A New Method to Measure and Assess Tooth Size and Tooth Size Discrepancy Via Circumferential Measurements using Stereomicroscope

Abstract

An accurate evaluation of tooth size and tooth size discrepancy is critically important in orthodontic diagnosis and treatment planning. The purpose of this study was to establish a new method to measure and assess tooth size and tooth size discrepancy with accuracy and reproducibility, named as circumferential tooth size (CFT), circumferential anterior tooth size ratio (CAR), circumferential overall tooth size ratio (COR) respectively. Total 128 dental models were scanned via Hirox digital stereomicroscope for the fabrication of the digital models. Dental models were selected on the basis of inclusion criteria. All the measurements were obtained with the accuracy of 0.1×10-6 mm; the mean and the SD for the CFT, CAR and COR were calculated. The developed norms for the CFT, demonstrated significantly greater values for males in relation to females. More precisely, there were statistically significant differences observed in different variables (*p 0.05 to ***p 0.001). CAR and COR ratio show slight greater value for males without any statistically significant differences. The findings provide valuable information that CFT cover the tooth size in all dimensional aspects. For the prediction of ideal occlusion to be achieved at the finishing stage, orthodontist needs to evaluate CAR and COR ratios via proposed method.

Full text

Fazal Shahid et al.: Tooth Size Discrepancy Via Circumferential Measurements
Original
A New Method to Measure and Assess Tooth Size and Tooth Size Discrepancy
Via Circumferential Measurements using Stereomicroscope
Fazal Shahid1), Mohammad Khursheed Alam1), Mohd Fadhli Khamis2), Atsuo Komori3),
Katsutoshi Kubo3) and Hatsuhiko Maeda3)
1) Orthodontic Unit, School of Dental Science, Universiti Sains Malaysia, Kelantan, Malaysia
2) Forensic Dentistry Unit, School of Dental Science, Universiti Sains Malaysia, Kelantan, Malaysia
3) Department of Oral Pathology, School of Dentistry, Aichi Gakuin University, Nagoya, Japan
(Accepted for publication, July 13, 2015)
Abstract: An accurate evaluation of tooth size and tooth size discrepancy is critically important in orthodontic
diagnosis and treatment planning. The purpose of this study was to establish a new method to measure and
assess tooth size and tooth size discrepancy with accuracy and reproducibility, named as circumferential tooth
size (CFT), circumferential anterior tooth size ratio (CAR), circumferential overall tooth size ratio (COR)
respectively. Total 128 dental models were scanned via Hirox digital stereomicroscope for the fabrication of the
digital models. Dental models were selected on the basis of inclusion criteria. All the measurements were
obtained with the accuracy of 0.1×10-6 mm; the mean and the SD for the CFT, CAR and COR were calculated.
The developed norms for the CFT, demonstrated significantly greater values for males in relation to females.
More precisely, there were statistically significant differences observed in different variables (*p 0.05 to
***p 0.001). CAR and COR ratio show slight greater value for males without any statistically significant
differences. The findings provide valuable information that CFT cover the tooth size in all dimensional aspects.
For the prediction of ideal occlusion to be achieved at the finishing stage, orthodontist needs to evaluate CAR
and COR ratios via proposed method.
Key words: Circumferential tooth size, Tooth size discrepancy, Digital dental models.
Correspondence to: Dr. Mohammad Khursheed Alam, Orthodontic Unit,
School of Den tal Science, Universiti Sains Malaysia, Kubang Kerian,
16150 Kot a Bharu, Kelantan, Malaysia; Tel: + 60142 926 987; Ema il:
dralam@gmail.com, dralam@usm.my
Introduction
In ort ho don tic diagnos is and trea tmen t plann in g, great
importance has been attached to evaluating the tooth size and tooth
size discrepancy. Linear measurements have been incorporated
into various dental model analyses to help the clinician to measure
the tooth size and tooth size discrepancies to establish the most
appropriate treatment plan1-3).
