ± 4.6
P>0.05
III
14
78.2 ± 3.7
I
24
91.8 ± 2.2
Tooth ratios
BA
BO
II
27
91.7 ± 2.8
III
14
92.1 ± 2.4
P>0.05
Table 6. Comparison between previous studies on the Bolton’s analysis.
Population
Sample size
Occlusion
Bolton
Orthodontic
55
Ideal
Crosby and Alexander
Orthodontic
109
Class I, II
Smith
Orthodontic
180
No data
Johe
Orthodontic
60
Class I, II, III
Smith
Orthodontic
180
No data
Johe
Orthodontic
62
Class I, II, III
Smith
Orthodontic
180
No data
Fernandez-Riveiro
Paredes
Orthodontic
100
No data
Author
White Americans
Blacks
Hispanics
Europeans
Dunn’s posthoc test
I-II= 0.47
II-III= 0.77
I-III= 0.31
I-II= 0.86
I-II= 0.86
II-III= 0.67
I-III= 0.76
BA
77.2
77.5
79.6
77.5
79.3
77.4
80.5
80.6
78.3
BO
91.3
91.4
92.3
91.6
93.4
91.3
93.1
93.4
91.2
Strujić
Orthodontic
111
Class I, II, III
78.2
91.8
Dominican Americans
Present Study
Santoro
Orthodontic
Orthodontic
647
54
Class I, II, III
No data
78.8
78.1
91.8
91.3
Peruvians
Bernabè
School children
200
Malaysians
Othman
School children
40
No data
78.8-75.8
91.8 - 90.8
Saudi Arabians
Iranians
Sulaimani
Ta
Zhang
Fattahi
Orthodontic
School children
Orthodontic
Orthodontic
98
110
110
200
Class I, II, III
Class I, II, III
No data
Class I, II, III
81.1
77.5
77.6
79.0
93.9
90.9
91.1
91.7
Jordanians
Al-Omari
School children
367
No data
78.6
92.2
Chinese
mean as reported by various authors [11,21,26]. Originally a
ratio greater than ± 1 SD from Bolton mean values indicated
a need for diagnostic consideration [8]. A significant
discrepancy in the anterior ratio was found in 61.5% of the
patients (BA > ± 2 SD); on the other hand, a discrepancy > ± 2
3
Different malocclusions 77.8-78.4
90.8 - 91.3
SD in the total ratio (BO) was found in 33.8% of the subjects.
Even if BA and BO mean values of our sample were not
so different when compared with Bolton’s results, the analysis
of our population’s SD range putted in evidence a greater
difference with the Bolton’ standard. This evidence might
OHDM - Vol. 13 - No. 3 - September, 2014
find answer in the sample chosen by Bolton who selected 55
subjects with an ideal occlusion, while our sample was made
by pre-orthodontic treatment patients. So the Bolton standards
may underestimate the incidence of tooth-size discrepancies
in a treated population [21]. Furthermore it seems to be
interesting to evaluate the great variability of our sample with
respect to the interact relationship, as confirmed by most other
authors in different populations [11,21,26]. This could require
a deeper understanding of its possible clinical therapeutic
evaluation in a large portion of the population.
Bolton’s analysis remains the key point in the orthodontic
treatment plan, nevertheless several authors [1,2,12,16,20]
found some limitation in his studies. Bolton’s sample was
obtained from 55 models with excellent occlusion - 44
orthodontically treated and 11 untreated. Furthermore Bolton
didn’t explain in detail the population’s ethnicity and the
gender composition. Unlike the initial Bolton’s sample, our
study was conducted on all young patients (12 to 21 years)
from Southern Italy. This aspect could be very interesting
considering that, as clearly reported in Table 6, BA and
BO values seemed to vary consistently among different
populations in relation to their ethnicity.
Comparison of tooth size discrepancies between different
malocclusion classes
Different results have been proposed in literature concerning
the relationship between the malocclusion classes and the
tooth size ratios.
Strujić [20] and Qiong [28] found statistically significant
differences among the malocclusion classes, especially
regarding the overall ratio.
Sperry, Lavelle, Nie [10,14,29] showed in their studies
that Class III subjects presented an higher mandibular
tooth size and smaller maxillary teeth. Also Araujo and
Souki [24] reported that individuals with Angle Class I and
III malocclusion had more tooth size discrepancies when
compared with Class II subjects.
On the contrary, in our research, the statistical analysis
of Bolton anterior and overall ratios calculated in the three
classes of malocclusion studied showed no significant
difference (P = 0.88 and P= 0.69 respectively for BA and BO,
Table 5).
Our results was in agreement with other authors’ findings:
in fact Laino [27] studied 94 dental cast and reported no
relationship between the three malocclusion group and the
Bolton index; Crosby [11] found a large number of inter-arch
tooth size discrepancies in the three malocclusion samples
but none of these was statistical significant; finally Johe [21]
reported that Bolton Index was not influenced by the Angle’s
skeletal classification and confirmed no statistical differences
among malocclusion groups.
Tooth size discrepancy between genders
The results of the present study showed no significant
differences for overall and anterior ratios between male and
female (Table 1). This findings supports a diffuse conclusion
in literature as recently reported by O’Mahony [22], Johe
[21], Al Sulaimani [26], Araujo [24] and Othman [23]. On
the contrary, other authors founded differences in tooth width
ratio between male and female samples [13-16] but it is
important to note that in studies where differences have been
found, they have been small, with male having slightly larger
ratios [20].
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- No statistically significant differences have been found
concerning tooth-size disharmony among the three
malocclusion groups.
- Analogously no gender difference has been discovered
between male and female subjects.
- Even if the mean values of BA and BO of our
Italian sample were similar to Bolton standards, our
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on the evaluation of the obtained standard deviation
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