Variatio ns in too th size and tooth size rati o have been
connected with diverse ethnic foundations and occlusion status4-
9). Inter maxillary tooth size discrepancy is not infrequent in many
populations1,10,11). From a clinical point of view, ideal balance ought
to exist between the mesiodistal tooth sizes of the maxillary and
mandibular arches to assure correct interdigitation, overbite and
overjet at the consummation of orthodontic treatment12-14).
The time in which the orthodontic practice is currently being
known as “digital era” the computerized advances are no doubt
used to resolve the past confinement of the patient record keeping
and management15). Digital models have facilitated the automated
calculation of tooth size ratios once the mesial and distal points
of each t oo th have been id en tified16- 21). D igital models have
advantages of being faster and providing easier storage of data14,
22). Digital study models have been found to be an appropriate
altern ative to t ho se der ived usin g plas ter models and d igital
calipers14 ,16-18,23 ).
Analysis o f tooth size discrep ancy24, 25) is of extraord inary
importance for orthodontic diagnosis and treatment planning and
con si dered a s a seventh “key” to o cc lusion26) . Some stud ies
investigated ra ce an d sex di fferences1 ,5) . Other auth ors have
suggested no significant differences in the tooth size ratio with
different malocclusion10 ,27,28).
A specific measurement should assess the tooth size and tooth
size discrepancy, independent of mesiodistal, buccolingual and
diagon al lin ear measurements. Our study investigated a new
method to measure the tooth size and tooth size discrepancy and
named as circumferential tooth size (CFT), circumferential anterior
tooth size ratio (CAR), circumferential overall tooth size ratio
(COR) respectively. CFT, CAR and COR do not depend on any
Journal of Hard Tissue Biology 24[4] (2015) 305- 310
© 2015 T he Hard Tissue Biology Netwo rk Association
Printed in Ja pan, All rights res erved.
CODEN-JHT BFF, ISSN 1341-7649
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J.Hard Tissue Biology Vol. 24(4):305 -310, 2015
Figure 1. Circumferential tooth size measurement Figure 2. Hirox digital stereomicroscope
Fig ure 3. Fabrication of the di gital models vi a hirox digit al
stereomicroscope and circumferential tooth size measurements
linear measurement, CFT would be especially valuable whenever
previously established tooth size measurements, such a s the
mesiodistal, buccolingual and diagonal cannot be used accurately
because of their dependence on varying factors like caries and
tooth wear.
The CFT, CAR and COR
The CFT, CAR and COR are the new measurements for
assessing the tooth size and tooth size discrepancy of the maxilla
and the mandible via digital dental models.
CFT
The CFT can be found by locating the maximum perimeter of
the tooth (Fig. 1).
CAR and COR
The CAR and COR can be used to iden tify the tooth size
discrepancy. Fo r CFT in orthodontics CAR and COR c an be
obtained by the following formula
CAR = ×100
COR = ×100
The purposes of this study were to establish the norms for
Pakistani population with regard to CFT, CAR and COR using
stereomicroscopic digital dental models. In addition to the norms
of ci rc umferential dimension s an d ra ti os, the sex an d side
differences were also investigated.
Materials and Methods
Dental impression and personal information were collected
only after informed consent has been obtained from the subjects.
This study was approved by the Human Ethics Committee of the
Universiti Sains Malaysia (USM). Current research was outlined
and directed as indicated by the ru les of st rength ening the
Reporting of Observational studies in Epidemiology (STROBE),
and we used the STROBE guidelines in this manuscript29).
Sample size calculation
Sample size were calculated based on our pilot study by using
PS software30). The p ar amet ers we re a s follo w: p ower 0 .8,
significant level 0.05, standard deviation (from the pilot study)
1.8mm, mean difference 0.9mm and equal ratio between groups.
The estimated sample size was 64 females and 64 males. Three
thousand five hundred eighty-four variables were measured with
the following inclusion and exclusion criteria.
Inclusion criteria
The in clusion criteria incl ude hea lt hy subject s with a ge
between 18 – 24 years, having full dentition in both arches
excluding the third molars, no history of orthodontic treatment,
ideal occlusions with class I incisor relationship according to
British standards institute, class I molar and canine relationship,
no crowding, no spacing, no rotation s along with good quality
study models for digital scanning and acquisitions were selected.
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Fazal Shahid et al.: Tooth Size Discrepancy Via Circumferential Measurements
Table 1. Norms based Circumferential Tooth Size Measurements
Variables* Male Female 95% CI P
Mean SD Mean SD Mean diff. Lower Upper
11 27.24 1.82 25.75 1.73 1.49 0.89 2.09 .001 ***
12 22.47 1.78 21.52 1.84 0.95 0.35 1.56 .002 **
13 25.60 1.75 24.41 1.79 1.20 0.60 1.79 .001 ***
14 27.35 2.02 26.24 1.94 1.10 0.44 1.77 .001 ***
15 26.76 1.84 25.50 2.10 1.26 0.60 1.92 .001 ***
16 37.32 2.31 35.88 1.73 1.43 0.74 2.12 .001 ***
17 31.98 2.91 29.92 3.02 2.06 1.06 3.06 .001 ***
21 27.24 1.82 25.75 1.73 1.49 0.89 2.09 .001 ***
22 22.47 1.78 21.52 1.84 0.95 0.35 1.56 .002 **
23 25.60 1.75 24.41 1.79 1.20 0.60 1.79 .001 ***
24 27.34 2.02 26.24 1.94 1.10 0.43 1.77 .001 ***
25 26.76 1.83 25.50 2.10 1.26 0.60 1.92 .001 ***
26 37.32 2.31 35.88 1.73 1.43 0.74 2.12 .001 ***
27 31.98 2.91 29.92 3.02 2.06 1.06 3.06 .001 ***
31 19.32 1.54 18.34 1.64 0.99 0.45 1.52 .001 ***
32 20.12 1.36 18.97 1.49 1.15 0.67 1.63 .001 ***
33 23.08 1.44 21.48 1.84 1.60 1.05 2.15 .001 ***
34 23.90 1.68 23.02 1.81 0.89 0.30 1.47 .003 **
35 25.34 1.55 24.43 2.11 0.91 0.29 1.53 .004 **
36 36.18 2.30 34.18 4.08 2.00 0.91 3.09 .001 ***
37 33.57 2.64 32.38 2.26 1.19 0.36 2.02 .005 **
41 19.32 1.54 18.34 1.64 0.99 0.45 1.52 .001 ***
42 20.12 1.36 18.97 1.49 1.15 0.67 1.63 .001 ***
43 23.08 1.44 21.48 1.84 1.60 1.05 2.15 .001 ***
44 23.90 1.68 23.02 1.81 0.89 0.30 1.47 .003 **
45 25.34 1.55 24.43 2.11 0.91 0.29 1.52 .004 **
46 36.18 2.30 34.18 4.08 2.00 0.91 3.09 .001 ***
47 33.57 2.64 32.38 2.26 1.19 0.36 2.02 .005 **
*FDI notation; CI:
confidence interval; SD: standard deviation; Mean diff.: mean differences (***p 0.001), (**p 0.01) and (*p 0.05).
Table 2. Right and Left Comparison for Circumferential Measurements
Maxilla Mandible
variables Mean diff. SD 95% CI P Mean diff. SD 95% CI P
Lower Upper Lower Upper
CI 0.01 .004 -.001 .001 .946 0.01 .002 -.001 .000 .224
LI 0.01 .005 .000 .001 .303 0.01 .002 .000 .001 .258
CI 0.01 .004 -.001 .001 .963 0.01 .004 .000 .001 .221
IPM 0.01 .007 -.001 .002 .584 0.01 .003 -.001 .000 .328
2PM 0.01 .002 -.001 .000 .504 0.01 .003 -.001 .000 .151
IM 0.01 .002 -.001 .000 .028 0.01 .003 .000 .001 .741
2M 0.01 .003 -.001 .000 .392 0.01 .003 -.001 .000 .106
CI: central incisor; LI: lateral incisor; C: canine; IPM: 1st premolar; 2PM: 2nd premolar; IM: 1st molar; 2M: 2nd molar;
CI: confidence interval; Mean diff.: mean differences; SD: standard deviation.
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Table 3. CAR and COR Ratios with Sexual Dimorphism.
Sex Mean SD SE 95%CI
Lower Upper p
CAR M 83.09 3.52 0.41
F 82.05 4.01 0.50
COR M 88.79 3.13 0.36
F 88.16 5.27 0.66
CAR: ci rcumferential anterior ratio; COR: circumferential overall ration; CI: confidence in terval;
SD: standard deviation; SE: standard error mean.
Exclusion criteria
Subject who have inter proximal caries or restoration, missing
or supern umerary teeth, teeth wear that affect the tooth size
measurement and damage casts were excluded. Dental impressions
of the upper and lower arches of the each subject were taken with
alginate impression material (Zhermack Orthoprint alginate ISO
1563 –ADA 18 made in Italy) and poured with dental stone (Type
III hard plaster quick stone made in China) in accordance with
the manufacturer’s instructions and labeled accordingly.
Error study
20 % of dental cast were randomly selected for intra observer
errors. The time interval b etween the first and second reading
were approximately 2 weeks. The method error was analyzed by
the Dahlberg’s double determination formula31). ME = Σ (x1-x2)
2/2n; n = number of sample.
Measurement of CFT
Dental models of each subject for maxillary and mandibular
arches were scanned via Hirox digital stereomicroscope (HIROX
KH7700, Japan) for the fabrication of the digital models. CFT
were carried out via stereomicroscope (SM) scanned digital models
for maxillary and mandibular arches (Figs. 2 and 3). SM was
proven as valid19) and reliable tool for such measurements with
the accuracy of 0.1×10-6mm.
Statistical analysis
Data collected by the investigators were first entered into Excel
(Microsoft, Redmond, Washington, USA). Collected data were
screened for any missing values or outliers and for validity of
distributio n assumptions. To summarize the data, means a nd
standard deviations of CFT were calculated. An independent
samples t-test was used to evaluate differences for CFT in males
and females. The paired sample t test was u sed to determine
differences in teeth size between the right and left side of the
maxillary and mandibular arches. A P value 0.05 was considered
to be statistically significant. All statistical analyses were performed
in SPSS (IBM SPSS Statistics Version 22.0, Chicago, USA).
Results
Error of the method
The method error was analyzed by the Dalhberg’s double
determination formula, showed the value of 0.973mm for CFT.
The co mb in ed error fo r any of the variables was sma ll and
considered to be within acceptable limit31 ).
CFT norms and inter sex disparities
Table 1 shows CFT comparisons between males and females
using stereomicroscopic digital models. The developed norms for
the CFT, demonstrated with significantly greater values for males
in relation to females. Mo re precisely, there were statistically
significant differences observed in different variables (*p 0.05
to ***p 0.001).
CFT com pariso n s ide s dis pariti es for the max ill ar y a nd
mandibular teeth
Table 2 shows disparities between the right and left side for
the CFT maxillar y and mandibular teeth size. There were no
statistically significant differences observed in all variables.
CAR and COR ratio and inter sex disparities
Table 3 shows CAR and COR ratio norms with slight greater
value for males without any statistically significant differences.
Discussion
In orthodontic diagnosis and treatment planning, the evaluation
of the tooth size and tooth size discrepancy is an indispensable
step and this investigation is generally determined by study model
analysis. To evaluate this relationship, various linear measurements
by sliding calipers and digital models have b een used3, 14,1 6-19 ).
Digital dental models were considered as a valid and reliable tool
for d i ff ere nt t o oth size measu r em ents 17 ,1 9, 20 ,3 2) . Too th size
measurements were done with the accuracy of 1×10-2mm using
digital caliper on the plaster models, emodels, and anatomodels
and suresmile software with 0.1 mm33) the current study SM digital
models is with the accuracy of 0.1×10-6 mm which is a valid
tool19).
The most popular parameter for assessing the tooth size and
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-0.80 2.06 0.385
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Fazal Shahid et al.: Tooth Size Discrepancy Via Circumferential Measurements
tooth size discrepancy remains the mesiodistal tooth width, but it
is affected by various factors and can often be misleading. When
using the mesiodistal tooth width, factors such as the patient’s
age, attrition and time consumption, which makes the interpretation
of this tooth size and tooth size discrepancy much more complex.
To overcome these problems, investigator measured the tooth size
vi a mesio d i s t al1, 12 ), bucc o l i n gual 34) an d diag o n a l cr own
diameters35). Current study investigated the tooth size via CFT to
assess the tooth size via alternate method. Tooth size may assume
an imperative part in the etiology of malocclusions, should be
considered for various analyses in orthodontic examination and
treatment5). Thus CFT is the alternate way to measure the tooth
size from different perspective to help in the examination and
treatment planning. The proposed CFT values will be of great
importance in orthodontics for the ideal treatment to finish with
proper interdigitation, overbite and overjet.
Nature has given a perfect proportion for teeth to occlude in
proper relation. These relations were explored by means of mesial
distal tooth estimate by Bolton24,25 ). In orthodontic diagnosis and
treatment planning tooth size ratio is of extreme value. Some
studies reflect that various tooth-size ratios show indigenous and
sex differences1,8). Others found no significant differences in either
an t e r i or o r ov e r al l r a t io s in s u bj e c t s wi t h di ffe r e n t
malocclusion27,2 8). Investigator in addition offered the newest
formula for tooth size discrepancy36) . Current study investigated
the tooth size ratio via CFT for CAR and COR which is an alternate
novel method to assess the tooth size discrepancy in orthodontics.
CAR and COR showed no significant differences in relation to
gender. In reality, without perfect proportional relationships in
the circumferential tooth size, we cannot give ideal occlusion to
the patients at the finishing stage of orthodontics treatment.
Human teeth have lots of variations in size in relation to race
and sex37,38). Tooth size disproportion is the lack of accord between
the intermaxillary tooth size or group of teeth. Any disharmony in
the tooth size can lead to either spacing in one arch or effect the
functional relationship. To achieve an ideal occlusion the teeth
size shoul d be in ide al relation from all dimensions, such as
mesiodistal, buccolingual and diagonal tooth size. The CFT cover
th e to o t h si ze in all dime n sional as p ects . Thu s for the
accomplishment of good occlusion with the accurate overbite and
overjet, the maxillary and mandibular teeth must be proportional
in size form all dimensional aspects. For the prediction of ideal
occlusion to be achieved at the finishing stage, orthodontist needs
to evaluate CAR and COR ratios via proposed method. Current
study investigated the tooth size and tooth size discrepancies for
both sexes.
CFT, CAR and COR norms will be of great value in forensic
dentistry and dental anthropology investigations in addition to
orthodontic treatment planning. CFT, CAR and COR need to be
further investigated on other population for sexual dimorphism.
In conclusion th e, no rms were d eveloped for CFT us ing
stereomicroscopic digital models; there is no difference between
the CFT of right and left side of the maxillary and mandibular
arches; norms were developed for the CAR and COR ratio to assess
tooth size discrepancy; CFT presented the sexual dimorphism with
the greatest value for male were observed; the developed norms
CAR and CO R ratios will be h elpful adjun ct in orthodontic
treatment planning for understanding the tooth size discrepancies.
Acknowledgement
The authors would like to acknowledge the support from the
Universiti Sains Malaysia 304/PPSG/61313104 short-term grant.
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